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Geotech Report V1
s, �IJ V rr� AI ! GEOTECHNICAL INVESTIGATION PREVAIL WEST SUBDIVISION 5385 South Meridian Road Meridian, ID PREPARED FOR: Mr. Matt Schultz Schultz Development, LLC PO Box 1115 Meridian, ID 83680 PREPARED BY: Atlas Technical Consultants, LLC 2791 South Victory View Way Boise, ID 83709 December 13, 2021 B212997g 2791 South Victory View Way Boise, ID 83709 (208) 376-4748 1 oneatlas.com December 13, 2021 Atlas No. B212997g Mr. Matt Schultz Schultz Development, LLC PO Box 1115 Meridian, ID 83680 Subject: GeotechnicalInvestigation Prevail West Subdivision 5385 South Meridian Road Meridian, ID Dear Mr. Schultz: In compliance with your instructions, Atlas has conducted a soils exploration and foundation evaluation for the above referenced development. Fieldwork for this investigation was conducted from November 18 to 19, 2021. Data have been analyzed to evaluate pertinent geotechnical conditions. Results of this investigation, together with our recommendations, are to be found in the following report. We have provided a PDF copy for your review and distribution. Often, questions arise concerning soil conditions because of design and construction details that occur on a project. Atlas would be pleased to continue our role as geotechnical engineers during project implementation. If you have any questions, please call us at (208) 376-4748. Respectfully submitted, Bailey Hereford Engineering Technician 13,� ElizabethBrown Geotechnical Se rl SOCC, EN NS�4898 /13/2021 p q Nig P �ZgeETH BR�� CONTENTS 1. INTRODUCTION...................................................................................................................1 1.1 Project Description........................................................................................................1 1.2 Authorization.................................................................................................................1 1.3 Scope of Investigation...................................................................................................1 2. SITE DESCRIPTION.............................................................................................................2 2.1 Site Access...................................................................................................................2 2.2 Regional Geology.........................................................................................................2 2.3 General Site Characteristics.........................................................................................2 2.4 Regional Site Climatology and Geochemistry...............................................................3 3. SEISMIC SITE EVALUATION...............................................................................................3 3.1 Geoseismic Setting.......................................................................................................3 3.2 Seismic Design Parameter Values...............................................................................3 4. SOILS EXPLORATION.........................................................................................................4 4.1 Exploration and Sampling Procedures..........................................................................4 4.2 Laboratory Testing Program.........................................................................................4 4.3 Soil and Sediment Profile..............................................................................................5 4.4 Volatile Organic Scan...................................................................................................5 5. SITE HYDROLOGY...............................................................................................................5 5.1 Groundwater.................................................................................................................5 5.2 Soil Infiltration Rates.....................................................................................................6 5.3 Infiltration Testing..........................................................................................................6 6. FOUNDATION AND SLAB DISCUSSION AND RECOMMENDATIONS .............................7 6.1 Foundation Design Recommendations.........................................................................8 6.2 Foundation Drain Recommendations...........................................................................8 6.3 Crawl Space Recommendations...................................................................................9 6.4 Floor, Patio, and Garage Slab-on-Grade......................................................................9 7. CONSTRUCTION CONSIDERATIONS................................................................................9 7.1 Earthwork....................................................................................................................10 7.2 Dry Weather................................................................................................................10 7.3 Wet Weather...............................................................................................................11 7.4 Soft Subgrade Soils....................................................................................................11 7.5 Frozen Subgrade Soils...............................................................................................11 7.6 Structural Fill...............................................................................................................12 7.7 Backfill of Walls...........................................................................................................13 7.8 Excavations.................................................................................................................13 7.9 Groundwater Control...................................................................................................14 8. GENERAL COMMENTS.....................................................................................................14 Atlas No. 13212997g Page I i Copyright © 2021 Atlas Technical Consultants Mrs 9. REFERENCES....................................................................................................................15 TABLES Table 1 — Seismic Design Values.................................................................................................4 Table 2 — Groundwater Data......................................................................................................... 6 Table 3 — Infiltration Test Results................................................................................................. 7 Table4 — Soil Bearing Capacity.................................................................................................... 8 APPENDICES Appendix I Warranty and Limiting Conditions Appendix II Vicinity Map Appendix III Site Map Appendix IV Geotechnical Investigation Test Pit Log Appendix V Geotechnical General Notes Appendix VI Important Information About This Geotechnical Engineering Report Atlas No. 13212997g Page I ii Copyright © 2021 Atlas Technical Consultants 1. INTRODUCTION This report presents results of a geotechnical investigation and analysis in support of data utilized in design of structures as defined in the 2018 International Building Code (IBC). Information in support of groundwater and stormwater issues pertinent to the practice of Civil Engineering is included. Observations and recommendations relevant to the earthwork phase of the project are also presented. Revisions in plans or drawings for the proposed development from those enumerated in this report should be brought to the attention of the soils engineer to determine whether changes in the provided recommendations are required. Deviations from noted subsurface conditions, if encountered during construction, should also be brought to the attention of the soils engineer. 1.1 Project Description The proposed development is in the southern portion of the City of Meridian, Ada County, ID, and occupies a portion of the SE'/4NE'/4 of Section 36, Township 3 North, Range 1 West, Boise Meridian. This project will consist of construction of 243-lot residential subdivision with associated streets. The site to be developed is approximately 37.34 acres in size. Total settlements are limited to 1 inch. Loads of up to 4,000 pounds per lineal foot for wall footings, and column loads of up to 50,000 pounds were assumed for settlement calculations. Additionally, assumptions have been made for traffic loading of pavements. Retaining walls are not anticipated as part of the project. Atlas has not been informed of the proposed grading plan. 1.2 Authorization Authorization to perform this exploration and analysis was given in the form of a written authorization to proceed from Mr. Matt Schultz of Schultz Development, LLC to Clinton Wyllie of Atlas Technical Consultants (Atlas), on October 26, 2021. Said authorization is subject to terms, conditions, and limitations described in the Professional Services Contract entered into between Schultz Development, LLC and Atlas. Our scope of services for the proposed development has been provided in our proposal dated October 26, 2021 and repeated below. 1.3 Scope of Investigation The scope of this investigation included review of geologic literature and existing available geotechnical studies of the area, visual site reconnaissance of the immediate site, subsurface exploration of the site, field and laboratory testing of materials collected, and engineering analysis and evaluation of foundation materials. The scope of work did not include design recommendations specific to individual residences. Atlas No. 13212997g Page 11 Copyright © 2021 Atlas Technical Consultants 2. SITE DESCRIPTION 2.1 Site Access Access to the site may be gained via Interstate 84 to the Meridian Road exit. Proceed south on Meridian Road approximately 2.6 miles to its intersection with Quartz Creek Road. The site occupies the northwest corner of this intersection. The location is depicted on site maps included in the Appendix. 2.2 Regional Geology The project site is located within the western Snake River Plain of southwestern Idaho and eastern Oregon. The plain is a northwest trending rift basin, about 45 miles wide and 200 miles long, that developed about 14 million years ago (Ma) and has since been occupied sporadically by large inland lakes. Geologic materials found within and along the plain's margins reflect volcanic and fluvial/lacustrine sedimentary processes that have led to an accumulation of approximately 1 to 2 km of interbedded volcanic and sedimentary deposits within the plain. Along the margins of the plain, streams that drained the highlands to the north and south provided coarse to fine-grained sediments eroded from granitic and volcanic rocks, respectively. About 2 million years ago the last of the lakes was drained and since that time fluvial erosion and deposition has dominated the evolution of the landscape. The project site is underlain by "Gravel of Amity Terrace" as mapped by Othberg and Stanford (1993). The Amity terrace is the fifth terrace above the modern Boise River and represents the first level of Quaternary incision by the Boise River. The terrace, which has been correlated with Deer Flat terrace deposits to the west, is modified extensively by erosion and faulting. Where little erosion has taken place the terrace is mantled with loess 1.6-7 feet thick. 2.3 General Site Characteristics The site to be developed is approximately 37.34 acres in size. Currently, a residence is present in the eastern portion of the site. This residence fronts Meridian Road, which runs along the eastern property boundary. The remainder of the site is relatively flat and level agricultural land. Vegetation on the site consists of native weeds, grasses, and mature trees around the residence. Regional drainage is southwest toward Indian Creek. Stormwater drainage for the site is achieved by both percolation through surficial soils. The site is situated so that it is unlikely that it will receive any drainage from off -site sources. Stormwater drainage collection and retention systems are not in place on the project site and do not currently exist within the vicinity of the project site. Atlas No. 13212997g Page 12 Copyright © 2021 Atlas Technical Consultants 2.4 Regional Site Climatology and Geochemistry According to the Western Regional Climate Center, the average precipitation for the Treasure Valley is on the order of 10 to 12 inches per year, with an annual snowfall of approximately 20 inches and a range from 3 to 49 inches. The monthly mean daily temperatures range from 21 OF to 950F, with daily extremes ranging from roughly -250F to 111 °F. Winds are generally from the northwest or southeast with an annual average wind speed of approximately 9 miles per hour (mph) and a maximum of 62 mph. Soils and sediments in the area are primarily derived from siliceous materials and exhibit low electro-chemical potential for corrosion of metals or concretes. Local aggregates are generally appropriate for Portland cement and lime cement mixtures. Surface water, groundwater, and soils in the region typically have pH levels ranging from 7.2 to 8.2. 3. SEISMIC SITE EVALUATION 3.1 Geoseismic Setting Soils on site are classed as Site Class D in accordance with Chapter 20 of the American Society of Civil Engineers (ASCE) publication ASCE/SEI 7-16. Structures constructed on this site should be designed per IBC requirements for such a seismic classification. Our investigation did not reveal hazards resulting from potential earthquake motions including: slope instability, liquefaction, and surface rupture caused by faulting or lateral spreading. Incidence and anticipated acceleration of seismic activity in the area is low. 3.2 Seismic Design Parameter Values The United States Geological Survey National Seismic Hazard Maps (2008), includes a peak ground acceleration map. The map for 2% probability of exceedance in 50 years in the Western United States in standard gravity (g) indicates that a peak ground acceleration of 0.194 is appropriate for the project site based on a Site Class D. The following section provides an assessment of the earthquake -induced earthquake loads for the site based on the Risk -Targeted Maximum Considered Earthquake (MCER). The MCER spectral response acceleration for short periods, SMs, and at 1-second period, SMI, are adjusted for site class effects as required by the 2018 IBC. Design spectral response acceleration parameters as presented in the 2018 IBC are defined as a 5% damped design spectral response acceleration at short periods, SDs, and at 1-second period, SDI• The USGS National Seismic Hazards Mapping Project includes a program that provides values for ground motion at a selected site based on the same data that were used to prepare the USGS ground motion maps. The maps were developed using attenuation relationships for soft rock sites; the source model, assumptions, and empirical relationships used in preparation of the maps are described in Petersen and others (1996). Atlas No. B212997g Page 13 Copyright © 2021 Atlas Technical Consultants Table 1 — Seismic Design Values Site Class D "Stiff Soil" Ss 0.283 (g) S1 0.104 (g) Fa 1.573 Fv 2.393 SMs 0.446 SM1 0.248 Sos 0.297 SD1 0.165 4. SOILS EXPLORATION Exploration and Sampling Procedures Field exploration conducted to determine engineering characteristics of subsurface materials included a reconnaissance of the project site and investigation by test pit. Test pit sites were located in the field by means of a Global Positioning System (GPS) device and are reportedly accurate to within ten feet. Upon completion of investigation, each test pit was backfilled with loose excavated materials. Re -excavation and compaction of these test pit areas are required prior to construction of overlying structures. In addition, samples were obtained from representative soil strata encountered. Samples obtained have been visually classified in the field by professional staff, identified according to test pit number and depth, placed in sealed containers, and transported to our laboratory for additional testing. Subsurface materials have been described in detail on logs provided in the Appendix. Results of field and laboratory tests are also presented in the Appendix. Atlas recommends that these logs not be used to estimate fill material quantities. 4.2 Laboratory Testing Program Along with our field investigation, a supplemental laboratory testing program was conducted to determine additional pertinent engineering characteristics of subsurface materials necessary in an analysis of anticipated behavior of the proposed structures. Laboratory tests were conducted in accordance with current applicable American Society for Testing and Materials (ASTM) specifications, and results of these tests are to be found in the Appendix. The laboratory testing program for this report included: Atterberg Limits Testing — ASTM D4318, Grain Size Analysis — ASTM C117/C136, and Resistance Value (R-value) and Expansion Pressure of Compacted Soils — Idaho T-8. As to date, the R-value test results have not been received and, therefore, have not been included within this report. Atlas will forward the results in the form of an addendum once the R-value test results have been received. Atlas No. B212997g Page 14 Copyright © 2021 Atlas Technical Consultants 4.3 Soil and Sediment Profile The profile below represents a generalized interpretation for the project site. Note that on site soils strata, encountered between test pit locations, may vary from the individual soil profiles presented in the logs, which can be found in the Appendix. Lean clay soils were encountered at ground surface. These soils were brown, dry to slightly moist, and soft to very stiff, with fine to medium -grained sand. Organic materials were measured to depths of roughly 3.9 feet and 6 inch plow zones were noted throughout. Sandy lean clay soils were observed below the lean clay soils in test pit 5. These soils were brown, dry to slightly moist, medium stiff to stiff, and contained fine to medium -grained sand. Silty sand sediments were encountered beneath clay soils. These sediments were light brown, dry to slightly moist, and medium dense to very dense. Fine to coarse -grained sand and weak to strong calcium carbonate cementation was present throughout. Basalt was found at depth in test pit 2. Basalt was gray, slightly weathered, and strong. At depth in the remaining test pits, poorly graded gravel with silt and sand sediments were exposed. Poorly graded gravels were light brown to brown, dry to slightly moist, and loose to dense. Fine to coarse -grained sand, fine to coarse gravel, and 6-inch minus cobbles were noted throughout. Competency of test pit sidewalls varied little across the site. In general, fine grained soils remained stable while more granular sediments readily sloughed. However, moisture contents will also affect wall competency with saturated soils having a tendency to readily slough when under load and unsupported. 4.4 Volatile Organic Scan No environmental concerns were identified prior to commencement of the investigation. Therefore, soils obtained during on -site activities were not assessed for volatile organic compounds by portable photoionization detector (PID). Samples obtained during our exploration activities exhibited no odors or discoloration typically associated with this type of contamination. No groundwater was encountered. 5. SITE HYDROLOGY Existing surface drainage conditions are defined in the General Site Characteristics section. Information provided in this section is limited to observations made at the time of the investigation. Either regional or local ordinances may require information beyond the scope of this report. 5.1 Groundwater During this field investigation, groundwater was not encountered in test pits advanced to a maximum depth of 15.1 feet bgs. Soil moistures in the test pits were generally dry to slightly moist throughout. Atlas has previously performed 4 geotechnical investigations within 0.30 mile of the project site. Information from these investigations has been provided in the table below. Atlas No. 13212997g Page 15 Copyright © 2021 Atlas Technical Consultants Table 2 — Groundwater Data Furthermore, according to United States Geological Survey (USGS) monitoring well data within approximately'/2-mile of the project site, groundwater was measured at depths ranging between 90 and 127 feet bgs. For construction purposes, groundwater depth can be assumed to remain greater than 20 feet bgs throughout the year. 5.2 Soil Infiltration Rates Soil permeability, which is a measure of the ability of a soil to transmit a fluid, was tested in the field. For this report, an estimation of infiltration is also presented using generally recognized values for each soil type and gradation. Of soils comprising the generalized soil profile for this study, lean clay soils generally offer little permeability, with typical hydraulic infiltration rates of less than 2 inches per hour. Silty sand and poorly graded gravel with silt and sand sediments usually display rates of 4 to 8 inches per hour; though calcium carbonate cementation may reduce this value to near zero. Infiltration rates through basalt rock can be highly variable, ranging from nearly zero to greater than 6 inches per hour in some cases. Movement of water through the basalt may be more characteristic of fracture flow. Infiltration testing is required to determine site - specific infiltration rates for drainage design once proposed locations of infiltration facilities are determined. 5.3 Infiltration Testing Infiltration testing was conducted in general accordance with the Ada County Highway District (ACHD) Policy Manual. Test pit areas will need to be re -excavated and compacted prior to construction of structures that will be sensitive to settlement. Test locations were presoaked prior to testing. Pre-soaking increases soil moistures, which allows the tested soils to reach a saturated condition more readily during testing. Saturation of the tested soils is desirable in order to isolate the vertical component of infiltration by inhibiting horizontal seepage during testing. Atlas No. B212997g Page 16 Copyright © 2021 Atlas Technical Consultants Testing was conducted on November 19, 2021. Details and results of testing are as follows: Table 3 — Infiltration Test Results In accordance with the ACHD Policy Manual, a factor of safety of 2 has been applied to the stabilized infiltration rates achieved during testing to obtain the design infiltration rates listed above. The reason for the decreased infiltration rate is to account for long term saturation of the soils and the potential for less permeable soils to settle into the bottom of the infiltration facilities. Atlas recommends that all infiltration facilities be constructed in accordance with the local municipality requirements. 6. FOUNDATION AND SLAB DISCUSSION AND RECOMMENDATIONS Various foundation types have been considered for support of the proposed development. Two requirements must be met in the design of foundations. First, the applied bearing stress must be less than the ultimate bearing capacity of foundation soils to maintain stability. Second, total and differential settlement must not exceed an amount that will produce an adverse behavior of the superstructure. Allowable settlement is usually exceeded before bearing capacity considerations become important; thus, allowable bearing pressure is normally controlled by settlement considerations. Considering subsurface conditions and the proposed construction, it is recommended that the development be founded upon conventional spread footings and continuous wall footings. Total settlements should not exceed 1 inch if the following design and construction recommendations are observed. Presently, there are approximately 243 lots proposed for the project site. The followina recommendations are not specific to the individual structures. but rather should be viewed as guidelines for the subdivision -wide development. Atlas No. 13212997g Page 17 Copyright © 2021 Atlas Technical Consultants 6.1 Foundation Design Recommendations Based on data obtained from the site and test results from various laboratory tests performed, Atlas recommends the following guidelines for the net allowable soil bearing capacity: Table 4 — Soil Bearing Capacity Footings must bear on competent, undisturbed, 1,500 Ibs/ft' native lean clay, sandy lean clay, silty sand soils, or Not Required for Native compacted structural fill. Existing organic materials Soil A Y3 increase is allowable must be completely removed from below foundation for short-term loading, elements.' Excavation depths ranging from roughly 95/o o for Structural Fill which is defined by 0.8 to 3.9 feet bgs should be anticipated to expose seismic events or proper bearing soils.' designed wind speeds. 'It will be required for Atlas personnel to verify the bearing soil suitability for each structure at the time of construction. 'Depending on the time of year construction takes place, the subgrade soils may be unstable because of high moisture contents. If unstable conditions are encountered, over -excavation and replacement with granular structural fill and/or use of geotextiles may be required. The following sliding frictional coefficient values should be used: 1) 0.35 for footings bearing on native lean clay, sandy lean clay, and silty sand soils and 2) 0.45 for footings bearing on granular structural fill. A passive lateral earth pressure of 300 pounds per square foot per foot (psf/ft) should be used for lean clay and sandy lean clay soils and 393 psf/ft for silty sand soils. For compacted sandy gravel fill, a passive lateral earth pressure of 496 psf/ft should be used. Footings should be proportioned to meet either the stated soil bearing capacity or the 2018 IBC minimum requirements. Total settlement should be limited to approximately 1 inch, and differential settlement should be limited to approximately '/2 inch. Objectionable soil types encountered at the bottom of footing excavations should be removed and replaced with structural fill. Excessively loose or soft areas that are encountered in the footings subgrade will require over -excavation and backfilling with structural fill. To minimize the effects of slight differential movement that may occur because of variations in the character of supporting soils and seasonal moisture content, Atlas recommends continuous footings be suitably reinforced to make them as rigid as possible. For frost protection, the bottom of external footings should be 24 inches below finished grade. oundation Drain Recommendations Considering the presence of shallow cemented soils across the site, Atlas recommends that foundation drains be installed. The drains should be placed at the footing elevation, sloped at least 2 percent, and be directed to suitable discharge points at least 10 feet away from the structures. Discharge points should be protected to prevent erosion. Atlas No. 13212997g Page 18 Copyright © 2021 Atlas Technical Consultants 6.3 Crawl Space Recommendations All residences constructed with crawl spaces should be designed in a manner that will inhibit water in the crawl spaces. Atlas recommends that roof drains carry stormwater at least 10 feet away from each residence. Grades should be at least 5 percent for a distance of 10 feet away from all residences. In addition, rain gutters should be placed around all sides of residences, and backfill around stem walls should be placed and compacted in a controlled manner. 7loor, Patio, and Garage Slab -on -Grad Plow zones with organic materials were encountered in portions of the site. Atlas recommends that the organic materials be removed. If plow zones remain after organic materials have been removed, the exposed subgrade must be compacted to at least 95 percent of the maximum dry density as determined by ASTM D1557. Atlas personnel must be present during excavation to identify these materials. Organic, loose, or obviously compressive materials must be removed prior to placement of concrete floors or floor -supporting fill. In addition, the remaining subgrade should be treated in accordance with guidelines presented in the Earthwork section. Areas of excessive yielding should be excavated and backfilled with structural fill. Fill used to increase the elevation of the floor slab should meet requirements detailed in the Structural Fill section. Fill materials must be compacted to a minimum 95 percent of the maximum dry density as determined by ASTM D1557. A free -draining granular mat should be provided below slabs -on -grade to provide drainage and a uniform and stable bearing surface. This should be a minimum of 4 inches in thickness and properly compacted. The mat should consist of a sand and gravel mixture, complying with Idaho Standards for Public Works Construction (ISPWC) specifications for 3/4-inch (Type 1) crushed aggregate. The granular mat should be compacted to no less than 95 percent of the maximum dry density as determined by ASTM D1557. A moisture -retarder should be placed beneath floor slabs to minimize potential ground moisture effects on moisture -sensitive floor coverings. The moisture -retarder should be at least 15-mil in thickness and have a permeance of less than 0.01 US perms as determined by ASTM E96. Placement of the moisture -retarder will require special consideration with regard to effects on the slab -on -grade and should adhere to recommendations outlined in the ACI 302.1 R and ASTM E1745 publications. Upon request, Atlas can provide further consultation regarding installation. CONSTRUCTION CONSIDERATIONS Recommendations in this report are based upon structural elements of the project being founded on competent, native lean clay, sandy lean clay, silty sand soils, or compacted structural fill. Structural areas should be stripped to an elevation that exposes these soil types. Atlas No. B212997g Page 19 Copyright © 2021 Atlas Technical Consultants 7.1 Earthwork Excessively organic soils, deleterious materials, or disturbed soils generally undergo high volume changes when subjected to loads, which is detrimental to subgrade behavior in the area of pavements, floor slabs, structural fills, and foundations. Mature trees, weeds, and thick grasses with associated root systems were noted at the time of our investigation. It is recommended that organic or disturbed soils, if encountered, be removed to depths of 1 foot (minimum), and wasted or stockpiled for later use. However, in areas where trees are/were present, deeper excavation depths should be anticipated. Stripping depths should be adjusted in the field to assure that the entire root zone or disturbed zone (plow depths) or topsoil are removed prior to placement and compaction of structural fill materials. Exact removal depths should be determined during grading operations by Atlas personnel, and should be based upon subgrade soil type, composition, and firmness or soil stability. If underground storage tanks, underground utilities, wells, or septic systems are discovered during construction activities, they must be decommissioned then removed or abandoned in accordance with governing Federal, State, and local agencies. Excavations developed as the result of such removal must be backfilled with structural fill materials as defined in the Structural Fill section. Atlas should oversee subgrade conditions (i.e., moisture content) as well as placement and compaction of new fill (if required) after native soils are excavated to design grade. Recommendations for structural fill presented in this report can be used to minimize volume changes and differential settlements that are detrimental to the behavior of footings, pavements, and floor slabs. Sufficient density tests should be performed to properly monitor compaction. For structural fill beneath building structures, one in -place density test per lift for every 5,000 square feet is recommended. In parking and driveway areas, this can be decreased to one test per lift for every 10,000 square feet. 7.2 Dry Weather If construction is to be conducted during dry seasonal conditions, many problems associated with soft soils may be avoided. However, some rutting of subgrade soils may be induced by shallow groundwater conditions related to springtime runoff or irrigation activities during late summer through early fall. Solutions to problems associated with soft subgrade soils are outlined in the Soft Subgrade Soils section. Problems may also arise because of lack of moisture in native and fill soils at time of placement. This will require the addition of water to achieve near -optimum moisture levels. Low -cohesion soils exposed in excavations may become friable, increasing chances of sloughing or caving. Measures to control excessive dust should be considered as part of the overall health and safety management plan. Atlas No. B212997g Page110 Copyright © 2021 Atlas Technical Consultants 7.3 Wet Weather If construction is to be conducted during wet seasonal conditions (commonly from mid -November through May), problems associated with soft soils must be considered as part of the construction plan. During this time of year, fine-grained soils such as silts and clays will become unstable with increased moisture content, and eventually deform or rut. Additionally, constant low temperatures reduce the possibility of drying soils to near optimum conditions. 7.4 ;oft Subgrade Soils Shallow fine-grained subgrade soils that are high in moisture content should be expected to pump and rut under construction traffic. During periods of wet weather, construction may become very difficult if not impossible. The following recommendations and options have been included for dealing with soft subgrade conditions: Track -mounted vehicles should be used to strip the subgrade of root matter and other deleterious debris. Heavy rubber -tired equipment should be prohibited from operating directly on the native subgrade and areas in which structural fill materials have been placed. Construction traffic should be restricted to designated roadways that do not cross, or cross on a limited basis, proposed roadway or parking areas. Soft areas can be over -excavated and replaced with granular structural fill. Construction roadways on soft subgrade soils should consist of a minimum 2-foot thickness of large cobbles of 4 to 6 inches in diameter with sufficient sand and fines to fill voids. Construction entrances should consist of a 6-inch thickness of clean, 2-inch minimum, angular drain -rock and must be a minimum of 10 feet wide and 30 to 50 feet long. During the construction process, top dressing of the entrance may be required for maintenance. Scarification and aeration of subgrade soils can be employed to reduce the moisture content of wet subgrade soils. After stripping is complete, the exposed subgrade should be ripped or disked to a depth of 1'/2 feet and allowed to air dry for 2 to 4 weeks. Further disking should be performed on a weekly basis to aid the aeration process. Alternative soil stabilization methods include use of geotextiles, lime, and cement stabilization. Atlas is available to provide recommendations and guidelines at your request. 7.5 Frozen Subgrade Soils Prior to placement of structural fill materials or foundation elements, frozen subgrade soils must either be allowed to thaw or be stripped to depths that expose non -frozen soils and wasted or stockpiled for later use. Stockpiled materials must be allowed to thaw and return to near -optimal conditions prior to use as structural fill. Atlas No. B212997g Page 111 Copyright © 2021 Atlas Technical Consultants The onsite, shallow clayey and silty soils are susceptible to frost heave during freezing temperatures. For exterior flatwork and other structural elements, adequate drainage away from subgrades is critical. Compaction and use of structural fill will also help to mitigate the potential for frost heave. Complete removal of frost susceptible soils for the full frost depth, followed by replacement with a non -frost susceptible structural fill, can also be used to mitigate the potential for frost heave. Atlas is available to provide further guidance/assistance upon request. 7.6 Structural Fill Soils recommended for use as structural fill are those classified as GW, GP, SW, and SP in accordance with the Unified Soil Classification System (USCS) (ASTM D2487). Use of silty soils (USCS designation of GM, SM, and MIL) as structural fill may be acceptable. However, use of silty soils (GM, SM, and ML) as structural fill below footings is prohibited. These materials require very high moisture contents for compaction and require a long time to dry out if natural moisture contents are too high and may also be susceptible to frost heave under certain conditions. Therefore, these materials can be quite difficult to work with as moisture content, lift thickness, and compactive effort becomes difficult to control. If silty soil is used for structural fill, lift thicknesses should not exceed 6 inches (loose), and fill material moisture must be closely monitored at both the working elevation and the elevations of materials already placed. Following placement, silty soils must be protected from degradation resulting from construction traffic or subsequent construction. Recommended granular structural fill materials, those classified as GW, GP, SW, and SP, should consist of a 6-inch minus select, clean, granular soil with no more than 50 percent oversize (greater than 3/4-inch) material and no more than 12 percent fines (passing No. 200 sieve). These fill materials should be placed in layers not to exceed 12 inches in loose thickness. Prior to placement of structural fill materials, surfaces must be prepared as outlined in the Construction Considerations section. Structural fill material should be moisture -conditioned to achieve optimum moisture content prior to compaction. For structural fill below footings, areas of compacted backfill must extend outside the perimeter of the footings for a distance equal to the thickness of fill between the bottom of foundation and underlying soils, or 5 feet, whichever is less. All fill materials must be monitored during placement and tested to confirm compaction requirements, outlined below, have been achieved. Each layer of structural fill must be compacted, as outlined below: • Below Structures and Rigid Pavements: A minimum of 95 percent of the maximum dry density as determined by ASTM D1557. • Below Flexible Pavements: A minimum of 92 percent of the maximum dry density as determined by ASTM D1557 or 95 percent of the maximum dry density as determined by ASTM D698. Atlas No. 13212997g Page112 Copyright © 2021 Atlas Technical Consultants The ASTM D1557 test method must be used for samples containing up to 40 percent oversize (greater than 3/4-inch) particles. If material contains more than 40 percent but less than 50 percent oversize particles, compaction of fill must be confirmed by proof rolling each lift with a 10-ton vibratory roller (or equivalent) until the maximum density has been achieved. Density testing must be performed after each proof rolling pass until the in -place density test results indicate a drop (or no increase) in the dry density, defined as maximum density or "break over" point. The number of required passes should be used as the requirements on the remainder of fill placement. Material should contain sufficient fines to fill void spaces, and must not contain more than 50 percent oversize particles. 7.7 Backfill of Walls Backfill materials must conform to the requirements of structural fill, as defined in this report. For wall heights greater than 2.5 feet, the maximum material size should not exceed 4 inches in diameter. Placing oversized material against rigid surfaces interferes with proper compaction, and can induce excessive point loads on walls. Backfill shall not commence until the wall has gained sufficient strength to resist placement and compaction forces. Further, retaining walls above 2.5 feet in height shall be backfilled in a manner that will limit the potential for damage from compaction methods and/or equipment. It is recommended that only small hand -operated compaction equipment be used for compaction of backfill within a horizontal distance equal to the height of the wall, measured from the back face of the wall. Backfill should be compacted in accordance with the specifications for structural fill, except in those areas where it is determined that future settlement is not a concern, such as planter areas. In nonstructural areas, backfill must be compacted to a firm and unyielding condition. 7.8 Excavations Shallow excavations that do not exceed 4 feet in depth may be constructed with side slopes approaching vertical. Below this depth, it is recommended that slopes be constructed in accordance with Occupational Safety and Health Administration (OSHA) regulations, Section 1926, Subpart P. Based on these regulations, on -site soils are classified as type "C" soil, and as such, excavations within these soils should be constructed at a maximum slope of 1'/2 feet horizontal to 1 foot vertical (11/2:1) for excavations up to 20 feet in height. Excavations in excess of 20 feet will require additional analysis. Note that these slope angles are considered stable for short-term conditions only. and will not be stable for Iona -term conditions. During the subsurface exploration, test pit sidewalls generally exhibited little indication of collapse; however, sloughing of native granular sediments from test pit sidewalls was observed. For deep excavations, native granular sediments cannot be expected to remain in position. These materials are prone to failure and may collapse, thereby undermining upper soil layers. This is especially true when excavations approach depths near the water table. Care must be taken to ensure that excavations are properly backfilled in accordance with procedures outlined in this report. Atlas No. 13212997g Page113 Copyright © 2021 Atlas Technical Consultants Shallow soil cementation (caliche) was observed throughout much of the site and may cause difficulties during foundation development and utility placement. Cemented soils should be anticipated throughout the site. 7.9 Groundwater Control Groundwater was not encountered during the investigation and is anticipated to be below the depth of most construction. Excavations below the water table will require a dewatering program. It may be possible to discharge dewatering effluent to remote portions of the site, to a sump, or to a pit. This will essentially recycle effluent, thus eliminating the need to enter into agreements with local drainage authorities. Should the scope of the proposed project change, Atlas should be contacted to provide more detailed groundwater control measures. Special precautions may be required for control of surface runoff and subsurface seepage. It is recommended that runoff be directed away from open excavations. Silty and clayey soils may become soft and pump if subjected to excessive traffic during time of surface runoff. Ponded water in construction areas should be drained through methods such as trenching, sloping, crowning grades, nightly smooth drum rolling, or installing a French drain system. Additionally, temporary or permanent driveway sections should be constructed if extended wet weather is forecasted. d. GENERAL COMMENTS Based on the subsurface conditions encountered during this investigation and available information regarding the proposed development, the site is adequate for the planned construction. When plans and specifications are complete, and if significant changes are made in the character or location of the proposed development, consultation with Atlas must be arranged as supplementary recommendations may be required. Suitability of subgrade soils and compaction of structural fill materials must be verified by Atlas personnel prior to placement of structural elements. Additionally, monitoring and testing should be performed to verify that suitable materials are used for structural fill and that proper placement and compaction techniques are utilized. Atlas No. 13212997g Page 114 Copyright © 2021 Atlas Technical Consultants 9. REFERENCES Ada County Highway District (ACHD) (2017). Ada County Highway District Policy Manual (August 2017). [Online] Available: <http://www.achdidaho.org/AboutACHD/PolicyManual.aspx> (2021). American Concrete Institute (ACI) (2015). Guide for Concrete Floor and Slab Construction: ACI 302.1 R. Farmington Hills, MI: ACI. American Society of Civil Engineers (2021). ASCE 7 Hazards Tool: Web Interface [Online] Available: <https://asce7hazardtool.online/> (2021). American Society of Civil Engineers (ASCE) (2013). Minimum Design Loads for Buildings and Other Structures: ASCE/SEI 7-16. Reston, VA: ASCE. American Society for Testing and Materials (ASTM) (2017). Standard Test Method for Materials Finer than 75-um (No. 200) Sieve in Mineral Aggregates by Washing: ASTM C117. West Conshohocken, PA: ASTM. American Society for Testing and Materials (ASTM) (2014). Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates: ASTM C136. West Conshohocken, PA: ASTM. American Society for Testing and Materials (ASTM) (2012). Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort: ASTM D698. West Conshohocken, PA: ASTM. American Society for Testing and Materials (ASTM) (2012). Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Modified Effort: ASTM D1557. West Conshohocken, PA: ASTM. American Society for Testing and Materials (ASTM) (2013). Standard Test Methods for Resistance Value (R-Value) and Expansion Pressure of Compacted Soils: ASTM D2844. West Conshohocken, PA: ASTM. American Society for Testing and Materials (ASTM) (2017). Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System): ASTM D2487. West Conshohocken, PA: ASTM. American Society for Testing and Materials (ASTM) (2017). Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils: ASTM D4318. West Conshohocken, PA: ASTM. American Society for Testing and Materials (ASTM) (2011). Standard Specification for Plastic Water Vapor Retarders Used in Contact with Soil or Granular Fill Under Concrete Slabs: ASTM E1745. West Conshohocken, PA: ASTM. Desert Research Institute. Western Regional Climate Center. [Online] Available: <http://www.wrcc.dri.edu/> (2021). International Building Code Council (2018). International Building Code, 2018. Country Club Hills, IL: Author. Local Highway Technical Assistance Council (LHTAC) (2017). Idaho Standards for Public Works Construction, 2017. Boise, ID: Author. Othberg, K. L. and Stanford, L. A., Idaho Geologic Society (1993). Geologic Map of the Boise Valley and Adloining Area, Western Snake River Plain, Idaho. (scale 1:100,000). Boise, ID: Joslyn and Morris. Atlas No. 13212997g Page115 Copyright © 2021 Atlas Technical Consultants U.S. Department of Labor, Occupational Safety and Health Administration. CFR 29, Part 1926, Subpart P: Safety and Health Regulations for Construction, Excavations (1986). [Online] Available: <www.osha.gov> (2021). U.S. Geological Survey (2021). National Water Information System: Web Interface. [Online] Available: <http://waterdata.usgs.gov/nwis> (2021). Atlas No. B212997g Page116 Copyright © 2021 Atlas Technical Consultants Appendix I WARRANTY AND LIMITING CONDITIONS Atlas warrants that findings and conclusions contained herein have been formulated in accordance with generally accepted professional engineering practice in the fields of foundation engineering, soil mechanics, and engineering geology only for the site and project described in this report. These engineering methods have been developed to provide the client with information regarding apparent or potential engineering conditions relating to the site within the scope cited above and are necessarily limited to conditions observed at the time of the site visit and research. Field observations and research reported herein are considered sufficient in detail and scope to form a reasonable basis for the purposes cited above. Exclusive Use This report was prepared for exclusive use of the property owner(s), at the time of the report, and their retained design consultants ("Client"). Conclusions and recommendations presented in this report are based on the agreed -upon scope of work outlined in this report together with the Contract for Professional Services between the Client and Atlas Technical Consultants ("Consultant"). Use or misuse of this report, or reliance upon findings hereof, by parties other than the Client is at their own risk. Neither Client nor Consultant make representation of warranty to such other parties as to accuracy or completeness of this report or suitability of its use by such other parties for purposes whatsoever, known or unknown, to Client or Consultant. Neither Client nor Consultant shall have liability to indemnify or hold harmless third parties for losses incurred by actual or purported use or misuse of this report. No other warranties are implied or expressed. Report Recommendations are Limited and Subject to Misinterpretation There is a distinct possibility that conditions may exist that could not be identified within the scope of the investigation or that were not apparent during our site investigation. Findings of this report are limited to data collected from noted explorations advanced and do not account for unidentified fill zones, unsuitable soil types or conditions, and variability in soil moisture and groundwater conditions. To avoid possible misinterpretations of findings, conclusions, and implications of this report, Atlas should be retained to explain the report contents to other design professionals as well as construction professionals. Since actual subsurface conditions on the site can only be verified by earthwork, note that construction recommendations are based on general assumptions from selective observations and selective field exploratory sampling. Upon commencement of construction, such conditions may be identified that require corrective actions, and these required corrective actions may impact the project budget. Therefore, construction recommendations in this report should be considered preliminary, and Atlas should be retained to observe actual subsurface conditions during earthwork construction activities to provide additional construction recommendations as needed. Atlas No. B212997g Page 117 Copyright © 2021 Atlas Technical Consultants Since geotechnical reports are subject to misinterpretation, do not separate the soil logs from the report. Rather, provide a copy of, or authorize for their use, the complete report to other design professionals or contractors. Locations of exploratory sites referenced within this report should be considered approximate locations only. For more accurate locations, services of a professional land surveyor are recommended. This report is also limited to information available at the time it was prepared. In the event additional information is provided to Atlas following publication of our report, it will be forwarded to the client for evaluation in the form received. Environmental Concerns Comments in this report concerning either onsite conditions or observations, including soil appearances and odors, are provided as general information. These comments are not intended to describe, quantify, or evaluate environmental concerns or situations. Since personnel, skills, procedures, standards, and equipment differ, a geotechnical investigation report is not intended to substitute for a geoenvironmental investigation or a Phase II/III Environmental Site Assessment. If environmental services are needed, Atlas can provide, via a separate contract, those personnel who are trained to investigate and delineate soil and water contamination. Atlas No. B212997g Page 118 Copyright © 2021 Atlas Technical Consultants Vicinity Map Figure 1 Lr LLI MAP NOTES: TTT:Meridian w N • Delorme Street Atlas Sonna Zi • Not to Scale Beatty W FRANKLIN RD r— W FRANKLIN RD N E FRANKLIN RD N LEGEND �N Ln j ` Approximate Site rn5_ fw M p Location 30 D o rn 30 55 30 55 /f I ( N E OVERLAND RD to n Cyr) A j0 D. v^ r M A 69 �' F I� T 0 E VICTORY RD oc z� o Site Location rn j0 TF ;^ 0 v < M H v D r rn 1 � v Prevail West Subdivision 5385 South Meridian Road to Meridian, ID rn C) Modified from DeLorme by: CCW December 8, 2021 rrn 69 ;0 Drawing: 13212997g /i I � 2791 S. Victory View Way Phone: (208) 376-4748 Boise, ID 83709 Fax: (208) 322-6515 COLUMBIA R6 Web: oneatlas.com Site Map Figure 2 N NOTES: ° Not to Scale TP-6 TP-5 LEGEND Approximate Site N Boundary O Approximate Atlas Test Pit Location TP 4 8 m 0 TP 3 ® D z O LEI N Prevail West Subdivision 5884 South Meridian Road 0 Meridian, ID Modified by: CCW December 8, 2021 Drawing: B212997g TP-2 TP-1 ® /ir1 2791 S. Victory View Way Phone: (208) 376-4748 QUARTZ CREEK ROAD Boise, ID 83709 Fax: (208) 322-6515 Web: oneatlas com Appendix IV GEOTECHNICAL INVESTIGATION TEST PIT LOG Test Pit Log #: TP-1 Date Advanced: November 18, 2021 Excavated by: Turn of the Century Homes Logged by: Jack Hood Latitude: 43.5539275 Longitude:-116.3942279 Depth to Water Table: Not Encountered Total Depth: 15.1 feet bgs Depth Field Description and USCS Soil and Sample Sample Depth e. Lab bgs)JL .. Test ID Lean Clay (CL): Brown, dry to slightly moist, 0.0-1.4 very stiff, with fine-grained sand. GS 0.5-1.0 2.5-2.75 A --Organic material to 2.3 feet bgs. --Plow zones to 6 inches. Silty Sand (SM): Light brown, dry, dense to 1.4-11.4 very dense, with fine to coarse -grained sand. --Weak to moderate calcium carbonate cementation throughout. Poorly Graded Gravel with Silt and Sand (GP- 11.4-15.1 GM): Light brown, dry, loose to medium dense, with fine to coarse -grained sand, fine to coarse gravel, and 5-inch-minus cobbles. Notes: See Site Map for test pit location. Atlas No. 13212997g Page 121 Copyright © 2021 Atlas Technical Consultants GEOTECHNICAL INVESTIGATION TEST PIT LOG Test Pit Log #: TP-2 Latitude: 43.5540777 Date Advanced: November 18, 2021 Longitude:-116.3987397 Excavated by: Turn of the Century Homes Depth to Water Table: Not Encountered Logged by: Jack Hood Total Depth: 9.0 feet bgs Depth Field Description and USCS Soil and Sample Depth L (feet .. bgs) Tes e. Lean Clay (CL): Brown, dry to slightly moist, soft to medium stiff, with fine to medium- 0.0-1.2 grained sand. 0.5 --Organic material to 3.9 feet bgs. -- Plow zones to 6 inches. Silty Sand (SM): Light brown, dry, medium dense to dense, with fine to coarse -grained 1.2-9.0 sand. GS 2.5-3.0 B --Some weak to moderate calcium carbonate cementation throughout. Below 9.0 Basalt: Gray, slightly weathered, strong. Notes: See Site Map for test pit location. "Sieve results skewed due to calcium carbonate cementation. Test Pit Log #: TP-3 Date Advanced: November 18, 2021 Excavated by: Turn of the Century Homes Logged by: Jack Hood Latitude: 43.5554313 Longitude:-116.3963046 Depth to Water Table: Not Encountered Total Depth: 9.3 feet bgs Depth 9IWield Description and USCS Soil and r Sample Depth e. Lab .. .� .. Test ID Lean Clay (CL): Brown, dry to slightly moist, 0.0-1.6 stiff, with fine-grained sand. 1.5-1.75 --Organic material to 2.4 feet bgs. -- Plow zones to 6 inches. Silty Sand (SM): Light brown, dry, medium 1.6-7.9 dense to dense, with fine to coarse -grained sand. Poorly Graded Gravel with Silt and Sand (GP- 7 9-9 3 GM): Light brown, dry to slightly moist, medium dense, with fine to coarse -grained sand and fine to coarse gravel. Notes: See Site Map for test pit location. Percolation testing conducted at 9.3 feet bgs. Atlas No. B212997g Page 122 Copyright © 2021 Atlas Technical Consultants GEOTECHNICAL INVESTIGATION TEST PIT LOG Test Pit Log #: TP-4 Date Advanced: November 18, 2021 Excavated by: Turn of the Century Homes Logged by: Jack Hood Latitude: 43.5564355 Longitude:-116.3963374 Depth to Water Table: Not Encountered Total Depth: 13.0 feet bgs Depth Field Description and USCS Soil an4 Sample Depth e. .. .. es Lean Clay (CL): Brown, dry to slightly moist, 0.0-1.3 medium stiff, with fine-grained sand. 0.5-0.75 --Organic material to 1.0 foot bgs. -- Plow zones to 6 inches. Silty Sand (SM): Light brown, dry, medium dense to dense, with fine to coarse -grained 1.3-11.2 sand. --Weak to moderate calcium carbonate cementation from 2.7 to 4.4 feet bgs. Poorly Graded Gravel with Silt and Sand (GP- 11.2-13.0 GM): Light brown to brown, dry, medium dense, with fine to coarse -grained sand and fine to coarse gravel. Notes: See Site Map for test pit location. Percolation testing conducted at 13.0 feet bgs. Atlas No. 13212997g Page 123 Copyright © 2021 Atlas Technical Consultants GEOTECHNICAL INVESTIGATION TEST PIT LOG Test Pit Log #: TP-5 Date Advanced: November 18, 2021 Excavated by: Turn of the Century Homes Logged by: Jack Hood Latitude: 43.5570658 Longitude:-116.3943630 Depth to Water Table: Not Encountered Total Depth: 15.0 feet bgs Depth Field Description and USCS Soil and Sample Depth e. • (feet•• AN •• Test ID Lean Clay (CL): Brown, dry to slightly moist, 0.0-1.3 stiff, with fine-grained sand. 1.75-2.0 --Organic material to 0.8 foot bgs. -- Plow zones to 6 inches. Sandy Lean Clay (CL): Brown, dry to slightly 1.3-4.0 moist, medium stiff to stiff, with fine to medium- GS 2.0-2.5 C grained sand. Silty Sand (SM): Light brown, dry, dense to 4.0-4.4 very dense, with fine to coarse -grained sand. --Moderate to strong calcium carbonate cementation throughout. Poorly Graded Gravel with Silt and Sand (GP- 4.4-15.0 GM): Light brown, dry, loose to medium dense, with fine to coarse -grained sand, fine to coarse gravel, and 6-inch-minus cobbles. Notes: See Site Map for test pit location. Test Pit Log #: TP-6 Date Advanced: November 18, 2021 Excavated by: Turn of the Century Homes Logged by: Jack Hood Latitude: 43.5571875 Longitude:-116.3986528 Depth to Water Table: Not Encountered Total Depth: 15.0 feet bgs • VIField Description and USCS ••Depth Aamp QP •• • • bgs) Test ID Lean Clay (CL): Brown, dry to slightly moist, 0.0-1.2 stiff, with fine-grained sand. 1.0-1.75 --Organic material to 1.0 foot bgs. -- Plow zones to 6 inches. Silty Sand (SM): Light brown, dry to slightly moist, medium dense to dense, with fine to 1.2-15.0 coarse -grained sand. --Weak to moderate calcium carbonate cementation from 4.0 to 5.4 feet bgs. Notes: See Site Map for test pit location. Atlas No. B212997g Page 124 Copyright © 2021 Atlas Technical Consultants Appendix V GEOTECHNICAL GENERAL NOTES Major Divisions Unified Soil Classification Symbol Soil Descriptions Coarse- Grained Soils < Gravel & Gravelly Soils < 50% coarse GW Well -graded gravels; gravel/sand mixtures with little or no fines GP Poorly -graded gravels; gravel/sand mixtures with little or no fines GM Silty gravels; poorly -graded gravel/sand/silt mixtures GC Clayey gravels; poorly -graded gravel/sand/clay mixtures 50% passes sieve sieve Sand & Sandy Soils > 50% coarse fraction SW Well -grad d sands; gravelly sands with little or no fines SP Poorl -raded sands; gravelly sands with little or no fines SM Silt sands;poorly-graded sand/gravel/silt mixtures SC Clayey sands; poorly -graded sand/gravel/clay mixtures Fine- Grained Soils > 50% Silts & Clays LL < 50 ML Inorganic silts; sandy, gravelly or clayey silts CL Lean clays; inorganic, gravelly, sandy, or silty, low to medium - plasticity clays OL Organic, low -plasticity clays and silts passes No.200 sieve Silts & Clays LL > 50 MH Inorganic, elastic silts; sandy, gravelly or clayey elastic silts CH Fat clays; high -plasticity, inorganic clays OH Organic, medium to high -plasticity clays and silts Highly Organic Soils PT Peat, humus, hydric soils with high organic content tive Density and Consistency Coarse -Grained Soils SPT Blow Counts N) Very Loose: < 4 Loose: 4-10 Medium Dense: 10-30 Dense: 30-50 Very Dense: > 50 Fine -Grained Soils SPT Blow Counts N Very Soft: < 2 Soft: 2-4 Medium Stiff: 4-8 Stiff: 8-15 Very Stiff: 15-30 Hard: > 30 Particle Boulders: Size > 12 in. Cobbles: 12 to 3 in. Gravel: 3 in. to 5 mm Coarse -Grained Sand: 5 to 0.6 mm Medium -Grained Sand: 0.6 to 0.2 mm Fine -Grained Sand: 0.2 to 0.075 mm Silts: 0.075 to 0.005 mm Clays: < 0.005 mm sture Description Content and Cementation Classification Field Test Dry Absence of moisture, dry to touch Slightly Moist Damp, but no visible moisture Moist Visible moisture Wet Visible free water Saturated Soil is usually below water table Description Field Test Weak Crumbles or breaks with handling or slight finger pressure Moderate Crumbles or breaks with considerable finger pressure Strong Will not crumble or break with finger pressure GS Acronym grab sample LL Liquid Limit M moisture content NP non -plastic PI Plasticity Index QP penetrometer value, unconfined compressive strength, tsf V vane value, ultimate shearing strength, tsf Atlas No. B212997g Page 125 Copyright © 2021 Atlas Technical Consultants Geotechnical-Engineering Report The Geoprofessional Business Association (GBA) has prepared this advisory to help you - assumedly a client representative - interpret and apply this geotechnical-engineering report as effectively as possible. In that way, you can benefit from a lowered exposure to problems associated with subsurface conditions at project sites and development of them that, for decades, have been a principal cause of construction delays, cost overruns, claims, and disputes. If you have questions or want more information about any of the issues discussed herein, contact your GBA-member geotechnical engineer. Active engagement in GBA exposes geotechnical engineers to a wide array of risk -confrontation techniques that can be of genuine benefit for everyone involved with a construction project. Understand the Geotechnical-Engineering Services Provided for this Report Geotechnical-engineering services typically include the planning, collection, interpretation, and analysis of exploratory data from widely spaced borings and/or test pits. Field data are combined with results from laboratory tests of soil and rock samples obtained from field exploration (if applicable), observations made during site reconnaissance, and historical information to form one or more models of the expected subsurface conditions beneath the site. Local geology and alterations of the site surface and subsurface by previous and proposed construction are also important considerations. Geotechnical engineers apply their engineering training, experience, and judgment to adapt the requirements of the prospective project to the subsurface model(s). Estimates are made of the subsurface conditions that will likely be exposed during construction as well as the expected performance of foundations and other structures being planned and/or affected by construction activities. The culmination of these geotechnical-engineering services is typically a geotechnical-engineering report providing the data obtained, a discussion of the subsurface model(s), the engineering and geologic engineering assessments and analyses made, and the recommendations developed to satisfy the given requirements of the project. These reports may be titled investigations, explorations, studies, assessments, or evaluations. Regardless of the title used, the geotechnical-engineering report is an engineering interpretation of the subsurface conditions within the context of the project and does not represent a close examination, systematic inquiry, or thorough investigation of all site and subsurface conditions. Geotechnical-Engineering Services are Performed for Specific Purposes, Persons, and Projects, and At Specific Times Geotechnical engineers structure their services to meet the specific needs, goals, and risk management preferences of their clients. A geotechnical-engineering study conducted for a given civil engineer will not likely meet the needs of a civil -works constructor or even a different civil engineer. Because each geotechnical-engineering study is unique, each geotechnical-engineering report is unique, prepared solely for the client. Likewise, geotechnical-engineering services are performed for a specific project and purpose. For example, it is unlikely that a geotechnical- engineering study for a refrigerated warehouse will be the same as one prepared for a parking garage; and a few borings drilled during a preliminary study to evaluate site feasibility will not be adequate to develop geotechnical design recommendations for the project. Do not rely on this report if your geotechnical engineer prepared it: • for a different client; • for a different project or purpose; • for a different site (that may or may not include all or a portion of the original site); or • before important events occurred at the site or adjacent to it; e.g., man-made events like construction or environmental remediation, or natural events like floods, droughts, earthquakes, or groundwater fluctuations. Note, too, the reliability of a geotechnical-engineering report can be affected by the passage of time, because of factors like changed subsurface conditions; new or modified codes, standards, or regulations; or new techniques or tools. If you are the least bit uncertain about the continued reliability of this report, contact your geotechnical engineer before applying the recommendations in it. A minor amount of additional testing or analysis after the passage of time - if any is required at all - could prevent major problems. Read this Report in Full Costly problems have occurred because those relying on a geotechnical- engineering report did not read the report in its entirety. Do not rely on an executive summary. Do not read selective elements only. Read and refer to the report in full. You Need to Inform Your Geotechnical Engineer About Change Your geotechnical engineer considered unique, project -specific factors when developing the scope of study behind this report and developing the confirmation -dependent recommendations the report conveys. Typical changes that could erode the reliability of this report include those that affect: • the site's size or shape; • the elevation, configuration, location, orientation, function or weight of the proposed structure and the desired performance criteria; • the composition of the design team; or • project ownership. As a general rule, always inform your geotechnical engineer of project or site changes - even minor ones - and request an assessment of their impact. The geotechnical engineer who prepared this report cannot accept responsibility or liability for problems that arise because the geotechnical engineer was not informed about developments the engineer otherwise would have considered. Most of the "Findings" Related in This Report Are Professional Opinions Before construction begins, geotechnical engineers explore a site's subsurface using various sampling and testing procedures. Geotechnical engineers can observe actual subsurface conditions only at those specific locations where sampling and testing is performed. The data derived from that sampling and testing were reviewed by your geotechnical engineer, who then applied professional judgement to form opinions about subsurface conditions throughout the site. Actual sitewide-subsurface conditions may differ - maybe significantly - from those indicated in this report. Confront that risk by retaining your geotechnical engineer to serve on the design team through project completion to obtain informed guidance quickly, whenever needed. This Report's Recommendations Are Confirmation -Dependent The recommendations included in this report - including any options or alternatives - are confirmation -dependent. In other words, they are not final, because the geotechnical engineer who developed them relied heavily on judgement and opinion to do so. Your geotechnical engineer can finalize the recommendations only after observing actual subsurface conditions exposed during construction. If through observation your geotechnical engineer confirms that the conditions assumed to exist actually do exist, the recommendations can be relied upon, assuming no other changes have occurred. The geotechnical engineer who prepared this report cannot assume responsibility or liability for confirmation -dependent recommendations if you fail to retain that engineer to perform construction observation. This Report Could Be Misinterpreted Other design professionals' misinterpretation of geotechnical- engineering reports has resulted in costly problems. Confront that risk by having your geotechnical engineer serve as a continuing member of the design team, to: confer with other design -team members; help develop specifications; • review pertinent elements of other design professionals' plans and specifications; and be available whenever geotechnical-engineering guidance is needed. You should also confront the risk of constructors misinterpreting this report. Do so by retaining your geotechnical engineer to participate in prebid and preconstruction conferences and to perform construction - phase observations. Give Constructors a Complete Report and Guidance Some owners and design professionals mistakenly believe they can shift unanticipated -subsurface -conditions liability to constructors by limiting the information they provide for bid preparation. To help prevent the costly, contentious problems this practice has caused, include the complete geotechnical-engineering report, along with any attachments or appendices, with your contract documents, but be certain to note conspicuously that you've included the material for information purposes only. To avoid misunderstanding, you may also want to note that "informational purposes" means constructors have no right to rely on the interpretations, opinions, conclusions, or recommendations in the report. Be certain that constructors know they may learn about specific project requirements, including options selected from the report, only from the design drawings and specifications. Remind constructors that they may perform their own studies if they want to, and be sure to allow enough time to permit them to do so. Only then might you be in a position to give constructors the information available to you, while requiring them to at least share some of the financial responsibilities stemming from unanticipated conditions. Conducting prebid and preconstruction conferences can also be valuable in this respect. Read Responsibility Provisions Closely Some client representatives, design professionals, and constructors do not realize that geotechnical engineering is far less exact than other engineering disciplines. This happens in part because soil and rock on project sites are typically heterogeneous and not manufactured materials with well-defined engineering properties like steel and concrete. That lack of understanding has nurtured unrealistic expectations that have resulted in disappointments, delays, cost overruns, claims, and disputes. To confront that risk, geotechnical engineers commonly include explanatory provisions in their reports. Sometimes labeled "limitations;' many of these provisions indicate where geotechnical engineers' responsibilities begin and end, to help others recognize their own responsibilities and risks. Read these provisions closely. Ask questions. Your geotechnical engineer should respond fully and frankly. Geoenvi ron mental Concerns Are Not Covered The personnel, equipment, and techniques used to perform an environmental study - e.g., a "phase -one" or "phase -two" environmental site assessment - differ significantly from those used to perform a geotechnical-engineering study. For that reason, a geotechnical-engineering report does not usually provide environmental findings, conclusions, or recommendations; e.g., about the likelihood of encountering underground storage tanks or regulated contaminants. Unanticipated subsurface environmental problems have led to project failures. If you have not obtained your own environmental information about the project site, ask your geotechnical consultant for a recommendation on how to find environmental risk -management guidance. Obtain Professional Assistance to Deal with Moisture Infiltration and Mold While your geotechnical engineer may have addressed groundwater, water infiltration, or similar issues in this report, the engineer's services were not designed, conducted, or intended to prevent migration of moisture - including water vapor - from the soil through building slabs and walls and into the building interior, where it can cause mold growth and material -performance deficiencies. Accordingly, proper implementation of the geotechnical engineer's recommendations will not of itself be sufficient to prevent moisture infiltration. Confront the risk of moisture infiltration by including building -envelope or mold specialists on the design team. Geotechnical engineers are not building -envelope or mold specialists. GEOPROFESSIONAL ,ff :VA AFM BUSINESS - ASSOCIATION Telephone: 301 / 565-2733 e-mail: info@geoprofessional.org www.geoprofessional.org Copyright 2019 by Geoprofessional Business Association (GBA). Duplication, reproduction, or copying of this document, in whole or in part, by any means whatsoever, is strictly prohibited, except with GBAs specific written permission. Excerpting, quoting, or otherwise extracting wording from this document is permitted only with the express written permission of GBA, and only for purposes of scholarly research or book review. Only members of GBA may use this document or its wording as a complement to or as an element of a report of any kind. Any other firm, individual, or other entity that so uses this document without being a GBA member could be committing negligent or intentional (fraudulent) misrepresentation.