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HomeMy WebLinkAboutPZ - Geotech Report_Addendum �TrT-G7T_� March 12, 2025 Atlas No. B250101 g Mark Hess J&J Hess, LLC 519 East Karcher Road Nampa, ID 83687 Subject: Addendum #1 — Pavement Recommendations Durango Subdivision 5630 West Ustick Road Meridian, ID Dear Mark Hess: This addendum report presents test results unavailable at the time of the previously issued Atlas Geotechnical Engineering Report (B250101 g). Descriptions of general site characteristics and the proposed project are available in the previous report. Unless otherwise noted in this addendum, all initial recommendations, limitations, and warranties expressed in the previous report must be adhered to. RECOMMENDED PAVEMENT SECTIONS Pavement Design Parameters Project specific traffic loading information has not been provided. Based on the character of the proposed construction, Atlas has used a traffic index of 6 for residential roadways to determine the necessary pavement cross-section for the site. Atlas can provide a project specific pavement design upon request. Atlas collected a sample of near-surface soils for Resistance Value (R-value) testing representative of soils to depths of 1.5 to 2.0 feet below existing ground surface. This sample, consisting of lean clay collected from test pit 3, yielded a R-value of less than 5; therefore, a R- value of 4 was used for the onsite lean clay soils. Results of the test are graphically depicted in the Appendix. Atlas recommends a routine maintenance program that includes crack sealing on a regular basis and possible seal coating to extend the life span of the pavement section. The following are minimum thickness requirements for assured pavement function. Depending on site conditions, additional work, e.g. soil preparation, may be required to support construction equipment. These have been listed within the Soft Subgrade Soils section of the original report. Atlas No. B250101 g Page11 Copyright©2025 Atlas Technical Consultants �TrTG7T�� Flexible Pavement Section The Gravel Equivalent Method, as defined in Section 500 of the State of Idaho Department of Transportation (ITD) Materials Manual, was used to develop the pavement sections. ACHD parameters for traffic index and substitution ratios, which were obtained from the ACHD Policy Manual, were also used in the design. Atlas recommends that materials used in the construction of asphaltic concrete pavements meet the requirements of the ISPWC Standard Specification for Highway Construction. Construction of the pavement section should be in accordance with these specifications. Table 1 — Gravel Equivalent Method Flexible Pavement Specifications ComponentPavement Section Asphaltic Concrete 2.5 Inches Aggregate Base 4.0 Inches Structural Subbase 14.0 Inches Compacted Subgrade See Pavement Subgrade Preparation Section 'It will be required for Atlas personnel to verify subgrade competency at the time of construction. • Asphaltic Concrete: Asphalt mix design shall meet the requirements of ISPWC Section 810. Materials shall be placed in accordance with ISPWC Standard Specifications for Highway Construction. • Aggregate Base: Material complying with ISPWC Standards for Type 1 Crushed Aggregate Materials. • Structural Subbase: Material complying with ISPWC Section 801 for 3-inch or 6-inch Uncrushed Aggregate Materials. The maximum material diameter cannot exceed 2/3 the component thickness. Pavement Subgrade Preparation 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 D698 for flexible pavements. Atlas personnel must be present during excavation to identify these materials. Common Pavement Section Construction Issues The subgrade upon which above pavement sections are to be constructed must be properly stripped, compacted (if indicated), inspected, and proof-rolled. Proof rolling of subgrade soils should be accomplished using a heavy rubber-tired, fully loaded, tandem-axle dump truck or equivalent. Atlas No. B250101 g Page12 Copyright©2025 Atlas Technical Consultants �lrl—G7T�11 Verification of subgrade competence by Atlas personnel at the time of construction is required. Fill materials on the site must demonstrate the indicated compaction prior to placing material in support of the pavement section. Atlas anticipated that pavement areas will be subjected to residential traffic. Subgrade clayey and silty soils near and above optimum moisture contents may pump during compaction. Pumping or soft areas must be removed and replaced with granular structural fill. Fill material and aggregates in support of the pavement section must be compacted to no less than 95 percent of the maximum dry density as determined by ASTM D698 for flexible pavements and by ASTM D1557 for rigid pavements. If a material placed as a pavement section component cannot be tested by usual compaction testing methods, then compaction of that material must be approved by observed proof rolling. Minor deflections from proof rolling for flexible pavements are allowable. Deflections from proof rolling of rigid pavement support courses should not be visually detectable. If you have any questions, please call us at (208) 376-4748. Respectfully submitted, c54�z5rir* Sydney Shockley Elizabeth Brown, PE Staff Geologist National Practice Manager— Geotechnical Attachments: R-Value Laboratory Test Data Atlas No. B250101 g Page13 Copyright©2025 Atlas Technical Consultants R-VALUE LABORATORY TEST DATA Source and Description: TP-3: 1.5-2.0', Lean Clay Date Obtained: January 27, 2025 Sample ID: 25-0041 Sampling and Preparation: ASTM D75: AASHTO T2: X ASTM AASHTO X D421: T87: Test Standard: ASTM AASHTO Idaho T8: X D2844: T190: Sample A B C Dry Density Ib/ft3 NA NA NA Moisture Content % NA NA NA Expansion Pressure psi NA NA NA Exudation Pressure psi NA NA NA R-Value NA NA NA R-Value @ 200 psi Exudation Pressure = Less than 5** **ASTM D2844 Note 2: Occasionally, material from very plastic clay-test specimens will extrude from under the mold and around the follower ram during the loading operation. If this occurs when the 800-psi point is reached and fewer than five lights are lighted, the soil should be reported as less than 5 R-value. Atlas No. B250101 g Pagel4 Copyright©2025 Atlas Technical Consultants