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HomeMy WebLinkAboutCC - Geotechnical Addendum #1 Pavement arm I �lrT—G7T�� January 2, 2025 Atlas No. B242134g Adam Capell Tresidio Homes 2973 North Eagle Road Meridian, ID 83646 Subject: Addendum #1 — Pavement Recommendations Burning Ridge Estates 2365 W Victory Road Meridian, ID Dear Adam Capell: This addendum report presents test results not requested at the time of the previously issued MTI Geotechnical Engineering Report (13191818g). 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. As required by Ada County Highway District (ACHD), Atlas has used traffic indexes of 6 for residential roadways and 8 for collector streets to determine the necessary pavement cross-sections for the site. Atlas previously collected a sample of near-surface soils for Resistance Value (R-value) testing representative of soils to depths of 2 feet below existing ground surface. This sample, consisting of lean clay collected from test pit 12, yielded a R-value of 8. Results of the test available in the previously issued MTI Geotechnical Engineering Report (13191818g). 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. Flexible Pavement Sections 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 No. B242134g Page11 Copyright©2024 Atlas Technical Consultants TrT ME7V 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 . . b"ON WL- Asphaltic Concrete 2.5 Inches 3.5 Inches Aggregate Base 4.0 Inches 6.0 Inches Structural Subbase 12.0 Inches 16.0 Inches Compacted Subgrade See Pavement Subgrade See Pavement Subgrade Preparation Section 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 Uncontrolled fill and plow zones with organic material were encountered in portions of the site. Atlas recommends that these fill materials be removed to a depth of at least 1 foot below existing grade. If fill materials and organic free plow zones remain after excavation, the exposed subgrade must be compacted to at least 95 percent of the maximum dry density as determined by ASTM D698. The excavated fill materials can be replaced in accordance with the Fill Placement and Compaction section of the original report provided that all organic material and debris is completely removed. However, the existing fill materials are not suitable for use as either the base or subbase components of the recommended pavement section. Once final grades have been determined, Atlas is available to provide additional recommendations. Common Pavement Section Construction Issues The subgrade upon which above pavement sections are to be constructed must be properly stripped, 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. 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 moderate 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. Atlas No. B242134g Page12 Copyright©2024 Atlas Technical Consultants �TrT—G7T�� 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, 1-3-2025 Sydney Shockley Jacob Schlador, PE Staff Geologist Geotechnical Practice Manager- Northwest Atlas No. B242134g Page13 Copyright©2024 Atlas Technical Consultants