Laserfiche WebLink
June 13,2023 <br />HWA Project No. 2022-188-2 1 <br />Structural fill should be moisture conditioned, placed in loose horizontal lifts less than 8-inches <br />thick, and compacted to at least 95o/o of maximum dry density as determined using test method <br />ASTM D 1557 (Modified Proctor) for material containing less than 30olo coarse gravel by <br />weight. Achievement of proper density of a compacted fill depends on the size and type of <br />compaction equipment, the number of passes, thickness of the layer being compacted, and soil <br />moisture-density properties. In areas where limited space restricts the use of heavy equipment, <br />smaller equipment can be used, but the soil must be placed in thin enough layers to achieve the <br />required compaction. <br />When the first fill is placed in a given area, andlor anytime the fill material changes, the area <br />should be considered a test section. The test section should be used to establish fill placement <br />and compaction procedures required to achieve proper compaction. The geotechnical consultant <br />should observe placement and compaction of material in the test section to assist in establishing <br />an appropriate compaction procedure. Once a placement and compaction procedure is <br />established, the contractor's operations should be monitored and sufficient periodic density tests <br />performed to veriff that proper compaction is being achieved throughout. <br />4.12,3 Ground Water Control <br />We anticip ate that groundwater seepage may be encountered locally in the fine-grained alluvium <br />or within the coarse-grained alluvium. Ground water monitoring conducted by others indicates <br />that the ground water level is likely higher during the summer months during the local inigation <br />season. Therefore, we recommend that excavation in excess of what is required for subgrade <br />preparation take place in the fall months after local irrigation has been terminated. <br />During construction, the Contractor should be prepared with appropriate means and methods to <br />ensure work takes place in relatively dry conditions during over-excavation and removal and <br />replacement of compressible soils as necessary. It is recommended that if excavation takes place <br />during the inigation season the Contractor be prepared to control ground water through use of a <br />combination of sumps and pumps and ditching to convey water away from the work area. The <br />Contractor should limit the area opened up to that which can be backfilled with minimal sidewall <br />sloughing during one shift. Quarry spalls or other permeable rockfill may be used to backfill <br />below the ground water table and provide a stable base for placement of structural fill. Where <br />quarry spalls or permeable rockfill is used, a non-woven geotextile meeting the requirements for <br />separation found in Table 3 of Sectiong-33.2(l) of the WSDOT Standard Speci/ications <br />(WSDOT, 2023) shall be installed over the rockfill prior to placement of structural fiIl. <br />4,12.4 Temporary Slope Cuts <br />We anticip ate that the foundation cuts for the new transfer station building, and the new scale <br />facility can be made with conventional excavating equipment. However, excavation wherever <br />the coarse-grained alluvium is encountered, difficult digging conditions may be expected to <br />exist, and the Contractor should be prepared to encounter cobbles and boulder-sized material. <br />2022-188-21 KCTS - Final Geotechnical Report 23 HWA GEoSCIENCES INC.