607 RIVERSIDE RD Geotech Report 2022-10-25 (2)

1 March 22,2016 ' Project No. T-7388 Structural fill should be placed in uniform loose layers not exceeding 12 inches and compacted to a minimum of 95 percent of the soil's maximum dry density, as determined by American Society for Testing and Materials (ASTM) Test Designation D-698 (Standard Proctor). The moisture content of the soil at the time of compaction should be within two percent of its optimum, as determined by this ASTM standard. In nonstructural areas, the degree of compaction can be reduced to 90 percent. Surcharge The surcharge program consists of placing fill material over the building footprint to pre-consolidate the compressible soils. The amount and rate of settlement is monitored and once primary settlements have occurred, the surcharge is removed and building construction can commence. We recommend placing a minimum of four feet of fill above the finished floor grade in the building area. The surcharge fill does not need to meet any special requirements other than having a minimum in place unit weight of 120 pounds per cubic foot (pef). However, it may be advisable to use a good quality fill that can be used to raise grades in other portions of the site, such as parking and driveway areas, if necessary. The surcharge fill should extend a minimum of two feet beyond the edge of the perimeter building footings. We estimate that total settlement under the building and surcharge fill will be in the range of four to seven inches. It is estimated that 90 percent of the consolidation settlement will occur in about six to eight weeks following full application of the surcharge. To verify the amount of settlement and the time rate of movement,the surcharge program should be monitored by installing settlement markers. The settlement markers should be installed on the existing grade prior to placing any surcharge fill. Once installed,elevations of both the fill height and marker should be taken daily until the full height of the surcharge is in place. Once fully surcharged, readings should continue weekly until the anticipated settlements have occurred. Monitoring data should be forwarded to us within two days after it is obtained for ' review and comment. A typical settlement marker detail is shown on Figure 3. It is critical that the grading contractor recognize the importance of the settlement marker installations. All efforts must be made to protect the markers from damage during fill placement. It is difficult, if not impossible, to evaluate the progress of the preload program if the markers are damaged or destroyed by construction equipment. If the markers are impacted, it may be necessary to install new markers and extend the surcharging time period in order to ensure that settlements have ceased and building construction can begin. Following the successful completion of the surcharge program, with foundations supported on a minimum of two ' feet of granular structural fill and dimensioned as recommended in Section 5.4 of this report, estimated post construction settlement due to primary consolidation is less than one-half inch. Potential long-term settlement due to secondary compression of the very soft silt and clay layer may also occur. These secondary settlements cannot be fully mitigated during the surcharge program. The magnitude of this settlement will be greater in the early years diminishing with time. Estimated total settlement due to secondary compression ranges from '/2 inch to one inch in 10 years. Approximately 50 percent of the total secondary settlement will be differential in nature due to the varying thickness and compressibility characteristics of the silt and clay layer. 1 Page No. 6 I