Excavation observations and compaction testing

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AMEC Geomatrix, Inc. Project BL-09-03483 September 18, 2009 Page 2 The proposed basement and lower garage floor was planned at elevation 956.67. Visual observations of the excavation were completed from outside of the excavation. The soils observed in the excavation bottom consisted of glacially deposited sandy lean clay. Based on watching the backhoe complete its work, these soils were judged to be stiff to very stiff. Compaction Testing Imported sand was then used to backfill most of the excavation. The sand was placed in thin lifts with each lift compacted by a remote-controlled vibratory compactor that was lifted into the excavation after each lift was placed. The sand fill was placed in this fashion until it had been placed and compacted to an approximate elevation of 952. On-site sandy lean clay fill was then used to fill the remainder of the excavation up to about elevation 956. Based on the depth of the excavation, we recommended that the fill placed in this excavation be compacte�+to a minimum of 98 percent of the standard Proctor dry density (ASTM D 698). We also recommended that most of the material used to fill the excavation consist of clean sand. This was to limit the amount of potential settlement that deep fills (greater than 10 feet thick) can experience. To evaluate the density of the engineered fill that had been placed, density tests were taken in the sand and clay fill. As you review the compaction test results, you will note that some of the tests taken in ihe clay fill initially failed to meet minimum density requirements. These areas were re-compacted and then retested. The tests, or retests, taken met or exceeded 98 percent of the standard Proctor dry density. The compaction and Proctor test results are attached to this report for your review. Conclusions Based on the results of our visual observations, it is our opinion that the natural soils observed in the bottom and sidewalls of this excavation are suitable for the proposed house. However, we did not observe the soils in the remainder of the house excavation. Based on the results of the compaction tests, it appears that the engineered fill placed below footings and basement floor slabs has been properly compacted and suitable for foundation and floor slab support. Even though mostly sand fill was used to fill this excavation, the fill soils could experience some settlement,estimated to be �to 1/2 inch. As the house �oads are incrementally applied, the sand fill will adjust almost immediately. Therefore, we recommend that the finish work be delayed until the framing and roofing has been substantially complete. !�JTEI:TE�: