711 112TH ST SE 7 ELEVEN Geotech Report 2018-01-02 MF Import

Proposed 7-Eleven Properry 9.1 Rock- or CDF-Filled Trenches Subsurjace Erploration and Geotechnica! Engineering Repon Foundation support for the proposed 7-Eleven building could be provided by rock-filled or CDF-filled trenches that extend through the fill and topsoil to medium dense to very dense, natural sediments. CDF is a fluid mixture of cement, water, fly ash, and fine aggregate that hardens without settlemcnt several hours after placement. CDF can be re-excavated by hand or hackhoe after it hardens, depending on the specified design mir. In exploration pits EP-1 �nd EF-2, the depth to suitable nan:ral bearing sediment was approximately 4 to 4�h feet deep. ff trenches are used, they should be backfilled ro footing grade with either 2- to 4-inch crushed rock or CDF. Rock-filled trenches should have a minimum width of 4 feet (or as designated by the field er.ginecdengineerir.g geologisq, and CDF-filled trenches should have a minimum width of 3 fer,t and extend at least 1 foot beyond the footing edges. Column footings need to be excavated so the quarry rock extends beyond the edge of the footing a distance equal to approximately half the thickness of thc rock or at least 1 foot outside the edge of the footing if CDF is used. The use of a larger, track-mounted excavator will greatly speed trench excavation over the use of a conventional, rubber-tired backhoe. in order to reduce disturbance of the soils exposed in the trench, it is recommended that the excav�ror bucket be equipped wid� a smooth cutting edge. To determine when suitable bearing has bcen achieved, and to verify proper placement for crushed rock or CDP, the geotechnical engineer or their representative must be present on a full-time basis dur:ng trench excavation and backfill. Rock trenches shoulJ be backfilled with 2- to 4-inch-sized crushed rock. We do not anticipate caving. However, if caving is encountered, it would be appropriate to backfill the trenches as the excavation proceeds to reduce caving. The crushed rock must be tamped into place to achieve a tighdy packed mass; this map be done with either a hoepac compactor or, more rypically, with thc bucket of the trackhoe itself. Staging areas should be maintained so that the rock is not contaminated by mud prior to placement in the trench. CDF-filled trenches should be backfilled using CDF with a minimum compressive strength of 300 psi. 9.2 Sprcad FootinQ Foundations S;�read footings may be used for building support when placed �ver properly a,�structed '.renches filled with crushed rock or CDi', as described above. Footings placed in this manner must be designed for an allowable bearing pressure of 2,000 pounds per square foot (ps�, ,tivrrli l 9, 200; ASSOCIATED E1RTH SGENCES SR/l iyr . I': �MA91.91/ � D�JCP'up� 1-01 - l{:R Page l� �l/ R