6624 BROADWAY 2018-01-02 MF Import

Imoisture -sensitive soil in structural fills should be limited to favorable dry weather conditions. The on -site soils generally contained significant amounts of silt and are considered moisture - sensitive. Existing fill also contained significant organic material and asphalt rubble, and excavated exi�'.ing fill is not expected to be suitable 'or use in structural fill applications. Imported fill, if needed, should consist of predominantly granular, non -organic soil free of demolition waste or other unsuitable material, with the amount of fine-grained material limited to 5 percent by weight when measured on the minus No. 4 sieve fraction and at least 25 t percent retained on the No. 4 sieve. A representative from our firm should inspect the stripped subgrade and be present during placement of structural fill to observe the work and pet form a representative number of in - place density tests. In this way, the adequacy of the earthwork may he evaluated as filling progresses and any problem areas may be corrected at that time. It is important to understand that taking random compaction tests on a part-time basis will not assure uniformity or acceptable performance of a fill. As such, we are available to aid the owner in developing a suitable monitoring and testing program. Structural Support Depending on the locations selected for the buildings, they will be underlain either by suitable native soils which are suitable for foundation support or existing fill that is not suitable for foundation support. Ideally, the buildings will be situated in areas underlain by suitable native sediments. If underlain by suitable native sediments, the buildings may be constructed with conventional shallow foundations. Spread footings may be used for building support when founded on undisturbed, native sediments, or rock -filled trenches, as discussed in this section. We recommend that an allowable bearing pressure of 2,500 pounds per square foot (pso be utilized for design purposes, including both dead and live loads. An increase of one-third may be used for short- term wind or seismic loading. Perimeter footings should be buried at least 18 inches into the surrounding soil for frost protection; interior footings require only 12 inches burial. However, all footings must penetrate to the prescribed bearing stratum, and no footing should be founded in or above loose, organic, or existing fill soils. To limit settlements, all footings should have a minimum width of 18 inches. If needed, rock -filled trenches below foundations should extend laterally beyond all foundation elements by at least 1 foot, and should have a minimum width of 4 feet (or as designated by the field engineer/engineering geologist). All rock trenches should be excavated down to expose underlying native sediments. Because of the potential for caving, the actual trench width may be greater than specified. It would be appropriate to backfill the trenches as the excavation proceeds to reduce caving. The use of a larger, track -mounted backhoe will greatly speed trench excavation over the use of a conventional, rubber -tired backhoe. In order to reduce disturbance of the bearing soils exposed in the trench, we recommend that the teeth of the backhoe bucket be covered with a digging plate. R