6107 BERKSHIRE DR SEPA 016 - 041 Geotech Report 2025-04-14

Catholic Housing Services JN 16298 November 1, 2016 Page 5 allowable pile load. The appropriate number of load tests would need to be determined at the time the contractor and installation method are chosen. As a minimum, Schedule 40 pipe should be used. The site soils are not highly organic, and are not located near salt water. As a result, they do not have an elevated corrosion potential. Considering this, it is our opinion that standard "black" pipe can be used, and corrosion protection, such as galvanizing, is not necessary for the pipe piles. Pile caps and grade beams should be used to transmit loads to the piles. Isolated pile caps should include a minimum of two piles to reduce the potential for eccentric loads being applied to the piles. Subsequent sections of pipe can be connected with slip or threaded couplers, or they can be welded together. If slip couplers are used, they should fit snugly into the pipe sections. This may require that shims be used or that beads of welding flux be applied to the outside of the coupler. Lateral loads due to wind or seismic forces may be resisted by passive earth pressure acting on the vertical, embedded portions of the foundation. For this condition, the foundation must be either poured directly against relatively level, undisturbed soil or be surrounded by level compacted fill. We recommend using a passive earth pressure of 300 pounds per cubic foot (pcf) for this resistance. If the ground in front of a foundation is loose or sloping, the passive earth pressure given above will not be appropriate. We recommend a safety factor of at least 1.5 for the foundation's resistance to lateral loading, when using the above ultimate passive value. If lateral resistance from fill placed against the foundations is required for this project, the structural engineer should indicate this requirement on the plans for the general and earthwork contractor's information. Compacted fill placed against the foundations can consist of on-site soil that is.tamped into place using the backhoe or is compacted using a jumping jack compactor. It is necessary for the fill to be compacted to a firm condition, but it does not need to reach even 90 percent relative compaction to develop the passive resistance recommended above. Due to their small diameter, the lateral capacity of vertical pipe piles is relatively small. However, if lateral resistance in addition to passive soil resistance is required, we recommend driving battered piles in the same direction as the applied lateral load. The lateral capacity of a battered pile is equal to one-half of the lateral component of the allowable compressive load, with a maximum allowable lateral capacity of 1,000 pounds. The allowable vertical capacity of battered piles does not need to be reduced if the piles are battered steeper than 1:5 (Horizontal:Vertical). DRILLED CONCRETE PIERS Drilled, concrete-filled piers may be used, if it is uneconomical to excavate to bearing soil. Based on our explorations, it appears that the piers can be constructed by open-hole methods. These piers should be drilled with conventional auger drills, but the drilling contractor should have access to casing, in case sloughing occurs in the near-surface soil. If water is in a hole at the time of pouring, the concrete should be tremied to the bottom of the hole. A wide variety of depths and pier diameters are possible, but we recommend using a minimum pile diameter of 16 inches. For a minimum embedment of 5 feet into the very dense soil and a pile diameter of 16 inches, we recommend assuming an allowable compressive capacity of 30 tons per pier. Center-to-center pier spacing should be no less than three times the pile diameter. We recommend reinforcing each pile its entire length. This typically consists of a cage of rebar extending a portion of the pile's length, with a full-length center bar. For design of the reinforcing, GEOTECH CONSULTANTS,INC.