4805 BELVEDERE AVE 2016-01-01 MF Import

Subsurface Fxpforation, Geafogic Hatard, and Bcl��edere Lors Enst Prelintinary Gtotechnica! Enginecnng Report £�crcrr R'ashin ron P�e(iminarv Design Rerommendationt Typically, drilled piles are ins�alled utilizing a track-mounted auger drill rig. Once the prescribed auger depth is reached, s steel reinforcing cage or wide flange beam is lowered into the hole. Strucmral concrete is then pumped into the hole around the reinforcing steel and filled ro the gruund surface. Near-surface soils at the si[e consist predominatelV of loose io medium dense sand and borings drilled fot pile installation may not stay open during placemcnt of steel and concrete. Because of the potential for caving inside the boreholes, we recommend that the contractor be prepared to case the borings. Alternatively, the drifled piling could be completcd using the augercast method. Soil arching between the piles will be relied upon tu retain the potential slide mass upslope of the wall. As a result, no inte.rior lagging is used and no excavation is required. During a major seismic event the soil arr,hing wall should pre�ent the majority of landslide soil from failing downslope and undermining the residences. However, if landsli�ing does occur and tbe sandy soils between the piles are exposed, they �;�ill be prone to raveling and sloughing over time, and would require work to provide permancnt stabilization and support. lf piles with a steel reinforcing cage are used, permanent stabilization may include consvuction of a shotcrete wall between the piles. If piles with a wide flange beam are used, stabilization may indude placement of lagging between the piles. Alternatively, the new construction could utilize piles with wide Ilange beams widi lagging, in anticipation of fumre loss of slope soils below the soil arch wall. Installation of the lagging would require excavation to the base of the landslide mass, and then backfill of the lagging. We recommend that the drilled pile soil arch wall should be designed to aithstand lateral soil pressures based on "active" conditions. This design pressure, assuming a horizontal backslope, is in the form of an eyuivalent fluid eyual to 50 pounds per cubic foot (pe� triangular distribution u�ithin the upper loose soil and potential landslide zone. Within the dense to very dense bcaring soils at dcpth, an equivalent fluid equal to 45 pcf should be used for design. These equi��alent (luid loads indude seismic forces as determined b�' the Mononohc-0kahc equation. I3ecause the �IIL'$ are to be designed as a soil arch N'all, soil- arching e(fects between piles will concentrate on each pile the soil pressure from the contributory arca behveen the pile centers. Please refer to the equivalent fluid pressure diagram sho��n on Figure 3, Soil Arch �'�'all Pressure Diagram. The use of active pressure for the shoring s}�stem assumes sufficient deforniation in the soil occurs to develop an active condition -- typically on the order of 0.001 times the retained soil height on d�e pile. The retained soil ��•all height will increase ti�ith increasing proximity to the slope crest, as shown on Tahle 4. Acti��e soil forces ti�ill act over the pile spacing on the retained height and oves one pile diameter belo�a the retained soil hcight. For r;ie sloping toc condition, the upper portion of the piles may be designed for passive soil resistance against lateral translation using an equivalent iluid eyual to ]00 pcf. At a depth of S fcet below thc retained soil hcight, a passive soi) resistance of 350 pcf may be used. The rassive cyui��alent fluid pressure diagram hegins at the base of the retained soil height as sho��n on Table 4. Passive resistance ��alues include a factor of safety equal to 3 in order to reJuce the amount of movement necessary to generate full passive resistance. Passive soil resistance may he applied to a width equal to 2 pile diameters. Afnrt'h 5. �0�1 ASSOCU7ED E�RTNSC/£NCES, /NC. ,.r i,: er,�,,;,v .,,,�.�,��:.,,��n�r.ur u_� Page 16