3005 PANAVIEW BLVD 2016-01-01 MF Import

July 10,1997 6 S73-1164 4.2 Site Drunage Condiflone �' There wae a gutter downspout drain located on the north side of your house,as shown on Figure 1. The gutter downspout was mnnected to a flexible PVC pipe that appears to be routed underground to the east in the direction oE the slope failure. There was a �' small PVC yard drain grate located in the northeast mrner of your grass lawn,and in discussions with you it was explained that all of the roof gutter downspouta am tight- lined bo tlus yard drain. The yard drain is then tight-lined to the base of the slope at the �� creek We observed no signs of drainage pipes discharging onto the slope. �'" 5. CONCLUSIONS AND RECOMMENDATIONS ,.� S.1 Genenl � The mud/landslide debris flow located on the slope east of your house occurred in surficial,saturated mlluvium and weathered soils overlying dense mmpetent till and ' outwash deposits. We did not obsezve any evidence to support the existence of a deep . seated failure involving the dense,underlying glacial soila. The portion of the slope that slumped immediately north of the mud/landslide debris flow is potentially unstable '"' during prolonged wet weather periods and may fail withost adequate preventative � a►easurns. Therefore,as described later in section 5.2,we have recommended mntinuation of the zock buttress across the slope under this portion oF the slope to add � atability. It is imporFant M understand the proceasea occurring on the slope at and anound the ' alide in order to assesa remediation options. The material involved in the mud/debris � flow,mlluvium,is formed from the natural weathering and vegetaflve action acting to break down the underlying native soils. The thickness of the mlluvium layer increases ' ' with time. Under severe wet weather conditions or man-made alterations,the . mlluvium layer on steep slopes is subject to failure. Once a slide has occurred and removed the colluvium layer from a slope the processes of rebuilding the colluvium layer starts all over again. The length of time it takes to create the mlluvium layer is � highly variable from a few to tens of years. The remmmendationa mntained in the following sections are designed,if pmperly - icnplemented,to siabilize the existing unstable main scarp,provide slope erosion protection in the failure area,restore accesa to the lower portions of the slope,and help �r,9n;rn;�p the risk of additional failures in the future. 5.2 Remedial Recommendationa Our remedial remmmendations have been crafted to achieve yo•.0 goals of re- establishing lost yard space and allowing access to the lower portion of your property — near the creek As we discussed previously,the site mnditions appear adequate to • — Golder Associates