3007 PANAVIEW BLVD 2016-01-01 MF Import

September 2,1997 3 973-1164.100 thousand yeais ago. The geologic mnditions as observed in the ravine are mmposed of dense glacial sediments mnsistingofadvance ouhvash sand and till. These soils wern — rnnsolidated by the vast weight of the overlying glacier ice. Over tune the natural pracess of weathering and erosion has sculpted the deposits forming river valleys and ravines. On the slopes bordering these features,the exposed sediments weather and — form a loose soil layer which is called mlluvium Colluvium deposits are found on most elopea overlying the native geologic units and are generally thickest near the toe of the slope. 'Phis loose mlluvium soil la�er is susceptible to failure particularly during periods — of heavy rainfall when it may bernme sahuated. We undeiatand from incervieH s of several homeowners in your area that the east-facing steep elopes in your neighborhood have generally been stable kr the past twenty years or a►ore. Colluvium layers on the slope wete thick and in many areas fill was also � placed on the slope during house mnstruction. However,during the snow and rain — atorm of Decercber,1996 and January,1997 there were numerous slope failures (slumps and mud/debris flows)on the east-facing alopes. The failures were predominately � mud/debris flowa indicating intense saturation of the mlluvium layer on the slope. The � unuaual climate mnditions rnntributed to these failures when over a foot of snow was j immediately followed by warming condiHons and heavy rainfall causing rapid melting of the snow and ground saturation of the near surface soils. .., Based upon the geologic mapping and subsurface explorations,the stra6graphic � sequence of soiLs exposed in the area of the slide appears to be as follows (from oldest to youngest): Glacial Till-Till is characterized by a non-stratified,unsorted mi�chue mntaining particle sizea ranging from clay to boulders. Till is deposited at the base of a glacier , and has been overridden and mnsolidated by its great weight. Because of its high denaity and generally high silt and clay mntent,till generally has a low • permeability. Till was enmuntered in HA-1 from 10 feet to a reEusal depth of 12 feet,and in HA-3 ' from 11.5 feet to a refusal depth of 12 feet. The till was weathered and mmprised of , looae to mmpact,blueiah gray,wet,silty medium to fine sand with some marse to fine gravel and a trace of rootleb. a: Fill-Fill is a generic term used to classify soiLs that have been placed by humans, typically for the purpose of site grading and mnstruction. Fill cam m�sist of on-site ' material that has been cut and re-graded,or offsite(imported)material. Standards . for the placement of fill for construction purposes require that it be mmpacted to assure its ability to support structures and if placed on a slope,properly benched or keyed into the slope in order to assure stability. a, �.. Golder Associates