4841 GLENWOOD AVE 2018-01-02 MF Import

� f � May 5, 2008 Mr. Ron Riach/JRR Enginecring, Inc. L&A Job No. 8A043 Page 2 SUBSURFACE CONDITIONS Geologic Setting The Geoloeic Map of the Gverett 7.5-Minute Ouadran�le, Snohomish Countv. Washin�on, by James P. Minard, published by U. S. Geological Survey in 1985, was referenced for the geologic and soil conditions at the site. According to this publication, the su�cial soil unit at and in the vicinity of the subject msidence is mapped as Vashon Till (Qn). The geology of the Puget Sound Lowland has been modified by the advance and retmat of several glaciers in the past and subseque��t deposits and erosion. The latest glacier advanced to the Puget Sound Lowland is referred to as the Vashon Stade of the Fraser Glaciation, which has occmred during the later stages of the Pleistocene Cpoch and retreated from the region some I 14,500 ycars ago. The Vashon till soil unit was plowed under the glaciat icc during the most recent glacial period as it advanced over an croded, irregular surface of older formations and sediments. It is a mixture of unsorted clay, silt, sand, gravel, and scattercd cobbles and boulders. The till soils over the top two to thrce feet are normalty weathered to a medium-dense state, and is moderately permeable and compressible. 'I'hc underlying fresh till soils are very dense and we�ildy cemented, and are commonly referred to as "hard pan". 'The Gcsh till soils possess a shear strength comparable to that of lo�wgrade conerete and can stand in steep natural slopes or man-make cuts for a long period. Thc fresh till soils are ulso of exVemely low permeability and are practically impervious to storniwater infiltration. If rcmains undiswrbed and well-drained, the fresh till soils can providc exccllcnt foundation support to structures with little settlement expected. LIU & ASSOCIATES, INC. ��