3815 SHORE AVE 2020-05-20 - Laserfiche WebLink

Geologically Hazardous Areas: Geotechnical Letter Kennedy Single Family Residence 3815 Shore AVenue March 23, 2018 RN File No, 3279-001A Page 4 classified in general accordance with the Unified Soil Classification System, a copy of which is presented as Figure 3, The logs of the test pits are presented in Figure 4. Subsurface Conditions A brief description of the conditions encountered in our explorations is included below. For a more detailed clescriptiOn of the soils encountered, review the Test Pit.Logs in Figure 4. Our explorations generally encountered a surficial layer of sod that was less than 0.5 feet in thickness. Underlying the sod, we encountered fill and possible fill consisting of very loose to medium dense sand and silty sand with varying amounts of gravel and roots that extended to depths ranging from about 2 to 4 feet below existing ground surface. Below the fill in Test Pits 1 and 2 we observed medium dense sand to depths ranging from about 4 to 8 feet. Underlying the medium dense sand, the explorations disclosed medium dense to dense sand and sand with silt and gravel interbedded with thickening 1-to 4-inch layers of stiff silt to the depths explored. Hydrologic Conditions Shallow groundwater seepage was encountered at approximately 9 feet in Test Pits 1 and 2_ We consider this water to be perched along the contact of the cleaner sand layers of the outwash with the underlying silt layers of the transitional beds. During the wetter times of the year, we expect perched water conditions will occur as pockets of water within the outwash layer. Perched water does not represent a regional groundwater "table" within the upper soil horizons. Volumes of perched groundwater vary depending upon the time of year and the upslope recharge cenditions. We observed seepage over the silty face of the steep slope.We interpret this as perched water flowing out of the face of the slope at the contact between the sand layers and silt layers as encountered in our subsurface explorations.. CONCLUSIONS AND RECOMMENDATIONS General It is our opinion that the site is compatible with the planned development. The planned setback of 70 to 80 feet is adequate considering the slow regression of the slope face. Also, the planned drainage improvements as stated in this letter should improve the stability. The underlying medium dense to dense or stiff glacial outwash or transitional bed deposits are capable of supporting the planned structures. We recommend that the foundations for the structures extend throUgh any fill, topsoil, loose, or disturbed soils, and bear on the underlying medium dense or firmer, native glacial outwash or transitional beds, or on structural fill extendingto these soils. Based on our site explorations, we anticipate these soils will generally be encountered at depths ranging from about 4 to 6 feet. Therefore, the planned footing depths will be within the undisturbed native soils. Robinson Noble, Inc.