SR 06:201 - Laserfiche WebLink

Page 3 P-6748 EVALUATION AND CONCLUSIONS It is our opinion that the geotechnical investigation performed by BGC for this parcel generally conforms to accepted geotechnical standards of practice. However, a number of issues should be addressed by BGC as the project progresses. These items are discussed individually below. I. Additional information is needed regarding possible landslide activity in the large swale on Lot 6 (it should be noted this area is shown as a landslide on the published landslide map by Majmundar, 1996). More explanation of the basal contact and overlying deposits exposed in TP- 5, and the stability of deposits located downslope, including the prominent hillside bulge at the elevation of the former dirt road on Lot 6, is required to adequately confirm or deny the presence of potentially unstable landslide deposits. We recommend that the possibility of slope movement on Lot 6 be more fully addressed, either by additional exploration or by removing landslide debris, if present, during grading. In our opinion, it may not be sufficient to have the cut portions of the pads subexcavated to a depth of at least three feet, as proposed by BGC. Rather, we recommend that all cuts are beneath the depth of any landslide debris, if present, and unstable areas rebuilt with properly compacted fill. 2. Additional evaluation should be performed regarding the extent of landslide deposits in the swa1e northeast of the water tank to confirm renewed landslide activity does not progress into the water tank pad. Similar to Item I, overexcavation at the pad level may be insufficient to adequately protect the tank. 3. Further evaluation should be performed in the possible landslide area on Lot 4 discussed earlier. Development of remedial work recommendations should be provided, as needed, to protect the new access roadway. 4. The presence of deeply incised gullies suggests that erosion due to concentrated drainage may be a problem on the property. We recommend that downslope erosion, including stream incision on the northeastern portion of the lot, be more fully addressed prior to construction. Specific remediation of the gullies may be required in the final surface and subsurface drainage plans. 5. Further discussion should be provided regarding the impact of mapped landslides, and adjacent instabilities that may encroach into the building pads on Lots 5 and 7. Additional field exploration may be necessary to eva1uale the existing pad on Lot 5. LIMITATIONS Our services have been performed in accordance with generally accepted geotechnical principles and practices. This warranty is in lieu of all other warranties, either expressed or implied. Our services have been provided at the request of the City of P1easanton. Our role has been to provide technical assistance to the City as it considers its permit decisions in this application, and we understand our firm is provided the same protection as the City under State law. ALAN KROPP & ASSOCIATES, INC.