SR 06:209 - Laserfiche WebLink

FYr~n<;;'1Vf" S{")11~ While expansive soils do not produce the catastrophic impacts of a large earthquake, their cumulative economic cost to a community can be considerable. Shrink-swell activity in subsurface soils can seriously damage building foundations, streets and other paved areas, sidewalks, curbs and gutters, underground utilities, and swimming pools. When expansive soils are present on a slope, they can promote downslope creep of the entire thickness of surficial deposits present on the slope (in some cases to depths of more than ten feet). The CalifOrnia Building Code contains minimum requirements for construction on expansive soils. These requirements have become more stringent since the 1970's and early 1980's when a number of Pleasanton's residences were constructed and have since suffered some structural and foundation damage due to expansive soils. The City has adopted policies which now require a soils engineer report for development in areas of moderate to highly expansive soils, and all buildings in these areas must be constructed according to the engineer's recommendations. The engineer must also inspect piers and foundations for compliance with the recommendations. Where specific geotechnical reports identify expansive soils, they must address how those soils may impact development. Where warranted, these reports must include mitigation, such as over-excavating expansive soils and replacing them with suitable materials. GPolog;r H~7M'c1 A h~tpmf"nt 01~tr1rt (GH A 0) In areas most prone to landslides or other geologic hazards, the City may require the establislunent of a Geologic Hazard Abatement District (GHAD) as a requirement for development. GHADs are districts formed specifically to address geologic concerns. A GHAD may be formed to prevent, mitigate, abate, or control a geologic hazard and also to abate structural hazards that are pardy or wholly caused by geologic hazards. A "geologic hazard" is broadly defined as an actual or threatened landslide, land subsidence, soil erosion, or any other natural or unnatural movement of land or earth. The formation of a GHAD would not allow development in areas otherwise thought to be unstable or at risk due to geologic hazards, but would assure that hi1lside development infrastructure such as drainage ditches, subdrains, erosion protection, etc. remain properly maintained such as to adequately control geologic hazard risks. Damage that is the result of an earthquake or fault movement is specifically exempted from coverage by the GHAD, in part because the assessments to include protection from land movement due to earthquake would be prohibitively high. Accordingly, residents should not consider the existence of a GHAD as a substitute for earthquake insurance. P~rthql1~kp Tmr~rt... It is not possible to predict with accuracy the extent of damage in the event of a significant earthquake. However, some types of damage can be generally expected. (See Table V-1, above, for a breakdown of Public Safcry 082906, clean V-13 City CouncilB/29/2006