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,�,8.B. - Page 128 5-Lot Residential Development December 9, 2010 <br /> � <br /> �r <br /> Su�ace Manifestation <br /> The boundary curve for d;scriminating between occurrence and nonoccurre�ace of surface effects <br /> of ]iquefaction, after Ishihara 1985 (Youd and Gariris, 1995), in Fig-ure C2�A, indicates that <br /> s�ace manifestation due to liquefaction of the deeper sand layer is low. Deterit�ination of the <br /> point within the plot involves es�abjishing the thickness of the non-liquefiable layer and <br /> co�paring that with the thickness of liq�efiab�e sand layer as determined using the diagrams <br /> presented in�igure C2-B. <br /> 5.0 CONCLUSI�NS <br /> Site SuiEabili <br /> The subject site is suitable for the proposed residential development from a geotechnical <br /> engineering standpoint provided the recoznmendations inc�uded in this report are followed. <br /> Site Preparation and Gradin� <br /> As the site is present�y roughly le�el, it is anticipated that anly zninor cuts ar�d fi�ls would be <br /> required to develop the site. Addit�onal anticipated grading aperations include stxipping of <br /> organically contaminated soils a.rid removaZ of existing foundations and utilities at the site and <br /> the recompaction of surficial soils disturbed by demalition. Due to the presence of variable <br /> density creek baz�k deposits averlying the fat clay at the site, building pad areas sbould be <br /> reworked to a depth of 2 feefi or to the top of�e fat clay, whiche�ver is less. <br /> Ex ansion Potential <br /> The Atterbezg Limits laboratory tests performed by Terrasearch (1995) from the near surface <br /> soils on the adjacent property resulted i.n Plasricity Indices of 42 and 49, indicating high <br /> expansion potential. Special mitigation measures will be necessary to protect tbe proposed <br /> residences from the effects of expansive soils. Mitigation �neasures vvill inc�ude the use of a <br /> post-tensioned concrete slab foundation and possible presoakfng of the foundation Excavations <br /> and subgrade surfaces pzior to pla.cement of concrete. <br /> Soil Concietions <br /> Jn g�neral, the soil materials rnaterials consist of S to 9 feet of dark gray ex�ansi�e clays <br /> overlying bzown silty to sandy clays and clayey sands and silts to the ma�imum depth explored. <br /> 8 <br />