Laserfiche WebLink
„_ /.,SI �fdar,r <br />A'alionu! ,Sci.rmic Nnrnrd �l7nps prcparcd by Ihc U.S. Gcoingical Survey indic�ic thn� a penk bedrock sitc <br />acccicr;Uion cocfficient nf about 030 i. appropriate I'or an carthqu�ke l��iving a 10-perecnl prohahility of <br />exceed�mce in 50 yem:s (cnrresponding m a rchirn inlerval of 475 ycurs). Bascd on our test probe, <br />pnrtions of tlie sitc soils abrn�e ,1U-leel bgs may be suscepiible tu liqucl:iction. Por purposes of'scisntic <br />site charncteriziuion, the obscrved soil conditians �vcre exlrapol;ttcd hcloa� �hc horing terminnlion deplh, <br />based on n revic��� oFgcologic maps and o�n kno�vlcdge ol'regin; :d ��_ology. <br />CONCLUSIONS ANU IiIiCOMD1l3�'llA'CIONS <br />Cunen� devclopment plans call for conslruc�iun ol';i ncw conununica�iun io���cr anci nssociated cellid.0 <br />equipmenl cabincls, t3ased on Ihe subswliice conditions encounicred in otn• soil boring 13-I, wc <br />recommend Uie proposed tower be supporled on a drilled pier finmcl�linn ���hich fully penetrates ihe <br />poteniially lic�ucii.�ble deposits. Design criteria for compressive, ���rn �»a i1«��t ,�����,�� ��r�i��u�d n;�, <br />fnundatinns nre nresented below. Our specific recommend.itions concerning site prepara�iou, equipmenl <br />cabinel fouudations, to���er foimdvtiuns. accexs drivew:ry and s�ructur:il (iIl are presen�ed in ihe follo�eing <br />SCCh0115. <br />l.iq��efircliu�i Anrrlpsis <br />Liqucfaction is Ihc lcmpornry loss of slicar sU'cngth in � satw;ucd soil mass suhjected to cyclical shaking. <br />lienvily lo,uled (oundalions supponed dirccQ}� �vithin or abnve liquelinble soils lypically suffer Gom largc <br />total and differential setdements �d1er a s��s�» �� ��.�m �r s��rr����u �,,:,��,��,��� �� ��,�,� ic�i���Gictiou. ln <br />.iddition, ihc laleral capacity of Ihe soil is likewise reduced u���ing tu Il�c Icmporary loss ol'shear strent!Ih. <br />The evaluatiun of liqueibc�ion liaz�ud is �^sed on corr�lntiau bet�t�ecn soil Ic�huc, soil dcnsity, anA thc <br />tnagnitude and dmation ofground shaking. Por a cicposi� lo bc liqucfiablc, thc soilx must be s�turated, and <br />exhibit low densiq� and p�r�iculnr grain sizc distrihution susceptiblc to liquef:iction. Plnsuc dny soils <br />cxliibil much hi�her resislunce to hqucfaclion ih;m cohesiatless deposits of sintilar lue� densily. 1i'urk by <br />Ishil�.na aud olhers indica�es the :idverse eftects of liqucf:ic�ion, such as snnd boils or grointd ruplw e, m;q� <br />nnl bc m�mitcsicd ai thc grnund surface sn long as adequale thickncst ol'non-liqucfi��blc soils m'c presenl <br />ahovc ihc poicniial liquefiaUle deposils. At Ihis sile, ground���aler w;is encountered uear ihc ground <br />surf.�ce nt G-feel belo��� ground surlaca Thc lop 24-tccl of n��ti��c soils deposiis encowucred in otu <br />c�plorrtions bdo�v Ihc gi'omtd �vater leeel are considered susceptible to liquct:iction dw�ing � significam <br />scisntic e�•enl. A typic:d dcsign carlhquakc for �he Pncific Norih�eesl rcgion has a Richler scalc <br />magnihide of G.S, horizontal peak ground acccleiation of 0?g, and :�I Icasl 2Q cycles ol' significanl <br />shnking. <br />A number of cunstruction mGhods are ;�vail��bfe to mitigatc Ihe poteutial for liquelaction al lhe sitc. <br />7'hcsc includc dccp foundations, such as driaen or augercasl piles, ���liich fully penclr:ue Ihc liqueliable <br />deposils. Al�ernali��ely, vibro0u�miou, rock er stone colunms, or compaclion piling m;q� bc used to <br />dcnsif�� the ncar-sm'lace deposits tu reducc Ihc polculial ibr liqucfacliou. Anp uf ihcsc ntcthods �vould <br />add substantial cost �o thc fuundaiion systcnt A� ihe pruposed tawcr location. Ihe nativc dcposits ��rould <br />�'cii:an \\'irelrxs Au�Usl J.?UUi <br />�\dap� I'nncn ku. \l4\Oi-97P ��ir� � � <br />� <br />