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� Mr. Ken Pruett <br /> � October 27, 2004 <br /> q <br /> e <br /> � <br /> G�roundwatcr <br /> � Groundwater �cns encountered during drilling of the test borings at deptns of i I fcet and 12 feet in Borin�s B-1 <br /> and B-2, respectively. The ground���ater�vas obsen�ed at depths approximately equivalent�eith the standing «•ater <br /> � elevations observed in die ponds. <br /> The preeeding discussion is intended as a brief revie�� of the soil �nnditions encountued. Por mure detailed <br /> 1 descriptio��s, pleasc refer ro dic Borine Logs, Figures d and �. <br /> I 5LOPC STr\[3ILIT]' ANALYSIS <br /> ) Slope stability analyses were complcted in crder to asse,s relati�e slope stability of�A�e berm for the existing aed <br /> � pos[-coustruction condi[ions. The analyses ���ere pertixmed tit critical locations chosen as Cross-Section r�-:\' <br /> (northern slope face) and Cross-Section B-B' (soudiern siope face) usine the computer p�ogram \1'INST�,BL. <br /> f The cross-section locations are shown on Pigurc 2. <br /> I <br /> The analyses �+�ere perf'ormed for dte cases of ezistine conditions, and conditions after constniction �:mpq pond). <br /> � Wc also examined the case of the poud at maximum sen ice lecel and unlincd, such tliat if impoundment occurred <br /> for a suflicient length of time, a phreatic surface would decelop in the embankment. The "rapid dra�vduwn" casz <br /> ��as also calwlated for the northern slope face. Finally, the post-constructior case was analyzed tha[ includcd <br /> ;ining tlie pond as a mitigating factcr for berm stabiliq�. <br /> The analyses incorporated static conditions and, includes a inform constructior. traffic surcharee of 2�0 pound; <br /> per square foot. (ps�. Wliere pertinent, seismic load conditions using a horizontal acceleration �alue of 0.20g <br /> were also analyzed. This ground acceleration va!ue n•as chosen bascd on a re�•ie�c of' Peak Acceleration i:lap <br /> I (Univcr.:ity of If�nshington Pncific Nort6nest Seism:o Nenra•k) for the Nisqually Earthquake(M 6.8), «�hich ma�; <br /> surface peak groand accelerations ranging from 0.08 g to 0.20 g within a radius of�0 km from the earthquake'; <br /> epicenter. In tlieir discussion regarding the probabilistic approach to estim ting design ground motiors at a site, <br /> iDSO states that "in seismic assessments of projects in the Puget Sound area, a random NICE (maximum credibl�� <br /> � earthquake)of magnitude G li2 within the NAP (Nonh American Platej has becn a common assump:ion." <br /> Based on our fie:d esplomtion v�d labormury'te,ting, ��'e cho;e tha Collon'ing parameters for use in tltis:tnalysis: <br /> I <br /> Tctblc 1 <br /> Slupc Stabilih� Anal}�sis Soil Parametcrs <br /> Suil"I�}'pc Unit R'eigh[(pcQ Grictinn Angle(degrees) Cohcsion (psQ <br /> - Ncwbennstrucmralfll 13� =� ]00 <br /> Existing upper bcrm till 12� 33 100 <br /> Exis[ing lower bonn till 120 30 �0 <br /> Nati�e d_nsc sand rith silt 12� 30 0 <br /> Project No. T-»69 <br /> � Page No. 3 <br /> /�' <br />