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I�ccemhcr 15. 1992 1� 923-1184 <br />Sile preparation in the areas o( structural fills and pavemenls should consisl of grubbing the <br />exisling vegetalion and lopsoil from Ihe arcas tvherc the gradc will Uc raised less lhan lhrcc <br />fccl. ln areas tvherc lhe raise in gradc is in excess of Ihree feet, Ihe topsoil should bc Ic(t in <br />��lacc and only lhe surface vegefalion should bc rcmoved. This should hclp minimize <br />dislurbance of lhe sensilive subgrades. Disruption of Ihc subgrade slwidd be minimized by <br />restricling machinery and foot traf(ic over lhe surface. I Iand cleaning of Ihe subgrade is <br />usually Ihe masl nffeclivc methoJ of preparalion and residls in minimal degredalion. In <br />arcas of exlensivc saluralion or slanding watcr, it may be necessary lo sl. bilizc lhe subgrade <br />priur lo fill placemrnt ulilizin� a sepantion gcotexlil�• (abric, soil cemenl, an imporled, <br />oversize pit-run base-course, or a co�nbinalion cf Ihese products/methods. I.ocalized <br />dewaterin� may also be necessary. Conducling �rading operalions in Ihe dryer, summer <br />monlhs is slrongly recommended lo roinimize Ilie impacl Ihal surface waler and loc�liud <br />groimdwaler tnay have on the projecL We expect all the site soils can be excavaled tvilh <br />conventional carthmovin� equipmenl. <br />1( groundwalcr is present or thc suhgrades arc in a saturaled condilion, ��rooLrolling should <br />nol br perfonned. 7'he subgradc soils Ihroughout lhc silc are considered modenlcly to <br />highly n�oislure sensilivc due lo thcir silt and pmo6rolling thcsc lypcs of soils rvhen in a <br />salureled condition tvoiild only degnde Iheir be�rin� capacity and slrudural inte�rily. <br />Subgrade ��reparaliun in lhesc inslances should mnsisl uf lhoroughly cicaning Ihc exposed <br />sur(ace of any loose, saluraled soils (ollowed by prompt placemenl of the overlying <br />componenls. <br />Prior lo conslniction of slaUs-on-grede or pavemenl, we recommend proof-rolling of Ihe <br />exposed subrrade. This can be accomplished �vilh a self-propelled smooth drum roller or by <br />whecl-rolling tvilh a(ully loaded dump lruck, whichcvcr is dcemed a��proprialc by Ihc <br />en�inccr. All proo(-rolling sliould be obscrved by a representative of thc geolechnical <br />en�;inccr to dMerminc Ihe suilabilily of thc sub�radc. Soft, yicldin� arcas tvill require removal <br />and re��lacenunl wilh compacled, slruclural backfill. <br />Winlcr construclion is fcasiblc at Ihis silc but may havc a si�nificant adversc impact on <br />project construction and cosls. l3ased on our experience wilh similar soil condilions, tvinler <br />conslructiom m�y rcquire conlraclor rr.medialion o( suU�rades dislurbed di�rin� wel �vealher <br />grading operelions residling in significanl incrrases in use of off-sile (ills, disposal of <br />unsuilable soils, and conslruclion delays. <br />5.'J:1 7'emporaty Slo��es <br />Safe construction excavalion sloprs are the responsibilily of the conlraclor and should comply <br />wilh all OSFIA and olher applicable sa(cly re�;ulalions. 13ascd upon lhc enmunlcred subsoils, <br />it is anlicipaled Ihat shalb�v, lemporary conslruction slopes (Iess than six feel in height) can <br />be excavated at �;rades of 1h1:IV (horizonlal lo verlical) in Ihe till soils provided adverse <br />growidwatcr condiliuns do nol result in exlcnsivc caving of slou�hing. Gxposcd cut faces <br />should be ��rolected wilh a facing such as visqueen lo preclude erosion during rainy periods. <br />Excavations �rcalcr than 4 fcet in deplh in Ihe (ill an�l peal should be shored lo precludc <br />ca��in� and sloughin� o( thesc loosc soils. <br />Golder Assoclales <br />