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� . <br /> IIf csicrior rctaining �calls arc to bc constructed. �rc rccommcnd Ih:n hackfill ��ilhin 2 kct of <br /> walls consist of frcc-draining matcrial. N'c ako rccommcnd installing a�-inch-diamctcr�rfixaicd <br /> Icollector pipe �vithin the frce-draining material a� Ihc hase of the���all. N'e rccommend using cidicr <br /> hca��-wall solid pipc or rigid currugatcd pol��cthylcnc pipc. \Vc rccommcnd agains� using flcsihlc <br /> tubing for���all drains. <br /> � The pipe should bc laid ��ith a minimum slope of one-half perccnt and dischargc inlo thc <br /> sromiwater collcction systcm to convcy the water o(1=si�e. Tiu pipc installations should includc <br /> ( cleanout risers with covcrs. N'e rccommend against discharging mof downs�uts iulo ihc <br /> � perforated pipe pro�iding wall drainage. <br /> .4ltematively, the extcrior �ralls can be pmvidcd with weepholcs to discharge �ealer from thc <br /> � free draining �vall bar�;rll material. The �reepholes should be 3 inches in diamc�cr, and spaced <br /> about e�-cry 8 fcet centervto-center abng the base of ihe walls. Tlie Hecpholes should he backed <br /> Iwith ¢alvaniud hea�•�•wire mesh to prevcnt loss ofthc backfill matcrial. <br /> 4.5.3 Construction Considerations <br /> ' Carc should be taken by the contractor during filling adjacent to walls to avoid overstressing ihe <br /> �valis. Fill placed �cithin about 5 fret of��•alls should be compacted ��ith hand-operated or small <br /> � self-propelled equipment. Hea�� compacrors should not bc used within about 5 fctl of�ralls. <br /> 4.6 STORMWATER VAULT <br /> � 4.6.1 Foundatfon Support <br /> \1'e recommend that the stormwater detention vault be s�pported on conventional spread <br /> footines bcaring direcdy on the native undiswrbed advance outw•ash sand. Based on Ihe msults of <br /> � borines B-6 through B-8 that ��ere drilled east of the vault location, we anticipate lhat the advance <br /> ouh�ash sand�vill be encountered below Ele��ation 421 fcet. <br /> 11�e recommend that the e�7erior footings be Tounded a minimum of 18 inches below the lowest <br /> � adjacent grade. Continuous vault���all footings should have a minimum width of 24 inches. <br /> The vault footines may be designed using an allo���able soil bearing value of 4,500 psf on <br /> � undisturbed advance ouhvash sand. The allowable soil bearing values apply to the total of dead and <br /> lone-tertn live loads and may be increased b�•up to one-third for wind or seismic loads. <br /> Provided all loose soil is rcmoved and the subgrade is prepared as rccommcnded in the <br /> � Eanhwork section,���e estimate the total senlement of shallo���foundations will be on the order of%, <br /> [o '/. inch. Tlte settlemenu will occur rapidly, essentially az loads are applied. Differential <br /> I settlements measured along 25 feet of wall foundations arc ezpected to be less than '/. inch. <br /> Nc recommcnd that ihe condition of all footing excavations be observed by a representative <br /> from our firtn to e��atuate if ilie subgrade is prepared in accordance with our recommendations and <br /> Ithat the subsudace conditions are as expected. <br /> 4.6.2 Subsur�ace Walls <br /> IWe understand that Ihe subsurface �ealis for the��a�it �rill be consWc.ed as cast-in-place �valls <br /> or using til[-up methods. The �+alis will be designed uith wecp holes and therefore [he walls ��ill <br /> � <br /> � G e o L' n g i n e e r s 15 PileNo. 75gq.p02-0p.�130\05DI01 � Y�� <br /> / � <br />