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�.09.2 '�rcnch Escavation <br /> Thc IcngUi of trench excavation in advance of pipc laying shall be kcpt to a <br /> minimum and in no casc shall �,xcced I50 feet unlcss specilically authorized by <br /> the city enginecc Thc mar.imwn pemiissible trench width behvecn the <br /> foundation lcacl to the top of'thc pipe shall Uc 40 inches for pipc 15 inchcs or <br /> s�ualler inside dimneter; or I-U2 LD. plus 18 inches for pipe 18 inches or larger. <br /> If thc maximum trench width is exceeded without written authori•r.ation of the <br /> city engine�r, the developer/contractor will be reqi:ired to providc pipe of highcr <br /> strcngth classification or lo provide a liigher class of bedding, as required by the <br /> city enginccr. <br /> 3.09.3 Trench Backfill <br /> Suitable native matcrial cxcavated d�aring trenching shall be uscd for trench <br /> backfill unless notificd Uy thc city engineer that the native matcrial is <br /> unsuitable. The city cngineer or his rcpresentative will examine cxcavated <br /> native matcrial at the time of excavation lo deterniin.: its suitability for use as <br /> backfill. Native material will be considered suitable for trench b�ckfill if it is: <br /> A. Capable of attaining the degree of compaction specified in Section 3 <br /> Compaction. <br /> B. Within reasonable tolerance of optimum moisture content. <br /> C. Reasonably free of organic material, clay, frozen lumps, rocks or othcr <br /> deleteriaus matter. <br /> Unsuitablc backGll niaterial shall be removed from the sitc and hauled to an <br /> approved disposal site. The city cngin�er shall bc provided with thc location of <br /> all disposa( sites to be used and also copies of thc perniits and approvals for <br /> such disposal sitcs. <br /> Imported malcrial shall meet thc rcquiremenls oCGravcl Borrow as spccificd in <br /> Section 3 of these Standards or Cnishcd Surfacing Top Course as specificd. of <br /> the WSDOT/APWA Standard Specifications and Section 3 of thcse Standards. <br /> 3.09.4 Comnaction <br /> 7'rench Uackfill shall be sprcad in laycrs and compacted Uy mechanical tampers <br /> of the impact t}7�c approved by the city engineer. The backfill material shall be <br /> placcd in succcssivc Iayers with the first laycr not to exceed 2 feet abovc the <br /> pipc, and thc following layers not cxcceding 12 inches in loose thick�ess with <br /> cach layer bcing compacted to the dcnsity spccified bclow: <br /> A. Improved areas such as strect and sidewalks shall be compacted to 90% of <br /> maximum dry dcnsity to wilhin 3 feet of suUgrade. The lasl 3 fecl shall be <br /> compacted te 95%oCmaximum dry density. <br /> [7 <br />