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Sec. 6.3 Liquid Containment (Pond) Liners 429 vk = the average horizontal stress in anchor trench Koov, a,, = -y N,,,:, y = the unit weight of backfill soil, H„,. a the average depth of anchor trench (requires an csiirnate), Ko a 1 — sin 4, 4 = the angle of shearing resistance of backfill soil, and dAT s the (unknown) depth of anchor treach. Note that this situation re=sults in one equation with two unknowns,thus a choice of Lao or dAT is necessary to calculate the other. As with the previous situation the factor of safety's placed on the goomembrane fone T, which is used as an allowable value,i.e., Ta.. An example Illustrates the procedure. Exampk: Repeat the previous problem of a 30 mil CPE geomembrane of allowable stress 350 lb./in-2 on an 3(M to I(l7 side slope. 'There is a 12-in.cover soil placed over the geornembrane weigh- ing 100 lb./ft.3(also the unit weight of the backfill soil). 71w friction angle between the liner and soil is 20 deg. and the soil itself is 30 deg. Detamine the required lettgth Of runotrt for a 12-in.-deep anchor trench and for a zerode* anchor trench to check the previous,prob- lem. Solution: Using the previously developed design oquations basad on Figure 5.28: i T",. =Fu + FL + 2F'AT 0+ q tan 8(LRo)+2(Koav� tan 8(dAr) to.(350 x 144) \ 121 — 0 + (1.0)(100)tan 20'(LRo) + 2(0.5)(2.0 X 100)tan 20°(dAT) t 126 — 36.4 Lao+ 72.8 dAT which for der 1.0 ft-,Leo - 1.5 ft.,and for dAT C 0 ft.,LRo —3.5 ft.(which chocks do previous answer reasonably well). Exanipic Develop a set of design curves using due pmvious problem but now asiag variass geOaneM- .� brave allowabk straw of 700, 523 and 350 lb.rrn.2. 4. Sohtdow As befoae, but now witb au,.being the variable: . (a,ra,.,. X 144) 0.030} ® 36.4 LRo+ 72.E dT C 12 / a 0.36 v.a... - 36.4 Lego + 72.$dAT r' which when plottod produces the following to of croaks. Nott that as o.a..,inatues the roquirod LRo and dAT values also U=rAse FIporliooXWy. R 5