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December 21, 2022 <br /> Job No. 4031.101 <br /> Page 10 <br /> <br />BERLOGAR STEVENS & ASSOCIATES <br />7.11.3. Retaining Wall Drainage <br /> <br />The above recommended lateral pressure on retaining walls assumes drained conditions. To <br />prevent hydrostatic pressure build-up, the retaining walls should be provided with permanent <br />backdrains. The backdrain should consist of a 12-inch thick vertical blanket of Class 2 Permeable <br />Material (conforming to Section 68-2.02F of the State of California Standard Specifications, dated <br />May 2015) and a 4-inch diameter perforated PVC pipe (SDR 35). The vertical blanket should start <br />at the base of the retaining wall and extend vertically to 12 inches below finish grade. The <br />perforated pipe should have two rows of holes and be placed face down at the bottom of the wall <br />to carry collected water to a suitable gravity discharge. The perforated pipe should be placed on <br />top of 2 inches of Class 2 Permeable Material and should have 6 inches of Class 2 Permeable <br />Material on the sides and top of the pipe. The subdrain pipe should tie into a solid pipe into a <br />suitable gravity discharge or storm drain system. <br /> <br />Alternately, a geocomposite can be used in lieu of the Class 2 Permeable system as follows: <br /> <br />1. Install Miradrain 6200 at the back wall extending from the top of footing to 12 inches <br />below the top of backfill. The plastic side of the Miradrain should be placed tightly <br />against the back of the retaining wall. <br /> <br />2. Place Advanedge (12 inch) Drain tightly against the Miradrain. <br /> <br />3. Install a round pipe adaptor and install a solid round pipe to carry water to a suitable <br />gravity surcharge. <br /> <br />4. Use caution during backfilling not to collapse the MiraDrain. <br /> <br /> PAVEMENT RECOMMENDATIONS <br /> <br />7.12.1. Flexible Pavement Section – Asphalt Concrete <br />R-value testing on a bulk sample collected during our investigation resulted in a value of less than <br />5. The following preliminary pavement analyses are based upon an assumed R-value of 5 for the <br />subgrade soil, the Caltrans Design Method for Flexible Pavement (20-year life cycle), and traffic <br />indices (TI), which are indications of load frequency and intensity. <br /> <br />Preliminary Pavement Sections <br />Traffic Index AC (in) Class 2 AB (in) Total (in) <br />4.5 3 8 11 <br />5 3 10 13 <br />6 4 12 16 <br />7 4 16 20