11-10-1986 Council Packet - Laserfiche WebLink

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86-681 Tennis West, Ltd. -2- October 16, 1986 this wall, the natural ground G 1� upward from the wall at an estimated angle of 2:1 (hori4 L.vertical). The wall is to be constructed using 5 by 6-inch pressure treated timbers. Approximately 2 1/2 timbers will be buried below grade to provide sliding resistance for the toe. The anchor `;stem is to be constructed using timbers ranging from 6 to 8 feet in length. The cross members are proposed to be 8 feet in length. The anchor ties will be placed on f fe ^^ters with each anchor system retaining about 16 lineal feet (-. A single soil sample representing the proposed backfill and the natural bank soil was provided to us. The sample consisted (.: fine-grained sandy lean clay to clayey sand with some gravel. The sample was dry. For purposes of this evaluat— a, we have assumed the predominant soil will be the sandy lean clay. ANALYSIS AND RECOMMENDATIONS We initially evaluated the "active" zone behind the wall using a long-term internal friction angle of the backfill of 20 degrees. For design purposes, all anchors should extend behind this theoretical plane. For the lower wall, this plane intersects the surface at a distanc-_ of about 5 feet behind the wall or within 1 foot of the upper wall. Because of this and the wall con- figuration, we recommend that the distance between the walls be increased to at least 8 feet. In review of the ancnorage sysLem proposed for the lower wall, our calculations indicate that the resistance generated by the anchors as compared to the force of the soil_ on the wall will provide for a factor of safety of at least 2.0 if only the soil characteristics are taken into account. It should be noted that this analysis aid not taken into account the structural capacity of the retaining wall. Thus, the factor of safety may be slightly greater than we calculated. Therefore, the proposed anchorage system should be adequate to resist the forces exerted on the wall. However, given e limited embedment (6 to 8 feet) of the anchors beyone the "active" zone, it would be necessary that the wall resist a por- tion of the soil load instead of having the anchors resist the forces. To increase th;- amount of passive pressure generated, thus reducing the soil load on the wall, we recommend that the anchorF- be extended such that the top two anchors extend at least 10 feet behind the wall. The lower anchor should then be a minimum of 5 feet long. These lengths assume the anchor configuration as shown in the attached sketch. If more tiebacks are used, thy, length can be rPauced to 8-foot lengths. Our ,.,BRA uo