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M03086GE <br />1~ <br />We suggest that the minimum free length of the soil anchors be <br />sufficient to extend beyond the theoretical calculated failure <br />surface which is at least fifty (50) feet beyond the surface of the <br />construction excavation slope inclination of one and one-half (1- <br />} lf2) to one (1). A steeper excavation cut slope may result in a <br />longer required free length to extend beyond the theoretical <br />calculated failure surface. If the anchor encounters formational <br />material the free length may be shorter and/or the design capacity <br />may be much higher. We should be contacted to observe the soil <br />anchor system installation to verify the conditions encountered and <br />modify our recommendations if needed. <br />The soil anchors should be designed with a minimum bond length of <br />ten (10) feet and a maximum bond length of twenty-five (25) feet. <br />Typically maximum pull out resistance is developed in soil anchor's <br />with a maximum bond length of twenty-five (25) feet with no appre- <br />ciable increase in pull out resistance developed for soil anchors <br />with a bond length greater than twenty-five (25) feet. <br />'. We suggest that the soil anchors be constructed with pressurized <br />grout in anchor borings approximately four (4) to six (6) inches in <br />diameter. The soil anchors should be drilled into the competent <br />soil material at an angle of fifteen (15) degrees or greater down <br />from the horizontal but nor greater than forty-five (45) degrees <br />down from the horizontal. The steel tendon diameter should be <br />~• - determined by the structural engineer based on the required load <br />criteria. The grout strength used should have a minimum compres- <br />sive strength of 4,000 psi after twenty-eight (28) days. The an- <br />chor ultimate capacity will not be achieved until the grout has <br />properly cured. The actual anchor capacity should be determined <br />during the construction using load tests. The load tests should be <br />I conducted using actual materials designed for use in the rock. <br />anchors and with the equipment and contractor anticipated to <br />install the anchors. We recommend load testing of control anchors <br />1 be conducted before anchor installation. <br />The anchor spacing should be determined by the stresses needed to <br />provide a stable slope during and post construction. The stresses <br />needed to provide a calculated stable slope condition will depend <br />on the final configuration of the proposed excavation cut slope and <br />the soil materials supporting the anchors. Once the final slope <br />configuration is determined we should be contacted to provide <br />additional stability analysis and provide needed anchor spacing and <br />anchor capacity. We are available to discuss this with you. , <br />• <br />~Lam6ert anD ~,ooociateo <br />CONSULTING GEOTEOHHIUL ENGWEERS •HO <br />MATE RILL TESTING <br />