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1812A.4 Design and Testing
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The geotechnical report for the earth retaining shoring shall address the following:
- Minimum diameter and minimum spacing for the anchors including consideration of group effects.
- Maximum unbonded length and minimum bonded length of the tie-back anchors.
- Maximum recommended anchor tension capacity based upon the soil or rock strength/grout bond and anchor depth/spacing.
- Allowable bond stress at the ground/grout interface and applicable factor of safety for ultimate bond stress for the anchor. For permanent anchors, a minimum factor of safety of 2.0 shall be applied to ground soil interface as required by PTI-2004 Section 6.6.
- Minimum grout pressure for installation and post-grout pressure for the anchor. The presumptive post grout pressure of 300 psi may be used for all soil type.
- Class I corrosion protection is required for all permanent anchors. The geotechnical report shall specify the corrosion protection recommendations for temporary anchors.
- Performance test for the anchors shall be at a minimum of two (2) times the design loads and shall not exceed 80 percent of the specified minimum tensile strength of the anchor rod. A creep test is required for all prestressed anchors that are performance tested. All production anchors shall be tested at 150 percent of design loads and shall not be greater than 70 percent of the specified minimum tensile strength of the anchor rod.
- Earth pressure, surcharge pressure and the seismic increment of earth pressure loading, when applicable.
- Maximum recommended lateral deformation at the top of the soldier pile, at the tie-back anchor locations, and the drilled pier concrete shafts at the lowest grade level.
- Allowable vertical soil bearing pressure friction resistance, and lateral passive soil resistance for the drilled pier concrete shafts and associated factors of safety for these allowable capacities.
- Soil-pier shaft/pile interaction assumptions and lateral soil stiffness to be used in design for drilled pier concrete shaft or pile lateral loads.
- Acceptable drilling methods.
- Geotechnical observation and monitoring recommendations.
- Tendons shall be thread-bar anchors conforming to ASTM A722.
- Anchor design loads shall be based upon the load combinations in Section 1605A.3.1 and shall not exceed 60 percent of the specified minimum tensile strength of the tendons.
- The anchor shall be designed to fail in grout bond to the soil or rock before pullout of the soil wedge.
- Design of shoring system shall account for as-built locations of soil anchors considering all specified construction tolerances in Section 1812A.8.
- Design of shoring system shall account for both short and long-term deformation.
- The geotechnical engineer shall keep a record at job site of all test loads, total anchor movement, and report their accuracy.
- The contractor shall determine the cause of failure — variations of the soil conditions, installation methods, materials, etc.
- The contractor shall propose a solution to remedy the problem. The proposed solution will need to be reviewed and approved by the geotechnical engineer, shoring design engineer and building official.
- After a satisfactory test, each anchor shall be locked-off in accordance with Section 8.4 of PTI 2004.
- The shoring design engineer shall specify design loads for each anchor.
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