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预应力锚杆以抗拔力、截水帷幕及微型桩以抗剪强度共同提高了复合土钉墙的整体稳定性。叠加这些复合构件的抗力作用并对组合效果进行折减,是复合土钉墙整体稳定性验算目前最成熟有效的方法。验算公式的关键是土、土钉及各复合构件分项抗力系数(抗力系数即构件抗力产生的抗滑力矩与土体下滑力矩之比)的折减系数。折减系数是经验数值,可按一定的假设条件从实际工程数据反算整理得出。对多个接近临界稳定状态基坑的分析研究及数百个基坑的验证结果表明:这些复合构件单独及共同与土钉墙作用时,折减系数存在着合理范围,分别为预应力锚杆0.5～0.7、截水帷幕0.3～0.5及微型桩0.1～0.3。此外,土体和土钉的分项抗力系数之和(不计其它构件作用)存在着合理下限,大致为0.86～0.97,如果在满足整体稳定性安全系数的同时满足此条件,复合土钉墙基坑位移一般不大。
Prestressed anchors to anti-pull, cut-off curtains and micro-pile shear strength together to improve the overall stability of the composite soil nail wall. Superposition of these composite components of the resistance effect and the combination of reduction, is the overall stability of composite soil nailing checking the most mature and effective method. The key of the checking formula is the reduction factor of soil, soil nails and the sub-item resistance coefficient of each composite component (the resistance coefficient is the ratio of the anti-skid moment generated by component resistance to the sliding moment of soil). Reduction factor is the empirical value, according to certain assumptions from the actual project data obtained by back-finishing. The analysis of several near-steady-state foundations and the verification results of hundreds of foundation pits show that there is a reasonable range of reduction coefficient for these composite members acting alone and together with soil nailing walls, namely, prestressed anchor 0.5 ~ 0.7, 0.3 ~ 0.5 water curtain and 0.1-0.3 micro pile. In addition, the sum of the sub-resistance coefficients of soils and soil nails (excluding the effects of other components) has a reasonable lower limit of approximately 0.86 to 0.97. If this condition is satisfied while the overall stability safety factor is satisfied, Pit displacement is generally not large.