土钉墙+排桩在明挖隧道深基坑支护中的几个问题

就当前土钉墙+排桩在明挖隧道深基坑支护中的几个问题，开展了有针对性的研究。采用理论分析和数值计算方法，结合工程实例，深入探讨了土钉墙坡比i，排桩桩径-间距（D-S），以及设有内支撑时，桩-撑相对刚度等参数的选取原则。结果表明：（1）i越小，土钉墙越稳定，但排桩弯矩、水平位移越大。在土钉墙自身滑动稳定前提下，i宜取大值。（2）D-S越大，排桩水平位移越小，排桩混凝土、钢筋量越少，造价越低，但桩间土的防护越困难。在工程地质好、地下水位低的情况下取大桩径、大间距，反之取小值。（3）弱桩强撑的支护效果好，但对施工干扰大；强桩（非悬臂）弱撑造价低。选择桩-撑的相对刚度需从工程地质、周边环境要求、工期、造价等因素综合考虑，方能达到安全可靠，经济合理的目的。

Several issues on the soil nailing wall combined with row piles in bracing the deep foundation pits of open cut tunnel

Targeted research is performed on several problems about the application of the soil nailing wall combined with row piles in tunnel deep foundation pit support. Based on the theoretical and numerical analysis of engineering examples, the selection principle are proposed for the slope ratio i of soil nailing wall, the diameter-separation distance of the row pile as well as the relative stiffness between row pile and inner support while the inner support is applied. It is shown that 1) the smaller the value of i , the more stable the soil nailing wall, but the larger the moment and the displacement on the row pile are. The value of i should take a small value when the sliding stability of the soil nailing wall is fulfilled. 2) The larger the diameter and space between the piles, the smaller the horizontal displacement of the row pile, so that less concrete and steel rebar is required, resulting in a more cost-effective design, though the protection for the soil between piles will be more difficult. Hence, the diameter and the space between the pile should assume larger values when the engineering geological conditions is good and the water level is low, and vice versa. 3) Supporting effect of weak pile with strong support is better, but the construction interference for the surroundings is larger, while the cost of the strong pile (non-cantilever) with weak support is less. To achieve the purpose of safety and reliability and economical efficiency, it is necessary to consider engineering geological conditions, surrounding environment requirements, construction period, cost, and so on, in selecting the relative stiffness of the pile need.