土钉墙面层土压力的计算分析

在目前的土钉墙设计中,面层通常被当作构造处理而不参与计算,墙后的主动土压力全部由土钉承担。实际上,土钉墙面层承受一部分土(水)压力。文中把土钉墙面层看作是弹性地基上的有限长梁,基于试验,推导了成层地基上土钉墙面层在土钉拉力作用下的挠曲线、转角、弯矩和剪力方程,并与实测数据进行了比较分析,验证了模型的合理性,得到的解析解基本上可以反映土钉墙面层土压力的分布。在此基础上,探讨了不同土性土层中土钉墙面层土压力的分布。面层土压力在土层的分界面上,位移连续,土压力发生突变;软弱土层分布的面层土压力较硬土层为大;上软下硬型较上硬下软的土层分布更能使面层土压力得到充分发挥,同时计算了面层土压力换算成荷载与土钉拉力的比值,其值随着开挖深度的增加越来越大,面层对于土压力的作用随着深度的增加表现得愈加明显,并提出针对不同地区、不同深度和不同土性条件下应给出比值的建议值,以使土钉墙的设计更符合其真实的作用机制,得到的结论和上述比值的计算方法对于进一步研究土钉墙的作用机制及设计中如何充分发挥面层的作用等具有重要的理论意义和实际应用价值。

Analysis of facing earth pressure in soil-nailing walls

Present designers of soil-nailing walls consider the facing as accessory structure rather than the main one, and all active earth pressures of soil-nailing walls are born by nails. However It is absolutely sure that the facing bear against water and earth pressure. Facing isolated and considered as finite beam on elastic foundation simply, solutions of displacement, angles of rotation, bending moment and shear force of soil-nailing walls are gained on basis of field tests in layered soil. Rationality of the model is tested and verified. The results that can disclose laws of distribution of facing earth pressure are in agreement with the actual measurement data. Earth pressure in bounding surface shows abrupt changes while displacement of facing exhibits continuous characteristics. Earth pressure of facing applied by soft soil presents bigger values than that of hard soil. Earth pressure in “upper soft and lower hard layers” can be easily gained than that of “lower soft and upper hard layers” soils. The laws of facing earth pressure in various soil layers are studied that the curves of earth pressure in good layers such as sand soil and hard plastic clay have characteristics of zigzag shape rather than smooth one in bad soil layers of silt soil and soft plastic clay. At the meantime, ratios of earth pressure to nail tension are calculated; and effects of facing on earth pressure become clearer and clear with depth of pit excavation. The ratios of earth pressure to nail tension become larger with excavation depth. In order to meet the necessity of mechanics of soil-nailing walls, rations of facing earth pressure to nail tension in various soil layers and depths should be put forward for references. The results and the method of calculating above ratios based on precise elasticity theory are very significant and have engineering use value for further research of mechanics of soil-nailing walls and for designers considering the facing action against earth pressure.