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.