Study On Additional Stress And Transverse Displacement Of Soil Caused By Shield Tunneling Under Existing Buildings

Shield tunneling under existing buildings may cause some damage to underground structures and gas pipelines within the scope of construction,and may also cause settlement,inclination,cracking and even collapse of surface buildings.In order to avoid the above risks,this paper considers the influence of superstructure loads on the stress and displacement fields of soils during shield construction,and gives a simplified calculation method.At the same time,on the basis of the existing research,the influence of the friction between the panel-cutter and the spoke-cutter on the additional stress and lateral displacement of soil is considered.Based on the Mindlin solution of elastic mechanics,the calculation formulas are deduced by coordinate transformation,integration and superpo-sition.Combining with engineering examples,the distribution of additional stress and lateral displacement of soil caused by various factors in shield construction stage under existing superstructure loads and their effects on surrounding environment are analyzed.The effects of different superstructure loads on additional stress of soil and total lateral displacement of stratum caused by shield construction are also analyzed.For the additional stress of surrounding soil caused by various factors during shield tunneling under the load of existing superstructure,the analysis of engineering examples shows that the influence of cutter head friction on the additional stress of surrounding soil is small,but the additional stress caused by toroidal friction on the front and circumferen-ce of cutter head has a certain degree of fluctuation.Among them,the effect of additional stress fluctuation caused by frontal friction of spoke cutter head is particularly significant.The influence of different building loads on the additional stresses?_x and?_y caused by shield shell friction is obvious,and the effect of?_x affected by building loads is the most significant.For the stratum lateral displacement caused by various factors during shield tunneling under the load of existing superstructure,the analysis of engineering examples shows that the stratum lateral displacement value caused by each factor decreases with the increase of depth and gradually diffuses to the deep soil.In a certain range around the advancing face of the cutter head,the distribution of the positive and negative zones of the total lateral displacement of strata is related to the rotation direction of the cutter head.Centered at a location near the depth of the tunnel axis,the total lateral displacement of stratum caused by shield tunneling increases with the increase of the load of the upper building within a certain range of influence.