| The Foshan area is located in the coastal soft clay layer.The Shield tunnel will bear extremely complicated loads when passing through this layer.Due to the complex engineering characteristics of soft clay,it is difficult to form an arch effect on the tunnel above the tunnel.The weight of the soil cover,so the accurate analysis of the type of load on the lining structure in the design work is the key to ensure construction safety and structural life.The method commonly used by Chinese design workers is to use the calculation model with uniform vertical load distribution and linear load distribution to calculate the internal force of the structure.However,with the vigorous development of underground engineering,China's engineering construction gradually challenges various complex geological conditions.In this case,if the existing calculation model is also used,it will undoubtedly cause calculation deviation and material waste.In order to study the distribution law of external load on lining segments under special geological conditions in Foshan area,firstly,from the theoretical point of view,combined with the actual situation of the region,a comprehensive analysis of the four load distribution modes is assumed,and then the force of the prototype is simulated by model test.The inverse analysis is carried out in combination with the finite element numerical calculation.Finally,based on the back analysis results and related data,the load distribution pattern suitable for Foshan area is proposed.1.Based on the existing load distribution research and engineering geological survey of Foshan Metro Line 2,four load distribution modes are assumed,namely,the combination of vertical load distribution and horizontal load distribution,the combination of vertical load distribution and horizontal load parabola distribution,the combination of vertical load parabola and horizontal load distribution,and the combination of vertical load parabola and horizontal load distribution as well as the combination of vertical and horizontal load parabola distribution.2.Using kaolin and bentonite as the main substrate and adding a certain proportion of loess and river sand to prepare artificial clay,the final geotechnical test results show that the similar formation soil meets similar requirements.The gypsum is used as the casting material of the model lining,and the 0.6mm steel mesh simulation reinforcement is used to make themodel tunnel by pouring.Combined with the physical and mechanical tests,the elastic modulus of the gypsum and water according to 1:0.7 and the borax accounted for 1.5% of the water is explored.The prototype lining is similar.3.The internal force and earth pressure monitored by the model test are generally symmetrically distributed,and the mechanical properties of the homogeneous ring model are verified.The maximum bending moment is 92.4KN·m at the vault,the minimum bending moment is-39.9KN·m at the left arch waist,the maximum axial force is-960 KN at the left lower half of the arch waist,and the minimum axial force is-1275.75 KN on the upper right.Half arched.The vault monitoring pressure is applied to the four modes as known loads.It is found that each mode has different degrees of deviation from the measured internal force values.The magnitude of the deviation is mainly affected by the horizontal load distribution mode.The impact is slightly smaller.4.Calculate the calculation model corresponding to the four load mode by ABAQUS14.0 finite element software,and test the measured internal force as the known quantity,and analyze the load value by the load-internal force curve and return to the calculation model to calculate the internal force.After the final data comparison analysis,it is considered that the internal force of the combination of the dome uniform and the horizontal parabola is the closest to the measured value,and the internal force distribution is relatively uniform.The lining material is reasonable and most consistent with the characteristics of the stratum load value. |
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