Research On Mechanical Properties Of Basalt Fiber Phosphogypsum-based Tunnel Filling Laye

Phosphogypsum（PG）is the main industrial waste generated in the wet process of phosphoric acid production.In China,there is a large amount of phosphogypsum,which needs to be further processed and utilized in the field of transportation construction to solve the problems of land occupation and environmental pollution caused by phosphogypsum.The application of phosphogypsum in railway tunnel filling layer undoubtedly provides another effective way to solve this problem.The tunnel filling layer is the main bearing structure between the monolithic ballast bed and the inverted arch in the railway tunnel.Its main function is to transfer the dynamic load of the train on the upper part of the filling layer and the static load of the track bed and other structures to the surrounding rock of the tunnel.Therefore,the research on the adaptability of phosphogypsum railway tunnel filling layer structure under the dynamic static coupling is the key to judge whether phosphogypsum material can be used in the railway tunnel filling layer.Based on this,this paper preliminarily explored the applicability of phosphogypsum railway tunnel filling layer from four aspects:the elastoplastic damage constitutive relationship of phosphogypsum material,mechanical parameters of phosphogypsum material,structural dynamic response of phosphogypsum tunnel filling layer,and the influence of local seepage on phosphogypsum tunnel filling layer.Specific work contents are as follows:（1）Based on the literature data fitting,an phosphogypsum constitutive relationship suitable for the calculation of phosphogypsum material damage model is proposed.Combined with the tension compression damage evolution equation,an elastoplastic damage constitutive model of phosphogypsum material under cyclic loading is established.The stress-strain curve of the material output from the numerical modeling calculation is analyzed and compared with the measured fitting constitutive curve of phosphogypsum material,and the correctness of the damage constitutive model of phosphogypsum material is confirmed.（2）The mechanical parameters of standard compressive strength,peak strain and elastic modulus of 8 groups of phosphogypsum materials with different mix proportions were tested by pouring and stamping processes,the cracking strain-damage parameter curve was drawn,and the improvement of properties of phosphogypsum materials by basalt fiber and stamping process was analyzed.The water resistance of basalt fiber phosphogypsum material was tested by water resistance test.（3）The three-dimensional numerical model of high speed train-railway tunnel（phosphogypsum filling layer）-surrounding rock is established according to the damage constitutive law of phosphogypsum material and the mechanical parameters of the tested phosphogypsum material.The dynamic stress characteristics,deformation characteristics and damage distribution law of the phosphogypsum tunnel filling layer under the vibration load of high-speed train are emphatically analyzed,and the adaptability evaluation of the structural dynamic response of the phosphogypsum tunnel filling layer is made.（4）The beam and plate on elastic foundation model is transformed for the structure of phosphogypsum filled layer softened by local seepage,the surface settlement value of phosphogypsum tunnel filled layer at the softening position is calculated approximately.The softening coefficient K_90dis used to reduce the strength and stiffness of phosphogypsum material,and the structural dynamic response after the strength and stiffness of phosphogypsum tunnel filled layer are weakened due to local softening is analyzed and calculated numerically.