| The rammed earth building have attracted widespread attention due to their unique advantages such as energy saving,environmental protection,low cost,convenient material acquisition,and livability.However,due to the special layered and segmented ramming process,there are a lot of horizontal weak interfaces in rammed earth wall.Through investigation,it is found that the damage forms of many rammed earth houses after the earthquake are mainly shear damage,and the damage at the interface of rammed earth layer is particularly serious.However,there are few studies on the shear performance of rammed earth materials and weak interfaces in the existing literature.In addition,there are many numerical simulation methods for rammed earth wall;but the applicability of existing simulation methods is lacking.Therefore,in order to explore the shear properties of rammed earth materials and various weak interfaces,a numerical analysis method suitable for rammed earth wall,a series of shear tests and numerical simulation studies are carried out in this paper.The main research contents and conclusions are as follows:(1)The effects of specimen size and shear rate on the shear performance of rammed earth materials were studied through large-scale direct shear tests.Based on the characteristics of the rammed earth mixture and the actual working conditions of the wall,it is recommended that the size of the specimen of the direct shear test of the rammed earth materials be 200mm×200mm×200mm,and the shear speed be 2mm/min.(2)Large-scale triaxial tests and large-scale direct shear tests were carried out on rammed earth specimens with different modification ratios to observe their failure morphology,and the effects of curing agents and test methods on the shear resistance of rammed earth materials were analyzed.The results show that cement,lime and other curing agents improve the shear strength of rammed earth materials by improving the cohesion of rammed earth materials,but curing agent will reduce the internal friction angle of rammed earth materials.The cohesion measured by the large-scale triaxial test is small,but the internal friction angle is slightly biger.(3)Based on the previous research results,large-scale direct shear tests were carried out on rammed earth specimens with different modification ratios and different interfaces.The effects of the curing agent on the shear characteristics of the rammed earth layer interface and the interface between rammed earth materials and each building plate were compared and analyzed.The results show that the curing agent can significantly improve the shear strength of the interface between adjacent rammed earth layers,while the shear performance between rammed earth materials and building board is affected by normal stress,plate surface roughness,and strength of rammed earth materials.(4)ABAQUS was used to establish a large triaxial test and a pseudo-static test model to study the influence of weak interfaces on the numerical analysis of rammed earth wall and the applicability of existing numerical simulation methods.Based on this,A new simulation idea was proposed.The results show that the weak interface has little effect on the compressive bearing capacity of the rammed earth wall,while it has a greater effect on the shear bearing capacity of the wall.The final failure mode of the CDP model without the interface layer is the tensile failure at the bottom.The Mohr-Coulomb model without interface will overestimate the shear capacity of the test wall.The Mohr-Coulomb model with interface have phenomena such as large cloud image dispersion,low calculate,and too full hysteresis curve.Through improvement of interface processing method and reduction of elastic modulus,it was found that the improved model can not only reproduce the failure process of the test wall,but also its cracking load,cracking displaceme,shear capacity,and hysteresis curve before failure are in good agreement with the test results. |
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