| The true triaxial apparatus is a geotechnical test equipment that can be loaded under complex stress paths and measure the strength and deformation characteristics of soil.A new type of threedimensional rigid loading true triaxial apparatus has been developed by the Institute of Geotechnical Engineering of Xi ’an University of Technology.The instrument has a high-precision measurement system and has the characteristics of an automatic control system for independently applying three-dimensional principal stress to the oil pressure generated by the servo motor driving the piston.Firstly,this paper lists the loading characteristics of true triaxial apparatus at home and abroad,and then introduces the loading principle and hydraulic system principle of three-way rigid loading true triaxial apparatus in detail,and carries out the performance test and debugging of the new true triaxial apparatus.Finally,using the true triaxial apparatus,finally,the equal b equal σ3 true triaxial test of remolded loess was carried out,and the strength characteristics of remolded loess under different conditions were analyzed.Through the above work,the following understanding is obtained(1)The loading method of three-dimensional rigid true triaxial apparatus of Xi ’an University of Technology is two groups of rigid plate loading in horizontal direction and vertical rigid specimen cap loading.The height of the specimen is 18 cm.Two sets of rigid plates in the horizontal direction are loaded on the 16 cm shear layer through multiple sets of horizontal slides.The rigid plates do not interfere with each other and move naturally during loading.The equivalent layer of the upper 2 cm is loaded axially.Through this design,three-way independent loading and no interference are realized.After debugging and testing,the instrument system is stable and accurate.(2)After debugging and improving the instrument.the consolidation test,stress-controlled equal b equal σ3 true triaxial test and strain-controlled equal b equal σ3 true triaxial test can be completed.(3)Through the analysis of the test results of remolded loess under different water content,different intermediate principal stress b value and different consolidation stress conditions,it is shown that under the same water content and consolidation stress conditions,the strength of loess increases with the increase of b value,and the curve shows a hardening trend.Under the same consolidation stress and b value path,the increase of water content of the sample reduces the strength of the loess.Under the same water content and b value,the increase of consolidation stress is accompanied by the increase of loess strength.Through a large number of failure specimens,the shear plane mode of rigid true triaxial test is divided into no shear band mode,single shear band mode,conical shear band mode,X-type shear band mode and multi-shear band mode.(4)By comparing the failure curves of remolded loess on the π plane under different conditions,it is found that the shape similarity of the failure line is large.With the increase of water content,the failure line shrinks inward,and with the increase of consolidation stress,the failure line expands outward.By comparing the failure lines of different criteria on the π plane with the test points,it is found that the(?)spatially mobilized plane is closer to the test points,The SMP criterion is smaller than the measured value.(5)The damage criterion considering the influence of intermediate principal stress is derived into its reation of φb-b.The φb value of loess considering b value is predicted by the φ0 value under axisymmetric stress state when b=0.Through comparison,it is found that the SMP criterion is most suitable for the prediction of Xi’an loess,and the modified L-D criterion is more suitable for the prediction of shear strength parameters of Lanzhou loess. |
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