Experimental Study On Mechanical Properties Of Cohesionless Soil Under Small Gravity Fields

The mechanical and engineering properties of lunar soil is the basis and key for construction and exploitation of mineral resources on the moon.The existing research,which was mainly based on terrestrial mechanics or numerical simulation methods leading to the lack of simulation of the small gravity fields,indicates that it is difficult to systematically,accurately and reliably reveal the relationships between the mechanical and engineering properties of the lunar soil and the gravity field environment.Therefore,in this thesis,a new type of magnetic-sensitive cohesionless soil granular material is developed by using cement powder and Fe₃O₄ magnetic powder.Using the magnetic gravity field physical model test system,the different gravity fields can be accurately simulated in magnetic environment.By further optimizing the particle size and grading of the materials,the consistency with the real lunar soil on the physical dimensions such as particle size and grading is preliminarily achieved.The triaxial compression tests,static penetration tests,and plate load test under different small gravity fields have been carried out to study the influence of gravity fields on the mechanical and engineering properties such as the strength,macroscopic deformation,and bearing capacity of cohesionless soils.Firstly,the triaxial compression tests under small gravity fields and low confining pressure are used to systematically analyze the relationship between the macroscopical mechanics parameters and gravity fields,such as deformation modulus,Poisson's ratio,peak strength,critical internal friction angle and cohesion of the cohesionless soil specimen during shear deformation.The macroscopic deformation of the specimen showed a clear change of shear dilation after shearing.The shear dilatancy of the specimen showed a decreasing trend in the final shear failure with the increase of confining pressure and gravity field,and the variation of the dilatancy angle of the specimen with the change of the gravity field was analyzed.Secondly,through the static penetration model test under small gravity fields,the variations of the cone tip resistance and the normalized cone tip resistance with the change of gravity fields were systematically analyzed.The cone tip resistance increased with the increase of the gravity fields,and the normal cone tip resistance increased with the decrease of the gravity fields.The fitting relationship between the stiffness ratio and other mechanical parameters of the sample and the gravity field was analyzed,and Tatsuoka's formula was modified to consider the gravity field.Further qualitatively studied the effect of penetration rate,relative density,and cone shape on the cone tip resistance under the simulated 1/6g lunar environment,and verified the reliability of the modified Tatsuoka's formula.Finally,through the plate load model test under small gravity fields,the relationship between the bearing capacity of the specimen and the gravity fields was systematically analyzed.The experimental study found that the bearing capacity of the sample increased with the increase of the gravity field.At the same time,the influence of the gravity field on the bearing capacity was more different than the influence of bearing plate size and relative density.Furthermore,the relationship between the mechanical parameters and the gravity field such as the deformation modulus and the bed coefficient was also analyzed.