A novel specimen preparation method for TJ-1 lunar soil simulant in hollow cylinder apparatus

Conventional methods for hollow cylinder apparatus （HCA） specimen preparation are not applicable for T J-1 lunar soil simulant due to its wide particle size distribution. A novel method to prepare uniform T J-1 specimen for HCA tests is put forward. The method is a combination of the multi-layering dry-rodding method and a new under-compaction criterion in the multi-layer with under-compaction method （UCM）. In the novel method, the specimen is prepared with 5 layers by dry-rodding and the UCM is used to determine the height after each layer is compacted. The density uniformity of specimen is evaluated by the freezing method to find out the best under-compaction criterion. Two HCA specimens with the same target density are prepared by the novel method and examined in the tests of pure rotation of the principal stresses. Their conformable mechanical behaviors ascertain the effectiveness of the method to produce uniform and reproducible HCA specimens. Four groups of HCA tests are carried out to investigate the anisotropic and non-coaxial behaviors of TJ-I lunar soil simulant. The results indicate that the principal stress direction, the deviator stress ratio, the stress level and the coefficient of the intermediate principal stress significantly influence the strength and deformation properties of T J-1 lunar soil simulant.

Cumulative Deformation of Soft Clay Under Cyclic Loading

Reconstituted specimens are prepared by means of vacuum preloading. Both static and cyclic triaxial tests are carried out, with the specimens consolidated under different principal stress ratios. A finite element method is put forward for calculating the cumulative deformation of soft clay under cyclic loading.

Sources of variability in laboratory rock test results

Appropriate rock characterization is beneficial in providing a reliable judgment on rock properties which is crucial for the design process of rock engineering applications.However,it can be difficult to obtain consistent mechanical parameters due to substantial variations in rock properties.In this research,uniaxial compression tests on dolerite specimens collected from a gold mine in Western Australia showed substantial scatter in the results.Rock categorization based on the P-wave velocities is as accurate as the thin section analysis,which suggests that they can be used together to gain a more accurate initial understanding of the rock types before any laboratory testing.The quality of specimen preparation and rockemachine interaction greatly affect the test results.For instance,non-parallelness of loading platens can lead to considerable scatter of the testing results,which would be perceived as rock variability.It is suggested that the current testing standards should be modified towards a better control of the loading machine performance and equipment precision.Finally,the possibility of pre-existing microcracks in rock,neither detected by the thin section analysis nor by the ultrasonic measurement,must be examined by computed tomography(CT)scanning as they can affect the test results.This study will enhance our knowledge about the sources of variability in laboratory test results of rock which is essential for obtaining reliable data.

Experimental study on compaction-induced anisotropic mechanical property of rockfill material

The anisotropy of rockfill materials has a significant influence on the performance of engineering structures.However,relevant research data are very limited,because of the difficulty with preparing specimens with different inclination angles using traditional methods.Furthermore,the anisotropy test of rockfill materials is complex and complicated,especially for triaxial tests,in which the major principal stress plane intersects with the compaction plane at different angles.In this study,the geometric characteristics of a typical particle fraction consisting of a specific rockfill material were statistically investigated,and the distribution characteristics of particle orientation in specimens prepared via different compaction methods were examined.For high-density rockfill materials,a set of specimen preparation devices for inclined compaction planes was developed,and a series of conventional triaxial compression tests with different principal stress direction angles were conducted.The results reveal that the principal stress direction angle has a significant effect on the modulus,shear strength,and dilatancy of the compacted rockfill materials.Analysis of the relationship between the principal stress direction angles,change in the stress state,and change in the corresponding dominant shear plane shows that the angle between the compacted surface and dominant shear plane is closely related to interlocking resistance associated with the particle orientation.In addition,different principal stress direction angles can change the extent of the particle interlocking effect,causing the specimen to exhibit different degrees of anisotropy.