Experimental Study On Sample Preparation Method Of Sand Model With Different Particle Gradation

The model test has been rapidly developed with its unique advantages in solving geotechnical engineering problems.However,the most critical part of the model test is the preparation of model samples.The preparation method of model samples,especially centrifugal model samples,has a great influence on the test results,and it also has different effects on the test results of different soil materials.At present,the methods of preparing model samples mainly include sand rain method and layered compaction method.In this paper,the dry sand rain method,underwater sand rain method and layered compaction method are used to study the artificially prepared sand with different gradations.The influence of the preparation method on the test results of the model sample uniformity and CPT is discussed.In this paper,three kinds of different graded test sands with similar curvature coefficients and uneven coefficients Cu of 1.43,2.05,6.71,etc.were configured by manual screening with a standard screen.The model samples with different relative densities were prepared by the underwater sand rain method,dry sand rain method and layered compaction method,combined with the micro-CPT penetration test and the self-made bottom sealing ring knife soil box buried at different depths and plane positions measuring density,two methods to evaluate the spatial uniformity of model samples prepared by different sample preparation methods.Aiming at the sand rain method,two methods of spraying dry sand in air and water were used to discuss the influence of the sand head's falling distance,moving speed and particle level on the relative density of the model sample when the shape and size of the sand head are fixed.For the underwater sand rain method,the effect of water surface height is also discussed.The micro-CPT penetration test was used to obtain the probe tip resistance in the depth direction of the three sample materials prepared by different sample preparation methods,and the CPT end resistance of the model samples with different densities of the sample preparation method and particle grading was discussed.Impact.The analysis of the test results found that:the model preparation method of underwater sand rain method,dry sand rain method and layered compaction method can all prepare model samples with good planar and vertical uniformity,but the planar uniformity of the underwater sand rain method for sample preparation is better than the dry sand rain method and the points Layer compaction method.For the dry sand rain method,when the hole diameter D/maximum particle size dmax?4 of the sand outlet and the hole diameter D/average particle diameter d50 of the sand outlet are about 12,a sample with good plane uniformity can be prepared.As the moving speed of the sand outlet increases,the plane uniformity of the sample improves.For the model sample prepared by the dry sand rain method,when the moving speed of the sand head is fixed,the relative density D_r increases significantly with the increase of the falling distance h,However,the D_r of the underwater sand rain method showed a very slowly increasing trend with the increase of the distance h.When the falling distance h is fixed,the D_r of the 2#coarse sand and 3#fine sand model samples prepared by the dry sand rain method and the underwater sand rain method increase with the increase of the sand head moving speed v,and coarse particles can get a denser state than fine particles.The variation of Dr with the moving velocity v of the model sample prepared with uniform grain grading 1#coarse sand shows the inconsistency of 2#coarse sand with d50 close to it and uneven grain grading when the falling distance h is large.The influence of the water surface height h_w on the sample D_r is much greater than the drop distance h,and the relative density of the underwater sand rain method is generally lower than that of the dry sand rain method.For the 1#coarse sand and 2#coarse sand,the CPT end resistance of the model sample prepared by the layered compaction method is below a certain penetration depth,which is generally greater than the dry sand rain method sample;The CPT end resistance of the model sample with the D_r of 37%prepared by the underwater sand rain method is less than that of the dry sand rain method;The layered compaction method is used to prepare the medium-dense samples,and the CPT results of the model samples are partly affected by the particle gradation.When the model sample is in a dense state,the CPT end resistance of the particle-level paired model sample has little effect;when the medium-dense sample is prepared by the dry sand rain method,the CPT end resistance of the particle-level paired model sample has a certain effect.The sand rain method is limited by factors such as sand spreading equipment,and can only prepare a certain range of relative density,while the layered compaction method can prepare model samples of any density from loose to dense.From the perspective of the density range of prepared samples,the layered compaction method has more advantages.