Experimental Study On Deformation And Strength Characteristics Of Remolded Loess Under High Stress

In recent years,with the development of urbanization and the expansion of the construction scale,a large number of high loess-filled projects have emerged.Because of the high filling thickness and high foundation stress engineering characteristics of high loess-filled projects,and lack of overall understanding and in-depth research on mechanical properties of high loess-filled projects,a large number of engineering disasters have occurred in the project.In view of the actual problems encountered in the above-mentioned projects,through theoretical analysis and the laboratory tests,the compaction characteristics,deformation characteristics,and strength characteristics of remolded loess under high stress were obtained.The main conclusions are as follows:(1)Considering four different compaction energies,the compaction tests were carried out and the compaction change behavior of remolded loess under different compaction energies was obtained.The dry density generally increases with the increase of compaction energy.The optimum moisture content decreases with the increase of compaction energy,and it has an exponential function relationship.The maximum dry density increases with the increase of compaction energy.When the compaction energy is relatively low,the maximum dry density increases rapidly with the increase of compaction energy,and when the compaction energy is relatively large,the maximum dry density increase gradually with the increase of compaction energy.(2)In order to obtain the consolidation compression deformation law of remolded loess under various compaction energy,compaction degree,moisture content and consolidation pressure,the high-pressure consolidation compression test was carried out.Under the condition of high stress,the difference of the total void ratio is the smallest and the change rate is the smallest,when the moisture content is controlled to be the optimum moisture content.The soil is relatively densest and which also has higher compression resistance.By controlling the optimum moisture content,relatively small compaction energy can also achieve better compaction results.In the e-p curve under the condition of compaction energy and moisture content,the void ratio and the consolidation pressure show a hyperbolic relationship,when the consolidation pressure is less than 800 kPa.The pore ratio and the consolidation pressure show a good linear relationship,when the consolidation pressure is greater than 800 kPa.The e-lgp curves of each compaction energy and moisture content have a good linear relationship.When the compaction degree and the consolidation pressure are constant,the void ratio of remolded loess decreases with the increase of moisture content.When the moisture content and the consolidation pressure are constant,the void ratio of remolded loess decreases with the reduction of compaction degree.When the consolidation pressure is transformed into logarithm,the void ratio is basically linearly related to the consolidation pressure.(3)In order to obtain the creep deformation law of remolded loess under various moisture content and compaction degree,the high-pressure consolidation creep test was carried out.Decreasing the moisture content or increasing the degree of compaction can reduce the soil's creep to a certain extent.As the consolidation pressure increases,the time required for the sample to stabilize is longer.The stability time is the shortest at the low consolidation pressure(100 kPa)and can be stabilized within 50 h to 70 h.The longest stabilization time is at the maximum consolidation pressure(2400 kPa),which requires 190 h to 290 h.Using the logarithm function fitting,the creep constitutive model of the high loess-filled project in Yan'an area is obtained,which can reflect the deformation characteristics of the project under high stress.(4)In order to obtain the change law between shear strength,shear strength index and compaction energy,moisture content,consolidation pressure,direct shear tests were carried out.The shear strength increases linearly with the vertical pressure.Under each compaction energy condition,the shear strength increases with the increase of moisture content on the dry side of the optimal moisture content.On the wet side of the optimal moisture content,the shear strength decreases with increasing moisture content.At the optimal moisture content,the shear strength is the maximum.With the increase of compaction energy,the cohesion has increased to some extent.Under each compaction energy condition,the cohesive force on the dry side of the optimal moisture content increases with the increase of the initial moisture content.On the wet side of the optimum moisture content,the cohesion decreases with increasing water content.At the optimum moisture content,the cohesion is the maximum.(5)The triaxial tests under high confining pressure conditions were carried out,and the law of strength variation under each condition of compaction energy,confining pressure and moisture content was obtained.Under the effect of high confining pressure,all the final consolidated undrained specimens showed shear-type failure.Under high stress conditions,different compaction energies and different confining pressures,the curve of deviation stress and axial strain shows anisotropy,but all show softening stress type.The stress-strain curves of remolded loess show three stages under high stress,which are the linear growth phase,transition phase and mitigation phase.While the peak intensity increase is limited,increased from the minimum compaction energy to the maximum compaction energy.