Experiment Study On The Characteristic Of Compressibility And Microstructure Of Remold Loess And Lime Stabilized Loess

The land creation project of Yan’an is the largest geotechnical engineering project in collapsible loess areas throughout the world. Fill depth of local filling area is more than one hundred meters. Facing with a so large scale high filling project, engineering geological problems, such as, the stability of the foundation and ground subsidence etc. directly related to compressive conformation are serious and prominent. Filling projects quality in loess region is closely related to filler and its compaction quality. Compressibility is one of the important indicators of physical mechanical properties, and also the main indicator of examining soil compaction effect. Limes are often used to modify and improve loess engineering properties in construction in loess area. Analysis of the compression changes of the loess with the incorporation of lime and its influencing factors are crucial for designing the best improvement program. Soil compression is closely related to the microstructure. The soil macroscopic physical properties can be better explained by the study of its microstructure. Therefore, experimental study on this topic for the loess compressibility and microstructure can enrich the compression deformation properties and microstructure theory study and provide technical support for engineering practice.We carried out the following studies for loess compression properties through field investigation, laboratory test on the basis of vast previous research.(1) Representative samples were taken in Yan’an new district for routine soil tests including compaction test, test particle analysis, critical moisture content test, which helped to determine the basic physical properties of remold loess. Malan and Lishi loess were the main loess in the study area, both of which optimum moisture content(ωopt) were about 16%, the maximum dry density of Malan loess was a little bigger; clay percentage of Malan loess was less than Lishi, while sand percentage of Lishi was more; liquid limit and plastic limit of Lishi loess were slightly greater than Malan loess.(2) Consolidation tests were conducted to study the impact of moisture content, dry density and pressure on compression characteristics. Compressibility variation of Malan loess and Lishi loess were nearly the same. Soli compression increased with the increasing of moisture content, decreased with the increasing of dry density and decreased with the increasing of vertical pressure. Moisture content should be strictly controlled and no more than the optimum moisture of 3%(ωopt+3%). Soil compression coefficient could be reduced by increasing the density, but it should be considered that the influence of moisture and properly compacted as well. The test results showed that it could basically satisfy the requirements when the dry density was controlled about 1.65 g/cm3.(3) Loess was stabilized with the incorporation of lime. Routine soil tests were carried out to determine the basic physical properties of improved loess. When compared with remold loess, optimum moisture content of lime stabilized loess increased and its maximum dry density decreased; clay percentage reduced, while sand percentage was bigger; liquid limit and plastic limit increased. Consolidation test of lime stabilized loess showed that compression coefficient increased with the increasing of initial moisture content, decreased with the increasing of initial dry density. Compression coefficient first decreased with mixed ratio then increased. Compression coefficient of lime stabilized loess was lower than remold loess. The optimum mixed ratio was determined as 9% considering the test results and actual economic situation.(4) Microstructural analysis techniques were used to study and analyze the microstructure features of remold loess and lime stabilized loess from both qualitative and quantitative point of view. Efforts had been made to link microstructure parameters with macroscopic physical properties. The result showed that soil compressibility was proportional to macro and medium pores content, surface porosity of macro and medium pores and particle fractal dimension, but inversely proportional to the degree of orientation of pores.