Study On Engineering Characteristics And Moisture-heat Coupling Effect Of Compacted Laterite Soil

Laterite soil is a kind of special clay,which is widely distributed in most parts of our country,,especially in Hunan and Guangxi provinces.It features water sensitivity of losing-water shrink cracks and softening by absorbing water.With the undertaking of a large number of communication infrastructure construction,the use of Laterite soil as roadbed filling is becoming an inevitable project problem.However,it's difficult to achieve the heavy compaction standard in construction stage as a result of the high nature moistuer content;meanwhile,it may cause the performance attenuation during using period due to the water sensitivity.Therefore,the compaction control index at the subgrade filling stage as well as the long-term stability of the subgrade under the effects of environment factors have been studied in this paper.In this paper,Laterite soil adjacent to some stake of the highway in Chenzhou, Hunan section from Xiamen to Chengdu was used to investigate the deformation characteristics and protection methods of the Laterite soil subgrade under the influence of environment factors.Properties like water-holding capacity,capillary rise, coupled heat-moisture transfer and wetting deformation of samples under different compactness were studied through a series of laboratory tests.In addition,by using meteorological data of two consecutive years in Chenzhou,coupled process of moisture transfer and subgrade deformation was stimulated under the impacts of groundwater and the atmosphere.Specific work done in this paper is as follows:(1) Samples under different compactness were subjected to a series of conventional laboratory tests,such as permeability,consolidation,contraction,shear test and etc.Based on these test results,relationships between mechanical indexes obtained from the above tests versus compactness have been analyzed in this paper. And the sensitivity of the index changes with respect to compactness changes is referred to as the distinguish basis for the decreasing of subgrade compactness—values with a little lower than that of the inflection points of these curves are seen as the critical reference values of the decreasing of subgrade compactness,which provides a reference method for the control of compactness of roadbed filling of the Laterite soil.(2) Pressure plate extractor was used to study the soil-water characteristic curves(SWCC) of specimens under four different compactness and the obtained SWCC were distinctly different from those of the other clays.In the SWCC,there has appeared plateau stage in the process of suction increasing.What's more,the length of the plateau stage is intimately related to the dry density of samples—the lower the dry density is,the longer the length of the plateau stage is.Through the combination of test methods of freeze at liquid nitrogen and mercury injection,pore size distributions of samples under four different compactness have been measured.It was found that there are two peaks in the distribution curves and that small pore sizes and the corresponding distribution density are not sensitive to dry density of soils whereas big pore sizes and the corresponding distribution density are interrelated with dry density of soils.Based on this study,the water holding capacity of specimens under different compactness is also explained with it.(3) A capillary rise apparatus was self-made to stimulate the capillary-effect of subsoils under the impact of groundwater.Under constant groundwater table boundary condition,water content distributions along the heights of capillary rise of samples under three different compactness are presented in this paper.And the isothermal moisture diffusion coefficient was also obtained by Bruce method.(4) To investigate the mechanism of moisture transfer of the subsoils under the influence of atmospheric temperature,a coupled heat-moisture apparatus has been self-designed and processed.Under adiabatic boundary condition,water transport characteristics were studied for specimens of three different water contents and compactness.It can be found that the absolute moisture transport of soils are related to their initial water contents.Lots of moisture transport will appear once the optimum water content is reached,which provides a theoretical basis for the practice of the Laterite soil rolling under a wetter condition.In the end,heat and moisture diffusion coefficient was obtained by REN-Fenzhi method.(5) A new moistening deformation apparatus were made based on the theory of triaxial apparatus and the traditional single line and double line testing methods were modified.By using the moistening deformation apparatus,the deformation characteristics of specimens of different compactness were stimulated under the effects of water humidification,and a constitutive model of matric suction and wetting deformation were thus proposed.(6) Based on the Philip&de Vries heat-moisture coupling model and taking into account the impacts of wetting deformation on the volumetric water content of soils, the evolution law of temperature,moisture,and deformation fields of subgrade under the influence environmental factors were stimulated by using finite element calculation method and the corresponding protection methods of roadbed diseases were proposed on this basis.