Investigation On The Effect And Mechanism Of Aggregate Size On The Hydro-mechanical Behaviors Of Lateritic Clay

Lateritic clay,as a special clay with great shrinkage and water sensitivity,is widely distributed in the tropical and subtropical regions of southern China.Researchers had carried out extensive research on the mechanical behaviors of lateritic clay in different regions until now.And they investigated the influence of initial dry density,moisture content,soil structure and other factors on the hydraulic and mechanical properties of clay.However,the effect of aggregate size on the physical and mechanical properties of lateritic clay,are need to be further investigated to improve the existing research results.Therefore,the paper investigates the swelling-shrinkage characteristics by the swelling tests with different loads in the oedometer and shrinkage tests from saturation,on the compacted specimens with different aggregate sizes.Then,the pressure plate instrument and GDS unsaturated soil triaxial instrument were used to measure the water retention curve and stress-strain curves of the specimens over a wide range suction by combining the axial translation technique and vapor equilibrium technique,respectively.The tests were carried out to investigate the influence of aggregate size on the water retention characteristics and mechanical behaviors of clay.Finally,the pore size distributions(PSDs)of specimens with different aggregate sizes and suctions,were obtained from mercury intrusion porosimeter(MIP).Based on the evolutions of PSDs with increasing suctions and particle sizes,the mechanism on the evolution of hydraulic and mechanical properties of lateritic clay with aggregates size was discovered from microstructure.The detailed research results are as follows:(1)Lateritic clay is characterized as the high shrinkage and low swelling in general.The test results of swelling with different loads show that the swelling rate increases with the increasing initial dry density.On the contrary,the swelling rate decreases with the increasing load and aggregate size.The test results of shrinkage show that the linear shrinkage and volume shrinkage of lateritic clay gradually decrease with the increasing of initial dry density and aggregate size,respectively.(2)The moisture content and saturation of soil progressively decrease with the increasing suction under the same initial dry density.The air-entry values of compacted specimens and the slopes in the transition zone gradually decrease with the increasing aggregate size.However,the residual value of soil is not affected by the aggregate size.In addition,the coincidence of water retention curves of different aggregate sizes in the high suction range(s ≥ 3.29 MPa)demonstrates that the aggregate size of prepared specimen only has an effect on the water retention curve in the low suction range,while it has not an effect on the water retention curve in the high suction range.(3)The stress-strain curve of compacted lateritic clay progressively varies from shear contract-hardening to dilatancy-softening with the increasing suction.Furthermore,the more peak strength and more obvious dilatancy-softening can be observed from the stress-strain curve for specimen with higher suction.In addition,more peak strength can be observed in the larger aggregate size specimens with the same initial dry density and suction,and the difference in the peak strength between aggregate sizes is more obvious with the increasing suction.(4)The pore size distribution(PSDs)of saturated lateritic clay is typical unimodal.The peak of PSDs increases with the decreasing aggregate size,while the pore diameter corresponding to the peak decreases with the decreasing aggregate size.The results indicate that more uniform distribution in the pore size for the specimens with smaller aggregate size.With the progressively increase of suction,the pore size distribution of clay gradually varies from unimodal to bimodal,and the diameter of macro-pore size corresponding to the peak progressively increases with the increasing suction,while the diameter of micro-pore corresponding to the peak decreases with the increasing suction progressively.The results demonstrate that the diameter of macro-pore in the lateritic clay increases,while the diameter of micro-pore progressively decreases with increasing suction in the specimen.(5)The consistence of water retention curves measured from tests and predicted from pore size distributions indicates that the water retention characteristic of lateritic clay is closely related to their pore size distributions.The good correlation existing in the lateritic clay between the peak strength and the cumulative macro-pore void ratio,demonstrates that the peak strength is mainly affected by the cumulative macro-pore void ratio.Moreover,the relationship shows that the larger the cumulative macro-pore void ratio,the smaller peak strength in the lateritic clay.Figure [52] table [8] reference [107]...