Factors Affecting Water Retention Capacity And Consolidation Of Loess

The engineering properties of backfill loess have always been a critical issue in the project in Western China.Although many studies have focused on it,there is still no comprehensive and systematic understanding of its influencing factors and mechanisms.In recent years,with the large-scale cutting and filling project developing in Western Loess area,the water retention capacity and consolidation of backfill loess have become a major subject which need to be solved urgently in engineering construction.And it has guiding significance in improving engineering efficiency and ensuring production safety.In cutting and filling project,loess will be affected by such factors as structural disturbance,changes in mineral composition and particle size distribution,and changes in pore water chemistry caused by groundwater seepage.All these factors will change the water retention capacity and consolidation of loess.In this paper,the response of water retention capacity and consolidation to these factors and mechanism of those response are studied by field sampling,laboratory tests and theoretical analysis.A series of soil water retention curve(SWRC)tests,consolidation-rebound tests were carried out.Malan loess in Lanzhou Jiuzhoutai area were selected as the main material in SWRC test,and remolded samples,artificial mixed samples with different particle size distribution and saline soil samples were prepared.Considering the region,classification,stress history and environmental effects of loess,natural loess from different regions or geologic ages was also determined SWRC.In view of the large scale and wide coverage of cutting and filling project in Lanzhou,consolidationrebound tests were carried out on the undisturbed and remolded loess from Qingbaishi area in addition to the loess from Jiuzhoutai area and the above-mentioned soil samples prepared indoor.In order to obtain more sample detail,basic parameter test,X-ray diffraction(XRD)and scanning electron microscopy(SEM)were used as auxiliary tests.Based on the test results,the factors affecting water retention capacity and consolidation of loess were discussed.SWRC shows that due to the difference of pore distribution and pore connectivity caused by different loess structure,the water retention capacity of loess changes.Increasing the content of hydrophilic minerals can enhance the water retention capacity in the residual stage,while increasing the content of hydrophobic minerals can weaken the water retention capacity in the saturation stage.Increasing the content of fine particles will enhance the water retention capacity,but the increasing of coarse particle content in the test range will not affect the water retention capacity of artificial samples.The SWRCs of saline soil samples show that the water retention capacity decreases with the increase of cation concentration and cation valence in pore water,and increases with the cation radius.The effect of the valence on the water retention capacity is stronger than that of the cation radius.The fitting results of van Genuchten model for SWRC show that the larger the specific surface area,the stronger the water retention capacity of loess.In consolidation test,the spatial arrangement of soil particles and the strength of connection between soil particles influences the sample settlement during compression and consolidation.For the artificial soil samples,the compression during consolidation reaches maximum value when the clay particle content reaches 20%.However,the increasing of coarse particle content could significantly reduce the compressibility of loess during consolidation.For the saline soil samples,the consolidation settlement decreases firstly and then gets increasing with the cation concentration increase,and the critical sodium ion concentration appears in 6% to 10%.Increasing the content of fine particles in soil sample will increase the rebound effect,while the coarse particles have the strongest weakening effect when its incorporation rate reaches 10%.When the cation concentration exceeds 10%,the rebound of soil sample will increase.This paper reveals the change of water retention capacity and consolidation of loess affected by cutting and filling projects through experimental research,which has reference value and guiding significance for the study of the settlement of backfill loess foundation and the stability of filling slope.