Study On Soil-water Characteristic Curve Of Cracked Soil Considering Crack Network Dynamic Development

Cracks are widely present in natural and engineered soils. Cracks can providepreferential pathways for water flow and significantly increase the hydraulicconductivity of the soil mass, which, in turn, results in a decreasing shear strength.Cracks can induce many geotechnical engineering problems such as slope instability,dam failures and contaminant transport and so on. The study of soil-watercharacteristic curve (SWCC) for the cracked soil is essential for analyzing the effectof cracks on geotechnical engineering problems. The effect of cracks on soil-watercharacteristic curve of unsaturated soil was attended by more and more geotechnicalscholars. However, due to the complexity of cracks and the time-consuming ofexperiment, there are few research results for soil-water characteristic curve of thecracked soil. During the study of soil-water characteristic curve for the expansivesoils, many researchers often do not consider the presence of cracks in soils or donot consider the crack volume change, but the error is difficult to predict. What’smore, the reliability of the getting conclusions through the indirect methods has yetto be verified. Therefore, it is necessary to study the soil-water characteristic curveof cracked soil considering dynamic process of cracks through theoretical and testmethods.The main contents of this paper include the following four aspects:(1) By using image processing technology, the surface cracks of cracked soilsample was studied quantitatively during drying and wetting process. The crack rateand the crack aperture distribution of sample surface under different water contentconditions were getted. The cracks development path during drying and wettingprocess were analyzed. The results show that the process of crack development canbe divided into three stages during drying and wetting process under naturalconditions in the laboratory. But the cracks rate increases slightly first and then thecracks almost do not closed in permeability apparatus.(2) According to double porous continuous medium theory, the cracked soil canbe viewed as an over-lapping continuum of a crack network system and a soil matrixsystem. Based on the capillary law and the pore-size distributions for the two poresystems, the soil-water characteristic curve of cracked soil considering crack network dynamic development is estimated. An example is demonstrated based on alaboratory experiment and the SWCC for a cracked soil considering crack networkdynamic development is predicted by using this method. The results show that thesoil water characteristic curves of cracked soil considering crack network dynamicdevelopment have bimodal characteristics. The effect of cracks on SWCC for soil ismainly in the lower suction range and the SWCC of cracked soil is mainlycontrolled by soil in higher suction.(3) A large-size permeability apparatus is designed and used to study thesoil-water characteristic curve of the cracked soil considering crack networkdynamic development. This apparatus can be used to measure the soil-watercharacteristic curve of cracked soil. It is considered the representative elementaryvolume (REV) of cracked soil, requirement of high precision for low suction rangeand requirement of easily observed for crack development during the test. Thelarge-size permeability apparatus, which can accommodate a cracked soil specimenwith a diameter of280mm and height not more than200mm, can basically meet therequirement of the representative elementary volume (REV) and crack developmentin the cracked soil. Usually the aperture of cracks in cracked soil is large, based onthe capillary law, the matric suction in the test equipment can be controled with aaccuracy of0.005kPa within10kPa. The pressure chamber of the permeabilityapparatus is made of transparent plexiglass and it is easy to observe the developmentof cracks during the test.(4)The soil-water characteristic curves of the cracked soil considering cracknetwork dynamic development are studied by using the large-size permeabilityapparatus. The test results show that the soil-water characteristic curves of thecracked soil considering crack network dynamic development show bimodal feature.And the bimodal phenomenon in drying process is more obvious than that in wettingprocess. The soil-water characteristic curve of the cracked soil sample which is usedin the laboratory test is predicted by using this theoretical method. The theoreticalresults reflect the effect of crack network on soil-water characteristic curve of thecracked soil in a certain degree, but there is still a certain degree of error betweenthe theoretical results and measured results.