Internal Erosion Mechanism Of Sand And Its Influence On Permeability Under Complex Conditions

Engineering accidents caused by internal erosion of sand is not uncommon,such as floods caused by dam collapses,damage to surrounding buildings caused by collapse of foundation pits,road surface collapse caused by tunnel damage,etc.,often causing major economic losses and casualties.Aiming at the two typical modes of internal erosion of sand—suffosion and quicksand,this paper conducts a large number of experiments by using a triaxial erosion test device developed by ourselves to study the two typical internal erosion mechanisms and their effects on permeability.It has certain scientific research value and application prospect.The main research contents include:A new type of triaxial erosion test device has been developed,which can be used to carry out two types of experimental research: suffosion and quicksand.The confining pressure control system of the device can simulate the stress state of the soil;The water supply system can achieve long-term stability of erosion heads;The three-axis pressure chamber system can realize two loss modes: full-section loss and centralized loss;The collection system can realize the measurement of erosion amount and permeability coefficient,and has the characteristics of automatic solidliquid separation and continuous data collection.Suffosion tests on sand with 5 hydraulic gradients and 3 kaolin contents were carried out.During the development of suffosion,the permeability coefficient of the sample and the concentration of kaolin loss increased with the increase of the hydraulic gradient.The smaller the kaolin content,the more obvious this phenomenon is.At the same time,the permeability coefficient of the sample decreased significantly with the increase of kaolin content,but the effect of kaolin content on its loss concentration was only significant when the hydraulic gradient was large.Secondly,the triaxial test after suffosion shows that the phenomenon of strain softening and body swelling gradually weakened with the increase of kaolin content and hydraulic gradient.In addition,when the kaolin content is 10%,the amount of remaining kaolin decreases with the increase of the hydraulic gradient,but when the kaolin content is 15% and 20%,the effect of the hydraulic gradient is not obvious.Quicksand tests with 4 hydraulic gradients and 3 leakage pore sizes were carried out.With the development of quicksand,the loss and permeability coefficient of quartz sand in the sample gradually increased and stabilized.With the increase of the hydraulic gradient,the depressed surface of the sample gradually moves away from the leakage hole,and the start time of quicksand is advanced,and the rate of loss and permeability increase.Secondly,when the sample compaction coefficient is 70%,the loss of quartz sand and the permeability coefficient are not sensitive to the change of the leakage pore size.However,when the compaction coefficients of the samples were 75% and 80%,the loss of quartz sand increased with the increase of the leakage pore size.