Experimental Study On Internal Erosion Caused By Water Gushing And Sand Gushing Of Underground Engineering In High Water-rich Sand Layer

In recent decades,the exploitation and utilization of underground space has been vigorously developed around the world.However,engineering disaster occurs frequently during the construction and operation period of underground structure at home and abroad,which not only threatens the safety of human's lives and property,but also causes serious social impacts.Underground engineering in high water-rich sand layers can easily develop into disaster due to the loss of soil and water.However,few studies have investigated the mechanism of internal erosion induced by water gushing and sand gushing,and the basis for formulating risk prevention and control measures for underground engineering disaster need to be improved.Aiming at the disaster caused by water gushing and sand gushing in underground engineering,this paper discusses the development process of soil internal erosion and the characteristics of cavity under the influence of different factors(soil type,gushing location,water level conditions)through model tests.The specific work and main results are as follows:(1)By analyzing the experimental phenomena,the similarities and differences of the erosion characteristics of different types of soil layers in the process of internal erosion are summarized and compared.In the single sand layer test,the shape of the top of the cavity remained nearly semi-circular,and the section of the cavity showed straight slope-shaped and bowl-shaped shapes due to the compactness and the different dominant erosion forces of the fine sand and coarse sand,respectively.In the ideal state,the developmental model of the cavity of the composite sand layer test is the developmental model of the cavity of a single fine sand layer accompanied by the erosion of the slope foot by the soil flow.In addition,compared with a single sand layer,different phenomena such as the development of ‘soil hole' and the loss of all fine sand may occur in the composite sand layer.(2)Based on the experimental phenomena and relevant data,the characteristics of the cavity after the erosion is stabilized are analyzed.In those tests which soil flow do not destroy cavity,the space shape of cavity is basically a semicircular truncated cone.As the water level increases,the volume of the cavity in all tests increases.In a single sand layer test,the equivalent radius at the top of the cavity and the cavity height are in linear relationship in a certain water level.When the location of the gushing outlet is the same,under the same water level,the order of soil disturbance and cavity collapse range in different soil layer tests is: composite sand layer > single fine sand layer > single coarse sand layer.(3)By analyzing the measured water level after the internal erosion has stabilized,the characteristics of seepage slope and seepage field distribution in the range of measurement points in different types of soil layers are compared.In the composite sand layer test which the gushing outlet is located in the fine sand layer,the closer to the gushing outlet,the greater the vertical seepage slope value in the ‘interface',and the trend of the vertical seepage slope value of a single sand layer test under the same conditions is opposite.At the same time,when the gushing outlet is far from the fine-coarse sand interface,the water flow is approximately vertical infiltration at the bottom of the fine sand layer.