Study On Calculation Method And Variation Rule Of Earth Pressure Of The Check Dam Of Debris Flow

Debris flow is a common geological disaster in mountainous area of our country,which is characterized by sudden,obvious scourging and destructive,often resulting in serious economic loss and casualty.Sand dam is one of the common measures used in debris flow control engineering.It is mainly used to intercept solid material of debris flow,stabilize gully bed,reduce the scale of debris flow and so on.It plays a vital role in debris flow control engineering system.However,under the influence of debris flow accumulation,impact,erosion and other multiple factors,the structure damage and instability of the sand dam are easy to occur,which affects its normal use and leads to the failure of the treatment project.Accurate analysis and calculation of the dam load is the prerequisite for evaluating the stability of the dam.With the continuous accumulation of debris flow solid material,the accumulated soil will produce earth pressure on the dam body.At present,the calculation of earth pressure behind a dam mainly refers to the relevant theories of earth pressure behind a traditional retaining wall.However,the deduced hypothesis of earth pressure behind a retaining wall is inconsistent with the situation of the soil behind a debris flow retaining dam,and there are great differences in the formation process and properties of the soil,so the existing calculation method is inconsistent with the actual situation.Therefore,the earth pressure behind a debris flow retaining dam is taken as the research object in this thesis.The calculation method and variation rule of earth pressure behind DAMS are studied by combining theoretical analysis with experimental research.The main research work and results are as follows:1.By considering the existence of potential sliding surface and the absence of potential sliding surface,the horizontal differential element method is used to establish the calculation method of earth pressure behind the dam,and the expression of earth pressure coefficient is obtained.According to the accumulation characteristics of dilute debris flow and viscous debris flow behind the dam,the soil and water division method is proposed to calculate the earth pressure behind the mudstone dam.The calculation method of earth pressure behind dam under different storage capacity conditions is also established.2.Combined with the indoor geotechnical experiment and model test,the rationality of the theoretical calculation method of earth pressure behind the dam is verified,and the influence of six factors on the earth pressure behind the dam,such as the coefficient of earth pressure,the slope of gully bed,the Angle of internal friction,the dip Angle of wall back and fill,and the frequency of debris flow are analyzed by numerical calculation.The results show that the earth pressure behind the dam presents a parabolic distribution,the static soil pressure coefficient is "stable first and then decreases to 0" with the increase of the slope of the gully bed,the soil internal friction Angle is inversely proportional to the earth pressure,and the tilt Angle of the wall back and the slope Angle of the fill surface are proportional to the static soil pressure coefficient.3.The theory of earth pressure variation behind dam is proposed,which takes into account the variation of soil liquid volume fraction and water level,and the rationality of the proposed method of earth pressure analysis behind dam is verified by model tests.4.According to the model test results,the four influencing factors of debris flow type,soil sample grading,storage capacity condition and dam foundation cushion are analyzed,and the soil pressure variation and the law of soil water dissipation behind the debris flow dam are revealed.The results show that:(1)Under the condition of dilute debris flow,the dissipation law of internal water body behind the dam is approximately linear,while under the condition of viscous debris flow,the dissipation trend of internal water body behind the dam is parabolic with time.(2)The higher the thickness ratio is,the faster the seepage dissipation rate is.(3)The dissipation rate of water in full storage condition is lower than that in half empty storage condition.(4)The permeability characteristics of the cushion soil of dam foundation have obvious influence on the permeability of the soil behind the dam.(5)The variation range of earth pressure behind the dam under the condition of viscous debris flow is greater than that under the condition of dilute debris flow dam.(6)The greater the ratio of thickness to fineness of particle composition,the greater the variation range of soil pressure;(7)The influence degree of dam foundation cushion on earth pressure behind dam under viscous debris flow condition is greater than that of dam foundation cushion on thin debris flow condition.