Experimental Study On Ground Collapse Induced By Hydraulic Pipeline Leakage

In recent years,ground collapse accidents frequently occur in cities,which not only cause huge property losses,but also pose a great threat to people's lives.Through the investigation and analysis of the causes of ground collapse,it is found that among the many causes of ground collapse,the damage of hydraulic pipeline is the main cause of ground collapse.The damage and leakage of the hydraulic pipeline cause the increase of water content and water level of the surrounding soil to change the soil and hydraulic conditions,and the erosion of the surrounding soil to form a hidden underground cavity.With the continuous development of the underground cavity,the final cause of ground collapse or greater hidden area to endanger public security.Therefore,it is of great significance to study the mechanism of ground collapse caused by hydraulic pipeline damage and leakage to protect people's life and property safety.Aiming at promoting the "rain sewage diversion" drainage pattern,under the condition of rain sewage pipeline damage at the same time,as a condition of hydraulic pipeline for water and wastewater pipeline sand channel rainwater pipeline as a row,the study of complex surface collapse accident hydraulic conditions,and based on a large number of research cases,developed a set of hydraulic model test system collapse,double line test system by experimental model box,measuring system,data acquisition system,pressure feed water system,etc,can be simulated simultaneously pipeline damage after the penetration of the water leakage and its influence on the development of the erosion of the complex hydraulic conditions.The model test box adopts a semi-structure model,which is composed of an inlet pipe and a sand discharge pipe.The dynamic water condition is provided by the simulated hydraulic pipeline through the inlet pipe,and the sand outlet channel is provided by the unpressurized damaged pipeline through the sand outlet pipe to simulate the ground collapse accident caused by the pipeline damage.By means of theoretical analysis and laboratory model test,the relationship between water velocity and erosion development in hydraulic pipeline and the influence of different influencing factors on the development state of erosion were studied.Specific research contents are as follows:(1)aiming at the problem that soil reaches the state of flowing sand and percolates along other damaged pipelines due to water leakage after the hydraulic pipeline damage,the critical velocity of water flow in the hydraulic pipeline when soil starts to lose is deduced by establishing the critical hydrostatic pressure equilibrium condition.(2)in view of the phenomenon that underground cavity can still be stable after soil loss,the effect of matric suction is introduced to study the effect of soil arch effect on soil support after saturated soil is infiltrated by capillary action,and the water velocity in the hydraulic pipeline and the ultimate bearing capacity of unsaturated soil arch are derived.(3)in view of the erosion and damage to soil after the damage of the hydraulic pipeline,the force analysis of single particle is carried out to deduce the initial flow velocity of movable fine particles at different damaged positions of the pipeline,and the initial flow velocity range of movable particles is obtained.(4)Through the indoor model test,the development process of damaged and corroded soil in hydraulic pipeline,the amount of sand soil lost,the amount of water seepage in hydraulic pipeline and the final development state of erosion were studied under different sand parameters,different hydraulic conditions and different relative positions of pipelines.The limit equilibrium theory of unsaturated soil was introduced to obtain the law of erosion development under different conditions,and the theoretical analysis was verified.The results of theoretical analysis and indoor model test show that after the damage of the hydraulic pipeline,the water seepage causes the soil to reach the state of "flowing sand",and loss occurs along other channels.Under the initial state after the occurrence of flowing sand,the soil arching effect can remain stable due to the action of the soil matric suction and cohesion.With the continuous increase of sand and soil loss,the scope of underground cavity keeps expanding,which makes the ultimate pressure of soil arch unable to bear itself and the upper load finally collapse.Increasing sand compactness and coarse particle content in sand can effectively reduce the size of collapse mouth,but it is more likely to form hidden underground cavity,which still has a great threat.When the water velocity in the hydraulic pipeline is relatively small,the erosion speed is slow and the water and soil erosion along other damaged pipelines forms hidden cavities after reaching a certain water level.When the velocity in the hydraulic pipeline is fast,the erosion develops rapidly.Although a smaller collapse area is formed,the collapse speed is fast.At the same time,changing the relative position of pipeline can effectively inhibit the development pattern of void.