Experiment Of The Characteristics And Prevention Of Water And Sand Bursting In The Case Of Hydraulic Coupling

The resource exploitation and engineering construction often encounter water and sand burst disasters in water-rich sand layer,which are fierce,harmful and difficult to prevent.The research on hydraulic coupling process still needs to be in-depth,and the reliable and efficient treatment technology is seriously lacking.The critical conditions and burst process of water sand burst caused by different factors such as sand layer particle size,in-situ stress,water pressure and fracture width were tested based on the self-developed visual hydraulic coupling water sand burst test device.The concept of true solution was used to prevent and control water and sand burst.The research results will be of great significance to improve the water sand coupling theory and prevent the water sand burst disaster in the construction and operation of water-rich sand layer.The main results are as follows:(1)The calibration tests of micro earth pressure sensor under different inclination,backrest,dry and wet environment and different particle size were carried out by means of weight counterweight stacking.The pore water pressure sensor was calibrated by water standard test,and its calibration coefficient was obtained.(2)The water sand burst tests of sand samples with five particle size ranges were carried out under the conditions of dry without vertical pressure,dry applied vertical pressure and hydraulic coupling.The critical fracture width and critical pressure,the evolution process of sand burst morphology,the process line of sand burst volume and the variation characteristics of in-situ stress and pore water pressure were measured.When dry vertical pressure is applied,the critical fracture width of each particle group is between 2?5 mm,the critical fracture width of 0.18?0.38 mm sand group is the smallest,and the critical fracture width of sand larger or smaller than this particle size increases with the increase or decrease of particle size,and the collapse speed is same as the particle size.The collapse failure surface shape under different particle size and formation pressure is measured and fitted by quadratic curve.When the particle size is small,the failure surface shape is relatively narrow.The final subsidence pit is in a nearly inverted triangular shape,and the slope of the pit edge increases with the decrease of particle size,that is,the smaller the particle group,the deeper the subsidence pit and the steeper the pit wall.Under the condition of water saturation without vertical pressure and water pressure,the sand layer collapse of each particle group is not easy to occur,and there is no collapse after the reserved 20 mm joint width of the test device is fully opened in the device.Under the hydraulic coupling action of vertical pressure of 0.2 MPa and water pressure of 0.1 MPa,the sand of 0.18?0.38 mm group suddenly breaks out of the sand water mixture under the condition of critical fracture width of 2 mm,the breaking process is very fast,and the opening of the failure surface is larger than that of dry and non in-situ stress,but much smaller than that of dry in-situ stress;The shape of the final subsidence pit is very different from that of the dry state,showing the characteristics of vertical collapse.(3)The process of water and sand bursting is a repeated and continuous changeable process in which the stress arch in the sand layer is continuously established and destroyed;The fluctuation of in-situ stress measured by micro earth pressure sensors on both sides of the gap before the gap width which does not exceed the critical value reflects the formation and failure of soil arch;When the joint width reaches the critical value,the stable soil arch will be difficult to form and the collapse will continue to occur,and the earth pressure in the sand layer will immediately decrease sharply to about 1/3 of the in-situ stress;During the burst process,the internal stress near the crack side is small,while the internal stress far away from the crack is large.(4)The concept of real solution treatment is put forward.Through the investigation and primary selection of real solution curing agent,a new type of sodium silicate ester slurry is selected as the curing material for the collapse and surge disaster of water saturated sand layer.The curing time and strength of sand samples in dry sand environment and water saturated environment are measured.It is suggested that the slurry ratio is sodium silicate:1,4-butanediol:binary ester:water=100:7:8:85,the curing time is 500?600 s,and the cost is less than 7.5 yuan/kg.After 24 hours of curing,the internal friction angle of sand sample is slightly increased,the increase of cohesion is more than 20 k Pa,and the curing effect is good.Under the grouting pressure of 0.3 MPa,the diffusion radius of the slurry in the water saturated sand layer with particle group of 0.18?0.38 mm and density of 1.426 g/cm~3 is about1 m,and it can solidify within 600 s,indicating that the spacing of grouting holes can be at least 2 m in engineering practice,which has good engineering practicability and good treatment effect.