Mechanism Of Slurry Diffusion And Cumulative Damage In Fractured Rock Mass Under Pulse Pressure

Grouting is a common technique of strengthening and plugging water in various fields of geotechnical engineering.At present,constant pressure grouting is the main technology.Although some problems have been solved,with the increasing of deep geotechnical engineering and soft rock engineering,problems such as "low pressure and difficult to penetrate,high pressure slurry running and uneven diffusion" are often encountered.Therefore,it is necessary to solve the problem of grouting construction of hard to inject rock mass.The pulse grouting technology can change the pressure action mode,effectively open the micro fracture of rock mass,increase the range and uniformity of slurry diffusion.At present,the pulse grouting technology has been carried out in related engineering practice,but it has not improved the effect of grouting on site obviously,and lacks systematic research on the scientific problem of grouting principle.Therefore,the paper studies the diffusion law and cumulative damage mechanism of slurry under the action of fracture pulse pressure by theoretical analysis,numerical simulation,laboratory test and field practice.The main results are as follows:(1)The macroscopic diffusion law of slurry in fracture under impulse pressure is obtained.The pulse pressure makes the diffusion speed and range of the slurry far exceed the constant pressure grouting.The pulse frequency increases the rate of pressure change,which can effectively overcome the friction resistance,weaken the damping of the crack wall to the diffusion speed of the slurry,enhance the pressure holding capacity of the slurry,and promote the further diffusion of the slurry.The higher the frequency,the lower the pressure attenuation gradient in the slurry.(2)The distribution of pressure along the fracture and the mechanism of loss of pulse pressure slurry in the micro scale are revealed.The pulse pressure propagates in the fracture in the form of wave,and the pressure distribution and the along-course loss of slurry in the rock fracture also show obvious periodicity.The pulse pressure increases the interference in the rock fracture and enlarges the pressure near the tip,while the pulse pressure frequency is constant,which can keep the pressure.(3)The criterion of judging the initiation of micro fracture by pulse pressure is determined.The crack propagation must have enough potential energy to overcome the surface energy of the wall.Based on Griffith theory,the critical conditions for crack tip initiation are determined.The crack opening and expansion is dominated by the extreme strength factor of the fracture,which is only related to the material properties and the crack length.(4)The mechanism of cumulative damage of the crack tip by pulse pressure is revealed.The pressure increase in pulse period will cause the damage at the crack tip.The damage accumulation causes the tip strength to decrease to a certain extent,and the damage increases rapidly,and the tensile shear failure occurs,while the slow damage is tensile failure.When the pulse stamping decreases in a single period,the displacement of fracture wall rebounds,and the pressure increases,which can provide energy to promote the fracture wall to continue to move to the depth.The deformation of the fracture wall surface in multiple cycles is shown as continuous vibration,not continuous normal displacement.The pulse pressure continuously replenishs energy to make the displacement of fracture wall increase continuously until the tensile stress at the tip of fracture is beyond its ultimate strength,and finally the fracture will start to expand.(5)The macroscopic damage characteristics of fractured rock mass under impulse pressure are obtained.The main reason for the cumulative fracture damage by impulse pressure is the pressure change rate,the pressure change rate has significant difference on the damage process and effect of different rock mass.The pulse pressure parameters should be subdivided to achieve the micro damage but not to damage at macro level.High frequency and low pressure pulse grouting is needed for muddy rock mass,and low frequency and high pressure pulse grouting is required for hard rock with high stress.The research results are carried out in the muddy rock roadway and high stress sandstone roadway in yuanzigou coal mine,and the grouting effect is improved significantly.There are 64 figures,7 tables and 160 references in this dissertation.