Study On Treatment Technology Of Weak Fractured Zone In The High Arch Dam Foundation

The western part of China contains extremely abundant hydropower resources,large-scale construction of water conservancy and hydropower projects has been carried out in recent decades.Concrete arch dams are widely used in the hydropower industry at home and abroad because of their economical cost and safe operation.Concrete high arch dam has become one of the main dams of large reservoirs and power stations in the southwest and northwest mountainous areas of China.High arch dams have higher requirements for topography and geological conditions,the stability of dam foundation and abutment resistance body is the key to the construction of such concrete dams.However,influenced by the geological structure,there are inevitably various geological defects in the foundation of arch dam,which may cause dam failure and then threaten the operation of hydropower station.Catastrophic accidents caused by high-dam dam foundation failure and dam abutment failure are appeared in many cases.Therefore,according to the geological characteristics of dam foundation and the actual situation of geological defects,it is the core problem in the construction of hydropower station to take scientific,reliable and economical disposal measures.There is no reliable standard for foundation treatment and reinforcement on super high arch dam,as a basis and successful engineering example as a reference.Therefore,based on the reinforcement project of the weak rock mass in left bank dam foundation of the 300 m high arch dam of Jingping?hydropower station,based on the engineering geological characteristics of dam foundation's bad rock mass(F5 fault),based on the thorough investigation and analysis of the engineering geological characteristics,the influence of safety and stability to different locations on dam foundation is analyzed,the tests and numerical simulations of the main disposal technologies(grouting,washing replacement,anchoring,etc.)are carried out respectively,it reveals the internal mechanism and feasibility of various disposal technologies,the rationality of disposal plan has been discussed,the reinforcing effect has been evaluated based on the monitoring data and feedback analysis.The main research works and the achievements are as follows:(1)A complete set of technical treatment scheme for typical geological defects(f5 fault)of high arch dam foundation has been established.The spatial distribution and material composition of the fracture zone,inter laminar extrusion dislocation,lamprophyre,deep fracture and the IV 2 rock mass and III 2 rock mass are analyzed from the regional structure and the engineering geological conditions of the dam site,the rock mass quality of the base surface is evaluated.Aiming at the typical f5 faults,the engineering characteristics(such as surrounding rock mass characteristics,fracture zone structural characteristics,mechanical properties and parameter values)are analyzed,based on this,a preliminary technical plan system for comprehensive treatment of typical geological defect—f5 fault is put forward,is "replacement(washing)+ cement grouting + chemical grouting + anchorage + drainage" technology system,a set of integrated treatment technology.The treatment measures are targeted to the adverse effects of the f5 fault zone on the different parts of dam foundation,which can effectively improve the fracture zone and its influence on the anti-slip and deformation resistance,and improve the permeability stability.(2)A series of grouting materials suitable for formation characteristics and groutability requirements has been developed,solved the problems of low groutabilitiy of low permeability rock zone in fault fracture zone and controllable grounting in the large opening fractures.The rheological properties,groutability,water separation rate and stability of cement grouting materials are studied by laboratory tests,the study shows that the slurry belongs to three different flow patterns,and the influence of water cement ratio on the flow pattern of pure cement slurry has been found,Thus,the boundary point between the water slurry ratio of the cement slurry in Newtonian liquid,Bingham fluid or power law fluid was verified.By the results of minimum groutable width test,it is revealed that the slurry with a water-cement ratio of 0.5 can only be filled with cracks of 0.4 mm;the slurry with a water-cement ratio of 0.8 can be filled with cracks of 0.1 mm,but the grouting rate is slow;When the water-cement ratio is greater than 1.0,the slurry can be completely filled with micro-cracks of 0.1 mm and has a certain filling rate.Using Newtonian fluid constitutive theory,the fluid diffusion differential equation is established based on the force balance of micro-elements,and the method of increasing the grouting time by increasing the filling time.By theoretical analysis it is more economical and reasonable to increase the grouting diffusion radius by increasing the grouting time,that is the theoretical basis of "long-term,low-rate,infiltration and percolation" grouting method.The flow pattern of cement grout and chemical slurry is studied systematically,which provides a basis theoretical study on grouting diffusion.Through the experimental study of chemical grouting materials with different proportions,the law of slurry viscosity changing with time is obtained.and the problem of the low permeability rock zone groutability in fault zone is solved.Considering the physical and mechanical characteristics of the fracture zone,determined the grouting material and the corresponding ratio of the four types in fault fracture zone,such as weak and low permeability fault zone,micro fissures affected by fault zone,reinforcement grouting area,and large fracture zone.According to the rock mass characteristics of each part of the f5 fault and the stress condition of the arch dam,the grouting design scheme of the corresponding part has been proposed,namely: concrete grid replacement + encryption consolidation grouting(below 1730 m elevation): Arrange two replacement holes with a height of 10 m at 1730 m and 1670 m elevation.The widths of the replacement hole and the inclined well are determined according to the actual width of the f5 fault.Anti-seepage curtain cement grouting: Arrange 3 rows of anti-seepage curtain grouting holes,axis spacing 1.3m,spacing 1.0m;anti-seepage curtain cement-chemical compound grouting treatment: after the completion of ordinary cement material infusion,two rows of chemical-cement Compound grouting.The requirements for post-irrigation inspection are also proposed for all types of grouting.(3)A high-pressure flush washing replacement technology has been developed(High pressure reciprocating punching and washing + group hole enlarging and flushing + concrete replacement and backfill technology),which provide new conception and technics of weak fractured zone reinforcement.Combined with ANSYS and LS-DYNA software system,the effect of high-pressure gas liquid jet on washing and breaking rock is studied,and a high-pressure diffusion calculation model for washing and washing is put forward.The research shows that the high pressure technology can achieve the expected goal for treating soft fractured rock by washing and backfilling concrete.At the beginning of high pressure,stress concentration will occur at the contact part of the hole wall with the jet,which causes the rock mass in contact area deformation and failure,and the block movement downward under the high pressure of the gas and liquid jet.As time goes on,the stress wave of the gas and liquid jet extends from the contact area to the external rock mass,and gradually damage to the external rock mass.After high pressure of gas and liquid jet,the pore size of 320 mm expands to 1100 mm after washing.Therefore,the effective range of high-pressure puncture flushing is proposed: the hole diameter is 320 mm,35-40 MPa high-pressure water and 1.0-1.5MPa high-pressure wind,and the rocking and crushing action of the rock mass is less than 0.4m from the hole wall.After the rinsing action,the pore size of 320 mm was expanded to 1100 mm,and the amount of slag was 43.4 m3.The high-pressure,through-flushing backfilling scheme,is scientific,economic,safe,and effective,and it can achieve the intended purpose.High pressure technology improves the physical and mechanical properties of fault rock mass,it solves the difficult problem of the wide fault fracture zone in certain environment,and provides a new way of thinking and specific treatment for the reinforcement in fault fracture zone.(4)The similarity theory was used to develop the similar materials of the unloading rock mass affected by the f5 fault zone,and the physical model test of the pressure-dispersed anchor cable to reinforce the unload rock mass was designed.The experimental analysis shows that the long-distance anchor cable of the pressure-distributed anchor cable is loose and the anchor cable is overloaded.The nonlinear deformation characteristics of the rock mass are obvious.The displacement calculation of the rock mass was derived by combining the Mindlin's stress solution and the nonlinear constitutive of the unloading rock mass;The rock mass farther away from the anchor cable is less stressed,and its nonlinear deformation was not obvious;The additional stress of the adjacent anchorage to the rock mass is small,and the index of the adjacent anchor can be calculated according to the deformation superposition principle.The additional displacement caused by the adjacent anchor cable can be calculated based on the superposition principle,and the formula of pre-stress loss caused by the cable.The numerical simulation of single-anchor and double-anchor is carried out on the pressure-dispersed anchor cable by FLAC3 D.The simulation results are correspondence with the physical test,it revealed the group anchor effect: when the anchor cable spacing is 5.0 meters the stress influence range of the cable is relatively small,and the stress between adjacent anchor cables is relatively low.A numerical simulation test of the group anchor support system of pressure-dispersed anchor-anchor combined with covered panel(or slab beam concrete)has been carried out,it shows that the support method is scientific and reasonable,and it has strong adaptability to complex rock mass structure,which bring the anchoring effect into full play.(5)Through the inspection and analysis of the f5 fault after grouting,the slurry is fully filled into the cracks and faults,the grouting effect is obvious,the water permeability of the consolidated grouting is greatly reduced compared with that before,the drills of Lugeon value larger than 3Lu are all eliminated,the cement slurry has obvious effect on the filling of the f5 fault zone..The results of geophysical examination show that the acoustic wave values of various rock grades have been significantly improved.The modulus of each unit has been greatly improved compared with that before irrigation.The average injection volume per unit with grouting decreases significantly with the increase of grouting order.The permeability of the formation is obviously improved;the chemical grouting is used to reinforce the fine cracks and special geological areas that cannot be reached by ordinary cement slurry;after the high pressure wear-through flushing and backfilling,the water permeability is significantly reduced,and the acoustic wave and the transformation mode are significantly improved to meet the design specifications.The analysis result of monitor data shows that,f5 fault and its influence zone in the left bank dam foundation on high arch dam can meet the requirements for the safe operation of high arch dam after adopting the comprehensive disposal measures.After the f5 fault and its influence zone in the left bank dam foundation of Jinping high arch dam are strengthened,after four stages of water storage test,the displacement increment of the left bank abutment slope has no obvious change trend,and the overall change is not big at present(no more than 5mm);The shallow multi point displacement meter of the left bank slope(the cumulative value is no more than 30mm),the loss rate of anchorage force is about 15%,and there is no obvious deformation phenomenon of surrounding rock in the flat hole,and the stability of rock mass is generally stable.The reduction coefficient of the seepage pressure meter after the dam foundation curtain is less than the design control value,there is a positive correlation between the water level change and the upstream water level,which is in line with the general law of the uplift pressure distribution in dam foundation;Percolation changes before and after storage conform to general change law;After controlling the water level near the height of 1880.0m,the seepage and seepage pressure of each part changes steadily.From the current monitoring situation,seepage control works are generally designed within the scope of the work.After more than four years of monitoring and evaluation,all the monitoring indicators are stably controlled and can meet the requirements of safe operation of high arch dams.This fully demonstrates that the f5 fault zone reinforcement treatments(encryption consolidation grouting,cement-chemical composite grouting,high-pressure water flush and pre-stressed anchoring)are scientific,reasonable,safe and effective.