Study On Fluctuation Mechanism And Stabilization Automatic Control Method Of Grouting Pressure In Rocky Dam Foundation

Abstract:With water conservancy and hydropower projects greatly enlarged in China at present, grouting technology has been widely used as a major reinforcement method of dam foundation constructions. As continuous upgrading for the height of concrete dam, the anti-seepage ability and durability of the foundation impervious curtain for high concrete dam become much more significant. Due to subtle characteristics of grouting engineering, both its construction quality and grouting effect are difficult to visually detect, which must be assessed by analysis on the grouting parameters. Because of the influence of many factors including pressure fluctuations, slurry rheological properties and geometry characteristics of rock fracture, automation degree of grouting quality monitoring and control are not high in practice now. In particular, the grouting pressure feedback control still take manual adjustment in which control accuracy and response time could not meet the actual needs, meanwhile engineering accidents are vulnerable to happen because of overrun grouting pressure caused by operational errors.In view of above, according to the methods of theory and practice, mechanism of grouting control are researched by analyzing the seepage characteristics of grout in fracture of rocky dam foundation, the integrated design principles of grouting pressure are proposed by analyzing rock deformation and calculate methods of grouting pressure, the grouting pressure automatic control system (GPAC) is developed based on the grouting pressure fluctuation mechanism studying, hydrodynamics mathematical modeling of grouting pipe network and automatic control theory analysis, GPAC system is improved by indoor grouting experiments and in-situ curtain grouting tests of Nuozhadu hydropower station. The major study contents are listed as follows:(1) The composition of grouting pressure and related calculation methods such as empirical method, reverse method of dam foundation curtain grouting, grouting experiment method including water pressure test and hydraulic jacking test are studied in detail. According to analyzing the occurrence mechanism of hydraulic fracturing effect, crack expansion effect and pressure compaction effect, the integrated design principles of grouting pressure is proposed.(2) On the basis of flow-pressure drop relationship of grouting piping systems and rheological properties of grouting slurry, fluctuation mechanism of grouting pressure is studied. Damping characteristics of grouting formation, flow characteristics and opening degree of regulating valve, and fluctuation characteristics of grouting pump are thought to be the main influencing factors causing the grouting pressure change in the circulating grouting pipe system. The static equilibrium equations of pipeline system are established based on flow-pressure drop relationship in one-dimensional model of grouting slurry flow in pipelines. In order to establish the basic differential equations of pipeline system, transient analysis on grouting slurry flow in pipelines is made based on hypothesis that flow is compressible and unsteady. Then characteristic method is used to mesh generation and finite difference, afterward, the equations are solved by Newton-Raphson method according boundary conditions. The whole grouting pipelines are simplified and represented as series of nonlinear algebra equations, which describe the grouting pipes, equipments, grouting hole and regulating valves. Meanwhile calculation methods on damping coefficients of fundamental composition in grouting system are studied in order to provide accurate calculation control values for pressure stabilization. Finally, the hydrodynamic model of grouting pressure stabilization and related control parameters is proposed for programming pressure fluctuation control software.(3) The algorithm principle and controller design of PID control and fuzzy control are studied in order to summarize their respective advantages and limitations. According to the fluctuation characteristics of grouting pressure, control accuracy and response time requirements during automatic control process, a set of composite control algorithm with particularities of parameter self-tuning and adaptive control rules which named as TS-FPID is proposed by combining the PID control algorithm and fuzzy control algorithm.(4) Grouting pressure automatic control system (GPAC) which based on hydrodynamics mathematical modeling of grouting pipeline system and the TS-FPID control algorithm is illustrated in detail through the software interface, basic functions and hardware composition. The upper software of GPAC system is developed on SIEMENS WINCC V7and STEP7, the hardware of GPAC system is composed by SIEMENS S7-400programmable logic controller (PLC), PROFIBUS DP is used as system network.(5) Indoor simulation grouting test such as grout pump pulsation characteristics tests, regulating valve damping coefficient tests, grouting pressure automatic control tests and etc are performed according to the actual grouting conditions. The simulation results show that grouting pressure can be automatic controlled in5-6s and control precision can be kept on less than5%of designed pressure value by GPAC system when the grouting pressure changes in the range of0-5MPa, the design target of pressure fluctuations control is met. GPAC system is used for real-time monitoring and feedback control on grouting pressure in dam foundation curtain in-situ grouting test of Nuozhadu hydropower, the test results show that grouting effect of test zone is well, rock fracture and water seepage channel are fully packed by slurry whilst mechanical properties of rock mass and strata integrity are greatly improved, the design standard of anti-penetration capability is met. Compared to manual regulation, control accuracy and response time of GPAC system are more superior which have better benefit on engineering economic and security in addition. GPAC system should be promoted to widely use in other engineering practice.