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Abstract
Dams are mainly located at the deep alluvium, where large amount of sand and gravel is adverse to prevention of seepage and maintenance of stability of the dams. Therefore it is necessary to reinforce the dams by grouting, and the primary task is to do research on the laws of diffusion and distribution of the slurry in the alluvial layer. The present study is based on the traditional theory of grouting and the laws of diffusion and distribution of the slurry, the slurry splitting mechanism, the characteristics of soil reinforcement are obtained. In addition, it is found by on-site grouting model tests that the slurry is generally filling and splitting along the interface between the earth and rock, and mainly splitting in the horizontal direction in grouting reinforcement process. To improve the reinforcement effect, the repeated injection should be adopted in grouting process. The study results will facilitate future dam grouting reinforcement projects in alluvial layer.
... Specifically, Hu et al. and Han et al. performed simulated grouting test in fractured rock mass and then obtained the uniaxial compressive strength of the rock mass after grouting [15][16], respectively. Cheng et al. carried out grouting field tests in the sedimentary layer to reveal the grouting reinforcement mechanism, as well as to obtain the strength of soil after grouting [17]. Besides, Yang et al. developed grouting tests in gravel to study the relationship between the compressive strength of consolidation body and the injection parameters, as well as the grout properties [18]. ...
... The experimental system can realize porous grouting and multi-step grouting in different media, which have a realtime monitoring of the internal physical parameters of the rock mass. These features are important to the study of the permeability and reinforcement mechanism of the grouting slurry [19][20][21]. AC. Houlsby simulated the flowing of slurry through a single crack. ...
Grouting plays an important role in the construction of projects. The influence of dynamic water pressure and confining pressure on grouting has not been considered by traditional grouting theory. This study used a "geological engineering multifunctional experimental system" to explore the influence mechanism of dynamic water pressure and confining pressure on the grouting effect. Four groups of indoor grouting model experiments were adopted and compared. The influence of dynamic water pressure and confining pressure on the grouting effect was analyzed under different conditions. Experimental results demonstrate that the diffusion of the slurry is divided into pressure diffusion and migration diffusion. The dynamic water pressure causes the grouting slurry to be diluted, and the pressure in the cracks of the rock mass structure increases. As a result, serious loss of slurry occurs, and the slurry obviously shows migration diffusion. The confining pressure leads to closing of structural cracks, and the grouting effect of closed cracks mainly affect the pressure diffusion of the slurry. A coupling effect exists between the dynamic water pressure and the grouting pressure. The final dynamic water pressure increases by 25% compared with the initial value under dynamic water pressure only. By contrast, the final dynamic water pressure increases by 31% compared with the initial value under the combined effect of dynamic water pressure and confining pressure. The grouting effect can be improved by increasing the grouting pressure, decreasing the dynamic water pressure, and extending the grouting time.
A 3D grouting model test system, which consists of bearing test rig, servo voltage supply unit, grouting unit, multivariate information monitoring unit and image acquiring unit, is developed to investigate the grouting diffusion process and reinforcement mechanism. The main functions of this system are the lacunose, multiple sequence and parameter flexible model test of the grouting and the real-time collection of the physics field information during the grouting. The major advantages of the system include: (1) The test cavity is designed as composite barrel structured, strong leak tightness and convenient disassembly, in favor of studying grouting solid details; (2) the loading method of multi-cavity control hydraulic pneumatic joint can provide continuous steady pressure groundwater environment; (3) a multi information parallel real-time monitoring system can collect the information of the total pressure, pore water pressure and displacement of different spatial positions in the injected rock body, and realize the spatial and temporal variation of physical parameters in the grouting process. The testing system is used to perform the simulation tests of single hole grouting and grouting in a single hole, and the variation of grouting pressure P and the mechanical response of soil are obtained. The p-t curve shows multiple peak-trough cycle and characterizes strengthening mode of splitting grouting. The total pressure, pore water pressure, effective stress and grouting pressure change almost synchronously under the grouting loading; reach the peak values at the end point of grouting, and then begin to attenuate and gradually to be stabilized. Compared with single-hole grouting method, the multi-hole grouting method can improve the effective stress of soil dramatically. It is demonstrated that fracturing grouting is the main clay medium. The contact relationship between different orders of slurry veins is complex, and can be divided into 3 basic modes: shear splitting, in situ splitting and intrusion splitting. The test method of porous and small grouting rate can reduce the disturbance of surrounding rock, increase the amount of grouting and the degree of consolidation of soil, and improve the effect of grouting reinforcement.
Based on the curtain grouting engineering of Zhongjiashan tunnel, a large-scale model test device is designed to simulate the process of fracture grouting in fault fracture zone. The variation law of key parameters during the grouting are recorded and analyzed by layouting monitoring components, and the distribution of grouting veins are exposed intuitively by excavating the filling medium. The test results show that the fracturing pressure presents a pulse-like law during the grouting process, and the first fracturing pressure under the conditions of this test is 0.12 MPa which is made a comparative analysis with the existing theoretical solution. The change mechanism of fracturing pressure is analyzed based on the conversion of slurry diffusion form, saturation of primary and secondary fracturing channels, formation of new fracturing channels and saturation of the follow-up fracturing zone. The definition methods of primary and secondary fracturing pressure are proposed; then 7 primary fracturing pressure and 53 secondary fracturing pressure under the conditions of this test are found to show an increasing law approximately. Based on the p-t curve, the fracturing process of soil are divided into 3 stages including the energy accumulation, soil fracturing and slurry energy transfer from the perspective of energy dissipation. The spatial distribution law and coexistence law of primary and secondary grouting veins are found by excavating the filling medium. The site application test is carried out in curtain grouting engineering of Zhongjiashan tunnel to verify the correctness of test results. The test results play a guiding role on the understanding of grouting theory and the application of grouting engineering to some extent.
The multiple drillings and sequenced curtain grouting experiment for water-rich broken rock mass is carried out using self-developed 3D grouting model test system. The spatio-temporal characteristics of total pressure, pore pressure and displacement are obtained by the optical fiber parallel real-time monitoring system. The total pressure and pore pressure greatly change and have 4 periods: rapid growth, peak-value fluctuation, progressive attenuation and gradual stability. The slurry advantage-fracture diffuses in the vault and arch bottom, leading to displacements around the tunnel. The permeability decreases because of compression and consolidation of the grouted rock mass, and the pore pressure is significantly improved during sequent grouting. After the grouting experiment, the reinforced body is exposed and its irregular form is studied. The penetration-splitting grouting reinforcement model for broken rock mass and the splitting grouting reinforcement model for argillaceous weak rock mass are summarized. The mechanism of repeated grouting of splitting grouting veins is revealed. The SEM images of grouting-reinforced body reflect that the interface between grouting vein and clay can be divided into penetrating type and split type, and the micro slurry veins improve the surface roughness and strength. A fractured crack develops to be closer to the clay, which suggests that physical and mechanical saltation takes place over there, which is the potential broken link of reinforced rock mass. The research improves the grouting experiment method and explores the slurry diffusion laws and grouting reinforcement mechanism, thus providing technical support for grouting management under similar conditions. ©, 2015, Chinese Society of Civil Engineering. All right reserved.
Control of soil deformation induced by tunnelling is one of the major objectives of fracturing grouting. Prediction accuracy of tunnel deformation depends mainly on the equivalent elastic parameters of composite soils with fracture grouting. Firstly, according to equivalent grouting area and the existing model of fracturing grouting, a simplified 2D model for equivalent unit cell is developed for composite soils with fracturing grouting, and the analytical solutions of the equivalent elastic parameters of this model are derived based on deformation compatibility principle and homogenization theory. Secondly, finite element method is employed to calculate and analyze the equivalent elastic parameters of the simplified model and existing model, respectively; meanwhile, the comparisons are made between the finite element and analytical results of the simplified model. Lastly, the influence of grouting volume ratio, soil elastic parameters, and grouting concretion elastic parameters on equivalent elastic parameters are analyzed by means of the analytical solution. The results indicate: (1) the equivalent grouting area method is feasible, and the simplified model can be applied to theoretical analysis in the elastic deformation stage; (2) the analytical results are in good agreement with the finite element results, and hence the analytical results are reasonable; (3) the equivalent elastic modulus and equivalent Poisson's ratio of composite soils are mainly influenced by the grout volume ratio and modulus of grouting concretion body; the Poisson's ratio of grouting concretion has slight influence on the equivalent elastic modulus of composite soils.
The mass data in whole process of physical model test were real-time recorded; and the implementing mechanisms, reinforcement efficiency, construction technology of new horizontal flexible reinforced grouting technology were studied with physical model test in field. This paper focuses on the test design, manufacture scheme of model, testing method and research methods of experimental research. The test results show that the new horizontal flexible reinforced grouting technology contains enormous advantages including easy processing, effectiveness, and development and utilization value. It is indicated by the results of the experiment that the test results combining with the theoretical calculation have the guiding meaning for modifying the designing parameters. Meanwhile, the test results and construction parameters of the new technology can be used in real design and similar engineering for the test conditions of model test are basically in consistence with the conditions of actual operation.
Compaction grouting and fracture grouting are studied by use of a grouting simulation test device dereloped by the authors. The generation and development of grout balls and fractures in clay are performed by laboratory tests. The results show that pressure filtration effect exists throughout the grouting process. That is to say, free water in the grout penetrates through the clay under high pressure, so that the water-cement ratio of the grout increases. Pressure filtration effect increases with the increase of the permeability of soil, water-cement ratio of the grout and grouting pressure. So it must be taken into account when grouting in the soil has good permeability. The increase of grouting pressure will lead to the decrease of the diameter of grout balls; it also will cause the increase of the number of grout fractures and result in the decrease of the width of the grout fracture. Under certain grouting pressure, the diffusion of grout will gradually turn from the compaction grouting to the fracture grouting as the water-cement ratio increases. The fracture grouting in the clay can be divided into three stages: grout ball stage, first fracture surface stage, and following fracture surface stage. Every fracture occurs in the weakest surface. By use of the scanning electron microscope, differences among the natural clay, consolidated clay and grouting clay are analyzed. Under the effect of pressure filtration, Ca2+ ions can travel into the clay and improve the strength of the soil. The results are important to both the theoretical researches and the application of grouting.
By the grouting simulation test in sandy gravels, the influences of grouting pressure p, grouting time t, water cement ratio m, permeability coefficient k, porosity n upon grout diffusion radius R, concretion strength P and their correlation were analyzed. It was shown that R increased with the increasing of p, t, m and k. Distinct influencing factor on grout diffusion radius R was p and k, but the influences of t and m was small. Strength P of grouted gravels increased with the increasing p, t, n, and decreased with the decreasing of m. By regressing test data with computer, the theoretical relation was educed.
The construction technology, implement mechanism, reinforcement efficiency of implementing method of backfill of abutment back with horizontal flexible-reinforced grouting technology were studied by in-situ experimental research combining with laboratory study. The in-situ test results show that the backfill of abutment back reinforced by the new horizontal flexible reinforced grouting technology has enormous advantages including easy processed, effectiveness, development and utilization value. On the processing of the in-situ test many valuable construction parameters and experimental data were obtained; and a lot of material resource could be used for changing the design and construction parameters so as to perfect the construction technology of the new technology. At the same time, a new engineering solution for the prevention and treatment of bridgehead jump-driving was offered.
This paper mainly presents the definition and forming process of deepwater sediment, as well as the characteristics of deepwater sequence stratigraphy and sedimentary elements. The deepwater sediment is deposited in deepwater environment by the gravity flow, forms during the drop and earlier rise of relative water level, and mainly distributes in lowstand systems tract. The deepwater sequence is bounded by condensed section. Mass transport deposits form the beginning of a sequence formation and sit on the sequence boundary. Then they are overlaid by channel-levee deposits. The typical deepwater sedimentary elements include channel, levee and overbank, sheet sand, and mass transport deposits. These elements are systematically deposited in time and space. Channel is the main sediment conduit and deposition area. From updip to downdip area, the sinuosity of channel increases and the flow energy decreases. The channel migrates laterally and evolves from lower low sinuous sand-rich to upper high sinuous mud-rich channel. Levee and overbank are dominated by muddy deposits, and levee distributes along the channel and exhibits wedge shape. The proximal levee is characterized by high content of sandstone, thicker deposit and big dip angle, while the distal levee is characterized by low content of sandstone, thinner deposit, small dip angle, good lateral continuity and poor vertical communication. Sheet sand is the distal unconfined deposits of the deepwater fan and can be divided into conglomerate and layered types, and conglomerate sheet sand has a good lateral continuity and vertical communication. The layered sheet sand has a good lateral continuity and poor vertical communication. Mass transport deposits are the slumps, slides and debris flow due to the slope failure during lowstand period. It can erode the underlying strata, and the deformation structure is very common in mass transport deposit, and it can also serve as a good seal for oil and gas.
In order to analyze the mechanical mechanism of compression grouting and give the analytical solution of the ultimate grouting pressure, the process of compaction grouting is considered as the question of cavity expansion in infinite soil mass. The ultimate grouting pressure is given by the law of conservation, in which the volume change of cavity expansion is balanced with the compression of soil and the energy given out from cavity expansion is absorbed by the volume change and shear strain caused in soil. The stress-strain-volume change relationships under the high stresses caused by compression grouting are described. The theoretical values agree with the measured values from the field test; and the conclusion that the grouting pressure of columniation cavity is higher than the sphere cavity is gained.
On the assumption that the soil mass is in compliance with Mohr-coulomb failure criterion, crack grouting is the grout injection into the compressed and yielded soil mass under grouting pressure. The compression process is considered as the question of cavity expansion in infinite soil mass. According to the stress-strain-volume change relationships of the soil mass in energy dissipation area under grouting pressure and static soil pressure in the process of grouting, energy and volume change conservation principle and yield criterion, formula for computing the beginning grouting pressure caused by crack grouting is deduced. The calculation results obtained from this formula agree well with field test results. In the view of energy dissipation, energy dissipation of the soil mass during crack grouting process is analyzed. Analysis results show that the main energy is dissipated in crack, crack expansion and the plastic deformation of soil mass. Other dissipation is less compared with the above main energy dissipation.