Anchorage Structure Repeatable Grouting Technique And Its Mechanism

Along with the high-speed development of national economy, especially in recent years, our government keep constructing water conservancy, transportation, energy and other infrastructure, there has a huge demand on anchor, the anchor support technology got rapid development. In practical engineering applications, generally, we increase the bearing capacity of anchor structure by adjusting the diameter of anchor hole, anchor structure length and other methods, but in some cases, due to the weak stratum, the red line site, the adjacent existing buildings etc. are to close, the length of the bolts or cables is limited.At this point, the most simple and effective method to improve bearing capacity of bolts or cables is through grouting. Currently, the traditional grouting method of Geotechnical anchoring structure (including the anchor ron, anchor rope, etc.) are always one-way grouting at home and abrod. Serum enter into the rock and soil layer through pressure grouting tube, But actually the one-way grouting method exists many main problems, such as cannot effectively control the spread of the size range, uneven distribution of slurry at the bottom and poor controllability, greatly reduces the pull-out force of anchorage structure. For a long time, the one-way grouting problems has been affecting the anchoring structure uplift force.If we can accomplish the repeatable grouting technology(Repeatable grouting with good controllability and uniform size distribution at the bottom, improve the pulling force and reliability of anchoring structure, and many other advantages),certainly will improve the pulling force of single anchorage structure, and reduce the number and length of the anchor structure, reduce project cost.In the second chapter of this paper, through the actual field soil nailing repeatable pressure grouting test, the idea of the grouting technology applied in the anchorage structure is enforced, the tests result show that the limit drawing force of the soil nails are improved sharply after using the repeatable pressure grouting technique. The first group:compared to one-way grouting, the bearing capacity increased by68.3%after2times grouting, three times grouting ultimate bearing capacity is48.5%higher than that of two times, three times grouting ultimate bearing capacity is 150%higher than that of one-way grouting. The second group:compared to one-way grouting, the bearing capacity increased by22.0%after2times grouting, three times grouting ultimate bearing capacity is100.7%higher than that of two times, three times grouting ultimate bearing capacity is144.9%higher than that of one-way grouting. The third group:compared to one-way grouting, the bearing capacity increased by54.5%after2times grouting, three times grouting ultimate bearing capacity is94.2%higher than that of two times, three times grouting ultimate bearing capacity is200%higher than that of one-way grouting. According to the effect after3times grouting, the increase of the limit drawing force has a certain relationship with the soil conditions. The first group and the second group of soil nail have the same length(6m), and through the same soil layer, mainly silty clay, increase close to144.5-150%; The length of third group soil nails are9m, through silty clay layer and the silty clay soil, improve200%, significantly higher than the former two groups soil nails.The third chapter of this paper gives out the analytical analysis of the repeatable grouting. Concluded that the repeatable fracturing grouting pressure can be derived by using the column cavity expansion theory, divide the combination around the anchor hole into elastic region and plastic region, and obey the Moore-Coulomb criterion. Can use the power-law fluid in the parallel narrow gap to calculating diffusion radius of the anchorage structure fracturing grouting. The anchorage section can be divided into elastic and plastic section, the stress integral of the two respectively regions is the bearing capacity of the repeatable grouting anchor structure. Meanwhile, this paper gives the simplified calculation formula of the fracturing grouting pressure, diffusion radius, bearing capacity of the anchor structure after repeatable grouting. By comparing with and the actual measured data, it can meet the engineering needs. But it must be noted that, mostly belong to the empirical formula, especially some of those parameters, in order to improve the accuracy of the calculation results, it is best to confirmed by field test when the conditions allow.The fourth chapter of this paper comprehensive analysis characteristic of the anchorage structure repeatedable grouting in different stage. The first time are mainly filling grouting, the second and third times repeated grouting bias for pressure grouting. Results show that the slurry grout diffusion range is related with material properties, grouting pressure and performance of the slurry. When effective slurry pressure is0.5MPa, the coefficient of permeability of the layer is in1.0E-8m/s magnitude, the effective diffusion area is about1times the diameter of anchor hole, when the permeability coefficient is1.0E-7m/s level and1.0E-6m/s level, the effective diffusion range respectively2times and5times the diameter of anchor hole. The enhancement body formated by grouting is inhomogeneous shape. The second repeatable grouting forms nearly cylindrical reinforcement, from the anchor end to anchor head, reinforcement diameter increase gradually. The third repeatable grouting forms approximate spherical reinforcement. Obviously, after repeatedly grouting, when the anchor structure under axial load, it will not only to overcome the frictional resistance between anchoring body and surrounding soils, but also to overcome the soil pressure of the pressure expansion parts, such end-bearing effect can greatly improve the bearing capacity of anchor rod. In the chapter v of this paper, on the basis of field test, the bearing properties of repeated grouting anchor structure are analyzed. Though simulation and field test results have certain differences, but on the whole, to assume the reinforcement after twice and three times grouting as nearly cylindrical reinforcement and local cylindrical body is appropriate. The bearing capacity of grouting anchor structure increases with increasing enhancement diameter, but the increasing amplitude gradually decreases, and the most economic and effective diffusion range is1to2times the diameter of anchor hole, the increase body strength and deformation parameters have a little effects on the anchoring force, interface performance parameters Influence on the load-carrying performance, laying position of local enhancement body has a great influence on axial force distribution, from the point of stress effect, layout on the anchor end is suggested.In the chapter vi of this paper, the anchorage structure repeated grouting technique are summarized respectively from the construction equipment and personnel organization, repeatable grouting device production, repetitive grouting construction process and grouting construction control points and some other aspects, and compiled a set of relatively mature construction technology, in order to promotion, accumulate experience for similar projects.Finally, the paper has made a summary to the entire research result, obtained the corresponding conclusions, and put forward the advice for the further research work..All in all, this paper based on the summarize of the anchor grouting technology research status at home and abroad, presents a new repeatable grouting technology of anchor structure, and through the field test, obtained the very good effect. Then do analytical analysis to the craft puts forward the practical simplified calculation formula of parameter. Carry on the simulation analysis respectively from grouting traits and the bearing characteristics after grouting to the process. Finally, the whole process are summarized, and sort out a set of complete, mature quality control methods, to promote the technology, provide more choices for the similar projects in future.