Application of post-wall grouting technology in the construction of auxiliary shaft of Sishanling Iron Mine

         1. Project Overview

Iron Mountain Mine auxiliary shaft Si wellhead elevation + 215.2m, bottom elevation 1288.7m (including back 600mm thick), the depth of the wellbore 1503.9m, net borehole diameter 10.0m.
At present, the working face has been drilled to the height of the wellbore -553.5m, and the depth of the well is 766.7m. During the construction process, it was found that the wellbore water level of the wellbore level below -461.8m was serious, and the total inflow of the measured wellbore reached 52.38m3/h. Water leakage from the well wall has many adverse effects on construction operations and safety. After joint research by the construction unit and the school, the wellbore was suspended and the post-wall grouting was carried out on the -461.8~-550m well section to reduce the water leakage in the well wall and ensure the safety and efficiency of the construction work.
2. Post-wall grouting mechanism
Post-wall grouting is to break the wall to the design depth, and the slurry is injected into the cracks or pores of the shaft wall with a certain pressure to achieve the effect of water blocking and reinforcement of the wellbore. The slurry diffuses along the well wall cracks and the weak fracture layer under the pressure of the grouting pump, and the pore passage is blocked, which causes the pressure to rise, which causes the surrounding surrounding rock to expand, and the cracks in the slurry penetrate into the rock mass to form the split grouting [1] -2]. The split grouting forms a vertical vein grout around the grouting hole to strengthen the broken surrounding rock. Since the hardened shapes are different and cross each other, the ability to resist shear damage of the rock mass can be improved.
3. Design of grouting scheme after wall
3.1 Grouting plan selection
With the increasing depth of the excavation depth of the Sishanling Iron Mine, the problem of water in the well wall has become more prominent (the highest water inflow has reached 50m3/h). If water blocking measures are not taken, the drainage costs will be greatly increased, and the excavation conditions will be deteriorated, the life of the wellbore will be reduced, and potential mining operations will be hidden. In order to seal the aquifer to reduce the water in the wellbore and to reinforce the wellbore, the mine decided to use post-wall grouting.
(1) If shallow hole grouting is used, the pressure of the wellbore in the deep well is likely to cause local damage (fracture or bursting) of the rock mass, which eventually leads to failure of grouting and water shutoff. Therefore, deep well grouting should be carried out by deep-hole high-pressure grouting, so that the grouting depth exceeds the well wall, and a multi-hole multi-hole refilling method is adopted.
(2) Grouting method: According to the characteristics of the surrounding rock exposed by the wellbore and the characteristics of the water in the well wall, and considering that the hanging plate is close to the bottom of the well, the grouting behind the wall adopts the upward pre-injection and the downward re-injection.
3.2 Grouting material and slurry preparation
(1) Slurry material. Because ordinary Portland cement is rich in source, low in cost, simple in process equipment and convenient in operation, in this grouting construction, the grouting material is mainly made of ordinary Portland cement, and it is sealed with grouting with water glass slurry. hole. Consider using chemical slurry in the seriousness of rock mass breakage and water leakage, such as Kaisu gel polymer grouting material used in the most serious water in the shaft to achieve the purpose of rapid plugging and improve the effect of grouting and water blocking.
Kaisu gel polymer grouting material is less prone to particle segregation than granular pulp such as cement slurry, and generally has low viscosity, good fluidity and good injectionability. It is easy to enter the small cracks or pores of the rock mass, even the extremely fine (such as 0.1mm or less) gap can be injected. Kaisu gel polymer grouting material is divided into KSN-1F type main agent and curing agent, the expansion coefficient is 1.5 times, the compressive strength is 42MPa, and the tensile strength is 16MPa. With the increase of the depth of the shaft excavation, the Kaisu gel polymer chemical grouting material was gradually used instead of ordinary cement for grouting and water blocking.
(2) Preparation of the slurry. When preparing cement slurry, we strive to supply the material in a correct and strict manner. First, add a certain amount of water to the mixer, and add cement under continuous stirring to avoid the mixer getting stuck. After the mixture is evenly stirred, add the additive. The water glass slurry generally has a high concentration and needs to be diluted with water before use. According to the water inflow condition of the well wall and the post-wall grouting requirements, the ratio of the grouting ratio is: the water-cement ratio of the cement slurry is controlled at 0.65 to 1:1; the water glass concentration is 30-40° Be'; The ratio of cement slurry to water glass is controlled at 1:0.5 to 0.8. Kaisu gel polymer grouting material is divided into KSN-1F type main agent and curing agent. It is necessary to carry out slurry proportioning test according to the degree of well wall fracture and water seepage, and adjust the addition amount of catalyst to accurately control the gel time.
3.3 Grouting parameter selection
(1) Grouting pressure. Grouting pressure is the driving force to overcome the various flow resistance, so that the slurry is diffused and filled with compaction. It is an important parameter of grouting operation. The grouting pressure is not only related to the engineering geological conditions such as the crack width and the additional load of the stratum, but also depends on factors such as grouting depth, grouting speed and grouting amount. The pressure behind the wall grouting should be 0.5-1.5 MPa larger than the hydrostatic pressure. When the rock mass is relatively developed, the grouting pressure can be appropriately increased.
The well wall strength check formula is:

Where: p———the pressure that the borehole wall can withstand at the grouting site, MPa;
E———wall thickness, take 0.6m; R
0———the net diameter of the shaft, taking 10.0m;
K———The allowable compressive strength of the lining material, the strength of the concrete shaft wall is C45, so take K=45MPa;
η - - safety factor, may take 2;
Pc - the final pressure of grouting, MPa.
The well wall strength p=6.13 MPa calculated by the formula (1), so the whole process pressure after the wall grouting cannot exceed 6.13 MPa.
(2) Grouting diffusion radius.

Where: g———gravitational acceleration;
h——— grouting pressure;
A—the equivalent radius of the rock gap;
Γ—the bulk density of water;
s———the shear strength of the slurry;
β———The time coefficient.
On-site construction can adjust the permeability of the slurry, the gelation speed and the final pressure of the grouting to make the effective diffusion radius of the post-grouting of the wall greater than 2.5m.
3.4 Grouting hole arrangement and single hole suction amount
(1) Grouting hole arrangement. The range of post-wall grouting is -461.8~-550m, and the grouting height of the well wall is 88.2m. In order to achieve the purpose of grouting and sealing the aquifer of the wellbore, a row of grouting holes is arranged every 2m, totaling 44 rows, and the rows are staggered; each row of 16 holes, the grouting hole depth is 4m, a total of 704 holes (estimated The effective grouting holes are: 704/3 = 234), as shown in Figure 1.

(2) Single hole suction amount. The single hole suction amount can be calculated as follows:

Where: A - the slurry consumption coefficient, here take 1.35;
R———effective diffusion radius, take 2.5m;
L———effective length of drilling (non-wellbore grouting section length), take 3.2m;
n——— is the porosity after the wall, take 0.03;
B————For the slurry filling coefficient, take 0.88.
The single hole suction amount was calculated to be 2.24 m 3 /well.
3.5 mechanical equipment
(1) Drilling equipment. The YT-28 air-leg rock drill was used to drill a grouting hole with a hole depth of 4 m. The grouting orifice tube made of seamless steel pipe has a diameter of 38 mm and a length of 1.2 m. One end of the buckle retaining ring, the other end of the 100mm range of 10mm diameter of the flower eye, the number is 20. The main function of the retaining ring is to limit the position of the orifice tube to prevent the orifice tube from fully entering the borehole.
(2) Grouting equipment. The slurry was prepared by ZBQ-15/5 pneumatic high-pressure grouting pump, and the slurry was prepared by a self-made pneumatic stirrer.
4. On-site grouting construction
(1) Holes and orifice pipes are buried. The rock driller uses the YT-28 gas-leg rock drill to inject the slurry hole according to the predetermined hole position. After the hole is formed, the hole tube is buried, which can effectively prevent the grouting hole from collapsing and returning to the slurry, and bear the pressure at the top of the grouting hole to avoid the surface crack of the well wall. Wrap the leaded oil on the horse's buckle of the prefabricated orifice tube, and use a sledgehammer to pry the orifice tube into the grouting hole. The exposed tube is 50 to 70 mm long. The ball valve is then screwed onto the wire end of the grouting hole. The cement-water glass cement is used to seal the orifice, which can be grouted after solidification.
(2) Water injection hole. In order to obtain better grouting quality, water injection before grouting is an indispensable task. The first purpose is to remove impurities such as rock powder and debris in the cracks behind the wall, to avoid clogging the grouting channel and affecting the perfusion of the slurry. Second, based on the water injection condition, the initial displacement of the grouting pump and the adjustment range of the slurry parameters are estimated. The amount of water injection depends on the reinforcement range of the rock mass and the development of the fracture. When the water injection pressure is not more than 3 MPa, it is considered that the grouting hole can be grouted.
(3) Pressing the slurry. The cement slurry is filtered through two stages and then pressed into the grouting hole by a grouting pump. The grouting concentration is the first thick slurry and the thick slurry. The single-liquid grouting pressure does not exceed 5 MPa, and the two-liquid grouting pressure does not exceed 6 MPa. Always pay attention to the injection rate of the slurry and the grouting pressure to prevent the occurrence of high pressure and large injection rate. If the pressure does not rise, the single hole grouting should not exceed 2t. Finally, the grouting holes are sealed with a water glass slurry which is diluted as required and filtered. After the grouting is completed, the exposed portion of the orifice tube is cut.
When the grouting pressure reaches the final pressure, the gushing water point to be blocked is no longer leaking, there is no running phenomenon around, and after 10 minutes, the grouting valve is opened without water leakage, and the hole grouting can be ended; when the concentrated water outlet point is not more than the water 0.5m3/h means that the grouting section has reached the engineering requirements and the grouting can be stopped.
5. Conclusion
In general, post-wall grouting is still the most reasonable and effective way to control the problem of water and water in the well wall. In this construction, the following experiences are summarized: no matter whether the water is drilled or not, grouting is required to prevent the water from being squeezed out when other holes are grouted. When controlling the final pressure of grouting, avoid repeatedly grouting in one position and grouting in place as much as possible. After the grouting is finished, the appropriate amount of clean water should be injected into the grouting pipeline, so that the residual slurry in the grouting equipment enters the waste liquid pool (the waste liquid pool is located on the hanging pan), and then is taken to the ground for disposal. After each grouting, the grouting equipment and piping should be cleaned and overhauled in order to prepare for the next grouting work.
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Author: Li Ming House, Zhang Lianheng; China, China Metallurgical Group Corporation, Beijing 100176;
Zhao Xingdong, Ji Xiang, Xu Jitao; Research Center for Mine Lane and Ground Pressure Control, Northeastern University, Shenyang 110819, China;
Source: Mining Technology 2015, 15(5);

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