What is the specific content of shaft engineering excavation and safety support? Zhongda Consulting will answer it for you below.
1. Overview
From the current commonly used methods for shaft engineering excavation in hydropower systems, vertical guide shafts are generally dug first, and full-section main shaft excavation is rarely used. There are two construction methods for vertical guide shafts: one is the forward guide shaft construction method; the other is the anti-guide shaft construction method. In all cases, a vertical guide shaft is first dug, and then the shaft is expanded from top to bottom, and the well slag is transported away from the tunnel.
2. Guide shaft excavation method
For vertical guide shaft excavation with a raise drilling rig, the vertical guide shaft is first dug with a raise drilling rig. The diameter of the guide shaft is 1.2~2.0m. , after the vertical guide shaft is drilled, it is expanded and supported from top to bottom, which is the fastest method of shaft excavation.
If there is no condition for raise drilling, a hand pneumatic drill will be used, and the vertical pilot shaft will be drilled first.
2.1. If the forward shaft construction method is adopted, the topography of the shaft must be divided into the topography of the open pit after digging into the mountain and the topography of the shelter shaft in the hole.
When digging an open well, the surrounding rock on the surface is generally relatively broken and prone to weathering and deformation, which is common in shaft excavation projects. In response to this common phenomenon, before expanding the shaft, mechanically excavate the surrounding rock at the wellhead to a depth of 3-5m. It is best to consider digging an additional 50-60cm outside the excavation line from the design point of view, and place the reinforced concrete at the lock. Outside the excavation line, that is, the concrete surface behind the lock mouth is flush with the excavation surface, and a control point is set on the concrete surface of the wellhead. The vertical shaft expansion suspension line controls the size of the excavation, and safety protection fences and lifting equipment are installed at the wellhead. Structural parts.
The lifting equipment must be installed before the shaft is expanded. The function of the lifting equipment must comprehensively consider the overall use functions of shaft excavation, concrete pouring, gate installation and second-stage concrete pouring. It is best to be a track-type mobile type. of. It has the function of loading and unloading construction materials from inside the well to outside the well, and from outside the well to inside the well. After the lifting equipment is installed and debugged normally, there will be a way to discharge slag when straightening the guide shaft, but construction water and groundwater must have an outlet in the guide shaft. The general method of finding a way out of construction water and groundwater is to use a geological drilling rig to drill a hole in the center of the shaft, and water flows out of the hole. This hole can improve the blasting effect and create a free surface.
The shaft is locked, a protective fence is installed, there is a means to lift slag, and the water has an outlet, so the conditions for the excavation of the forward shaft are met. Use a hand pneumatic drill to drill a vertical guide shaft, preferably with a diameter of 2.0m. A vertical guide shaft with a diameter of 2.0m is convenient for drilling and removing slag. At the same time, it creates extremely favorable conditions for shaft expansion. Regardless of whether it is flat excavation or expansion excavation with several different bucket shapes, there is no need to worry about large rocks blocking the guide shaft. It can drill and blast deep holes and expand the excavation very quickly. Shape of vertical guide shaft: round shaft is preferred. The circular shaft itself has strong stability, which is conducive to the safety of vertical guide shaft excavation.
The excavation of guide shafts is different from the expansion of vertical shafts, especially the excavation of guide shafts on Class I broken surrounding rock. While excavation, about 5cm of concrete must be sprayed in time to assist the stability of the surrounding rock itself. Ensure that the surrounding rock does not deform or fall apart. The lifting equipment lifts slag from deep wells, and people go up and down with the cage. For safety reasons, an insurance factor of about 10 times should be left to ensure that the lifting process is foolproof. This is the basic requirement for the excavation of the forward guide shaft.
The schematic diagram of the forward guide well construction method is as follows:
2.2 Anti-guide well excavation
The guide well is dug from bottom to top. Generally, the anti-guide well is In the construction procedure, while the anti-guide shaft is being drilled from bottom to top, the surrounding rock at the top of the shaft is excavated, the well head is locked, a safety guardrail network is built, and lifting equipment is installed and debugged. When the vertical guide shaft is opened, the installation and commissioning of the shaft lock, safety fence, and lifting equipment can also be completed, and the shaft expansion stage has entered.
There are two common ways to excavate anti-guide shafts: one is to dig reinforcements in the guide shaft, weld ladder points on the reinforcements, hang ladders to climb people up and down, and transport materials. and tools to the work surface. People are removing dangers on ladders, building structures, and drilling and blasting on simple structures. The advantages of this excavation method: construction water and groundwater can be naturally drained away, and the slag after blasting can fall directly into the hole and be transported by a loader, without manual cleaning; the disadvantage is: the risk removal after each blasting requires people below There is nowhere to hide. Every time a cannon is fired, the feng shui pipes and scaffolding must be withdrawn and re-erected. The ladder solder joints also need to be repaired.
Another way to excavate an anti-missile well is to use a geological drill to drill a hole in the center of the shaft, and then lower the hoist, wire rope cage, materials, tools, and geomantic pipes from the hole. The operators go up and down with the cage and perform drilling and blasting operations in the cage. This excavation method solves the problem of removing, re-erecting and repairing fengshui pipes, scaffolding and ladder welding joints every time. However, there are still new shortcomings: during the lifting process of the winch, it is inconvenient to communicate with the top and bottom. Although there are modern communication tools, they are not available underground in the cave. A slight error in operation may cause safety problems. Secondly, the dangerous rocks on the top of the cage fell down and hit him.
The construction method of the sheltered well is exactly the same as that of the open well. The difference is that the foundation of the lifting equipment is on the concrete platform poured by Dongbang on both sides. Rails are installed on the platform, and mobile lifting is installed on the rails. Equipment and lifting equipment can load and unload materials inside and outside the well, as well as perform the entire lifting task of gate installation.
Based on the pros and cons of the forward well excavation method and the anti-conduction well excavation method, the speed of progress and the cost are basically equal. The operation is difficult and easy, the construction is safe, and the excavation of the forward guidance well is better than the anti-conduction well excavation method.
3. Excavation methods for shaft expansion
There are two ways to expand shafts: one is plane expansion, using a small electric shovel or other small equipment to pour slag into the guide shaft ; The other is staggered excavation in the shape of a bucket, using the terrain to naturally slide slag into the well.
Plane expansion method: mostly used in shaft expansion projects with larger excavation sections. For vertical shaft expansion projects with an excavation section of about 100m2, plane expansion is generally less used. For horizontal excavation, small equipment needs to be installed to dump slag. There is equipment underground, which takes up space, and the equipment needs to be protected from being damaged. Therefore, it is not possible to expand the entire section and spray protection at one time. Each layer is divided into two drilling and blasting operations, which virtually increases the number of processes and reduces efficiency. The equipment that can go down the well generally has low horsepower, takes a long time to dump slag, the loose gravel cannot be shoveled, the bottom cleaning workload is large, the labor intensity of workers is high, and the loose gravel at the bottom cannot be shoveled, and the drill is stuck and holes are plugged. Explosives cannot be loaded and the blasting effect is poor. The flat excavation method has low work efficiency, high production cost, and high labor intensity for workers. On the vertical shaft excavation section of about 100m2, the flat excavation method is rare.
Another way of shaft expansion: staggered number of bucket-shaped expansions. With this excavation method, no slag dumping equipment takes up space underground. Each layer can have full-section deep holes staggered with several units for one-time expansion and one-time spray protection. The blast slag makes full use of most of the terrain and naturally slides into the guide shaft. It has high work efficiency, good blasting effect and low production cost. This expansion method is widely used on the vertical shaft expansion section of about 100m2. is the right choice. This excavation method can make full use of terrain features, reduce workers' labor intensity, improve work efficiency, and reduce production costs. Specific methods: 1. On the rock surface of the last step, make a platform and lay a steel mesh on it for inserting bars, spraying concrete, and installing steel supports. The platform is also the safety net on the top of the expanded excavation surface. It is raised and lowered by lifting equipment and made at one time. The entire expansion project is easy to use and saves time and labor. 2. The stepped type can carry out deep hole blasting, creating conditions for most of the blast slag to slip into the guide shaft, and the workload of cleaning the slag is small. The hole depth is calculated as 3m, the staggered platform spacing is calculated as 1.2m, and the width of the step top after blasting is 70-80cm. There is limited slag on the steps, so drilling from top to bottom and cleaning the slag at the same time reduces a large construction cycle of dumping slag and cleaning the slag from the bottom. 3. Step-type slag cleaning has short distance, small area, and little interference between loose gravel and gravel. The gravel on the table can be cleaned cleanly. The drilling will not get stuck or block the hole. The drilling speed is fast and the blasting effect is good. 4. The step-type blasting has a large air surface. With a slight adjustment of the blasting network, three sides of the air surface will be faced, and the minimum resistance line will all face the center. Deep hole blasting will not destroy the self-stabilizing ability of the surrounding rock, which will ensure the stable bearing and safety of the shaft itself. The support work is very beneficial. On the shaft expansion section of about 100m2, the expansion method of staggering several chutes in the shape of the chute should be the first choice.
4. Safety support work for shafts
Safety support work for shafts must start from the correct locking of the shaft. No matter what kind of surrounding rock the shaft is dug, the shaft must be Digging vertically close to the mountain will affect the stability of the mountain and the loose deformation of the surrounding surface rocks. After the shaft is dug to a depth of 3-5m, grouting and reinforcing bars are installed along the shaft, and the reinforced concrete locks the wellhead to stabilize the mountain and the surface surrounding rock at the wellhead from loosening and deformation. This is the correct way to lock the wellhead. It is not advisable to use plain concrete locks or mortar stone locks. According to experience, when the geological conditions are particularly harsh, it is a safe and reliable construction method to consider excavation of the upper 20 meters according to the designed shape and concrete pouring according to the permanent lining every 5 meters from the construction procedure.
Insert bars and lock the wellhead with reinforced concrete, and the surface surrounding rock within 3 to 4m outside the well forms a load-bearing ring. The surface surrounding rock at the top of the shaft is not loose and deformed, and the bearing capacity of the downward shaft relies on its own stability. Protecting the stability of the surrounding rock itself starts with the excavation process. Control the spacing, depth and verticality of photoblast holes to be completely consistent, strictly control over- and under-excavation, limit the amount of charge in photoblast holes, and ensure that there are no cracks on the wall of the half-hole left by photoblast after detonation, and the well walls are flush. It is necessary to drill down the upper part according to the measurement line at the junction of two shots, without overshooting or undershooting. The over-excavation of the lower part shall not be greater than 10cm, and the average over-excavation shall not be greater than 5cm. Secondary under-excavation treatment is not allowed to damage the stability of the surrounding rock itself. The excavation process can be done without destroying the stability of the surrounding rock itself. Generally, Class I and II surrounding rock is relatively hard, complete, and not easy to decompose. The shaft is locked and the shaft wall is grouted and reinforced by light blasting, which satisfies the safety of the shaft project. However, there are cracks on the wall of the half hole left by the photoblast, or a secondary under-excavation process was performed. This will destroy the self-stability of the surface surrounding rock. A thin layer of 3-5cm of concrete should be sprayed to prevent rock ballast from scattering and injuring people.
Shaft support on Class III horizontal rock formations. When a vertical shaft is drilled on a horizontal rock layer, the surrounding rock itself has a strong bearing capacity. The shaft lock, light blast treatment of the shaft wall, and grouting and reinforcement can meet the safety needs of the shaft project. If the upright Class III rock formation has large smooth surfaces on both sides of the shaft after the shaft is expanded, and there are basically no traces of the half-hole left by the light explosion on the shaft wall, it will not meet the safety needs of the shaft project. For rock formation support of this type of shape, grouting anchors or anchor cable rivets usually have large smooth surfaces on both sides. The outside of the anchor hole is divided into a curved groove, and steel bars larger than 32mm are used to weld transversely parallel to the hooks. The distance between the anchors is about 2.5m, and the height between the rows is about 2.0m. The W-shaped shapes between the rows are welded into a whole, and the steel bars are hung with nets. About 10cm of sprayed concrete can meet the safety requirement of shaft engineering.
Support on Class IV horizontal rock formations. Safety needs can be met by following the standards for erecting rock formations in Category III. If there are Category IV standing rock formations or broken surrounding rocks, the anchor holes in the curved ditch should be changed to steel grids or I-beam supports. The connection method and the thickness of the shotcrete remain unchanged.
Shaft support on Class V surrounding rock. The lock wellhead is made of the same type of surrounding rock and is made of reinforced concrete. However, protecting the self-bearing capacity of Class V surrounding rock is particularly important in shaft engineering. The surrounding rock itself cannot bear the load, and neither can the steel supports. The most economical and simple way to protect the self-bearing capacity of Class V surrounding rock is to carry out dense hole shock-absorbing treatment on the Jingbang. The distance between the dense holes should be between 15-20cm, and 2 or 3 empty holes should be left to disperse the charge. The amount of charge per meter of hole is controlled to about 50 grams, which is dispersed and adhered to the detonating cord. After detonation, the remaining half of the hole left by the Jingbang light explosion is basically intact. The bearing capacity of the surrounding rock itself is not destroyed. Concrete is sprayed in time to maintain the surrounding rock. It is stable and not loose. Then add reinforcing bars to a distance of about 2.5m. The supporting steel grating or I-beam, about 2.0m high, is welded into a whole body with the W-shaped front row support. The steel bars are hung on the net, and then concrete is sprayed. The total thickness of the two sprays is about 10cm, which can meet the safety needs of the shaft project. This is a safe support that does not damage the stability of the surrounding rock itself.
After the shock-absorbing light explosion detonated, Jingbang collapsed, and no half-hole left by the light explosion could be found. The surrounding rock's own stability has been destroyed. There are two reasons for this situation: one may be its own fault, the holes are not standardized, the shock-absorbing effect is not achieved, there is no dispersed charge, or the dosage is too large, which will all cause the above situation. What can eliminate its own causes is natural causes. This type of surrounding rock is type I surrounding rock that is relatively broken and prone to toppling.
For safe support on relatively broken and easily toppling Class I surrounding rock, in addition to retaining dense holes for shock absorption and light explosion measures, if necessary, add advanced anchor bolts to stabilize the well, system grouting reinforcements should be deepened appropriately, and steel grids or engineering The height of the steel support is appropriately reduced, steel needles or fibers are added to the shotcrete, and the thickness is appropriately increased, and grouting holes are drilled around the Jingbang to help stabilize the surrounding rock itself, so that the Class I surrounding rock, which is relatively fragile and easy to topple, can bear its own weight. Protecting the self-stability of the surrounding rock starts with the excavation process. The drilling and blasting process does not destroy the stability of the surrounding rock, which is the key to the safe support of the shaft and the key to the safety of the shaft project.
5. Conclusion
During the shaft excavation construction process, it is very important to choose the correct construction procedures and construction methods. For large-section excavation wells with complex geological conditions, the treatment of the wellhead is a key process and the basis for other work. It must be done solidly as required. It is best to excavate and support according to the designed size to avoid additional excavation and increase the size of the well. Cross-sections cause unsafe conditions and incur additional costs. In the excavation of shafts, it is important not to rush into progress from the beginning. Instead, you should rely on construction organization and management to gain progress when the geological conditions in the middle and lower parts are good.
For more information about engineering/service/purchasing tender document writing and production to improve the bid winning rate, you can click on the official website customer service at the bottom for free consultation: /#/?source=bdzd