CN112523788B - Method for improving stability of primary support structure in soft rock tunnel construction - Google Patents

Abstract

The invention discloses a method for improving the stability of a primary support structure in tunnel step method construction, wherein the restraint anchor adopts an arrangement form of 'upper step small-pipe-diameter restraint anchor + middle step large-pipe-diameter restraint anchor rod', wherein the upper step restraint anchor rod adopts a hot-rolled seamless steel pipe with the diameter of 42-50mm and the length of 6-7m, and holes are drilled obliquely downwards at an angle of 5-10 degrees by a handheld pneumatic drill; the middle step restraint anchor rod is a hot-rolled seamless steel pipe with the diameter of 76-108mm and the length of 6-9m, and holes are drilled obliquely downwards at an angle of 10-20 degrees through a crawler-type down-the-hole drill. The invention gives full play to the respective advantages of the hand-held pneumatic drill drilling and the crawler-type down-the-hole drill drilling, not only greatly accelerates the construction progress of the constraint anchoring rod, but also avoids the outstanding problems of easy slurry leakage, difficult slurry stopping, poor grouting effect and the like when the constraint anchoring rod is obliquely upwards drilled, ensures the supporting effect of the constraint anchoring rod, and further effectively improves the stability of the primary supporting structure of the soft rock tunnel.

Description

A Method of Improving the Stability of Primary Support Structure in Soft Rock Tunnel Construction

technical field

The invention belongs to the field of tunnel engineering, and in particular relates to a method for improving the stability of an initial support structure in soft rock tunnel construction.

Background technique

After the excavation of soft rock tunnels, the surrounding rocks are easily weathered, spalled, and collapsed rapidly. In addition, the lack of effective restraint of the initial support during the tunnel excavation process will induce the continuous expansion of the surrounding rock relaxation, which often leads to the failure of the initial support of the tunnel. The structure is unstable and damaged, which is manifested in the twisting and breaking of the steel frame, the cracking and peeling of the shotcrete, and the deformation of the initial support. The arch is forced to be frequently removed and replaced, resulting in delays in the construction period, a sharp increase in costs, and a loss of safety control. In order to solve the problem that the initial support is prone to instability and damage in the construction of soft rock tunnels, the existing technology has tried to install restraint anchor rods or locking anchor rods on the upper and middle steps of the tunnel, trying to improve the initial support by exerting its anchoring force. the stability of the structure.

Engineering application practice shows that the existing technical solutions for restraint anchor rods or locking anchor rods have the following deficiencies:

(1) As shown in Figure 1, during the partial excavation of the existing soft rock tunnel, the upper and middle steps use restraint anchor rods with a uniform diameter. The length is generally 6m, and one is installed between the two adjacent steel frames on the left and right sides of the upper and middle steps, and each steel frame is equipped with a total of 4. Due to the large diameter of the constrained anchor rod, it exceeds the drilling range of the hand-held pneumatic drill commonly used in the tunnel, and a relatively large power down-the-hole drilling machine must be used for drilling. However, due to the limited space for construction work on the upper steps of the tunnel and the higher position of the upper steps, it is often difficult to carry out drilling operations with conventional down-the-hole drilling rigs, while choosing small down-the-hole drilling rigs has difficulties in positioning, insufficient recoil, Prominent problems such as poor maneuverability lead to very low drilling efficiency of the upper step restraint anchor rod, which seriously affects the construction progress.

(2) Existing restraint anchor rods or locking anchor rods are designed to exert their anchoring force, and they are all installed obliquely upwards. The hole is drilled obliquely upward. During the grouting operation, the grout will flow and overflow towards the hole hole under the action of gravity and grouting pressure, making it difficult to stop the grouting at the hole, which will restrict the actual grouting anchoring effect of the anchor rod. The request could not be met. Due to the influence of the above factors, the support effect of the existing restraint anchor rods or locking anchor rods is greatly limited, and it is difficult to effectively improve the stability of the primary support structure.

In summary, the existing restraining anchor rods or locking anchor rods are time-consuming and labor-intensive in actual construction operations, and it is difficult to ensure the effect. It is urgent to form an effective way to improve the stability of the primary support structure in soft rock tunnel construction. Methods.

Contents of the invention

In order to solve the deficiencies in the prior art, the object of the present invention is to provide an effective method for improving the stability of the primary support structure in soft rock tunnel construction.

To achieve the above object, the present invention adopts the following technical solutions:

A method for improving the stability of the initial support structure in the construction of soft rock tunnels, the soft rock tunnels are constructed using the three-step method, the restraint anchor rods of the upper steps of the tunnel are set at the arch waist of the upper steps of the tunnel, and the upper steps The restraint anchor rods are hot-rolled seamless steel pipes with a diameter of 42-50mm and a length of 6-7m, and 2-4 rods are arranged between the two adjacent steel frames on the left and right sides;

The middle step restraint anchor rod of the tunnel is set in the middle of the side wall of the middle step of the tunnel. The middle step restraint anchor rod is a hot-rolled seamless steel pipe with a diameter of 76-108mm and a length of 6-9m. There are two adjacent steel frames on the left and right sides. Each set 1-2 between;

The fixing hole of the constraint anchor rod on the upper step is obtained by drilling with a hand-held pneumatic drill;

The fixing holes of the constraining anchor rods on the upper steps are drilled by crawler-type down-the-hole drilling rigs.

In the method for improving the stability of the initial support structure in the construction of soft rock tunnels, the fixing holes of the upper step constraining anchor rods are drilled obliquely downward, and the included angle with the horizontal plane is 5°-10°.

In the method for improving the stability of the primary support structure in the construction of soft rock tunnels, the fixing holes of the middle-step constraint anchor rods are drilled obliquely downward, and the included angle with the horizontal plane is 10°-20°.

Compared with the prior art, the beneficial effects of the present invention are as follows:

(1) The present invention selects restraint anchor rods with the same pulling force as those in the prior art but with different pipe diameters on the upper and middle steps of the tunnel, and correspondingly, the types of drilling rigs used are also different. Among them, the upper steps use small-diameter restraint anchor rods with a diameter of 42-50mm, which are drilled by hand-held pneumatic drills; the middle steps use large-diameter restraint anchor rods, with a diameter of 76-108mm, and are drilled by crawler-type down-the-hole drilling rigs . The upper step restraint anchor rod is drilled with a hand-held pneumatic drill. The drilling operation is flexible, fast, and high in efficiency. It is carried out at the same time as the tunnel locking foot anchor pipe and the advanced small conduit drilling operation, saving man-hours. Compared with the existing technology, the construction efficiency of the present invention can be increased by more than 3 times; in addition, the middle steps are drilled by crawler-type down-the-hole drilling rigs, which have strong maneuverability and high drilling efficiency, and increasing the diameter of the restraint anchor rod can not only fully utilize the potential The advantages of the hole drilling machine, but also has a better support effect.

(2) The restraining anchor rods of the upper and middle steps of the tunnel in the present invention adopt the method of driving obliquely downward. During the grouting operation of the restrained anchor rod, the grout can automatically flow to the anchoring section in the deep part of the surrounding rock under the action of its own weight, avoiding the easy grout leakage, difficulty in stopping the grout, and grouting effect in the prior art when the restrained anchor rod is arranged obliquely upward And a series of problems such as poor anchoring effect have greatly improved the grouting quality of the restraint anchor rod and ensured the grouting anchorage effect of the restraint anchor rod. In addition, when the restraint anchor rod is driven obliquely downward, the restraint anchor rod can also function as an inclined pile, so that even if the restraint anchor rod does not go deep into the stable rock formation and fails to play the expected anchoring role, it can still be used as an inclined pile It plays a strong vertical support role for the initial support of the tunnel and effectively resists the settlement and deformation of the soft rock tunnel.

Description of drawings

Fig. 1 is a schematic diagram of a two-dimensional plane layout of a constrained anchor rod in the background art.

Fig. 2 is a schematic diagram of a two-dimensional plane layout of a constrained anchor rod in the present invention.

Among them: 1 - upper step restraint anchor rod, 2 - middle step restraint anchor rod, 3 - upper step lock foot anchor tube, 4 - middle step lock foot anchor tube, 5 - lower step lock foot anchor tube, 6 - upper step, 7-middle steps, 8-lower steps.

Detailed ways

In order to make the content, technical solutions and features of the present invention clearer, the present invention will be further described in detail in conjunction with the accompanying drawings and embodiments.

The present invention proposes a method for improving the stability of the initial support structure in the construction of the tunnel step method for the three-step construction method. As shown in Figure 2, the upper step constraint anchor rod 1 is located , and between two adjacent steel frames on the right side, 2 in total, 4 in total; according to the results of the grouting pull-out test of restraint anchor rods, the pulling force of a 6m-long φ42 steel pipe is 267kN, and a 6m-long φ76 The pulling force of the steel pipe is 530-540kN. Obviously, the pulling force of two 6m long φ42 steel pipes is equivalent to that of one 6m long φ76 steel pipe. Then, setting 2 to 4 φ42 restraint anchor rods between the two adjacent steel frames on the left and right sides of the upper step can also achieve the reinforcement effect shown in Figure 1.

The mid-step restraint anchor rod 2 is located in the middle of the side wall of the middle step of the tunnel, and one is installed between the two adjacent steel frames on the left and right sides of the middle step, totaling two. The upper step constraining anchor rod 1 is made of a small-diameter hot-rolled seamless steel pipe with a diameter of 50mm and a length of 6m, which is laid obliquely downward with an angle of 10° with the horizontal plane; the middle-step constraining anchor rod 2 is made of a large-diameter hot-rolled steel pipe. Seamless steel pipe with a diameter of 108mm and a length of 6m is drilled obliquely downward, with an angle of 20° to the horizontal plane. In addition to the restraint anchor rods of the upper and middle steps, two locking foot anchor pipes are installed at the arch feet of the upper, middle and lower steps respectively. The upper step locking foot anchor pipe 3, the middle step locking foot anchor pipe 4 and the lower step locking foot anchor pipe 5 all have a diameter of 42mm and a length of 4m, and are laid obliquely downward. The angle is 20°, and the included angle between the middle step lock foot anchor pipe 4 and the lower step lock foot anchor pipe 5 and the horizontal plane is 30°.

In the background art, the restraint anchor rods are arranged obliquely upward, and are anchored by grouting to play a suspending effect on the primary support of the tunnel. This is only a technical effect or purpose that is theoretically intended to be achieved. But in fact, since the anchoring effect of oblique upward grouting cannot be guaranteed, it is difficult to realize the theoretical technical effect in reality, and even the supporting effect of the restrained anchor rod cannot be exerted. The present invention adopts an oblique downward grouting angle of 5°-10°, which is not only beneficial to grouting, but also effectively plays the role of grouting and anchoring, and can also inhibit the initial support settlement at the same time. Apparently, compared with the background art, it is difficult or even impossible to play the supporting role of the restraint anchor rods. The technical solution of the present invention can effectively exert the support function of the restraint anchor rods, and it is better than the obliquely upward arrangement of the restraint anchor rods in the background technology. The actual effect of play is stronger.

The concrete construction steps of above-mentioned method are as follows:

(1) Construction of steps 6 on the tunnel. After the excavation of the upper step 6 of the tunnel, the steel frame of the upper step is erected, and the locking foot anchor pipe 3 of the upper step is installed. Drill the hole at a lower angle of 10°. After clearing the hole, put the upper step restraint anchor rod 1 into the drill hole. The anchor rod 1 is grouted, and finally the step-up shotcrete operation is carried out.

(2) Construction of steps 7 in the tunnel. After the excavation of the middle step 7 of the tunnel is completed, the steel frame of the middle step is erected, and the locking foot anchor pipe 4 of the middle step is installed. The down-the-hole drilling rig drills at an angle of 20° downward. After clearing the hole, send the mid-step restraint anchor rod 2 into the drilled hole. Connect, then carry out grouting to the restraint anchor rod 2 of the middle step, and finally carry out the shotcrete operation of the middle step.

(3) Construction of the lower step 8 of the tunnel. After the excavation of the lower step 8 of the tunnel is completed, the lower step steel frame is erected, and the lower step lock pin anchor pipe 5 is laid, and then the lower step shotcrete operation is carried out.

In the above-mentioned method of improving the stability of the primary support structure in the construction of the tunnel step method, the arrangement form of "small diameter restraint anchor rod on the upper step + restraint anchor rod with large diameter pipe on the middle step" is adopted, which is different from that adopted in the existing technical scheme. The layout of "both the upper and middle steps adopt large-diameter restraint anchor rods" mainly has the following advantages:

(1) Two small-diameter restraint anchor rods 1 (50mm in diameter and 6m in length) are used on the left and right sides of the upper steps, and the holes are drilled with a hand-held pneumatic drill, which is flexible and efficient, and does not need to be drilled with a down-the-hole drilling machine to avoid Solve the problems of clumsy drilling rig, limited space and low efficiency when using large-diameter restraint anchor rods to drill holes in the upper steps. In addition, in terms of support performance, the pullout force of two 6m long φ50 restraint anchor rods is greater than the pullout force of one 6m long φ76 steel pipe in the background technology, and the corresponding support effect is better.

(2) The middle steps use large-diameter restraint anchor rods 2 (108m in diameter and 6m in length), and are drilled by crawler-type down-the-hole drilling rigs. Due to the wide mid-step site, the performance of the crawler down-the-hole drilling rig can be fully displayed, which greatly improves the drilling efficiency of the restraint anchor rod. Moreover, the diameter of the mid-step restraint anchor rod 2 is increased to 108mm, and its anti-settlement effect and anchoring effect are more significant.

(3) The restraint anchor rod 1 of the upper step and the restraint anchor rod 2 of the middle step are both set obliquely downward. During the grouting operation of the restrained anchor rod, the grout can automatically flow to the anchoring section in the deep part of the surrounding rock under the action of its own weight, avoiding the easy grout leakage, difficulty in stopping the grout, and grouting effect in the prior art when the restrained anchor rod is arranged obliquely upward And a series of problems such as poor anchoring effect have greatly improved the grouting quality of the restrained anchor rod and ensured the anchoring effect of the restrained anchor rod. In addition, when the restraint anchor rod is driven obliquely downward, the restraint anchor rod can also function as an inclined pile, so that even if the restraint anchor rod does not go deep into the stable rock formation and fails to play the expected anchoring role, it can still be used as an inclined pile It plays a strong vertical support role for the initial support of the tunnel, effectively resists the settlement deformation of the soft rock tunnel, and improves the stability of the initial support structure of the soft rock tunnel.

The present invention is not limited to the above-mentioned embodiments, and multiple embodiments can be formed according to different restraining anchor rod diameters and setting angles, all of which fall within the scope of protection required by the present invention.

Claims (1)

1. A method for improving the stability of a primary support structure in soft rock tunnel construction is provided, wherein the soft rock tunnel is constructed by a three-step method, and is characterized in that: the restraint anchor rods of the upper step of the tunnel are arranged at the arch waist position of the upper step of the tunnel, the restraint anchor rods of the upper step are hot-rolled seamless steel pipes with the diameter of 42-50mm and the length of 6-7m, and 2-4 steel frames are respectively arranged between two adjacent steel frames on the left side and the right side;

the middle step constraint anchor rod is a hot-rolled seamless steel pipe with the diameter of 76-108mm and the length of 6-9m, and 1-2 steel frames are arranged between two adjacent steel frames on the left side and the right side;

the fixing holes of the constraint anchoring rods of the upper step are drilled by a handheld air drill; the fixing holes of the restraining and anchoring rods of the middle step are drilled by a crawler-type down-the-hole drill;

the fixing hole of the upper step constraint anchoring rod is obliquely downwards arranged, and the included angle between the fixing hole and the horizontal plane is 5-10 degrees; the fixing holes of the middle step constraint anchoring rods are obliquely downwards arranged, and the included angle between the fixing holes and the horizontal plane is 10-20 degrees.

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