Method for evaluating shaft lining stability and support force under vertical tension crack existing on shaft surface

Abstract

The application discloses a method for evaluating the stability and supporting force of a shaft wall under a vertical tensile crack on a shaft surface, and comprises the following steps: (1) determining the gravity of the shaft wall which destroys the surrounding rock according to the surrounding rock condition of the shaft, the position of the vertical tensile crack on the surface and the like; (2) calculating the stability safety factor of the shaft wall, which comprises calculating the sliding force, the anti-sliding force and the corresponding stability safety factor; and (3) judging whether the shaft wall is safe or not, and if not, calculating the supporting force required for maintaining the stability of the shaft wall. The application provides a quantitative evaluation method for the stability analysis of the shaft wall under the vertical tensile crack on the shaft surface, and the shaft wall stability safety factor under different positions of the tensile crack on the surface and different depths of the tensile crack can be evaluated through the method; the shaft wall supporting force can also be analyzed and determined, thereby providing a reference for the shaft supporting design, solving the problem of the stability evaluation of the stratum, and being beneficial to taking measures in advance.

Description

Technical Field

[0001] This invention belongs to the field of shaft construction technology, specifically relating to a method for evaluating the stability and support force of the shaft wall under vertical tensile cracks on the ground surface. Background Technology

[0002] Vertical shafts are crucial auxiliary passageways in the construction of long tunnels. Currently, most extra-long tunnels in China utilize vertical shafts to shorten the tunnel length and accelerate construction progress. For example, the Tianshan Victory Tunnel, the world's longest highway tunnel, employs four vertical shafts, with the largest shaft reaching a depth of 706 meters. During shaft excavation, tension cracks often appear on the ground surface due to factors such as excavation unloading. The presence of tension cracks affects the safety and stability of the shaft. However, there is limited literature on the impact of surface tension cracks on shaft stability, particularly regarding the theoretical analysis of shaft wall stability and support force determination under tension cracks. Shaft wall stability is a prerequisite for safe construction; therefore, determining the stability of a shaft under surface tension cracks is a primary concern for construction units, design units, and especially construction companies. Summary of the Invention

[0003] The purpose of this invention is to address the aforementioned technical problems in the prior art by providing a method for evaluating the stability and support force of the shaft wall in the presence of vertical tensile fractures on the surface of a shaft.

[0004] The above-mentioned objective of the present invention is achieved through the following technical solution: The method for assessing the stability of the shaft wall and the support force in the presence of vertical tensile fractures on the surface includes the following steps: (1) Based on the surrounding rock conditions of the shaft and the location of vertical tensile cracks on the ground surface, determine the gravity that causes the shaft to break the surrounding rock, which is calculated using the following formula: ; In the formula, W The gravity that causes the shaft to break through the surrounding rock; The density of the surrounding rock of the shaft; L The distance from the vertical tension crack on the ground to the shaft; h The depth of vertical tensile cracks on the ground surface; The fracture angle of the surrounding rock is calculated using the following formula: ; In the formula, The internal friction angle of the surrounding rock; (2) Calculate the wellbore stability safety factor, which includes the following steps: (I) Calculate the sliding force using the following formula: ; In the formula, For downward force; (II) Calculate the anti-skid force using the following formula: ; In the formula, For anti-slip force; c The cohesion of the surrounding rock; (III) Calculate the stability safety factor, which is calculated using the following formula: ; In the formula, K The stability safety factor of the wellbore; (3) Determine whether the well wall is safe. If it is not safe, calculate the support force required to maintain the stability of the well wall. This includes the following steps: (I) Compare the obtained stability safety factor with the allowable safety factor. If If the wellbore is safe, then the wellbore is safe; where [K] is the allowable stability safety factor. (II) If If the well wall is unsafe, the well wall support force needs to be further determined, which is calculated using the following formula: ; In the formula, P S For wellbore support; This allows us to assess the location of tensile fractures on different surfaces and the stability safety factor of the shaft wall at different fracture depths; it also allows us to analyze and determine the support force of the shaft wall.

[0005] The advantages of this invention compared with existing research methods are as follows: Traditional shaft stability analysis considers the situation of surface tension cracks, especially the theoretical analysis of the impact of the depth of surface tension cracks on shaft stability is rare. Existing literature mostly focuses on case studies of shafts without surface cracks, and the methods used are mostly numerical simulation software.

[0006] This invention provides a quantitative assessment method for the stability analysis of vertical shafts with tensile cracks on the ground surface. This method can evaluate the location of tensile cracks on different surfaces and the stability safety factor of the shaft wall under different tensile crack depths. It can also analyze and determine the support force of the shaft wall, thus providing a reference for the design of shaft support. This solves the problem of difficulty in assessing the stability of this stratum and is conducive to taking countermeasures in advance, such as strengthening the shaft wall support and grouting to reinforce the surface cracks, thereby ensuring the safety of shaft construction. Attached Figure Description

[0007] Figure 1 This is a calculation diagram illustrating the method of evaluating the stability of the well wall and the support force of a vertical shaft under the presence of vertical tensile cracks on the ground surface, according to the present invention.

[0008] In the diagram: 1 represents the shaft; 2 represents the ground surface; 3 represents the tension crack. W The gravity that causes the shaft to break through the surrounding rock; The density of the surrounding rock of the shaft; L The distance from the vertical tension crack on the ground to the shaft; h The depth of vertical tensile cracks on the ground surface; P is the fracture angle of the surrounding rock. S For wall support force.

[0009] Figure 2 The safety factor of the shaft at different fracture depths h is given by the condition that the location of the surface tension fracture remains unchanged. Detailed Implementation

[0010] The present invention will now be further described with reference to the accompanying drawings and embodiments.

[0011] The specific data for this embodiment of the project are as follows: The unit weight γ of the surrounding rock of a certain vertical shaft is 24kN / m 3 Cohesion of surrounding rock c 200 kPa The internal friction angle of the surrounding rock is 25°, the distance L from the vertical tensile crack on the surface to the shaft is 8m, the depth h of the vertical tensile crack on the surface is 3m, and the allowable stability safety factor [K] is 1.2.

[0012] See Figure 1 The method of this invention for evaluating the stability of the well wall and the support force of a shaft with vertical tensile cracks on the ground surface is as follows: Step 1: Based on the surrounding rock conditions of the shaft and the location of vertical tensile cracks on the ground surface, determine the gravity that will cause the shaft to break through the surrounding rock, which is calculated using the following formula: ; In the formula, W The gravity that causes the shaft to break through the surrounding rock; The density of the surrounding rock of the shaft; L The distance from the vertical tension crack on the ground to the shaft; h The depth of vertical tensile cracks on the ground surface; The fracture angle of the surrounding rock is calculated using the following formula: ; In the formula, The internal friction angle of the surrounding rock; Step 2: Calculate the wellbore stability safety factor, which includes the following steps: (I) Calculate the sliding force using the following formula: ; In the formula, For downward force; (II) Calculate the anti-skid force using the following formula: ; In the formula, For anti-slip force; c The cohesion of the surrounding rock; (III) Calculate the stability safety factor, which is calculated using the following formula: ; In the formula, K The stability safety factor of the wellbore; Step 3: Determine if the wellbore is safe. If not, calculate the support force required to maintain the stability of the wellbore, which includes the following steps: (I) Compare the obtained stability safety factor with the allowable safety factor. If If the wellbore is safe, then the wellbore is safe; where [K] is the allowable stability safety factor. (II) If If the well wall is unsafe, the well wall support force needs to be further determined, which is calculated using the following formula: ; In the formula, P S This is for the support force of the well wall.

[0013] Based on the above method and steps, the vertical shaft stability safety factor K = 2.28 can be obtained, which is greater than the allowable safety factor, and the shaft wall will not become unstable.

[0014] Furthermore, with other parameters remaining constant, changing the tension crack depth h yields the corresponding safety factor (see [reference]). Figure 2 As the depth h of the tension crack increases, the safety factor K decreases.

Claims

1. A method for evaluating the stability of the well wall and the support force of a shaft with vertical tensile fractures on the ground surface, characterized in that... Includes the following steps: (1) Based on the surrounding rock conditions of the shaft and the location of vertical tensile cracks on the ground surface, determine the gravity that causes the shaft to break the surrounding rock, which is calculated using the following formula: ； In the formula, W The gravity that causes the shaft to break through the surrounding rock; The density of the surrounding rock of the shaft; L The distance from the vertical tension crack on the ground to the shaft; h The depth of vertical tensile cracks on the ground surface; Let be the fracture angle of the surrounding rock, which is calculated using the following formula: ； In the formula, The internal friction angle of the surrounding rock; (2) Calculate the wellbore stability safety factor, which includes the following steps: (I) Calculate the sliding force using the following formula: ； In the formula, For downward force; (II) Calculate the anti-skid force using the following formula: ； In the formula, For anti-slip force; c The cohesion of the surrounding rock; (III) Calculate the stability safety factor, which is calculated using the following formula: ； In the formula, K The stability safety factor of the wellbore; (3) Determine whether the well wall is safe. If it is not safe, calculate the support force required to maintain the stability of the well wall. This includes the following steps: (I) Compare the obtained stability safety factor with the allowable safety factor. If If the wellbore is safe, then the wellbore is safe; where [K] is the allowable stability safety factor. (II) If If the well wall is unsafe, the well wall support force needs to be further determined, which is calculated using the following formula: ； In the formula, P S For wellbore support; This allows us to assess the location of different surface tensile fractures and the stability safety factor of the shaft wall at different fracture depths. It can also be used to analyze and determine the wellbore support force.

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