Construction method for fixing feet of oblique piles in cat holes in two sides of soft tunnel

Abstract

The invention relates to the technical field of tunnel construction, and particularly discloses a soft tunnel two-side cat hole inclined pile foot fixing construction method which comprises the following steps: S1, inclined pile foundation construction: digging cat holes in two sides of a tunnel in sequence according to survey lofting, and immediately drilling to construct a cylindrical inclined pile foundation after single-side digging is completed, a cat hole in the other side is excavated, holes are drilled, empty slag at the bottoms of the holes is removed after the holes are drilled, quick-setting concrete is poured into a lower pile foundation reinforcement cage to reach the elevation of the bottom face of an arch foot of a secondary lining, and a primary supporting type steel arch frame section is pre-buried during pouring; s2, annular excavation and supporting are carried out, arch annular excavation is carried out, primary supporting is constructed after excavation is completed, a steel arch frame is erected to be connected with an arch foot pre-embedded steel arch frame, and concrete is sprayed to complete primary supporting; s3, circular construction is carried out, after the strength of sprayed concrete reaches 70% or above, next circular construction is carried out, and the step S1 and the step S2 are repeated; the inclined pile foundations are arranged on the arch feet on the two sides of the tunnel, so that the supporting strength of the arch feet is remarkably improved, and the arch feet are effectively prevented from disengaging and primary support settlement.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel construction, in particular to a method for constructing cat-ear holes on both sides of a weak tunnel with inclined piles for fixing feet. Background Art

[0002] Currently, weak tunnel construction technology is primarily based on the unique geological conditions of weak surrounding rock and its impact on safety. Combined with the frequent tunnel accidents in recent years and the need for technological development, a technical system centered on advanced prediction, dynamic support, and comprehensive reinforcement has been developed. Weak surrounding rock typically refers to Class IV and V surrounding rock, including clay, fully weathered rock, and crushed mudstone. These rock types exhibit low bearing capacity, well-developed joints, and poor self-stability. In fault zones or areas with developed groundwater, the surrounding rock tends to become plastic or fragmented, and after excavation, a loose zone easily forms, leading to deformation or collapse.

[0003] According to statistics, among tunnel accidents involving weak rock, portal collapse accounts for 20%, face deformation collapse accounts for 33%, and rear collapse ("closure") accounts for 47%. The main causes are insufficient advance forecasting, inadequate support measures or insufficient primary support strength, and untimely secondary lining closure. Tunnels with weak rock are often located in shallow areas, passing under buildings or highways, requiring strict control of surface settlement and deformation, and complex geological and hydrological conditions must be considered during construction.

[0004] Tunnel construction in weak surrounding rock has always been a technical challenge. Due to the low strength, bearing capacity, and inherent stability of the surrounding rock, the primary arch footing must bear the full pressure of the loosened rock and soil at the excavation surface. Furthermore, overexcavation is prone to occur during construction, leading to the arch footing becoming vacant and causing primary support settlement. This, in turn, expands the extent of soil loosening, exceeds the support system's bearing capacity, and ultimately deforms the primary support, leading to collapse. This not only severely impacts construction progress but also poses a significant threat to construction safety. During operation, settlement is also prone to occur, causing cracking in the secondary lining and damage and leakage of waterproofing sheets. Traditional construction methods often employ double-wall, single-wall, or three-step excavation. However, these methods employ an upward-then-down construction sequence, with each step measuring approximately 3-5 meters. During lower excavation, the primary arch footing is stabilized by only two locking anchors, often resulting in varying degrees of sinking. Furthermore, the complex construction process and narrow working surface lead to a low level of mechanization, low construction efficiency, and a long interval between primary support and secondary lining construction, making it difficult to meet the safety and efficiency requirements of modern tunnel construction. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the technical problem solved by the present invention is to provide a method for constructing cat-ear hole inclined piles on both sides of a weak tunnel, so as to solve the problem of weak bearing capacity of the arch foot of a tunnel with weak surrounding rock, resulting in initial support settlement during construction and insufficient support stability during operation.

[0006] To solve the above problems, the technical solution adopted by the present invention is: a method for constructing cat ear holes on both sides of a weak tunnel with inclined piles, comprising the following steps: S1: Construction of the inclined pile foundation: Cat-ear holes are excavated on both sides of the tunnel in sequence according to the survey and layout. After excavation on one side, a cylindrical inclined pile foundation is immediately drilled and constructed. Cat-ear holes and holes are excavated and drilled on the other side. After drilling is completed, the pile foundation reinforcement cage is cleaned and quick-setting concrete is poured to the bottom elevation of the arch foot of the secondary lining. Primary support steel sections are pre-embedded during pouring. S2: Circular excavation and support: Carry out circular excavation of the arch. After the excavation is completed, the initial support is applied. The steel arch frame of the arch is erected and connected with the pre-embedded steel arch frame at the arch foot to form a closed ring. The initial support is completed by spraying concrete. S3: Cycle construction. After the strength of the shotcrete reaches more than 70%, proceed to the next cycle of construction and repeat steps S1 and S2.

[0007] Furthermore, the drilling construction in S1 was carried out using a rotary drilling rig, with a drill chuck length of less than 80 cm, a drill bit length of 120 cm, and a drill rod section length of 100 cm.

[0008] Furthermore, a ratchet-type tunnel boring machine was used for the circular excavation of the middle arch of S2, with the excavation range covering the tunnel arch, and the excavation step length matched the construction step length of the inclined pile foundation.

[0009] Furthermore, after the steel arch is erected in S2, advance support can be applied.

[0010] Furthermore, the cat ear hole is excavated with an outer contour width of 2.5-3m, a height of 3-4m, and a depth of 0.8-1.6m, and is excavated to the bottom surface elevation of the second lining arch foot.

[0011] Furthermore, the inclined pile foundations are staggered in two rows, with both sides of the primary supporting steel arch frame placed on the outer inclined pile foundations, and the arch feet on both sides of the secondary lining placed on the inner inclined pile foundations.

[0012] Furthermore, the diameter of the inclined pile foundation is 50-80 cm, and the inclination angle of the inclined pile foundation is 0-6 degrees.

[0013] The beneficial effects of this program are: 1. Simple and efficient construction process: Compared with the double-side wall pilot tunnel construction method and the three-step seven-step excavation method, the inclined pile footing construction method of the present invention has a maximum excavation step distance of 160 cm. The arch foot pile foundation uses rapid-setting concrete, which shortens the construction technology interval time. After the pile foundation is poured, the arch construction can be carried out. It takes about 6 hours to complete the full section closure into a ring and complete the primary support system. The process is compact and, except for the reserved core soil, it is similar to full-section excavation. In addition, mechanized parallel flow operation can be adopted, which greatly shortens the relaxation time of the surrounding rock of the tunnel excavation face and maintains the inherent stability of the surrounding rock. 2. Enhanced arch foot support strength: By installing inclined pile foundations at the arch feet on both sides of the tunnel, and placing the primary steel arch frame and secondary lining arch feet on the inclined pile foundations, the arch foot support strength is significantly improved, effectively preventing arch foot voiding and primary support settlement, and fundamentally improving the stability of the support system for soft surrounding rock tunnels; 3. Improve construction safety: Through the firm support of the arch foot pile foundation, the time and range of rock and soil relaxation are reduced, the stability of the surrounding rock is ensured to the greatest extent, the risk of safety accidents such as collapse during construction is reduced, the technical interval time between the primary support and the secondary lining is shortened, and the safe step distance between the secondary lining and the tunnel face is shortened, thereby reducing safety risks; 4. Reduce construction costs: The adoption of mechanized assembly line operations reduces the number of on-site workers, improves construction efficiency, thereby speeding up construction progress and reducing construction costs; 5. Reduce project cost: Since the arch foot foundation is strengthened and the initial support is ringed in time, the deformation can be reduced, the reserved deformation can be reduced and the number of excavation projects can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a schematic diagram of the inclined pile foundation of the present invention; Figure 2 This is a schematic diagram of the inclined pile foundation and cat ear hole of the present invention; Figure 3 A top view of the inclined pile foundation of the present invention; Figure 4 This is a schematic diagram of drilling holes for the inclined pile foundation of the present invention; DETAILED DESCRIPTION The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0015] Implementation example Figures 1 to 4 A method for constructing cat-ear holes on both sides of a weak tunnel with inclined piles is shown, comprising the following steps: S1: Construction of the inclined pile foundation: Cat-ear holes are excavated on both sides of the tunnel in sequence according to the survey and layout. After excavation on one side is completed, a cylindrical inclined pile foundation is immediately drilled and constructed. Cat-ear holes and holes are excavated and drilled on the other side. After drilling is completed, the pile foundation reinforcement cage is cleaned and quick-setting concrete is poured to the bottom elevation of the arch foot of the secondary lining. During the pouring process, primary support steel is embedded to form a solid support structure. S2: Circular excavation and support: Carry out circular excavation of the arch. After the excavation is completed, the initial support is carried out. The steel arch frame of the arch is connected with the pre-buried steel arch frame of the pile foundation to form a closed ring and the initial support is completed by spraying concrete. S3: Cycle construction. After the strength of the shotcrete reaches more than 70%, proceed to the next cycle of construction and repeat steps S1 and S2.

[0016] The drilling construction in S1 is carried out using a rotary drilling rig with a drill chuck length of less than 80cm, a drill bit length of 120cm, and a drill rod section length of 100cm. The drilling depth is determined according to the tunnel surrounding rock conditions and design requirements. The circular excavation of the arch in S2 uses a ratchet tunnel boring machine to reduce disturbance to the surrounding rock. The excavation range is the tunnel arch, and the excavation step distance is synchronized with the inclined pile foundation. After excavation, the primary support is closed in time to reduce the time and range of rock and soil relaxation. After the steel arch frame is erected in S2, advanced support can be applied to improve the stability of the initial support.

[0017] The cat ear hole excavation step width is 2.5-3m, the height is 3-4m, and the depth is 0.8-1.6m. The specific values ​​are determined according to the surrounding rock conditions. The excavation is carried out to the bottom elevation of the secondary lining arch foot. If instability such as collapse occurs, temporary support measures such as advance support and anchor spraying can be adopted; the inclined pile foundation can be staggered in two rows depending on the geological bearing capacity. The two sides of the primary support steel arch frame are placed on the outer inclined pile foundation. When the secondary lining is constructed, the arch feet on both sides of the secondary lining are placed on the inner inclined pile foundation to form an effective support. The diameter of the inclined pile foundation is 50-80cm, which is suitable for primary support and secondary lining. The inclination angle of the inclined pile foundation is 0-6 degrees. Since the space of the cat ear hole is small, setting the inclined piles at a certain angle when drilling can facilitate drilling operations.

[0018] The specific implementation process is as follows: According to the measurement and layout, cat ear holes are excavated on both sides of the tunnel in sequence. The outer contour width of the cat ear holes is 2.5-3m, the height is 3-4m, and the depth is 0.8-1.6m. The specific values ​​are determined according to the surrounding rock conditions. The excavation is carried out to the elevation of the second lining arch foot. After the excavation on one side is completed, the cylindrical inclined pile foundation is immediately drilled and constructed. The cat ear holes on the other side are excavated and drilled. The rotary drilling machine is used for drilling. The rotary drilling machine can be modified from the excavator to a rotary drilling machine. It is suitable for drilling holes in cat ear holes with narrow space, effectively ensuring the drilling quality of the inclined pile foundation. The drilling depth is determined according to the tunnel surrounding rock conditions and design requirements. After the drilling is completed, the slag at the bottom of the hole is cleared and the piles are driven in. The foundation steel cage is pre-embedded with primary support steel arch frame segments, and quick-setting concrete is poured to the arch foot bottom elevation of the secondary lining. After the inclined pile foundation is poured, the tunnel arch is excavated in a circular manner. After excavation is completed, the primary support is installed. The arch steel arch frame is erected on the pre-embedded steel arch frame to form a closed ring. Advanced support is applied and concrete is sprayed to complete the initial support. The primary support steel arch frame is placed on both sides of the outer inclined pile foundation. The primary support steel arch frame is an H-shaped steel arch frame. The thickness and strength of the sprayed concrete should meet the design and specification requirements. After the concrete strength reaches more than 70%, the next construction cycle is carried out, repeating the excavation of cat ear holes, inclined pile foundations, and primary support. After the primary support is stable, the secondary lining is applied. By installing inclined pile foundations on the arch feet on both sides of the tunnel, the supporting strength of the arch foot is significantly improved, effectively preventing the arch foot from being emptied and the primary support from settling.

[0019] Comparison with existing methods: When using the double-wall pilot method, the excavation progress within a 24-hour period must be calculated based on the specific surrounding rock grade and construction conditions. Based on analysis of existing construction technologies, the double-wall pilot method is suitable for poor surrounding rock conditions (such as Class V rock). Excavation requires multiple pilot pits, resulting in shorter excavation progress for each pilot pit. With the double-wall pilot method, the progress per cycle is typically 0.5 to 1 meter. Based on construction experience, the cycle time for the double-wall pilot method is generally 10 to 12 hours. The progress within a 24-hour period is calculated by assuming a 12-hour cycle, meaning two cycles can be completed within 24 hours. If the progress per cycle is 0.5 meters, the total progress per 24-hour period is: 2 x 0.5 = 1 meter. If the progress per cycle is 1 meter, the total progress per 24-hour period is: 2 x 1 = 2 meters. When using the double-wall pilot method, the actual excavation is in the pilot pit, and this progress needs to be converted to full-section progress. Typically, the ratio of pilot tunnel footage to full-section footage is approximately 1:3. Therefore, the full-section footage within a 24-hour period ranges from 1÷3≈0.33m to 2÷3≈0.67m. In summary, when using the double-sidewall pilot tunnel method, the full-section footage within a 24-hour period is approximately between 0.33m and 0.67m, with the specific value adjusted based on actual surrounding rock conditions and construction parameters.

[0020] When using the three-bench, seven-step excavation method, the excavation advance within 24 hours must be calculated based on the specific surrounding rock conditions and construction parameters. The following analysis shows that the three-bench, seven-step excavation method is suitable for excavation sections of 100-180 square meters in Grade IV and V surrounding rock. The construction steps are divided into three steps: upper, middle, and lower, with a total of seven excavation faces. Excavation support is staggered across each section. The length of each excavation must not exceed 1.5 meters, determined by the spacing of the initial support steel frames. Based on construction experience, the advance per cycle is typically 0.5-1.5 meters. In Grade IV surrounding rock, a larger advance (e.g., 1.5 meters) is acceptable; in Grade V surrounding rock, a smaller advance (e.g., 0.5 meters) is typically used. Each cycle typically takes 8-10 hours, with larger excavation steps increasing the duration. Two to three cycles can be completed within 24 hours (24 hours ÷ 10 hours / cycle = 2 cycles, 24 hours ÷ 8 hours / cycle = 3 cycles). Assuming the advance per cycle is 1.5 meters, the advance within 24 hours is: 2×1.5=3 meters. Assuming the advance per cycle is 0.5 meters, the advance within 24 hours is: 3×0.5=1.5 meters. Converted to full-section advance: In the three-bench, seven-step excavation method, the actual excavation is the step-by-step excavation surface, and its advance needs to be converted to full-section advance. Normally, the ratio of step-by-step excavation advance to full-section advance is approximately 1:1. Therefore, when using the three-bench, seven-step excavation method, the full-section advance within 24 hours ranges from approximately 1.5 meters to 3 meters. The specific value needs to be adjusted according to the actual surrounding rock conditions and construction parameters.

[0021] The method for constructing cat-ear holes on both sides of a weak tunnel with inclined piles combines the advantages of a double-side wall method and a reserved core soil circular excavation method, abandons complicated procedures such as up and down steps, adopts a double-sided cat-ear hole form to construct an arch foot pile foundation and a reserved core soil circular excavation method to construct the initial support of the arch, combines mechanized construction flow operation, greatly simplifies the construction process, and is suitable for IV-V grade surrounding rock. According to previous construction experience, it is estimated that 1-3 initial supports (0.5-1.5 meters) can be excavated in each cycle depending on the stability of the surrounding rock itself. If an excavator is used to successively excavate two cat-ear holes on the left and right sides with a width of about 2.5-3m, a height of 3-4m, and a depth of 0.8-1.6m, it will take about 1-2 hours. After drilling with a parallel flow rotary drilling machine, it will take about 1-1.5 hours to pour the quick-setting concrete pile foundation. After the circular excavation of the arch, it will take about 2-3 hours to apply the initial support. During the technical interval of the initial spraying of quick-setting concrete, it will take about 1.5-2 hours to excavate the core soil and remove the debris. The time for each cycle is: minimum 1+1+2+1.5=5.5 hours, maximum 2+1.5+3+2=8.5 hours; 2-4 cycles can be constructed for the entire section in 24 hours (24 hours ÷ 5.5 hours / cycle ≈ 4 cycles, 24 hours ÷ 8.5 hours / cycle ≈ 2.8 cycles), and the advance of the entire section is 1-4 meters. In comparison, the full-section circular excavation method with inclined piles on both sides of a weak tunnel according to the present invention can adopt mechanized parallel flow operations, which is superior to the existing methods in terms of process, method, progress, quality, safety, cost, etc.

[0022] The above is only an embodiment of the present invention, and the common knowledge such as the specific structure and characteristics of the scheme is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for constructing cat-ear holes on both sides of a weak tunnel with inclined piles, characterized in that: The following steps are involved: S1: Construction of the inclined pile foundation: Cat-ear holes are excavated on both sides of the tunnel in sequence according to the survey and layout. After excavation on one side is completed, a cylindrical inclined pile foundation is immediately drilled. Cat-ear holes and holes are excavated on the other side. After drilling is completed, the bottom of the hole is cleared of loose slag. After the pile foundation reinforcement cage is installed, quick-setting concrete is poured to the bottom elevation of the arch foot of the secondary lining. Primary support steel segments are pre-embedded during pouring. S2: Circular excavation and support: Carry out circular excavation of the arch. After the excavation is completed, the initial support is carried out. The steel arch frame is erected and connected with the pre-embedded steel arch frame at the arch foot to form a closed ring. The initial support is completed by spraying concrete. S3: Cycle construction. After the strength of the shotcrete reaches more than 70%, proceed to the next cycle of construction and repeat steps S1 and S2.

2. The method for constructing cat-ear holes on both sides of a weak tunnel with inclined piles according to claim 1 is characterized by: The drilling construction in S1 was carried out using a rotary drilling rig, with a drill chuck length of less than 80 cm, a drill bit length of 120 cm, and a drill rod section length of 100 cm.

3. The method for constructing cat-ear holes on both sides of a weak tunnel with inclined piles according to claim 1 is characterized by: A ratchet-type tunnel boring machine is used for the circular excavation of the middle arch of S2. The excavation range is the tunnel arch, and the excavation step distance matches the construction step distance of the inclined pile foundation.

4. The method for constructing cat-ear holes on both sides of a weak tunnel with inclined piles according to claim 1 is characterized in that: After the steel arch frame is erected in S2, advance support can be applied.

5. The method for constructing cat-ear holes on both sides of a weak tunnel with inclined piles according to claim 1 is characterized in that: The cat ear hole excavation step has an outer contour width of 2.5-3m, a height of 3-4m, and a depth of 0.8-1.6m, and is excavated to the bottom surface elevation of the second lining arch foot.

6. The method for constructing cat-ear holes on both sides of a weak tunnel with inclined piles according to claim 1 is characterized in that: The inclined pile foundations are staggered in two rows, with both sides of the primary steel arch frame placed on the outer inclined pile foundations, and the arch feet on both sides of the secondary lining placed on the inner inclined pile foundations.

7. The method for constructing cat-ear holes on both sides of a weak tunnel with inclined piles according to claim 1 is characterized by: The diameter of the inclined pile foundation is 50-80 cm, and the inclination angle of the inclined pile foundation is 0-6 degrees.

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