An excavation method for an ultra-small clear distance double-hole rectangular tunnel passing under an underground structure

Abstract

The present invention discloses a method for excavating an ultra-small clearance double-hole rectangular tunnel under an underground structure. The tunnel section is divided into upper and lower steps for excavation. The upper step is first excavated and penetrated, and the upper main structure is constructed. The upper main structure is used as the force transmission system of the pile foundation. The upper pile group is replaced one by one through segmented construction, effectively controlling the settlement of the tunnel upper structure and protecting the safety of the tunnel body and the upper structure. When excavating the lower step, when the pile foundation of the underground structure intrudes into the tunnel on one side of the tunnel, a small end face excavation method is used to excavate a trench. The lower step is directly excavated and penetrated. Then, the corresponding trench segments are excavated to both sides to the designed boundary line for subsequent construction. The trench construction method can increase the working surface to speed up the on-site construction progress, greatly shorten the construction period, and save construction costs. The present invention reduces construction risks and ensures the safety and stability of underground structures through effective measures.

Description

Technical Field

[0001] The present invention relates to the field of tunnel construction, and particularly to an excavation method for an ultra-small clear distance double-hole rectangular tunnel passing under an underground structure. Background Art

[0002] A small clear distance tunnel refers to a special tunnel structure form in which the thickness of the middle wall rock (intermediate rock) column between tunnels is less than the recommended value in the tunnel specification. Generally, the clear distance of a small clear distance tunnel should be greater than 6.0 - 8.0 m. An ultra-small clear distance tunnel (clear distance ≤ 6.0 m) is a special tunnel structure form with a smaller clear distance than the commonly used spacing of ordinary small clear distance tunnels.

[0003] During the process of traffic construction, tunnel construction is a common engineering building. With the continuous development of underground traffic facilities and the large-scale development of underground space in China, the intersection of underground traffic tunnels and underground complexes is increasing, and a large number of cases of adjacent construction of underground structures have emerged. Adjacent construction of underground structures will encounter many problems. Especially when closely passing under an underground structure and its group of piles with a small left-right clear distance for a double-track tunnel, during the construction process, not only the deformation of the floor structure of the underground structure above the tunnel due to excessive ground deformation needs to be considered, but also the pile foundation replacement problem for the piles invading the tunnel, and the stability of the intermediate rock between the double-track tunnels needs to be ensured. The simultaneous occurrence of various problems increases the construction difficulty. In addition, the poor geological conditions and the complex construction of the retaining structure lead to great difficulty in controlled blasting. It can be seen that when closely passing under an underground structure and its group of piles for an ultra-small clear distance double-hole rectangular tunnel, it is very difficult to solve the above construction problems well if the conventional middle diaphragm method or pilot tunnel method is adopted. Summary of the Invention

[0004] In order to solve the problems of the prior art, the purpose of the present invention is to provide an excavation method for an ultra-small clear distance double-hole rectangular tunnel passing under an underground structure.

[0005] In order to achieve the above purpose, the present invention discloses an excavation method for an ultra-small clear distance double-hole rectangular tunnel passing under an underground structure. The two ends of the ultra-small clear distance double-hole rectangular tunnel are arranged in parallel on the side walls where the underground structure intersects. The cut-and-cover top-down method is adopted, and the tunnel section is divided into upper and lower parts. First, the upper bench tunnel is completely excavated, then the upper main structure is constructed all at once, and finally the lower bench is excavated. During the excavation process, the pile foundation invading the tunnel of the underground structure needs to be properly treated. The specific excavation steps are as follows:

[0006] Step S1, before excavation, the portal section of the ultra-small clear distance double-hole rectangular tunnel is pre-supported by pipe-roofing and the portal is demolished.

[0007] Step S2: Divide the tunnel section into upper and lower parts. First, conduct sectional excavation of the upper bench, using a reverse trapezoidal slope excavation method. Excavate the first section of the upper bench first, and initially spray concrete. During the excavation process, timely conduct slope grouting reinforcement, and carry out steel arch support and bolt installation. The middle rock wall is arranged with grouting pipes in a plum blossom shape and grouted for reinforcement to ensure the stability of the middle interlayer rock. After the excavation of the first section is completed, proceed with the excavation of the next section. In step S2, to ensure safety during the upper bench excavation, the excavation face on one side lags behind the excavation face on the other side by about 10 m. When the pile foundation of the underground structure invading the tunnel does not extend into the lower bench, pile connection reinforcement is required. The excavation method combines mechanical breaking and static blasting. Since the ultra-small clear distance double-track rectangular tunnel closely passes under the underground structure and its group of piles, the middle rock wall and the underground structure need to be protected from being disturbed during the excavation process, and blasting excavation is strictly prohibited.

[0008] Step S3: After the upper bench excavation is completed, construct the entire upper main structure at one time, and use the pile foundation underpinning method to transfer the load of the underground structure to the side walls on both sides of the tunnel. The pile foundation underpinning adopts the "passive underpinning" mode, and the load of the upper structure is transferred from the underpinning beam to the side walls on both sides of the tunnel. The pile foundation underpinning joints are treated by the method of anchoring steel bars and pile foundation keyways. Specifically, before pouring the underpinning cross beam, notch the pile body within the range of the cross beam of the pile to be underpinned, and at the same time, use the chemical rebar planting method to implant Φ20 deformed steel bars. It should be noted here that during the pile foundation underpinning process, the lower part of the pile foundation needs to be connected to the underpinning cross beam, and the force is transferred to the side walls on both sides through the underpinning cross beam. If the tunnel cross-section form is arched or horseshoe-shaped, it is not convenient for the connection between the pile foundation and the main structure, while the rectangular tunnel is very suitable.

[0009] Step S4: Use the millisecond delay blasting technology to excavate the lower bench, construct in sequence according to multiple segments, and timely conduct slope support.

[0010] Step S5: Conduct the construction of the lower main structure and pile foundation removal. Immediately conduct the construction of the main structure after the excavation of each segment is completed. The specific construction sequence is as follows: First, conduct the treatment of the lower bench base, then conduct the comprehensive grounding, followed by the installation of the bottom formwork and the binding of the bottom steel bars and the pouring of the bottom concrete. Then, conduct the construction of the side walls of the lower bench, including the installation of the side wall formwork and the binding of the steel bars and the pouring of the concrete. After the strength of the main structure meets the design requirements, cut off the pile foundation of the underground structure invading the tunnel, and then proceed with the construction of the next segment.

[0011] Step S6: After conducting the waterproof treatment of the roof and the side walls on both sides, conduct the concrete backfilling.

[0012] Preferably, in step S3, after the construction of the upper main structure, the soft rock and soil at the bottom of the upper bench need to be grouted and reinforced to meet the requirement of the bearing capacity of the foundation.

[0013] Preferably, in step S4, when excavating and constructing the lower step, the two excavation lines (left line and right line) are constructed at staggered segment positions to avoid excavating the same segment position at the same time;

[0014] Preferably, in step S4, during the excavation of the lower step, different excavation methods are used depending on the location of the pile foundation of the underground structure intruding into the tunnel. When the pile foundation of the underground structure intruding into the tunnel is in the middle of the tunnel, the excavation is carried out in sections and the intruding pile foundation is cut off. When the pile foundation of the underground structure intruding into the tunnel is on one side of the tunnel, a small end face excavation method is used to excavate a trench, directly excavating the lower step through. The trench width is about 4m and the depth is about 4.5m. Excavation is carried out from the corresponding trench segment to both sides to the design boundary line. After the excavation and support of the corresponding segment are completed, the main structure of the segment is immediately constructed. During the excavation process, attention should be paid to protecting the rock at the bottom of the side wall of the upper main structure. It should also be pointed out that since the two ends of the ultra-small clearance double-hole rectangular tunnel are arranged parallel to the side wall where the underground structure intersects, when excavating the lower step or trenching, excavation can be carried out from the two ends in opposite directions to save excavation time.

[0015] The beneficial effects of the present invention are:

[0016] (1) The construction method provided by the present invention is different from the middle partition wall method or pilot hole method of conventional large-section dark-excavated tunnels. It adopts the dark-excavated reverse method, dividing the tunnel section into upper and lower steps for excavation. The upper step is first excavated through and the upper main structure is constructed. The upper main structure is used as the force transmission system of the pile foundation. The upper pile group is replaced one by one through the segmented construction method, which effectively controls the settlement of the tunnel upper structure and protects the safety of the tunnel main body and the upper structure.

[0017] (2) The construction method provided by the present invention adopts different excavation methods in the excavation of the lower step according to the different positions of the pile foundations of the underground structure intruding into the tunnel; wherein: when the pile foundations of the underground structure intruding into the tunnel are on one side of the tunnel, a small end face excavation method is used to excavate a trench, directly excavating the lower step through, and then excavating from the corresponding trench segments to both sides to the designed edge for subsequent construction. The trench construction method can increase the working surface to speed up the on-site construction progress, greatly shorten the construction period, and save construction costs;

[0018] (3) The construction method provided by the present invention adopts a method combining mechanical demolition and static blasting when excavating the upper steps, and smoothly excavates and penetrates without affecting the stability and safety of the underground structure, effectively solving the impact of the excavation process on the stability of the rock wall between the two holes, and ensuring the construction quality and construction period. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a construction flow chart of upper step excavation in a method for excavating a double-hole rectangular tunnel with ultra-small clearance under an underground structure provided by the present invention;

[0020] Figure 2 This is a construction flow chart of lower step excavation in a method for excavating a double-hole rectangular tunnel with ultra-small clearance under an underground structure provided by the present invention;

[0021] Figure 3 This is a construction flow chart of upper step rock and soil excavation in a method for excavating an ultra-small clearance double-hole rectangular tunnel passing under an underground structure provided by the present invention;

[0022] Figure 4 This is a front view of the construction structure when excavating a trench on the lower step in a method for excavating a double-hole rectangular tunnel with an ultra-small clearance under an underground structure provided by the present invention;

[0023] Figure 5 This is a three-dimensional structural diagram of the construction when excavating a trench on the lower step in a method for excavating a double-hole rectangular tunnel with an ultra-small clearance under an underground structure provided by the present invention;

[0024] Figure 6 This is a construction sequence diagram of lower step excavation in a method for excavating a double-hole rectangular tunnel with ultra-small clearance under an underground structure provided by the present invention;

[0025] Figure numerals: 1-tunnel upper structure, 2-middle rock wall, 3-underpinning beam, 4-side wall, 5-left line underpinning pile foundation, 6-right line underpinning pile foundation, 7-trench. DETAILED DESCRIPTION

[0026] The following describes the specific embodiments of the present invention in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0027] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0028] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0029] refer to Figure 1 and Figure 2, A method for excavating an ultra-small clear distance double-hole rectangular tunnel under a subterranean structure, which is applied to a double-track tunnel with an ultra-small clear distance between a closely adjacent subterranean structure and its group of piles that intersects with an underground building. The two ends of the ultra-small clear distance double-hole rectangular tunnel are arranged in parallel on the side walls of the intersection of the subterranean structure. Using the top-down excavation method, the tunnel section is divided into upper and lower parts. First, the upper bench tunnel is fully excavated, then the upper main structure is constructed in one go, and finally the lower bench is excavated. During the excavation process, the piles of the subterranean structure invading the tunnel need to be properly handled;

[0030] The specific excavation steps are as follows:

[0031] Step S1, the portal section of the ultra-small clear distance double-hole rectangular tunnel before excavation is pre-supported by pipe-roofing and the portal is demolished;

[0032] Step S2, the tunnel section is divided into upper and lower parts. First, the upper bench is excavated. The slope excavation of an inverted trapezoid is adopted. The side slope gradient is 1:0.2, the upper soil layer slope of the middle rock wall is 1:0.5, and the lower fractured and moderately weathered rock layer is excavated with a vertical wall. First, the first section of the upper bench is excavated, and the concrete is initially sprayed. During the excavation process, the slope is grouted and reinforced in a timely manner, and the steel arch support and anchor rods are installed. The middle rock wall is grouted and reinforced with grouting pipes arranged in a plum blossom shape to ensure the stability of the middle interlayer rock. For linear rock fissures, the grouting pipes are arranged along the fissure trend to drill holes. After the excavation of the first section is completed, the next section is excavated; Preferably, in step S2, when excavating the upper bench, to ensure safety, the excavation face on one side lags behind the excavation face on the other side by 10 m; When the piles of the subterranean structure invading the tunnel do not extend into the lower bench, pile connection and reinforcement are required.

[0033] Further, referring to Figure 3 , Since the ultra-small clear distance double-track rectangular tunnel closely passes under the subterranean structure and its group of piles, the middle rock wall and the subterranean structure need to be protected from being disturbed during the excavation process. Blasting excavation is strictly prohibited. The present invention adopts an excavation method combining mechanical demolition and static blasting. First, a down-the-hole drill with a diameter of is used to drill holes on the excavation face. The hole spacing is 1.0 * 1.0 m, and the holes are arranged in a plum blossom shape. Then, a hydraulic splitting machine is used to split the rock. During this period, a hydraulic breaker is used to cooperate with the excavation. Finally, the larger pieces of rock are broken by a hydraulic breaker and transported by a loader. Due to the unevenness of the excavation face, local protruding rocks often appear on the middle vertical rock wall. If the same mechanical crushing method is used, it will greatly affect the stability of the middle rock wall. To reduce the disturbance, the static blasting method is adopted. First, a row of holes is drilled with a rock drill. The diameter of the drill hole is 3.5 cm. Then, a static expansion agent is poured, the hole mouth is sealed with mortar, and then it is left standing for 12 hours to expand.

[0034] Step S3: After the upper bench excavation is completed, the upper main structure is constructed all at once. The load of the underground structure is transferred from the transfer cross beam to the side walls on both sides of the tunnel by using the pile foundation underpinning method. The pile foundation underpinning joints are treated by the method of combining anchor bars and pile foundation keyways. The specific construction method is as follows: Before pouring the transfer cross beam, the pile bodies within the range of the cross beam to be underpinned are chiseled to form keyways with a height of 100 mm, a depth of 20 mm, and a spacing of 100 mm. At the same time, by using the chemical rebar planting method, Φ20 deformed bars are implanted with a drilling diameter of 25 mm, a hole depth of 22 cm, and a hole spacing of 30*30 cm. The deformed bars are arranged in a plum blossom shape. Preferably, after the construction of the upper main structure, the soft rock and soil at the bottom of the upper bench need to be grouted and reinforced to meet the requirement of the bearing capacity of the foundation.

[0035] Step S4: The lower bench is excavated by using the millisecond delay blasting technology. The specific operation is as follows: The blasting depth is 1.5 m each time along the heading face, and the blasting is carried out in 3 layers. To ensure that the disturbance to the upper completed main structure is reduced during the blasting process and to prevent the blasting vibration from damaging the joints of the underpinning piles and the transfer cross beam, a row of shock-absorbing holes with a diameter of 5 cm are drilled 50 cm away from the side wall of the upper structure. The depth of the shock-absorbing holes reaches 0.5 m into the bottom plate, and the hole spacing is 30 cm. The blasting is carried out by the method of drilling more holes and charging less explosives and layered blasting; the construction is carried out in sequence according to multiple segments, and the slope support is carried out in a timely manner; further, when excavating and constructing the lower bench, the two excavation lines (left line and right line) are constructed at the staggered segment positions to avoid simultaneous excavation at the same segment position.

[0036] During the excavation of the lower bench, different excavation methods are adopted according to the different positions of the piles of the underground structure invading the tunnel. When the piles of the underground structure invading the tunnel are in the middle of the tunnel, the excavation is carried out in segments in sequence and the invading piles are truncated; when the piles of the underground structure invading the tunnel are on one side of the tunnel, a small-end face excavation method is adopted to excavate the trench, and the lower bench is directly excavated through. The width of the trench is about 4 m and the depth is about 4.5 m. The excavation is carried out from the corresponding trench segments to both sides to the design side line. After the excavation and support of the corresponding segment are completed, the construction of the main structure of this segment is immediately carried out. During the excavation process, attention needs to be paid to the protection of the rock at the bottom of the side wall of the upper main structure. In addition, it should be noted that since the two ends of the ultra-small clear distance double-hole rectangular tunnel are parallel to the side wall where the underground structure intersects, during the excavation of the lower bench or the construction of the trench, the excavation can be carried out from both ends towards each other to save the excavation time.

[0037] Step S5: Carry out the construction of the lower main structure and the removal of pile foundations. Immediately after the excavation of each section is completed, the construction of the main structure is carried out. The specific construction sequence is as follows: First, carry out the treatment of the lower bench foundation. After comprehensive earthing, install the formwork for the floor slab, bind the steel bars of the floor slab, and pour the concrete of the floor slab. Then, carry out the construction of the side walls of the lower bench, specifically including the installation of side wall formwork, binding of steel bars, and pouring of concrete. After the strength of the main structure meets the design requirements, cut off the pile foundations that intrude into the tunnel of the underground structure, and then carry out the construction of the next section. Further, when cutting off the pile foundations, in order to ensure that the damage to the already completed main structure is reduced during the cutting process, a core drill is used for contact. The core drill drills holes in the pile foundations, horizontally drills a row of holes, and the drilling layout form is similar to that of secant piles. During the core drilling process, two longitudinal steel bars of the pile foundation are reserved to prevent the sudden collapse of the lower pile foundation from causing harm to construction workers.

[0038] Step S6: After carrying out the waterproof treatment of the top slab and the side walls on both sides, carry out the concrete backfill.

[0039] Engineering application example: The platform layer of the underpass section of Xiamen Railway Station closely passes under the operating underground commercial street and the viaduct. The method provided by the present invention can be applied to this project. It should be noted that since the construction environments of the left line and the right line are different during the excavation of the lower bench in this project, the excavation is carried out according to different situations. The following gives a detailed introduction to the construction process of the excavation of the lower bench in this project:

[0040] After the excavation of the upper bench is completed and all the upper main structures are constructed, the load of the upper structure 1 of the tunnel is transferred from the underpinning cross beam 3 to the side walls 4 on both sides of the tunnel by using the underpinning method. Then, the excavation of the lower bench is carried out. At this time, the construction structure diagram and the construction sequence diagram of the excavation of the lower bench refer to Figures 4 to 6, the left line is constructed by two-way excavation from both ends in 7 segments. First, the excavation of the first segment at the entrance of the left-line tunnel is carried out. During the excavation process, measures such as increasing the lighting in the tunnel, installing anti-collision devices on the surface of the pile foundation, and enhancing the driver's operation and safety awareness are taken to protect the pile foundation that has been jacked but not cut off (hereinafter referred to as "jacked pile foundation"); after the excavation is in place, slope support is carried out, and the middle rock wall 2 is protected. After the strength of the first-section main structure meets the design requirements, the left-line jacked pile foundation 5 is cut off. Since the right-line jacked pile foundation 6 is close to the side wall, in order to accelerate the on-site construction progress and prevent the on-site construction personnel from having work delays during the waiting for the concrete strength, first, the small-end face excavation method is used to excavate the trench 7, and the lower channel is directly excavated through. The width of the trench 7 is about 4m, and the depth is about 4.5m to increase the working face. During the excavation process, shotcrete is promptly sprayed on both sides of the trench 7 to ensure the stability of the slope. One-way excavation construction is carried out in 8 segments, and excavation is carried out from the corresponding trench 7 segments to both sides to the design edge line. After the excavation and support of the corresponding segment are completed, the construction of the main structure of this segment is immediately carried out. First, the first, third, fifth, and seventh segments are constructed respectively, and then the second, fourth, sixth, and eighth segments are constructed. When using this method of construction with adjusted compartments, it is also necessary to wait for the strength of the concrete in the previous segment to meet the design requirements before proceeding with the construction of the next segment. During the excavation process, attention needs to be paid to protecting the rock at the bottom of the side wall of the upper part of the main structure.

[0041] The preferred embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0042] In addition, it should be noted that, in the case of no contradiction, the various specific technical features described in the above specific embodiments can be combined in any appropriate way. To avoid unnecessary repetition, the present invention will not describe the various possible combination methods separately.

[0043] In addition, any combination can be made between the various different embodiments of the present invention as long as it does not violate the idea of the present invention, and it should also be regarded as the content disclosed by the present invention.

Claims

1. A method for excavating an ultra-small clear distance double-hole rectangular tunnel under a subterranean structure, wherein the two ends of the ultra-small clear distance double-hole rectangular tunnel are arranged in parallel on the side walls where the subterranean structures meet, and is characterized in that: It includes the following steps: Step S1: Before excavation, advanced pre-support is carried out on the portal section of the ultra-small clear distance double-hole rectangular tunnel using pipe roofs, and the portal is demolished. Step S2: The tunnel section is divided into upper and lower parts. First, the upper bench is excavated in segments. The slope excavation in an inverted trapezoid shape is adopted. The first segment of the upper bench is excavated first, and the concrete is initially sprayed. During the excavation process, the slope is grouted and reinforced in a timely manner, and the steel arch support and anchor rods are installed. The middle rock wall is arranged with grouting pipes in a plum blossom shape and grouted and reinforced to ensure the stability of the middle rock stratum. After the excavation of the first segment is completed, the next segment is excavated. Step S3: After the upper bench excavation is completed, the upper part of the main structure is constructed all at once, and the load of the underground structure is transferred to the side walls on both sides of the tunnel by means of pile foundation underpinning. Step S4: The lower bench is excavated using the millisecond delay blasting technology, and the construction is carried out in multiple segments in sequence, and the slope support is carried out in a timely manner. Step S5: The construction of the lower part of the main structure and the pile foundation removal are carried out. The construction of the main structure is carried out immediately after the excavation of each segment is completed. Step S6: After the waterproof treatment of the roof and the side walls on both sides, the concrete backfill is carried out.

2. The excavation method of the ultra-small clear distance double-hole rectangular tunnel under a subterranean structure according to claim 1, characterized in that: In step S2, to ensure safety during the excavation of the upper bench, the excavation face on one side lags behind the excavation face on the other side. When the pile foundation of the underground structure invading the tunnel does not extend into the lower bench, pile connection and reinforcement are required.

3. The excavation method of the ultra-small clear distance double-hole rectangular tunnel under the underground structure according to claim 1, characterized in that: In step S2, the excavation method combines mechanical demolition and static blasting.

4. The excavation method of the ultra-small clear distance double-hole rectangular tunnel under a subterranean structure according to claim 1, characterized in that: In step S3, after the construction of the upper part of the main structure, the soft rock and soil at the bottom of the upper bench need to be grouted and reinforced to meet the requirements of the foundation bearing capacity.

5. The excavation method for an ultra-small clear distance double-hole rectangular tunnel under a subterranean structure according to claim 1, characterized in that: In step S4, during the excavation and construction of the lower bench, the construction is carried out at the staggered segment positions of the two excavation lines to avoid simultaneous excavation at the same segment position.

6. The excavation method of the ultra-small clear distance double-hole rectangular tunnel under the underground structure according to claim 1, characterized in that: In step S4, during the excavation of the lower bench, different excavation methods are adopted according to the different positions of the pile foundations of the underground structure invading the tunnel. When the pile foundation of the underground structure invading the tunnel is in the middle of the tunnel, the excavation is carried out in segments in sequence and the invading pile foundation is truncated. When the pile foundation of the underground structure invading the tunnel is on one side of the tunnel, the small-end face excavation method is adopted to excavate the trench, and the lower bench excavation is directly completed. The excavation is carried out from the corresponding trench segments to both sides to the design edge line. After the excavation and support of the corresponding segment are completed, the construction of the main structure of this segment is carried out immediately. During the excavation process, attention needs to be paid to the protection of the rock at the bottom of the side wall of the upper part of the main structure.

7. The excavation method of the ultra-small clear distance double-hole rectangular tunnel under the underground structure according to claim 1, characterized in that: In step S5, the specific construction sequence is as follows: First, the base treatment of the lower bench is carried out. After the comprehensive grounding, the formwork installation and steel bar binding of the bottom slab are carried out, and the bottom slab concrete is poured. Then, the side wall construction of the lower bench is carried out, specifically including the formwork installation and steel bar binding of the side wall and the concrete pouring. After the strength of the main structure meets the design requirements, the pile foundation of the underground structure invading the tunnel is cut off, and then the construction of the next segment is carried out.

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