Construction method for butt joint of unequal-diameter shield penetrating through sand layer in long distance in underwater soil layer

Abstract

The invention discloses a construction method for butt joint of unequal-diameter shields penetrating through a sand layer in a long distance in an underwater soil layer. The method comprises the steps that 1, a large-diameter normal-pressure cutterhead shield and a small-diameter conventional cutterhead shield conduct tunneling in the opposite directions; 2, the large-diameter normal-pressure cutterhead shield reinforces stratums around the large-diameter normal-pressure cutterhead shield and in front of the cutterhead in the butt joint area in a freezing mode; 3, the small-diameter conventional cutterhead shield reinforces the stratum around the small-diameter conventional cutterhead shield and in front of the cutterhead in a freezing mode at the position 1-2 m away from the large-diameter normal-pressure cutterhead shield, and a complete freezing reinforcement area is formed; 4, when the small-diameter conventional cutterhead shield conducts tunneling till the distance between the small-diameter conventional cutterhead shield and the large-diameter normal-pressure cutterhead shield is smaller than 10 cm, the large-diameter normal-pressure cutterhead shield retracts, and tunneling is completely suspended after the large-diameter normal-pressure cutterhead shield is tightly attached; 5, dismounting equipment in the two shield tunneling machines; and 6, a connecting structure is constructed in the butt joint area. The method solves the technical problem that tools of a small-diameter conventional cutterhead shield are frequently replaced in unequal-diameter shield tunnel construction penetrating through a sand layer in a long distance.

Description

Technical Field

[0001] This invention relates to the field of shield tunnel construction technology, and in particular to a construction method for underwater docking of shields of unequal diameter that traverse long distances through sand layers. Background Technology

[0002] When existing small-diameter conventional cutterhead shield tunnels traverse wide water systems such as the Yangtze River or complex strata in South China, the tunnels often pass through dense sand or rock layers with high quartz content in certain areas.

[0003] When river scouring depth is significant, tunnel burial depth needs to be increased. This necessitates small-diameter underwater shield tunnels traversing long distances through complex geological formations or dense sand layers with high quartz content. Abrasive minerals such as quartz cause severe wear on the cutting tools, requiring frequent tool replacements. For example, the China-Russia East Route Yangtze River Shield Tunnel required three tool replacements during its excavation.

[0004] Currently, when replacing cutterheads in loose, highly permeable, and high-water-pressure underwater strata, two methods are commonly used: normal pressure cutterhead replacement and pressurized hatch cutterhead replacement.

[0005] 1. Atmospheric Pressure Cutterhead Replacement: In a cutterhead with hollow spokes and replaceable cutter barrels, workers enter the hollow spokes and replace the cutterheads under atmospheric pressure. This eliminates the need for pressurized operation, resulting in a short replacement cycle, high construction efficiency, and low risk. Currently, atmospheric pressure cutterhead replacement technology is relatively mature in tunnel boring machines (TBMs) with diameters exceeding 11m. However, small-diameter conventional cutterhead TBMs face operational risks due to space constraints, including narrow working space, susceptibility to mechanical collisions, and limited operating radius of the cutterhead replacement robotic arm, making the application of atmospheric pressure cutterhead structures difficult. Currently, the world's smallest diameter atmospheric pressure cutterhead TBM has been successfully applied to the Sino-Russian East Line Yangtze River Tunnel, with a diameter of 7.95m, tunneling 10.2km under the Yangtze River and implementing three atmospheric pressure cutterhead replacements. For small-diameter conventional cutterhead TBM tunnels (φ < 6m), adopting an atmospheric pressure cutterhead structure requires increasing the TBM diameter, increasing investment, and resulting in poor economic efficiency.

[0006] 2. Pressurized Chamber Cutterhead Replacement: Under the premise of ensuring the stability of the excavation face, the operators enter the pressure chamber in a pressurized environment to repair and replace the cutters. To ensure the stability of the excavation face, a layer of airtight mud film (mud slurry infiltration film) is formed at the stratum excavation face, so that the air pressure in the pressure chamber balances the water and soil pressure in the stratum.

[0007] Some publicly available literature also points out that when replacing cutterheads in loose, highly permeable, and high-water-pressure underwater strata, methods such as pressurized air entry for cutterhead replacement, pressurized mixed gas entry for cutterhead replacement, and saturated gas entry for cutterhead replacement can be used. Typical examples include the Nanjing Weisan Road Tunnel, the Istanbul Bosphorus Strait Tunnel, and the Hong Kong Tuen Mun to Chek Lap Kok Cross-Harbour Tunnel. However, the above methods have the following problems:

[0008] (1) In the loose, highly permeable, and high-pressure underwater formations, it is difficult to maintain the mud film and the air pressure, which poses a great risk to opening the chamber and changing the cutterhead under pressure.

[0009] (2) When using ultra-high pressure cabin entry operations (water pressure > 0.6MPa), saturation diving cabin opening and cutterhead replacement technology is often required. During the cabin opening operation, the operators live in the ground high-pressure living chamber. The high-pressure shuttle cabin connects with the shield machine's pressure chamber, and the operators enter the pressure chamber to work. After completing one operation, they return to the ground high-pressure living chamber through the high-pressure shuttle cabin. This process is repeated until the work is completed and a decompression exit is performed. When implementing ultra-high pressure cabin opening and cutterhead replacement for small-diameter conventional cutterhead shields, the high-pressure shuttle cabin is connected to the shield machine's personnel gate. Due to space constraints, it may be necessary to increase the shield diameter or temporarily remove part of the shield's frame system, which will significantly reduce the shield construction efficiency and significantly increase the shield investment. For example, the Portman Tunnel in Canada, with a shield diameter of about 3.5m and a tunnel length of about 1km, stopped at about 800m due to equipment cutterhead problems. The original plan was to replace the cutterhead under pressure with saturated submersion, but due to the small diameter of the shield, the final solution adopted was to build a construction platform in the middle of the river and then repair the cutterhead after freezing it with liquid nitrogen.

[0010] In existing technologies, small-diameter conventional cutterhead tunnel boring machines (TBMs) are limited by the internal space of the main unit and the cutterhead, making it difficult to apply atmospheric pressure cutterhead structures. If an atmospheric pressure cutterhead structure is used, the TBM diameter needs to be increased, significantly increasing project investment and resulting in poor economic efficiency.

[0011] However, when using a conventional cutterhead structure, the operation of changing cutters in loose, highly permeable, and high-water-pressure formations underwater is usually risky due to the use of pressurized hatch opening.

[0012] When a small-diameter conventional cutterhead shield undergoes ultra-high pressure cabin opening and cutter replacement, the high-pressure shuttle cabin needs to be connected to the shield's personnel gate cabin. This may require increasing the shield diameter or temporarily removing part of the shield vehicle frame system, which will significantly reduce the shield construction efficiency and greatly increase the shield investment.

[0013] In addition, due to ecological and environmental protection requirements and navigation restrictions, it is often difficult to set up temporary working shafts or temporary artificial islands for cutter replacement and maintenance operations in ultra-long shield tunnels that cross large bodies of water such as the Yangtze River and large lakes.

[0014] For ultra-long shield tunnels that cross large bodies of water such as the Yangtze River and large lakes, none of the above solutions can simultaneously meet the requirements of cutterhead replacement construction safety, economic efficiency, technical reliability, environmental protection, and navigation.

[0015] Therefore, how to overcome the technical bottleneck in the construction of small-diameter conventional cutterhead shield tunnels that traverse long distances through sand layers has become a key technical problem that urgently needs to be solved in the field of underwater tunnel engineering. Summary of the Invention

[0016] In view of the above-mentioned deficiencies of the prior art, the present invention provides a construction method for connecting unequal diameter shield tunnels in underwater soil layers over long distances through sand layers. The purpose is to solve the technical problem that wear-out cutters are difficult to replace when small-diameter conventional cutterhead shield tunneling machines are excavating over ultra-long distances in water-rich sand layers.

[0017] To achieve the above objectives, the present invention discloses a construction method for underwater docking of shield tunnels with unequal diameters that traverse long distances through sand layers. The method includes a larger diameter section that is excavated using a large-diameter atmospheric pressure cutterhead shield tunneling machine for sections traversing water-rich sand or rock layers over a distance of more than 1 km, a smaller diameter section that is excavated using a small-diameter conventional cutterhead shield tunneling machine for sections traversing soft soil layers, and a docking zone located between the larger diameter section and the smaller diameter section.

[0018] The large-diameter atmospheric pressure cutterhead shield and the small-diameter conventional cutterhead shield are coaxially connected.

[0019] The construction steps are as follows:

[0020] Step 1: The large-diameter atmospheric pressure cutterhead shield and the small-diameter conventional cutterhead shield tunnel advance towards each other according to the designed route. The large-diameter atmospheric pressure cutterhead shield tunnel advances first and arrives at the docking area before the small-diameter conventional cutterhead shield tunnel.

[0021] Step 2: When the large-diameter atmospheric pressure cutterhead shield reaches the docking area, the tunneling is suspended, and the ground around the large-diameter atmospheric pressure cutterhead shield and in front of the cutterhead is reinforced by freezing through the corresponding large shield radial freezing pipes.

[0022] Step 3: After the small-diameter conventional cutterhead shield approaches to a distance of 1m to 2m from the large-diameter atmospheric pressure cutterhead shield, the tunneling is suspended. The ground around the small-diameter conventional cutterhead shield and in front of the cutterhead is reinforced by freezing through the corresponding small shield radial freezing pipes, forming a complete frozen reinforcement area in the ground of the docking area to be constructed.

[0023] Step 4: After reinforcement is completed, the small-diameter conventional cutterhead shield tunneling machine advances at a speed of 2 mm / min to 10 mm / min until it approaches the large-diameter atmospheric pressure cutterhead shield tunneling machine and is less than 10 cm away. Then, the large-diameter atmospheric pressure cutterhead shield tunneling machine retracts at a speed less than that of the small-diameter conventional cutterhead shield tunneling machine and stops tunneling completely when the cutterheads of the large-diameter atmospheric pressure cutterhead shield tunneling machine and the small-diameter conventional cutterhead shield tunneling machine are in close contact.

[0024] Step 5: While maintaining the tail seal between the large-diameter atmospheric pressure cutterhead shield and the small-diameter conventional cutterhead shield and the corresponding shield segments, gradually dismantle the equipment inside the shield shell of the large-diameter atmospheric pressure cutterhead shield and the small-diameter conventional cutterhead shield.

[0025] Step 6: Construct the gradually changing cross-section connection structure in the docking area using an integral cast-in-place process.

[0026] Preferably, both the large-diameter atmospheric pressure cutterhead shield and the small-diameter conventional cutterhead shield are equipped with a cryogenic cutterhead and a double-layer shield shell.

[0027] Preferably, in steps 2 and 3, core drilling or advanced geological prediction methods are used to detect the reinforcement effect of the strata around and in front of the large-diameter atmospheric pressure cutterhead shield reinforced by freezing, as well as the reinforcement effect of the strata around and in front of the small-diameter conventional cutterhead shield.

[0028] Preferably, during step 4, secondary grouting is performed simultaneously behind the wall to ensure that the shield shells of both the large-diameter atmospheric pressure cutterhead shield and the small-diameter conventional cutterhead shield are in a compacted state with respect to the surrounding soil.

[0029] Preferably, during step 5, the reinforced concrete segment closest to the docking area of ​​both the larger diameter segment and the smaller diameter segment is simultaneously fixed to the shield shell of the corresponding large-diameter atmospheric pressure cutterhead shield or the corresponding small-diameter conventional cutterhead shield by welding anti-reverse steel plates, so as to prevent the shield from retracting and to transmit longitudinal loads.

[0030] Preferably, when performing step 5, a continuous steel plate is welded to the inner surface of the segment with the larger diameter and / or smaller diameter to prevent water leakage caused by loosening of the segment.

[0031] Preferably, before performing step 6, it is detected whether there are cavities on the outer shell of the large-diameter atmospheric pressure cutterhead shield and the small-diameter conventional cutterhead shield; if so, each cavity is filled with grout; in addition, anti-corrosion and waterproof coatings such as polyurea are sprayed inside the shield shell.

[0032] The beneficial effects of this invention are:

[0033] This invention, through its innovative approach to underwater docking technology for shield tunnels with unequal diameters, effectively solves the problems of high cutter replacement risk, low efficiency, and complex procedures in traditional ultra-long-distance small-diameter conventional cutterhead shield tunnels. It also reduces the high-precision docking measurement requirements for underwater docking of traditional shield tunnels in high-water-pressure and highly permeable strata.

[0034] Compared to traditional solutions, this invention is safer and more reliable. It adopts segmented docking of shield tunnels with unequal diameters to avoid the risk of shield equipment failure during ultra-long unidirectional tunneling, and avoids multiple opening and cutterhead replacement operations under high water pressure, thus significantly reducing construction risks.

[0035] In this invention, the limited space within a small-diameter conventional cutterhead shield further increases the difficulty of ultra-long-distance docking measurements. In this patent, the diameters of the preceding and following shields are different, and the following shield needs to be advanced into the shield body of the preceding shield, which can appropriately reduce the accuracy of docking measurements and increase the tolerance for docking errors.

[0036] In addition, since the rear-entry shield (small-diameter conventional cutterhead shield) needs to be advanced into the shield body of the preceding shield (large-diameter shield), the dismantling and disassembly process of the preceding and following shields after docking will be under the dual protection of the frozen soil layer and the shield shell, which ensures high safety.

[0037] Compared to traditional solutions, this invention is more economical and efficient, reducing the need for working wells in the river and lowering the cost of temporary engineering works.

[0038] The shield tunneling is carried out in segments. Larger diameter, atmospheric pressure cutterhead shields are used to tunnel through dense sand and rock layers, while smaller diameter conventional cutterhead shields are used to tunnel through soft soil layers. This greatly improves the efficiency of shield tunneling, saves project investment, and shortens the project period.

[0039] Compared to traditional solutions, this invention is more eco-friendly, as it eliminates the need for temporary working wells (artificial islands) in the river, thus minimizing the impact on aquatic ecosystems and shipping.

[0040] This docking technology and construction method provide a safe, economical, and environmentally friendly system solution for similar ultra-long-distance underwater shield tunnels, and has broad application value.

[0041] The following will further explain the concept, specific structure, and technical effects of the present invention in conjunction with the accompanying drawings, so as to fully understand the purpose, features, and effects of the present invention. Attached Figure Description

[0042] Fig. 1 This diagram illustrates the state of step 2 in one embodiment of the present invention.

[0043] Fig. 2 This diagram illustrates the state of step 3 in one embodiment of the present invention.

[0044] Fig. 3 This diagram illustrates the state of step 4 in one embodiment of the present invention.

[0045] Fig. 4 This diagram illustrates the state after step 6 is completed in one embodiment of the present invention. Detailed Implementation

[0046] Example: Figs. 1 to 4As shown, the construction method for connecting unequal diameter shield tunnels in underwater soil layers over long distances through sand layers includes a larger diameter section that is excavated by a large-diameter atmospheric pressure cutterhead shield 1 for sections of more than 1km through water-rich sand or rock layers, a smaller diameter section that is excavated by a small-diameter conventional cutterhead shield 2 for sections through soft soil layers, and the connection zone located between the larger diameter section and the smaller diameter section.

[0047] Large-diameter atmospheric pressure cutterhead shield tunneling machine and small-diameter conventional cutterhead shield tunneling machine are coaxially connected;

[0048] In practical applications, based on the geological survey report, ultra-long shield tunnels with a tunneling length of ≥3km are divided into two sections. The section that crosses sand or rock layers for more than 1km is tunneled using a large-diameter, atmospheric pressure cutterhead shield 1, while the section that crosses soft soil layers is tunneled using a small-diameter, conventional cutterhead shield 2.

[0049] The construction steps are as follows:

[0050] Step 1: The large-diameter atmospheric pressure cutterhead shield 1 and the small-diameter conventional cutterhead shield 2 tunnel towards each other according to the design route. The large-diameter atmospheric pressure cutterhead shield 1 goes first and arrives at the docking area before the small-diameter conventional cutterhead shield 2.

[0051] Step 2: When the large-diameter atmospheric pressure cutterhead shield 1 reaches the docking area, the tunneling is suspended, and the ground around the large-diameter atmospheric pressure cutterhead shield 1 and in front of the cutterhead is reinforced by freezing through the corresponding large shield radial freezing pipe 3-1.

[0052] Step 3: After the small-diameter conventional cutterhead shield 2 approaches to a distance of 1m to 2m from the large-diameter atmospheric pressure cutterhead shield, the tunneling is suspended. The ground around the small-diameter conventional cutterhead shield 2 and in front of the cutterhead is reinforced by freezing through the corresponding small shield radial freezing pipes 3-2, forming a complete frozen reinforcement area 4 in the ground of the area to be connected.

[0053] Step 4: After reinforcement is completed, the small-diameter conventional cutterhead shield 2 advances at a speed of 2 mm / min to 10 mm / min until it approaches the large-diameter atmospheric pressure cutterhead shield 1 and is less than 10 cm away. Then, the large-diameter atmospheric pressure cutterhead shield 1 retracts at a speed less than that of the small-diameter conventional cutterhead shield 2 and stops advancing completely when the cutterheads of the large-diameter atmospheric pressure cutterhead shield 1 and the small-diameter conventional cutterhead shield 2 are in close contact.

[0054] Step 5: While maintaining the tail seal between the large-diameter atmospheric pressure cutterhead shield 1 and the small-diameter conventional cutterhead shield 2 and the corresponding shield segments, gradually dismantle the equipment inside the shield shells of the large-diameter atmospheric pressure cutterhead shield 1 and the small-diameter conventional cutterhead shield 2.

[0055] Step 6: Construct the gradually changing cross-section connection structure 5-3 in the docking area using the integral cast-in-place process.

[0056] This invention addresses the situation where, in ultra-long-distance, small-diameter conventional cutterhead shield tunnels traversing waterways, the shield needs to pass through complex strata or dense sand layers with high quartz content over long distances. In such cases, abrasive minerals such as quartz will cause severe wear on the cutterheads, necessitating frequent cutterhead replacements.

[0057] In water-rich sand layers, atmospheric pressure cutterhead shield tunneling machines are used as large-diameter atmospheric pressure cutterhead shield tunneling machines 1, while in soft soil layers, conventional cutterhead shield tunneling machines are used as small-diameter conventional cutterhead shield tunneling machines 2. The machines are connected at suitable docking points to achieve safe and efficient construction of pipeline shield tunnels that traverse sand layers over long distances.

[0058] This invention utilizes an innovative underwater docking technology for unequal-diameter shield tunnels. This technology addresses the challenges of high cutterhead replacement risks, low efficiency, and complex procedures inherent in traditional ultra-long-distance, small-diameter conventional cutterhead shield tunnels. It also reduces the high-precision docking measurement requirements for underwater docking in high-water-pressure, highly permeable strata. This technology can be widely applied to various types of underwater shield tunnels, and is particularly suitable for unequal-diameter shield docking construction scenarios where small-diameter conventional cutterhead shields traverse long distances through composite strata or dense sand layers with high quartz content.

[0059] In some embodiments, both the large-diameter atmospheric pressure cutterhead shield 1 and the small-diameter conventional cutterhead shield 2 are equipped with a cryogenic cutterhead and a double-layer shield shell.

[0060] In some embodiments, for both large-diameter atmospheric pressure cutterhead shield tunnels and small-diameter conventional cutterhead shield tunnels, in steps 2 and 3, core drilling or advanced geological prediction methods are used to detect the reinforcement effect of the strata surrounding and in front of the cutterhead of the large-diameter atmospheric pressure cutterhead shield 1 reinforced by freezing, as well as the reinforcement effect of the strata surrounding and in front of the cutterhead of the small-diameter conventional cutterhead shield 2.

[0061] In some embodiments, secondary grouting is performed simultaneously behind the wall during step 4 to ensure that the shield shells of both the large-diameter atmospheric pressure cutterhead shield 1 and the small-diameter conventional cutterhead shield 2 are in a dense state with the surrounding soil.

[0062] In some embodiments, when performing step 5, the reinforced concrete segments 5-1 and 5-2 closest to the docking area of ​​the larger diameter segment and the smaller diameter segment are simultaneously fixed to the shield shell of the corresponding large-diameter atmospheric pressure cutterhead shield 1 or the corresponding small-diameter conventional cutterhead shield 2 by welding anti-reverse steel plates.

[0063] In practical applications, the above-mentioned technical means can solve the problems of backlash prevention and longitudinal load transmission for large-diameter atmospheric pressure cutterhead shield 1 and small-diameter conventional cutterhead shield 2.

[0064] In some embodiments, when performing step 5, a continuous steel plate is welded to the inner surface of the segment with a larger diameter and / or smaller diameter.

[0065] In practical applications, the above-mentioned technical means can prevent water leakage caused by loosening of the pipe segments.

[0066] In some embodiments, before performing step 6, it is detected whether there are cavities on the outer shell of the large-diameter atmospheric pressure cutterhead shield 1 and the small-diameter conventional cutterhead shield 2; if so, each cavity is filled with grout; in addition, anti-corrosion and waterproof coatings such as polyurea are sprayed inside the shield shell.

[0067] In practical applications, based on geological survey reports, this invention divides ultra-long shield tunnels into two sections. The section traversing sand or rock layers exceeding 1 km utilizes a large-diameter, atmospheric-pressure cutterhead shield machine (Shield 1), while the section traversing soft soil layers employs a small-diameter, conventional cutterhead shield machine (Shield 2). This reduces the risk of equipment failure and minimizes the risks associated with shield construction and cutterhead replacement. The shield machine can be equipped with a cryogenic cutterhead and a double-layered shield shell, depending on the hydrogeological conditions.

[0068] During construction, the two shield tunnel sections are excavated towards each other. The area with a longitudinal distance of ≤200m between the two tunnel sections is defined as the docking zone. A detailed investigation of the engineering geology, hydrogeology, and engineering environment of the docking zone should be conducted, and the following aspects should be given priority consideration when selecting it:

[0069] 1) Geological conditions: docking construction should be avoided in strata containing high permeability, poor stability, and biogas.

[0070] 2) For confined aquifers, avoid confined aquifers and areas with underlying confined aquifers as much as possible;

[0071] 3) For the horizontal and vertical alignment of the tunnel, locations with straight horizontal sections and small longitudinal slopes should be selected as much as possible;

[0072] 4) Avoid the main shipping lane.

[0073] The large-diameter atmospheric pressure cutterhead shield 1 is excavated first, and its docking point is adjusted appropriately according to the actual excavation parameters. After the large-diameter atmospheric pressure cutterhead shield 1 reaches the predetermined docking point, the small-diameter conventional cutterhead shield 2 adjusts its own axis appropriately with the axis of the actual center of the cutterhead of the advance shield.

[0074] After the tunnel boring machine (TBM) enters the docking zone, it is necessary to strengthen docking measurements and check the attitude and relative position of the TBM at different mileages. Based on the relative position of the two, the tunneling route should be corrected to ensure that the two TBM sections tunnel towards each other along the same axis at the docking point and dock smoothly.

[0075] For the docking section:

[0076] (1) After the large-diameter atmospheric pressure cutterhead shield tunnel 1 has been excavated to the predetermined position, the shield shell section and the strata in front of the cutterhead shall be reinforced by grouting or freezing methods within the shield body of the large-diameter atmospheric pressure cutterhead shield tunnel 1. After the reinforcement is completed, the reinforcement effect shall be tested by core drilling or advanced geological prediction.

[0077] (2) When the small-diameter conventional cutterhead shield tunneling machine 2 approaches the preceding shield tunneling machine (approximately 1m to 2m away), the following shield tunneling machine should suspend its excavation. Grouting or freezing methods should be used to reinforce the shield shell section and the strata in front of the cutterhead within the shield body of the following shield tunneling machine. After reinforcement is completed, core drilling or advanced geological forecasting methods should be used to test the reinforcement effect.

[0078] (3) After the surrounding strata of the docking area are reinforced, the subsequent shield tunneling machine shall slowly advance. When the distance between the preceding and following shield tunnels is less than 10cm, the preceding shield tunneling machine shall slowly retract and the following shield tunneling machine shall slowly advance until the cutterheads of the preceding and following shield tunnels are in close contact. At the same time, secondary grouting shall be carried out behind the segment wall in a timely manner to ensure that the filling between the shield shell and the surrounding soil is dense.

[0079] (4) Gradually dismantle the main equipment inside the shield shell of the tunnel boring machine (TBM), while preserving the tail seal between the TBM and the shield segments. During the dismantling process, simultaneously fix the reinforced concrete segment closest to the docking area to the TBM steel shell by welding a backlash plate to solve the problems of shield backlash and transmission of longitudinal loads. In addition, if necessary, a continuous steel plate can be welded to the inner surface of the segments within a certain range from the shield body to prevent water leakage caused by segment loosening.

[0080] (5) Check for cavities on the outside of the shield shell and fill them with grout if necessary; spray anti-corrosion and waterproof coatings such as polyurea inside the shield shell;

[0081] (6) The gradual cross-section connection structure is constructed in the docking area using the integral cast-in-place process 5-3.

[0082] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A construction method for connecting unequal-diameter shield tunnels that traverse long distances through sand layers underwater; characterized in that, The larger diameter section is excavated by a large-diameter, atmospheric pressure cutterhead shield (1) for a long distance of more than 1 km through water-rich sand or rock layers, and a smaller diameter section is excavated by a small-diameter, conventional cutterhead shield (2) for a section through soft soil layers, as well as the docking area between the larger diameter section and the smaller diameter section. The large-diameter atmospheric pressure cutterhead shield and the small-diameter conventional cutterhead shield are coaxially connected. The construction steps are as follows: Step 1: The large-diameter atmospheric pressure cutterhead shield (1) and the small-diameter conventional cutterhead (2) tunnel towards each other according to the designed route, and the large-diameter atmospheric pressure cutterhead shield (1) goes first and arrives at the docking area before the small-diameter conventional cutterhead shield (2); Step 2: When the large-diameter atmospheric pressure cutterhead shield (1) reaches the docking area, the tunneling is suspended, and the strata around the large-diameter atmospheric pressure cutterhead shield (1) and in front of the cutterhead are reinforced by freezing through the corresponding large shield radial freezing pipe (3-1). Step 3: When the small-diameter conventional cutterhead shield (2) approaches to a distance of 1m to 2m from the large-diameter atmospheric pressure cutterhead shield (1), the tunneling is suspended. The ground around the small-diameter conventional cutterhead shield (2) and in front of the cutterhead is reinforced by freezing through the corresponding small shield radial freezing pipe (3-2). A complete frozen reinforcement area (4) is formed in the ground of the docking area to be constructed. Step 4: After reinforcement is completed, the small-diameter conventional cutterhead shield (2) advances at a speed of 2 mm / min to 10 mm / min until it approaches the large-diameter atmospheric pressure cutterhead shield (1) and is less than 10 cm away. Then, the large-diameter atmospheric pressure cutterhead shield (1) retracts at a speed less than that of the small-diameter conventional cutterhead shield (2) and stops advancing when the cutterheads of the large-diameter atmospheric pressure cutterhead shield (1) and the small-diameter conventional cutterhead shield (2) are in close contact. Step 5: While maintaining the tail seal between the large-diameter atmospheric pressure cutterhead shield (1) and the small-diameter conventional cutterhead shield (2) and the corresponding shield segments, gradually dismantle the equipment inside the shield shells of the large-diameter atmospheric pressure cutterhead shield (1) and the small-diameter conventional cutterhead shield (2). Step 6: Construct the gradually changing cross-section connection structure in the docking area using the integral cast-in-place process (5-3).

2. The construction method for underwater docking of unequal-diameter shield tunnels traversing long-distance sand layers according to claim 1, characterized in that, Both the large-diameter atmospheric pressure cutterhead shield (1) and the small-diameter conventional cutterhead shield (2) are equipped with a cryogenic cutterhead and a double-layer shield shell.

3. The construction method for underwater docking of unequal-diameter shield tunnels traversing long-distance sand layers according to claim 1, characterized in that, In steps 2 and 3, the reinforcement effect of the strata around and in front of the large-diameter atmospheric pressure cutterhead shield (1) reinforced by freezing method and the reinforcement effect of the strata around and in front of the cutterhead of the small-diameter conventional cutterhead shield (2) are detected by core drilling or advanced geological prediction.

4. The construction method for underwater docking of unequal-diameter shield tunnels traversing long-distance sand layers according to claim 1, characterized in that, During step 4, secondary grouting is performed simultaneously behind the wall to ensure that the shield shells of the large-diameter atmospheric pressure cutterhead shield (1) and the small-diameter conventional cutterhead shield (2) are in a dense state with the surrounding soil.

5. The construction method for underwater docking of unequal-diameter shield tunnels traversing long-distance sand layers according to claim 1, characterized in that, During step 5, the larger diameter segment and the smaller diameter segment closest to the docking area of ​​the reinforced concrete pipe segment (5-1, 5-2) are simultaneously fixed to the shield shell of the corresponding large-diameter atmospheric pressure cutterhead shield (1) or the corresponding small-diameter conventional cutterhead shield (2) by welding anti-reverse steel plates.

6. The construction method for underwater docking of unequal-diameter shield tunnels traversing long-distance sand layers according to claim 1, characterized in that, When performing step 5, a continuous steel plate is welded to the inner surface of the segment of the larger diameter section and / or the segment of the smaller diameter section.

7. The construction method for underwater docking of unequal-diameter shield tunnels traversing long-distance sand layers according to claim 1, characterized in that, Before performing step 6, check whether there are cavities on the outer shell of the large-diameter atmospheric pressure cutterhead shield (1) and the small-diameter conventional cutterhead shield (2); if so, grouting is performed to fill each cavity; in addition, anti-corrosion and waterproof coatings such as polyurea are sprayed inside the shield shell.

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