Construction method for shield tunneling through river course in water-rich sand layer area

Abstract

The present application relates to a kind of water-rich sand layer area shield ultra-shallow buried crossing river construction method, comprising the following steps: step 1, shield ultra-shallow buried crossing river construction method before construction method;Step 2, shield ultra-shallow buried crossing river tunneling construction method.The present application has the superior technical effect in that: before shield passes, need not to improve shield traditional technology, process is simple and applicable, saves shield construction period 10%;Shield under-crossing advanced river when river bottom will not be uplifted, also will not occur spouting the turnover time of the Larsen steel sheet pile used is short, safe and reliable, low cost;The tunneling technical parameter in the construction process of shield machine under-crossing construction, such as shield machine construction speed, cutterhead speed, driving thrust, torque control, shield machine horizontal posture control parameter, has universal reference, guiding significance in shield water-rich sand layer area shield ultra-shallow buried crossing river construction.

Description

Technical Field

[0001] This invention belongs to the field of subway construction technology, specifically relating to a method for tunnel boring machines to pass under the bottom of a channel at a shallow distance in water-rich sandy areas. Background Technology

[0002] The project involves tunneling under a canal at a shallow distance in a water-rich sandy area. In the construction section, the closest distance between the tunnel arch and the riverbed is only 3.1 meters, far less than one shield diameter (6 meters), classifying it as an ultra-shallow shield tunneling project. Furthermore, the tunnel is entirely situated in medium sandy strata, with the water level within the tunnel body. The river above is a flood discharge channel, approximately 27.0 meters wide at the top, 11 meters wide at the bottom, and 5.5 meters deep, paved with M7.5 cement mortar and masonry. The river's water level fluctuates significantly between day and night. During shield tunneling, there is an extremely high risk of the tunnel boring machine (TBM) breaching the riverbed, allowing river water to flow back into the tunnel.

[0003] Among the existing publicly available patent documents, Chinese invention patent application number 201010105681 discloses a method for constructing a subway shield tunnel through an operational tunnel with extremely shallow overburden. The method is characterized by the following steps: a. Pre-construction preparation, including: (1) Before the commencement of the project, a survey of the above-ground and underground structures and buildings within the area of ​​the tunnel with extremely shallow overburden and an assessment of obstacles along the tunneling route are conducted. Based on the survey data, the construction risks of the shield tunneling process with extremely shallow overburden are identified and assessed, and a construction plan is formulated; (2) The shield equipment is modified according to the survey data; (3) The tunnel segments are modified; (4) The underground pipelines within the tunneling area are protected. b. Actual construction, including: (1) segmented tunneling, further including: dividing the shield tunneling area with shallow overburden into a test section, a crossing section and a post-crossing control section. When the shield tunneling is in the test section, the optimal parameter configuration of the shield tunneling construction is collected, and the collected optimal parameter configuration is used to guide the shield tunneling construction in the crossing section; (2) implementing anti-buoyancy measures in the crossing area; (3) after the shield tunneling passes through, secondary tracking grouting is carried out in the construction tunnel to the upper part of the tunnel being crossed, further stabilizing the later deformation of the soil; (4) during the construction process, the ground deformation and the settlement of the tunnel being crossed are monitored, and the monitoring data is summarized to the computer terminal of the command center.

[0004] For example, Chinese invention patent application number 201910978416.3 discloses a method for constructing a water-bag gravel mixed soil layer earth pressure shield tunnel across a river, characterized in that the construction method includes the following steps:

[0005] S1) If continuous gushing occurs at the screw conveyor position of the earth pressure shield machine during the tunnel excavation phase and the earth pressure shield machine is used to cross the soil layer below the river, the earth pressure shield machine construction shall be suspended.

[0006] S2) Inject bentonite into the tail of the earth pressure shield machine and the soil chamber, and then rotate the cutterhead at predetermined intervals to prevent the earth pressure shield machine from seizing.

[0007] S3) Inject double-liquid grout behind the diaphragm segment wall within a predetermined range from the tail of the earth pressure shield machine to form a water-stopping ring;

[0008] S4) Divert the river channel to a predetermined distance from the tail of the earth pressure shield tunneling machine.

[0009] S5) Install multiple dewatering wells at intervals along both sides of the original river channel and complete the dewatering operation;

[0010] S6) Adjust the earth pressure chamber pressure of the earth pressure shield machine to resume the earth pressure shield machine construction and continue to tunnel through the soil layer below the original river channel with the predetermined earth pressure chamber pressure.

[0011] None of the above-mentioned invention patent applications have solved the safety problem of ultra-shallow buried shield tunneling in water-rich sandy areas where the tunnel is entirely located in medium sandy strata. Summary of the Invention

[0012] The method for ultra-shallow buried tunnel crossing of water-rich sandy areas described in this invention mainly involves reinforcing the channel bottom with Larssen sheet piles and steel sheet anti-uplift caps. At the same time, it innovates and optimizes conventional slag improvement technology, reduces the amount of foam used during the tunnel boring machine's passage, increases the concentration of bentonite, increases the injection of composite soil (high molecular polymer), optimizes tunneling parameters, and continuously controls the opening of the upper and lower gates of the screw conveyor according to the slag discharge situation during the tunneling process. These measures ensure the safe and efficient passage of the tunnel boring machine.

[0013] The construction method for ultra-shallow buried shield tunneling across river channels in water-rich sandy areas, as described in this invention, includes the following steps:

[0014] Step 1: Construction steps before shield tunneling crosses an ultra-shallow river channel:

[0015] Step 1.1 Construct a half-width diversion channel on one side of the Larssen sheet pile cofferdam:

[0016] Use a long-arm excavator to remove the rubble masonry from both sides and the bottom of the river.

[0017] The Larssen sheet piles are interlocked. After interlocking each Larssen sheet pile, a layer of mixed oil is applied. The volume ratio of the mixed oil is grease: dry bentonite: dry sawdust = 5:5:3.

[0018] 9m long Larssen sheet piles were erected along the longitudinal middle of the open channel, gradually advancing from upstream to downstream. A long-arm vibratory pile driver was used to drive the 9m long Larssen sheet piles into the channel bottom to a depth of 6m, leaving a 3m height above the channel bottom. Then, another section of sheet pile was driven in, and this process was repeated until the cofferdam was closed. After closure, the water remaining in the open channel was pumped out. Then, along the longitudinal direction of the river, Larssen sheet piles were constructed from one end to the other, forming a "U" area to close the construction range of the pull-out pile driver along the longitudinal direction of the river. The water remaining in the closed area was pumped out, the site was leveled, and the pull-out pile driver was installed.

[0019] Step 1.2, Construction of one side half of the anti-tension piles and anti-uplift cover plate:

[0020] The anti-tension piles were constructed using mud-wall drilling and grouting. After the holes were drilled using a rotary drilling rig, the pile heads were excavated and broken to expose the concrete pile heads. Then, a hydraulic breaker was used to break the concrete laitance within 500mm of the pile top until the original concrete was exposed. The anti-uplift cover plate was then constructed. The anti-uplift cover plate was made of 50cm thick reinforced concrete. The anti-uplift cover plate was connected to the main reinforcement of the steel cage exposed by the removed concrete at the top of the anti-tension pile. After the concrete was poured, the anti-uplift cover plate and the anti-tension pile formed a whole, covering the entire river area through which the shield tunnel passed.

[0021] Step 1.3, diversion construction on the other half:

[0022] Three rows of anti-uplift piles are arranged longitudinally along the river channel, parallel to the direction of shield tunneling, and the construction is carried out in sections. First, Larssen steel sheet piles are used to close half of the river channel, and then two rows of longitudinal anti-uplift piles and anti-uplift cover plates are constructed. Then, the water flow in the river channel is restored, and steel sheet piles are used to close the other side of the river channel. After the other side is completed, a row of anti-uplift piles and anti-uplift cover plates are constructed.

[0023] Step 1.4, Construction of the anti-uplift friction piles and anti-uplift cover plates on the other half:

[0024] The preferred method is to use mud-walled bored piles, which are drilled using a rotary drilling rig. After completion, the pile head is excavated and broken to expose the concrete pile head of the anti-uplift pile. The anti-uplift cover plate is then constructed. The cover plate is made of 50cm thick reinforced concrete, and the anti-uplift cover plate reinforcement is anchored to the anti-uplift pile reinforcement. A hidden beam is set at the pile body of the cover plate to enhance the overall integrity of the cover plate.

[0025] Step 1.5: Remove the sheet piles, treat the joints of the anti-uplift cap plates, and complete the reinforcement.

[0026] When the water level outside the cofferdam is high, water is first poured into the cofferdam to maintain a water level difference of 1 to 1.5 meters between the inside and outside to reduce the squeezing pressure of the Larssen sheet piles. Then, the Larssen sheet piles are gradually removed from the downstream to the upstream. During the construction of the Larssen sheet piles, water-permeable gaps are left on the left and right cover plates. After the Larssen sheet piles are removed, C40 underwater concrete is poured and vibrated to compact the concrete.

[0027] Step 2, Shield tunneling for ultra-shallow river crossing:

[0028] Step 2.1 Technical parameter control during tunnel boring machine (TBM) tunneling construction:

[0029] 2.1.1 Earth pressure control during tunnel boring machine (TBM) tunneling construction:

[0030] When the tunnel boring machine is tunneling, the burial depth is from deep to shallow and then from shallow to deep. Every 4-5 rings, the theoretical value of the soil pressure needs to be calculated. That is, the pressure of the upper soil chamber is controlled between 0.6 and 1.0 bar, and the pressure of the lower soil chamber is controlled between 0.4 and 0.8 bar.

[0031] Step 2.1.2 Control of tunneling technical parameters during the tunnel boring machine's underpass construction:

[0032] The tunnel boring machine's construction speed is controlled at 4-6 cm / min, and the cutterhead rotation speed is controlled at 0.9-1.2 r / min; the tunneling thrust is controlled at 10000-15000 KN, and the torque is controlled at 1500-2800 KN.m; the horizontal and vertical attitudes of the tunnel boring machine are controlled within ±15 mm respectively.

[0033] Step 2.1.3 Simultaneous grouting construction: Grouting is carried out while excavation is underway, with a simultaneous grouting volume of 7m³ per ring. 3 The grouting pressure is controlled at 0.3–0.4 MPa;

[0034] The grouting adopts a dual-control construction process of grouting volume and grouting pressure. Before the tunnel boring machine goes under, the grouting mix ratio of the normal section and the crossing section is optimized, and the gelation time and consistency of the grout are adjusted. The gelation time is adjusted from the conventional 12h to 6-10h; the grout consistency is 8-12cm.

[0035] Step 2.1.4 The tail grease injection pressure of the tunnel boring machine shall not be less than 20 bar, and the tail grease pressure shall be maintained above 3 bar during the process transition.

[0036] Step 2.2 Measures for handling excavated soil in normal tunnel boring machine (TBM) sections and river crossing sections:

[0037] Step 2.2.1 During the tunnel boring machine's advance in normal sections, the soil amendment adopts the form of bentonite + foam. After each ring segment (1.5m) is excavated, inject 30-50L of foam solution / ring and 2-3m of bentonite.3 / ring, the slump of the improved sandy soil is 120-140mm;

[0038] Step 2.2.2 Measures for handling excavated soil in the section where the tunnel boring machine passes under the river:

[0039] During the tunnel boring machine's (TBM) crossing of the river, the mass ratio of bentonite to water is 1:5; composite soil is added, with a mass ratio of composite soil to water of 1:20, to give the excavated soil good plasticity, water-stopping properties, and fluidity, making it easier for the TBM's screw conveyor to output the excavated soil.

[0040] After the improvement, when the slump of the slag is 100-120mm, the upper and lower gates of the screw conveyor are opened to 3 / 5; when the slump of the slag is less than 100mm, the upper and lower gates of the screw conveyor are opened to 4 / 5.

[0041] Step 2.3, Segment assembly during tunnel boring machine (TBM) river crossing construction:

[0042] The tunnel boring machine uses C-shaped perforated segments for the river crossing section. Multiple grouting is carried out in multiple directions and angles through the added grouting holes to ensure full grouting.

[0043] Check the adhesion of the waterproofing material on the tunnel segments: check the adhesion quality of the water-swellable sealing strips;

[0044] Immediate secondary grouting treatment should be carried out at the locations of water leakage in the tunnel segments;

[0045] The bolts of the tunnel segments were tightened three times. The first tightening was carried out after the tunnel segments were assembled. The second tightening was carried out when the next ring was advanced to 1.4 meters and the bolts of the previous ring were tightened. The third tightening was carried out after the tunnel segments were removed from the shield tail.

[0046] Step 2.4: After the tunnel boring machine completes the tunneling work across the river, the reverse side of each ring of segments is grouted with a double-liquid grout until the reverse side of each ring of segments is fully grouted.

[0047] The construction method for ultra-shallow buried shield tunneling across rivers in water-rich sandy areas described in this invention has the following superior technical effects compared with existing technologies in this field:

[0048] 1. In traditional construction, when a tunnel boring machine (TBM) passes through a river with a cover of less than 6 meters, the shallow cover can cause the riverbed to bulge and crack. Water from the river can then enter the TBM's soil chamber through these cracks, leading to a blowout. The construction method for ultra-shallow buried TBM crossings in water-rich sandy areas described in this invention utilizes Larssen sheet piles to partially close the riverbed for diversion before the TBM passes through, and constructs anti-uplift piles and anti-bulging cover plates in sections. The anti-uplift piles and anti-bulging cover plates form a unified whole. As the TBM passes through, the pressure on the riverbed is initially borne by the anti-bulging cover plates. Even if the cover plates tend to move upwards due to the thrust of the TBM, the friction between the anti-uplift piles and the soil firmly fixes the cover plates, preventing upward deformation. This ensures that the riverbed does not bulge or blowout when the TBM passes under the preceding river.

[0049] 2. The construction method for ultra-shallow buried shield tunneling across river channels in water-rich sandy areas described in this invention is completed before the shield tunnel passes through, without the need to modify the traditional shield tunneling process. The process is simple and applicable, saving 10% of the shield tunneling construction time.

[0050] 3. The construction method for ultra-shallow buried shield tunneling across rivers in water-rich sandy areas described in this invention uses Larssen steel sheet piles, which have a short turnaround time, are safe and reliable, and are inexpensive.

[0051] 4. The construction method for ultra-shallow buried shield tunneling across rivers in water-rich sandy areas described in this invention, and the tunneling technical parameters summarized during the shield tunneling process, such as shield tunneling speed, cutterhead rotation speed, tunneling thrust, torque control, and shield tunneling horizontal attitude control parameters, have general reference and guiding significance for shield tunneling ultra-shallow buried shield tunneling across rivers in water-rich sandy areas. Attached Figure Description

[0052] Figure 1 Construction steps before a shield tunnel crosses an ultra-shallow river channel;

[0053] Figure 2 The steps for shield tunneling in ultra-shallow buried river crossings. Detailed Implementation

[0054] The following is a detailed description of the construction method for ultra-shallow buried shield tunneling across river channels in water-rich sandy areas, as described in this manual, with reference to the accompanying drawings.

[0055] like Figure 1-2 As shown, the construction method for ultra-shallow buried shield tunneling across river channels in water-rich sandy areas includes:

[0056] Step 1: Construction steps before shield tunneling crosses an ultra-shallow river channel:

[0057] Step 1.1 Construct a half-width diversion channel on one side of the Larssen sheet pile cofferdam:

[0058] Use a long-arm excavator to remove the rubble masonry from both sides and the bottom of the river.

[0059] The Larssen sheet piles are interlocked. After interlocking each Larssen sheet pile, a layer of mixed oil is applied. The volume ratio of the mixed oil is grease: dry bentonite: dry sawdust = 5:5:3.

[0060] 9m long Larssen sheet piles were erected along the central longitudinal section of the open channel, progressing gradually from upstream to downstream. A long-arm vibratory pile driver was used to drive the 9m long Larssen sheet piles 6m into the channel bottom, leaving a 3m clearance above the bottom. If the construction machinery was unable to complete the central Larssen sheet pile construction due to operational limitations, sandbags were backfilled in the completed area to serve as a temporary construction platform. The next section of sheet piles was then driven, and this process was repeated until the cofferdam was closed. After closure, the water remaining in the open channel was pumped out. Then, along the longitudinal direction of the channel, Larssen sheet piles were constructed from one end to the other, forming a "U"-shaped area to close the range of the pull-out pile driver. The water remaining in the closed area was pumped out, the site was leveled, and the pull-out pile driver was then deployed.

[0061] Step 1.2, Construction of one side half of the anti-tension piles and anti-uplift cover plate:

[0062] The anti-tension piles were constructed using mud-wall drilling and grouting. After the holes were drilled using a rotary drilling rig, the pile heads were excavated and broken to expose the concrete pile heads. Then, a hydraulic breaker was used to break the concrete laitance within 500mm of the pile top until the original concrete was exposed. The anti-uplift cover plate was then constructed. The anti-uplift cover plate was made of 50cm thick reinforced concrete. The anti-uplift cover plate was connected to the main reinforcement of the steel cage exposed by the removed concrete at the top of the anti-tension pile. After the concrete was poured, the anti-uplift cover plate and the anti-tension pile formed a whole, covering the entire river area through which the shield tunnel passed.

[0063] Step 1.3, diversion construction on the other half:

[0064] Three rows of anti-uplift piles are arranged longitudinally along the river channel, parallel to the direction of shield tunneling, and the construction is carried out in sections. First, Larssen steel sheet piles are used to close half of the river channel, and then two rows of longitudinal anti-uplift piles and anti-uplift cover plates are constructed. Then, the water flow in the river channel is restored, and steel sheet piles are used to close the other side of the river channel. After the other side is completed, a row of anti-uplift piles and anti-uplift cover plates are constructed.

[0065] Step 1.4, Construction of the anti-uplift friction piles and anti-uplift cover plates on the other half:

[0066] The preferred method is to use mud-walled bored piles, which are drilled using a rotary drilling rig. After completion, the pile head is excavated and broken to expose the concrete pile head of the anti-uplift pile. The anti-uplift cover plate is then constructed. The cover plate is made of 50cm thick reinforced concrete, and the anti-uplift cover plate reinforcement is anchored to the anti-uplift pile reinforcement. A hidden beam is set at the pile body of the cover plate to enhance the overall integrity of the cover plate.

[0067] Step 1.5: Remove the sheet piles, treat the joints of the anti-uplift cap plates, and complete the reinforcement.

[0068] When the water level outside the cofferdam is high, water is first pumped into the cofferdam to maintain a water level difference of 1-1.5m between the inside and outside to reduce the compressive stress on the Larssen sheet piles. Then, the Larssen sheet piles are gradually removed from downstream to upstream.

[0069] During the construction of Larssen sheet piles, water-permeable gaps were left in the two cover plates on the left and right sides. After the Larssen sheet piles were removed, C40 underwater concrete was poured and vibrated to compact the concrete.

[0070] Step 2, Shield tunneling for ultra-shallow river crossing:

[0071] Step 2.1 Technical parameter control during tunnel boring machine (TBM) tunneling construction:

[0072] 2.1.1 Earth pressure control during tunnel boring machine (TBM) tunneling construction:

[0073] When the tunnel boring machine is tunneling, the burial depth is from deep to shallow and then from shallow to deep. Every 4-5 rings, the theoretical value of the soil pressure needs to be calculated. That is, the pressure of the upper soil chamber is controlled between 0.6 and 1.0 bar, and the pressure of the lower soil chamber is controlled between 0.4 and 0.8 bar.

[0074] Step 2.1.2 Control of tunneling technical parameters during the tunnel boring machine's underpass construction:

[0075] The tunnel boring machine's construction speed is controlled at 4-6 cm / min, and the cutterhead rotation speed is controlled at 0.9-1.2 r / min; the tunneling thrust is controlled at 10000-15000 KN, and the torque is controlled at 1500-2800 KN.m; the horizontal and vertical attitudes of the tunnel boring machine are controlled within ±15 mm respectively.

[0076] Step 2.1.3 Simultaneous grouting construction: Grouting is carried out while excavation is underway, with a simultaneous grouting volume of 7m³ per ring. 3 The grouting pressure is controlled at 0.3–0.4 MPa;

[0077] The grouting adopts a dual-control construction process of grouting volume and grouting pressure. Before the tunnel boring machine passes under, the grouting mix ratio of the normal section and the crossing section is optimized. The optimized mix ratio is shown in Table 1 below. The gelation time and consistency of the grout are also adjusted. The gelation time is adjusted from the conventional 12h to 6-10h; the grout consistency is 8-12cm.

[0078] Table 1

[0079] Normal segment 150 320 100 700 450 Crossing Section 200 320 100 800 450

[0080] Step 2.1.4 The tail grease injection pressure of the tunnel boring machine shall not be less than 20 bar, and the tail grease pressure shall be maintained above 3 bar during the process transition.

[0081] Step 2.2 Measures for handling excavated soil in normal tunnel boring machine (TBM) sections and river crossing sections:

[0082] Step 2.2.1 During the tunnel boring machine's advance in normal sections, the soil amendment adopts the form of bentonite + foam. After each ring segment (150cm wide, 600cm outer diameter, 540cm inner diameter) is excavated, inject 30-50L of foam solution per ring and 2-3m of bentonite. 3 / ring, the slump of the improved sandy soil is 120-140mm;

[0083] Step 2.2.2 Measures for handling excavated soil in the section where the tunnel boring machine passes under the river:

[0084] During the tunnel boring machine's (TBM) crossing of the river, the mass ratio of bentonite to water is 1:5; composite soil is added, with a mass ratio of composite soil to water of 1:20, to give the excavated soil good plasticity, water-stopping properties, and fluidity, making it easier for the TBM's screw conveyor to output the excavated soil.

[0085] After the improvement, when the slump of the slag is 100-120mm, the upper and lower gates of the screw conveyor are opened to 3 / 5; when the slump of the slag is less than 100mm, the upper and lower gates of the screw conveyor are opened to 4 / 5.

[0086] Step 2.3, Segment assembly during tunnel boring machine (TBM) river crossing construction:

[0087] The tunnel boring machine uses C-shaped perforated segments for the river crossing section. Multiple grouting is carried out in multiple directions and angles through the added grouting holes to ensure full grouting.

[0088] Check the adhesion of the waterproofing material on the tunnel segments: check the adhesion quality of the water-swellable sealing strips;

[0089] Immediate secondary grouting treatment should be carried out at the locations of water leakage in the tunnel segments;

[0090] The bolts of the tunnel segments were tightened three times. The first tightening was carried out after the tunnel segments were assembled. The second tightening was carried out when the next ring was advanced to 1.4 meters and the bolts of the previous ring were tightened. The third tightening was carried out after the tunnel segments were removed from the shield tail.

[0091] Step 2.4: After the tunnel boring machine completes the tunneling work across the river, during the segment assembly process, it is required that the reverse side of each ring of segments be grouted with double-liquid grout twice until the reverse side of each ring of segments is fully grouted.

Claims

1. A method for constructing a shield tunnel through a shallowly buried river in a water-rich sandy area, characterized in that, Includes the following steps: Step 1, Construction method before shield tunneling through a shallow river channel: Step 1.1 Constructing a half-width diversion dike on one side of a Larssen sheet pile cofferdam: Use a long-arm excavator to remove the rubble masonry from both sides and the bottom of the river. For the Larssen sheet piles, a layer of mixed oil is applied after each Larssen sheet pile is locked. The volume ratio of the mixed oil is grease: dry bentonite: dry sawdust = 5:5:

3. 9m long Larssen sheet piles were erected along the longitudinal middle of the open channel, gradually advancing from upstream to downstream. A long-arm vibratory pile driver was used to drive the 9m long Larssen sheet piles into the channel bottom to a depth of 6m, leaving a 3m height above the channel bottom. Then, another section of sheet pile was driven in, and this process was repeated until the cofferdam was closed. After closure, the water remaining in the open channel was pumped out. Then, along the longitudinal direction of the river, Larssen sheet piles were constructed from one end to the other, forming a "U" area to close the construction range of the pull-out pile driver along the longitudinal direction of the river. The water remaining in the closed area was pumped out, the site was leveled, and the pull-out pile driver was installed. Step 1.2, Construction of one side half of the anti-tension piles and anti-uplift cover plate: The anti-tension piles were constructed using mud-wall drilling and grouting. After the holes were drilled using a rotary drilling rig, the pile heads were excavated and broken to expose the concrete pile heads. Then, a hydraulic breaker was used to break the concrete laitance within 500mm of the pile top until the original concrete was exposed. The anti-uplift cover plate was then constructed. The anti-uplift cover plate was made of 50cm thick reinforced concrete. The anti-uplift cover plate was connected to the main reinforcement of the steel cage exposed by the removed concrete at the top of the anti-tension pile. After the concrete was poured, the anti-uplift cover plate and the anti-tension pile formed a whole, covering the entire river area through which the shield tunnel passed. Step 1.3, diversion construction on the other half: Three rows of anti-uplift piles are arranged longitudinally along the river channel, parallel to the direction of shield tunneling, and the construction is carried out in sections. First, Larssen steel sheet piles are used to close half of the river channel, and then two rows of longitudinal anti-uplift piles and anti-uplift cover plates are constructed. Then, the water flow in the river channel is restored, and steel sheet piles are used to close the other side of the river channel. After the other side is completed, a row of anti-uplift piles and anti-uplift cover plates are constructed. Step 1.4, Construction of the anti-uplift friction piles and anti-uplift cover plates on the other half: The preferred method is to use mud-walled bored piles, which are drilled using a rotary drilling rig. After completion, the pile head is excavated and broken to expose the concrete pile head of the anti-uplift pile. The anti-uplift cover plate is then constructed. The cover plate is made of 50cm thick reinforced concrete, and the anti-uplift cover plate reinforcement is anchored to the anti-uplift pile reinforcement. A hidden beam is set at the pile body of the cover plate to enhance the overall integrity of the cover plate. Step 1.5: Remove the sheet piles, treat the joints of the anti-uplift cap plates, and complete the reinforcement. When the water level outside the cofferdam is high, water is first poured into the cofferdam to maintain a water level difference of 1 to 1.5 meters between the inside and outside to reduce the squeezing pressure of the Larssen sheet piles. Then, the Larssen sheet piles are gradually removed from the downstream to the upstream. During the construction of the Larssen sheet piles, water-permeable gaps are left on the left and right cover plates. After the Larssen sheet piles are removed, C40 underwater concrete is poured and vibrated to compact the concrete. Step 2: Method for tunneling ultra-shallow buried river crossings using shield tunneling.

2. The construction method for ultra-shallow buried shield tunneling across a river in a water-rich sandy area according to claim 1, characterized in that, in step 2, the ultra-shallow buried shield tunneling method for crossing a river includes the following steps: Step 2.1 Technical parameter control during tunnel boring machine (TBM) tunneling construction: 2.1.1 Earth pressure control during tunnel boring machine (TBM) tunneling construction: When the tunnel boring machine is tunneling, the burial depth is from deep to shallow and then from shallow to deep. Every 4-5 rings, the theoretical value of the soil pressure needs to be calculated. That is, the pressure of the upper soil chamber is controlled between 0.6 and 1.0 bar, and the pressure of the lower soil chamber is controlled between 0.4 and 0.8 bar. Step 2.1.2 Control of tunneling technical parameters during the tunnel boring machine's underpass construction: The tunnel boring machine's construction speed is controlled at 4-6 cm / min, and the cutterhead rotation speed is controlled at 0.9-1.2 r / min; the tunneling thrust is controlled at 10000-15000 KN, and the torque is controlled at 1500-2800 KN·m; the horizontal and vertical attitudes of the tunnel boring machine are controlled within ±15 mm respectively. Step 2.1.3 Synchronous grouting construction: Grouting is carried out while excavating, with a synchronous grouting volume of 7m³ per ring and a grouting pressure controlled at 0.3-0.4MPa; The grouting adopts a dual-control construction process of grouting volume and grouting pressure. Before the tunnel boring machine goes under, the grouting mix ratio of the normal section and the crossing section is optimized, and the gelation time and consistency of the grout are adjusted. The gelation time is adjusted from the conventional 12h to 6-10h; the grout consistency is 8-12cm. Step 2.1.4 The pressure of the shield tail grease injection of the tunnel boring machine shall not be less than 20 bar, and the pressure of the shield tail grease shall be maintained above 3 bar during the process transition; Step 2.2 Measures for handling excavated soil in normal tunnel boring machine (TBM) sections and river crossing sections: Step 2.2.1 During the tunnel boring machine's advance in normal sections, the soil improvement is carried out using bentonite + foam. After each ring of tunnel segments is excavated, 30-50L of foam solution / ring and 2-3m³ of bentonite / ring are injected. The slump of the improved sandy soil is 120-140mm. Step 2.2.2 Measures for handling excavated soil in the section where the tunnel boring machine passes under the river: During the tunnel boring machine's (TBM) crossing of the river, the mass ratio of bentonite to water is 1:5; composite soil is added, with a mass ratio of composite soil to water of 1:20, to give the excavated soil good plasticity, water-stopping properties, and fluidity, making it easier for the TBM's screw conveyor to output the excavated soil. After the improvement, when the slump of the slag is 100-120mm, the upper and lower gates of the screw conveyor are opened to 3 / 5; when the slump of the slag is less than 100mm, the upper and lower gates of the screw conveyor are opened to 4 / 5. Step 2.3, Segment assembly during tunnel boring machine (TBM) river crossing construction: The tunnel boring machine (TBM) used C-shaped perforated segments throughout the river crossing section, employing secondary grouting from multiple directions and angles through additional grouting holes to ensure full grouting. Inspect the adhesion quality of the waterproofing material and water-swellable sealing strips for the tunnel segments; Immediate secondary grouting treatment should be carried out at the locations of water leakage in the tunnel segments; The segment bolts were tightened three times for reinforcement. The first tightening reinforcement is carried out after the segment assembly is completed. The second tightening reinforcement is carried out when the next ring advances to 1.4 meters and the bolts of the previous ring segment are tightened. The third tightening reinforcement is carried out after the segment is removed from the shield tail. Step 2.4: After the tunnel boring machine completes the tunneling work across the river, the reverse side of each ring of segments is grouted with a double-liquid grout until the reverse side of each ring of segments is fully grouted.

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