CN115467339A - Construction method of abutment foundation of river under soft soil condition of near tunnel shallow covering layer - Google Patents
Construction method of abutment foundation of river under soft soil condition of near tunnel shallow covering layer Download PDFInfo
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- 238000010276 construction Methods 0.000 title claims abstract description 79
- 239000002689 soil Substances 0.000 title claims abstract description 40
- 229910000831 Steel Inorganic materials 0.000 claims description 77
- 239000010959 steel Substances 0.000 claims description 77
- 238000009412 basement excavation Methods 0.000 claims description 30
- 238000005553 drilling Methods 0.000 claims description 20
- 238000000034 method Methods 0.000 claims description 15
- 239000004568 cement Substances 0.000 claims description 9
- 230000002829 reductive effect Effects 0.000 claims description 9
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 8
- 230000002787 reinforcement Effects 0.000 claims description 6
- 239000002002 slurry Substances 0.000 claims description 5
- 238000009987 spinning Methods 0.000 claims description 5
- 239000007921 spray Substances 0.000 claims description 5
- 239000004927 clay Substances 0.000 claims description 4
- 239000012528 membrane Substances 0.000 claims description 3
- 230000003014 reinforcing effect Effects 0.000 claims description 3
- 238000005336 cracking Methods 0.000 abstract description 4
- 238000005259 measurement Methods 0.000 abstract description 2
- 239000010410 layer Substances 0.000 description 18
- 238000003466 welding Methods 0.000 description 7
- 230000001681 protective effect Effects 0.000 description 6
- 230000002411 adverse Effects 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 238000007689 inspection Methods 0.000 description 2
- 238000005507 spraying Methods 0.000 description 2
- 230000001133 acceleration Effects 0.000 description 1
- 238000010009 beating Methods 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000008595 infiltration Effects 0.000 description 1
- 238000001764 infiltration Methods 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 230000009545 invasion Effects 0.000 description 1
- 230000000670 limiting effect Effects 0.000 description 1
- 230000002093 peripheral effect Effects 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 239000002356 single layer Substances 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
- 239000002023 wood Substances 0.000 description 1
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D17/00—Excavations; Bordering of excavations; Making embankments
- E02D17/02—Foundation pits
- E02D17/04—Bordering surfacing or stiffening the sides of foundation pits
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D15/00—Handling building or like materials for hydraulic engineering or foundations
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D19/00—Keeping dry foundation sites or other areas in the ground
- E02D19/02—Restraining of open water
- E02D19/04—Restraining of open water by coffer-dams, e.g. made of sheet piles
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D27/00—Foundations as substructures
- E02D27/32—Foundations for special purposes
- E02D27/34—Foundations for sinking or earthquake territories
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Abstract
The invention provides a construction method of a river abutment foundation under a soft soil condition close to a shallow covering layer of a tunnel, which comprises the following steps of S1, measurement and positioning: positioning according to the calculated abutment pile foundation position, excavating a ditch, and probing pipelines within the range of a foundation pit; s2, pile foundation construction; s3, constructing a foundation pit supporting structure; and S4, excavating and constructing the foundation pit. The invention can effectively solve the protection problem of the adjacent subway shield tunnel region under the condition of ensuring the construction efficiency and quality of the abutment foundation, avoids the conditions of seriously influencing the subway operation safety, such as the cracking of the structure, the leakage of joints and the like of the subway shield tunnel region caused by the construction influence, and can also reduce the influence of the construction on surrounding structures.
Description
Technical Field
The invention belongs to the technical field of bridge engineering, and particularly relates to a construction method of a river abutment foundation under the condition of soft soil close to a shallow covering layer of a tunnel.
Background
The bridge is a building which is erected for spanning mountain stream, unfavorable geology or meeting other traffic needs and enables the traffic to be more convenient. The bridge generally consists of an upper structure, a lower structure, a support and an auxiliary structure, wherein the upper structure is also called a bridge spanning structure and is a main structure for spanning obstacles; the substructure includes a bridge abutment, a pier and a foundation. The subway is a rapid, large-traffic and electric power traction rail transit built in cities. With the continuous acceleration of the construction of modern cities, the construction of subways is also in continuous planning and advancing. As described above, in the construction and planning of traffic facilities in large cities, due to the increasing number of subways, there sometimes occurs a situation where newly-built municipal bridges cross or conflict with the existing subways. Under the condition, the construction of bridge substructure, such as abutment foundation (foundation pit and pile foundation), will inevitably affect the adjacent subway shield tunnel region, mainly show that the settlement and convergence deformation of the tunnel are caused, and finally the disasters of the subway shield, such as structural cracking, seam leakage, invasion limit and the like, are seriously affected along with the deterioration of the deformation. Moreover, if the river-crossing bridge is close to the subway shield tunnel region, not only the influence of the river-crossing bridge on the tunnel structure needs to be considered to fully ensure the safety of the subway shield tunnel, but also the adverse influence of the adjacent river reach on the construction of the abutment foundation needs to be considered when the abutment foundation is constructed.
Therefore, for the construction of the abutment foundation adjacent to the river between the subway shield tunnels, in order to reduce the influence of the construction on the subway tunnels, ensure the construction period and ensure the construction quality of the abutment foundation, the problems to be researched are that which foundation pit supporting mode, pile foundation and foundation pit excavation construction process are selected.
Disclosure of Invention
Aiming at the problems, the invention provides a construction method of a near-river abutment foundation under the condition of soft soil of a near tunnel shallow covering layer, which can effectively solve the protection problem of a near-subway shield tunnel area under the condition of ensuring the construction efficiency and quality of the abutment foundation, avoid the conditions of seriously influencing the subway operation safety, such as the structural cracking, seam leakage and the like of the subway shield tunnel area caused by construction influence, and simultaneously reduce the influence of construction on peripheral structures.
The invention is realized by the following technical scheme.
The construction method of the abutment foundation of the river under the condition of soft soil close to the shallow covering layer of the tunnel is characterized by comprising the following steps of:
s1, measuring and positioning
Positioning according to the calculated abutment pile foundation position, excavating a ditch, and probing pipelines within the range of a foundation pit;
s2, pile foundation construction
Carry out engineering pile construction and carry out fender pile construction on the abutment side of not being near the river, engineering pile and fender pile's concrete construction mode as follows: adopting a spinning immersed tube mode, and using a rotary digging pressure head of a rotary digging machine as driving power to beat the steel casing section by section until the steel casing is beaten to a designed position; wherein, after each section of steel casing is beaten, the steel casing is controlled to be exposed out of the ground by 40-60 cm; after the first section of steel casing is drilled, a rotary drilling bucket takes soil in the first section of steel casing; after the last section of steel casing is drilled, namely the steel casing is drilled to the designed position, a rotary drilling bucket takes soil in all the sections of the steel casing, and timely puts down a reinforcement cage and underwater concrete for pouring, and the steel casing is not pulled out after the fender pile and the engineering pile are constructed;
s3, construction of foundation pit supporting structure
Firstly, driving high-pressure rotary jet grouting piles to 2.5-3.5 m below the ground in a shallow covering layer soft soil area at the bottom of a bridge foundation pit to pre-reinforce soft soil, and driving high-pressure rotary jet grouting piles in gaps among fender post piles; then, inserting steel pipes and high-pressure jet grouting piles into the micro piles constructed on the side, close to the river, in the abutment foundation pit for water stopping and reinforcing; finally, pile heads of the engineering piles and the fender piles are broken, crown beams are constructed at the pile heads of the fender piles, and the crown beams of abutment pile foundations on two sides of the river are supported and connected by steel pipes to form an integral structure;
s4, excavation construction of foundation pit
Firstly, excavating a foundation pit of an abutment at one side of the river, then excavating a foundation pit of an abutment at the other side of the river, adopting slope-releasing excavation on the side, facing the river, in the foundation pit of the abutment, and vertically excavating at a fender post part at the side, not facing the river, in the foundation pit of the abutment; the earthwork excavation adopts a comprehensive layered symmetrical excavation mode, the excavation depth of each layer is not more than 2m, one layer is supported on each layer of the net hanging spray surface, firstly, earthwork far away from one side of the tunnel is excavated, and then, earthwork near one side of the tunnel is excavated; and for each layer of shallow covering layer soft soil, the excavation depth is not more than 1m, the excavation length of each section is less than 10m, and excavation is carried out at intervals.
Preferentially, in the step S1, the exploratory trenches are excavated along the two sides of the foundation pit longitudinally attached to the abutment foundation pit, 1 exploratory trench crossing the foundation pit is excavated at intervals of 8-12 m, and the exploratory trench depth is 2-3 m.
Preferentially, in the step S2, the top of each section of steel protective cylinder is cut to form an ear plate, a joint hole is drilled in the ear plate, and a rotary excavating pressure head of the rotary excavating machine is connected and fixed on the steel protective cylinder through a bolt and the joint hole, so that the rotary excavating pressure head can be used as driving power to beat the steel protective cylinder section by section.
Preferentially, in the step S2, the engineering pile and the fender pile close to the tunnel are constructed firstly, and then the engineering pile and the fender pile far away from the tunnel are constructed.
Preferably, in the step S2, the length of each section of steel casing is 2.5 to 4m.
Preferentially, in the step S2, the steel casing is driven to 5-8 m below the bottom of the tunnel in the construction of the engineering pile, the steel casing is driven to 9-15 m below the ground in the construction of the fender pile, and the distance from the position of the tunnel to the top of the tunnel is not less than 2m when the steel casing meets the tunnel, namely the distance from the bottom end of the fender pile positioned right above the tunnel space to the top of the tunnel is not less than 2m.
Preferentially, for the construction of the enclosure pile, a three-step speed reduction mode is adopted at the position meeting the tunnel (namely the bottom of the enclosure pile positioned right above the tunnel space), namely the output torque of a power head of the rotary excavating machine is controlled to be 350-380 KN.M, the rotating speed of the power head is controlled to be 22-25 r/min, the first-stage construction is carried out, so that the enclosure pile is 4M below the ground, then the rotating speed of the power head is reduced to be 18-20 r/min, the second-stage construction is carried out, so that the enclosure pile is 8M below the ground, and finally the rotating speed of the power head is reduced to be 14-16 r/min, the third-stage construction is carried out, so that the depth of the enclosure pile meets the design requirement; the construction of the engineering piles and the surrounding piles at other positions can also adopt the three-step speed reduction mode, but the positions of the engineering piles are positioned at two sides of the tunnel or can be designed by avoiding the position of the tunnel, so the construction of the engineering piles has little influence on the tunnel, and in order to improve the construction efficiency, the output torque of the power head of the rotary excavator can be controlled to be 350-380 KN & M, and the rotating speed of the power head is controlled to be 20-22 r/min for construction.
Preferably, in the step S3, the high-pressure jet grouting pile adopts a double-pipe construction process, the cement slurry pressure is above 20MPa, the air pressure is not less than 0.7MPa, and the capacity of the air compressor is not less than 12m 3 (ii) a The lifting speed of the jet grouting pile is 8cm/min, the jet grouting speed is 15rpm, the water-cement ratio of cement slurry is 1, the unconfined compressive strength qu of a pile body in 28 days is not less than 1.2MPa, and the verticality deviation of the pile body is not more than 1%.
Preferably, in the step S4, a clay bag cofferdam is arranged at the revetment side outside the abutment foundation pit, and a waterproof civil membrane is laid at the revetment side and the river bottom outside the abutment foundation pit.
Preferentially, in the step S4, before earth excavation, an intercepting ditch should be built on the outer side of the abutment foundation pit in time; and after the earth excavation of the abutment foundation pit is in place, a drainage ditch and a water collecting well are built at the bottom of the abutment foundation pit in time.
Preferentially, in the step S4, after the earthwork is excavated, a waist beam is constructed at the middle part of the foundation pit along the inner periphery of the foundation pit, an inner supporting beam which obliquely spans the foundation pit is erected, and then the net is hung and the concrete panel is poured.
The invention has the beneficial effects that:
1) According to the invention, through an integrated full-circle full-casing following mode that the rotary immersed tube and the steel casing are not pulled out, and by combining a construction process for digging and taking soil in the hole in a rotary mode, the process has the advantages of small floor area, light weight, small vibration, strong flexibility, high construction speed and the like, so that the adverse effect of vibration of large static pressure equipment on a tunnel can be avoided, the problem that the tunnel is deformed or displaced due to positive and negative pressure in the traditional pile foundation construction is solved, and a certain limiting effect on the displacement of a soil body in a subway protection range can be realized; in addition, for the construction of the fender pile at the position meeting the tunnel, the three-step speed reduction mode is adopted to carry out the driving on the steel fender casing, the influence on the tunnel from the position far away from the tunnel in the vertical direction is smaller, so the driving is carried out by utilizing the higher rotating speed reduction of the power head, then the steel fender casing is gradually close to the tunnel area along with the continuous driving of the steel fender casing, and the rotating speed reduction of the power head is further needed, thereby being beneficial to maintaining the stability of soil body near the upper part of the tunnel.
2) Different from the traditional foundation pit support, the method has the advantages that the high-pressure jet grouting piles are constructed in the gaps among the retaining piles, and the high-pressure jet grouting piles are adopted at the bottom of the foundation pit for soft soil pre-reinforcement, so that the upward floating deformation of the subway shield can be controlled; the steel pipe supports are used for replacing the conventional concrete to connect the top beams of the abutment platforms at two sides, so that the load of the structure is reduced, a better integral stress structure can be formed, and the stability of foundation pit support is improved; through the interior miniature stake of face river side construction of abutment foundation ditch interpolation steel pipe and high pressure jet grouting pile be used for stagnant water reinforcement, domatic string net sprays concrete, can effectively prevent the slope infiltration.
3) According to the method, the earthwork of the abutment at two sides of the river is excavated respectively, so that the single excavation amount is reduced, and the subway tunnel structure floating caused by the rebound of the soil body due to the unloading of the foundation pit can be reduced by adopting a comprehensive layered and symmetrical excavation mode.
In conclusion, the invention can effectively solve the protection problem of the adjacent subway shield tunnel region under the condition of ensuring the construction efficiency and quality of the abutment foundation, avoid the conditions of seriously influencing the subway operation safety, such as the cracking of the subway shield tunnel region structure, the leakage of joints and the like caused by the construction influence, and simultaneously reduce the influence of the construction on surrounding structures.
Drawings
FIG. 1 is a schematic plan view of the construction method of the present invention;
FIG. 2 is a schematic sectional view of the construction method of the present invention (only the abutment foundation on the side of the river is shown);
FIG. 3 is a schematic view of the construction of a spinning immersed tube;
FIG. 4 is a schematic plan view of a soft soil pre-consolidated by constructing a high-pressure jet grouting pile according to the construction method of the present invention;
the meanings of the marks in the figures are as follows: 1-engineering pile, 2-fender pile, 3-rotary excavating press head, 4-high-pressure rotary spraying pile, 5-micro pile, 6-crown beam, 7-steel pipe support, 8-intercepting ditch, 9-abutment foundation pit, 10-waist beam, 11-internal supporting beam, 12-tunnel, 13-abutment, 14-foundation pit, 15-clay bag cofferdam, 16-waterproof civil membrane, 17-rotary excavator drill rod, 18-rotary excavator power head, 19-mud pit, 20-steel casing, 21-hanging net spraying concrete, 22-rotary excavator, 23-rotary excavator power head, 24-lug plate, 25-rotary excavator drill rod, 26-joint hole and 27-mud pit.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Examples
The construction method of the abutment foundation of the river under the condition of soft soil close to the shallow covering layer of the tunnel comprises the following steps:
s1, measuring and positioning
Positioning according to the calculated position of the abutment pile foundation, namely well performing measurement, rechecking and marking bottom crossing work, measuring and placing pile positions by adopting a total station, and tightly nailing by using wood piles, wherein the control error is not more than 3cm; excavating a ditch, manually probing pipelines in the range of the foundation pit, excavating the ditch along the longitudinal direction of the foundation pit by attaching two sides of the foundation pit, excavating 1 ditch which transversely penetrates through the foundation pit every 10m, and ensuring the ditch depth to be 2m;
s2, pile foundation construction
Carry out the construction of engineering stake 1 and carry out fender pile 2 construction on the abutment side of not being near the river, the concrete construction mode of engineering stake 1 and fender pile 2 is as follows:
in the step, the model of the rotary excavating machine 22 is XR400E, the total weight of the equipment is 113t, the maximum power torque is 400 KN.M, the rotating speed of a power head is 7-25 r/min, the maximum stress is 400KN, the maximum lifting force is 400KN, and the maximum drilling depth can reach 102 meters; firstly, cutting the top of each section of steel casing to form an ear plate 24, drilling a joint hole 26 (phi 120 mm) on the ear plate 24, and connecting and fixing a rotary drilling pressure head 3 (namely a rotary drilling bucket) of a rotary drilling machine 22 with the joint hole 26 through a bolt on the steel casing so that the rotary drilling pressure head can be used as driving power to carry out section-by-section drilling on the steel casing; the bridge pile steel casing is made of a steel plate with the thickness delta =20 mm, the support pile steel casing is made of a steel plate with the thickness delta =10 mm, the bridge pile steel casing is manufactured by mechanically centralized rolling in a factory, all welding seams are double-sided grooves, the length of the steel casing is 3 m/section, and the inner diameter D' = D +200mm (D is the designed pile diameter) of the steel casing;
adopting a spinning immersed tube mode, and using a rotary digging pressure head of a rotary digging machine as driving power to beat the steel casing section by section until the steel casing is beaten to a designed position; specifically, a first section of steel casing (with the length of 3 m) is driven to the exposed ground surface by 50cm, a rotary drilling bucket is used for taking soil in the casing, and artificial CO is used for assistance 2 Welding a second section of steel protective cylinder (the length is 3 m) by gas shielded welding, connecting the rotary drilling pressure head with the second section of steel protective cylinder after welding inspection, then continuously driving the second section of steel protective cylinder to expose 50cm of the ground by adopting a spinning immersed tube mode, and then assisting with manual CO 2 Welding a third section of steel casing (the length is 3 m) by gas shielded welding, connecting the rotary drilling pressure head with the third section of steel casing after welding inspection is finished, repeating the above beating actions to install the subsequent section of steel casing until the steel casing is beaten to the designed position, wherein the steel casing is beaten to 5-8 m below the bottom of the tunnel in the construction of the engineering pile 1; the construction of the fender pile 2 is implemented by driving a steel fender casing to 9-14 m below the ground, the distance from the position of the fender pile 2 to the top of the tunnel is not less than 2m, the engineering pile 1 and the fender pile 2 close to the tunnel 12 are constructed first, and then the engineering far away from the tunnel 12 is constructedPile 1 and fender pile 2; when the last section of steel casing is constructed, namely the steel casing is constructed to the designed position, the rotary drilling bucket takes the soil in all the sections of the steel casing (for the engineering pile, slurry with high concentration of not less than 1.3 is prepared in the normal drilling and soil taking process of the rotary drilling machine so as to ensure the quality of mud skin on the hole wall and prevent hole collapse), and a steel reinforcement cage is timely put down and underwater concrete is poured, so that the steel casing is not pulled out after the construction of the fender pile and the engineering pile is finished;
in the steps, a three-step speed reduction mode is adopted for the fender pile positioned right above the tunnel space, namely the output torque of a power head of the rotary excavator is controlled to be 350-380 KN.M, the power head rotating speed is controlled to be 22-25 r/min, the first-stage driving is carried out, the fender pile is driven to be 4M below the ground, then the power head rotating speed is reduced to be 18-20 r/min, the second-stage driving is carried out, the fender pile is driven to be 8M below the ground, and finally the power head rotating speed is reduced to be 14-16 r/min, the third-stage driving is carried out, and the depth of the fender pile reaches the design requirement; for the construction of engineering piles and guard piles at other positions, the output torque of the power head of the rotary excavating machine can be controlled to be 350-380 KN.M, and the rotating speed of the power head is 20-22 r/min for driving.
S3, construction of supporting structure
S31, driving high-pressure jet grouting piles 4 with the specification of phi 600mm @500mm to 2.5-3.5 m below the ground in a shallow covering layer soft soil area at the bottom of the abutment foundation pit to pre-reinforce the soft soil, and driving high-pressure jet grouting piles 4 with the specification of phi 600@1300 in gaps among piles of the fender pile 2; the high-pressure rotary jet grouting pile adopts a double-pipe construction process, the cement paste pressure is more than 20MPa, the air pressure is not less than 0.7MPa, and the capacity of an air compressor is not less than 12m 3 (ii) a The lifting speed of the jet grouting pile is 8cm/min, the jet grouting speed is 15rpm, the water-cement ratio of cement slurry is 1;
s32, inserting steel pipes into the miniature piles 5 constructed on the side, facing the river, in the abutment foundation pit and constructing high-pressure jet grouting piles 4 for water stopping and reinforcing; the specific construction method is that a drilling machine is adopted to form a hole at the design position on the side close to the river in the abutment foundation pit, the effective diameter of the formed hole is not less than 250mm, and the drilling depth exceeds 300mm according to the design requirement; sinking phi 250 x 10 casing pipes into the drill holes by using a drilling machine, inserting phi 219 x 10 steel pipes which are to be aligned with the casing pipes, installing grouting pipes along the steel pipe piles and sinking into the holes together, and finally performing C20 fine aggregate concrete pouring;
s33, pile heads of the engineering piles 1 and the fender piles 2 are broken, crown beams 6 are constructed at the pile heads of the fender piles, and the crown beams 6 of abutment pile foundations on two sides of the river are connected through steel pipe supports 7 to form an integral structure;
s4, excavation construction of foundation pit
After the age of the pile foundation is reached, detecting the strength of the high-pressure jet grouting pile after the foundation is reinforced, and excavating the earth after the strength reaches a design value; before the earthwork of the foundation pit is excavated, an intercepting ditch 8 is constructed on the outer side of the foundation pit in time, and the size of the intercepting ditch is 300mm multiplied by 300mm; firstly, excavating a foundation pit of an abutment at one side of the river, and then excavating a foundation pit of an abutment at the other side of the river to reduce the single excavation amount; adopting slope excavation on the river-facing side in the abutment foundation pit, and vertically excavating at the fender post on the non-river-facing side in the abutment foundation pit; the earthwork excavation adopts a comprehensive layered symmetrical excavation mode, the excavation depth of each layer is not more than 2m, one layer of net hanging spray surface is supported when each layer of net hanging spray surface is excavated, earthwork far away from one side of the tunnel is excavated firstly, and earthwork near one side of the tunnel is excavated; for the soft soil of the shallow covering layer, the excavation depth of each layer is not more than 1m, the excavation length of each section is less than 10m, and the shallow covering layer is excavated at intervals; after excavation of foundation pit earthwork is in place, constructing a drainage ditch and a water collecting well in time at the bottom of a pit, wherein the size of the drainage ditch is 300mm multiplied by 300mm, the size of the water collecting well is 500mm multiplied by 500mm, constructing a double-spliced HW350 steel girth beam 10 along the periphery in the foundation pit in the middle of the foundation pit, erecting an inner supporting beam 11 of an inclined cross foundation pit, then hanging a net (single-layer phi 8mm @250mm multiplied by 250 mm) and pouring a 60mm thick C20 concrete panel (namely, hanging net injection concrete 21 in figure 2), arranging a clay bag cofferdam 15 at the revetment side outside the abutment foundation pit, and laying a waterproof bank film 16 at the revetment side and the river bottom outside the abutment foundation pit.
Claims (10)
1. The construction method of the abutment foundation of the river under the condition of soft soil close to the shallow covering layer of the tunnel is characterized by comprising the following steps:
s1, measuring and positioning
Positioning according to the calculated abutment pile foundation position, excavating a ditch, and probing pipelines within the range of a foundation pit;
s2, pile foundation construction
Carry out engineering pile construction and carry out fender pile construction on the abutment side of not being near the river, engineering pile and fender pile's concrete construction mode as follows: adopting a spinning immersed tube mode, and using a rotary digging pressure head of a rotary digging machine as driving power to beat the steel casing section by section until the steel casing is beaten to a designed position; wherein, after each section of steel casing is beaten, the steel casing is controlled to be exposed out of the ground by 40-60 cm; after the first section of steel casing is constructed, a rotary drilling bucket takes soil in the first section of steel casing; after the last section of steel casing is drilled, namely the steel casing is drilled to the designed position, a rotary drilling bucket takes soil in all the sections of the steel casing, and timely puts down a reinforcement cage and underwater concrete for pouring, and the steel casing is not pulled out after the fender pile and the engineering pile are constructed;
s3, construction of supporting structure
Firstly, driving high-pressure rotary jet grouting piles in a shallow covering layer soft soil area at the bottom of a bridge foundation pit to 2.5-3.5 m below the ground for soft soil pre-reinforcement, and driving high-pressure rotary jet grouting piles in gaps among fender pile piles; then inserting steel pipes and high-pressure jet grouting piles into the miniature piles constructed on the side, facing the river, in the abutment foundation pit for water stopping and reinforcing; finally, pile heads of the engineering piles and the fender piles are broken, crown beams are constructed at the pile heads of the fender piles, and the crown beams of the abutment pile foundations on two sides of the river are supported and connected through steel pipes to form an integral structure;
s4, excavation construction of foundation pit
Firstly, excavating a foundation pit of an abutment at one side of the river, then excavating a foundation pit of an abutment at the other side of the river, adopting slope-setting excavation on a river-facing side in the foundation pit of the abutment, and vertically excavating a fender post at a non-river-facing side in the foundation pit of the abutment; the earthwork excavation adopts a comprehensive layered symmetrical excavation mode, the excavation depth of each layer is not more than 2m, one layer is supported on each layer of the net hanging spray surface, firstly, earthwork far away from one side of the tunnel is excavated, and then, earthwork near one side of the tunnel is excavated; for the shallow covering layer soft soil, the excavation depth of each layer is not more than 1m, the excavation length of each section is less than 10m, and the shallow covering layer soft soil is excavated at intervals.
2. The method for constructing the abutment foundation of the river under the condition of soft soil near the shallow cover layer of the tunnel according to claim 1, wherein in the step S1, the exploratory trench is excavated along the longitudinal direction of the foundation pit of the abutment near the two sides of the foundation pit, 1 exploratory trench crossing the foundation pit is excavated every 8-12 m, and the exploratory trench is 2-3 m deep.
3. The construction method of the abutment foundation of the river under the condition of the soft soil close to the shallow coverage of the tunnel according to claim 1, wherein in the step S2, the top of each section of the steel casing is cut to form an ear plate, a joint hole is drilled in the ear plate, and a rotary excavating pressure head of the rotary excavator is connected and fixed on the steel casing through a bolt and the joint hole, so that the rotary excavating pressure head can be used as driving power to beat the steel casing section by section.
4. The method for constructing a foundation of a river abutment under the condition of soft soil near a shallow covering layer of a tunnel according to claim 1, wherein in the step S2, engineering piles and fender piles close to the tunnel are constructed first, and then engineering piles and fender piles far away from the tunnel are constructed.
5. The construction method of the abutment foundation of the river under the condition of soft soil near the shallow covering layer of the tunnel according to claim 1, wherein in the step S2, the length of each section of steel casing is 2.5-4 m.
6. The construction method of the abutment foundation of the river under the condition of soft soil near the shallow covering layer of the tunnel according to claim 1, wherein in the step S2, the steel casing is driven to be 5-8 m below the bottom of the tunnel in the construction of the engineering pile; and (3) driving the steel casing to 9-14 m below the ground in the construction of the fender pile, wherein the distance from the position of the fender pile, which meets the tunnel, to the top of the tunnel is not less than 2m.
7. The method for constructing a river abutment foundation under the condition of soft soil near a shallow tunnel covering layer as claimed in claim 6, wherein in the step S2, for the construction of the engineering pile, the output torque of the power head of the rotary excavating machine is controlled to be 350-380 KN.M, and the rotating speed of the power head is controlled to be 20-22 r/min; for the driving of the enclosure pile, a three-step speed reduction mode is adopted at the position meeting the tunnel, namely the output torque of the power head of the rotary excavator is controlled to be 350-380 KN.M, the first-stage driving is carried out at the power head rotating speed of 22-25 r/min, the enclosure pile is driven to be 4M below the ground, then the power head rotating speed is reduced to be 18-20 r/min, the second-stage driving is carried out, the enclosure pile is driven to be 8M below the ground, and finally the power head rotating speed is reduced to be 14-16 r/min, the third-stage driving is carried out, and the depth of the enclosure pile reaches the design requirement.
8. The method for constructing a river abutment foundation under the condition of soft soil near a shallow tunnel covering layer as claimed in claim 1, wherein in the step S3, the high-pressure jet grouting pile adopts a double-pipe construction process, the cement paste pressure is more than 20MPa, the air pressure is not less than 0.7MPa, and the capacity of an air compressor is not less than 12m 3 (ii) a The lifting speed of the jet grouting pile is 8cm/min, the jet grouting speed is 15rpm, the water-cement ratio of cement slurry is 1, the unconfined compressive strength qu of a pile body in 28 days is not less than 1.2MPa, and the verticality deviation of the pile body is not more than 1%.
9. The method for constructing a river abutment foundation under the condition of soft soil near a shallow tunnel overburden as claimed in claim 1, wherein said step S4 further comprises the steps of arranging a clay bag cofferdam at the revetment side outside the abutment pit, and laying a waterproof civil engineering membrane at the revetment side and the river bottom outside the abutment pit.
10. The method for constructing a river-adjacent abutment foundation under the condition of soft soil near a shallow covering layer of a tunnel according to claim 1, wherein in the step S4, before earth excavation, a cut-off ditch is constructed on the outer side of an abutment foundation pit in time; after the foundation pit of the abutment is excavated in place, a drainage ditch and a water collecting well are built at the bottom of the foundation pit of the abutment in time; after the earthwork is excavated, a waist beam is constructed in the middle of the foundation pit along the inner periphery of the foundation pit, an inner supporting beam which spans the foundation pit obliquely is erected, and then a net is hung and a concrete panel is poured.
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