CN108316339B

CN108316339B - Construction method of water-permeable geological large arch bridge foundation

Info

Publication number: CN108316339B
Application number: CN201810117123.1A
Authority: CN
Inventors: 肖延军; 朱淑兰; 黄忠睦; 吴宇; 何鹏; 邓海洪; 徐荣会; 张恺; 狄宏伟; 孔晓辉; 黄明献; 朱宝林
Original assignee: Fifth Engineering Co Ltd of Shanghai Civil Engineering Co Ltd of CREC
Current assignee: Fifth Engineering Co Ltd of Shanghai Civil Engineering Co Ltd of CREC
Priority date: 2018-02-06
Filing date: 2018-02-06
Publication date: 2021-08-10
Anticipated expiration: 2038-02-06
Also published as: CN108316339A

Abstract

The invention discloses a construction method of a large permeable geological arch bridge foundation, which is characterized by comprising the following steps: the method comprises the following steps: island building cofferdam → constructing sidewalk → constructing reinforced concrete secant pile → constructing high-pressure grouting waterproof curtain and foundation pit inner base grouting construction simultaneously → constructing jet grouting pile waterproof curtain → constructing crown beam and first inner support beam → excavating to second inner support beam elevation → constructing waist beam and second inner support beam → excavating to third inner support beam elevation and third layer inner support beam construction → excavating to design base → constructing abutment foundation and dismantling inner support layer by layer → backfilling foundation pit; the construction method has the advantages that the construction progress is fast, the construction quality is stable, the waterproof curtain outside the pit enables the outer side of the foundation pit to form a circle of closed impermeable structural layer, and meanwhile, the high-pressure jet grouting pile at the top enables the soil layer outside the supporting pile to be hardened, so that the soil layer outside the foundation pit is further reinforced, and the situations of cofferdam landslide and collapse caused by flood erosion are effectively prevented; in addition, the special-shaped reinforcement cage saves concrete materials.

Description

Construction method of water-permeable geological large arch bridge foundation

Technical Field

The invention relates to the technical field of building design and building construction, in particular to a construction method of a large permeable geological arch bridge foundation.

Background

With the rapid development of economy and the enlargement of the scale of infrastructure in China and the development of river-crossing and river-crossing bridges, the engineering scale of deep foundation pits in water is larger and deeper at present, and when buildings are arranged around the deep foundation pits, the protection of the buildings provides a plurality of technical problems for the engineering world. In order to improve the efficiency, shorten the construction period, protect the environment, save energy and reduce emission, ensure the quality and the performance of a structure in the water-permeable deep foundation pit and promote the better development of foundation pit foundation engineering, the comprehensive supporting construction of the reinforced concrete secant pile and the water-stop curtain is the trend of the protective construction development of the water-permeable deep foundation pit; in the prior construction technology, the construction of water permeability geology needs to prevent the situation of large-area loose soil, the problem of engineering over-square is easy to occur after excavation, and the situations of water gushing and water seepage of the substrate and the like are caused by large water pressure difference of the substrate; the waterproof curtain outside the foundation pit is not enough in protection, and in addition, safety accidents such as foundation pit collapse and the like often occur due to technical reasons and the like in the process of excavating the foundation pit; in addition, the foundation pit of the existing reinforced concrete secant pile is filled with piles formed by the same type number, namely cylindrical reinforcement cage concrete, and the piles are used as waterproof curtains, so that certain defects exist in positioning, water resisting and soil collapse prevention, the quality of joints cannot be guaranteed when the reinforcement cage concrete piles are in butt joint with the piles, the problems of complex operation, time and labor consuming, low construction speed and the like are solved when the reinforcement cage concrete piles are in butt joint with the piles, the secant quality between the piles is poor, and concrete raw materials are wasted.

Aiming at the defects in the prior art, the invention provides a construction method of a large water-permeable geological arch bridge foundation, aiming at solving the defects in the prior art.

Disclosure of Invention

The construction method has the advantages that the construction speed is high, the pile forming time is shortened, the cost of concrete materials and the like is saved, and the construction period is shortened; intended to solve the drawbacks of the prior art.

The technical scheme adopted by the invention is as follows:

a construction method of a large-scale permeable geological arch bridge foundation is characterized by comprising the following steps:

the method comprises the following steps: island building cofferdam → constructing sidewalk → constructing reinforced concrete secant pile → constructing high-pressure grouting waterproof curtain and simultaneously constructing foundation grouting in foundation pit → constructing water-stopping curtain of jet grouting pile → constructing crown beam and first inner supporting beam → excavating to second inner supporting beam elevation → waist beam and second inner supporting beam construction → excavating to third inner supporting beam elevation and third inner supporting beam construction → excavating to design foundation → constructing abutment foundation and dismantling inner support layer by layer → backfilling foundation pit;

in the construction of the island-building cofferdam, firstly, arranging a steel mesh gabion at the toe of a slope, then filling clay to the designed top elevation, and protecting the side slope by adopting a mould bag concrete slope protection and a soil bag on the upstream side slope; the process flow of the island building cofferdam comprises the following steps: the slope toe section adopts mould bag concrete slope toe → filling clay to the designed elevation → upstream side slope and excavation side slope finishing → side slope protection construction;

the construction of the reinforced concrete secant pile comprises the following steps: the water facing surface of the foundation pit is a backfill soil side, a percussion drill is adopted for carrying out impact construction pore-forming, and a rotary drilling rig is adopted for carrying out drilling construction pore-forming on the non-water facing surface;

the reinforced concrete secant pile is supported around a foundation pit, the pile diameter is 1.5m, the pile spacing is 1.3m, the reinforced concrete secant pile is divided into two pile types, wherein a reinforcement cage pile containing an arc-shaped steel plate is a special-shaped reinforcement cage pile foundation, and a common reinforcement cage pile foundation is arranged between the special-shaped reinforcement cage pile foundations; the overall construction sequence of the reinforced concrete secant pile is that a special-shaped reinforcement cage pile foundation is constructed from the middle on one side of the foundation pit far away from the river bank, and then a common reinforcement cage pile foundation is constructed; the construction sequence of the secant pile is as follows:

the first step is as follows: firstly, drilling a special-shaped reinforcement cage pile foundation;

the second step is that: jumping piles at two sides of the constructed special-shaped reinforcement cage pile foundation to construct the special-shaped reinforcement cage pile foundation at two sides;

the third step: constructing a common reinforcement cage pile foundation in the middle of the constructed special-shaped reinforcement cage pile foundation, and ensuring that the pile forming time of the special-shaped reinforcement cage pile foundation is more than 24 hours and less than 48 hours when constructing the common reinforcement cage pile foundation in order to ensure the meshing quality and meet the requirement of a drilling machine construction process;

the fourth step: continuously jumping pile construction to form irregular reinforcement cage pile foundations on two sides;

the fifth step: constructing common reinforcement cage pile foundations on two sides, and cleaning the side walls of the special-shaped reinforcement cage by using a cylindrical wall brushing device after the common reinforcement cage pile foundations are formed into holes, so as to ensure the water stop effect of the reinforced concrete secant pile;

and a sixth step: and repeating the second step to the fifth step until the pile foundation is completely finished.

Preferably, the deformed steel bar cage pile foundation is formed by taking a deformed steel bar cage as a main framework, the deformed steel bar cage comprises a plurality of vertical supporting steel bars, a plurality of circles of outer-ring transverse reinforcing stirrups, inner-ring transverse reinforcing stirrups, transverse supporting steel bars and arc-shaped steel plates, the deformed steel bar cage is formed by welding, the arc-shaped steel plates comprise upper arc-shaped steel plates and lower arc-shaped steel plates, the transverse reinforcing stirrups are quadrangles with four sides being arcs formed by rolling closed circular steel bars, the circle center direction of an arc side one arc of a pair of opposite sides of the quadrangle with four sides being arcs is inward, and the circle center direction of an arc side two arcs of the other pair of opposite sides is outward;

the inner ring transverse reinforcing stirrup of the special-shaped reinforcement cage is a quadrilateral formed by two arc-shaped reinforcements and two straight-line reinforcements, the two arc-shaped reinforcements are arc-shaped edges III, and the arc-shaped edges III have the same arc radius as the arc-shaped edges I; vertical support reinforcing bar welds between pitch arc limit three and pitch arc limit one, the outer lane is transversely strengthened the stirrup and is welded connection with vertical support reinforcing bar adoption quincunx spot welding's mode.

The arc-shaped steel plate of the special-shaped reinforcement cage is welded on the arc line edge II which is outward in the arc circle center direction of a pair of opposite edges of the outer ring transverse reinforcement stirrup; the outer ring transverse reinforcing stirrup is welded on the second arc edge through two transverse supporting steel bars for connecting and reinforcing the second arc edge.

The manufacturing method comprises the following steps:

manufacturing of steel plate tire seat

The steel plate base is formed by welding 10# channel steel and an arc-shaped steel plate I with the thickness of 8mm, and is fixed in a reinforcing steel bar field by adopting embedded bars; the steel plate tire seat is formed for standby; the thickness of the arc-shaped steel plate I on the steel plate tire seat is 8mm, the horizontal projection width is 82.2cm, and the length is 1.5 m;

manufacturing process of irregular reinforcement cage

The specific construction process of the special-shaped reinforcement cage is as follows:

the first step is as follows: installing a lower arc-shaped steel plate on the steel plate tire bed, firmly welding a joint between the lower arc-shaped steel plate and the steel plate tire bed, and processing an outer ring transverse reinforcing stirrup;

the second step is that: welding a second arc edge of the outer ring transverse reinforcing stirrup on the lower arc steel plate; 2cm welding seams are arranged between the second arc edge and the lower arc steel plate every 0.2m for segmented welding,

the third step: welding an arc-shaped steel plate on the second arc edge of the outer ring transverse reinforcing stirrup; the welding seam setting is consistent with the second step;

the fourth step: welding a reinforcement cage vertical supporting reinforcement on one arc edge of the outer ring transverse reinforcing stirrup, and directly adopting electric welding between the reinforcement cage vertical supporting reinforcement and the arc edge;

the fifth step: installing the inner ring transverse reinforcing stirrup, wherein the joint of the inner ring transverse reinforcing stirrup adopts single-side welding and is firmly welded; the inner ring transverse reinforcing stirrup and the vertical supporting steel bar are subjected to quincunx spot welding.

Preferably, the specific implementation method for the high-pressure grouting waterproof curtain construction comprises the following steps: arranging a waterproof curtain at the periphery of the reinforced concrete secant pile, and simultaneously performing high-pressure grouting at the bottom of the foundation pit; the waterproof curtain outside the foundation pit is distributed outside the reinforced concrete secant pile and is arranged in two rows, and the waterproof curtain is divided into an in-rock grouting waterproof curtain and a soil layer high-pressure jet grouting pile waterproof curtain;

firstly, grouting holes at the bottom of a foundation pit are arranged in a quincunx mode, the distance is 1.0m, the grouting holes are uniformly distributed in the excavation range of the foundation pit, and the depth is 6m below the bottom of the foundation pit;

constructing a waterproof curtain: arranging soil layer high-pressure jet grouting pile waterproof curtains on the outer sides of the reinforced concrete secant piles, wherein the soil layer high-pressure jet grouting pile waterproof curtains are arranged in 2 rows, and high-pressure grouting is adopted for rock strata; constructing the soil layer waterproof curtain by adopting a double-pipe method after the construction of part of the reinforced concrete secant pile is completed; the soil layer high-pressure jet grouting pile waterproof curtain is arranged in a zigzag manner, the distance between piles is 0.5m, and the diameter of the pile is 0.6 m; 2 rows of soil layer high-pressure jet grouting pile water-stopping curtains are arranged, the row interval is 0.45m, the distance from the secant pile to the axis of one row of reinforced concrete secant pile is 0.25m, and the soil layer high-pressure jet grouting pile water-stopping curtains are overlapped with the reinforced concrete secant pile by 0.05 m;

the in-rock grouting waterproof curtain is arranged at the bottom of the soil layer waterproof curtain, and the bottom elevation is 5m below the bottom of the foundation pit; the distance between the grouting waterproof curtains in the rock is 1.5m, 2 rows are arranged in total, and the row distance is 0.6 m.

Preferably, the construction of the high-pressure jet grouting pile waterproof curtain adopts double-pipe jet grouting,

the dual tube method is a dual grouting tube using two channels; after the double grouting pipe is placed to the designed depth of the soil layer, a coaxial double nozzle is arranged on the bottom side surface of the double grouting pipe, and jet flows of two media of high-pressure slurry and air are jetted out to impact and damage the soil body; namely, slurry with pressure of more than 28MPa is ejected by a high-pressure generating device such as a high-pressure slurry pump and the like, and is ejected from a nozzle at high speed; compressing air with pressure of about 0.8Mpa, and spraying from an external nozzle; under the combined action of high-pressure slurry flow and the surrounding air flow of the outer ring, the nozzle sprays and rotates and lifts at the same time, and finally a cylindrical consolidation body is formed in soil.

Preferably, the construction of the crown beam and the first inner supporting beam further comprises an early preparation stage, which mainly comprises the following steps:

(1) formwork installation

The crown beam is more than 1m high and is used as a thin-wall retaining wall with the thickness of 30cm and the height of 2 m; the crown beam is assembled by adopting a combined steel mould, split screws are arranged between plates by using M20 full-tooth screws, the screw intervals are 140cm, and PVC pipes are sleeved outside the screws, so that the screws can be smoothly pulled out for recycling after the mould is removed; the height of a waist beam and an inner supporting beam is 1M, a template adopts a site-customized steel die, the large surface of the template adopts a steel plate with the thickness of 6mm, the size is 1.5M multiplied by 1.2M, a panel is provided with two parallel hollow steel pipes with the diameter of phi 22 as vertical rib backs, the interval between the vertical rib backs is arranged at @40cm, the vertical rib backs are provided with two parallel hollow steel pipes with the diameter of phi 48mm as transverse ribs, the interval between the transverse ribs is arranged at @50cm, M20 full-tooth screw rods are arranged into split screw rods with the interval of @50cm, the full-tooth screw rods penetrate through the two steel pipes and are fastened by butterfly buckles, PVC pipes are sleeved outside the screw rods, so that the screw rods can be smoothly pulled out for recycling after the template is disassembled, and the phi 22 hollow steel pipes and jacking supports are used as plate rear supports after the template.

(2) Reinforcing bar processing and installation

Straightening a reserved steel bar of the supporting pile, retesting the elevation of the pile top, arranging a crown beam template, embedding a retaining wall steel bar in advance, and erecting a construction support for installing the retaining wall steel bar after the crown beam is poured;

the processing and manufacturing of the steel bars are all carried out in a steel bar processing field, and the semi-finished steel bars are transported to the field to be installed according to the relevant regulations of the construction technical specifications. The steel bar manufacturing and installation are carried out according to the beam subsection construction times, enough lap joint length is reserved, and the positions of the stressed steel bar joints are staggered by not less than 35 d. And binding precast concrete cushion blocks on the main reinforcements after the reinforcement cage is installed so as to ensure the thickness of the protective layer.

The installation of the steel bars follows the principle of first lower part, then upper part, first main part and second sub part, namely, the exposed main reinforcement, the stirrup and the tie reinforcement are welded firstly, and then the main reinforcement is connected to bind the stirrup. The spacing is tightly controlled according to the design dimension. When the length is longer, the installation is in a sectional way. If the exposed steel bar is longer, a supporting frame needs to be erected.

Binding sequence of the steel bars: generally, a long shaft is firstly arranged and then a short shaft is arranged, the processes of marking, laying steel bars, penetrating stirrups, binding and forming are sequentially carried out from one end to the other end according to the requirements of drawings. The reinforcing steel bar installation should pay special attention to the fact that the longitudinal bars are exposed when the beam is constructed in a segmented mode so that two sections of the beam can be conveniently connected, in order to guarantee the accuracy of embedding of the reinforcing steel bars, the support is used for positioning, and a positioning frame is arranged on the top face of the beam reinforcing steel bars to guarantee the position accuracy of the reinforcing steel bars.

The steel bar welding adopts flash arc welding, the length of a double-sided welding seam is not less than 5d, and the length of a single-sided welding seam is not less than 10 d. The joint of each section does not exceed 50 percent of the total number of the steel bars, and the staggered distance of the front and the back of the joint is not less than 40 times of the diameter of the steel bars.

When the concrete waist rail construction is carried out in the earthwork excavation to the designed elevation, reinforcing steel bars with the diameter of phi 20mm are implanted into the support piles, the anchoring depth meets the standard requirement, a pulling resistance test is carried out after the anchoring depth meets the standard requirement, and the waist rail reinforcing steel bar construction is started after the anchoring depth is qualified;

(3) pouring of concrete

The concrete is transported by a commercial mixing tank truck, and is hoisted or pumped into a mold according to the height of the waist rail and the terrain, and the concrete is compacted by manual layered vibration of the inserted vibrator. Before pouring concrete, the template, the steel bars and the embedded parts are checked and recorded, and pouring can be performed after the requirements of design and specification are met;

preferably, the excavation of the foundation pit in the construction method comprises the following specific steps:

firstly, when a first layer of earthwork is excavated, two excavators are adopted to excavate the earthwork below a concrete support cushion layer, the earthwork is directly loaded and transported out of a foundation pit, and a crown beam and a concrete support are constructed;

step two: adopting two long-arm excavators to excavate a second layer of earthwork, reserving an excavation access between two steel supports in the middle of a foundation pit when the earthwork is excavated to the bottom of the second layer of earthwork, excavating layer by layer according to steps at the foundation pit of the arch foundation, arranging an inclined access at the side close to the soil layer of the tie beam, transferring the earthwork to the position of the soil layer at the bottom of the middle tie beam by the relay of the two excavators, and loading and transporting the earthwork by one excavator;

step three: the 1# excavator starts to pour soil upwards from the first step from top to bottom, the 2# excavator starts to load the earthwork excavated by the 1# excavator on the bottom soil layer of the tie beam, and the steps are sequentially circulated until the excavation is finished;

step four: after the earthwork in the foundation pit of the arch support foundation is cleaned, the No. 1 excavator is used for cleaning and leveling the earthwork on the sidewalk along the unearthed sidewalk, the No. 2 excavator is used for transporting the earthwork outside the foundation pit outside the working radius of the No. 2 excavator, and the earthwork is loaded and transported out until the whole earthwork excavation process is finished.

Preferably, the arch foundation construction method comprises the following specific steps:

the arch support foundation adopts a reinforced concrete structure to enlarge the foundation, the top surface of the arch support foundation is inwards inclined, the included angle between the top surface of the arch support foundation and the horizontal plane is 10 degrees, the longitudinal bridge direction length of the arch support foundation is 30m, the transverse bridge direction width is 16m, the maximum height is 17.622m, and the contact surface between the bottom of the longitudinal bridge direction foundation and the bedrock is arranged to be step-shaped; the arch foundation is poured layer by adopting the thickness of every 2m, the concrete of each layer of arch foundation adopts a bamboo plywood vertical mould, steel bars are bound, and the arch foundation is poured in blocks; and roughening the concrete contact surface of each layer of arch base, and arranging anchoring steel bars.

The invention has the beneficial effects that:

(1) the construction method of the invention adopts the technical principle of special waterproof construction; the foundation high-pressure grouting can further harden the foundation pit bottom at the position of the stroke-induced rock stratum, and the large-area loosening condition can not occur due to disturbance when the foundation developed by karst joints is excavated, so that the engineering over-square problem after excavation is greatly reduced, and the foundation high-pressure grouting is also favorable for preventing the foundation water burst, water seepage and other conditions caused by large water pressure difference.

(2) According to the construction method, the waterproof curtain outside the pit can enable the outer side of the foundation pit to form a circle of closed water seepage-proof structure layer, and meanwhile the high-pressure jet grouting piles at the top enable the soil layer outside the supporting piles to be hardened, so that the soil layer outside the foundation pit is further reinforced, and the situations of cofferdam landslide and collapse caused by flood erosion are effectively prevented.

(3) In the construction method, because the excavation depth of the foundation pit is larger and the foundation pit is constructed near the river, the structural form of the reinforced concrete special-shaped pile and the reinforced concrete circular pile is adopted to increase the design strength of the pile body in order to ensure that the integral strength of the pile body reaches the requirement of compressive strength; the special-shaped steel reinforcement cage pile foundation adopts an arc-shaped steel plate connector to ensure that the special-shaped steel reinforcement cage pile foundation is fully occluded with a standard round pile foundation by 20cm, and a cylindrical wall brushing device is adopted to clean the arc-shaped steel plate connecting surface after the drilling of the common round steel reinforcement cage pile foundation is finished, so that the occlusion quality is ensured; the orientation of the steel plate connector is controlled by lofting and shaft position on the pile foundation casing and the arc-shaped steel plate connector, so that accurate positioning during drilling of a common cylindrical pile is ensured, the arc-shaped steel plate connector is prevented from being bitten, the efficiency of quick positioning is improved, and the work efficiency is improved.

(4) The construction method adopts the technical principle of special slope protection construction, refers to the dam body construction technology, and adopts the construction method of the mold bag concrete and the soil bag to protect the slope according to the field condition. The cofferdam is a backfilled earth cofferdam, the structure is loose and is soaked in river water, after earthwork is filled to the designed elevation, a mechanical slope brushing forming installation mold bag is adopted, the construction period is short, the full-area coverage can be achieved, the water blocking effect is good, and the construction progress is fast.

(5) The special-shaped reinforcement cage is used in a large-span bridge foundation construction facility after being formed, plays a role in supporting and stopping water, and is distributed at intervals with a common reinforcement cage, so that the formed supporting foundation is more stable; according to the special-shaped reinforcement cage, the column body volume of the special-shaped reinforcement cage in the integral filling and pouring process is much smaller than that of a traditional cylindrical support pile, and the special-shaped reinforcement cage is used for pouring a pile, so that the concrete raw material is saved, and the effect of saving the cost is further achieved.

Drawings

FIG. 1 is a flow chart of the construction method of the present invention;

FIG. 2 is a schematic view of a manufacturing process of the jig frame according to the present invention;

FIG. 3 is a flow chart of the present invention for manufacturing a deformed reinforcement cage;

FIG. 4 is a flow chart of the excavation steps of the foundation pit according to the present invention;

fig. 5 is a schematic view of the overhead structure of the special-shaped reinforcement cage of the present invention;

FIG. 6 is a reference diagram of an example of the combination of the special-shaped reinforcement cage and the general reinforcement cage of the present invention;

in the attached drawings, 1 represents a 10# channel steel support frame, 2 represents a steel plate, 3 represents a deformed steel bar cage, 4 represents a curled limiting steel plate, 200 represents an outer ring transverse reinforcement stirrup, 100 represents an arc-shaped steel plate, 201 represents a first arc edge, 203 represents a second arc edge, L1 represents the arc length of the first arc edge, R1 represents the arc radius of the first arc edge, L2 represents the arc length of the arc-shaped steel plate, R2 represents the arc radius of the arc-shaped steel plate, A represents a common steel bar cage support pile, and B represents a deformed steel bar cage support pile.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings by way of examples of preferred embodiments. It should be noted, however, that the numerous details set forth in the description are merely for the purpose of providing the reader with a thorough understanding of one or more aspects of the present invention, which may be practiced without these specific details.

Example 1

the method comprises the following steps: island building cofferdam → sidewalk construction → reinforced concrete secant pile construction → high pressure grouting water stop curtain construction → jet grouting pile water stop curtain construction → crown beam and first inner support beam construction → excavation to second inner support beam elevation → waist beam and second inner support beam construction → excavation to third inner support beam elevation and third inner support beam construction → excavation to design foundation → abutment foundation construction and inner support removal layer by layer → foundation pit backfilling;

the specific implementation mode is as follows:

island-building cofferdam

1. Island filling

In the island-building cofferdam construction, firstly, reinforcing mesh gabions are arranged at the slope feet, then, clay is filled to the designed top elevation, and the side slope on the upstream face is protected by adopting mould bag concrete slope protection and soil bag side slope protection.

The process flow comprises the following steps: and (3) slope toe section mould bag concrete slope toe → clay filling to designed elevation → upstream side slope and excavation side slope finishing → side slope protection construction.

2. Slope surface protection construction

The cofferdam is a backfill cofferdam, the slope is seriously scoured by water flow, the stability is poor, in order to enhance the anti-scouring capability of the slope protection, the thickness of the concrete of the engineering mould bag is determined to be 25cm, and the concrete adopts C25 pump commercial concrete.

And (3) carrying out underwater slope management on the slope surface by adopting a method of 'cutting slope at a protruding part and backfilling a pit part', and for the soil pit slope surface of a nearby river channel, adopting riprap filling and filling pits, and paving graded broken stones with the thickness of 10cm on the surface for leveling.

Pouring anchored concrete at the top of the slope, throwing and filling a flaky stone presser foot at the bottom of the slope, conveying the molded bag to a construction site after being processed and formed in a factory, sewing the molded bag by a sewing machine at the bank side, laying the molded bag from top to bottom, and constructing the molded bag concrete by adopting a pump pouring method; and pouring is sequentially carried out from bottom to top, namely the toe part is poured firstly, the face part is poured, and the top platform part is poured finally.

And after the construction of the mould bag concrete is finished, constructing a soil bag slope protection at the position of the top of the mould bag concrete slope, wherein the filling thickness along the slope is 1m, and backfilling to the elevation of the top of the slope.

Construction of reinforced concrete secant pile

1. Construction of drilled pile

In order to ensure the pile forming quality, the impact drilling machine is adopted to carry out the impact construction on the upstream surface of the foundation pit and the side-drilled pile for backfilling soil, and the rotary drilling machine is adopted to carry out the drilling construction on the rest piles.

The periphery of a foundation pit is supported by reinforced concrete secant piles, the pile diameter is 1.5m, the pile spacing is 1.3m, the secant piles are divided into two pile types, wherein the irregular reinforcement cage pile foundation containing an arc-shaped steel plate is uniformly named as an A-type pile foundation, a common cylindrical reinforcement cage pile foundation is arranged between the A-type piles, and the common cylindrical reinforcement cage pile foundation is uniformly named as a B-type pile foundation; the construction process and pile quality of the secant pile are fully considered, the overall construction arrangement of the secant pile is to construct an A-type pile foundation from the middle of one side of the foundation pit far away from the river bank, and then construct a B-type pile.

As shown in fig. 5 and 6, in this step, the deformed steel bar cage pile is formed by using a deformed steel bar cage as a main framework, the deformed steel bar cage includes a plurality of vertical supporting steel bars, a plurality of circles of outer-ring transverse reinforcing stirrups 200, inner-ring transverse reinforcing stirrups, transverse supporting steel bars and arc-shaped steel plates 100, and the deformed steel bar cage is formed by welding, the arc-shaped steel plates include an upper arc-shaped steel plate and a lower arc-shaped steel plate, the outer-ring transverse reinforcing stirrups are quadrangles with four sides being arcs formed by rolling closed circular reinforcing steel bars, the circle center direction of the arc-shaped side one arc 201 arc with one pair of opposite sides of the quadrangle with four sides being arcs is inward, and the circle center direction of the arc-shaped side two arcs 203 arcs with the other pair of opposite sides is outward;

the inner ring transverse reinforcement stirrup is a quadrilateral formed by two arc-shaped steel bars and two straight-line steel bars, the two arc-shaped steel bars are arc-shaped edges III, and the arc-shaped edges III are the same as the arc radius of the arc-shaped edge I201; vertical support reinforcing bar welds between arc limit three and arc limit 201, the horizontal reinforcement stirrup 200 of outer lane adopts the mode of plum blossom shape spot welding to carry out welded connection with vertical support reinforcing bar.

The arc-shaped steel plate 100 of the deformed reinforcement cage is welded on the second arc line 203 of the outer ring transverse reinforcement stirrup 200, wherein the arc center of the pair of opposite edges of the arc line is outward; the outer ring transverse reinforcing stirrup 200 is also welded on the second arc edge 203 through two transverse supporting steel bars for connecting and reinforcing the second arc edge 203.

The construction sequence of the reinforced concrete secant pile is arranged as follows:

the first step is as follows: according to the arrangement condition of a field, an A-type pile foundation is planned to be selected for drilling to form a pile foundation;

the second step is that: jumping piles at two sides of the constructed A-type pile foundation to construct the A-type pile foundation at two sides;

the third step: constructing a B-type pile foundation in the middle of the A-type pile foundation, and ensuring that the pile forming time of the A-type pile foundation pile is longer than 24 hours and shorter than 48 hours when constructing the B-type pile foundation in order to ensure the engagement quality and meet the requirement of a drilling machine construction process;

the fourth step: and continuously jumping the A-shaped piles on the two sides of the pile.

The fifth step: construction both sides B type pile foundation, after B pile foundation pore-forming, adopt brush wall ware clean up connector lateral wall, ensure reinforced concrete secant pile stagnant water effect.

And a sixth step: repeating the second step to the fifth step until the pile foundation is completely finished, and increasing or decreasing drilling machine equipment according to actual conditions so as to meet the technical requirements of secant pile construction!

2. Fabrication of reinforcement cage

The steel reinforcement cage is processed in the processing canopy, transports to the building site with the flatbed of field processing. The reinforcement cages are all processed into whole cages in a processing field and then conveyed to a site for hoisting into a hole.

1) Manufacture of common reinforcement cage

The reinforcement cage is processed and formed on a special mould. The steel reinforcement cage reinforcing bar is according to design drawing size laying-out preparation owner muscle, strengthening rib and stirrup to mark the position of owner muscle on the strengthening rib circle, make the mark alignment stiffening rib mark at main muscle middle part of main muscle on the strengthening rib during the welding, right the strengthening rib, rectify the straightness that hangs down of strengthening rib and main muscle, then spot welding, weld on the main muscle after having welded whole strengthening ribs, put the skeleton on the support, arrange the spiral muscle according to the design position, plum blossom shape spot welding or ligature are on the main muscle.

2) Manufacturing method of special-shaped reinforcement cage

Manufacturing of steel plate tire seat

As shown in fig. 2: because the A-type pile foundation reinforcement cage is provided with the steel plate connector, the A-type pile foundation reinforcement cage is a special-shaped reinforcement cage, and the jig frame is specially manufactured on the part of the reinforcement cage. The steel plate tire seat is arranged as follows:

and setting the length of the steel plate tire seat according to the design length of the steel reinforcement cage. The steel sheet child seat chooses 10# channel-section steel and 8 mm's I welding of arc steel sheet to form for use, adopts the bar planting to be fixed in the reinforcing bar field. And (4) blanking the steel plate in advance according to the requirements of the design drawing. The thickness of the arc-shaped steel plate I on the plate tire seat is 8mm, the width is 82.2cm, and the length is 1.5 m. After the rolling is finished, a quality inspector repeatedly inspects the steel plate, and the arc length and the chord length of the steel plate are ensured to meet the design requirements. And after the steel plate base is manufactured and the steel plate is processed, manufacturing the A-type pile foundation reinforcement cage.

Manufacturing process of irregular reinforcement cage

As shown in connection with fig. 3: the specific construction process of the special-shaped reinforcement cage is as follows:

the first step is as follows: the lower arc-shaped steel plate is installed on the steel plate tire bed, the joint between the lower arc-shaped steel plate and the steel plate tire bed is firmly welded, and the reinforcing hoop is processed at the same time.

The second step is that: and arc line edges II of the outer ring transverse reinforcing stirrup are welded on the lower arc steel plate. During installation, the axes of the framework and the steel plate are consistent, and the positioning is accurate. And 2cm welding seams are arranged between the second arc edge and the lower arc steel plate every 0.2m and are welded firmly in a segmented mode.

The third step: and welding an arc-shaped steel plate on the second arc edge of the outer ring transverse reinforcing stirrup. During installation, the axes of the upper steel plate, the lower steel plate and the framework are consistent, and the positioning is accurate. The weld setting is identical to the second step.

The fourth step: and welding vertical supporting steel bars on the arc line edge I of the outer ring transverse reinforcing stirrup, and directly welding the vertical supporting steel bars and the arc line edge. When the welding machine is installed, the current of the welding machine is well controlled, and the welding is firm.

The fifth step: and (4) installing the stirrup, wherein the stirrup joint adopts single-side welding and is firmly welded. The stirrup and the main bar adopt quincunx spot welding.

Mounting acoustic pipe

The installation of the sounding pipe is carried out after the whole processing of the special-shaped steel reinforcement cage is finished, and the sounding pipe is installed: according to the requirements of design drawings, pile foundations are detected by an ultrasonic non-damage detection method, and a three-hole detection method is adopted for the pile foundations with the pile diameter of 1.5 m. The detection pipes are arranged at equal intervals along the periphery of the stirrup. The lower end of the detection pipe extends to the bottom of the pile, and the lower end is firmly welded by sealing the bottom with a steel plate; the upper end of the pile is 100cm higher than the top surface of the broken pile head, and the joint, the bottom end and the top end are subjected to waterproof treatment to realize no water leakage; connect long sound test pipe in concatenation steel reinforcement cage, it is firm to tie up with the iron wire between sound test pipe and reinforcing bar to carry out the ligature with sound test pipe and steel reinforcement cage in bottom, centre, top, come up when preventing to pour into underwater concrete, the hole depth is not enough during the detection. After the reinforcing cage is placed and positioned, clear water is filled in the pipe before the top end of the acoustic pipe is sealed, and concrete cement paste is prevented from permeating into the pipe.

Hoisting reinforcement cage

In the first hole cleaning process of hole forming acceptance inspection, sleeper piles which are 10cm higher than the protective barrel are erected around the hole openings by using sleepers, so that the reinforcing cage, the guide pipe and the funnel can be supported conveniently. And after the hole is cleaned for the first time to be qualified, hoisting the reinforcement cage into the hole by using a truck crane. When the steel reinforcement cage is transferred, the falling speed is uniform, the framework is placed in the middle, and the hole wall is not collided. When the special-shaped steel reinforcement cage is installed, the contour position needs to be set out on the pile casing, the axis position of the steel plate is controlled, and the construction of the adjacent side secant pile cannot be influenced.

When the center adjusting framework is lowered to the designed elevation, the steel reinforcement cage is hung on the sleeper pile by a hanging ring; measuring the center of the reinforcement cage by using the guard piles around the orifice, wherein the center deviation of the reinforcement cage is not more than 3 cm; the top end of the reinforcement cage utilizes the concrete cushion block to ensure the thickness of the net protective layer around the pile body reinforcement.

3) Underwater concrete pouring

The underwater concrete pouring is performed according to the underwater concrete pouring construction of the drilled pile.

Constructing the lattice column,

the lattice column adopts a cast-in-place pile foundation, adopts a steel pipe with the diameter of 630mm x 10mm, is connected with the pile foundation under the column, and has the following construction steps:

the first step is as follows: inserting the latticed column into the reinforcement cage for 3m at a processing site, and connecting the reinforcement cage with a reinforcement stirrup of the reinforcement cage by adopting a # -shaped reinforcement; the part without the stiffening stirrup is connected with the main reinforcement of the reinforcement cage by adopting a method of increasing the tie bars nearby.

The second step is that: hoisting a steel reinforcement cage: and (3) placing the reinforcement cage into the hole by using an automobile crane, pre-burying 1m of an exposed hole opening of the lattice column of the reinforcement cage section during the hole entering, and clamping and fixing the reinforcement cage at the position of the hole opening by using rail steel.

The third step: and integrally hoisting the connected reinforcement cage and the lattice column into the hole.

The fourth step: and (5) pouring underwater concrete after hoisting is finished, wherein the elevation of the top surface of the poured concrete is controlled to be 50cm above the elevation of the top surface of the pile.

The fifth step: after the concrete of the column pile is finally set, filling sand into the soil layer section embedded in the lattice column to fix the lattice column at the center of the hole.

After the lattice column is installed, the main protection is achieved, and the situation that the lattice column is inclined or bent due to mechanical collision such as hoisting, earth excavation and the like, and the working performance of the lattice column is affected is prevented. If the lattice column inclines or is damaged, the lattice column should be reinforced or replaced in time, and accidents caused by falling of the support are prevented.

High-pressure grouting water-stopping construction

The periphery of a foundation pit of an arch support of the east and west banks of the bridge is supported by reinforced concrete secant piles. And arranging a waterproof curtain at the periphery of the support pile and performing high-pressure grouting at the bottom of the foundation pit. The outer waterproof curtain of the foundation pit is distributed outside the support piles and arranged in double rows, and the outer waterproof curtain is divided into an in-rock grouting waterproof curtain and a soil layer high-pressure jet grouting pile waterproof curtain.

Firstly, the grouting holes of the base are arranged in a quincunx shape, the distance is 1.0m, the grouting holes are uniformly distributed in the excavation range of the foundation pit, and the depth is 6m below the bottom of the foundation pit. Before the foundation high-pressure grouting construction, the axes are arranged according to the arrangement principle and lofting hole positions, then the axes are inserted and positioned, and a machine is moved to the positioning position for drilling construction.

Constructing a waterproof curtain: and arranging soil layer high-pressure jet grouting pile waterproof curtains on the outer sides of the reinforced concrete secant piles, wherein the soil layer high-pressure jet grouting pile waterproof curtains are arranged in 2 rows, and high-pressure grouting is adopted for rock strata. The high-pressure jet grouting waterproof curtain of the soil layer is constructed by adopting a double-pipe method and is carried out after the construction of part of the reinforced concrete secant pile is completed. The soil layer high-pressure jet grouting pile waterproof curtain is arranged in a zigzag manner, the distance between piles is 0.5m, and the diameter of the pile is 0.6 m. 2 rows of soil layer high-pressure jet grouting pile waterproof curtains are arranged, the row interval is 0.45m, the distance from the axis of one row close to the reinforced concrete secant pile is 0.25m, and the soil layer high-pressure jet grouting pile piles and the reinforced concrete secant pile are overlapped by 0.05 m.

The in-rock grouting waterproof curtain is arranged at the bottom of the soil layer waterproof curtain, and the bottom elevation is 5m below the bottom of the foundation pit. The distance between the grouting waterproof curtains in the rock is 1.5m, 2 rows are arranged in total, and the row distance is 0.6 m.

High-pressure jet grouting waterproof curtain construction

The dual tube method is a dual grouting tube using two channels. After the double grouting pipe is placed to the designed depth of the soil layer, a coaxial double nozzle is arranged on the bottom side surface of the double grouting pipe, and jet flows of high-pressure slurry and air are jetted out simultaneously to impact and damage the soil body. That is, a slurry having a pressure of 28MPa or more is discharged from a high-pressure generator such as a high-pressure slurry pump at a high speed through a nozzle. And compressed air is sprayed out from the outer nozzle by about 0.8 Mpa. Under the combined action of high-pressure slurry flow and air flow around the outer ring, the nozzle can spray and lift the slurry, and finally a cylindrical consolidation body is formed in the soil.

Construction of crown beam, waist beam and internal stay beam

(1) Formwork installation

The height of the crown beam is 1m, and the thickness of the retaining wall made of the crown beam is 30cm and 2 m. The crown beam is assembled by adopting a combined steel die, an @140cm split screw is arranged between plates by using an M20 full-tooth screw, and a PVC pipe is sleeved outside the screw, so that the screw can be smoothly pulled out for recycling after the die is removed.

The height of a waist beam and an inner supporting beam is 1M, a template adopts a site-customized steel die, the large surface of the template adopts a steel plate with the thickness of 6mm, the size is 1.5M multiplied by 1.2M, a panel is provided with two hollow steel pipes with the diameter phi 22 side by side as vertical rib backs, the interval between the vertical rib backs is arranged at @40cm, the vertical rib backs are provided with two hollow steel pipes with the diameter phi 48mm side by side as transverse ribs, the interval between the transverse ribs is arranged at @50cm, M20 full-tooth screw rods are arranged at the interval @50cm oppositely-pulled screw rods, the full-tooth screw rods penetrate through the two steel pipes and are fastened by butterfly buttons, the PVC pipes are sleeved outside the screw rods, so that the screw rods can be smoothly pulled out for recycling after the template is removed, and a jacking support and the phi 22 hollow steel pipes are used as plate back supports after the template is removed.

(2) Processing and installing steel bars

And (3) straightening the supporting pile to reserve a steel bar, retesting the pile top elevation, arranging a top beam template, pre-embedding a retaining wall steel bar, and erecting a construction support to install the retaining wall steel bar after the top beam is poured.

When the concrete waist beam construction is carried out in the process of excavating earthwork to a designed elevation, reinforcing steel bars with the diameter of phi 20mm are implanted into the supporting piles, the anchoring depth meets the standard requirement, a pulling resistance test is carried out after the anchoring depth meets the standard requirement, and the waist beam reinforcing steel bar construction is started after the anchoring depth is qualified.

(3) And pouring the concrete

The concrete is transported by a commercial mixing tank truck, and is hoisted or pumped into a mold according to the height of the waist rail and the terrain, and the concrete is compacted by manual layered vibration of the inserted vibrator. Before pouring concrete, the template, the steel bars and the embedded parts are checked and recorded, and pouring can be performed after the requirements of design and specifications are met.

Excavation construction of foundation pit

The excavation of the foundation pit is carried out in layers, the exposure time of the foundation pit is not too long, the components are timely checked and accepted after the construction is finished, and the foundation pit is backfilled immediately after the components are qualified. The method is characterized in that a BIM technology is applied before construction and a GIS technology is combined to carry out three-dimensional modeling on the terrain, the landform and the geological survey data of the foundation pit, a three-dimensional field model is built through digital elevation, the distribution of rock strata is analyzed according to the geometric dimension of the foundation pit, the three-dimensional field model is used for simulating the optimal sequence and the optimal route of earth and rockfill excavation, a more reasonable excavation mode is selected according to a three-dimensional geological model, and the threat of blasting technology to the stability of the foundation pit is avoided.

1) And determining the underground water level before excavation.

If the underground water level is high, a water collecting well is arranged at every 30m of the bottom surface of the excavation pit along the periphery, and when the underground water level is reduced to 0.5m below the bottom of the excavation pit by pumping water by a sand pump, excavation can be carried out so as to avoid collapse caused by too high excavation speed, difficult support due to too large soil moisture content and incapability of timely supporting.

2) And carrying out layered excavation, and reasonably determining the excavation sequence and the layered excavation depth.

(1) Principle of excavation

The foundation pit earthwork excavation must be carried out according to the requirements of the foundation pit engineering construction regulations. The space-time effect is fully utilized to improve the construction quality of the project and ensure the construction safety.

Firstly, foundation pit excavation must be carried out until the strength of the support piles, the top beams and the concrete support concrete reaches 100%, underground water is required to be located 1m below a foundation during the foundation pit excavation process, and otherwise, the underground water level is reduced by adopting a dewatering well excavation mode.

Secondly, when the foundation pit is excavated, the longitudinal and transverse side slopes are calculated and determined according to the geology, the environmental conditions and the safe slope during excavation and the geological condition, but the longitudinal and transverse side slopes are not steeper than 1:3, and the longitudinal and transverse side slopes need to be segmented, partitioned, layered and symmetrically processed, so that the foundation pit cannot be over-excavated. The exposed width of each excavation is preferably controlled to be 3m-6m, the excavation depth of each layer is not more than 2m, and one-time excavation is strictly forbidden under one working condition.

Thirdly, when the longitudinal slope is placed and excavated, a water intercepting ditch or a water retaining earth dike is arranged outside the top of the slope to prevent surface water from scouring the slope surface and prevent drainage water outside the foundation pit from flowing back to infiltrate into the pit.

Fourthly, after the foundation pit is excavated, a drainage ditch and a water collecting well in the pit are arranged in time to prevent water from accumulating at the bottom of the pit.

Fifthly, the sequence and the method of the earth excavation are consistent with the design working condition and follow the principle of 'supporting by slotting, digging after supporting, layered digging and strictly forbidden over digging'.

And sixthly, the excavation and the installation of the steel support under each working condition are not carried out for more than 12 hours.

Seventhly, when the soil is dug mechanically, 200-mm thick soil layers are reserved at the bottom of the pit and leveled by manual digging, so that the disturbance of the soil at the bottom of the pit is prevented.

When mechanical excavation is adopted, the excavating machinery and vehicles can not directly walk on the supports to operate, and the excavating machinery is strictly forbidden to collide the supports, the upright posts, the well point pipes and the fender piles. The top surface of the steel support is strictly forbidden to stack sundries.

And ninthly, when the earthwork is excavated, the spoil stack is required to be beyond the range of 2 times of the excavation depth of the foundation pit.

(2) Excavation sequence, see FIG. 4

The excavation of the foundation pit in the construction method comprises the following specific steps:

Excavation and supporting erection construction of a foundation pit are the most important processes in the foundation pit construction of the arch support, construction must be strictly operated according to construction specifications in the construction, the construction is organized according to the space-time effect principle, five main points of layering, substep, symmetry, balance and time limitation are mastered in the excavation process, and the construction principle of vertical layering, longitudinal partition segmentation, first support and later excavation is followed.

In consideration of the convenience of construction and the protection of a foundation pit supporting structure, longitudinal slope-releasing excavation is adopted, and the principle of supporting one section by one section in the transverse bridge direction step excavation is adopted.

The first layer of earthwork is excavated to 0.5m below the first layer of concrete supporting bottom, and the distance between the first layer of earthwork and the original ground is about 0.5 m. And constructing a first concrete support in time after the earthwork excavation is finished. The earthwork on the layer is directly excavated and loaded by a back-hoe excavator, and is transported by a dump truck. In order to reduce the influence of steel support installation on earth excavation, a groove with the width of 4-5m is formed in the middle of the foundation pit along the longitudinal direction, slopes are arranged along the longitudinal direction, and supports are sequentially installed according to the height of the excavation depth.

The excavation height of the second layer of earthwork and the third layer of earthwork is 7-10m, 2 PC400LC long arm excavators are adopted at the foundation pit side of the arch foundation on the outer side of the foundation pit to excavate the second layer of earthwork, 2 PC200 type excavators are adopted to cooperatively excavate until the third layer of earthwork begins, a dump truck is used for outward transportation, and PC120 type small excavators are adopted at the corners for cleaning. And the earthwork exceeding the working range of the long-arm excavator in the transverse range of the foundation pit is transported to the working range of the 2# excavator by the 1# excavator, and the 2# excavator excavates and loads and is transported outside by a dump truck. And after excavating to 0.5m below the second support, installing the supports in time and pre-adding the supports to the designed stress value.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be construed as the protection scope of the present invention.

Claims

1. A construction method of a large-scale permeable geological arch bridge foundation is characterized by comprising the following steps:

the method comprises the following steps: constructing island cofferdam → constructing sidewalk → constructing reinforced concrete secant pile → constructing high-pressure grouting waterproof curtain and simultaneously constructing foundation grouting in foundation pit → constructing high-pressure jet grouting pile waterproof curtain → constructing crown beam and first inner support beam → excavating to second inner support beam elevation → waist beam and second inner support beam constructing → excavating to third inner support beam elevation and third inner support beam constructing → excavating to design foundation → constructing abutment foundation and dismantling inner support layer by layer → backfilling foundation pit;

the reinforced concrete secant pile is supported around a foundation pit, the pile diameter is 1.5m, the pile spacing is 1.3m, the reinforced concrete secant pile is divided into two pile types, wherein a reinforcement cage pile containing an arc-shaped steel plate is a special-shaped reinforcement cage pile foundation, and a common reinforcement cage pile foundation is arranged between the special-shaped reinforcement cage pile foundations; the overall construction sequence of the reinforced concrete secant pile is that a special-shaped reinforcement cage pile foundation is constructed from the middle on one side of the foundation pit far away from the river bank, and then a common reinforcement cage pile foundation is constructed; the special-shaped reinforcement cage pile foundation is formed by taking a special-shaped reinforcement cage as a main framework, the special-shaped reinforcement cage comprises a plurality of vertical supporting reinforcements, a plurality of circles of outer-ring transverse reinforcing stirrups, inner-ring transverse reinforcing stirrups, transverse supporting reinforcements and arc-shaped steel plates, and is formed by welding, each arc-shaped steel plate comprises an upper arc-shaped steel plate and a lower arc-shaped steel plate, each outer-ring transverse reinforcing stirrup is a quadrangle with four sides being arcs formed by rolling a closed circular reinforcement ring, the circle center direction of an arc-line-side first arc with a pair of opposite sides of the quadrangle with four sides being arcs is inward, and the circle center direction of an arc-line-side second arc with the other pair of opposite sides is outward; the inner ring transverse reinforcing stirrup of the special-shaped reinforcement cage is a quadrilateral formed by two arc-shaped reinforcements and two straight-line reinforcements, the two arc-shaped reinforcements are arc-shaped edges III, and the arc-shaped edges III have the same arc radius as the arc-shaped edges I; the vertical supporting steel bars are welded between the third arc edge and the first arc edge, and the outer ring transverse reinforcing hoop and the vertical supporting steel bars are welded and connected in a quincunx spot welding mode; the manufacturing method comprises the following steps:

manufacturing of steel plate tire seat

manufacturing process of irregular reinforcement cage

step S1: installing a lower arc-shaped steel plate on the steel plate tire bed, firmly welding a joint between the lower arc-shaped steel plate and the steel plate tire bed, and processing an outer ring transverse reinforcing stirrup;

step S2: welding a second arc edge of the outer ring transverse reinforcing stirrup on the lower arc steel plate; 2cm welding seams are arranged between the second arc edge and the lower arc steel plate every 0.2m for segmented welding,

step S3: welding an arc-shaped steel plate on the second arc edge of the outer ring transverse reinforcing stirrup; the welding seam setting is consistent with the step S2;

step S4: welding a vertical supporting steel bar on one arc line edge of the outer ring transverse reinforcing stirrup, and directly welding the vertical supporting steel bar and the arc line edge;

step S5: installing the inner ring transverse reinforcing stirrup, wherein the joint of the inner ring transverse reinforcing stirrup adopts single-side welding and is firmly welded; the inner ring transverse reinforcing stirrup and the vertical supporting steel bar are subjected to quincunx spot welding;

the construction sequence of the reinforced concrete secant pile is as follows:

the third step: constructing a common reinforcement cage pile foundation in the middle of the constructed special-shaped reinforcement cage pile foundation;

2. The construction method of the large permeable geological arch bridge foundation of claim 1, wherein: the specific implementation method of the high-pressure grouting waterproof curtain construction and the simultaneous base grouting construction in the foundation pit comprises the following steps: arranging a waterproof curtain at the periphery of the reinforced concrete secant pile, and simultaneously performing high-pressure grouting at the bottom of the foundation pit; the waterproof curtain outside the foundation pit is distributed outside the reinforced concrete secant pile and is arranged in two rows, and the waterproof curtain is divided into an in-rock grouting waterproof curtain and a soil layer high-pressure jet grouting pile waterproof curtain;

constructing a waterproof curtain: arranging soil layer high-pressure jet grouting pile waterproof curtains on the outer sides of the reinforced concrete secant piles, wherein the soil layer high-pressure jet grouting pile waterproof curtains are arranged in 2 rows, and high-pressure grouting is adopted for rock strata; constructing a soil layer high-pressure jet grouting pile waterproof curtain by adopting a double-pipe method, and after the construction of part of reinforced concrete secant piles is completed; the soil layer high-pressure jet grouting pile waterproof curtain is arranged in a zigzag manner, the distance between piles is 0.5m, and the diameter of the pile is 0.6 m; 2 rows of soil layer high-pressure jet grouting pile water-stopping curtains are arranged, the row interval is 0.45m, the distance from the axis of one row close to the reinforced concrete secant pile is 0.25m, and the soil layer high-pressure jet grouting pile water-stopping curtains are overlapped with the reinforced concrete secant pile by 0.05 m;

3. The construction method of the large permeable geological arch bridge foundation of claim 1, wherein: the construction of the high-pressure jet grouting pile waterproof curtain adopts a dual-pipe jet grouting method, wherein a dual-pipe grouting pipe with two channels is used in the dual-pipe jet grouting method; after the double grouting pipe is placed to the designed depth of the soil layer, a coaxial double nozzle is arranged on the bottom side surface of the double grouting pipe, and jet flows of two media of high-pressure slurry and air are jetted out to impact and damage the soil body; namely, slurry with pressure of more than 28MPa is ejected by a high-pressure generating device such as a high-pressure slurry pump and the like, and is ejected from a nozzle at high speed; and compressed air of 0.8Mpa is sprayed out from the outer nozzle; under the combined action of high-pressure slurry flow and the surrounding air flow of the outer ring, the nozzle sprays and rotates and lifts at the same time, and finally a cylindrical consolidation body is formed in soil.

4. The construction method of the large permeable geological arch bridge foundation of claim 1, wherein: the construction method of the top beam, the waist beam and the first to third inner supporting beams comprises the following specific steps:

(1) formwork installation

The crown beam is more than 1m high and is used as a thin-wall retaining wall with the thickness of 30cm and the height of 2 m; assembling the crown beams by adopting combined steel moulds, arranging split screws with an interval of @140cm between every two plates by using M20 full-tooth screws, and sleeving PVC pipes outside the screws;

the height of a waist beam and an inner support beam is 1M, a template adopts a site-customized steel die, the large surface of the template adopts a steel plate with the thickness of 6mm, the size is 1.5M multiplied by 1.2M, a panel is provided with two hollow steel pipes with the diameter of phi 22mm side by side as vertical rib backs, the interval between the vertical rib backs is arranged at @40cm, the vertical rib backs are provided with two hollow steel pipes with the diameter of phi 48mm side by side as transverse ribs, the interval between the transverse ribs is arranged at @50cm, M20 full-tooth screws are arranged to form an interval @50cm split screw, the full-tooth screws penetrate between the two steel pipes and are fastened by butterfly buckles, the screws are sleeved with PVC pipes so as to be beneficial to smoothly pulled out and recycled after the template is removed, and a jacking support and the hollow steel pipes with the diameter of phi 22mm are used as plate back supports after the template is removed;

(2) reinforcing bar processing and installation

the steel bar manufacturing and installation are carried out according to the beam subsection construction times, enough lap joint length is reserved, and the positions of stressed steel bar joints are staggered for not less than 35 d; binding a precast concrete cushion block on the main reinforcement after the reinforcement cage is installed;

the installation of the reinforcing steel bars follows the principle of first lower, first upper and second lower, and the binding sequence of the reinforcing steel bars: the long axis and the short axis are sequentially carried out from one end to the other end;

the steel bar welding adopts flash arc welding, the length of a double-sided welding seam is not less than 5d, and the length of a single-sided welding seam is not less than 10 d; the joint of each section does not exceed 50 percent of the total number of the steel bars, and the staggered distance of the front and the back of the joint is not less than 40 times of the diameter of the steel bars;

when the concrete waist beam construction is carried out in the earthwork excavation to the designed elevation, reinforcing steel bars with the diameter phi of 20mm are implanted into the supporting piles, the anchoring depth meets the standard requirement, a pulling resistance test is carried out after the anchoring depth meets the standard requirement, and the waist beam reinforcing steel bar construction is started after the anchoring depth is qualified;

(3) pouring of concrete

The concrete is transported by a tank truck, and is hoisted or pumped into the mould according to the height of the waist rail and the terrain, and the inserted vibrator is manually and compactly vibrated in layers.

5. The construction method of the large permeable geological arch bridge foundation of claim 1, wherein: the excavation of the foundation pit in the construction method comprises the following specific steps:

the method comprises the following steps: when a first layer of earthwork is excavated, two excavators are adopted to excavate below a concrete support cushion layer, the earthwork is directly loaded and transported out of a foundation pit, and a crown beam and a concrete support are constructed;

6. The construction method of the large permeable geological arch bridge foundation of claim 1, wherein: the arch support foundation construction method comprises the following specific steps: the arch support foundation adopts a reinforced concrete structure to enlarge the foundation, the top surface of the arch support foundation is inwards inclined, the included angle between the top surface of the arch support foundation and the horizontal plane is 10 degrees, the longitudinal bridge direction length of the arch support foundation is 30m, the transverse bridge direction width is 16m, the maximum height is 17.622m, and the contact surface between the bottom of the longitudinal bridge direction foundation and the bedrock is arranged to be step-shaped; the arch foundation is poured layer by adopting the thickness of every 2m, the concrete of each layer of arch foundation adopts a bamboo plywood vertical mould, steel bars are bound, and the arch foundation is poured in blocks; and roughening the concrete contact surface of each layer of arch base, and arranging anchoring steel bars.