CN110952586A

CN110952586A - Construction process for bearing platform below expressway

Info

Publication number: CN110952586A
Application number: CN201911243373.0A
Authority: CN
Inventors: 李鹏
Original assignee: China Railway 18th Bureau Group Co Ltd; Building Installation Engineering Co Ltd of China Railway 18th Bureau Group Co Ltd
Current assignee: China Railway 18th Bureau Group Co Ltd; Building Installation Engineering Co Ltd of China Railway 18th Bureau Group Co Ltd
Priority date: 2019-12-06
Filing date: 2019-12-06
Publication date: 2020-04-03

Abstract

The invention discloses a construction process of a bearing platform below a highway, which comprises construction preparation, bearing platform foundation pit excavation, pile head treatment, template installation, bearing platform steel bar installation, bearing platform concrete pouring, concrete form removal and foundation pit backfilling. By adopting the construction process for the bearing platform below the expressway, the stability of the foundation pit is ensured, the construction safety is ensured, and risk factors are reduced.

Description

Construction process for bearing platform below expressway

Technical Field

The invention relates to the technical field of bridge construction, in particular to a construction process of a bearing platform below an expressway.

Background

With the rapid development of the urbanization construction in China and the complication of traffic routes, more and more foundation pits are excavated below the high-speed railway, and how to ensure the stability of the foundation pits below the high-speed railway and the safety of the high-speed railway becomes difficult. When the foundation pit is positioned below the high-speed railway, two sides of the foundation pit are adjacent to the pier of the high-speed railway, and after foundation soil is dug in the foundation pit, the whole foundation pit and the surrounding soil body are influenced by buildings and other loads far away from the foundation pit, so that the upwelling phenomenon is presented, namely the soil body around the foundation pit floats upwards. In addition, when the soil body surmounts upwards around the foundation ditch, can drive pier basis also to move together to make high-speed railway pier also present the come-up trend, lead to the pier difference settlement relative increase that closes on the foundation ditch both sides, cause the high-speed railway roadbed to appear warping, in case the deflection exceeds warning value, will seriously influence driving safety.

The foundation pit excavation at the present stage is mainly carried out according to a normal construction method and standard requirements, but for a high-speed railway with higher requirements on settlement and deformation, the foundation pit excavation below the foundation pit excavation must adopt a scientific and reasonable construction method and combine precise detection to ensure the construction safety, thereby ensuring the safety of the high-speed railway. However, no effective construction method has been found.

Disclosure of Invention

The invention aims to provide a construction process of a bearing platform below an expressway, which ensures the stability of a foundation pit, ensures the construction safety and reduces risk factors.

In order to achieve the aim, the invention provides a construction process of a bearing platform below an expressway, which comprises construction preparation, bearing platform foundation pit excavation, pile head treatment, template installation, bearing platform steel bar installation, bearing platform concrete pouring, concrete form removal and foundation pit backfilling;

(1) preparation for construction

Leveling a working surface, investigating geological conditions and simultaneously investigating underground pipelines; measuring and paying off, namely measuring an excavation side line of the bearing platform by adopting a total station;

(2) bearing platform foundation pit excavation

Adopting a construction method of mechanical excavation and manual cooperation cleaning, directly excavating a bearing platform foundation pit by an excavator, wherein in the excavation process, an excavation side line is expanded by 1.0 meter more than a bearing platform side line, adopting a corresponding slope gradient according to soil quality, and supporting the foundation pit wall; the method comprises the following steps that (1) all pile foundation parts are excavated manually, 20-30 cm of foundation is reserved on a base and cleaned through manual excavation, a drainage system is arranged in a foundation pit, a water collecting well is arranged at one corner of the foundation pit, drainage ditches are excavated around the foundation pit, and water is drained by a submersible pump after water seepage is gathered;

(3) the pile head processing comprises pile head chiseling construction, pile head separation, pile head leveling and pile foundation detection;

(4) the bearing platform steel bar installation comprises steel bar binding, steel bar pre-embedding and bound concrete cushion blocks;

(5) concrete for pouring bearing platform

Watering and wetting the pile head, the groove bottom and the template, pouring concrete in layers, wherein the thickness of each layer is 30cm, and pouring the concrete is continuously carried out;

(6) foundation pit backfill

Backfilling as soon as possible after construction is finished, wherein the backfilled soil does not contain silt, humus soil and organic substances.

Preferably, the pile head chiseling construction steps are as follows:

s1, measuring the elevation of the pile head, marking, chiseling the pile head to be higher than the designed elevation of the pile top by using an air pick, and chiseling the rest part to be the designed elevation of the pile top by using manual work;

a. paying off, erecting a level gauge, adding 0.1m of position of the pile top elevation in lofting, and marking on two sides of the pile body;

b. cutting, namely winding a circle of iron wires at the marked height along the periphery of the pile, and cutting by using an angle grinder as a reference;

c. removing the groove, namely removing the groove along the position 2cm above the cutting line by using an air pick, horizontally removing the groove to form a plane, then obliquely removing the groove from top to bottom until the position of the outer skin of the steel bar of the pile body is reached, wherein the height of the groove opening is 20cm-30cm, and thus a free face is formed;

d. removing the steel bars, arranging hole positions and intervals in the horizontal direction, finding three pile body main bars forming an equilateral triangle according to the pile foundation main bars exposed by removing the grooves, and chiseling holes at the positions of the pile heads corresponding to the three points; arranging hole positions and intervals in the vertical direction, and drilling holes by using a rock drill according to the thickness of the concrete protective layer and the positions of pile body reinforcing steel bars, which are found by groove removal, along the hole positions and intervals in the vertical direction of the pile head;

chiseling concrete outside pile foundation steel bars, removing the steel bars 3 times along the pile body, putting a support into the drilled hole site, and striking the support by a hammer to crack the concrete and the pile body steel bars; separating the pile body concrete and the steel bars by using a steel chisel; carrying out decomposition and drilling on large concrete blocks containing reinforcing steel bars for 2 times at intervals of 30-40 cm, and directly removing concrete from small concrete blocks by using an air pick to expose the reinforcing steel bars;

s2 pile head separation

Hole site arrangement: arranging 4 continuous 'eyes' on the cross section separated by the pile head by using a rock drill, lifting a drill rod by 0.5cm from the horizontal direction, wherein the depth of the drill rod is 25 cm;

separating the pile head: putting the support into a hole position, and striking the support to a position where the pile head is separated by a big hammer to form a through crack;

hoisting the pile head: the pile head 1/3 is tied firmly by a steel wire rope and is lifted away from the pile body;

s3, leveling the pile head, manually leveling the pile head by using an air pick, leveling the surface of the pile head after chiseling, and ensuring that the distance height difference between adjacent convex points and concave points is not more than 2cm and the height difference of all the convex points is within 2 cm;

and S4, pile foundation detection.

Preferably, the step of installing the bearing platform steel bars is as follows:

s1 checking the formed steel bar

S2, binding steel bars: binding the steel bars sequentially from the long axis to the short axis, sequentially from one end to the other end, and finally forming;

s3, embedding steel bars: the reinforcing steel bars of the pile top extending into the bearing platform, the embedded reinforcing steel bars of the pier body on the bearing platform and the grounding reinforcing steel bars are bound;

s4, binding a concrete cushion block: the bottom reinforcing steel bar is provided with a concrete cushion block, and the thickness of the cushion block is 4 blocks per square meter based on the thickness of a protective layer.

Preferably, the construction steps of the bearing platform embedded part are as follows:

s1, arranging cooling pipes in the bearing platform, wherein the cooling pipes are uniformly arranged in the bearing platform, the distance between pipelines is 1m, and 1 layer of cooling pipes is arranged when the height of the bearing platform is less than or equal to 3 m; 2 layers of cooling pipe networks are arranged when the height of the bearing platform is 3-5M, each layer of cooling pipe is arranged in a continuous M shape, each layer of cooling pipe is provided with a water inlet and a water outlet, and the water inlet is 0.4M higher than the water outlet;

s2, carrying platform settlement observation mark: 2 settlement observation marks are arranged on the even bearing platforms, the settlement observation marks are arranged at the diagonal positions of the bearing platforms, and the top surfaces of the settlement observation marks are 1cm higher than the concrete surface.

Therefore, the construction process for the bearing platform below the expressway is adopted, the stability of the foundation pit is guaranteed, the construction safety is guaranteed, and risk factors are reduced.

The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.

Drawings

FIG. 1 is a table of slopes of a pit wall of a foundation pit in the construction process of a bearing platform under a highway;

FIG. 2 is a supporting diagram for slope releasing and excavation in the construction process of a bearing platform below an expressway of the invention;

FIG. 3 is a schematic view of chiseling concrete on the outer side of a pile foundation reinforcement in the construction process of a bearing platform below a highway;

FIG. 4 is a flow chart of a pile head chiseling process in the construction process of a bearing platform under an expressway of the invention;

FIG. 5 is a schematic view of a pile head after removing reinforcing steel bars in the construction process of a bearing platform under a highway.

Detailed Description

Embodiments of the present invention will be further described with reference to the accompanying drawings.

As shown in fig. 1-5, the process for constructing the bearing platform under the expressway comprises the steps of construction preparation, foundation pit excavation of the bearing platform, pile head treatment, template installation, steel bar installation of the bearing platform, concrete pouring of the bearing platform, formwork removal of the concrete and foundation pit backfilling.

1. Preparation for construction

The method is characterized in that site conditions are investigated before construction, a working surface inconvenient for mechanical operation is leveled, geological conditions are investigated, an excavation mode and a slope rate are determined, and underground pipelines are investigated simultaneously.

2. Measuring line

The method comprises the steps of checking and checking a coordinate base point, a leveling point and measurement data thereof provided by a design unit, introducing the coordinate base point, the leveling point and the measurement data into a construction site, measuring an excavation sideline of a bearing platform by adopting a total station according to design and slope placement and pit reserved size in combination with geological conditions, and spraying an excavation boundary line by using lime for facilitating mechanical excavation.

3. Bearing platform foundation pit excavation

The bearing platform adopts a construction method of mechanical excavation and manual cooperation cleaning, an excavator directly excavates a bearing platform foundation pit, excavation is carried out by adopting a jumping method, backfill soil is placed between the two bearing platforms, a construction access is guaranteed, the bearing platforms are stacked into a trapezoid, and redundant soil is discarded.

In the excavation process: the side line of the excavation is expanded by 1.0 meter than the side line of the bearing platform, a proper slope gradient (as shown in figure 1) is adopted according to the soil condition, and the excavation is properly supported according to the stable condition of the foundation pit wall. The pile foundation part is all by manual excavation, prevents to cause mechanical damage to the pile foundation, reserves 20 ~ 30cm at the basement and adopts manual excavation clearance, avoids the ground original soil to receive the disturbance, fills after strictly prohibiting the overexcavation. After the foundation pit is dug in place in rainy season and flood season: and a drainage system is arranged in the foundation pit, a water collecting well is arranged at one corner of the foundation pit, drainage ditches are excavated around the foundation pit, and the seepage water is collected and then drained by a submersible pump.

4. Precipitation treatment scheme

Factors such as rainy seasons and the like are considered according to the construction site conditions, the safety of foundation pit construction is ensured, and a small-range water pumping and dewatering construction scheme is adopted for dewatering treatment.

As shown in fig. 2, the excavation of the foundation pit should be performed in combination with the drainage of the water collecting well in the foundation pit as follows:

(1) drainage ditches are arranged around the upper part of the foundation pit to block ground water from flowing into the pit and draining away.

(2) And (3) increasing open trench drainage in the pit during excavation of the foundation pit, namely, a method for simultaneously excavating the foundation pit and simultaneously draining water.

(3) And (3) excavating drainage ditches around the bottom of the foundation pit, arranging water collecting wells at four corners of the bottom of the foundation pit, enabling water in the pit to flow to the water collecting wells through the drainage ditches, and then pumping out of the pit by using a water pump and draining away.

5. Construction for chiseling pile head

And measuring the elevation of the discharged pile head, marking, chiseling the pile head to be higher than the designed elevation of the pile top by using an air pick, and chiseling the rest part to be the designed elevation of the pile top by using manual work. In the process of chiseling the pile head, the broken slag is timely removed out of the foundation pit, meanwhile, the loose concrete on the pile top is completely chiseled, if the pile top is lower than the designed elevation, the pile top is cleaned and then is lengthened by the concrete with the same grade as the pile foundation, and the part of the pile top extending into the bearing platform is cleaned. When the pile head is chiseled off, attention is paid to the protection of the anchoring steel bars, as shown in fig. 4.

a. And (6) paying off.

And (5) erecting a level gauge, adding 0.1m of position to the pile top elevation of lofting, and painting paint by hands to mark two sides of the pile body.

b. Slotting

And winding a circle of iron wires at the height marked on the periphery of the pile, and cutting the pile by using an angle grinder for 2-3cm depth as a reference. The method has the following effects: the top surface of the cut pile is a plane; the second action is as follows: the integrity of the pile body is prevented from being influenced when the concrete is damaged during groove picking.

c. Groove picking

And (5) picking the groove at a position 2cm above the cutting line by using an air pick. The pick is horizontally picked to form a plane and then is obliquely picked from top to bottom. And (4) removing the pile body to the position of the steel bar sheath until the height of the notch is 20-30 cm to form a blank surface.

d. Removing steel bar

(1) Horizontal arrangement of holes and spaces

And finding three pile body main reinforcements forming an equilateral triangle according to the pile foundation main reinforcements exposed by the slot picking. The mark is made by hand painting. And drilling holes symmetrically at the positions of the pile heads corresponding to the three points.

(2) The hole sites and the spaces are arranged in the vertical direction

And (4) according to the thickness of the concrete protective layer found by the groove removal and the position of the pile body steel bar. Drilling holes by using the rock drill, wherein the hole positions and the hole intervals are along the vertical direction of the pile head, as shown in figure 3, only one row of vertical hole positions are shown, and the like.

(3) Direction of hole site

And drilling holes according to the positions and the intervals to realize the separation of the concrete and the pile foundation steel bars.

(4) Concrete for chiseling out steel bar of pile foundation

① removing reinforcing bars along pile body for 3 times

In order to reduce the turnover frequency of the stool and improve the speed, a method of removing the steel bars for 3 times is adopted to completely separate the steel bars from the concrete outer skin.

a, placing a support into a drilled hole position, knocking the support by a big hammer to form a crack between the concrete and the pile body reinforcing steel bar, and separating the pile body concrete from the reinforcing steel bar by using a steel chisel.

b if the concrete block is bigger and contains reinforcing steel bars, performing 2 times of solution to avoid damaging the reinforcing steel bars.

② treatment of the remaining concrete

The remaining concrete is large, and 2 holes are drilled at the distance of 30-40 cm, so that the purpose of separating the reinforcing steel bars from the concrete outer skin can be achieved; the concrete in the rest part is smaller, and the concrete is directly removed by an air pick to expose the reinforcing steel bars.

(5) And (4) removing the pile head after the reinforcing steel bars are removed, as shown in figure 3.

(6) Pile head separation

① hole site arrangement

4 'holes' are arranged on the cross section separated by the pile head by using a rock drill, the drill rod is lifted by 0.5cm in the horizontal direction, the depth of the drill rod is 25cm, and the distance is determined according to the distance between the pile foundation steel bar main reinforcements. The holes are arranged in 4 spaces formed by continuous 5 steel bars.

② separating pile head

The pile head is slightly shaken after the support is placed in a hole position and beaten by a big hammer, and a through crack is formed at the separation position of the pile head, which indicates that the pile head is broken.

③ pile head for hoisting

The pile head 1/3 is tied firmly by steel wire rope to ensure the lifting process is in an inclined state, and the crane transfers the redundant pile head away from the pile body.

(7) Pile head flattening

And (3) manually leveling the pile head by using an air pick, so that the surface of the pile head after chiseling is approximately flat, the distance height difference between the adjacent convex points and the concave points is not more than 2cm, and the height difference of all the convex points is within 2 cm.

And after the pile head is chiseled, whether the offset of the rechecking pile is within the construction allowable error range or not is checked. If the error is out of the construction allowable error range, the treatment is carried out in time.

(8) Pile foundation detection

And (3) analyzing the influence of the pile foundation detection result on the next procedure by adopting an acoustic transmission method for detecting the whole pile foundation: the I-type and II-type piles can directly enter the next working procedure,

the detection result is the pile foundation of the III-class pile, which indicates that the pile body has obvious defects and influences the bearing capacity of the pile body structure, the core drilling and sampling are carried out on the III-class pile, and the grouting treatment is carried out at the crack and the cavity.

And (5) detecting the pile foundation of the IV-type pile, and abandoning the original pile foundation and re-drilling the hole.

6. Cushion layer construction of bearing platform

The surface of the cushion layer is required to be substantially flat.

And (3) taking concrete elevation control measures of the cushion layer: after the foundation pit of the bearing platform is excavated, four reinforcing steel bars are nailed at four corner points of the bearing platform, the bearing platform is hung according to the elevation of the cushion layer within the size range, retest is carried out before cushion layer concrete is poured, and pouring is carried out after the requirement is met.

And (3) controlling the elevation of the cushion layer: the flatness of the cushion layer is 10mm/m, and the height of the cushion layer is consistent with the height of the designed cushion layer.

7. Manufacturing and installing bearing platform steel bars

(1) Preparation for construction

And performing a raw material test and a welding test on the approach reinforcing steel bars according to the specification, and using the approach reinforcing steel bars after the approach reinforcing steel bars are qualified. The reinforcing steel bars are intensively discharged in the processing shed, and the flat car is transported to the site. The semi-finished product steel bars should be stacked orderly in classification, clear in identification and accurate in size. Before binding the reinforcing steel bars of the bearing platform, the appearance quality of the reinforcing steel bars is checked, whether the surfaces of the reinforcing steel bars are clean or not is checked, and oil stains, corrosion and the like need to be removed.

(2) Bearing platform steel bar construction process flow

And (4) measuring and placing the axis and the contour line of the bearing platform on the cushion layer, performing paint marking on four corners, and marking the distribution line of the reinforcing steel bars by using chalk. And marking the positions of the pier dowel bars and the embedded parts by using paint.

The steel bar construction process flow comprises the following steps: checking the semi-finished product of the steel bar → binding the steel bar → installing the embedded part → binding the concrete cushion block

a. Checking the formed steel bars: before binding the steel bars, checking the processed semi-finished steel bars according to a design drawing. The specification, shape, model and variety are inspected, and then the cards are hung and stacked.

b. Binding steel bars: the steel bars should be bound in sequence, generally, the long axis and the short axis are sequentially bound from one end to the other end. During operation, the line is drawn, the iron is paved, the hoop is penetrated, the binding is carried out and finally the forming is carried out according to the requirements of the drawing.

c. Embedding reinforcing steel bars: the position of the reserved hole is correct; the steel bars of the pile top extending into the bearing platform, the embedded steel bars of the pier body on the bearing platform and the grounding steel bars are bound according to drawings, the binding is firm, cross fasteners are used for binding or welding, the sizes of the elevation, the position, the lap joint anchoring length and the like are accurate, and omission and displacement are avoided.

d. Binding a concrete cushion block: the concrete cushion is filled up under the bottom reinforcing bar, and the thickness of cushion is used for satisfying the thickness of protective layer as the standard, and 4 per square meter, the cushion of side should be with the reinforcing bar tie firmly, should not omit.

(3) Matters of attention

a. And (4) calculating to ensure that the number of the welded joints of the steel bars is not more than 50% of the same section, and the steel bars must be concentric.

b. If the bearing platform steel bar is abutted to the pile body and the pier body steel bar, the bearing platform steel bar can be properly adjusted, and the position of the pier body steel bar must be ensured to be correct.

c. In order to facilitate construction, proper manhole holes are reserved when the top-layer steel bars of the bearing platform are installed, and the size of the manhole holes is reserved by adjusting the distance between the top-layer steel bars of the bearing platform.

d. In order to facilitate the positioning of the steel bars, proper quantity of erection steel bars are matched according to the installation requirement. The reinforcing steel meshes are firmly welded by adopting erected reinforcing steel bars, the alignment of upper and lower layer grids is realized, the interlayer spacing is correct, and the thickness of a protective layer of the reinforcing steel bars is ensured.

e. The installation speed of the steel bars is accelerated, and the exposure time of the foundation pit is shortened. The embedded ribs of the pier body and other embedded parts are installed and firmly positioned according to specified positions.

(4) Construction of embedded parts of the bearing platform:

a. cooling a pipe: in order to reduce the difference between the internal temperature and the surface temperature of the concrete, cooling pipes are required to be arranged on part of the bearing platform, the cooling pipes are uniformly arranged in the bearing platform and are made of phi 32 galvanized steel pipes, and the distance between the pipes is 1 m. 1 layer of cooling pipes are arranged when the height of the bearing platform is less than or equal to 3 m; and 2 layers of cooling pipe networks are arranged when the height of the bearing platform is 3-5 meters. Each layer of cooling pipe is provided with a water inlet and a water outlet, the water inlet is 0.4 meter higher than the water outlet, each layer of cooling pipe must ensure sealing and water leakage prevention, and two openings are blocked by foam materials when the bearing platform is poured, so that cement paste is prevented from blocking the pipeline.

b. Bearing platform settlement observation mark: 2 settlement observation marks are arranged on the even bearing platforms, the settlement observation marks are arranged at the diagonal positions of the bearing platforms, and the top surfaces of the settlement observation marks are 1cm higher than the concrete surface.

8. Bearing platform formwork construction

(1) Bearing platform formwork construction process

The template installation process flow comprises the following steps: determining the scheme of assembling steel templates → installing steel templates → pre-inspecting templates

a. Scheme for determining assembled steel templates

Firstly, an assembling scheme of assembling the steel template by the bearing platform is worked out, and the diameter, the length, the position, the distance between side rod points and the size and the position of the split bolt are determined by calculation. When the steel template does not have modulus, a wooden template can be additionally added for gap filling.

b. Installing steel form

The assembled steel shuttering consists of plane shuttering, male and female angle shuttering. The U-shaped clamps, bolts and other spare and accessory parts for splicing the longitudinal ribs and the transverse ribs are complete and firm, and are not loosened and omitted. The outer side is reinforced by section steel. The inner side of the formwork is drilled with a percussion drill, the anchor rods are arranged, and the pull rods are used for pulling and fixing, so that the firmness of the formwork is ensured, the transverse spacing of formwork supports is not more than 0.6m, the longitudinal spacing is not more than 0.7m, and the support length is not too short. The support form is as follows: the inclined support is not adopted as much as possible, and when the inclined support is adopted, the angle is not more than 15 degrees. The back of each support is provided with a retaining plate, and the contact surface of the retaining plate is firm and reliable.

c. Template pre-inspection

After the template is installed, the cross section size and elevation, the split bolts, the connecting rod supports and the like are subjected to pre-detection. All should meet the requirements of design drawings and quality standards.

(2) Matters of attention

a. And (3) removing rust and coating a release agent before installing the template.

b. And the template is installed after the reinforcing steel bars are installed. The templates are hoisted and installed in blocks and are assembled from the center to the two sides in sequence. The template installation must be firm, and the seam is closely knit, must not leak thick liquid.

c. When the side forms are removed, the strength of the concrete reaches the strength required by design, when the side forms are not required by design, the strength of the concrete is not less than 2.5Mpa when the side forms are removed, the surface and the edges are not damaged by removing the template, and the temperature difference between the surface of the concrete and the environment is not more than 20 ℃ when the side forms are removed.

9. Concrete pouring and maintaining of bearing platform

Before concrete pouring, the template, the steel bars, the bracket and the embedded parts are checked, records are made, and pouring can be performed after the concrete meets the design requirements. Sundries, accumulated water and dirt on the steel bars in the template are cleaned up. If the template has gaps, the template should be tightly filled. The concrete is made of corrosion-resistant concrete with corresponding grade, and is intensively mixed and transported by a concrete transport vehicle.

(1) Pouring of concrete

The pile head, the groove bottom and the side mould (wood mould) should be watered and moistened.

When concrete is poured on the bearing platform, the elevation of the top surface is measured before the concrete is poured, marks are made on the bearing platform template, the concrete is poured by adopting a pump truck or a sliding chute, the blanking position is convenient to adjust in time, the blanking is carried out corresponding to the pile head when the concrete is poured so as to prevent the soil below from being flushed into the concrete, and the blanking is carried out symmetrically from two ends to the middle so as to prevent the embedded ribs of the pier body, the embedded parts and the bearing platform template from inclining or displacing due to uneven stress.

The concrete pouring adopts layered pouring, and the thickness of each layer is controlled to be 30 cm. The vibrating method is characterized in that the vibrating rod is uniformly and compactly arranged along the pouring sequence direction of the bearing platform by adopting an oblique vibrating method, the angle between the vibrating rod and the horizontal plane is about 3 degrees, the rod head advances forwards, the vibrating rod is inserted into the previous layer for 5-10 cm, and the distance between two times of vibrating is not more than 1.5 times of the working radius of the vibrating rod. The distance between the vibrating rod and the bottom die and the side die is 5-10 cm, the template is easy to deform when the vibrating rod is too close, and the phenomenon of vibration leakage is easy to occur when the vibrating rod is too far, so that pitted surfaces or large-area bubble holes on the surface of concrete are formed. The vibration degree is based on the concrete surface which is overflowed with air bubbles or water bubbles. Leakage vibration and excessive vibration are not allowed. When the free falling body of the concrete is told to exceed 2m, the concrete is prevented from being separated by adopting a string cylinder or a chute for blanking. The surface of the concrete is vibrated and marked according to the height line, is trowelled by wood, is trowelled for the second time after sizing, and is polished or napped.

The placement of the concrete should be continuous, for example, when it is necessary to be interrupted for this reason, the interruption time should be shorter than the initial setting time or the remodeling time of the front concrete, and the allowable interruption time should be determined by experiments. Otherwise, processing according to the construction joint.

Arranging full-time testers to retain concrete samples according to standards on a construction site in the concrete pouring process, and timely delivering the standard health-preserving samples to a central laboratory for health preservation after the samples are demoulded.

(2) Construction joint treatment

The cement mortar and the weak layer on the surface of the concrete of the treatment layer should be chiseled, but when chiseling, the concrete of the treatment layer must reach the following strength: when the chiseling is washed by water, the pressure needs to reach 0.5 MPa; when the chisel is manually removed, the pressure is required to reach 2.5 MPa; when the air motor is used for chiseling, 10MPa is required. And (3) flushing the chiseled concrete surface by using water, brushing a layer of cement paste on the vertical construction joint before pouring the next-layer concrete, and paving a layer of 1: 2, cement mortar.

In the concrete pouring process, a specially-assigned person is required to check the stability conditions of the bracket, the template, the steel bar, the embedded part and the like, and when looseness, deformation and displacement are found, the concrete should be processed in time.

(3) Concrete curing

After concrete is poured, plastering and slurry collecting are started, surface shrinkage cracks are controlled, water evaporation is reduced, the concrete is covered and maintained as soon as possible after slurry is collected, and the concrete is covered and maintained in a mode of covering a plastic film on the inner side and covering a geotextile on the outer side. The concrete is maintained by covering, watering and maintaining in a manner of being responsible for by a specially-assigned person, and the water for maintaining adopts drinking water and neutral water. The maintenance water is supplied by a water supply pipeline arranged along the line.

The concrete of the bearing platform is large-volume concrete, and the curing period is 28 days. Geotextiles are covered during summer curing, and the surface of the formwork and the concrete is kept wet frequently. When the temperature is lower than 5 ℃ in winter, the straw mat should be covered for moisture preservation, and the curing agent should be coated, so that water cannot be sprayed on the concrete surface.

The curing time of the concrete is to carry out curing according to the mineral admixture and the water-cement ratio in the concrete mixing ratio, the humidity, the temperature and the concrete temperature of the environment and the like, wherein the days specified by the acceptance standard of the concrete construction of the passenger special line are required, during the curing of the concrete, the difference between the internal temperature and the surface temperature of the concrete and the difference between the surface temperature and the environment temperature are not more than 20 ℃, the difference between the curing water temperature and the surface temperature of the concrete is not more than 15 ℃, and curing personnel carry out curing record during the curing of the concrete.

During concrete curing, a water tank can be placed at a position higher than the water inlet, water in the water tank is injected into the water inlet of the cooling pipe through the rubber pipe, and water flow passes through the cooling pipe network which is arranged in a rotating mode in an M shape and is discharged from the water outlet of the cooling pipe. The internal temperature of the concrete of the bearing platform can be effectively reduced through water circulation. The water circulation needs to be monitored by a specially-assigned person, the temperature of water at the water inlet and the water outlet can be respectively measured by adopting a thermometer in the monitoring mode, and the water circulation can be stopped when the temperature of the two positions has no obvious temperature difference. And after the cooling pipe cooling maintenance work is finished, the pipeline is filled and blocked by adopting cement paste.

During maintenance, when the structure is in contact with flowing surface water or underground water, water should be pumped firstly, so that the concrete is prevented from being washed away by flowing water and accumulated for cooling in 7d after pouring, and temperature difference cracks are avoided.

Before the strength of the concrete reaches 1.2MPa, the concrete cannot bear loads of people, templates, scaffolds and the like. After the bearing platform reaches a certain strength, the next construction can be carried out. But the bearing platform still needs to be maintained, and backfilling construction is carried out after seven days.

(4) Chiseling of concrete

And after the strength of the concrete reaches 2.5mpa, chiseling the contact surface of the lower layer concrete and the pier in an artificial chiseling mode.

10. Concrete form removal

After the concrete strength reaches 2.5mpa, and the concrete surface and the edges are not damaged due to form removal, the formwork can be removed, and the formwork is removed in the sequence of firstly supporting and then removing, and then removing firstly. The temperature of the concrete can not be too high when the concrete is dismantled, so that the concrete is prevented from cracking due to too fast temperature reduction when contacting air, and the mould can not be dismantled before the temperature of the interior of the concrete is reduced. Immediately organizing supervision and acceptance after the formwork is removed, and timely backfilling the foundation pit.

11. Foundation pit backfill

The bearing platform foundation should be backfilled as soon as possible after the construction is finished, and the following requirements should be met before backfilling:

① the strength of the foundation concrete of the bearing platform should reach 70% of the designed strength.

② before backfilling the foundation pit, removing the accumulated water in the foundation pit, wherein the backfilled soil does not contain silt, humus soil and organic substances, the backfilled soil should be layered and tamped when backfilling the foundation pit, and the support can be removed when each layer of loose pavement is not more than 30 cm. and backfills to about 1m below the support.

In addition, concrete quality assurance measures need to meet the following conditions:

1. concrete pouring quality

Before pouring concrete, carefully checking the position, the quantity and the fastening degree of the cushion blocks of the reinforcing steel bar protective layer, and appointing a special person to check the rechecking property, wherein the cushion blocks on the side surface and the bottom surface of the component are at least 4/m²And the iron wire head for binding the cushion block and the steel bar cannot extend into the protective layer.

Measuring working performance indexes such as the mold-entering temperature, the slump and the air content of the concrete; and the mixture can be poured into a mold after the performance of the mixture meets the requirements of the standard test and the related technical specification. The pouring of the concrete is carried out in a layered continuous propulsion mode, the pouring clearance time is not more than 90min, and a construction joint cannot be reserved at will.

When the falling height is less than 2m, adopting free falling; when the thickness is larger than 2m, the concrete is conveyed by the aid of the sliding chutes, the string cylinders, the funnels and other devices, and the layered segregation phenomenon of the concrete is avoided. The pouring of the concrete needs to be continuously carried out, and the uniformity and the compactness of the concrete are strictly controlled in the pouring process.

2. Concrete vibrating mass

The concrete can be vibrated by adopting an inserted high-frequency vibrating bar and attached flat vibrator vibrating equipment. The template, the steel bar and the pre-buried iron piece cannot be collided during vibration. The concrete is vibrated according to the process and the method specified in advance, the concrete is uniformly and timely vibrated and compacted in the concrete pouring process, the vibration time of each point is based on surface slurry spreading or large bubbles, the time is generally not more than 30s, and over-vibration is avoided. In the process of vibrating concrete, the stability of the template support and the sealing condition of the joint are detected in a reinforcing mode, and slurry leakage is prevented. After the concrete is poured, the concrete surface is carefully compacted and smoothed, and water is strictly forbidden when the concrete is smoothed.

3. Concrete curing quality

And after the concrete is vibrated, timely adopting a moisture-preserving measure to maintain the concrete. When the newly cast concrete has an exposed surface, the exposed surface concrete is firstly leveled, then the exposed surface is covered by linen, and measures such as spraying and sprinkling water are timely adopted to carry out moisture preservation and maintenance on the concrete for more than 7 days. When the concrete is maintained in a mode of maintaining with a mold, the concrete at the joint of the template is ensured not to be dehydrated and dried.

When the strength of the concrete meets the requirement of form removal, and the temperature difference between the core concrete and the surface concrete and the temperature difference between the surface concrete and the environment are not more than 15 ℃, the form can be removed (the form cannot be removed before the interior of the concrete begins to be cooled). And after the mold is removed, the concrete is quickly maintained in the later period by using the health-preserving cloth.

During concrete curing, temperature monitoring is carried out on a representative structure, parameters such as the temperature of a concrete core part, the temperature of a surface layer, the ambient temperature, the relative humidity and the wind speed are measured at regular time, a curing system is adjusted in time according to the change conditions of the temperature and the ambient parameters of the concrete, and the internal and external temperature difference of the concrete is strictly controlled to meet the requirements.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the invention without departing from the spirit and scope of the invention.

Claims

1. A construction process of a bearing platform below an expressway is characterized by comprising the following steps: the construction method comprises the steps of construction preparation, pile cap foundation pit excavation, pile head treatment, template installation, pile cap steel bar installation, pile cap concrete pouring, concrete form removal and foundation pit backfilling;