CN117738192A - Construction method combining deep well shallow excavation and open caisson method - Google Patents
Construction method combining deep well shallow excavation and open caisson method Download PDFInfo
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Abstract
The invention relates to the technical field of construction of a cyclone basin open caisson, in particular to a construction method combining deep well shallow excavation and an open caisson method. Compared with the prior art, the construction method ensures the stability of surrounding structures, reduces the amount of earth excavation, saves the cost of mechanical shifts and labor, shortens the construction period, improves the working efficiency, and completes technical innovation in the aspects of earth excavation construction, precipitation technology, sinking technology of a sinking well and the like.
Description
Technical Field
The invention relates to the technical field of construction of a cyclone basin open caisson, in particular to a construction method combining deep well shallow excavation and an open caisson method.
Background
For open caisson construction of a cyclone basin, the following 3 methods are conventionally adopted:
(1) extensive description of the effect of traditional means on perimeter-heavy excavation: the depth of the foundation pit of the cyclone pool is 22.5m, and the minimum slope ratio of the heavy excavation is 1:1, large working area and large soil digging amount have great influence on surrounding roads and old factory buildings;
(2) underground continuous wall: the underground diaphragm wall needs enough space to meet the station position of construction machinery, and the normal underground diaphragm wall construction needs a grooving machine, but if the diaphragm wall has a middle sand layer when meeting soil, the diaphragm wall is easy to collapse in the grooving process, and the construction requirement cannot be met;
(3) traditional open caisson: the requirements on the field flatness are high, and larger fields and spaces are needed.
For a certain cyclone sedimentation tank project, the following limitations exist:
1. the current situation is that the ground is uneven, the height difference is about 5m, the north side of the rotational flow pool is an in-site temporary road Gao Chengyao m, the center is about 19m, the south side is an old factory area Gao Chengyao 15.4.4 m, and the normal passing of the temporary road and the normal production of the old factory are ensured in the construction process.
2. The structural form is a reinforced concrete circular shaft, the inner diameter is 30m, the wall thickness is 1.1m/1.0m (outer step), and the open caisson construction process is adopted. The term + -0.000 m corresponds to absolute elevation +18.800m (all elevations in this scheme are relative elevations except for the noted). The height of the open caisson of the cyclone sedimentation tank is 20.8m, the top standard height of the open caisson is +0.3m, and the elevation of the bottom of the cutting edge foot is-20.5 m.
In summary, the requirement of the new project cannot be met by adopting the traditional construction method of the cyclone pool.
Disclosure of Invention
The invention aims to overcome the defects and provides a construction method for a cyclone basin open caisson in a special environment.
In order to achieve the above object, the present invention is achieved by:
1. a construction method combining deep well shallow excavation and open caisson method is characterized in that: comprising
Step 1, measuring and paying-off
Measuring and positioning according to the coordinates of a design drawing and a datum point provided by a first party, arranging coordinate control points and temporary level points around the open caisson and outside a construction influence range, wherein the precision of the established control points is +/-1 mm; arranging gantry piles around the open caisson, drawing a central axis of the open caisson and a contour line of a foundation pit by lime powder, and measuring the elevation and other construction drawings in the occupied place of the cyclone pool as the basis for programming the open caisson construction scheme;
step 1.1, wire measurement
The wires are laid according to the total plane diagram, and the positions of the wires select clear zones;
step 1.2, angle measuring and testing
The angle observation is carried out by adopting a full circle return method, and the return number and the measurement limit difference are the same as the square grid angle observation requirement;
step 1.3, elevation measurement
The engineering elevation measurement control network is established by adopting a three-level measurement method, a four-level measurement method and the like, and the absolute elevation of the level network is guided and measured according to an advanced level point provided by an owner and is connected with one point in the network to serve as a basis for calculating the elevation;
Step 1.4, pile burying
The wire control point and the elevation control point are far away from the sinking area of the sinking well, the stake is deeply buried, and a protection device is arranged;
step 2, supporting steel sheet piles
The temporary road can be ensured to pass only by protective measures due to overlarge field height difference, the construction road is protected by adopting a steel sheet pile supporting mode through field confirmation, and the steel sheet pile is 15m in Larson IV type and is arranged along one side of the road;
step 3, shallow excavation of the foundation pit;
according to the current situation that the rotational flow pool is located on the ground, the height difference is about 5m, the north side of the rotational flow pool is provided with an in-situ temporary road Gao Chengyao m, the center is about 19m, the south side is provided with an old factory area Gao Chengyao 15.4.4 m, the temporary construction road cannot be broken according to the construction requirement, and the construction process cannot influence the production of the old factory.
And (3) selecting a slope-releasing excavation mode, namely excavating a foundation pit in the current situation of ground elevation +1.3m, excavating a foundation pit bottom elevation-3.5 m, excavating a depth of 4.8m, and excavating along the circumferential direction of a well wall. Considering the width of a working face for manufacturing the open caisson, the bottom edge line of the foundation pit is 2m of the outer expansion of the well wall. According to the geological survey report and the technical Specification of construction side slope engineering (GB 50330-2013), the slope releasing rate is 1:0.75. slope protection can be adopted if necessary, and a slope protection mode adopts a cement mortar spraying protection surface. The foundation pit excavation adopts the combination of mechanical excavation and manual trimming, the elevation of the excavation is strictly controlled, when the excavation is close to the pit bottom by 200 mm-300 mm, the manual slope trimming and the flat bottom are adopted, and in the process of the foundation pit excavation, the drainage ditch is combined with the water collecting pit to drain water so as to ensure the construction requirement of the foundation pit. According to the technical Specification for controlling underground water of construction and municipal engineering (JGJ 111-2016), a blind ditch with the width of 0.3m and the depth of 0.3m is arranged on the bottom surface of a foundation pit of a sunk well, the gradient is 0.2%, 8 water collecting wells with the diameter of 300mm are arranged along the inner side and the outer side of the periphery of the sunk well, and the water collecting wells are symmetrically arranged. The bottom surface floating mud should be cleaned and kept in a flat and dry state.
Step 4, paving a sand cushion layer, a concrete cushion layer and manufacturing a brick bed-jig
Step 4.1, paving a sand cushion layer
And after the foundation pit is excavated, paving a sand cushion layer. The sand cushion layer adopts middle coarse sand, is paved according to 30cm layers, is vibrated and compacted by a flat plate while sprinkling water according to the water content of 15%, the compaction coefficient is more than or equal to 95%, and the compression bearing capacity characteristic value is more than or equal to 150kPa. And after the lower layer meets the requirement, paving a second layer. In order to prevent factors such as rainy days, a blind ditch is arranged at the bottom of the foundation pit to concentrate water to a water collecting well and then the water is pumped out by a water pump so as to soak the sand-preventing cushion layer in the water.
Step 4.2, plain concrete cushion layer manufacturing
And a plain concrete cushion layer with the thickness of 15cm and C20 is paved below the cutting edge on the sand cushion layer, so that the pressure on the sand cushion layer is reduced, and the external expansion width of the plain concrete cushion layer is 20cm respectively at two sides outside the well wall. After the sand cushion is paved, pouring a plain concrete cushion on the sand cushion, wherein the plain concrete cushion is ensured to be horizontal, and the error is less than 5mm, so that the template construction is facilitated.
Step 4.3, manufacturing the brick moulding bed
The cutting edge is built by adopting a brick moulding bed, the plane position of the open caisson is accurately measured and placed on the sand cushion layer and the plain concrete cushion layer according to the designed well position, the brick moulding bed is constructed, low-grade cement mortar is adopted when bricks are built, the inclined plane of the cutting edge is smooth, the brick moulding bed is painted by lime and a small amount of cement mixture, and the hole site of the pull rod bolt of the open caisson wall template is reserved in the brick moulding bed.
And (3) chiseling the brick bed-jig and the plain concrete cushion layer by adopting a symmetrical chiseling method before sinking the open caisson, and if the open caisson has a height difference, correcting the deviation by adjusting the chiseling sequence of the brick bed-jig and the plain concrete cushion layer.
Step 5, precipitation of the open caisson
The key to success of drainage is the effect of well-point precipitation. The engineering is to adopt the pipe well for dewatering so as to meet the requirement of the sinking well drainage for underwater sinking.
The pipe well dewatering is non-critical work, namely the construction is planned to be arranged in synchronization with the production of the open caisson structure, the completion of the pipe well construction is ensured before the open caisson is submerged, and the dewatering reaches the design requirement of 1.0m below the excavation surface, so that the dewatering operation period is shortened, the influence period of the dewatering on the periphery is reduced, and the cost is saved.
Well site arrangement
15 phi 273mm pipe wells (12 dewatering wells and 3 standby wells) are annularly arranged along the open caisson so as to meet the dewatering requirement in open caisson construction. The dewatering wells are 8m away from the outer wall of the open caisson, the intervals between the dewatering wells are 10m, and the well depth is 31m.
And finally determining the number and distribution form of the dewatering wells according to the on-site water pumping experiment. The standby dewatering well is also used as an observation well, and the change of the underground water level is monitored at any time.
Step 6, precipitation well construction and design requirements
Step 6.1, wellhead: the well mouth is set 0.5m above the ground to prevent the surface sewage from penetrating into the well, and is sealed by high-quality clay and cement slurry.
Step 6.2, a well wall pipe: the wall pipe adopts Q235B welded steel pipe, the wall thickness is 5mm, and the inner diameter phi 273mm.
Step 6.3, filter (strainer): the dewatering well adopts a bridge type water filtering pipe, two layers of 30-40 mesh nylon nets are wrapped outside the water filtering pipe, and the diameter of the pipe is the same as that of the well wall pipe;
step 6.4, sedimentation tube: the sedimentation pipe mainly plays a role in preventing the filter from affecting water inflow due to sand setting blockage in the well, the sedimentation pipe is connected to the bottom of the water filtering pipe, the diameter of the sedimentation pipe is the same as that of the water filtering pipe, and the bottom opening of the sedimentation pipe is sealed by an iron plate;
step 6.5, gravel filling: the water filtering pipe of dewatering well is filled with No. 4 sand with good grinding degree, and the water filtering pipe is filled with sand from bottom to top.
Step 6.6, filling cohesive soil and sealing holes: and (3) surrounding and filling high-quality clay to the ground surface above the surrounding and filling surface of the gravel, tamping, and sealing the outer surface of the wellhead pipe.
Step 7, deep well dewatering construction
1) And (3) construction sequence: equipment entering, well positioning, vertical drilling frame, hole forming, hole cleaning, steel well pipe discharging, sand recharging, well washing, water pumping, well dismantling and field returning.
2) And a GPS-15H type engineering driller is adopted for deep well pore-forming. The pore-forming depth is 31m, the pore diameter is 500 mm, and the pore-forming verticality deviation is less than or equal to 1%.
3) And (3) carefully cleaning the holes after hole forming, turning the slurry clear, measuring by a measuring rope, and continuously sinking the steel well pipe after the hole depth is determined to meet the requirement.
4) And hoisting the sinking steel sleeve by using a winch on a drilling machine, welding each section of single-section well pipe (4-5 m), and then installing in sections. The steel casing is exposed to the ground 0.5 m.
5) The filter tube at the lower end of the steel sleeve is wrapped with a 50-mesh filter screen for 4 layers and is fastened by 18# lead wires. After the steel sleeve is sunk, crushed stone of about 0.5 m is poured into the pipe to press the bottom, and then sand is uniformly poured around the sleeve until reaching the ground surface.
6) And (3) immediately flushing the well after sand filling is finished, wherein a piston type well flushing method is adopted for flushing the well. The piston is used for sinking into the bottom of the pipe by dead weight, then the winch is used for pulling up quickly, the muddy water is carried out together, and the process is repeated for a plurality of times until the carried-out muddy water is clear.
7) And after well flushing, the well is put into a submersible pump for trial pumping, and pumping is carried out according to construction requirements after water is discharged normally.
8) Special persons are dispatched during pumping to check pumping conditions, water level elevation and water yield are recorded, and found problems are solved in time;
step 8, precipitation operation
Step 8.1, test run
Before test operation, accurately measuring elevation of each wellhead and ground, and standing water level, and then starting test operation to check whether the water pumping equipment and the water pumping and draining system can meet precipitation requirements.
Step 8.2, precipitation operation
(1) The dewatering well is operated according to the construction progress of the open caisson.
(2) In the dewatering operation process, water level observation work of each well is performed, and the change condition of the water level in the well is mastered in time.
(3) When the water head in the well is reduced to the design requirement in the dewatering operation process, the water pumping quantity of the pressure-bearing water head is controlled by properly regulating and controlling the water pumping quantity of the pressure-bearing well.
(4) And during the precipitation operation, 24-hour duty system is implemented on site, and the operators on duty are carefully arranged to make various quality records, so that the accuracy and completeness are realized.
Step 9, sinking the open caisson
Sinking of the sinking well mainly comprises removing soil from a well hole, eliminating resistance under a blade foot and friction resistance of the well wall, and sinking by means of dead weight of the sinking well.
Step 9.1 preparation before sinking
The strength of the first concrete section of the open caisson manufactured by sections must reach the design strength before sinking, and the other sections must not be lower than 70% of the design strength.
Chiseling off the concrete cushion layer and the brick moulding bed of the cutting foot element before sinking. The cushion layer is removed firstly and then symmetrically, and broken bricks in the well are cleaned by a crane grab bucket. Dividing the cushion layer under the blade foot into 12 areas, symmetrically chiseling for 3 times, chiseling 1, 4, 7 and 10 areas, chiseling 2, 5, 8 and 11 areas, and chiseling 3, 6, 9 and 12 areas. And drawing a measuring scale on the wall of the well around the open caisson, and setting up a horizontal indicating scale.
Before the open caisson digs, the cutting edge of the open caisson is dug manually and comprehensively and simultaneously in layers, the dug earthwork is concentrated in the center, the open caisson is gradually sunk, the cutting edge of the open caisson is buried in a soil layer, and the gravity center of the open caisson is lowered. Because the sinking coefficient is larger in the initial sinking process of the open caisson, the open caisson adopts soil squeezing sinking.
In construction, 4 observation points are arranged on a sinking well wall, continuous tracking measurement is carried out, and measurement is carried out once per hour. The measurement result is arranged by taking the average value of the sinkers at 4 points as the sinkers at each time, taking the point with the largest sinkers as the reference and subtracting the sinkers at other points as the height difference of the points, so as to guide deviation correcting sinkers.
Step 10, drainage sinking process
The cyclone sedimentation tank open caisson adopts three times of manufacture and three times of sinking, adopts a drainage sinking process, and has a sinking elevation of +0.0m and a sinking depth of 20.5m.
Two 50T crawler cranes are matched with two 80 small digging machines to dig soil from the center of the open caisson to the periphery, so that the bottom of the boiler is formed, and the boiler is uniformly sunk to prevent sudden sinking. And finally, the dregs are lightered to a designated place by using a dump truck. And after final sinking in place, adopting a dry back cover.
Step 11, sinking control of the open caisson
According to the important point of quality control in the sinking process, the sinking construction is divided into the following three stages:
1. Stage of preliminary sedimentation
(1) 4 observation points are arranged on the sinking well wall, and tracking measurement is performed. The measurement results were collected by using the average value of the sinkers at 4 points as the sinkers at each time.
(2) The sinking depth of the open caisson is in the range of 0-3 m as a primary sinking stage. Firstly, the plain concrete cushion layer is symmetrically chiseled out from inside to outside. When the open caisson is inclined, the chiseling position is adjusted in time, so that the open caisson is cut into the soil stably.
(3) During primary sedimentation, the sinking coefficient of the open caisson is larger, the gravity center is high, and the stability is poor; the fluctuation phenomenon can occur, and when the height difference value of the open caisson in four directions (east, south, west and north) is larger, the deviation is corrected in time.
(4) When the deviation of the open caisson is overlarge in the primary sinking stage, the shoveling personnel are arranged to adjust the number of the soil taking bin or the soil taking position, the soil taking depth (less than or equal to 50 cm-100 cm) between each bin is controlled, when the measured height difference is good, the depth of the bottom of the pot is controlled, the open caisson is prevented from sinking suddenly, the uniform digging, the duty measurement and the soil correction are really realized, and the height difference is controlled well.
(5) The resistance to sinking of the open caisson in the initial stage is mostly due to the earth reaction force from the bottom edge tread and bottom surface of the bottom beam, and the outward friction force of the well increases with the increase of the sinking amount. The distribution condition of the soil reaction force is changed by adopting a mode of adjusting the soil digging mode at the bottom of the pot in construction.
2. Normal sinking stage
(1) At the end of the primary sinking stage, if various technical indexes of the open caisson are good, the depth of the bottom of the open caisson can be increased, the depth of the bottom of the caisson is generally controlled to be about 1.2m, the soil digging speed can be increased, the soil counter force is reduced, the resistance during sinking is reduced, and the construction progress is improved.
(2) If the height difference of the four control points of the open caisson is still large at the end of the primary sedimentation stage, the open caisson is adjusted according to the deviation correcting requirement of the primary sedimentation stage, so that the open caisson is restored to the normal construction condition. In the open caisson process of the second stage, when the height difference of the four-direction control point is larger than 30cm, correction (about 1m of height difference) should be immediately carried out, soil under the outer wall blade foot must be well controlled, the soil at the position is not easy to dig, and the phenomenon of soil gushing is prevented.
(3) When sinking the sinking well, the well cabin should be symmetrically dug, and the soil surface in the well should be uniformly sunk, and the height difference in the well should not be greater than 1.0m. When in construction, the sinking condition should be observed at any time, if the inclination is found, corrective measures are taken in time, and the phenomenon that the cutting edge foot is partially placed is forbidden. Recording work of sinking of the open caisson is performed in construction, a sinking rate chart is drawn, and reliable data basis is provided for final sinking construction.
3. Final sinking stage
(1) And when the sinking of the open caisson reaches the last 2m, the final sinking stage is started. The shape of the bottom of the earth-digging pot is gradually changed from a concave surface to a convex reverse bottom, the soil taking speed and quantity are properly slowed down, the soil taking range is strictly arranged according to a uniform and symmetrical principle, when the height difference of control points around the open caisson is more than 20mm, the correction is timely carried out, the correction method is mainly used for adjusting the soil digging depth, the soil body of the soil plug part of the outer blade foot is easy to gush in, and the soil is not excessively dug. The final sinking stage is the key moment of the open caisson, and needs to strengthen observation and strictly control the sinking rate of the open caisson.
(2) Once the elevation of the blade tread of the open caisson reaches the elevation of the design requirement, immediately stopping taking soil, and throwing and filling with large stones, measuring and observing closely, wherein the sinking of the open caisson is not more than 10mm within 24 hours. After the open caisson is constructed in place, the measurement requires that the four-angle direction height difference is observed every 4-6 hours.
(3) The sinking is required to continuously and stably sink to the designed elevation, the bottom is sealed in time, the power failure is stopped in the sinking prevention process, and the rest part is poured after the concrete strength of the bottom plate reaches the design strength.
Step 12, sinking assisting measures
The engineering contemplates the use of a thixotropic mud system to assist in sinking. After the sinking well is sunk in place, cement paste or cement mortar is adopted to replace thixotropic slurry.
The thixotropic slurry sinking-assisting method is a better sinking-assisting drag-reducing method, and can reduce the disturbance influence of the open caisson on surrounding soil to a great extent during construction. Thixotropic mud plays roles in reducing friction and maintaining soil wall stability in sinking of the open caisson.
1) Construction arrangement
According to the on-site situation, arranging a mud box, 1 slurry stirring machine, 2 slurry pressing pumps, and a slurry conveying pipeline, wherein the slurry pressing pipeline is constructed by adopting an in-well outer pipe method and a 1 inch PVC pipe. The horizontal pipes are respectively arranged 2 times along the circumferential direction and are positioned at the positions of 2.5m and 4.5m above the cutting edge, and the vertical pipes are directly raised above the well wall.
The angle steel L is arranged at the injection port, the length of 100 multiplied by 8 is 20cm to form an injection port enclosure, so that grouting blockage and direct injection of soil walls are prevented. In order to prevent the collapse of the ground soil layer and damage to the slurry cover, a ground surface enclosure is provided. Backfilling and layering tamping the outer side of the enclosure by using cohesive soil.
2) Slurry preparation
The slurry is prepared from high-quality bentonite, lime and water (mixing ratio is 4:1:15), and the water loss and mud skin thickness, static shear force and sand content of the slurry are controlled conventionally in construction.
3) Grouting
The grouting adopts a grouting pump, the normal pressure injection pressure is 100-800 kPa, the grouting adopts the hole-by-hole grouting, and the grouting is continuously supplemented along with the sinking of the sinking well, so that the mud surface is always kept at about 0.3m above the ground.
4) Grouting
And after sinking of the open caisson is completed, grouting the annular belt outside the open caisson to replace bentonite slurry. The cement slurry consists of ordinary silicate cement and cement slurry with water cement ratio not exceeding 0.45. Grouting should be a homogeneous mixture of cement and water, their consistency should be sufficiently fluid.
13. Open caisson high-connection backfill measure
By analyzing sinking of the open caisson, the slurry auxiliary sinking measure is adopted for the first sinking, so that the side friction resistance of the outer wall of the open caisson is reduced, the dead weight of the open caisson is increased after the third section is manufactured, and the stability is not satisfied; therefore, before the first sinking in place and the third joint height is manufactured, sand is filled back in the well to form a convex-shaped reverse bottom of the pan so as to increase the friction resistance of the inner wall of the well, thereby increasing the total friction resistance and ensuring the stability of the third joint height to meet the requirement.
1. And backfilling in the well to prevent sudden sinking:
(1) Before the sinking well is sunk for the first time, the depth of the bottom of the pan should be controlled, and the sinking rate is reduced. At this time, the cutting edge foot part should be ensured not to be dug as much as possible, and the dug part should be backfilled as much as possible.
(2) And immediately stopping slurry sinking assistance after the open caisson is sunk in place for the first time, and immediately backfilling.
(3) After the open caisson is sunk in place for the first time, the elevation of precipitation is controlled, and the elevation of groundwater is kept about 1m below the cutting edge, so that soil body disturbance caused by excessive precipitation is prevented, the bearing capacity of the soil body is reduced, even the soil body collapses, and the stability of the open caisson is affected.
(4) During backfilling, the edge foot part is filled up, and then the edge foot part is symmetrically and uniformly backfilled from the middle to the periphery in a layered manner.
(5) The monitoring frequency should be increased in the backfilling process, and the elevation change of the open caisson should be closely noted. If the sinking trend is continued, the small excavator is immediately informed to retreat to the central area of the open caisson, and then the sand is directly poured and backfilled along the periphery of the cutting edge, so that the peripheral area of the cutting edge is immediately filled, and the sinking potential head is restrained.
(6) In the manufacturing process of the third section of the open caisson, close attention should be paid to whether the open caisson has sedimentation or not, especially in the pouring process of the third section of concrete, the measurement is encrypted. In the third section of the open caisson high-junction manufacturing process, if the open caisson has a sinking trend, high-junction manufacturing should be stopped, and sand is continuously filled into the open caisson.
(7) Because the precipitation and sinking of the open caisson disturb the surrounding soil mass, the surrounding soil mass of the open caisson should be compacted after the open caisson is sunk in place for the first time. If the earthwork collapses, the open caisson is compacted after backfilling to ensure stability.
Detailed Description
The invention is further illustrated by the following specific examples.
A construction method combining deep well shallow excavation and open caisson method comprises
Step 1, measuring and paying-off
Measuring and positioning according to the coordinates of a design drawing and a datum point provided by a first party, arranging coordinate control points and temporary level points around the open caisson and outside a construction influence range, wherein the precision of the established control points is +/-1 mm; arranging gantry piles around the open caisson, drawing a central axis of the open caisson and a contour line of a foundation pit by lime powder, and measuring the elevation and other construction drawings in the occupied place of the cyclone pool as the basis for programming the open caisson construction scheme;
step 1.1, wire measurement
The wires are laid according to the total plane diagram, and the positions of the wires select clear zones;
step 1.2, angle measuring and testing
The angle observation is carried out by adopting a full circle return method, and the return number and the measurement limit difference are the same as the square grid angle observation requirement;
step 1.3, elevation measurement
The engineering elevation measurement control network is established by adopting a three-level measurement method, a four-level measurement method and the like, and the absolute elevation of the level network is guided and measured according to an advanced level point provided by an owner and is connected with one point in the network to serve as a basis for calculating the elevation;
Step 1.4, pile burying
The wire control point and the elevation control point are far away from the sinking area of the sinking well, the stake is deeply buried, and a protection device is arranged;
step 2, supporting steel sheet piles
The temporary road can be ensured to pass only by protective measures due to overlarge field height difference, the construction road is protected by adopting a steel sheet pile supporting mode through field confirmation, and the steel sheet pile is 15m in Larson IV type and is arranged along one side of the road;
step 3, shallow excavation of the foundation pit;
according to the current situation that the rotational flow pool is located on the ground, the height difference is about 5m, the north side of the rotational flow pool is provided with an in-situ temporary road Gao Chengyao m, the center is about 19m, the south side is provided with an old factory area Gao Chengyao 15.4.4 m, the temporary construction road cannot be broken according to the construction requirement, and the construction process cannot influence the production of the old factory.
And (3) selecting a slope-releasing excavation mode, namely excavating a foundation pit in the current situation of ground elevation +1.3m, excavating a foundation pit bottom elevation-3.5 m, excavating a depth of 4.8m, and excavating along the circumferential direction of a well wall. Considering the width of a working face for manufacturing the open caisson, the bottom edge line of the foundation pit is 2m of the outer expansion of the well wall. According to the geological survey report and the technical Specification of construction side slope engineering (GB 50330-2013), the slope releasing rate is 1:0.75. slope protection can be adopted if necessary, and a slope protection mode adopts a cement mortar spraying protection surface. The foundation pit excavation adopts the combination of mechanical excavation and manual trimming, the elevation of the excavation is strictly controlled, when the excavation is close to the pit bottom by 200 mm-300 mm, the manual slope trimming and the flat bottom are adopted, and in the process of the foundation pit excavation, the drainage ditch is combined with the water collecting pit to drain water so as to ensure the construction requirement of the foundation pit. According to the technical Specification for controlling underground water of construction and municipal engineering (JGJ 111-2016), a blind ditch with the width of 0.3m and the depth of 0.3m is arranged on the bottom surface of a foundation pit of a sunk well, the gradient is 0.2%, 8 water collecting wells with the diameter of 300mm are arranged along the inner side and the outer side of the periphery of the sunk well, and the water collecting wells are symmetrically arranged. The bottom surface floating mud should be cleaned and kept in a flat and dry state.
Step 4, paving a sand cushion layer, a concrete cushion layer and manufacturing a brick bed-jig
Step 4.1, paving a sand cushion layer
And after the foundation pit is excavated, paving a sand cushion layer. The sand cushion layer adopts middle coarse sand, is paved according to 30cm layers, is vibrated and compacted by a flat plate while sprinkling water according to the water content of 15%, the compaction coefficient is more than or equal to 95%, and the compression bearing capacity characteristic value is more than or equal to 150kPa. And after the lower layer meets the requirement, paving a second layer. In order to prevent factors such as rainy days, a blind ditch is arranged at the bottom of the foundation pit to concentrate water to a water collecting well and then the water is pumped out by a water pump so as to soak the sand-preventing cushion layer in the water.
Step 4.2, plain concrete cushion layer manufacturing
And a plain concrete cushion layer with the thickness of 15cm and C20 is paved below the cutting edge on the sand cushion layer, so that the pressure on the sand cushion layer is reduced, and the external expansion width of the plain concrete cushion layer is 20cm respectively at two sides outside the well wall. After the sand cushion is paved, pouring a plain concrete cushion on the sand cushion, wherein the plain concrete cushion is ensured to be horizontal, and the error is less than 5mm, so that the template construction is facilitated.
Step 4.3, manufacturing the brick moulding bed
The cutting edge is built by adopting a brick moulding bed, the plane position of the open caisson is accurately measured and placed on the sand cushion layer and the plain concrete cushion layer according to the designed well position, the brick moulding bed is constructed, low-grade cement mortar is adopted when bricks are built, the inclined plane of the cutting edge is smooth, the brick moulding bed is painted by lime and a small amount of cement mixture, and the hole site of the pull rod bolt of the open caisson wall template is reserved in the brick moulding bed.
And (3) chiseling the brick bed-jig and the plain concrete cushion layer by adopting a symmetrical chiseling method before sinking the open caisson, and if the open caisson has a height difference, correcting the deviation by adjusting the chiseling sequence of the brick bed-jig and the plain concrete cushion layer.
Step 5, precipitation of the open caisson
The key to success of drainage is the effect of well-point precipitation. The engineering is to adopt the pipe well for dewatering so as to meet the requirement of the sinking well drainage for underwater sinking.
The pipe well dewatering is non-critical work, namely the construction is planned to be arranged in synchronization with the production of the open caisson structure, the completion of the pipe well construction is ensured before the open caisson is submerged, and the dewatering reaches the design requirement of 1.0m below the excavation surface, so that the dewatering operation period is shortened, the influence period of the dewatering on the periphery is reduced, and the cost is saved.
Well site arrangement
15 phi 273mm pipe wells (12 dewatering wells and 3 standby wells) are annularly arranged along the open caisson so as to meet the dewatering requirement in open caisson construction. The dewatering wells are 8m away from the outer wall of the open caisson, the intervals between the dewatering wells are 10m, and the well depth is 31m.
And finally determining the number and distribution form of the dewatering wells according to the on-site water pumping experiment. The standby dewatering well is also used as an observation well, and the change of the underground water level is monitored at any time.
Step 6, precipitation well construction and design requirements
Step 6.1, wellhead: the well mouth is set 0.5m above the ground to prevent the surface sewage from penetrating into the well, and is sealed by high-quality clay and cement slurry.
Step 6.2, a well wall pipe: the wall pipe adopts Q235B welded steel pipe, the wall thickness is 5mm, and the inner diameter phi 273mm.
Step 6.3, filter (strainer): the dewatering well adopts a bridge type water filtering pipe, two layers of 30-40 mesh nylon nets are wrapped outside the water filtering pipe, and the diameter of the pipe is the same as that of the well wall pipe;
step 6.4, sedimentation tube: the sedimentation pipe mainly plays a role in preventing the filter from affecting water inflow due to sand setting blockage in the well, the sedimentation pipe is connected to the bottom of the water filtering pipe, the diameter of the sedimentation pipe is the same as that of the water filtering pipe, and the bottom opening of the sedimentation pipe is sealed by an iron plate;
step 6.5, gravel filling: the water filtering pipe of dewatering well is filled with No. 4 sand with good grinding degree, and the water filtering pipe is filled with sand from bottom to top.
Step 6.6, filling cohesive soil and sealing holes: and (3) surrounding and filling high-quality clay to the ground surface above the surrounding and filling surface of the gravel, tamping, and sealing the outer surface of the wellhead pipe.
Step 7, deep well dewatering construction
1) And (3) construction sequence: equipment entering, well positioning, vertical drilling frame, hole forming, hole cleaning, steel well pipe discharging, sand recharging, well washing, water pumping, well dismantling and field returning.
2) And a GPS-15H type engineering driller is adopted for deep well pore-forming. The pore-forming depth is 31m, the pore diameter is 500 mm, and the pore-forming verticality deviation is less than or equal to 1%.
3) And (3) carefully cleaning the holes after hole forming, turning the slurry clear, measuring by a measuring rope, and continuously sinking the steel well pipe after the hole depth is determined to meet the requirement.
4) And hoisting the sinking steel sleeve by using a winch on a drilling machine, welding each section of single-section well pipe (4-5 m), and then installing in sections. The steel casing is exposed to the ground 0.5 m.
5) The filter tube at the lower end of the steel sleeve is wrapped with a 50-mesh filter screen for 4 layers and is fastened by 18# lead wires. After the steel sleeve is sunk, crushed stone of about 0.5 m is poured into the pipe to press the bottom, and then sand is uniformly poured around the sleeve until reaching the ground surface.
6) And (3) immediately flushing the well after sand filling is finished, wherein a piston type well flushing method is adopted for flushing the well. The piston is used for sinking into the bottom of the pipe by dead weight, then the winch is used for pulling up quickly, the muddy water is carried out together, and the process is repeated for a plurality of times until the carried-out muddy water is clear.
7) And after well flushing, the well is put into a submersible pump for trial pumping, and pumping is carried out according to construction requirements after water is discharged normally.
8) Special persons are dispatched during pumping to check pumping conditions, water level elevation and water yield are recorded, and found problems are solved in time;
step 8, precipitation operation
Step 8.1, test run
Before test operation, accurately measuring elevation of each wellhead and ground, and standing water level, and then starting test operation to check whether the water pumping equipment and the water pumping and draining system can meet precipitation requirements.
Step 8.2, precipitation operation
(1) The dewatering well is operated according to the construction progress of the open caisson.
(2) In the dewatering operation process, water level observation work of each well is performed, and the change condition of the water level in the well is mastered in time.
(3) When the water head in the well is reduced to the design requirement in the dewatering operation process, the water pumping quantity of the pressure-bearing water head is controlled by properly regulating and controlling the water pumping quantity of the pressure-bearing well.
(4) And during the precipitation operation, 24-hour duty system is implemented on site, and the operators on duty are carefully arranged to make various quality records, so that the accuracy and completeness are realized.
Step 9, sinking the open caisson
Sinking of the sinking well mainly comprises removing soil from a well hole, eliminating resistance under a blade foot and friction resistance of the well wall, and sinking by means of dead weight of the sinking well.
Step 9.1 preparation before sinking
The strength of the first concrete section of the open caisson manufactured by sections must reach the design strength before sinking, and the other sections must not be lower than 70% of the design strength.
Chiseling off the concrete cushion layer and the brick moulding bed of the cutting foot element before sinking. The cushion layer is removed firstly and then symmetrically, and broken bricks in the well are cleaned by a crane grab bucket. Dividing the cushion layer under the blade foot into 12 areas, symmetrically chiseling for 3 times, chiseling 1, 4, 7 and 10 areas, chiseling 2, 5, 8 and 11 areas, and chiseling 3, 6, 9 and 12 areas. And drawing a measuring scale on the wall of the well around the open caisson, and setting up a horizontal indicating scale.
Before the open caisson digs, the cutting edge of the open caisson is dug manually and comprehensively and simultaneously in layers, the dug earthwork is concentrated in the center, the open caisson is gradually sunk, the cutting edge of the open caisson is buried in a soil layer, and the gravity center of the open caisson is lowered. Because the sinking coefficient is larger in the initial sinking process of the open caisson, the open caisson adopts soil squeezing sinking.
In construction, 4 observation points are arranged on a sinking well wall, continuous tracking measurement is carried out, and measurement is carried out once per hour. The measurement result is arranged by taking the average value of the sinkers at 4 points as the sinkers at each time, taking the point with the largest sinkers as the reference and subtracting the sinkers at other points as the height difference of the points, so as to guide deviation correcting sinkers.
Step 10, drainage sinking process
The cyclone sedimentation tank open caisson adopts three times of manufacture and three times of sinking, adopts a drainage sinking process, and has a sinking elevation of +0.0m and a sinking depth of 20.5m.
Two 50T crawler cranes are matched with two 80 small digging machines to dig soil from the center of the open caisson to the periphery, so that the bottom of the boiler is formed, and the boiler is uniformly sunk to prevent sudden sinking. And finally, the dregs are lightered to a designated place by using a dump truck. And after final sinking in place, adopting a dry back cover.
Step 11, sinking control of the open caisson
According to the important point of quality control in the sinking process, the sinking construction is divided into the following three stages:
1. Stage of preliminary sedimentation
(1) 4 observation points are arranged on the sinking well wall, and tracking measurement is performed. The measurement results were collected by using the average value of the sinkers at 4 points as the sinkers at each time.
(2) The sinking depth of the open caisson is in the range of 0-3 m as a primary sinking stage. Firstly, the plain concrete cushion layer is symmetrically chiseled out from inside to outside. When the open caisson is inclined, the chiseling position is adjusted in time, so that the open caisson is cut into the soil stably.
(3) During primary sedimentation, the sinking coefficient of the open caisson is larger, the gravity center is high, and the stability is poor; the fluctuation phenomenon can occur, and when the height difference value of the open caisson in four directions (east, south, west and north) is larger, the deviation is corrected in time.
(4) When the deviation of the open caisson is overlarge in the primary sinking stage, the shoveling personnel are arranged to adjust the number of the soil taking bin or the soil taking position, the soil taking depth (less than or equal to 50 cm-100 cm) between each bin is controlled, when the measured height difference is good, the depth of the bottom of the pot is controlled, the open caisson is prevented from sinking suddenly, the uniform digging, the duty measurement and the soil correction are really realized, and the height difference is controlled well.
(5) The resistance to sinking of the open caisson in the initial stage is mostly due to the earth reaction force from the bottom edge tread and bottom surface of the bottom beam, and the outward friction force of the well increases with the increase of the sinking amount. The distribution condition of the soil reaction force is changed by adopting a mode of adjusting the soil digging mode at the bottom of the pot in construction.
2. Normal sinking stage
(1) At the end of the primary sinking stage, if various technical indexes of the open caisson are good, the depth of the bottom of the open caisson can be increased, the depth of the bottom of the caisson is generally controlled to be about 1.2m, the soil digging speed can be increased, the soil counter force is reduced, the resistance during sinking is reduced, and the construction progress is improved.
(2) If the height difference of the four control points of the open caisson is still large at the end of the primary sedimentation stage, the open caisson is adjusted according to the deviation correcting requirement of the primary sedimentation stage, so that the open caisson is restored to the normal construction condition. In the open caisson process of the second stage, when the height difference of the four-direction control point is larger than 30cm, correction (about 1m of height difference) should be immediately carried out, soil under the outer wall blade foot must be well controlled, the soil at the position is not easy to dig, and the phenomenon of soil gushing is prevented.
(3) When sinking the sinking well, the well cabin should be symmetrically dug, and the soil surface in the well should be uniformly sunk, and the height difference in the well should not be greater than 1.0m. When in construction, the sinking condition should be observed at any time, if the inclination is found, corrective measures are taken in time, and the phenomenon that the cutting edge foot is partially placed is forbidden. Recording work of sinking of the open caisson is performed in construction, a sinking rate chart is drawn, and reliable data basis is provided for final sinking construction.
3. Final sinking stage
(1) And when the sinking of the open caisson reaches the last 2m, the final sinking stage is started. The shape of the bottom of the earth-digging pot is gradually changed from a concave surface to a convex reverse bottom, the soil taking speed and quantity are properly slowed down, the soil taking range is strictly arranged according to a uniform and symmetrical principle, when the height difference of control points around the open caisson is more than 20mm, the correction is timely carried out, the correction method is mainly used for adjusting the soil digging depth, the soil body of the soil plug part of the outer blade foot is easy to gush in, and the soil is not excessively dug. The final sinking stage is the key moment of the open caisson, and needs to strengthen observation and strictly control the sinking rate of the open caisson.
(2) Once the elevation of the blade tread of the open caisson reaches the elevation of the design requirement, immediately stopping taking soil, and throwing and filling with large stones, measuring and observing closely, wherein the sinking of the open caisson is not more than 10mm within 24 hours. After the open caisson is constructed in place, the measurement requires that the four-angle direction height difference is observed every 4-6 hours.
(3) The sinking is required to continuously and stably sink to the designed elevation, the bottom is sealed in time, the power failure is stopped in the sinking prevention process, and the rest part is poured after the concrete strength of the bottom plate reaches the design strength.
Step 12, sinking assisting measures
The engineering contemplates the use of a thixotropic mud system to assist in sinking. After the sinking well is sunk in place, cement paste or cement mortar is adopted to replace thixotropic slurry.
The thixotropic slurry sinking-assisting method is a better sinking-assisting drag-reducing method, and can reduce the disturbance influence of the open caisson on surrounding soil to a great extent during construction. Thixotropic mud plays roles in reducing friction and maintaining soil wall stability in sinking of the open caisson.
1) Construction arrangement
According to the on-site situation, arranging a mud box, 1 slurry stirring machine, 2 slurry pressing pumps, and a slurry conveying pipeline, wherein the slurry pressing pipeline is constructed by adopting an in-well outer pipe method and a 1 inch PVC pipe. The horizontal pipes are respectively arranged 2 times along the circumferential direction and are positioned at the positions of 2.5m and 4.5m above the cutting edge, and the vertical pipes are directly raised above the well wall.
The angle steel L is arranged at the injection port, the length of 100 multiplied by 8 is 20cm to form an injection port enclosure, so that grouting blockage and direct injection of soil walls are prevented. In order to prevent the collapse of the ground soil layer and damage to the slurry cover, a ground surface enclosure is provided. Backfilling and layering tamping the outer side of the enclosure by using cohesive soil.
2) Slurry preparation
The slurry is prepared from high-quality bentonite, lime and water (mixing ratio is 4:1:15), and the water loss and mud skin thickness, static shear force and sand content of the slurry are controlled conventionally in construction.
3) Grouting
The grouting adopts a grouting pump, the normal pressure injection pressure is 100-800 kPa, the grouting adopts the hole-by-hole grouting, and the grouting is continuously supplemented along with the sinking of the sinking well, so that the mud surface is always kept at about 0.3m above the ground.
4) Grouting
And after sinking of the open caisson is completed, grouting the annular belt outside the open caisson to replace bentonite slurry. The cement slurry consists of ordinary silicate cement and cement slurry with water cement ratio not exceeding 0.45. Grouting should be a homogeneous mixture of cement and water, their consistency should be sufficiently fluid.
13. Open caisson high-connection backfill measure
By analyzing sinking of the open caisson, the slurry auxiliary sinking measure is adopted for the first sinking, so that the side friction resistance of the outer wall of the open caisson is reduced, the dead weight of the open caisson is increased after the third section is manufactured, and the stability is not satisfied; therefore, before the first sinking in place and the third joint height is manufactured, sand is filled back in the well to form a convex-shaped reverse bottom of the pan so as to increase the friction resistance of the inner wall of the well, thereby increasing the total friction resistance and ensuring the stability of the third joint height to meet the requirement.
1. And backfilling in the well to prevent sudden sinking:
(1) Before the sinking well is sunk for the first time, the depth of the bottom of the pan should be controlled, and the sinking rate is reduced. At this time, the cutting edge foot part should be ensured not to be dug as much as possible, and the dug part should be backfilled as much as possible.
(2) And immediately stopping slurry sinking assistance after the open caisson is sunk in place for the first time, and immediately backfilling.
(3) After the open caisson is sunk in place for the first time, the elevation of precipitation is controlled, and the elevation of groundwater is kept about 1m below the cutting edge, so that soil body disturbance caused by excessive precipitation is prevented, the bearing capacity of the soil body is reduced, even the soil body collapses, and the stability of the open caisson is affected.
(4) During backfilling, the edge foot part is filled up, and then the edge foot part is symmetrically and uniformly backfilled from the middle to the periphery in a layered manner.
(5) The monitoring frequency should be increased in the backfilling process, and the elevation change of the open caisson should be closely noted. If the sinking trend is continued, the small excavator is immediately informed to retreat to the central area of the open caisson, and then the sand is directly poured and backfilled along the periphery of the cutting edge, so that the peripheral area of the cutting edge is immediately filled, and the sinking potential head is restrained.
(6) In the manufacturing process of the third section of the open caisson, close attention should be paid to whether the open caisson has sedimentation or not, especially in the pouring process of the third section of concrete, the measurement is encrypted. In the third section of the open caisson high-junction manufacturing process, if the open caisson has a sinking trend, high-junction manufacturing should be stopped, and sand is continuously filled into the open caisson.
(7) Because the precipitation and sinking of the open caisson disturb the surrounding soil mass, the surrounding soil mass of the open caisson should be compacted after the open caisson is sunk in place for the first time. If the earthwork collapses, the open caisson is compacted after backfilling to ensure stability.
Claims (1)
1. A construction method combining deep well shallow excavation and open caisson method is characterized in that: comprising
Step 1, measuring and paying-off
Measuring and positioning according to the coordinates of a design drawing and a datum point provided by a first party, arranging coordinate control points and temporary level points around the open caisson and outside a construction influence range, wherein the precision of the established control points is +/-1 mm; arranging gantry piles around the open caisson, drawing a central axis of the open caisson and a contour line of a foundation pit by lime powder, and measuring the elevation and other construction drawings in the occupied place of the cyclone pool as the basis for programming the open caisson construction scheme;
step 1.1, wire measurement
The wires are laid according to the total plane diagram, and the positions of the wires select clear zones;
step 1.2, angle measuring and testing
The angle observation is carried out by adopting a full circle return method, and the return number and the measurement limit difference are the same as the square grid angle observation requirement;
step 1.3, elevation measurement
The engineering elevation measurement control network is established by adopting a three-level measurement method, a four-level measurement method and the like, and the absolute elevation of the level network is guided and measured according to an advanced level point provided by an owner and is connected with one point in the network to serve as a basis for calculating the elevation;
Step 1.4, pile burying
The wire control point and the elevation control point are far away from the sinking area of the sinking well, the stake is deeply buried, and a protection device is arranged;
step 2, supporting steel sheet piles
The temporary road can be ensured to pass only by protective measures due to overlarge field height difference, the construction road is protected by adopting a steel sheet pile supporting mode through field confirmation, and the steel sheet pile is 15m in Larson IV type and is arranged along one side of the road;
step 3, shallow excavation of the foundation pit;
according to the current situation that the rotational flow pool is positioned on the ground, the height difference is about 5m, the north side of the rotational flow pool is provided with an in-site temporary road Gao Chengyao m, the center is about 19m, the south side is provided with an old factory area Gao Chengyao 15.4.4 m, the temporary construction road is not broken according to the construction requirement, and the construction process is not influenced by the old factory production;
the foundation pit excavation mode is selected to excavate on a slope, the current ground elevation is +1.3m, the foundation pit bottom elevation is-3.5 m, the excavation depth is 4.8m, and the pit wall is excavated in a circumferential direction;
considering the width of a working face manufactured by the open caisson, and expanding the bottom edge of the foundation pit for 2m outwards from the well wall;
according to the geological survey report and the technical Specification of construction side slope engineering (GB 50330-2013), the slope releasing rate is 1:0.75;
slope protection can be adopted if necessary, and a slope protection mode adopts a cement mortar spraying protection surface;
The foundation pit excavation adopts the combination of mechanical excavation and manual trimming, the elevation of the excavation is strictly controlled, when the excavation is 200 mm-300 mm close to the pit bottom, the manual slope trimming and flat bottom are adopted, and in the process of the foundation pit excavation, the drainage ditch is combined with the water collecting pit to drain water so as to ensure the construction requirement of the foundation pit;
according to the technical specification of underground water control of construction and municipal engineering (JGJ 111-2016), a blind ditch with the width of 0.3m and the depth of 0.3m is arranged on the bottom surface of a foundation pit of a sunk well, the gradient is 0.2%, 8 water collecting wells with the diameter of 300mm are arranged along the inner side and the outer side of the periphery of the sunk well, and the water collecting wells are symmetrically arranged;
the bottom surface floating mud should be cleaned and kept in a flat and dry state;
step 4, paving a sand cushion layer, a concrete cushion layer and a brick moulding bed;
step 4.1, paving a sand cushion layer
Paving a sand cushion layer after the excavation of the foundation pit is finished;
the sand cushion layer adopts middle coarse sand, each layer is paved in layers according to 30cm, 15% of water content is sprayed, and the sand cushion layer is vibrated and compacted by a flat plate, the compaction coefficient is more than or equal to 95%, and the compression bearing capacity characteristic value is more than or equal to 150kPa;
after the lower layer meets the requirement, paving a second layer;
in order to prevent factors such as rainy days, a blind ditch is arranged at the bottom of the foundation pit, water is concentrated to a water collecting well and then pumped out by a water pump, so that the sand-preventing cushion layer is soaked in the water;
Step 4.2, plain concrete cushion layer manufacturing
A plain concrete cushion layer with the thickness of 15cm and C20 is paved below the cutting edge on the sand cushion layer, the pressure on the sand cushion layer is lightened, and the outward expansion width of the plain concrete cushion layer is 20cm respectively at two sides outside the well wall;
after the sand cushion is paved, pouring a plain concrete cushion on the sand cushion, wherein the plain concrete cushion is ensured to be horizontal, and the error is less than 5mm, so that the template construction is facilitated;
step 4.3, manufacturing the brick moulding bed
The cutting edge is built by adopting a brick moulding bed, the plane position of the open caisson is accurately measured and placed on the sand cushion layer and the plain concrete cushion layer according to the designed well position, the brick moulding bed is constructed, low-grade cement mortar is adopted when bricks are built, the inclined plane of the cutting edge is smooth, the brick moulding bed is painted by lime and a small amount of cement mixture, and the hole site of a pull rod bolt of a wall template of the open caisson is reserved in the brick moulding bed;
the brick bed mould and the plain concrete cushion layer are chiseled by adopting a symmetrical chiseling method before sinking the open caisson, and if the open caisson has a height difference, the chiseling sequence of the brick bed mould and the plain concrete cushion layer can be adjusted to achieve the effect of correcting deviation;
step 5, precipitation of the open caisson
The key of success of the drainage water precipitation lies in the effect of well-point precipitation;
the engineering is to adopt pipe well dewatering to meet the requirement of sinking well drainage water sinking;
The pipe well dewatering is non-critical work, namely, the construction is planned to be arranged in synchronization with the production of the open caisson structure, the completion of the pipe well construction is ensured before the open caisson is submerged, and the dewatering reaches the design requirement of 1.0m below the excavation surface, so that the dewatering operation period is shortened, the influence period of the dewatering on the periphery is shortened, and the cost is saved;
well site arrangement
15 phi 273mm pipe wells (12 dewatering wells+3 standby wells) are annularly arranged along the open caisson so as to meet the dewatering requirement in the construction of the open caisson;
the dewatering wells are 8m away from the outer wall of the open caisson, the intervals between the dewatering wells are 10m, and the well depth is 31m;
according to the on-site water pumping experiment, the quantity and distribution form of dewatering wells are finally determined;
the standby dewatering well is also used as an observation well, and the change of the underground water level is monitored at any time;
step 6, precipitation well construction and design requirements
Step 6.1, wellhead: the wellhead is arranged 0.5m above the ground to prevent surface sewage from penetrating into the well, and is sealed by high-quality clay and cement slurry;
step 6.2, a well wall pipe: the wall pipe adopts Q235B welded steel pipe, the wall thickness is 5mm, and the inner diameter phi is 273mm;
step 6.3, filter (strainer): the dewatering well adopts a bridge type water filtering pipe, two layers of 30-40 mesh nylon nets are wrapped outside the water filtering pipe, and the diameter of the pipe is the same as that of the well wall pipe;
Step 6.4, sedimentation tube: the sedimentation pipe mainly plays a role in preventing the filter from affecting water inflow due to sand setting blockage in the well, the sedimentation pipe is connected to the bottom of the water filtering pipe, the diameter of the sedimentation pipe is the same as that of the water filtering pipe, and the bottom opening of the sedimentation pipe is sealed by an iron plate;
step 6.5, gravel filling: the water filtering pipe of the dewatering well is filled with 4# sand (green bean sand) with good particle roundness, and the water filtering pipe is upwards from the bottom of the well to the top of the filter;
step 6.6, filling cohesive soil and sealing holes: surrounding and filling high-quality clay above the surrounding and filling surface of the gravel, tamping, and sealing the wellhead pipe;
step 7, deep well dewatering construction
1) And (3) construction sequence: equipment entering, well positioning, vertical drilling frame, pore forming, pore cleaning, steel well pipe discharging, sand recharging, well flushing, water pumping, well dismantling and field returning;
2) The deep well pore-forming adopts a GPS-15H type engineering driller;
the pore-forming depth is 31m, the pore diameter is 500 mm, and the deviation of pore-forming verticality is less than or equal to 1%;
3) Carefully cleaning the holes after hole forming, turning the slurry clear, measuring by a measuring rope, and continuously sinking the steel well pipe after the hole depth is determined to meet the requirement;
4) Hoisting the sinking steel sleeve by using a winch on a drilling machine, welding each section of single-section well pipe (4-5 m), and then installing in sections;
The steel sleeve is exposed out of the ground for 0.5 meter;
5) The filter tube at the lower end of the steel sleeve is wrapped with a 50-mesh filter screen for 4 layers and is fastened by 18# lead wires;
after the steel sleeve is submerged, filling crushed stone of about 0.5 meter into the pipe to press the bottom, and then uniformly filling sand around the sleeve until the sand reaches the ground surface;
6) Immediately flushing the well after sand filling is finished, wherein a piston type well flushing method is adopted for flushing the well;
sinking the slurry into the bottom of the pipe by utilizing the dead weight of the piston, then rapidly pulling up the slurry by utilizing a winch, and repeatedly taking out the slurry until the slurry is clear;
7) After well flushing, putting a submersible pump for trial pumping, and pumping water according to construction requirements after water is discharged normally;
8) Special persons are dispatched during pumping to check pumping conditions, water level elevation and water yield are recorded, and found problems are solved in time;
step 8, precipitation operation
Step 8.1, test run
Before test operation, accurately measuring elevation of each wellhead and the ground, and standing water level, and then starting test operation to check whether a pumping device and a pumping and draining system can meet the requirement of precipitation;
step 8.2, precipitation operation
(1) The dewatering well operates according to the construction progress of the open caisson;
(2) In the dewatering operation process, water level observation work of each well is performed, and the change condition of the water level in the well is mastered in time;
(3) When the water head in the well is reduced to the design requirement in the dewatering operation process, the water pumping quantity of the pressure-bearing water head is controlled by properly regulating and controlling the water pumping quantity of the pressure-bearing well;
(4) During the precipitation operation, 24-hour duty system is implemented on site, and operators on duty are arranged to carefully make various quality records, so that the accuracy and completeness are realized;
step 9, sinking the open caisson
Sinking the sinking well mainly comprises removing soil from a well hole, eliminating resistance under a blade foot and friction resistance of the well wall, and sinking by means of dead weight of the sinking well;
step 9.1 preparation before sinking
The strength of the first concrete section of the open caisson manufactured by sections must reach the design strength before sinking, and the other sections must not be lower than the design strength by 70%;
chiseling off a blade foot plain concrete cushion layer and a brick moulding bed before sinking;
the cushion layer is removed firstly and then symmetrically, and broken bricks in the well are cleaned by a crane grab bucket;
dividing the cushion layer at the lower part of the blade foot into 12 areas, symmetrically chiseling for 3 times, chiseling 1, 4, 7 and 10 areas, chiseling 2, 5, 8 and 11 areas, and chiseling 3, 6, 9 and 12 areas;
drawing a measuring scale on the wall of the well around the open caisson, and setting up a horizontal indicating scale;
before the open caisson is dug, the cutting edge of the open caisson is firstly dug manually and comprehensively in layers at the same time, the dug earthwork is concentrated in the center, the open caisson is gradually sunk, the cutting edge of the open caisson is buried in a soil layer, and the gravity center of the open caisson is lowered;
Because the sinking coefficient is larger in the initial sinking process of the open caisson, soil squeezing sinking is adopted;
in construction, 4 observation points are arranged on a sinking well wall, continuous tracking measurement is carried out, and measurement is carried out once per hour;
the measurement result is arranged by taking the average value of the subsidence amounts of 4 points as the subsidence amount of each time of the open caisson, taking the point with the largest subsidence amount as the reference and subtracting the subsidence amounts of other points as the height difference of the points, so as to guide deviation correction subsidence construction;
step 10, drainage sinking process
The cyclone sedimentation tank open caisson is manufactured for three times by adopting three times, and is submerged by adopting a drainage submerged process, wherein the elevation of the sinking is +0.0m, and the sinking depth is 20.5m;
two 50T crawler cranes are matched with two 80 small digging machines to dig soil from the center of the open caisson to the periphery so as to form a pot bottom, sink uniformly and prevent sudden sinking;
finally, the dregs are lightered to a designated place by a dump truck;
after final sinking in place, adopting a dry back cover;
step 11, sinking control of the open caisson
According to the important point of quality control in the sinking process, the sinking construction is divided into the following three stages:
1. stage of preliminary sedimentation
(1) Setting 4 observation points on the sinking well wall, and tracking and measuring;
the measurement result is arranged by taking the average value of the sinking amounts of 4 points as the sinking amount of each time of the open caisson;
(2) The sinking depth of the open caisson is in the range of 0-3 m as a primary sinking stage;
firstly, symmetrically chiseling out an plain concrete cushion layer from inside to outside;
when the open caisson is inclined, the chiseling position is adjusted in time, so that the open caisson is cut into the soil stably;
(3) During primary sedimentation, the sinking coefficient of the open caisson is larger, the gravity center is high, and the stability is poor; the fluctuation phenomenon can occur, and when the height difference values of the open caisson in four directions (east, south, west and north) are larger, correction is performed in time;
(4) When the deviation of the open caisson is overlarge in the primary sinking stage, the earthmover is arranged to adjust the number of the soil taking bin or the soil taking position, the soil taking depth (less than or equal to 50 cm-100 cm) between each bin is controlled, when the measured height difference is good, the depth of the bottom of the pot is controlled, the open caisson is prevented from sinking suddenly, the uniform digging, the service measurement and the regular soil grabbing are really realized, and the height difference is controlled well;
(5) The resistance to sinking of the open caisson in the primary sinking stage is mostly the soil counter force from the bottom edge tread and the bottom surface of the bottom beam, and the external side friction force of the well is increased along with the increase of the sinking amount;
the distribution condition of the soil reaction force is changed by adopting a mode of adjusting the soil digging mode and the shape of the bottom of the pot during construction;
2. normal sinking stage
(1) At the end of the primary sinking stage, if various technical indexes of the open caisson are good, the depth of the bottom of the open caisson can be increased, the depth of the bottom of the caisson is generally controlled to be about 1.2m, the soil digging speed can be increased, the soil counter force is reduced, the resistance during sinking is reduced, and the construction progress is improved;
(2) If the height difference of the four control points of the open caisson is still large at the final stage of the primary sedimentation stage, the open caisson is adjusted according to the deviation correcting requirement of the primary sedimentation stage, so that the open caisson is restored to the normal construction condition;
in the sinking well process of the second stage, when the height difference of the four-direction control point is more than 30cm, correction (about 1m of height difference) is needed to be immediately carried out, soil under the outer wall blade foot is needed to be well controlled, the soil at the position is not needed to be dug, and the phenomenon of soil gushing is prevented;
(3) When the sinking well sinks, the well cabin should be symmetrically dug, and the well is uniformly sunk, and the soil surface height difference in the well is not more than 1.0m;
observing sinking condition at any time during construction, if inclination is found, timely taking corrective measures, and strictly prohibiting the phenomenon that the cutting edge foot is partially placed and the like;
recording work of sinking of the open caisson is performed in construction, a sinking rate chart is drawn, and reliable data basis is provided for final sinking construction;
3. final sinking stage
(1) Entering a final sinking stage when the sinking of the open caisson reaches the last 2 m;
the shape of the bottom of the earth-digging pan is gradually changed from a concave surface to a convex reverse bottom, the earth-taking speed and the quantity are properly slowed down, the earth-taking range is strictly arranged according to a uniform and symmetrical principle, when the height difference of control points around the open caisson is more than 20mm, the correction is timely carried out, the correction method is mainly used for adjusting the earth-digging depth, the soil body of the soil plug part of the outer blade foot is easy to gush in, and the earth is not excessively dug;
The final sinking stage is the key moment of the open caisson, and needs to strengthen observation and strictly control the sinking rate of the open caisson;
(2) Once the elevation of the blade tread of the open caisson reaches the elevation of the design requirement, immediately stopping taking soil, throwing and filling with large stones, measuring and closely paying attention to observation, wherein the sinking of the open caisson is not more than 10mm within 24 hours;
after the open caisson is constructed in place, observing the height difference in the four corners once every 4-6 hours;
(3) The sinking is required to continuously and stably sink to the designed elevation, the bottom is sealed in time, the power failure is stopped in the sinking prevention process, and the rest part is poured after the concrete strength of the bottom plate reaches the designed strength;
step 12, sinking assisting measures
The engineering considers that a thixotropic slurry system is adopted for auxiliary sinking;
after the sinking well is sunk in place, cement paste or cement mortar is adopted to replace thixotropic slurry;
the thixotropic slurry sinking-assisting method is a better sinking-assisting drag-reducing method, and can reduce the disturbance influence of the open caisson on surrounding soil to a great extent during construction;
thixotropic slurry plays roles in reducing friction and maintaining soil wall stability in sinking of the open caisson;
1) Construction arrangement
Arranging a mud box, 1 slurry stirring machine, 2 slurry pressing pumps and a slurry conveying pipeline according to the site situation, wherein the slurry pressing pipeline is constructed by adopting an in-well outer pipe method and adopting a 1 inch PVC pipe;
The horizontal pipes are respectively arranged 2 times along the circumferential direction and are positioned at the positions of 2.5m and 4.5m above the cutting edge, and the first vertical pipe is directly raised above the well wall;
setting angle steel L at the jet port, wherein the length of the angle steel L is 100 multiplied by 8 and is 20cm to form a jet port enclosure, so as to prevent grouting from blocking and directly punching the soil wall;
in order to prevent the collapse of the ground soil layer and damage the slurry sleeve, a ground surface enclosure is arranged;
backfilling and layering tamping the outer side of the enclosure by using cohesive soil;
2) Slurry preparation
The slurry is prepared from high-quality bentonite, lime and water (mixing ratio is 4:1:15), and the water loss of the slurry and the thickness of mud skin, static shear force and sand content are controlled conventionally in construction;
3) Grouting
Grouting adopts a grouting pump, the normal pressure injection pressure is 100-800 kPa, grouting adopts hole-by-hole grouting, and continuously supplements grouting along with sinking of a sinking well, so that the mud surface is always kept at about 0.3m above the ground;
4) Grouting
Grouting the ring belt outside the open caisson to replace bentonite slurry after the open caisson is submerged;
the cement paste consists of ordinary Portland cement and cement paste with the water cement ratio not exceeding 0.45;
grouting should be a homogeneous mixture of cement and water, their consistency should be sufficiently fluid;
13. high backfill measure for open caisson
By analyzing sinking of the open caisson, the slurry auxiliary sinking measure is adopted for the first sinking, so that the side friction resistance of the outer wall of the open caisson is reduced, the dead weight of the open caisson is increased after the third section is manufactured, and the stability is not satisfied; so we first sink in place, third section connect high before making, backfill sand in the well, form "protruding" and turn against the bottom of a pan in order to increase the friction resistance of the inner wall of the well, thus increase the total friction resistance, make the third section connect high stability meet the requirement;
1. And backfilling in the well to prevent sudden sinking:
(1) Before the sinking well is sunk for the first time, the depth of the bottom of the pan is controlled, and the sinking rate is reduced;
at the moment, the cutting edge foot part is ensured not to be dug as much as possible, and the dug part is backfilled as much as possible;
(2) Immediately stopping slurry sinking assistance after the open caisson is sunk in place for the first time, and immediately backfilling;
(3) After the open caisson is sunk in place for the first time, the elevation of precipitation is controlled, and the elevation of groundwater is kept about 1m below the cutting edge, so that soil body disturbance caused by excessive precipitation is prevented, the bearing capacity of the soil body is reduced, even the soil body collapses, and the stability of the open caisson is influenced;
(4) During backfilling, the edge foot part is filled up, and then the edge foot part is symmetrically and uniformly backfilled in layers from the middle to the periphery;
(5) The monitoring frequency is increased in the backfilling process, and the elevation change of the open caisson is closely noted;
if the sinking trend is continued, the small excavator is immediately informed to retreat to the central area of the open caisson, and at the moment, the sand is directly poured and backfilled along the periphery of the cutting edge, the peripheral area of the cutting edge is immediately filled, and the sinking potential head is restrained;
(6) In the manufacturing process of the third section of the open caisson, close attention should be paid to whether the open caisson has sedimentation or not, especially in the pouring process of the third section of concrete, the encryption measurement is carried out;
In the third section high-joint manufacturing process of the open caisson, if the open caisson has a sinking trend, stopping high-joint manufacturing, and continuously backfilling sand into the open caisson;
(7) Because the precipitation and sinking of the open caisson disturb the surrounding soil mass, the surrounding soil mass of the open caisson should be compacted after the open caisson is sunk in place for the first time; if the earthwork collapses, the open caisson is compacted after backfilling to ensure stability.
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