CN112081119A - Underground continuous wall construction method for ensuring grooving perpendicularity - Google Patents

Abstract

The invention discloses a method for constructing an underground continuous wall for ensuring grooving perpendicularity, and relates to the technical field of continuous wall construction. The method comprises the following steps: constructing a guide wall, and arranging a counter brace in a guide wall channel of the guide wall; performing grooving construction based on the sequence of firstly excavating a single hole and then excavating a partition wall, wherein the length of the partition wall is less than that of an opening bucket of a grab bucket, and the specific gravity of slurry is not less than 1.10 in the grooving construction process; after the completion of the grooving is determined, slurry replacement is carried out; hoisting the reinforcement cage, placing the guide pipe and pouring concrete. The method ensures the perpendicularity of the groove, can ensure that the slurry can more effectively protect the wall in the groove forming process, and can reduce the influence of the construction of the underground continuous wall on the adjacent pipeline. And, the problem that the guide wall is easy to displace is solved.

Description

Underground continuous wall construction method for ensuring grooving perpendicularity

Technical Field

The invention relates to the technical field of diaphragm wall construction, in particular to a method for ensuring the perpendicularity of a grooving of an underground diaphragm wall.

Background

In the building construction, the underground continuous wall has the characteristics of high rigidity, strong integrity, good impermeability and durability, can be used as an enclosure structure to play a role in retaining soil and water, and can also be used as a bearing structure. The method is suitable for various complex foundation conditions, and has the advantages of small occupied area during actual construction, high efficiency, short construction period, reliable quality and high economic benefit.

At present, in the construction process of grooving of an underground diaphragm wall, after a guide wall is finished, a hydraulic grab bucket is directly adopted to firstly carry out groove grabbing construction, and if the grab bucket cannot continue to carry out downward groove grabbing operation, a punching pile machine is adopted to punch a groove to the designed depth. However, the grooving verticality and the groove wall flatness on two sides are difficult to control, and due to the weak rock-entering capability of the hydraulic grab, a large number of punching pile machines are required to be added for matched construction, and the punching pile machine has low construction efficiency.

Disclosure of Invention

In view of this, the embodiment of the present invention provides a method for constructing an underground diaphragm wall, which can ensure the perpendicularity of a grooving, make slurry more effective in the grooving process to protect the wall, reduce the influence of the construction of the underground diaphragm wall on the adjacent pipeline, solve the problem that the guide wall is easy to displace, and have the advantages of simple construction, easy operation, cost saving, and the like.

To achieve the above objects, according to one aspect of the embodiments of the present invention, there is provided a method of constructing an underground diaphragm wall that ensures verticality of trenching.

The method for constructing the underground continuous wall for ensuring the perpendicularity of the groove comprises the following steps: constructing a guide wall, and arranging a counter brace in a guide wall channel of the guide wall; performing grooving construction based on the sequence of firstly excavating a single hole and then excavating a partition wall, wherein the length of the partition wall is less than that of an opening bucket of a grab bucket, and the specific gravity of slurry is not less than 1.10 in the grooving construction process; after the completion of the grooving is determined, slurry replacement is carried out; and hoisting a reinforcement cage, placing a guide pipe and pouring concrete.

Optionally, constructing a guide wall, and the step of arranging a diagonal brace in a guide wall trench of the guide wall includes: excavating a groove through a backhoe excavator, arranging a guide wall template in the groove, and placing a reinforcing mesh in the guide wall template; symmetrically pouring guide wall concrete; under the condition that the strength of the guide wall concrete reaches 70%, dismantling the guide wall template; and arranging a diagonal brace in the guide wall ditch, and paving a safety net sheet on the top surface of the guide wall, wherein the horizontal distance of the diagonal brace is 1 m.

Optionally, before performing mud replacement, the method further comprises: in the process of grooving construction, a steel wire rope weight hanging hammer is used as a guide, so that the wall brushing device is tightly attached to a joint in the wall brushing process; based on the inclined rib plates arranged inside the wall brushing machine, in the process of putting down the wall brushing machine, the vertical force of the slurry on the wall brushing machine is converted into a horizontal component force, so that the wall brushing machine is tightly attached to the joint; and repeating the steps until no attachments are attached to the wall brushing machine.

Optionally, the step of performing mud replacement comprises: an air liquid lifter is used, a crane is used for suspending the tank into the ground, an air compressor is used for delivering compressed air, and soil residue sludge deposited at the bottom of the tank is sucked and removed by a slurry reverse circulation method; and when the thickness of the measured sediment at the bottom of the tank is smaller than a preset threshold value, stopping moving the air liquid elevator, and replacing the slurry of which the bottom of the tank does not meet the quality requirement.

Optionally, the steel reinforcement cage is provided with a transverse truss and a longitudinal truss, a middle reinforcing truss of the transverse truss is formed by phi 28W-shaped steel bars, other trusses of the transverse truss are formed by phi 32X-shaped steel bars, and 250 × 150 × 20 steel plates are welded on two sides of the steel reinforcement cage below each main hoisting point; and protective layer positioning plates are arranged on the soil facing surface and the excavation surface of the reinforcement cage.

Optionally, the steps of placing the conduit and concreting comprise: placing the catheters, and determining that the horizontal distance between the placed catheters is not more than 3 meters; hanging a water-proof plug at a position close to the mud surface in the guide pipe; and grouting the wall bottom of the continuous wall through a grouting pipe with the inner diameter not less than 40mm based on the guide pipe.

Optionally, after the concrete pouring, the method further includes: and (3) under the condition that the strength of the underground diaphragm wall reaches 100%, based on the embedded scaffold pipes, adopting a hole-separating and jumping grouting mode to carry out wall toe grouting reinforcement construction.

One embodiment of the above invention has the following advantages or benefits: the guide wall is internally provided with the opposite supports, so that the problem that the guide wall is easy to displace is solved. The grooving construction is carried out based on the sequence of firstly digging a single hole and then digging the partition wall, and because the length of the hole partition wall is smaller than the length of the grab bucket, the grab bucket can be sleeved towards the partition wall for digging, so that the grab bucket is balanced in force, the deviation is effectively corrected, and the grooving perpendicularity is ensured. And the specific gravity of the slurry is not less than 1.10 during grooving, so that the slurry can effectively protect the wall during grooving, and the influence of the construction of the underground diaphragm wall on the adjacent pipeline can be reduced.

Further effects of the above-mentioned non-conventional alternatives will be described below in connection with the embodiments.

Drawings

The drawings are included to provide a better understanding of the invention and are not to be construed as unduly limiting the invention. Wherein:

FIG. 1 is a schematic view of a main flow of a method of constructing an underground diaphragm wall for ensuring perpendicularity of a groove according to an embodiment of the present invention;

FIG. 2 is a schematic illustration of a trenching operation;

FIG. 3 is a schematic illustration of trenching operations according to an embodiment of the present invention;

FIG. 4 is a schematic view of a brush wall according to an embodiment of the invention;

fig. 5 is a schematic diagram of a reinforcement cage drop arrangement according to an embodiment of the present invention; and

fig. 6 is a schematic diagram of a reinforcement cage protective layer according to an embodiment of the invention.

Detailed Description

Exemplary embodiments of the present invention are described below with reference to the accompanying drawings, in which various details of embodiments of the invention are included to assist understanding, and which are to be considered as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. Also, descriptions of well-known functions and constructions are omitted in the following description for clarity and conciseness.

Fig. 1 is a schematic view of a main flow of a method of constructing an underground diaphragm wall for ensuring trenching verticality according to an embodiment of the present invention, and as shown in fig. 1, the method of constructing an underground diaphragm wall for determining trenching verticality according to an embodiment of the present invention mainly includes:

step S101: and constructing a guide wall, and arranging a butt brace in a guide wall channel of the guide wall. Specifically, a trench is excavated through the backhoe excavator, a guide wall template is arranged in the trench, and a reinforcing mesh is placed in the guide wall template. And symmetrically pouring guide wall concrete. And (4) under the condition that the strength of the guide wall concrete reaches 70%, removing the guide wall template. Then, a diagonal brace is arranged in the guide wall ditch, and a safety net sheet is paved on the top surface of the guide wall. Wherein the horizontal distance of the opposite supports is 1 meter.

Step S102: performing grooving construction based on the sequence of firstly digging single holes and then digging partition walls, wherein the length of the partition walls is smaller than that of the grab bucket; and, in the process of grooving construction, the specific gravity of the slurry is not less than 1.10.

Step S103: and (5) after the completion of the grooving is determined, performing slurry replacement. In the process of grooving construction, a steel wire rope weight hanging hammer is used as a guide, so that the wall brushing device is tightly attached to the joint in the wall brushing process. Based on the inclined rib plates arranged inside the wall brushing machine, in the process of lowering the wall brushing machine, the vertical force of the slurry on the wall brushing machine is converted into a horizontal component force, so that the wall brushing machine is tightly attached to the joint; the method is repeatedly executed until no attachment exists on the wall brushing machine.

In the step of slurry replacement, an air lift is used, the tank is suspended by a crane, and an air compressor delivers compressed air to suck and remove the soil and slag sludge deposited at the bottom of the tank by a slurry reverse circulation method. And when the thickness of the measured sediment at the bottom of the tank is smaller than a preset threshold value, stopping moving the air liquid lifter and replacing the slurry of which the bottom of the tank does not meet the quality requirement.

Step S104: hoisting the reinforcement cage, placing the guide pipe and pouring concrete.

The steel reinforcement cage is provided with a transverse truss and a longitudinal truss, the middle strengthening truss of the transverse truss is composed of phi 28W-shaped steel bars, and the other trusses of the transverse truss are composed of phi 32X-shaped steel bars; and two sides of the steel cage below each main hoisting point are welded with 250 multiplied by 150 multiplied by 20 steel plates in a burning way; and protective layer positioning plates are arranged on the soil facing surface and the excavation surface of the reinforcement cage.

Placing the guide pipes, and in the concrete pouring process, placing the guide pipes, and determining that the horizontal distance between the placed guide pipes is not more than 3 m. And a water-proof plug is hung at the position close to the mud surface in the guide pipe. Grouting is performed based on the guide pipe, and the bottom of the continuous wall is grouted through a grouting pipe with the inner diameter not less than 40 mm. And after concrete pouring, under the condition that the strength of the underground continuous wall is confirmed to reach 100%, carrying out toe grouting reinforcement construction by adopting a hole-separating jumping grouting mode based on the embedded scaffold pipes.

In addition, in the embodiment of the invention, a phi 800@600 high-pressure jet grouting pile seam water stopping measure can be adopted at the joint of the continuous wall, so that the water leakage caused by improper treatment of the joint seam of the continuous wall can be effectively controlled.

According to the embodiment of the invention, the guide wall trench of the guide wall is internally provided with the opposite support, so that the problem that the guide wall is easy to displace is solved. The grooving construction is carried out based on the sequence of firstly digging a single hole and then digging the partition wall, and because the length of the hole partition wall is smaller than the length of the grab bucket, the grab bucket can be sleeved towards the partition wall for digging, so that the grab bucket is balanced in force, the deviation is effectively corrected, and the grooving perpendicularity is ensured. And the specific gravity of the slurry is not less than 1.10 during grooving, so that the slurry can effectively protect the wall during grooving, and the influence of the construction of the underground diaphragm wall on the adjacent pipeline can be reduced.

The main body enclosure structure of the embodiment of the invention adopts an underground continuous wall with the thickness of 800mm and a fore shaft pipe joint. In the implementation process of the embodiment of the invention, the construction road can be arranged at the inner side of the foundation pit, specifically, the construction main road with the width of 7-9m along the ground wall is firstly manually compacted and then flattened, then C30 reinforced concrete with the thickness of 20cm is paved on the construction main road, the phi 12@200 reinforced concrete is arranged in a bidirectional way, and the construction road must be ensured to be horizontal. The trenching earthwork of the underground diaphragm wall is provided with slurry and mashed mud which cannot be directly transported outside, 1 temporary soil collecting pit capable of accommodating 800m3 earthwork can be arranged in a construction area and used for temporarily collecting wet soil dug out in trenching operation, and the slurry is refuted and discarded after being drained.

According to the plane control point provided by a construction unit, a closed plane wire can be arranged at the periphery of the foundation pit. According to the closed conducting wires and the datum points at the periphery of the foundation pit, measuring control points and level points for construction are set up in a construction site, all main axis control points are put in, and then all axes are measured by a total station, so that the guide wall is constructed according to the axes strictly. In the construction process, especially the reference points at the periphery of the foundation pit can move due to the displacement of the continuous wall, and the reference control points of the lead and the axis are regularly retested.

For the form and manufacture of the guide wall, a back-hoe excavator is adopted to dig a groove, after the groove is dug, the slope is repaired manually, then a guide wall template is erected, and a reinforcing mesh is placed in the template. The guide wall is symmetrically poured, and the rear detachable formwork is used when the strength reaches 70%. In the embodiment of the invention, after the guide wall is dismantled, an upper round wood support and a lower round wood support with the diameter of 8cm can be arranged, the horizontal distance is 1m, the top surface of the guide wall is paved with the safety net sheets, and the two sides of the guide wall are provided with the railings and the color bar flags, so that the construction safety is ensured.

The following matters need to be noted in the construction of the guide wall:

before excavation, the condition of underground pipelines must be clearly known, the pipelines are known to be completely moved, for the sake of safety, sample trench sample holes are firstly excavated manually at the positions where the pipeline positions are marked on site, and mechanical excavation is strictly forbidden.

In the whole process of the guide wall construction, light well points are adopted for dewatering, and water is not accumulated in the guide wall ditch.

The waste pipeline which traverses or is close to the wall guide groove must be tightly plugged so as not to form a slurry leakage channel.

The side wall soil body of the guide wall ditch is an outer side soil mold when the guide wall is used for pouring concrete, and the guide wall ditch is prevented from being overetched or collapsed due to the width of the guide wall ditch.

When the cast-in-situ guide wall is constructed in sections, the horizontal steel bars are connected with the horizontal steel bars of the adjacent guide wall sections in a reserved mode, and meanwhile, the situation that the width of a joint is too close to the width of a groove section is avoided.

The guide wall is a guide object in the initial stage of hydraulic grab grooving operation, and the requirement of relevant specifications on the inner clear width dimension of the guide wall and the vertical precision of the inner wall surface must be ensured.

After the guide wall formwork erection is finished and before concrete pouring, the final rechecking is carried out on the guide wall lofting result, and a supervision unit is requested to check and accept a certificate.

After the concrete of the guide wall is poured and the inner formwork is removed, an upper support, a lower support and a horizontal support with the horizontal distance of 1m are arranged in the guide wall ditch, and earthwork is filled back into the guide wall ditch so as to prevent the guide wall from displacing.

When the guide wall concrete is naturally cured to over 70 percent of the design strength, grooving operation can be carried out, and heavy machinery such as vehicles, cranes and the like is forbidden to be close to the guide wall before the grooving operation is carried out.

The guide wall construction lofting is that the guide wall is a reference object of the underground continuous wall on the ground surface, and the plane position of the guide wall determines the plane position of the underground continuous wall, so the guide wall construction lofting is required to be correct.

The construction measurement coordinate system adopts an urban coordinate system or a special coordinate system specified by an owner or design.

The construction measurement of the guide wall adopts a wire measurement method, and the technical indexes of all levels of wire nets meet the relevant regulations.

In order to ensure that the leveling net can obtain reliable calculation basis and can check the stability of the leveling points, more than three leveling points are arranged at stable positions of a construction site, and the distance between the points is preferably 50-100 meters.

The final result of the construction measurement needs to be fixed by a method of burying stable and firm stake on the ground.

And the guide wall construction lofting takes the theoretical central line of the underground continuous wall in the engineering design drawing as the central line of the guide wall.

The guide wall ditch is provided with the stake which can restore the center line of the guide wall at two sides, so that the trend center line of the guide wall can be checked at any time under the condition that the guide wall ditch is excavated.

FIG. 2 is a schematic illustration of a trenching operation; FIG. 3 is a schematic illustration of trenching operations according to an embodiment of the present invention.

And at the corner of the enclosure structure, in order to ensure the grooving quality and the grooving size, the grooving section is reasonably adjusted. For the excavation of the unit groove section, when the grab bucket is used for excavating the groove, the groove hole is required to be vertical, the most important thing is to ensure that the grab bucket excavates the groove under the state of balanced soil-eating resistance, either bucket teeth on two sides of the grab bucket are eaten in the solid soil or the bucket teeth on two sides of the grab bucket fall into a cavity, and the grab bucket teeth are prevented from eating in the solid soil and falling into the cavity at the same time.

In the implementation process, the single holes at the two ends of the groove section are dug firstly, or the method of digging the second hole after the first hole is dug and jumping for a distance is adopted, so that the partition wall which is not dug is left between the two single holes, the grab bucket can be balanced in force when the single holes are dug, the deviation can be effectively corrected, and the straightness of the formed groove is ensured.

As shown in fig. 2 and 3, 1 and 2 shown in fig. 3 are dug first, and then 3 shown in fig. 3 is dug. Firstly, digging a single hole, and then digging a partition wall. Because the length of the hole partition wall is less than the opening length of the grab bucket, the grab bucket can be sleeved on the partition wall to dig, the grab bucket can be balanced in force, the deviation is effectively corrected, and the grooving perpendicularity is guaranteed.

Specifically, the grooves are dug along the length direction of the grooves. After the single hole and the hole partition wall are dug to the designed depth, the grab bucket is sleeved and dug along the length direction of the groove, when the grab bucket is used for digging the single hole and the partition wall, concave and convex surfaces formed by different verticality of the formed groove of the grab bucket are repaired to be smooth, and the groove section is ensured to have good linearity in the transverse direction.

And for digging and removing the sediment at the bottom of the tank, the grab bucket is lowered to the designed depth of the tank section to dig and remove the sediment at the bottom of the tank while the grab bucket digs along the length direction of the tank.

FIG. 4 is a schematic view of a brush wall according to an embodiment of the invention; the construction method comprises the following steps of 41-a steel wire rope, 42-a constructed underground wall, 43-a directional weight, 44-a directional pulley, 45-a wall brushing machine and 46-an underground wall bottom.

And when the construction of the slot wall is carried out, a layer of mud skin is often attached to the old joint, which can affect the quality of the slot wall joint and cause water leakage of the joint part. As shown in FIG. 4, the wire rope hanging weight is mainly used as a guide to make the wall brushing machine 45 tightly contact with the joint during the wall brushing process, so as to ensure the wall brushing effect. In addition, the inclined rib plates are arranged in the wall brushing machine 45, so that the vertical force of the slurry on the wall brushing machine is converted into a horizontal component force in the lowering process, the wall brushing machine 45 is tightly attached to the joint, and the process is repeated for several times until no attachment exists on the wall brushing machine 45.

For bottom cleaning, the hydraulic grab bucket for digging the groove can be used for directly digging and removing the sediment at the bottom of the groove. The replacement method is carried out after the grab bucket directly digs sediment at the bottom of the bucket, and small soil residues which cannot be dug by the grab bucket are removed. Wherein, a Dg100 air-lift device is used, a crane is used for suspending the tank into the ground, an air compressor is used for delivering compressed air, and soil and slag sludge deposited at the bottom of the tank is sucked and removed by a mud reverse circulation method.

When the bottom cleaning is started, the crane is suspended with the air lift device to enter the groove, the sludge suction pipe suspended with the air lift device cannot be placed to the depth of the bottom of the groove at once, and trial excavation or trial suction is firstly carried out at a position 1-2m away from the bottom of the groove, so that the suction inlet of the sludge suction pipe is prevented from sinking into soil slag to block the sludge suction pipe. When cleaning the bottom, the mud suction pipes are from shallow to deep, so that the bell mouth of the air liquid lifter moves up and down and left and right at a position 0.5m away from the bottom of the tank within the full length range of the tank section, and soil and slag sludge at the bottom of the tank is sucked and removed.

And the slurry replacement is the continuation of bottom cleaning operation by a replacement method, when the air liquid lifter does not suck out soil residue after reciprocating at the bottom of the tank, and the thickness of the settled residue at the bottom of the tank is actually measured to be less than 10 cm, the air liquid lifter can be stopped to be moved, and slurry which does not meet the quality requirement at the bottom of the tank is replaced. And regarding whether the bottom cleaning slurry is qualified or not, taking a sampling test as a standard, and when the slurry sampling test data of each sampling point at the tank bottom meets the specified index, the slurry density at 500cm of the tank bottom is not more than 1.15, and the bottom cleaning slurry is qualified.

In the whole process of bottom cleaning and slurry replacement, the balance of slurry suction amount and slurry supplement amount is well controlled, and slurry cannot overflow out of the tank or the slurry surface falls to be 30cm below the top surface of the guide wall.

The steel reinforcement cage is made into shape in a whole width on the steel reinforcement cage making platform, and hoisted into the groove in a whole width. The whole steel reinforcement cage is made by electric welding without binding with galvanized iron wires. And (4) performing a stretch bending test on various welded joints of the steel bars according to the specification, and welding the steel bars to manufacture a steel bar cage after the test piece is qualified. Various reinforcing steel bars are arranged according to the sample turning drawing, so that the reinforcing steel bars meet the requirements, the joints of the reinforcing steel bars are welded firmly, and the forming size is correct.

The protective layer positioning plates are reasonably arranged on the soil facing surface and the excavation surface of the reinforcement cage. The net size of the concrete conduit inserted into the channel is at least 5cm larger than the outer diameter of the conduit, and the lap joint of the guide reinforcing steel bars should be in smooth transition to prevent the occurrence of lap joint steps to clamp the conduit.

Fig. 5 is a schematic diagram of a reinforcement cage drop arrangement according to an embodiment of the present invention; fig. 6 is a schematic diagram of a reinforcement cage protective layer according to an embodiment of the invention. 51-a main hoisting beam, 52-a pulley, 53-a steel cable, 54-an auxiliary hoisting beam, 55-a transverse truss and 56-a longitudinal truss; and 61-a reinforcement cage protective layer.

In order to prevent the reinforcement cage from generating unrecoverable deformation in the hoisting process, longitudinal bending-resistant trusses are arranged on all kinds of reinforcement cages, and the corner-shaped reinforcement cage is additionally provided with a positioning diagonal draw bar. In order to ensure the hoisting safety of the reinforcement cage, the determination of the position of a hoisting point and the safety of a hoisting ring and a hoisting tool are subjected to design and checking calculation, and vertical reinforcements on the reinforcement cage must be firmly welded with each intersection point of intersected horizontal reinforcements from top to bottom.

In the hoisting process of the reinforcement cage, the worst hoisting groove section is an end well section, the width of the 800 m-thick underground wall is 6m, the longest reinforcement cage is 38.1m, and the mass of the reinforcement cage is about 30T at most. 150-ton and 70-ton crawler cranes are planned to be used for double-crane lifting, and the whole crawler crane is hoisted into a groove.

In the embodiment of the invention, the steel reinforcement cage hoisting adopts a 150T crawler crane and a 50T crawler crane double-crane hoisting method. The hoisting process is as follows: firstly, using a 150T crawler crane (main crane) and a 50T crawler crane (auxiliary crane) to lift and hoist the reinforcement cage horizontally, then lifting the main crane and placing the auxiliary crane to lift and straighten the reinforcement cage in an air. The hoisting reinforcement cage must use 150T crawler crane (main crane) alone, must make the reinforcement cage be in the vertical suspension state. The reinforcement cage is slowly placed in the groove section, and quick throwing is avoided, so that the reinforcement cage is prevented from deforming or causing the groove section to collapse.

In the embodiment of the invention, the steel reinforcement cage main crane has 6 points of 150-ton crane and 4 points of 70-ton crane auxiliary crane. And hoisting the reinforcement cage at 10 points in total. And 2 hoisting points of the main hoisting at the 1 st passage adopt phi 40 round steel. The other hoisting points also adopt phi 32 round steel.

The steel reinforcement cage is provided with a longitudinal truss 56 and a transverse truss 55, and comprises two hoisting main trusses and a middle reinforcing truss arranged in each steel reinforcement cage, wherein the main trusses are composed of phi 32X-shaped steel bars, and the reinforcing trusses are composed of phi 28W-shaped steel bars.

And adopting 250X 150X 20 steel plates, welding two sides of the steel cage which is about 30cm below each main hoisting point, temporarily placing the steel reinforcement cage after the steel reinforcement cage passes through the steel carrying pole, then changing the steel wire rope to change the hoisting point so as to continuously lower the steel reinforcement cage and finally temporarily placing the steel reinforcement cage to a designed elevation, cutting off the steel bar of the hoisting point after concrete pouring is finished for 24 hours, and taking out the steel carrying pole. Each cage requires 14 resting steel plates.

The calculation of the forces on the spreader, the lifting point and the shelving plate is as follows:

A. and (3) calculating the stress and strength of the steel wire rope:

the main hoisting steel wire rope for hoisting the steel cage uses 6 strands of steel wire ropes multiplied by 19, the length of each steel wire rope is 15m, two steel wire ropes are respectively arranged on two sides, the total number of the steel wire ropes is 4, the diameter of each steel wire rope is 37mm, the table look-up of the sum of the minimum breaking tension of the steel wire ropes is 72.3T, and the hoisting requirements of the engineering are met.

B. Calculating the strength of the shelving plate:

the breaking shear force of each piece of the shelving board is at least 150mm multiplied by 20mm multiplied by 120N/mm2 ÷ 9.8N/Kg ÷ 1000Kg/T ÷ 36>7.5T (each time 4 shelving boards bear the weight of 30 tons of reinforcement cage at the maximum) meets the requirement.

For the calculation of the stress of the hoisting points, 3 hoisting points of a 150-ton crane are hoisted, namely 6 hoisting points, phi 40 round steel is adopted, and phi 32 round steel is used as an auxiliary hoisting point. The stress condition of the lifting point is as follows:

A. calculation of stress of main hoisting steel bar

The weakest area of Q235 round steel atress is single and is cut, and its maximum shear strength is:

fv＝20mm×20mm×3.14×120N/mm2÷9.8N/Kg÷1000Kg/T＝15T；

the most unfavorable condition is that when the reinforcement cage is lowered to the last lifting point, four points of the two lifting points of the reinforcement at the head of the reinforcement cage bear the weight of 30 tons, and each point bears the weight of 7.5 tons. Therefore, the steel bars of the main hoisting point meet the requirements.

B. Auxiliary hoist reinforcement force calculation

The weakest area of Q235 round steel atress is single and is cut, and its maximum shear strength is:

fv＝16mm×16mm×3.14×120N/mm2÷9.8N/Kg÷1000Kg/T＝9.84T；

in the hoisting process of the reinforcement cage, the auxiliary crane bears 60% of the weight of one reinforcement cage at most, the auxiliary crane has 4 hoisting points in total, the bearing weight is 30 multiplied by 60%, the bearing weight is 18 tons, and each hoisting point bears 4.5T. 9.84T is greater than 4.5T, so the auxiliary hoisting point steel bar meets the requirement.

The welding requirements of each construction node must meet the requirements of JGJ18-2003, the hoisting point steel bars and the main steel bars on the truss are fully welded, the length of the welding seam is not less than 10d, the width of the welding seam is not less than 0.6d, and the thickness of the welding seam is more than 0.35 d; finally, fully welding the two sides of the shelving plate and the lifting bar steel bars, wherein the width of a welding line is not less than 0.6d, the thickness of the welding line is more than 0.35d, fully welding the other shelving steel plates and the two sides of the main bar, and the height of the welding line is more than 10 mm; the main ribs on the truss and the main ribs on the periphery of the steel cage are all welded with the distribution ribs by 100 percent, and the distribution ribs and the main ribs at other parts are spot-welded by 50 percent.

In the process of underwater concrete pouring, the mixing proportion of concrete for pouring the underground continuous wall is designed according to fluid concrete and meets the following regulations: the strength rating should be increased by one level of configuration over the design strength. The water-cement ratio should not be greater than 0.6. Cement usage per cubic meter of concrete: when the coarse aggregate is pebbles, the quantity is not less than 370 Kg; when the crushed stone is adopted, the weight of the crushed stone is not less than 400 Kg. Slump should be 180 and 220 mm. Other requirements are in accordance with the provisions of article 9.2.2, article 9.2.3 and article 9.2.4 of the subway engineering construction and acceptance code.

And, the construction and use of the catheter should meet the following requirements: the horizontal arrangement distance of the guide pipe is not more than 3m, the distance from the end part of the groove section is not more than 1.5m, and the lower end of the guide pipe is about 50cm away from the bottom of the groove. Before pouring concrete, a water-proof plug is hung in the position close to the slurry surface in the guide pipe. The conduit connection should be tight and firm, and the water-proof bolt passing test should be performed by trial assembly before use.

The concrete pouring should comply with the following regulations: and after the reinforcement cage is sunk in place, concrete should be poured in time, and the time for pouring the concrete should not exceed 4 hours. The initial irrigation amount of the concrete should ensure that the depth of the buried pipe is not less than 500 mm. The concrete should be poured uniformly and continuously, and the pouring interruption time should not exceed 30min for this reason. In the concrete pouring process, the depth of the conduit embedded into the concrete should be not less than 3.0m, and the height difference of the concrete in two adjacent conduits should not be more than 0.5 m. The concrete must not overflow the conduit and fall into the trough. The concrete pouring speed should not be lower than 2 m/h. The displaced mud should be disposed of in time and should not spill over the ground. The concrete pouring is preferably 300-500mm higher than the design elevation. Each unit groove section is 50m ³1 group of compressive strength test pieces is prepared from the concrete, and each groove section is not less than 1 group; and manufacturing 1 group of anti-seepage pressure test pieces per 5 unit groove sections, and 6 test pieces per group.

For the grouting of the wall bottom of the continuous wall, the inner diameter of a grouting pipe is not less than 40mm of a steel pipe, a black iron pipe or an electric wire pipe. And for slip pipe connections, wire pressure connections: the connecting sleeve needs to be prevented from being clamped by the steel reinforcement cage when the grouting pipe is lowered. Electric welding: the steel scaffold tube can be connected by electric welding, and the black iron tube and the wire tube are connected by wind welding. Holes and slag inclusion are avoided at the welding position, and the requirements on welding strength and water resistance are ensured. And welding slag is prevented from entering the hole, and smoothness in the hole wall after splicing is ensured. No matter what way to connect, after the connection is finished, the two layers are wrapped by the electric adhesive tape at the connection position to prevent slurry from leaking into the pipe.

And the upper part of the grouting pipe is fixed with the reinforcement cage in an electric welding manner, the distance from the bottom of the grouting pipe to the bottom of the reinforcement cage is not less than 30cm, after the reinforcement cage is placed, the welding point between the upper grouting pipe and the reinforcement cage is cut off, and the grouting pipe falls freely and is inserted into the soil layer.

For the protection of the grouting pipe, the bottom pipe opening of the grouting pipe is sealed by a gunny bag so as to prevent cement slurry from entering the grouting pipe to cause blockage. The top height of the grouting pipe is 15-20cm higher than the ground so as to avoid being buried by soil due to too low height or being bent due to too high height. After the grouting pipe is placed, the opening of the grouting pipe is immediately plugged by a wood plug, so that cement paste or garbage is prevented from entering the grouting pipe. And after the strength of the underground continuous wall reaches 100%, wall toe grouting reinforcement construction is carried out by embedding scaffold pipes, and 2m3 (adjusted according to design requirements) is grouted in each hole.

In the embodiment of the invention, 2 grouting pipes are arranged on each underground wall and inserted into the position 0.5m below the wall bottom, the grouting amount of each grouting pipe is not less than 3m3, the grouting range is 1.5m below the toe of the underground wall, grouting is stopped when the grouting pressure at the wall bottom is stabilized at 2Mpa, and the water-cement ratio of the grouting liquid is controlled to be 1: 1.

in order to ensure the construction quality during the toe grouting of the underground continuous wall, construction is carried out in a hole-separating and jumping grouting mode; the cement is 425# bagged ordinary silica cement. And (5) grouting pressure. Controlling the pressure to be 0.2-0.5 Mpa; the flow rate is controlled at 10-25L/min. Numbering and grouting recording are carefully made in the construction process, and the grouting amount is counted and calculated to prevent hole leakage; and when an abnormal condition occurs, the abnormal condition is reflected to the supervision in time. The grouting amount and pressure are used to control the grouting effect. During grouting, grouting pressure is properly increased, grouting quantity is controlled, and alternating frequency is controlled so as to control grouting diffusion radius and achieve the effect of uniform distribution of grouting quantity.

When the stable grooving of the soil body of the groove section is ensured by controlling the physical and mechanical indexes of the slurry, high-quality slurry with high viscosity and low water loss is selected to form the wall-protecting slurry with thin skin and strong toughness, so that the soil wall stability of the groove section in the repeated up-and-down movement process of the grooving machine is ensured, and each index of the slurry is determined and controlled through theoretical calculation.

Through repeated value trial calculation of h and alpha under various grooving conditions, the depth of the underground wall which is easy to collapse is determined to be within 10m range on the premise of 20KN/m2 ground overload, and the mud during grooving can meet the wall protection requirement of a conventional soil layer when the mud reaches the following index. The breast wall mud quality control criteria are given in the following table:

specific gravity of	Viscosity of the oil	PH	Sand content	Clay skin
					1.08-1.15	25-30″	8-10	<4％	1-1.5mm

The specific gravity of the slurry is 1.1-1.15 when the groove is formed, and the specific gravity of the slurry is less than 1.15 after the hole is cleaned.

And after grooving is finished, slurry replacement is carried out, the work of hoisting a reinforcement cage, placing a guide pipe and the like is carried out, and the steel reinforcement cage is placed stably, accurately and flatly, so that the problem that the wall of the groove is collapsed due to the fact that the reinforcement cage moves up and down is prevented.

The width of the framing in the construction is not too large, the width of the framing is appropriately shortened, so that the influence of the soil arch effect can be effectively utilized, the collapse of the tank wall is reduced, and meanwhile, because the framing is shortened, the construction time of each procedure is correspondingly shortened, the stability of the grooving is facilitated, and the construction quality is ensured.

The quality of the joint of the underground wall is guaranteed as the key point of underground wall construction, and the safety guarantee of foundation pit excavation in future, so that the joint of the underground wall must be protected, sludge in the joint range must be thoroughly removed, and the like, so that the joint water stop requirement is met. However, in construction, both the soil crumbling and the cement slurry flowing around in the tank can adhere to a lot of stubborn sludge on the joint, so that the joint is difficult to clean, and in addition, the generation of the sludge can form sludge inclusion on the joint. Therefore, effective measures must be taken to ensure the seepage-proofing effect of the underground wall joint, and the measures are taken as follows:

1. reducing sand content in slurry

The hole cleaning force is enhanced, the mud with large sand content is pumped out, and the sand content in the mud is reduced. The viscosity in the slurry is kept to be not less than 25 seconds, so that the sand can be suspended in the slurry for a long time, and the phenomenon that a large amount of sediment flows to joints and influences the concrete pouring speed in the concrete pouring process is avoided. The recovery quality of the slurry is strictly controlled, the slurry with the pH value of more than 12 needs to be discarded, the chemical property of the slurry is destroyed, the adjustment cannot be carried out, and the recovery and the use can destroy the good slurry, so that the separation of the slurry is caused, and the precipitation is increased.

2. Splice process control

After grooving is finished, firstly, the bucket teeth of the hydraulic grab bucket are stuck to the end head, and then, large sludge adhered to the joint is repeatedly scraped up and down.

3. Control in concrete pouring process

The depth of the conduit embedded into the concrete is strictly controlled to be kept between 2 and 6m all the time and cannot exceed 6m, otherwise, the conduit is blocked and the concrete cannot be turned over, so that the phenomenon of joint mud clamping is caused, and meanwhile, the conduit is absolutely not allowed to be pulled out, if the conduit is pulled out, the elevation of the concrete surface is measured immediately, the mud on the concrete surface is sucked and cleaned, and then the conduit is opened again and placed into the ball bladder for pouring the concrete. The supply amount of the commercial concrete is ensured, and construction technicians in construction sites must audit the concrete graded list provided by the mixing station and test the concrete slump after the concrete graded list reaches a construction site, so that the supply quality of the commercial concrete is ensured.

The above-described embodiments should not be construed as limiting the scope of the invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions can occur, depending on design requirements and other factors. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (7)

1. A method for constructing an underground diaphragm wall for ensuring grooving perpendicularity is characterized by comprising the following steps:

constructing a guide wall, and arranging a counter brace in a guide wall channel of the guide wall;

performing grooving construction based on the sequence of firstly excavating a single hole and then excavating a partition wall, wherein the length of the partition wall is less than that of an opening bucket of a grab bucket, and the specific gravity of slurry is not less than 1.10 in the grooving construction process;

after the completion of the grooving is determined, slurry replacement is carried out; and

hoisting the reinforcement cage, placing the guide pipe and pouring concrete.

2. The method of claim 1, wherein constructing a guide wall and providing a diagonal brace within a guide wall channel of the guide wall comprises:

excavating a groove through a backhoe excavator, arranging a guide wall template in the groove, and placing a reinforcing mesh in the guide wall template;

symmetrically pouring guide wall concrete;

under the condition that the strength of the guide wall concrete reaches 70%, dismantling the guide wall template; and

and arranging a diagonal brace in the guide wall ditch, and paving a safety net sheet on the top surface of the guide wall, wherein the horizontal distance of the diagonal brace is 1 m.

3. The method of claim 1, further comprising, prior to performing the mud replacement:

in the process of grooving construction, a steel wire rope weight hanging hammer is used as a guide, so that the wall brushing device is tightly attached to a joint in the wall brushing process;

based on the inclined rib plates arranged inside the wall brushing machine, in the process of putting down the wall brushing machine, the vertical force of the slurry on the wall brushing machine is converted into a horizontal component force, so that the wall brushing machine is tightly attached to the joint; and

the method is repeatedly executed until no attachment exists on the wall brushing machine.

4. The method of claim 1, wherein the step of performing a mud replacement comprises:

an air liquid lifter is used, a crane is used for suspending the tank into the ground, an air compressor is used for delivering compressed air, and soil residue sludge deposited at the bottom of the tank is sucked and removed by a slurry reverse circulation method; and

and when the thickness of the measured sediment at the bottom of the tank is smaller than a preset threshold value, stopping moving the air liquid lifter and replacing the slurry of which the bottom of the tank does not meet the quality requirement.

5. The method of claim 1, wherein the steel reinforcement cage is provided with a transverse truss and a longitudinal truss, the middle strengthening truss of the transverse truss is composed of phi 28W-shaped steel ribs, the other trusses of the transverse truss are composed of phi 32X-shaped steel ribs, and 250X 150X 20 steel plates are welded on two sides of the steel reinforcement cage below each main hoisting point; and protective layer positioning plates are arranged on the soil facing surface and the excavation surface of the reinforcement cage.

6. The method of claim 1, wherein the steps of placing a conduit and pouring concrete comprise:

placing the catheters, and determining that the horizontal distance between the placed catheters is not more than 3 meters;

hanging a water-proof plug at a position close to the mud surface in the guide pipe; and

grouting is performed based on the conduit, and the bottom of the continuous wall is grouted through a grouting pipe having an inner diameter of not less than 40 mm.

7. The method of claim 1, further comprising, after the placing of the concrete,: and (3) under the condition that the strength of the underground diaphragm wall reaches 100%, based on the embedded scaffold pipes, adopting a hole-separating and jumping grouting mode to carry out wall toe grouting reinforcement construction.

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