CN110230309B

CN110230309B - Karst area bridge karst cave pile foundation construction method

Info

Publication number: CN110230309B
Application number: CN201910069613.3A
Authority: CN
Inventors: 张瑞智; 郝玉锋; 谷加勇
Original assignee: Civil Engineering Co of CSCEC Xinjiang Construction and Engineering Group Co Ltd
Current assignee: Civil Engineering Co of CSCEC Xinjiang Construction and Engineering Group Co Ltd
Priority date: 2019-01-24
Filing date: 2019-01-24
Publication date: 2021-07-16
Anticipated expiration: 2039-01-24
Also published as: CN110230309A

Abstract

The invention discloses a karst area bridge karst cave pile foundation construction method, which comprises the following steps: punching and karst cave processing, wherein the punching and karst cave processing are repeatedly executed until a hole is formed finally; the karst cave processing specifically comprises the steps of identifying types and processing methods, wherein the identifying types are judging the types of the karst caves according to the vertical depth and the existence of fillers before drilling, in the drilling process and in the pouring process; the treatment method comprises pretreatment before construction, treatment in a drill hole and treatment in a concrete pouring process. The invention adopts different processing methods for different karst caves, so that the construction of the karst cave pile foundation is safer and more effective; the purposes of accelerating the hole forming progress, ensuring the pile forming quality and saving the construction cost are achieved.

Description

Karst area bridge karst cave pile foundation construction method

Technical Field

The invention relates to the technical field of construction of bridge pile foundations in karst development areas, in particular to a construction method of a karst area bridge karst cave pile foundation.

Background

The bridge pile foundation construction in the karst landform area is easy to cause safety accidents such as drill jamming, inclined drilling, hole collapse, ground collapse and the like. According to the construction method, the construction of the pile foundation of the 1 st standard section bridge of the south four ring lines in Wuhan city is taken as the background, and the pile foundation karst cave treatment method under different karst geological development forms is briefly explained by combining the actual karst cave treatment effect on site according to the karst cave height, karst cave layer number, burial depth, roof strata thickness and other data disclosed by geological survey data.

The 1 st standard section of the south four-ring line in Wuhan city mainly comprises two major parts, namely a Gong's laid interchange and an industrial one-way to Beijing Guangdong railway viaduct, and the total length of a main line is 5.129 km. The single cavern height found in the project is generally between 0.2m and 5m, and a small amount is between 5m and 34.5 m. The total height of the single-pile karst cave is generally between 1m and 15m, a small amount of the single-pile karst cave is between 15m and 37.4m, and the maximum height of the single-pile karst cave is 69.7 m.

Disclosure of Invention

Aiming at the defects, the technical problems to be solved by the invention are as follows: the karst region bridge karst cave pile foundation construction method is characterized in that karst cave pile foundations with different geological conditions and different karst cave types are constructed, and different karst cave treatment methods are adopted, so that the karst cave pile foundation construction is safer and more effective. The purposes of accelerating the hole forming progress, ensuring the pile forming quality and saving the construction cost are achieved.

In order to solve the technical problems, the technical scheme of the invention is as follows:

a karst area bridge karst cave pile foundation construction method comprises the following steps: punching and karst cave processing, wherein the punching and karst cave processing are repeatedly executed until a hole is formed finally; the karst cave treatment specifically comprises the following steps: identifying types, namely judging the type of the karst cave according to the vertical depth and the existence of fillers before drilling, in the drilling process and in the pouring process, wherein the type of the karst cave comprises general karst development, relatively karst development, extreme karst development and full filling; the treatment method comprises pretreatment before construction, treatment in a drill hole and treatment in a concrete pouring process; the pretreatment is to adopt a steel protective pipe follow-up mode for the karst cave with extremely developed lava, wherein the general development of karst, the relatively developed karst and the full filling of the karst cave are mainly filled with cement slurry and are assisted by double-liquid slurry; the treatment in the drilling is to backfill a certain proportion of rubbles, clay and cement in a mass ratio of 20:10: 1; the treatment in the concrete pouring process is concrete filling.

Preferably, the specific way of the identification type is as follows:

before drilling, carrying out preliminary statistics according to geological survey data, determining whether karst caves in partial drill holes are distributed in a bead-string shape, determining the distribution range of the karst caves, and determining whether the karst caves exist at the pier positions to be drilled according to detailed survey sampling; preliminarily determining whether a karst cave exists in a construction area according to the adjacent constructed pile foundation;

in the drilling process, if the water level in the hole drops and a wellhead steel wire rope is abnormally loosened, the slurry leakage situation is indicated; analyzing according to the slag sample to see whether the slag sample has abnormal change; judging according to the footage speed, finding abnormality in the drilling footage before slurry leakage in the drilling process, wherein the footage is faster than normal working time at ordinary times, and full filling may occur; judging according to whether the drill bit is inclined or not, finding out the position of the drill bit and the steel wire rope deviated from the center in the drilling process, and preliminarily determining that slope rocks, small karst caves or cracks appear;

and in the pouring process, the rising height of the top surface of the concrete has a larger difference with the theoretical rising height, and the concrete is judged to run off and a karst cave is formed.

Preferably, the method further comprises the following steps before construction: by carrying out statistics and analysis on geological survey data, drilling record, hole forming time, pouring record and pile forming quality of the constructed karst cave pile foundation, different karst cave treatment methods are adopted for karst cave pile foundation construction according to different geological conditions and different karst cave types, and the method specifically comprises the following steps:

for the pile position with poor covering layer geology and loose soil quality, processing the pile position by adopting a mode of lengthening the orifice casing to a rock stratum top plate; when slurry leakage occurs in the holes, according to different conditions of fillers, height and slurry leakage speed of the dissolution cavity, a method of backfilling rubble clay, concrete and bagged cement is adopted respectively, and a compact and stable retaining wall is formed by extruding a mixture of rubble and clay in a small stroke;

for large single karst cave and bead-string karst cave, a full casing follow-up treatment mode is adopted, and the steel casing directly penetrates through the karst cave to form a steel casing retaining wall.

Preferably, in the judging the type of the karst cave according to the vertical depth and the presence or absence of the filler, the specific judging method is as follows: the karst generally develops, h is less than 3, and no filling and half filling are performed; the karst is relatively developed, h is more than or equal to 3 and less than or equal to 5, and no filling or semi-filling is carried out; developing karst pole, h is more than 5m, and no filling or half filling is performed; and (4) fully filling.

Preferably, the pretreatment adopts single-liquid cement slurry grouting pretreatment, and the construction method comprises the following steps:

(1) measuring and lofting: calculating the coordinate position of the lead hole according to the distributed control point coordinates, discharging the hole position by using a total station, measuring the ground elevation by using a level gauge, and determining the depth of the lead hole;

(2) the drilling and hole-forming method comprises four steps of positioning of a drilling machine, sinking and drilling, bit lifting and shifting, wherein the drilling machine is arranged in position and then is stable, the bit is aligned with the position of a pile hole, and sinking and drilling are carried out; during drilling, the drilling machine is kept horizontal, the inclination of the pile is ensured to be smaller than a design required value, the drilling depth is required to reach a grouting consolidation section, and a record is made during the drilling process to provide reference data for grouting operation;

(3) injecting a casing material, inserting a non-porous steel pipe in the air, pressing the casing material through the pipe until slurry in the hole is completely ejected out of the hole, and pulling out the steel pipe;

(4) embedding the pipe, firstly connecting a sleeve valve pipe according to the depth of a lead hole, exposing the upper opening of the sleeve valve pipe to the ground for 20-30 cm, and sealing the lower opening of the connected sleeve valve pipe with a sharp bottom; then, the sleeve valve tube is put into the hole, the maximum error is not more than 20cm when the sleeve valve tube is ensured to be put to the bottom of the hole, if resistance is met in the inserting process, the reason is found out, the sleeve valve tube is strictly forbidden to be forcibly pressed by using excessive external force, water is filled into the hole after the sleeve valve tube is installed, and a protective cap is covered and marked;

(5) sealing, and plugging by adopting quick-setting cement mortar within the distance range from the ground around the orifice to 1m below the ground to prevent the slurry bleeding phenomenon in the grouting process;

(6) grouting and casing material maintenance for about 3 days, and performing retreating type sectional grouting after certain strength is achieved, wherein the grouting mode is from bottom to top, the length of each section of grouting is the grouting step distance, and the length of the open steel pipe is the grouting step distance. The grouting step pitch is generally selected to be 0.6-1 m, so that the influence of stratum heterogeneity on the grouting effect can be effectively reduced. In the grouting process, after each section of grouting is finished, the core pipe is moved upwards by a step distance, and the core pipe is generally 60 cm;

(7) and (3) moving by adopting lifting equipment, or manually and symmetrically clamping the core pipe by adopting 2 pipe tongs, and simultaneously uniformly exerting force on two sides to move the core pipe. And (4) removing a section of grouting core pipe every time the grouting length of 3-4 m is finished. After grouting, covering the upper cover of the grouting pipe with a blank cap to facilitate re-grouting construction.

(8) After the pipe is pulled out and each single hole is grouted, the grouting pipe is lifted by 60cm first, and the grouting is carried out after a while. And before finally pulling out the pipe, closing the bulb pipe valve on the grouting pipe while grouting, and then pulling out the grouting pipe.

Preferably, the double-fluid grouting method specifically comprises the following steps:

and (3) arranging grouting holes: grouting holes by using sleeve valve pipes;

mechanical equipment: ZMB-6 type hydraulic double-liquid grouting pump and slurry pump;

grouting pipes: the diameter inside the grouting pipe is 51mm, and the compression resistance is 35 Mpa;

slurry: cement and water glass are used as main agents;

tube laying: a phi 51 grouting steel pipe is arranged in the hole, the bottom end of the grouting pipe extends into the karst cave, the grouting pipe is a flower pipe, and the length of the flower pipe section of the pipe head is 2 m;

grouting control: carrying out a pressurized water test before grouting, gradually increasing the pressurized water pressure to a preset grouting pressure from small pressure, and continuing for 15 min; the formal double-fluid grouting is started after the pressurized water test is qualified; grouting adopts a double-liquid grouting system to perform full-hole grouting, and repeated grouting is performed for a small amount of times; the adopted materials are ordinary silica P.0.42.5 cement paste, water and glass slurry, and the mixture ratio temporarily takes values according to experience: the water-cement ratio is 0.8; the volume ratio of the cement paste to the water glass is 1: 0.5; cement: water: water glass: the weight ratio of the grouting agent is 1000 Kg: 800 Kg: 700 Kg: 50 Kg; the modulus of the water glass is 2.4-3.4, and the Baume degree is 22-40 degrees; controlling the grouting pressure within the range of 0.3-1 MPa; grouting speed is 15-20L/min, and minimum penetration diameter is 3.0 m;

during grouting, analyzing and determining the grouting speed and the end time through a PQ instrument on a grouting pump, and calculating the pressing-in amount according to the penetration radius and the consolidation volume;

and (5) finishing grouting standard: the grouting finishing standard comprises the final slurry suction amount and the duration when the preset design pressure is reached;

plugging a grouting pipe: after all hole bottom grouting is finished, the grouting pipes are not pulled out any more and are buried in the stratum; the grouting pipe adopts a PVC pipe with the diameter of 20mm to perform grouting and sealing filling on the grouting steel; the pressure is 0.3-1 Mpa; and in the sealing and filling process, the PVC pipe is lifted while grouting is performed, and the lifting speed is controlled according to the field condition.

Preferably, the steel protective pipe follows up, and specifically comprises:

for the pile position with poor covering layer geology and loose soil quality, processing the pile position by adopting a mode of lengthening the orifice casing to the top surface of the rock stratum;

when the steel casing is butted, the joint part is fully welded;

embedding an outer pile casing before pile foundation construction, wherein the diameter of the outer pile casing is 30-50cm larger than the diameter of a pile, the length of the outer pile casing is 5m, the position deviation of the pile casing is noticed during embedding, and the embedded position deviation is not more than 5 cm; drilling to a preset lowering position of the inner protective cylinder by using a drill bit which is 10cm larger than a normal hole forming drill bit, sinking the inner steel protective cylinder into a preset position in sections by using a 25T truck crane, and then performing impact hole forming;

in the construction process of sinking the steel pile casing, the crane must be stable and firmly hoisted on the top of the steel pile casing and centered on the plane position of the top surface of the steel pile casing; and meanwhile, the verticality of the connection of each section of pile casing is strictly controlled by adopting a horizontal ruler, so that the verticality can not exceed 1/200 required by construction specifications, and the steel pile casing is strived to vertically enter the soil.

Preferably, the treatment in the borehole comprises cement, clay, rubble filling and plain concrete backfilling;

the filling method of the cement, the clay and the rubble comprises the following steps:

when a karst cave suddenly appears in the drilling process, rubbles, clay and water are quickly supplemented, the backfill height exceeds the top opening of the karst cave and is not less than 1m, and then the clay and rubble mixture is impacted to the karst cave edge by adopting a small stroke to form a clay rubble outer protective wall;

after the rubble and the clay fully form the wall protection in the hole and the slurry leakage phenomenon completely disappears, the pile is shifted to normal punching, the pile is continuously drilled to the designed pile bottom elevation, and the pile foundation is formed into the hole;

when the slurry leakage phenomenon still exists after the primary backfill is repeatedly beaten, the cement can be prepared from the following components in percentage by mass: clay: flake stone

Continuously backfilling the rubbles and the clay according to the proportion of 1:10:20, and repeating the process until the pile foundation is formed;

the backfill materials are added in the order of cement, clay and rubble; drilling is continued, and if slurry and mud are seriously lost, the rubbles and the clay are repeatedly thrown until the karst cave is filled up, so that the slurry in the hole is prevented from leaking;

and (5) forming holes on the pile foundation, and continuously drilling until the holes are formed on the pile foundation. When slurry leakage occurs in the drilling process, the slurry leakage rate can be determined according to the following steps: clay: the mass ratio of the cement is 20:10:1, adding rubbles, clay and cement in proportion; the plain concrete filling specifically comprises the following steps:

when the height of the karst cave is within the range of 50-150 cm and the cavity is not filled or is half filled, filling with plain concrete; when drilling through a karst cave and leaking slurry or encountering an inclined rock surface, filling low-grade concrete, and after a certain time interval, adopting an impact drill to impact and form a hole;

the concrete label and the mix proportion, the concrete label usually adopts C20 plain concrete, and a certain early strength agent is added into the concrete;

according to the filling method, for the inclined rock surface, in order to correct hole positions, backfilling plain concrete is flush with the top surface of the inclined rock surface, and for the karst cave position, the backfilling top surface is 50cm higher than the top plate of the karst cave;

the worker notes: after backfilling for 8 hours, the drill can be cut again when the strength of the backfilled concrete reaches 70%;

drilling continuously until the pile foundation is formed;

and when slurry leakage occurs in the drilling process, the treatment is repeated according to the method.

Preferably, the single-liquid cement slurry is used for grouting,

when single-liquid grouting is carried out by adopting sleeve valve pipes, 4 holes are uniformly distributed at positions 20cm along the periphery of a pile body for a fully-filled karst cave pile position according to the development conditions of karst revealed by a pile foundation and grouting holes, and all exploration holes are sealed by timely injecting cement paste; the diameter of the opening of the grouting drill hole is required to be 100mm, and the vertical precision is less than 1.5%;

the sleeve valve pipe consists of a phi 90mm PVC outer pipe, a galvanized inner pipe, a rubber sleeve, a sealing ring and the like, grouting can be performed only to the outside of the pipe, and grout cannot be returned to the inside of the pipe, a group of grout injection holes are drilled in the PVC pipe every 50cm, and the bottoms of the grout injection holes are sealed;

grouting materials: the slurry adopts single-liquid slurry, the single-liquid slurry grouting material adopts P.O.32.5-grade ordinary portland cement, and the water cement ratio is 0.5: 1-1: 1;

the shell material formula comprises the following components: powdery clay: water 1:1.5:1.88,3d age compressive strength is 0.3 MPa.

Preferably, the karst cave treatment in the concrete pouring process specifically comprises the following steps:

controlling the slurry index to be 1.2-1.3 in the pile forming process, wherein the volume weight of the concrete is 2.4t/m 3;

before pouring, the mud retaining wall is intact, the mud retaining wall is broken or the backfill is squeezed open, the concrete begins to flow into cracks or karst caves, the concrete must be continuously poured, 3% -5% of accelerating agent is added into the poured concrete, the initial setting time of the concrete is controlled, and the pile foundation can be successfully poured at one time.

After the technical scheme is adopted, the invention has the beneficial effects that:

the construction method of the karst area bridge karst cave pile foundation comprises the following steps: punching and karst cave processing, wherein the punching and karst cave processing are repeatedly executed until a hole is formed finally; the karst cave processing specifically comprises the steps of identifying types and processing methods, wherein the identifying types are judging the types of the karst caves according to the vertical depth and the existence of fillers before drilling, in the drilling process and in the pouring process; the treatment method comprises pretreatment before construction, treatment in a drill hole and treatment in a concrete pouring process. According to the karst cave pile foundation construction method, different karst cave treatment methods are adopted according to the karst cave pile foundation construction under different geological conditions and different karst cave types, so that the karst cave pile foundation construction is safer and more effective. The purposes of accelerating the hole forming progress, ensuring the pile forming quality and saving the construction cost are achieved.

Drawings

FIG. 1 is a schematic diagram of a pile foundation pouring concrete encountering rock stratum fracture;

FIG. 2 is a schematic view of a karst cave encountered by pile foundation cast-in concrete;

FIG. 3 is a schematic view of a backfill material obtained by squeezing concrete cast on a pile foundation;

FIG. 4 is a schematic view of a solution cavity cementing hole arrangement;

FIG. 5 is a schematic diagram of determining the type of cavern based on vertical depth and presence of filler;

in the figure: 1-pile body, 2-grouting hole, 3-before pouring, 4-during pouring, and 5-after pouring.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

As shown in fig. 1 to 4, a karst region bridge karst cave pile foundation construction method includes the following steps: punching and karst cave processing, wherein the punching and karst cave processing are repeatedly executed until a hole is formed finally; the embodiment specifically includes: construction preparation, scheme initial selection, punching, cave treatment, continuous punching … … (cave treatment is carried out circularly, and a treatment scheme and punching are selected according to actual effects) and hole forming.

The karst cave treatment specifically comprises the following steps:

identifying types, namely judging the type of the karst cave according to the vertical depth and the existence of fillers before drilling, in the drilling process and in the pouring process, wherein the type of the karst cave comprises general karst development, relatively karst development, extreme karst development and full filling;

the treatment method comprises pretreatment before construction, treatment in a drill hole and treatment in a concrete pouring process;

for the karst cave with extremely developed lava, a steel protective pipe follow-up mode is adopted in the pretreatment, the general development of karst, the relatively developed karst and the full filling of the karst cave are mainly filled with cement slurry, and the double-liquid slurry is used as an auxiliary material;

the treatment in the drilling process is to backfill a certain proportion of rubbles, clay and cement in a mass ratio of 20:10: 1; the treatment in the concrete pouring process is concrete filling.

In this embodiment: the principle of the karst cave treatment mode is as follows:

1) aiming at the pile position with larger karst cave which is found in advance, pre-grouting treatment is carried out according to the karst cave condition, and the aim is to reduce casualties caused by geological disasters such as hole collapse, collapse and the like.

2) As the field is positioned in the high-rise land of the Yangtze river, the soluble rock surface is directly covered with clay and the like, and a drill hole directly covered with sand soil is not seen. Therefore, when the underlying bedrock is the calcareous sandstone conglomerate, karst ground collapse in construction engineering cannot occur; when the underlying bedrock is limestone and karst develops, firstly, whether a deep karst trench and a karst groove exist on the limestone surface or not and whether soft and flowing plastic red clay exists on the upper part of the trench are found, if the situation is found, karst earth cave type ground collapse can possibly occur, and pre-grouting treatment is carried out to ensure construction safety.

3) The method is characterized in that a non-filled or semi-filled karst cave with a vertical depth of less than 3m is mainly constructed by repeatedly impacting backfilled clay, broken stones, rubbles or concrete, and for the situation that no karst cave is found in the hole forming process due to the fact that exploration is not found, the rubbles, clay and cement are filled and re-beaten according to a certain proportion until holes are formed, if the karst cave is repeatedly backfilled and re-beaten, other additives can be properly added to increase the viscosity and the colloidal rate of slurry, and the quality of the slurry retaining wall is enhanced.

4) In the concrete pouring process, if a karst cave is found, the liquid level is lowered or does not rise, and the concrete is poured until a pile is formed.

5) For the beaded karst cave, pre-grouting, backfilling of rubbles and clay impact pore-forming treatment are adopted. High-quality slurry is prepared in the construction process, the slurry storage capacity is increased, and slurry leakage and hole collapse are prevented.

The specific way of identifying the type is as follows:

during the drilling process, the drill bit is driven,

slurry leakage: the water level in the hole drops and the steel wire rope at the wellhead is abnormally loosened.

Fishing a slag sample for analysis: and analyzing according to the slag sample to see whether the slag sample has abnormal changes, such as the situation of fillers such as clay after entering the rock.

Drilling footage speed: in the drilling process, the drilling footage before slurry leakage is abnormal, the footage is fast in normal work at ordinary times, and the fully-filled drill bit is possible to deflect: finding out the deviation of the drill bit and the steel wire rope from the center position in the drilling process, and preliminarily determining the occurrence of slope rocks, small karst caves or cracks; and in the pouring process, the rising height of the top surface of the concrete has a larger difference with the theoretical rising height, and the concrete is judged to run off and a karst cave is formed.

The method also comprises the following steps before construction: by carrying out statistics and analysis on geological survey data, drilling record, hole forming time, pouring record and pile forming quality of the constructed karst cave pile foundation, different karst cave treatment methods are adopted for karst cave pile foundation construction according to different geological conditions and different karst cave types, and the method specifically comprises the following steps:

for the pile position with poor covering layer geology and loose soil quality, processing the pile position by adopting a mode of lengthening the orifice casing to a rock stratum top plate; when slurry leakage occurs in the holes, according to different conditions of fillers, height and slurry leakage speed of the dissolution cavity, a method of backfilling rubble clay, concrete and bagged cement is adopted respectively, and a compact and stable retaining wall is formed by extruding a mixture of rubble and clay in a small stroke; for large single karst cave and bead-string karst cave, a full casing follow-up treatment mode is adopted, and the steel casing directly penetrates through the karst cave to form a steel casing retaining wall.

In judging the type of the karst cave according to the vertical depth and the existence of fillers, the specific judgment mode is as follows:

the karst generally develops, h is less than 3, and no filling and half filling are performed;

the karst is relatively developed, h is more than or equal to 3 and less than or equal to 5, and no filling or semi-filling is carried out;

developing karst pole, h is more than 5m, and no filling or half filling is performed;

fully filling; the classification of the caverns is shown in detail in fig. 5.

In the pretreatment method in this embodiment, cement slurry is mainly injected, and double-slurry is used as an auxiliary.

And (3) judging the development condition of the karst at the pile position by combining the analysis of the construction exploration hole, determining that the hole is deep to the boundary of a sediment layer, an impact layer, a residual layer and bedrock, limiting the grouting thickness to the stratum layer, and not performing pre-grouting. In the implementation, a geological survey report of pile-by-pile survey is taken as a criterion, and pre-grouting treatment is selectively performed in advance aiming at the pile positions and the quantity of the concrete karst caves in the report so as to ensure the construction safety. And drilling is started after the cement paste injection work is finished for 7 days. And the pressure control during pressure injection is determined according to the actual situation on site.

For the oversized karst cave or the semi-filled karst cave, in order to prevent the collapse of the hole wall caused by the sudden loss of mud, a high-pressure grouting filling and reinforcing method is adopted for processing before drilling. If the karst cave is found to be a communicated karst cave in the construction process, grouting reinforcement is only needed to be carried out on the largest karst cave.

And a grouting mode with single-liquid grouting as a main part and double-liquid grouting as an auxiliary part is adopted. And (3) adopting double-liquid grouting at the beginning stage of grouting and the water leakage position to plug the water leakage crack and the slurry leakage gap to form a slurry stopping layer.

After the double-liquid-slurry grouting achieves the water plugging and seam plugging effects, single-liquid-slurry supplementary grouting is performed, the slurry diffusion range is further enlarged, and the rock performance is improved.

And (4) adjusting the grouting mode and the grouting mixing ratio according to the field condition. And double-liquid-slurry plugging is carried out during slurry leakage, and single-liquid-slurry grouting is carried out after the effect is achieved to enlarge the diffusion range. After single-liquid grouting is carried out for a period of time, the grouting pressure cannot be increased, and double-liquid grouting treatment can be carried out again to enable the pressure to reach the design requirement. The gelation time of the double-liquid grouting is controlled within 3 minutes, so that the slurry diffusion and construction operation are facilitated, and the occurrence of pipe plugging faults is reduced.

As shown in fig. 4, during single-liquid cement grouting, when sleeve valve pipe single-liquid grouting is adopted, 4 holes are uniformly distributed along the 20cm position of the periphery of the pile body 1 for the fully-filled karst cave pile position according to the karst development condition revealed by the pile foundation and the grouting hole, and all exploration holes are sealed by timely injecting cement paste; the diameter of the opening of the grouting drill hole is required to be 100mm, and the vertical precision is less than 1.5%; the cement is bagged ordinary Portland P.O.32.5 cement (double-liquid slurry is P.O.42.5 cement), and the overdue, damp, caking and deteriorated poor-quality cement is strictly forbidden; the water-to-glue ratio was 0.27. After the slurry is solidified, the uniaxial unconfined compressive strength of the solid body is above 1.5MPa, and the grouting pressure is 0.3-1.0 MPa; the hole distribution is specifically shown in fig. 4 below.

Required materials and equipment grouting materials: the slurry adopts single-liquid slurry, the single-liquid slurry grouting material adopts P.O.32.5-grade ordinary portland cement, and the water cement ratio is 0.5: 1-1: 1.

sheathing materials: the basic function of the casing material is to seal the annular space between the sleeve valve pipe and the wall of the drill hole, prevent grout from flowing around during grouting, and force the grout to open a ring (break the casing material) in only one grouting section range to enter the stratum under the cooperation of the rubber sleeve valve and the grout stop plug. The casing material is a low-strength formula mainly comprising clay and cement, and the brittleness of the casing material can be improved by adding fine sand. The engineering uses the formula of the shell material for reference, and cement: powdery clay: water 1:1.5:1.88,3d age compressive strength is 0.3 MPa.

Hole guiding equipment: and (3) drilling a top plate of the karst cave by adopting an HGY-100 type engineering geological drilling machine, taking out the casing pipe and the drilling tool, and then adopting a PVC pipe with the diameter of 90mm meeting the quality requirement.

Grouting equipment: the ZMB-6 type hydraulic double-liquid grouting pump is provided with a grouting pipeline system and a pulping device for grouting.

Grouting pipes: the sleeve valve pipe is composed of a PVC outer pipe with the diameter of 90mm, a galvanized inner pipe, a rubber sleeve, a sealing ring and the like, grouting can be performed only to the outside of the pipe, grout can not return to the inside of the pipe, a group of grout injection holes are drilled in the PVC pipe every 50cm, and the bottom of the grout injection holes must be sealed.

The pretreatment adopts single-liquid cement slurry grouting pretreatment, and the construction method comprises the following steps:

And (5) finishing grouting standard: grouting by adopting cement slurry: reaching or exceeding the design final pressure; ② the final amount is less than 100L/min; and thirdly, stabilizing for 20-30 min.

And (3) starting hole sweeping 8 hours after the completion of grouting of the single-liquid cement slurry, wherein the general experience is that after the grouting reaches the completion standard and water is injected for 15-30 minutes, the pressure is released after the pressure gauge of the orifice naturally drops below 1MPa, and hole sweeping is started to carry out the next construction.

When the sleeve valve pipe is grouted, the pressure is not increased, the liquid level is not increased or the existing loss channel is plugged by adopting a method of pressing double-liquid-slurry to process, and after the loss channel is plugged, the sleeve valve pipe is continuously grouted with slurry.

The double-fluid grouting method specifically comprises the following steps:

and (3) arranging grouting holes: grouting holes by using sleeve valve pipes;

slurry: cement and water glass are used as main agents; the two are injected in a double-liquid mode according to a certain proportion, and an injection material consisting of an additive is added if necessary. The mixed slurry can be used for achieving the purpose of quickly stopping leakage in a stratum with larger groundwater flow velocity;

tube laying: a phi 51 grouting steel pipe is arranged in the hole, the bottom end of the grouting pipe extends into the karst cave, the grouting pipe is a flower pipe, and the length of the flower pipe section of the pipe head is 2 m; three pairs of through holes are drilled on the steel pipe, the outside of each through hole is wrapped and sealed by a rubber sheet of a tire, and cement paste is filled between the grouting pipe and the drilled hole.

during grouting, analyzing and determining the grouting speed and the end time through a PQ instrument on a grouting pump, and calculating the pressing-in amount according to the penetration radius and the consolidation volume; the formula is that R is penetration radius; h is the height of the karst cave; mu is the porosity of the filler, and is generally 1 to 5 percent; alpha is a super irrigation coefficient; λ is a regional empirical coefficient of about 0.3 to 0.9, and γ and β are a packing rate and a packing coefficient, depending on the rock formation properties. The values of these parameters and coefficients can be determined by field testing. The high-pressure pump (the pressure can reach 2MPa) is adopted for grouting.

And (5) finishing grouting standard: the grouting finishing standard comprises the final slurry suction amount and the duration when the preset design pressure is reached; the general cement-water glass double-liquid finishing standard is as follows: the grouting pressure reaches the design final pressure; the pulp suction amount is 50-100 Lmin, and the stabilization can be finished after about 20 min; under normal conditions, constant pressure grouting is generally adopted, and the grouting is finished when the grouting pressure reaches or approaches the final pressure, and when the pressure approaches the final pressure or reaches 80% of the final pressure, if large slurry leakage occurs, the grouting can also be finished when the pressure reaches or approaches the final pressure through an intermittent grouting logistics part.

Grouting construction attention items: in order to prevent the slurry from being wasted due to too far loss, the intermittent grouting mode is adopted, so that the slurry injected firstly and the sand (or gravel) filled in the karst cave are primarily glued and then are grouted, and the grouting is circulated for many times until the specified minimum grouting amount and the grouting pressure control value are reached. And after one hole is injected, continuously injecting slurry into the other holes, wherein the pressure of the post-injection must be increased, and finally sealing the holes. The grouting sequence is controlled by the field.

The cement-water glass grout has the main characteristics of fast gelling time (generally controlled within the range of 60-180 s), adopts the double-liquid mode for injection and has a more complex construction process than single liquid. The characteristics easily cause the occurrence of pipe blockage faults in the intermittent grouting process. The pipe blocking fault is a great problem in the construction of (cement-water glass) double-slurry. In order to reduce the occurrence of pipe plugging faults, the following points should be noted in the double-slurry construction process:

firstly, the installation of a slurry conveying pipeline needs to shorten the length of a slurry converging pipe as much as possible, and the length of the slurry converging pipe needs to be controlled within 1 meter; a pressure reducing valve is arranged on a three-way mixer at the junction of the cement and the water glass slurry, and the junction pipeline can be cleaned by injecting water through the pressure reducing valve;

secondly, stopping the water glass before the double-liquid grouting is stopped temporarily, grouting for 60 to 120 seconds in a single-liquid cement slurry mode, and replacing double-liquid mixed slurry in a grouting pipeline with pure cement slurry to prevent the blockage of a slurry conveying pipeline;

after water plugging and plugging are successful, the mixing proportion of the double-fluid slurry can be adjusted, and the initial setting time of the double-fluid slurry is prolonged;

and fourthly, preparation work before double-fluid grouting is fully carried out, and the temporary grouting stopping times and duration in the grouting process are reduced.

The steel protective pipe follow-up specifically comprises the following steps:

for the pile position with poor covering layer geology and loose soil quality, processing the pile position by adopting a mode of lengthening the orifice casing to the top surface of the rock stratum; and the rapid slurry leakage after the karst cave is punctured is prevented, and the hole wall loses the pressure support of the slurry protecting wall to cause collapse. After the scheme is adopted for treatment, the dependence of the soil covering layer on mud protecting walls is reduced, and even if slurry leakage occurs, the hole wall cannot collapse due to the instability of the soil covering layer. Avoiding the increase of manpower, materials, machinery and construction period caused by repeated backfilling and meeting the requirement of smoothly finishing the hole according to the period.

When the steel casing is butted, the joint part is fully welded; the problem that the upper and lower protective sleeves are deviated due to fracture of the protective sleeves caused by continuous increase of the bearing pressure along with increase of the sinking depth of the protective sleeves is avoided.

in the construction process of sinking the steel pile casing, the crane must be stable and firmly hoisted on the top of the steel pile casing and centered on the plane position of the top surface of the steel pile casing; and meanwhile, the verticality of the connection of each section of pile casing is strictly controlled by adopting a horizontal ruler, so that the verticality can not exceed 1/200 required by construction specifications, and the steel pile casing is strived to vertically enter the soil. If a deviation is found, the deviation is corrected immediately, and the possible deviation is eliminated in the bud state.

The treatment in the drilling hole comprises a cement, clay, rubble filling method and a plain concrete backfilling method;

the filling method of cement, clay and rubble comprises the following concrete steps:

when the karst cave is drilled to be close to the top of the karst cave, a small stroke is adopted, the top of the cave is gradually punctured to prevent hammer jamming, once the mud surface in the hole is found to be greatly reduced, when the karst cave suddenly appears in the drilling process, rubbles, clay and water are quickly supplemented, the backfill height exceeds the top opening of the karst cave and is not less than 1m, the size of the rubbles is preferably 30-50cm, and the rubbles and the clay are mixed according to the mass ratio of 2: 1, putting in water, supplementing water simultaneously to ensure that holes are not collapsed, ensuring that the backfill height of the rubbles exceeds the top opening of the karst cave by not less than 1m, and then adopting a small stroke to impact the clay and rubble mixture to the karst cave edge to form a clay and rubble outer retaining wall;

and (5) forming holes on the pile foundation, and continuously drilling until the holes are formed on the pile foundation. When slurry leakage occurs in the drilling process, the slurry leakage rate can be determined according to the following steps: clay: the mass ratio of the cement is 20:10:1, adding rubbles, clay and cement in proportion;

the plain concrete filling specifically comprises the following steps:

the concrete label and the mix proportion, the concrete label usually adopts C20 plain concrete, and a certain early strength agent is added into the concrete; in order to improve the strength of concrete as soon as possible and save construction time, a certain early strength agent is added into the concrete to improve the early strength of plain concrete.

Construction attention: and after 8h of backfilling, the drill can be restarted when the strength of the backfilled concrete reaches 70%.

construction attention: after backfilling for 8 hours, the drill can be cut again when the strength of the backfilled concrete reaches 70%;

drilling continuously until the pile foundation is formed;

The same method is adopted for the pile which does not have a karst cave according to the geological survey data but has a suddenly-reduced mud surface in the normal drilling process; for small or multilayer karst cave, in order to prevent it from channeling with adjacent hole or the hole pattern after forming hole has gourd shape, if necessary, low grade concrete can be poured for filling, and drilling is carried out after waiting for strength.

The karst cave treatment in the concrete pouring process specifically comprises the following steps:

controlling the slurry index to be 1.2-1.3 in the pile forming process, wherein the volume weight of the concrete is 2.4t/m 3; the volume weight difference between concrete and slurry (or water) is large, when rock stratum cracks or karst caves exist near the hole wall, the slurry wall protection is broken due to the difference of pressure intensity generated by the difference of volume weight in the concrete pouring process, and the concrete flows into the cracks or the karst caves.

As shown in fig. 1, fig. 2 and fig. 3, 3 mud retaining walls are intact before pouring, 4 mud retaining walls are broken or backfill is squeezed during pouring, concrete begins to flow into cracks or karst caves, concrete must be continuously poured, 3% -5% of an accelerating agent is added into the poured concrete, the initial setting time of the concrete is controlled, and the pile foundation can be successfully poured at one time; in the figure, 5 is after casting.

The construction method of the karst area bridge karst cave pile foundation has the following beneficial effects that:

by applying the karst cave treatment method and selecting a reasonable treatment scheme according to the type of the karst cave, the construction progress of the pile foundation engineering is accelerated; meanwhile, the hole forming quality and the construction safety of the pile foundation engineering are ensured, and the constructed karst cave pile foundation is detected by an ultrasonic detector, so that the pile foundation engineering quality is excellent and is I-type piles; and is beneficial to controlling the engineering cost of the karst cave pile foundation.

And (4) benefit analysis, in the construction process of the karst cave pile foundation, selecting an economical and feasible processing scheme according to the classification of the karst cave, controlling the construction cost of the karst cave pile foundation project by accelerating the construction progress, and reducing the mechanical shift and the labor cost. According to the statistics of the actual construction situation on site, a reasonable processing scheme is selected, each karst cave pile foundation can be constructed 3-5 in advance, and the corresponding cost is saved by 3480-5800 yuan (800 yuan/station × 3 days for a mechanical station, 120 yuan × 3 people × 3 days for a daily worker, 3480 yuan, 800 yuan/station × 5 days for a mechanical station, 120 × 3 people × 5 days for a daily worker, 5800 yuan). The cost of each karst cave pile foundation can be saved by 3480 yuan to 5800 yuan, about 220 karst cave pile foundations need special treatment according to geological survey data statistics, and the cost can be expected to be saved by 76.56 ten thousand yuan to 127.6 ten thousand yuan according to the size of the karst cave, the filling condition and the selected economic and feasible treatment technical scheme from the economic cost.

The application effect is that although the engineering has carried out geotechnical geological survey, the underground complex geological condition can not be completely detected due to the limitation of the position and the number of the drilling holes, part of complex geological forms have unpredictability, and serious quality, safety accidents and economic losses can be caused by slight carelessness in construction, so that the technical control measures for construction of the pile foundations in the karst area are summarized from the quality control of the whole process of the pile foundations in the karst area on the basis of analyzing the main construction process of the pile foundations in the karst area, and the method has important significance for controlling the construction quality, progress and cost of the pile foundations under the later-stage geological conditions.

The above-mentioned preferred embodiments of the present invention are not intended to limit the present invention, and any modifications, equivalent to the structural improvements of the karst region bridge karst cave pile foundation construction method and the paving method, etc. within the spirit and principle of the present invention shall be included in the scope of the present invention.

Claims

1. The construction method of the karst area bridge karst cave pile foundation is characterized by comprising the following steps: punching and karst cave processing, wherein the punching and karst cave processing are repeatedly executed until a hole is formed finally;

the karst cave treatment specifically comprises the following steps:

for the karst cave with extremely developed karst, a steel protective pipe follow-up mode is adopted in the pretreatment, the general development of the karst, the relatively developed karst and the full filling of the karst cave are mainly carried out by injecting cement slurry, and the auxiliary is carried out by double-liquid slurry;

the treatment in the drilling is to backfill a certain proportion of rubbles, clay and cement in a mass ratio of 20:10: 1;

the treatment in the concrete pouring process is concrete filling;

the specific mode of the identification type is as follows:

in the pouring process, the rising height of the top surface of the concrete has a larger difference with the theoretical rising height, and the concrete is judged to be lost and a karst cave is formed;

the double-fluid grouting method specifically comprises the following steps:

and (3) arranging grouting holes: grouting holes by using sleeve valve pipes;

slurry: cement and water glass are used as main agents;

tube laying: a phi 51 grouting pipe is arranged in the hole, the bottom end of the grouting pipe extends into the karst cave, the grouting pipe adopts a flower pipe, and the length of the flower pipe section at the pipe head is 2 m;

grouting control: carrying out a pressurized water test before grouting, gradually increasing the pressurized water pressure to a preset grouting pressure from small pressure, and continuing for 15 min; the formal double-fluid grouting is started after the pressurized water test is qualified; grouting adopts a double-liquid grouting system to perform full-hole grouting, and repeated grouting is performed for a small amount of times; the adopted materials are ordinary silica P.0.42.5 cement paste, water and water glass slurry, and the mixture ratio temporarily takes values according to experience: the water-cement ratio is 0.8; the volume ratio of the cement paste to the water glass is 1: 0.5; cement: water: water glass: the weight ratio of the grouting agent is 1000 Kg: 800 Kg: 700 Kg: 50 Kg; the modulus of the water glass is 2.4-3.4, and the Baume degree is 22-40 degrees; controlling the grouting pressure within the range of 0.3-1 MPa; grouting speed is 15-20L/min, and minimum penetration diameter is 3.0 m;

plugging a grouting pipe: after all hole bottom grouting is finished, the grouting pipes are not pulled out any more and are buried in the stratum; the grouting pipe adopts a PVC pipe with the diameter of 20mm to perform grouting and sealing filling on the grouting pipe; the pressure is 0.3-1 Mpa; and in the sealing and filling process, the PVC pipe is lifted while grouting is performed, and the lifting speed is controlled according to the field condition.

2. The karst region bridge karst cave pile foundation construction method of claim 1, further comprising the following steps before construction: by carrying out statistics and analysis on geological survey data, drilling record, hole forming time, pouring record and pile forming quality of the constructed karst cave pile foundation, different karst cave treatment methods are adopted for karst cave pile foundation construction according to different geological conditions and different karst cave types, and the method specifically comprises the following steps:

for the pile position with poor covering layer geology and loose soil quality, processing the pile position by adopting a mode of lengthening the orifice casing to a rock stratum top plate; when slurry leakage occurs in the holes, according to different conditions of fillers, height and slurry leakage speed of the dissolving cavity, a method of backfilling the rubbles, the clay, the concrete and the bagged cement is adopted respectively, and the mixture of the rubbles and the clay is extruded by a small stroke to form a compact and stable protective wall;

3. The karst region bridge karst cave pile foundation construction method according to claim 1, wherein in the judgment of the type of the karst cave according to the vertical depth and the presence or absence of fillers, the specific judgment mode is as follows:

and (4) fully filling.

4. The karst region bridge karst cave pile foundation construction method of claim 1, wherein the pretreatment adopts single-liquid cement slurry grouting pretreatment, and the construction method comprises the following steps:

(3) injecting a sleeve shell material, inserting a steel pipe without a hole into the hole, pressing the sleeve shell material through the pipe until slurry in the hole is completely ejected out of the hole, and pulling out the steel pipe;

(5) sealing, and plugging by adopting quick-setting cement mortar within the distance range from the ground around the orifice to 1m below the ground to prevent the slurry overflow phenomenon in the grouting process;

(6) grouting and casing material maintenance for about 3 days, and performing retreating type sectional grouting after certain strength is achieved, wherein the grouting mode is from bottom to top, the length of each section of grouting is a grouting step distance, the length of an opening steel pipe is the length of the grouting step distance, and the grouting step distance is generally selected from 0.6-1 m, so that the influence of stratum heterogeneity on the grouting effect can be effectively reduced, and in the grouting process, after each section of grouting is completed, the core pipe is moved upwards by one step distance, and the core pipe is generally 60 cm;

(7) moving by adopting lifting equipment or manually adopting 2 pipe tongs to symmetrically clamp the core pipe, uniformly applying force to two sides simultaneously, moving the core pipe, removing a section of grouting core pipe when the grouting length of 3-4 m is finished, and covering an upper cover of the grouting pipe after the grouting is finished so as to facilitate re-grouting construction;

(8) after the pipe is pulled out and each single hole is grouted, the grouting pipe is lifted by 60cm firstly, the grouting is carried out after a while, and before the pipe is pulled out, the bulb valve on the grouting pipe is closed while grouting is carried out, and then the grouting pipe is pulled out.

5. The karst region bridge karst cave pile foundation construction method of claim 1,

the steel protective pipe follow-up specifically comprises the following steps:

when the steel casing is butted, the joint part is fully welded;

embedding an outer pile casing before pile foundation construction, wherein the diameter of the outer pile casing is 30-50cm larger than the diameter of a pile, the length of the outer pile casing is 5m, the position deviation of the pile casing is noticed during embedding, and the embedded position deviation is not more than 5 cm; drilling to a preset lowering position of the inner protective cylinder by using a drill bit which is 10cm larger than a normal hole forming drill bit, sinking the inner steel protective cylinder into a preset position section by using a 25T truck crane, and then performing impact hole forming;

6. The karst area bridge karst cave pile foundation construction method of claim 1, wherein the treatment in the borehole includes cement, clay, rubble filling and plain concrete backfilling;

when the slurry leakage phenomenon still exists after the primary backfill is repeatedly beaten, the cement can be prepared from the following components in percentage by mass: clay: continuously backfilling the rubbles and the clay according to the proportion of 1:10:20, and repeating the process until the pile foundation is formed;

the backfill materials are added in the order of cement, clay and rubble; drilling is continued, and if the slurry loss is serious, the rubbles and the clay are repeatedly thrown until the karst cave is filled up, so that the slurry in the hole is prevented from leaking;

pile foundation pore-forming continues to drill, when the in-process of drilling appears leaking the thick liquid condition, can be according to the slabstone until pile foundation pore-forming: clay: the mass ratio of the cement is 20:10:1, adding rubbles, clay and cement in proportion;

the plain concrete filling specifically comprises the following steps:

drilling continuously until the pile foundation is formed;

7. According to claim4The construction method of the karst area bridge karst cave pile foundation is characterized in that the single-liquid cement slurry is grouted,

the sleeve valve pipe consists of a phi 90mm PVC outer pipe, a galvanized inner pipe, a rubber sleeve and a sealing ring, grouting can be performed only to the outside of the pipe, and grouting can not be performed to the inside of the pipe, a group of grouting holes are drilled in the PVC pipe every 50cm, and the bottoms of the grouting holes are sealed;

8. The karst region bridge karst cave pile foundation construction method of claim 1, wherein karst cave treatment in the concrete pouring process specifically comprises:

the slurry index is controlled to be 1.2-1.3 in the pile forming process, and the volume weight of the concrete is 2.4t/m³(ii) a Before pouring, the mud retaining wall is intact, the mud retaining wall is broken or the backfill is squeezed open, the concrete begins to flow into cracks or karst caves, the concrete must be continuously poured, 3% -5% of accelerating agent is added into the poured concrete, the initial setting time of the concrete is controlled, and the pile foundation can be successfully poured at one time.