CN113186924A

CN113186924A - Subway foundation pit deep-buried karst cave treatment method

Info

Publication number: CN113186924A
Application number: CN202110466708.6A
Authority: CN
Inventors: 姜智彬; 刘恒伏; 赵智强; 刘玉国; 刘雷; 崔建强; 韩朝翰; 刘辉; 殷浩; 郜天朋; 何强; 周平; 周飞聪
Original assignee: Southwest Jiaotong University
Current assignee: Shield engineering branch of China Railway 25th Bureau Group Co.,Ltd.; Southwest Jiaotong University; China Railway 25th Bureau Group Co Ltd
Priority date: 2021-04-27
Filing date: 2021-04-27
Publication date: 2021-07-30

Abstract

The invention discloses a subway foundation pit deep-buried karst cave treatment method, which relates to the field of foundation pit karst cave construction and comprises the following steps: s1: construction preparation work, namely mastering and knowing general conditions of karst grouting engineering in a construction area, and carrying out site leveling, measurement setting-out and settlement observation pile arrangement; s2: carrying out a process test, determining the proportioning parameters of a filling material, a grouting material and a grouting material of the karst cave, selecting a proper filling material, and preparing a grouting material; s3: drilling construction, namely performing construction edge detection on the karst cave to determine the type of the karst cave and the position of the hole; s4: grouting construction; s5: and sealing holes, cleaning sleeve valve grouting pipes, installing a sealing device at the end parts of the holes, and sealing and treating the karst cave after the grouting quality of the karst cave is checked to be qualified. The method can prevent the head falling and collapse of shield construction, prevent the accident of overlarge ground surface settlement or collapse, reduce the settlement difference after construction and meet the operation safety.

Description

Subway foundation pit deep-buried karst cave treatment method

Technical Field

The invention relates to the field of foundation pit karst cave construction, in particular to a subway foundation pit deep-buried karst cave treatment method.

Background

The karst is a general name of various geological actions, forms and phenomena generated by soluble rocks under the erosion action of water. The soluble rock includes carbonate rock and gypsum, salt rock, mirabilite and other soluble rocks. Karst collapse is the general term for caving deposits in caves and holes in soil formed by loss and migration of soil above the rock surface and causing ground deformation and damage in a karst development area with covering soil under specific hydrogeological conditions, and the soil cave is a special-form unfavorable geological phenomenon of lava, is fast in development and dense in distribution, and has larger influence on engineering than the karst cave sometimes. In recent years, karst floor collapse sometimes occurs, and the cover floor collapse caused by the hidden karst leads to serious damage to the property of residents or shutdown of the building engineering, and the like, so that the economic loss is very large. Therefore, in order to avoid shutdown caused by meeting karst in the subway construction process, further prevent the development of the karst cave and reduce the cost and risk of later-stage operation, the karst cave treatment method is applied to the subway construction karst area.

Disclosure of Invention

The invention aims to provide a subway foundation pit deep-buried karst cave treatment method which can prevent 'head falling' and 'collapse' in shield construction, can prevent ground surface settlement from being too large or collapse accidents from occurring, reduces post-construction settlement difference and meets the requirement of operation safety.

The purpose of the invention is realized by the following technical scheme:

a subway foundation pit deep-buried karst cave treatment method comprises the following steps:

s1: construction preparation work, namely mastering and knowing general conditions of karst grouting engineering in a construction area, and carrying out site leveling, measurement setting-out and settlement observation pile arrangement;

s2: carrying out a process test, determining the proportioning parameters of a filling material, a grouting material and a grouting material of the karst cave, selecting a proper filling material, and preparing a grouting material;

s3: drilling construction, namely performing construction edge detection on the karst cave to determine the type of the karst cave and the position of the hole;

s4: grouting, namely determining the type of the lower pipe and the construction of the lower pipe according to a processing principle;

then, feeding a material pipe into the hole to a depth of the top surface of the karst cave;

installing sleeve valve grouting pipes into the feeding pipes, wherein the sleeve valve grouting pipes are deep to the bottom of the karst cave, and the sleeve valve grouting pipes positioned at the karst cave section are provided with grout outlet holes;

a funnel is arranged at the top end of the feeding pipe, filler is fed into the funnel, and the sleeve valve grouting pipe is vibrated to enable the filler to enter the karst cave through the feeding pipe;

taking down the funnel, pulling out the feeding pipe, injecting casing materials into the karst cave, and then injecting grout stopping materials into the karst cave at a position 1.5-2.0 m away from the ground;

then, grouting is carried out on the sleeve valve grouting pipe, firstly, a double-plug grouting core pipe is installed in the sleeve valve grouting pipe, and grouting materials enter the sleeve valve grouting pipe at the lower part through the double-plug grouting core pipe and then enter the karst cave through a grout outlet in a layered pressure grouting mode to compact, permeate and solidify fillers in the karst cave;

s5: and sealing holes, cleaning sleeve valve grouting pipes, installing a sealing device at the end parts of the holes, and sealing and treating the karst cave after the grouting quality of the karst cave is checked to be qualified.

Preferably, the S1 measurement setting-out step includes the steps of setting-out a reinforcement range and each drilling point position according to construction drawing design requirements, hole position arrangement forms, intervals and reinforcement ranges, measuring and setting-out the reinforcement range and each drilling point position, measuring and recording the ground elevation of the corresponding hole opening, marking by using a stake, and using a white-grey circle point for the hole position; and the S1 settlement observation piles are arranged at the position with the largest deformation in the karst cave construction area according to geological conditions and pile shapes.

Preferably, the S2 cement mortar of the filling material of the karst cave: cement: the sand mixing ratio is 1: 2-1: 2.5, and the adopted macadam is hard and clean in texture, good in grain composition and 5-10 mm in grain size; the grouting material of the S2 karst cave is cement single slurry prepared by 42.5-grade ordinary portland cement or ordinary cement-water glass double-liquid slurry with the water glass modulus of 2.4-3.4 and the concentration of 35-40 Be.

Preferably, the step S3 of constructing edge probing, taking the drill holes revealing the soil and soil cavern as a reference point, performing a row of grouting drill holes at an interval of 2.0m in the vertical direction, then performing a row of grouting drill holes in the horizontal direction, wherein the drill holes and the vertical grouting holes are arranged in a quincunx shape at an interval of 2m, and then probing the holes from the center to other directions to reach the boundary of the cavern body; and determining the type of the karst cave according to the factors of the size of the construction edge detection boundary and the size of the karst cave.

Preferably, in the S4 grouting, at least one vent hole is selected for each hole, sleeve valve pipes are also adopted as the vent holes, the distance between the vent holes is less than 4m, the sleeve valve pipes of the vent holes are lowered to the top of the karst cave, the sleeve valve grouting pipes need to be lowered below the bottom plate of the karst cave by more than 0.5m, and the material feeding pipes are lowered to the holes below the top plate of the karst cave by no less than 1.0 m.

Preferably, in the S4 grouting, casing materials are injected between the outer pipe of the sleeve valve grouting pipe and the inner wall of the hole within the range of the opening of the sleeve valve grouting pipe being less than 2 m; the grout stopping material adopts quick-setting cement paste or non-woven wrapping water-swelling grout stopping material.

Preferably, the step of grouting the sleeve valve grouting pipe of S4:

s41, open loop: in the early stage of grouting, the ring is opened by dilution and pressurization; in the pressurizing process, once the pressure suddenly drops, the slurry inlet amount sharply increases to show that the ring is opened, and after the ring is opened, the grouting material according to the designed proportion begins to formally perform grouting to the karst cave;

s42, grouting: adopting a double-plug grouting core pipe for grouting, and grouting from the bottom to the top of a hole according to the requirements of each group of grouting parameters;

s43, grouting: and during grouting, the water-cement ratio is gradually adjusted according to the principle of firstly grouting, diluting and then grouting thick slurry, the grouting speed is 40-60L/min, and the pressure value of a grouting pump is 1.3-1.5 times of the designed pressure value.

The invention has the beneficial effects that: the method comprises the following steps: construction preparation work; carrying out a process test; drilling construction; the grouting process comprises the following steps: determining the type of the pipe laying and the pipe laying construction according to the processing principle; then, feeding a material pipe into the hole to a depth of the top surface of the karst cave; installing sleeve valve grouting pipes into the feeding pipes, wherein the sleeve valve grouting pipes are deep to the bottom of the karst cave, and the sleeve valve grouting pipes positioned at the karst cave section are provided with grout outlet holes; a funnel is arranged at the top end of the feeding pipe, filler is fed into the funnel, and the sleeve valve grouting pipe is vibrated to enable the filler to enter the karst cave through the feeding pipe; taking down the funnel, pulling out the feeding pipe, injecting casing materials into the karst cave, and then injecting grout stopping materials into the karst cave at a position 1.5-2.0 m away from the ground; then, grouting is carried out on the sleeve valve grouting pipe, firstly, a double-plug grouting core pipe is installed in the sleeve valve grouting pipe, and grouting materials enter the sleeve valve grouting pipe at the lower part through the double-plug grouting core pipe and then enter the karst cave through a grout outlet in a layered pressure grouting mode to compact, permeate and solidify fillers in the karst cave; then sealing and treating. The method can prevent the head falling and collapse of shield construction, prevent the accident of overlarge ground surface settlement or collapse, reduce the settlement difference after construction and meet the operation safety.

Drawings

FIG. 1 is a schematic process flow diagram of a treatment method of a subway foundation pit deep-buried cavern.

Detailed Description

The technical solutions of the present invention are further described in detail below with reference to the accompanying drawings, but the scope of the present invention is not limited to the following.

As shown in fig. 1, a method for treating a subway foundation pit deep-buried cavern comprises the following steps: construction preparation work, namely mastering and knowing general conditions of karst grouting engineering in a construction area, and carrying out site leveling, measurement setting-out and settlement observation pile arrangement; then, carrying out a process test, determining the proportioning parameters of the filling material, the grouting material and the grouting material of the karst cave, selecting a proper filling material, and preparing grouting material; then, drilling construction is carried out, and construction edge detection is carried out on the karst cave to determine the type of the karst cave and the position of the hole; then grouting is carried out, and the type of the lower pipe and the lower pipe construction are determined according to the treatment principle; then, feeding a material pipe into the hole to a depth of the top surface of the karst cave; installing sleeve valve grouting pipes into the feeding pipes, wherein the sleeve valve grouting pipes are deep to the bottom of the karst cave, and the sleeve valve grouting pipes positioned at the karst cave section are provided with grout outlet holes; a funnel is arranged at the top end of the feeding pipe, filler is fed into the funnel, and the sleeve valve grouting pipe is vibrated to enable the filler to enter the karst cave through the feeding pipe; taking down the funnel, pulling out the feeding pipe, injecting casing materials into the karst cave, and then injecting grout stopping materials into the karst cave at a position 1.5-2.0 m away from the ground;

and then grouting the sleeve valve grouting pipe, namely firstly installing a double-plug grouting core pipe in the sleeve valve grouting pipe, and enabling grouting material to enter the sleeve valve grouting pipe at the lower part through the double-plug grouting core pipe and enter the karst cave through a grout outlet in a layered pressure grouting mode to compact, permeate and solidify the filler in the karst cave.

Further, when the method is actually used, the first step is construction preparation, and in the construction preparation step, the following steps are required:

(1) familiarizing with the general situation of each karst grouting work point project, carrying out technical background and necessary technical training before construction, leading the technical personnel and constructors to be familiar with and master the key of each process, strictly designing construction, defining post responsibility, and strictly controlling each construction link according to the ISO-9000 standard;

(2) leveling the site, preparing a drainage facility on the construction site, and preparing surface water drainage and temporary drainage work to prevent surface water from seeping; the site is convenient for the drill to be in place for construction, and the construction site is ready for water and electricity and can be constructed; during construction, in order to ensure civilized construction, the construction site is enclosed;

(3) measuring and setting out, measuring and setting out a reinforcement range and each drilling point position according to a karst grouting hole position plane arrangement diagram and a designed hole position arrangement form, interval and reinforcement range, measuring and recording the corresponding hole opening ground elevation, marking by using a stake, and using a lime ring point for the hole position; according to the requirements of design drawings, burying a settlement observation pile, and performing settlement observation during construction;

(4) connecting construction water and electricity, and testing the operation of the drilling machine to ensure that the drilling machine can normally drill;

(5) detecting the states of all grouting equipment, ensuring the normal operation of the equipment, and reasonably arranging a cement shed, a mixing plant and accessory facilities;

(6) preparing cement, sand, water glass and fly ash for grouting, and establishing a quality inspection system; inspecting the raw materials entering the field, and strictly forbidding using engineering materials such as cement which do not meet relevant regulations;

(7) the technical staff and the quality inspector must be familiar with the drawings, and make a drawing review record and a necessary technical background construction record, the quality inspector is in full charge of engineering quality and safety production, and the technical staff assists in managing the quality.

Further, after construction is prepared, carrying out related process tests, determining the filling material, grouting material and proportioning parameters of the grouting material of the karst cave, selecting proper filling material and preparing grouting material;

the purpose of the process test is as follows: before large-area construction, parameters such as a reasonable grouting method, grouting pressure, grouting materials and the like are selected through field tests, and a basis is provided for large-area grouting construction, so that the construction quality of grouting treatment during large-area construction is ensured;

dissolving, filling soil cave, grouting material and proportioning requirement: the engineering materials for filling and grouting the karst cave are selected according to the factors such as the size, the filling condition, the water supply condition and the like of the karst cave, and the economy, the reliability and the durability are considered; the filling materials mainly comprise: plain concrete, cement mortar, and the like. The grouting materials mainly comprise: cement slurries, chemical slurries, and the like. When in construction, one proper filling and grouting material or several grouting materials are selected to be matched for use according to engineering requirements.

The selection of the grouting material follows the following principle (finally determined by combining with a karst grouting test):

(1) for the drilling holes, the height of the karst cave is not more than 1m, no filling karst cave and half filling karst cave are formed, and the full filling karst cave are directly subjected to static pressure type grouting by pure cement slurry;

(2) for the drill hole, the height of the karst cave is 1-3 m, no karst cave is filled, a half-filled karst cave is filled, and cement mortar intermittent static pressure grouting is generally adopted for grouting; after secondary grouting, the pressure is not raised, and an accelerator can be properly added into cement mortar;

(3) for unfilled karst caves and half-filled karst caves with the height of 3-5 m, firstly filling and throwing broken stones, and then adopting a grouting reinforcement method;

(4) when loss is serious in the process of grouting ordinary cement slurry, the karst cave is subjected to edge sealing treatment by adopting superfine cement slurry or double-fluid slurry, and then internal grouting treatment is carried out;

(5) for the karst cave with larger water inflow, chemical slurry can be considered for plugging, and the plugging and filling effects can be achieved by matching a plurality of materials;

(6) and the cement, aggregate, preparation requirements and the like in the filling and grouting materials meet the relevant standard.

The filling material of the soil dissolving and soil cave needs to meet the following requirements:

(1) cement mortar: cement: the mixing ratio of the sand is 1: 2-1: 2.5, and the sand can be properly adjusted according to a field test in the construction process;

(2) crushing stone: the crushed stone is hard and clean in texture and good in grain composition, and the grain size is 5 mm-10 mm;

grouting materials and proportions of the solution and soil cave meet the following requirements:

(1) and cement slurry: 42.5-grade ordinary portland cement is adopted;

(2) and ordinary cement-water glass double-liquid slurry: the modulus of the water glass is 2.4-3.4, and the concentration is 30-40 Be;

(3) other chemical slurries: polyurethane and Mary powder are used when the water amount is large and serious safety risk exists.

The relative proportions of the grouting materials can be prepared according to the following table, and the specific proportions are determined according to field tests and are shown in table 2:

TABLE 2 slip casting materials mixing ratio

Serial number	Name (R)	Water cement ratio W: C	Volume ratio C to S	Concentration of water glass	Remarks for note
						1	Single liquid slurry of ordinary cement	0.4:1~1:1
2	Cement-water glass double-liquid slurry	0.4:1~1:1	1:1~1:0.3	35~40Be

After the relevant parameters are determined by tests, pulping is carried out. Preparing and stirring cement slurry according to a cement slurry ratio selected in advance: weighing quantitative water according to the capacity of the pulping machine, injecting the quantitative water into the pulping machine, weighing cement with corresponding weight according to the water-cement ratio, starting the pulping machine, and adding the cement while stirring. The stirring time is more than 3 minutes, the slurry does not have obvious precipitation, and the cement slurry is poured into a slurry storage barrel after the stirring. The slurry is continuously stirred manually in the slurry storage barrel, so that the slurry is prevented from precipitating and separating. The cement paste is prepared from the following raw materials: qualified water and PO42.5 cement. Adding water, adding cement and an additive, stirring for 10-20 min, flowing the slurry into a filter sieve for filtering twice, and storing the slurry in a slurry pool; if the cracks and the karst caves are too large and double-liquid grouting is needed, water glass is added, and the indexes of the water glass meet the following regulations: the baume rate is 35-40 Be, and the modulus is 2.4-3.4. The compounding ratio at this time was prepared by a field test by a tester.

Further, after relevant parameters are determined by a process test, drilling construction can be carried out, and grouting is carried out after the drilling construction at a point to be described, so that the relevant parameters of the filling material and the grouting material can be synchronously implemented while the drilling construction is carried out, and the relevant parameters can be determined only before the drilling is finished. Before drilling construction, a foundation pit needs to be treated, and the treatment principle is as follows:

(1) the principle of coordinating and uniformly considering aspects such as karst treatment, substrate treatment, building envelopes, main structures, water inrush in construction period, risk prevention and control schemes in operation period and the like is required to be followed;

(2) and the solution (soil) holes affecting the engineering safety are processed;

(3) non-fully-filled soil holes in the engineering influence range are processed, and a processing scheme is determined for the fully-filled soil holes according to the properties of fillers, the bearing capacity of a foundation, the surrounding environment and other conditions;

(4) the shield tunnel karst treatment follows the principle of mainly treating on the ground and assisting in reserving treatment measures in the tunnel.

Treating the foundation pit in a range:

(1) all the found soil holes in the range of the foundation pit and below the bottom surface of the foundation pit are processed;

(2) the processing range of the open cut foundation pit karst cave development section is determined according to the following principle:

1) all karst caves within the range of 3 meters on both sides of the enclosure structure and 5 meters below the bottom plate are processed;

2) the karst cave is 5-10 m below the bottom plate, the height of the top plate of the stable rock surface of the karst cave is less than 3m or the coverage ratio is less than 1, and filling treatment is needed;

3) the full-filling karst caves in the excavation depth of the foundation pit can be left untreated, the non-filling karst caves with the height larger than 2m and the semi-filling karst caves with the height smaller than 2m need to be filled in advance, and the non-filling karst caves with the height smaller than 2m and the semi-filling karst caves with the height smaller than 2m can be left untreated, so that the construction safety is ensured by construction measures in the excavation process.

(3) Shield zone and communication channel (mining method) karst processing range:

1) all karst caves 3 meters on both sides of the tunnel structure and within a range of 5m below the bottom plate are processed;

3) when the 'beaded' karst caves exist in the processing ranges of the (1) and (2), when the thickness of the complete bedrock layer between the cave bodies is less than 0.5m, the karst caves at the lower layer are processed;

4) in view of the uncertainty of the karst cave development, if an oversize karst cave (more than or equal to 5 m) which is not in the processing range is found in the implementation process, a special conference and all parties need to research to determine whether to process and a corresponding processing scheme, so that the construction and later-period operation safety is ensured.

Further, after the foundation ditch is handled and is accomplished, alright visit the limit in order to carry out the construction, before the limit is visited in the construction, need carry out a series of technical preparation, wherein there are:

(1) the distribution condition of the underground pipelines is explored, the underground pipelines and local water wells are prevented from being damaged by the drilled holes, and water sources are prevented from being polluted;

(2) leveling a construction site in advance, digging a groove and a water collecting channel along the drilling position, arranging a necessary drainage slope to prevent surface water from seeping downwards, calibrating hole positions according to technical intersection bottoms, and retesting;

(3) accurately measuring the position and elevation of the placed grouting hole;

(4) connecting construction water and electricity, and testing the operation of the drilling machine to ensure that the drilling machine can normally drill; before construction, machines such as a drilling machine, a grouting pump, a stirring machine and the like are checked, debugged and maintained to keep good states;

(5) moving the drilling machine to a drilling position, and adjusting the angle of the drilling machine by using tools such as a slope ruler, a level ruler and the like, so that the drilling machine is firmly installed and stably positioned; various devices are installed nearby, grouting pipelines are fixed, and the length is not too long, generally 30-50m, so that pressure loss is prevented;

(6) preparing grouting materials such as cement, sand, water glass and the like for grouting, and inspecting the raw materials entering the field;

(7) detecting the states of all grouting equipment to ensure that the equipment can normally run;

(8) and carrying out technical end-of-line and off-post training on field operators.

Determining a good construction period, a labor force arrangement plan, construction machinery and equipment and the like according to the requirements of design files, and after the preparation is completed, carrying out construction edge detection according to the principle of the construction edge detection:

(1) when the long side of the karst cave projection surface is larger than 5m and the short side is larger than 3m, performing edge detection drilling on the geophysical prospecting contour line, and if the karst cave exists in the drilling and revealing process, continuously drilling 2m outwards to determine the boundary of the karst cave;

(2) and aiming at a large karst cave which spans 3m of side line outside the enclosure and has the vertical height of more than 5m, the boundary is further proved.

In the step of edge detection construction, the diameter of the karst cave edge detection and the hole forming is 91mm, and an XY-100 geological drilling machine is used for hole forming. Drilling in a mode of drilling along with a pipe and mud circulation wall protection until the target final hole is reached, pulling out a grouting pipe (sleeve valve pipe) under a sleeve pipe, and filling cement slurry for reinforcement. When the hole body boundary is searched, if no solution or soil hole is found in the peripheral drilled hole (or the disclosed solution hole does not conform to the processing principle), hole sealing processing is adopted. Well recording the solution (soil) hole to be processed exposed in the drilling process, and pouring a slurry pipe (sleeve valve pipe);

and (3) drilling construction, namely taking the drill holes revealing the soil and soil cavern as datum points, performing a row of grouting drill holes at intervals of 2.0m in the vertical direction, performing a row of grouting drill holes in the horizontal direction, wherein the drill holes and the vertical grouting drill holes are arranged in a quincunx shape, the hole intervals are 2.0m, and probing the holes from the center to other directions until the hole body boundary is reached, wherein the specific steps can be determined and reasonably adjusted according to the principle of construction edge probing.

Further, the pipe laying construction is subsequently performed. Determining the type of the karst cave according to the size of the construction edge detection boundary, the size of the karst cave and the like, and then determining the type of the lower pipe and the grouting scheme according to the processing principle. At least one vent hole is selected for each karst cave, the distance between the vent holes is not more than 4m, the vent holes 50 sleeve valve pipes are transferred to the top of the karst cave, the size of the starching brans 50 sleeve valve pipes required to be transferred below the bottom plate of the karst cave is not less than 0.5m, and the size of the branch brans 200 transferred to the cavity below the top plate of the karst cave is not less than 1.0 m;

after the drilling is finished, the hole is communicated with the soil dissolving hole and the soil hole, the soil dissolving hole and the soil hole are generally hollow, the hollow soil dissolving hole and the hollow soil hole are required to be processed, and the processing method comprises the following steps:

1. for semi-filled or non-filled soil holes and karst caves, firstly, throwing broken stones (plain concrete) for filling treatment, then adopting a sleeve valve pipe grouting method, and carrying out pressure grouting in a layering manner through double core plugs, so that loose fillers in the karst caves are compacted and penetrated by cement paste to form a consolidated body;

the method comprises the following steps:

(1) drilling, taking a core for surveying, and judging the size, position and depth of the karst cave, namely underground water and filling conditions;

(2) recording various parameters in the drilling process, and judging whether abnormal conditions such as drill dropping, water leakage and the like occur or not;

(3) analyzing according to the drilling data to determine a karst cave processing method and formulating reasonable filling and grouting construction parameters;

step two:

(1) a sleeve (a feeding pipe) is put into the cave to the top surface of the cave, and is fixed on the ground by a clamp;

(2) mounting sleeve valve grouting pipes, wherein the depth of each sleeve valve grouting pipe reaches the bottom surface of the karst cave, and a grout outlet ∅ 6@300 is formed in each sleeve valve pipe positioned at the karst cave section;

step three:

(1) installing a funnel;

(2) putting broken stones and filling the karst cave;

(3) when feeding, the sleeve valve pipe is vibrated to enable filler to smoothly enter;

step four:

(1) pulling out the sleeve (feeding pipe);

(2) injecting a jacket material;

(3) injecting grout stopping slurry 2 meters below the ground;

step five:

(1) installing a double-plug grouting core pipe;

(2) stirring cement slurry;

(3) performing layered pressure grouting to compact, penetrate and solidify the karst cave filling;

step six:

(1) pumping clear water and washing the sleeve valve pipe;

(2) installing an orifice protection device;

(3) carrying out grouting quality inspection, and judging whether back-up grouting is required or not according to an inspection result;

(4) and after the quality inspection is qualified, injecting M7.5 mortar for hole sealing.

2. For the full filling soil cave and karst cave, the flow is roughly as follows:

the method comprises the following steps:

step two:

(1) mounting sleeve valve grouting pipes, wherein the depth of each sleeve valve grouting pipe reaches the bottom surface of the karst cave, and a grout outlet ∅ 6@300 is formed in each sleeve valve pipe positioned at the karst cave section;

step three:

(1) injecting a jacket material;

(2) injecting grout stopping slurry 2 meters below the ground;

step four:

(1) installing a double-plug grouting core pipe;

(2) stirring cement slurry;

step five:

(1) pumping clear water and washing the sleeve valve pipe;

(2) installing an orifice protection device;

(4) if the grouting effect does not meet the design requirement, grouting can be carried out again;

step six:

(1) after the grouting quality is qualified, hole sealing can be carried out;

(2) hole sealing: m7.5 mortar is injected into the pipe, and the concrete pavement is recovered.

The steps of processing the half-filled or non-filled soil cavern and the karst cave are approximately the same as those of processing the full-filled soil cavern and the karst cave, and the steps are reasonably selected according to the construction site, so that the two methods are not described in a comparison manner.

3. For a karst cave which is 3m outside the enclosure structure (3 m on two sides of the tunnel structure) and does not reach the boundary, double-liquid slurry is firstly used for carrying out edge sealing at the 3m line outside the enclosure structure, and then filling or grouting treatment is carried out.

The filling materials of the soil dissolving and soil caving are selected from:

(1) and filling the crushed stone, wherein the crushed stone with hard and clean texture, good grain shape and good gradation is adopted, and the grain diameter is 5 mm-10 mm. And (3) adopting PVC pipes with the diameter of 200mm for drilling holes needing broken stone filling, wherein the distance between filling holes is 5-6 m, and the filling holes are uniformly distributed according to the karst cave boundary. The crushed stone is directly put into the hopper. The total filling amount of the crushed stones is controlled according to the calculation principle of the whole grouting amount, for a half-filled karst cave, the filling amount of the crushed stones is about 40 percent of the estimated volume of the karst cave, and for a non-filled karst cave, the filling amount of the crushed stones is about 50 percent of the estimated volume of the karst cave;

(2) c20 plain concrete, which is filled with 42.5 ordinary portland cement;

(3) and filling cement mortar, wherein the filling material adopts cement: and (3) cement mortar with the sand mixing ratio of 1: 2-1: 2.5. In the grouting process, a proper amount of admixture can be added according to the grouting condition to increase the fluidity of the grouting material; pouring cement mortar into an extrusion pump for grouting; and (3) pouring the slurry into a concrete extrusion pump for pouring, temporarily setting the oil pressure of the extrusion pump to be 6-10 Mpa, and if the slurry can not be continuously poured after being stabilized for several minutes when the pressure is 6-10 Mpa for pouring, finishing the filling.

The arrangement of the grouting holes needs to meet the following requirements:

1) for the drill hole (geophysical exploration), the height of the karst cave is not more than 1m of the karst cave, and the drill hole 1 is generally arranged at the exploratory drill hole where the karst cave is disclosed;

2) for the karst cave with the karst cave height of 1 m-3 m, 2 holes are arranged around the exploration drilling holes with the karst caves disclosed in a triangular mode, and the distance is 2.0m multiplied by 2.0 m;

3) for the karst cave with the karst cave height larger than 3m, the drill holes are arranged in a quincunx shape around the exploration drill holes with the karst cave disclosed, the distance is 2.0m multiplied by 2.0m, and the karst cave is detected to be 3m outside the structure; if the hole body is a limited boundary and no hole is found in the outermost row of holes, grouting is not needed for the hole, and a hole is shrunk inwards to be a side hole for grouting treatment;

4) the grouting holes are required to extend into the cavity below the bottom plate of the karst cave by not less than 0.5m, and the stone filling holes are required to extend into the cavity below the top plate of the karst cave by not less than 1.0 m. When the final hole section meets geological defects such as a karst or a fracture dense development zone with poor properties and large scale, drilling holes are deepened and extend into the complete rock mass at the lower part of the drill hole by 0.5 m;

5) the drill holes needing sand filling and blowing, broken stone filling and plain concrete filling adopt PVC pipes with the diameter of 200mm, the distance between filling holes is 5-6 m, and the PVC pipes are uniformly distributed according to the boundary of the karst cave; in order to ensure the grouting effect and reduce slurry mixing, the drilling holes needing grouting are provided with sleeve valve pipes or steel welded pipes, and construction units can properly adjust the drilling holes according to the field conditions;

6) and in the grouting process, air exhaust holes are arranged except for the selected grouting holes, and the number of the air exhaust holes is determined according to the size of the karst cave scale.

Furthermore, after the solution and soil cave are filled, grouting materials can be injected into the solution and soil cave. In the steps of the method, sleeve valve pipe grouting is adopted, and the method comprises the following steps:

(1) and ring opening: in the early stage of grouting, slurry (or clear water) is used for pressurizing and opening the ring. During the pressurization process, once the pressure suddenly drops, the pulp inlet amount sharply increases, which indicates that the ring is opened. After ring opening, formal grouting is started according to the design proportion;

(2) grouting: and (4) grouting by adopting a double-plug core pipe. According to the requirements of each group of grouting parameter tables, grouting is carried out from bottom to top of the hole, each row of holes is used as a grouting section, and the length of the section is 50 cm;

(3) and grouting: the single grout adopts 42.5 ordinary silica cement, and the water cement ratio of the grout is adjusted by 0.4, 0.6, 0.8 and 1.0; ordinary cement-water glass double-liquid slurry: the modulus of the water glass is 2.4-3.4, the concentration is 30-45 Be', and the volume ratio of the cement paste to the water glass is adjusted by 1: 1-1: 0.3; during grouting, the water-cement ratio is gradually adjusted according to the principle that thin slurry is poured first and then thick slurry is poured. The grouting speed is 30-70L/min, and the grouting speed can be adjusted according to actual conditions in construction. The grouting pressure is as follows: the first round of the peripheral holes is 0.2 MPa-0.3 MPa, and the final irrigation is 0.6 MPa-0.8 MPa; the first round of the central hole is 0.2MPa to 0.3MPa, and the final irrigation is 0.8MPa to 1.0 MPa. In addition, the pressure value of the grouting pump is 1.3-1.5 times of the design pressure. The grouting pressure can be gradually adjusted according to the field grouting test and construction requirements;

the grouting pressure is as follows: the first round of the peripheral holes is 0.2 MPa-0.3 MPa, and the final irrigation is 0.6 MPa-0.8 MPa; the first round of the central hole is 0.2MPa to 0.3MPa, and the final irrigation is 0.8MPa to 1.0 MPa. In addition, the pressure of the grouting pump is 1.3-1.5 times of the design pressure; the grouting pressure can be gradually adjusted according to the field grouting test and construction requirements;

when water gushes in a solution and a soil cave, construction can be properly adjusted according to the prior experience, and when water gushes in grouting, plugging is met, the grouting pressure can be calculated by adopting the following formula:

P=Po+（2~4）MPa

in the formula: p-grouting final pressure, Po-water burst pressure;

the detailed grouting sequence is as follows:

the first stage is as follows: constructing a side-exploring drill hole, determining a karst cave boundary, constructing a side-exploring drill hole on the geophysical prospecting contour line, and if the karst cave exists due to the exploration of the drill hole, continuously constructing the drill hole 2m outside to determine the karst cave boundary;

and a second stage: applying blanking holes, wherein the diameter of a drilled hole is 250, the diameter of a blanking pipe is 200, the distance between the blanking holes is 5-6 m, and filling is carried out according to broken stones;

and a third stage: grouting holes in the I area and the II area on the inner side by pressure, and skipping one hole or a plurality of holes after completing grouting one hole;

a fourth stage: injecting grouting holes in the III area by pressure, and skipping one hole or a plurality of holes after injecting one hole;

the fifth stage: and (5) drilling an inspection hole and inspecting the grouting effect.

And (3) gap grouting is adopted for grouting, after the full-hole section grouting is finished, the grouting is performed for the second time after the full-hole section grouting is performed for a period of time, and the intermittent time is controlled within 6-10 hours.

1) For a drill hole (geophysical exploration) which reveals a karst cave height of not more than 1m, a drill hole 1 is generally arranged at an exploratory drill hole which reveals the karst cave;

2) for the karst cave with the height of the karst cave revealed by the drill holes being 1 m-3 m, 2 holes are arranged around the exploration drill holes with the karst cave revealed in a triangular shape, and the distance is 2.0m multiplied by 2.0 m;

4) the grouting holes should extend into the cavity below the bottom plate of the karst cave by not less than 0.5m, and the stone filling holes should extend into the cavity below the top plate of the karst cave by not less than 1.0 m. When the final hole section meets geological defects such as a karst or a fracture dense development zone with poor properties and large scale, drilling holes are deepened and extend into the complete rock mass at the lower part of the drill hole by 0.5 m;

5) the method comprises the following steps of (1) adopting PVC pipes with the diameter of 200mm for drilling holes needing sand filling and blowing, broken stone filling and plain concrete filling, wherein the distance between filling holes is 5-6 m, and the filling holes are uniformly distributed according to the boundary of a karst cave; in order to ensure the grouting effect and reduce slurry mixing, the drilling holes needing grouting are provided with sleeve valve pipes or steel welded pipes, and construction units can properly adjust the drilling holes according to the field conditions;

Attention is required at the time of grouting: the grouting speed is controlled by adopting different control measures according to different conditions, the grouting speed mainly depends on the slurry absorption capacity (the porosity of the stratum) of the bottom layer and the power parameters of grouting equipment, and the grouting speed can be adjusted according to actual conditions in construction.

Secondly, attention needs to be paid to the grouting sequence, and the principle of the grouting sequence needs to follow: the grouting sequence principle is that the inner ring hole is firstly grouted, and then the outer ring hole is grouted; grouting the holes in the same sequence at intervals, skipping one hole or multiple holes after grouting; when the loss of slurry is large or the grouting pressure cannot meet the design requirement in the grouting process, the slurry concentration is adjusted or double-slurry is selected to plug the periphery of the karst cave; drilling according to the detailed exploration geophysical prospecting data provided by an exploration unit, and selecting blanking holes, grouting holes and exhaust holes according to the actual condition, wherein the number of the exhaust holes is sufficient, at least one exhaust hole is formed for ensuring the grouting effect, and the interval of the exhaust holes is not more than 4 m;

and the grouting diffusion radius needs to be noticed during grouting: the grouting diffusion radius can be selected by an engineering analogy method according to the filling grouting requirement, the properties of karst cave filling materials and the particle size of grouting materials. According to engineering experience and engineering analogy, the grouting diffusion radius is 1-1.5 m in a stratum with silt and silty cohesive soil as fillers and 2-2.5 m in a stratum with sandy soil as fillers, and the grouting diffusion radius is considered according to the sandy stratum under the condition that sand and gravel are filled firstly and then grouting is carried out. During construction, the grouting effect can be further corrected and determined after verification and evaluation according to a grouting test or a construction early-stage grouting effect.

And the overall grouting amount is calculated as follows:

the single-hole grouting amount is calculated according to the following formula according to the grouting diffusion radius and the rock stratum filling rate:

Q=πD^2/4·L·n·α·η

wherein, Q-grouting amount; d-grouting range; l-grouting section length; n-porosity of soil layer, fracture rate of rock stratum; the filling coefficient of alpha-slurry in rock fractures; eta-slurry consumption rate.

1) Formula for calculating grouting amount

The grouting amount meter usually adopts three methods, such as an empirical data method, an engineering geological simulation method, a single-hole grouting calculation method for uniformly diffusing the grout and the like. In view of the heterogeneity of the karst, the overall calculation is adopted, and the calculation formula is as follows:

P=V×η×α

v: estimating the volume for the karst cave; eta: a filling factor; α: the diffusion coefficient of the slurry;

a) for full fill:

cement grouting, P1= V × 0.4

b) For half-fill (cavern height greater than 3 m):

filling amount of broken stones: p2 (aggregate) = V × 0.8 × 0.5;

grouting cement slurry amount: p1 (cement slurry) = V × 0.8 × 0.5+ V × 0.8 × 0.5 × 0.4+ V × 0.1;

c) for half-fill (cavern height less than or equal to 3m and greater than 1 m):

cement mortar: p3= V × 0.8

d) For half-fill (cavern height less than or equal to 1 m):

cement paste: p1= V × 0.8

e) For no fill (cavern height greater than 3 m):

filling amount of broken stones: p2/aggregate = V × 0.5

Grouting cement slurry amount: p1/cement slurry = V × 0.5+ V × 0.5 × 0.4

f) For no filling (cavern height less than or equal to 3m and greater than 1 m):

cement mortar: p3= V

g) For no fill (cavern height less than or equal to 1 m):

cement paste: p1= V

f) Double slurry, other chemical slurry:

double-liquid slurry and other chemical slurry are used as auxiliary measures based on field metering.

2) Supplementary description of calculation method

a) The loss is not considered in the above calculation principle, and the calculation is only theoretical calculation;

b) considering the cracks of rock mass around the karst cave, the connectivity of the karst cave and the karst cave outside the treatment range and the slurry loss caused by underground water, determining the slurry diffusion coefficient in the grouting process according to a field test, and reporting to owners, supervision, design and the like to confirm;

c) and for 0.4 and 0.8 coefficient sources, the pore ratio of the filling coefficient is between 0.35 and 0.4, and 0.4 is recommended in calculation. The filling proportion of the half filling is difficult to accurately give, and the filling material accounts for about 20% according to the karst cave analysis of the half filling;

d) the estimated volume in the survey report is only the result of the cross-hole ct section, the blind area outside the cross-hole line cannot be accurately judged, and the cross-hole ct cannot be accurately judged on the karst cave boundary outside the drill hole, so that the estimated volume in the report has a certain difference with the actual volume;

e) the calculated grouting amount is only used as a reference for grouting process control and cannot be used as a basis for construction process calculated amount, and the calculation of the grouting amount is subject to the actual on-site occurrence amount.

In the whole grouting process step, the standard judgment of grouting ending is as follows:

(1) the single-hole grouting is combined with quantitative constant pressure according to the standard of finishing single-hole grouting;

1) and quantitative standard: when the grouting amount reaches 1.2 times of the designed single-hole grouting amount, the pressure still does not rise, five parties need to be held to determine whether measures such as double-liquid grouting are adopted to shorten the gel time or not, so that the pressure reaches the designed final pressure, and the hole grouting is finished;

2) and a constant pressure standard: all hole sections reach the design final pressure and are stabilized for 10min, the grouting speed is 1/4 of the starting grouting speed or the grouting amount reaches 80% of the designed grouting amount, and then the hole grouting can be finished;

(2) the whole section is finished;

1) all designed grouting holes reach the grouting end marking, and no leakage grouting phenomenon exists;

2) and designing inspection holes according to 5-10% of the total grouting holes, wherein the inspection holes meet the design requirements.

Other auxiliary materials for grouting are selected as follows:

1) and orifice grout stopping: hot 65x 3.75 welding steel pipes, anchoring agent and mechanical grout stop plugs;

2) grouting pipes: green 50 sleeve valve pipes;

3) feeding pipes: bronsted 200PVC pipes;

all grouting holes and inspection holes matched with the grouting holes are strictly subjected to hole sealing treatment; after the grouting quality is qualified, hole sealing can be carried out, and M7.5 mortar is injected into the pipe in a hole sealing mode; in order to ensure the sealing quality, all sealing construction is preferably carried out under the field guidance of supervision engineers.

Furthermore, after grouting is completed, holes after grouting need to be checked in order to determine the grouting effect, and the checking methods adopted in the embodiment include a permeability coefficient testing method, a check hole coring method and a standard penetration method;

1) and permeability coefficient test method: calculating the unit water absorption capacity and permeability coefficient of the stratum after grouting according to the water pressing test result to judge the grouting reinforcement effect;

2) and an inspection hole coring method: coring the inspection hole, and analyzing the coring rate of the inspection hole, the integrity of the rock core, the filling condition of the karst cave and the properties of the filling core sample to judge the grouting effect;

3) and a standard penetration method: and judging the grouting effect by adopting an in-situ standard penetration test.

In this embodiment, according to the inspection method, the detection principle and the number of the inspection holes satisfy:

1) the grouting effect strength evaluation is to compare test data before and after grouting, the number of the testability drill holes is not less than 5% of the total number of the grouting holes and not less than 3, and the number of detection points is properly increased for the karst foundation of the complex site;

2) the filling and reinforcing requirements are that each karst cave is detected for 1 time, and the distance between the drilled holes and the filling and grouting holes is 200-300 mm;

3) and the test point number is not less than 2% of the grouting hole number and the monomer engineering is not less than 3 points and meets the design requirement.

1. If meeting the unexpected slip casting interrupt when grouting, the measure of its adoption:

(1) finding out the reason of grouting interruption, solving as soon as possible and recovering grouting as soon as possible;

(2) if grouting can not be immediately recovered or thick slurry is poured to cause the danger of pipe burying, the core pipe is immediately washed, and then grouting is recovered;

(3) after grouting is resumed, the injection rate is obviously reduced, and remedial measures should be taken when grouting suction is stopped in a short time;

2. if a large amount of slurry leaks, the following principle is generally adopted for treatment:

(1) pouring by adopting a low-pressure thick slurry, flow-limiting, quantity-limiting and intermittent grouting method, wherein the intermittent time is 6-8 hours;

(2) when necessary, large gaps can be blocked by adopting mortar or other filling materials, and then the treatment is carried out by adopting the method 1;

(3) the setting time of the slurry is shortened, and cement-water glass or other quick setting materials are adopted for pouring;

3. if slurry is found to be mixed (slurry flows out of other drill holes in the grouting process), the following measures are taken:

enlarging the hole distance between the first sequence holes; properly prolonging the interval time between the successive construction of the two adjacent sequences, and starting the drilling and grouting work of the next sequence of holes after the grout of the previous sequence of hole grouting is basically solidified; if the serial grouting holes have grouting conditions, grouting can be carried out simultaneously, but one hole is needed to be grouted by one pump, otherwise, the serial grouting holes are plugged by plugs, after grouting of the grouting holes is finished, the serial grouting holes are subjected to hole sweeping and flushing, and then drilling and grouting are continued;

4. if the surface slurry is found, the following measures are taken:

when the surface bleeding is treated, low-pressure or self-flow grouting is adopted, the slurry concentration is increased, fine sand and other materials are added if necessary, after the bleeding passage is blocked, the grouting pressure is gradually increased, and the grouting is carried out according to the normal grouting pressure or by adopting an intermittent grouting method.

And further, after grouting is finished and the grouting is qualified, hole sealing treatment is carried out. And (3) after the quality inspection engineer checks, informing a supervision engineer to check and confirm the final hole condition, cleaning the sleeve valve grouting pipe, pulling the sleeve pipe, and simultaneously sealing the hole opening by adopting C15 concrete, wherein the sealing hole is tight and full, and the pipe is pulled out after being filled or while being filled so as to avoid the infirmity of backfilling. And after the grouting quality of the karst cave is qualified, sealing the karst cave and cutting off redundant sealing concrete leaked on the ground, and then backfilling and compacting.

Furthermore, the method can reduce the risks of collapse of the groove wall during the construction of the enclosure structure and the risks of toppling, falling, water burst of the base and the like of construction machines during the excavation of the foundation pit, and avoid damaging peripheral pipelines and buildings; the bearing capacity and deformation requirements of the station base are met; preventing further development of the karst (soil) cave and reducing later-stage operation risk; prevent the shield structure construction "head planting", "collapse", the emergence of the too big or collapse accident of earth's surface subside, reduce the difference subside behind the worker, satisfy the operation safety.

The foregoing is illustrative of the preferred embodiments of this invention, and it is to be understood that the invention is not limited to the precise form disclosed herein and that various other combinations, modifications, and environments may be resorted to, falling within the scope of the concept as disclosed herein, either as described above or as apparent to those skilled in the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. A subway foundation pit deep-buried karst cave treatment method is characterized by comprising the following steps:

2. The method for treating the deep-buried karst cave of the subway foundation pit as claimed in claim 1, wherein said S1 measures and pays out the line, measures and pays out the reinforcement range and each drilling point location according to the construction drawing design requirements and the hole location arrangement form, spacing and reinforcement range, measures and records the ground elevation of the corresponding hole opening, marks the hole location with a stake, and uses a white-grey circle point for the hole location; and the S1 settlement observation piles are arranged at the position with the largest deformation in the karst cave construction area according to geological conditions and pile shapes.

3. The method for treating the deep-buried karst cave of the subway foundation pit as claimed in claim 1, wherein said S2 cement mortar as a filling material of the karst cave is: cement: the sand mixing ratio is 1: 2-1: 2.5, and the adopted macadam is hard and clean in texture, good in grain composition and 5-10 mm in grain size; the grouting material of the S2 karst cave is cement single grout prepared from 42.5-grade ordinary portland cement or ordinary cement-water glass double-liquid grout with the water glass modulus of 2.4-3.4 and the concentration of 35-40 Be.

4. The method for treating the deep-buried karst cave of the subway foundation pit as claimed in claim 1, wherein said S3 construction edge probing, using the drill holes revealing the karst and soil cave as datum points, making a row of grouting drill holes at intervals of 2.0m in the vertical direction, then making a row of grouting drill holes in the horizontal direction, the drill holes and the vertical grouting holes being arranged in a quincunx shape at intervals of 2m, and probing holes from the center to other directions until reaching the boundary of the cave body; and determining the type of the karst cave according to the factors of the size of the construction edge detection boundary and the size of the karst cave.

5. The method for treating the deep-buried karst cave of the subway foundation pit as claimed in claim 1, wherein in the S4 grouting, at least one vent hole is selected for each hole, sleeve valve pipes are also adopted for the vent holes, the distance between the vent holes is less than 4m, the sleeve valve pipes of the vent holes are lowered to the top of the karst cave, the sleeve valve grouting pipes need to be lowered to be more than 0.5m below the bottom plate of the karst cave, and the feeding pipes are lowered to be not less than 1.0m in the holes below the top plate of the karst cave.

6. The method for treating the deep-buried karst cave of the subway foundation pit as claimed in claim 1, wherein in said S4 grouting, a jacket material is injected between an outer pipe of a sleeve valve grouting pipe and an inner wall of the cave within a range of less than 2m of a sleeve valve grouting pipe opening; the grout stopping material adopts quick-setting cement paste or non-woven wrapping water-swelling grout stopping material.

7. The method for treating a deep-buried cavern of a subway foundation pit as claimed in claim 1, wherein said step of grouting with an S4 sleeve valve grouting pipe comprises: