CN111042116A - Karst cave stratum pile foundation construction method - Google Patents
Karst cave stratum pile foundation construction method Download PDFInfo
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- CN111042116A CN111042116A CN201911409994.1A CN201911409994A CN111042116A CN 111042116 A CN111042116 A CN 111042116A CN 201911409994 A CN201911409994 A CN 201911409994A CN 111042116 A CN111042116 A CN 111042116A
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D5/00—Bulkheads, piles, or other structural elements specially adapted to foundation engineering
- E02D5/22—Piles
- E02D5/34—Concrete or concrete-like piles cast in position ; Apparatus for making same
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D17/00—Excavations; Bordering of excavations; Making embankments
- E02D17/18—Making embankments, e.g. dikes, dams
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D27/00—Foundations as substructures
- E02D27/32—Foundations for special purposes
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D5/00—Bulkheads, piles, or other structural elements specially adapted to foundation engineering
- E02D5/22—Piles
- E02D5/34—Concrete or concrete-like piles cast in position ; Apparatus for making same
- E02D5/38—Concrete or concrete-like piles cast in position ; Apparatus for making same making by use of mould-pipes or other moulds
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D2300/00—Materials
- E02D2300/0004—Synthetics
- E02D2300/0018—Cement used as binder
- E02D2300/002—Concrete
Abstract
The invention relates to the technical field of building construction, in particular to a karst cave stratum pile foundation construction method. The invention comprises the following steps: the method comprises the following steps: carrying out geographic survey on the construction section, wherein the geographic survey comprises measuring the size, the diameter and the depth of a karst cave, and determining the position and the distribution condition of a karst cave group; step two: grouping according to the vertical distribution and the horizontal distribution of the karst cave groups; step three: and (5) dividing independent operation units according to the karst cave group grouping condition in the step two, and performing unified drilling and unified backfilling operation on the operation units grouped by the unified karst cave group. The invention can carry out pile foundation construction in the karst cave area.
Description
Technical Field
The invention relates to the technical field of building construction, in particular to a karst cave stratum pile foundation construction method.
Background
The karst landform distribution area of China is wide, such as Guangdong, Fujian, Guangxi, Yunnan and the like. The karst landform is mainly characterized by the geographical phenomena of karst caves, craters and the like.
Surface water is eroded along joint surfaces or crack surfaces in the limestone to form a dissolution ditch (or a dissolution groove), and the surface water flows downwards along cracks of the limestone and is eroded, and a water falling hole is formed after the depth of the surface water exceeds 100 meters. The groundwater falling from the water falling cave flows transversely to the aquifer to form a karst cave. The surface of the underground cave collapses along with the formation of the underground cave, the depth of the collapse is large and small, the collapse funnel is called, and the collapse pond is called if the depth is small and the area is large. The erosion and collapse of the groundwater act in combination for a long time to form a sloping valley and an indigenous bridge. The ground rises, and the original karst cave, the underground river and the like are lifted out of the ground surface to form dry valley and stone forest. Rock has certain pores and fissures which are the main channels for the infiltration of mobile water. The larger the rock fracture is, the stronger the water permeability of the rock is, and the more remarkable the karst effect is. In the karst cave, the stronger the karst effect, the larger the karst cave is, the more underground pipelines are, the more complete the karst landform development is, and a continuously enlarged circulation network is formed.
In a karst intense development site, the minimum buried depth of the top of a karst cave of 9.50m, the average diameter of the cave is about 6m, the maximum diameter of the cave is about 30m (in a bead shape), the underground water of the karst cave site is deeply buried, the water level change amplitude is large, the water level of part of the site fluctuates up and down on an earth-rock interface, the development of the karst is rapid, and the stability of the karst site is unstable.
Based on the particularity of the karst geological structure, the continuity of the engineering geological conditions for punching pile construction in the karst cave section of the site is damaged by karst landform characteristics, and compared with common geological conditions, the technical difficulty is more complex, the types of diseases are more, and common construction diseases comprise slurry leakage, concrete leakage, drill sticking, buried drilling, deviated holes and the like.
Disclosure of Invention
The invention aims to: provided is a karst cave stratum pile foundation construction method which can carry out pile foundation construction in a karst cave section.
The invention is realized by the following technical scheme: a karst cave stratum pile foundation construction method is characterized in that: the method comprises the following steps:
the method comprises the following steps: carrying out geographic survey on the construction section, wherein the geographic survey comprises measuring the size, the diameter and the depth of a karst cave, and determining the position and the distribution condition of a karst cave group;
step two: grouping according to the vertical distribution and the horizontal distribution of the karst cave groups;
step three: and (5) dividing independent operation units according to the karst cave group grouping condition in the step two, and performing unified drilling and unified backfilling operation on the operation units grouped by the unified karst cave group.
For better implementation of the scheme, the following optimization scheme is also provided:
further, when the holes are uniformly drilled in the third step, the pile holes need to be drilled to the bottoms of the corresponding karst caves.
Further, the backfill operation adopts different backfill processing schemes according to the detected depth of each group of karst caves, and when the backfill operation is completed, the backfill operation adopts different backfill processing schemes
When the depth of the karst cave is less than 3 m, backfilling rubbles and clay after impacting and penetrating the upper cover of the karst cave, and continuously impacting and forming holes after 48 hours; when in use
When the depth of the karst cave is more than 3 meters and less than 10 meters, punching through the upper cover of the karst cave by adopting a punching hole, pouring underwater concrete by using a guide pipe, continuously pouring after 24 hours until the concrete surface is higher than the top cover of the karst cave, and continuously punching after 48 hours to form a hole; when in use
When the depth of the karst cave is more than 10 meters, drilling a 110mm hole at intervals of 400mm at the position 500mm away from the periphery of the pile in the planned pile area by using a geological drilling machine, inserting 25mm steel bars into the drilled holes, coating a 110mm PVC pipe outside the drilled holes, tying ropes outside the PVC pipe to form a retaining wall cofferdam at the periphery of the pile, pouring concrete into the karst cave to the top of the karst cave, and performing pile-forming construction after 4 days.
Further, the method also comprises the fourth step of: after each cave group is backfilled in a group, any adjacent cave groups are fully compacted with each other.
Preferably, C15 or C20 early strength concrete is adopted during backfilling operation.
Compared with the prior art, the invention has the beneficial effects that:
1. the invention considers the influence of the underground karst water of the karst cave on the washing of the backfill materials, so that the early-strength and quick-setting low-grade cement soil or concrete is adopted to solve the quality problems of hole collapse, partial hollowness, drill sticking and the like caused by the fact that the traditional backfill materials such as rubble, thin iron clad backfill and the like are restrained by the strength of the backfill materials when secondary hole washing is carried out on the traditional backfill materials such as rubble, thin iron clad backfill and the like.
2. Aiming at the large-area vertical beaded karst cave groups and the horizontal connected karst cave groups, the invention combines the previous exploration results and adopts the grouping construction of the karst cave groups according to the vertical distribution and the horizontal distribution, firstly uniformly drilling a group of pile holes connected with the karst cave to the bottom of the karst cave, uniformly backfilling and fully compacting each other, thereby greatly solving the problems of easy collapse, leakage, low pile foundation bearing capacity and the like of the multi-karst cave terrain.
Drawings
FIG. 1 is a construction process flow chart.
Detailed Description
The invention comprises the following steps:
the method comprises the following steps: carrying out geographic survey on the construction section, wherein the geographic survey comprises measuring the size, the diameter and the depth of a karst cave, and determining the position and the distribution condition of a karst cave group;
step two: grouping according to the vertical distribution and the horizontal distribution of the karst cave groups;
step three: and (5) dividing independent operation units according to the karst cave group grouping condition in the step two, and performing unified drilling and unified backfilling operation on the operation units grouped by the unified karst cave group.
The backfill operation adopts different backfill processing schemes according to the detected depth of each group of karst caves, and when the backfill operation is completed, the backfill operation adopts different backfill processing schemes
When the depth of the karst cave is less than 3 m, backfilling rubbles and clay after impacting and penetrating the upper cover of the karst cave, and continuously impacting and forming holes after 48 hours; when in use
When the depth of the karst cave is more than 3 meters and less than 10 meters, punching through the upper cover of the karst cave by adopting a punching hole, pouring underwater concrete by using a guide pipe, continuously pouring after 24 hours until the concrete surface is higher than the top cover of the karst cave, and continuously punching after 48 hours to form a hole; when in use
When the depth of the karst cave is more than 10 meters, drilling a 110mm hole at intervals of 400mm at the position 500mm away from the periphery of the pile in the planned pile area by using a geological drilling machine, inserting 25mm steel bars into the drilled holes, coating a 110mm PVC pipe outside the drilled holes, tying ropes outside the PVC pipe to form a retaining wall cofferdam at the periphery of the pile, pouring concrete into the karst cave to the top of the karst cave, and performing pile-forming construction after 4 days.
Step four: after each cave group is backfilled in a group, any adjacent cave groups are fully compacted with each other.
The early-strength concrete can adopt high-alumina cement, a water reducing agent, a chloride inorganic compound, slag powder and the like. C15 and C20 early strength concrete are generally adopted.
In order to make the ordinary skill in the art better understand the construction method, the description of the scheme is further specifically developed by taking a specific construction section as an example:
first, solution cavity processing scheme (the solution cavity processing scheme)
According to geological survey reports, the project is located in a karst strong development site, and the rate of karst holes in the site is 92.57%. Therefore, before large-area construction of the pile foundation, advanced drilling work is required to be carried out, whether a karst cave exists under each pile position is ascertained, and the position, size and form of the karst cave are used for guiding the construction of the pile foundation so as to avoid construction accidents.
Pile foundation karst treatment scheme
In order to take corresponding measures during punching according to the development scale of the karst cave, the karst cave needs to be judged and classified, and the karst cave is divided into a small-sized karst cave, a common karst cave, a large-sized karst cave and an oversize karst cave according to the size of the karst cave and the condition of the existence of fillers.
a) Smaller karst cave: and when the depth of the karst cave is less than 3 m, backfilling rubbles and clay (part of the clay is bagged behind the top cover of the karst cave) after impacting and penetrating the upper cover of the karst cave, and continuously impacting and forming holes after 48 hours.
b) When the depth of the karst cave is more than 3 meters, after the upper cover of the karst cave is punctured by punching holes, pouring underwater concrete by using the guide pipe, measuring whether the concrete surface rises along with the injection of the concrete at any time in the pouring process, stopping pouring once the concrete surface does not rise, pulling out the guide pipe, and after 24 hours, continuing pouring until the concrete surface is higher than the top cover of the karst cave. And continuously impacting to form holes after 48 hours. If the concrete surface does not rise when the secondary construction continues, the karst cave is judged to be a bottomless cave.
c) Treating without bottom holes: adopting a geological drilling machine, and arranging the following steps around the planned pile: drilling 110mm holes into the karst cave at intervals of 400mm at the position 500mm away from the periphery of the pile, inserting 25mm steel bars into the drilled holes, coating 110mm PVC pipes outside the drilled holes, and tying ropes outside the pipes to form the retaining wall cofferdam at the periphery of the pile. And pouring concrete into the karst cave to the top of the karst cave, and performing pile-forming construction after 4 days.
Third, construction process and method for treating karst of pile foundation
(1) The construction process is shown in figure 1
(2) Preparation for construction
1) Technical preparation
a. The construction scheme is as follows: and (3) analyzing the pile position geological histogram in detail according to geological drilling data and filler conditions, and designing a processing scheme, a punching method and an anti-collapse hole measure for corresponding karst caves according to the corresponding predicted karst cave position and karst cave height of each pile. The karst section punching mode adopts and strikes the pore-forming, so not only can overcome unfavorable geology phenomenon, improves foundation bearing capacity, can solve the problem that the construction precipitation of overlay type karst district is to building and environment construction on every side moreover.
The construction sequence is reasonably specified, and the construction is preferably separated and jumped, so that the holes are prevented from being mixed. During pile foundation construction, peripheral piles are arranged firstly, then middle piles are arranged, pile holes containing deeper, larger and more karst caves are arranged firstly, long pile construction is arranged firstly, and then short piles and smaller pile holes are arranged for construction.
b. Technical background matching: the technical director carries out bottom crossing according to a design labor point diagram, wherein the burial depth of the karst cave and the height between a top plate and a bottom plate of each layer of the karst cave and the top of the protective cylinder are specified in detail in the bottom crossing except for matters to be waited for in the punched piles in the karst cleaning areas; embedding length of the pile casing; punching sequence; the adopted process (whether steel casing follow-up is adopted); construction precautions and the like, and a geological histogram is attached;
c. field identification: each drilling machine is provided with a punching pile signboard which marks the length, diameter, karst cave, depth of the karst cave, drilling time, pouring time and the like of the pile, and a safety warning sign is arranged at an obvious position.
2) Material preparation
Before opening holes, a mixture of 10-20 cubic meters of flaky stones and clay is prepared near the hole openings, the proportion of the flaky stones is not less than 70%, and a part of bagged cement is prepared for emergency use. For the pier position with the earth surface being mucky soil or soft soil, when the underground karst cave is large, I22I-shaped steel with the length of 1 to 2 and 9 meters is still needed to be prepared, and the support is arranged below the pile machine during punching to prevent the drill from toppling over when the hole collapses.
3) Machine preparation
The special field configuration of one loader 1, one excavator and a plurality of transport vehicles is adopted, and once slurry leakage occurs, the loader is used for refilling spare rubble clay into the hole to prevent hole collapse. At least 6D 220 type mud pumps are required to be equipped for standby at a construction site.
4) Preparing a site: carry out "tee bend tie" to the place, operation platform compaction, the piece stone of filling in on soft foundation has sufficient intensity, guarantees that the rig does not take place to empty in the work progress, and operation platform sets up the escape canal all around. The mud pit should set up large capacity mud pit, in case the stake hole appears leaking thick liquid, can mend thick liquid immediately.
(3) Punching hole pile
Construction preparation: the rig floor must have sufficient strength to ensure that the rig does not tip over during construction. If the karst cave is large and the buried depth is shallow, I22I-steel with the length of 9m needs to be placed under the drilling machine, and the drilling machine cannot fall into the hole when the hole collapse of the punching pile is ensured. According to the size of a cave and the presence or absence of fillers, clay, rubbles and bagged PO42.5 cement are prepared, the materials are prepared according to the proportion of 1.5 times, the bagged cement is overhead and is not less than 40cm away from the ground, and tarpaulin is covered on the bagged cement to ensure that the cement is dry. The excavator, loader and crane are prepared at the construction site.
Punching: after the examination by the technician, the drill rig drills. The technician makes technical cross-bottom work for the rig operator, including a geological display. According to the geological condition, the impact energy of the drill bit is adjusted, and a small stroke is adopted when the drill bit drills to a karst stratum. The main purpose of the small stroke operation is to compact the hole wall by using the impact of the drill bit on the drill cuttings and the interbedded components of the rubble and clay. Because of the particularity of the stratum condition, the small-stroke operation can reduce engineering accidents such as drill jamming, drill falling, inclined holes, hole collapse and the like to a certain extent,
(5) clay-filled stone mixture and concrete
When slurry leakage occurs on the top plate of the karst cave through breakdown, the supply of slurry is increased, the mixture of clay and the rubble is timely filled in a throwing mode, the ratio is 3:7, the diameter of the rubble is 30-40 cm, the rubble is filled to the upper end of the karst cave, and drilling is continued. Punch → fill clay, slab mix → punch → fill clay, slab mix … … pore-forming-pouring concrete.
If the cavity is large (H is more than 2m), no filler is used and underground water flows, under the condition that the effect of backfilling the rubble clay mixture is poor, the concrete is poured by the guide pipe, and the punching construction can be carried out after 3 to 4 days of pouring.
5.2.3 problems common in construction process of karst punching pile and prevention and treatment measures
(1) Clamping hammer
1) The reasons include ① that the pile hammer is not repaired in time due to abrasion when a bedrock section is drilled, ② that objects and stones are dropped during impact, ③ that too much steel wire rope is blown down to cause the pile hammer to topple over and support the hole wall, and ④ that the bottom plate of the karst cave inclines or meets the half karst cave.
2) The prevention and treatment measures comprise ① slow test method, namely, when a drill bit is clamped at any position in the middle, the main rope is required to be slowly released, tightened, slowly released and tightened, the drill bit is repeatedly lifted out of an in-situ channel, ② impact method, namely, the main rope is loosened by 3-5m, a weight is hung by a drill bit auxiliary rope to downwards impact the drill bit, the main rope is loosened, the slow test method is repeated, ③ auxiliary lifting method, namely, a crane, a jack or a drill rig auxiliary rope penetrates through a pulley block to carry out force lifting, ④ underwater loosening blasting method, namely, after the height of the clamped drill bit is measured, emulsified waterproof explosives are quickly bundled into two groups, counterweights are symmetrically placed at the cutting edge of the drill bit, then the drill bit main rope is tightly pulled or is tightly lifted by the crane, an electric detonator is adopted for initiation, and when ⑤ can not actually take the hammer, a pile foundation modification scheme.
(2) Drop hammer
1) The reasons are that ① hammer mass has problems to cause hammer body fracture, ② steel wire rope fracture, ③ when running into a large karst cave and filler is soft plastic soil or a cavity, the hammer is dropped because the hammer is driven into the small cave cavity several meters at one stroke due to the control of the running into the small cave cavity.
2) The prevention and treatment measures include that ① appropriate fishing tools such as a fishing hook and a flushing and grabbing cone are selected to fish the hammer body, ② divers are used for fishing in the lower hole, ③ carefully carries out construction according to a designed geological column pile diagram, when a top plate is broken through quickly, low-stroke quick driving is needed to prevent the hammer from dropping due to large footage, and when ④ cannot be fished, a design unit is requested to put forward a pile foundation modification scheme.
(3) Buried drill for collapsed hole
1) The reason is as follows: during construction, a large amount of slurry is suddenly lost due to the fact that the slurry meets a karst cave or a crack communicated with the karst cave outside the pile position.
2) The prevention and treatment measures include timely slurry replenishing and water replenishing when slurry leakage occurs at ①, maintaining water head in the hole, preventing overlarge water head difference between the inside and the outside of the hole and quickly stopping leakage, and ② filling the karst cave with a mixture of steel casing follow-up and clay filling and stone chips to prevent slurry leakage and hole collapse.
(4) Sloping rock
1) The reason is as follows: due to karst geology, the diagenetic rock is caused.
2) The prevention and treatment measures comprise ① throwing and filling rubbles, concrete or reinforcing steel bars and the like to fill the other side of the inclined rock to enable the drill bit to be stressed uniformly, ② punching is carried out on one side of the inclined rock, and the side of the inclined rock is removed by adopting underwater blasting.
(5) Ground subsidence
1) The reasons are that ① the ground subsides due to the water level drop caused by pumping underground water by driving a motor-pumped well in karst punching pile construction, and ② the sand funnel type subsides and cracks near the pile foundation caused by pumping water and fillers in the karst cavity due to the punching pile construction.
2) The prevention and treatment measures are that ① need not pump underground water as much as possible as construction water, and a method of filling clay rubble and steel casing in a karst cave is adopted in ② punching pile construction.
(6) Pollution of ground water
1) The reason is that ① karst grouting pollutes the underground water body, and ② punching pile construction leaks and seeps mud and backfills cement and concrete, so that the underground water body is polluted.
2) ① when there are water works and pure water works nearby, grouting is used as little as possible in karst treatment, and backfilling cement and concrete are used as little as possible;
(7) attention points of pile foundation hole-forming construction
1) In the process of forming the hole, the hammer impact is needed to be reduced when the hole top of a soil cave or a karst cave is reached, so that the phenomena of hammer clamping and hammer falling are prevented.
2) When large soil cave or karst cave is encountered, enough rock blocks, clay and cement are prepared near the hole opening. When the top of the hole is perforated, once slurry leakage is found, the hole is quickly filled to prevent hole collapse. After the top of a general soil cave or a karst cave is punctured, mud in a pile hole can quickly descend, at the moment, a forklift is used for throwing prepared rock blocks, clay and cement in time according to a proper proportion until the mud in the hole stops descending and slowly rises, at the moment, a punching hammer can be used for properly extruding, the rock blocks, the clay and the cement are repeatedly thrown until the karst caves on two sides of a pile foundation are fully filled or blocked, finally, the mud is filled and the hole is formed again, and the pile is formed by punching again after 1-2 days when the karst caves are larger.
3) If the large soil cave or hollow cave is met, grouting is carried out firstly, and then hole forming is carried out, so that the phenomena of ground subsidence, hammer clamping and hammer falling can be prevented, and the foundation can be reinforced.
4) The section with soil cave and karst cave, especially those with large covered surface, contains several pile foundations, and during construction, the deep pile foundations are first constructed from deep to shallow to ensure safety.
5) If the rock surface is an inclined surface, the rock block needs to be thrown for many times to be inclined, and the time for beating the inclined rock is 3-5 times longer than that for beating the whole rock.
7) After final hole forming, hole probing must be carried out by using a steel cage hole probing device with the diameter of more than 5m, hole cleaning and slurry changing must be thorough, and particularly, sediments after secondary hole cleaning must meet the standard.
8) The concrete slump is preferably 18-22 cm; the pouring guide pipe must be well sealed, a water-isolating plug is placed in the pouring process, and the pouring of concrete must be continuous and rapid; the pouring concrete is sufficiently prepared.
5.3.2 karst punching pile construction attention problem
(1) The karst stratum punching pile should adopt and strike the pore-forming, and when the hole depth is longer, adopt and draw a sediment section of thick bamboo cooperation pore-forming, efficiency is higher.
(2) For a pile position with karst, the length of the steel casing is not less than 2 meters, and the steel casing with the length of 3 meters is generally adopted to be more reliable in combination with the condition of earth surface soil; if the earth surface is mucky soil, the pier position is dug and replaced, in order to ensure that the earth surface is not immersed by rainwater during construction, and the island is required to be built at a low-lying position (such as a fishpond, a paddy field and the like), the flaky stone clay can be adopted, the flat rolling compaction is adopted by an excavator, after the protective cylinder is buried, the periphery is backfilled by clay and small stones and tamped, and the protective cylinder is prevented from sinking or inclining during drilling. The supporting effect of the protective cylinder on the hole wall is ensured when the slurry leaks on a small scale.
(3) The specific gravity of the slurry is very critical, and when drilling in a karst, the specific gravity of the slurry needs to be increased, which is generally not less than 1.5, so as to enhance the supporting effect on the hole wall.
(4) In order to ensure that enough mud is supplemented once the mud leaks, the mud pit needs to be made into a large size properly, and according to the karst scale condition of a single pier, the mud pit is made into mud pits with different sizes of 50-100 m3 when the mud pit is excavated.
(5) The construction sequence of long piles and short piles must be maintained in the construction process.
(6) For small karst caves and karst caves processed by mud jacking (sand jacking or concrete), when drilling to about 1m of the top of the karst cave, the stroke is changed within the range of 1-1.5 m, and the top of the karst cave is gradually punctured to prevent drill jamming.
(7) For an empty karst cave or a semi-filled karst cave, before the top of the cave is punctured, a specially-assigned person needs to pay close attention to the change of the slurry surface in the pile casing, once the slurry surface descends, water should be rapidly supplemented, and then the weight of the pile casing is increased according to the size of the karst cave by 3:7, backfilling clay and rubbles according to the proportion of 7, and filling and extruding the whole package of cement to be compact, and only after the slurry leakage phenomenon completely disappears, turning to normal drilling, and repeatedly enabling the punched holes to smoothly pass through the karst cave.
(8) When large karst cave is met, enough stone, clay and cement are prepared near the hole. When the top of the hole is perforated, once slurry leakage is found, the hole is quickly filled to prevent hole collapse. After the karst cave is punctured, mud in a pile hole can quickly descend, at the moment, an excavator is used for throwing prepared stone blocks, clay and cement into the pile hole in time according to a certain proportion (1: 1-3: 2: 0.2) until the mud in the hole stops descending and slowly rises, at the moment, a punching hammer can be used for carrying out appropriate extrusion, the stone blocks, the clay and the cement are repeatedly thrown until the karst caves on two sides of the pile foundation are fully filled or blocked, finally, the mud is supplemented and the hole is formed again, and the hole is punched again after 1-2 days when the karst caves are larger.
(9) For the karst cave with the filling material of soft and weak viscous soil or silt, the clay and rubble mixture (ratio 1: 1) is also added into the cave after entering the karst cave, and the wall is impacted and fixed. When the drill bit passes through the karst cave, the condition of the big rope needs to be closely noticed so as to judge whether the drill bit is inclined. If the inclined drill is inclined, the following steps are carried out: 1 until the bent hole is more than 0.5m, and then punching and smashing again.
(10) During the punching process, the change of the slurry surface in the casing is closely noticed, when the slurry surface rapidly descends, the slurry leakage is proved to be firstly supplemented with water quickly, then a mud ball is thrown downwards, and then clay and rubbles are pressed according to the weight ratio of 1: the drill bit is driven downwards by about 2m according to the proportion of 1, and then the drill bit is driven again, so that the broken rubble and large-particle soil can fill the crack for a certain distance (to block the change of the width of the crack), and the drill bit can drill for a certain depth without slurry leakage. When the slurry leaks again, the slurry is processed according to the method, and the designed hole bottom elevation can be drilled step by step. The preparation of the slurry also determines the efficiency of pore-forming in the karst cave, and when the hole is punched to about 1m of a top plate of the karst cave, the specific gravity of the slurry is increased, and the small-stroke hole punching is adopted.
(11) If the repeated backfilling times in the punching process are not enough, the karst cave is not thoroughly treated, holes can be formed, but when underwater concrete is poured, the concrete has high specific gravity and high lateral pressure, when the concrete surface rises to a certain height, the retaining wall can be broken by squeezing, and the ash stopping surface can rapidly descend, so that the underwater concrete pouring of the karst layer punching pile can ensure enough burial depth of the guide pipe, and generally, during the underwater concrete pouring process, if the ash stopping surface can rise, the guide pipe does not need to be pulled out as lightly as far as possible.
(12) The daily maintenance of the drilling machine is very important, especially the steel wire rope is used as a key point to strengthen daily maintenance, and the drilling machine needs to be replaced in time when the wire is broken and is greatly abraded.
While the invention has been illustrated and described with respect to specific embodiments and alternatives thereof, it will be understood that various changes and modifications can be made without departing from the spirit and scope of the invention. It is understood, therefore, that the invention is not to be in any way limited except by the appended claims and their equivalents.
Claims (4)
1. A karst cave stratum pile foundation construction method is characterized in that: the method comprises the following steps:
the method comprises the following steps: carrying out geological exploration on the construction section, carrying out advanced drilling work, finding out whether a karst cave exists below each pile position, the size of the karst cave, the diameter of the karst cave, the depth of the karst cave and the form of the karst cave, and determining the position and the distribution condition of a karst cave group;
step two: grouping according to the vertical distribution and the horizontal distribution of the karst cave groups;
step three: and (5) dividing independent operation units according to the karst cave group grouping condition in the step two, and performing unified drilling and unified backfilling operation on the operation units grouped by the unified karst cave group.
2. The karst cave stratum pile foundation construction method according to claim 1, characterized in that: the backfill operation adopts different backfill processing schemes according to the detected depth of each group of karst caves, and when the backfill operation is completed, the backfill operation adopts different backfill processing schemes
When the depth of the karst cave is less than 3 m, backfilling rubbles and clay after impacting and penetrating the upper cover of the karst cave, and continuously impacting and forming holes after 48 hours; when in use
When the depth of the karst cave is more than 3 meters and less than 10 meters, punching through the upper cover of the karst cave by adopting a punching hole, pouring underwater concrete by using a guide pipe, continuously pouring after 24 hours until the concrete surface is higher than the top cover of the karst cave, and continuously punching after 48 hours to form a hole; when in use
When the depth of the karst cave is more than 10 meters, drilling a 110mm hole at intervals of 400mm at the position 500mm away from the periphery of the pile in the planned pile area by using a geological drilling machine, inserting 25mm steel bars into the drilled holes, coating a 110mm PVC pipe outside the drilled holes, tying ropes outside the PVC pipe to form a retaining wall cofferdam at the periphery of the pile, pouring concrete into the karst cave to the top of the karst cave, and performing pile-forming construction after 4 days.
3. The karst cave stratum pile foundation construction method according to claim 1, characterized in that: the method also comprises the following four steps: after each cave group is backfilled in a group, any adjacent cave groups are fully compacted with each other.
4. The karst cave stratum pile foundation construction method according to claim 1, characterized in that: c15 or C20 early strength concrete is adopted during backfilling operation.
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