CN114934538A

CN114934538A - Karst bridge pile foundation construction process

Info

Publication number: CN114934538A
Application number: CN202210385533.0A
Authority: CN
Inventors: 蔺忠平; 蒙光毫; 杨学营; 王兵兵; 张宝; 李鹏飞; 谢祥军; 王鹭鹭; 温健; 刘伦林; 兰平; 龚杨
Original assignee: China Railway No 3 Engineering Group Co Ltd; Guangdong Construction Engineering Co Ltd of China Railway No 3 Engineering Group Co Ltd
Current assignee: China Railway No 3 Engineering Group Co Ltd; Guangdong Construction Engineering Co Ltd of China Railway No 3 Engineering Group Co Ltd
Priority date: 2022-04-13
Filing date: 2022-04-13
Publication date: 2022-08-23

Abstract

The invention provides a karst bridge pile foundation construction process, and belongs to the technical field of bridge construction processes. The invention comprises the following steps: 1) for the approach bridge pile foundation, the condition of a pile bottom karst cave is explored by adopting an advanced drilling mode before construction; for a main bridge pile foundation, detecting the condition of a pile bottom karst cave by adopting a mode of detecting a pile of multiple holes and external pipe waves; 2) carrying out advanced grouting pretreatment on a bearing platform of a main bridge pile foundation with a detected underlying karst cave; 3) classifying the construction site karst caves according to the size, the forming reason, the filling state, the slurry leakage condition and the vertical number; 4) and adopting different pile foundation construction methods according to the classification result of the karst caves, whether the covering layer has the soil layer which is easy to collapse and whether the karst caves are adjacent to the building structure. The invention ensures that the construction of the karst cave bridge pile foundation is simpler as far as possible, and simultaneously, the construction is more stable and easier.

Description

Karst bridge pile foundation construction process

Technical Field

The invention relates to the technical field of bridge construction processes, in particular to a karst bridge pile foundation construction process.

Background

In bridge construction, different construction processes are required for different geological conditions. The karst cave is a cavity formed in the ground due to dissolution and erosion of a limestone stratum by rainwater or underground water, is also called as a stalactite cave and a limestone cave, is mostly distributed in karst areas, and has the characteristics of strong concealment, poor spatial distribution regularity, difficulty in prediction and the like. The karst cave has extremely important influence on the construction of the bridge pile foundation.

The bridge pile adopts reinforced concrete cast-in-place piles, a drill bit on a drilling machine is used for vertically drilling a hole downwards to a designed elevation at a position to be drilled to form a drilled hole, a slurry retaining wall is prepared at the same time, then the drill bit is taken out, a reinforcement cage and a guide pipe are placed in the drilled hole, the guide pipe is lifted while concrete is continuously cast until the concrete is cast, and a pile foundation is formed after consolidation. In the construction process of a bridge pile foundation, if a karst cave is met, the problem of hole collapse can occur, at present, the specific conditions of the karst cave are not distinguished by adopting a backfill method or vibrating full casing pile foundation construction equipment when the karst cave is met.

For example, chinese patent application CN102146672B discloses a pile foundation construction method in a karst area, 1, vertically drilling a hole to be drilled on a foundation of an engineering site to a designed elevation by using a percussion drill to form a drilled hole, preparing a slurry retaining wall, and taking out a drill bit; 2. when a cavern is found in the borehole, measuring the distance between the cavern and the orifice; 3. processing a tubular steel casing in multiple sections, and sequentially welding two ends of the steel casing together by adopting reinforcing steel bars so as to prevent the steel casing from deforming due to vibration or extrusion; 4. erecting a steel pipe support on the ground around the orifice, arranging pull anchors around the support to ensure the stability of the support, and arranging a plurality of sleepers as backing plates at the top of the steel casing to prevent the connected steel casing from being pulled apart by the lifting action of the vibration hammer; 5. placing the lower end of the steel casing into the orifice by a crane, then using a vibration hammer to act on the upper end of the steel casing so as to enable the steel casing to sink into the drill hole at a constant speed until the lower end of the steel casing reaches the position of the karst cave, and stopping vibration; 6. throwing the rubbles and the clay into the holes, and then utilizing a percussion drill to extrude the rubbles and the clay to the karst cave to block the karst cave so as to strengthen the soil body structure at the side of the karst cave; 7. continuously utilizing the vibratory hammer to act on the upper end of the steel casing until the lower end of the steel casing crosses the position of the karst cave, and stopping vibrating; 8. and finally, placing a steel reinforcement cage and a guide pipe in the drilled hole according to a conventional mode, and then lifting the guide pipe while continuously pouring concrete until the concrete is poured and solidified to finish the whole pile foundation construction process. The concrete conditions of the karst cave are not distinguished by the scheme, so that a unified construction method is adopted for different karst caves, and the problem that a pile foundation is unstable or the construction method is too complex can be caused.

The prior art has at least the following disadvantages:

1. the types of the karst caves are not distinguished, and a unified construction method is adopted, so that the problems that the pile foundation is unstable or the construction method is too complex are caused;

2. the construction is difficult for the integral discharge of the multi-section steel casing.

3. The bottom edge foot of the steel casing is reinforced, and the edge rolling is easy to occur in the beating process.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a karst bridge pile foundation construction process, which comprises the following steps: 1) combining geological drilling data of a construction site, and exploring the condition of a pile bottom karst cave by adopting an advanced drilling mode before construction for an approach bridge pile foundation; for a main bridge pile foundation, detecting the condition of a pile bottom karst cave by adopting a mode of detecting a pile of multiple holes and external pipe waves; 2) carrying out advanced grouting pretreatment on a bearing platform of a main bridge pile foundation with a detected underlying karst cave; 3) classifying the construction site karst caves according to the size, the forming reason, the filling state, the slurry leakage condition and the vertical number; 4) according to the classification result of the karst cave, whether the covering layer has a soil layer which is easy to collapse and whether the karst cave is close to the building structure or not, adopting different pile foundation construction methods: adopting a backfilling method for karst caves without easily collapsed soil layers; and a steel pile casing follow-up method is adopted for the karst cave with the soil layer which is easy to collapse, and the steel pile casing follow-up comprises single-layer steel pile casing follow-up and double-layer steel pile casing follow-up. The invention ensures that the construction of the karst cave bridge pile foundation is simpler as far as possible, and simultaneously, the construction is more stable and easier.

The invention provides a karst bridge pile foundation construction process, which comprises the following steps:

1) in combination with geological drilling data of a construction site, for an approach bridge pile foundation, a pilot drilling mode is adopted to find out the condition of a pile bottom karst cave before construction; for a main bridge pile foundation, detecting the condition of a pile bottom karst cave by adopting a mode of detecting a pile of multiple holes and external pipe waves;

2) carrying out advanced grouting pretreatment on a bearing platform of a main bridge pile foundation with a detected underlying karst cave;

3) classifying the construction site karst caves according to the size, the forming reason, the filling state, the slurry leakage condition and the vertical number;

4) according to the classification result of the karst caves, whether the covering layer has the soil layer which is easy to collapse and whether the karst caves are adjacent to the building structure, different pile foundation construction methods are adopted:

adopting a backfilling method for karst caves without easily collapsed soil layers;

and a steel pile casing follow-up method is adopted for the karst cave with the soil layer which is easy to collapse, and the steel pile casing follow-up comprises single-layer steel pile casing follow-up and double-layer steel pile casing follow-up.

Preferably, classifying the karst caves of the construction site according to the size, the forming reason, the filling state, the slurry leakage condition and the vertical number specifically comprises:

classifying the karst caves according to the sizes and the forming reasons of the karst caves, and classifying the karst caves into small karst caves, small soil caves, medium karst caves, medium soil caves, large karst caves and large soil caves;

classifying the karst caves according to the filling states of the karst caves, and dividing the karst caves into full-filling karst caves, half-filling karst caves and unfilled karst caves;

classifying the karst caves according to whether the karst caves leak the slurry or not, and dividing the karst caves into full slurry leakage karst caves, half slurry leakage karst caves and slurry leakage free karst caves;

classifying the karst caves according to the vertical number of the karst caves, and dividing the karst caves into single-layer karst caves, multilayer karst caves and beaded karst caves;

preferably, according to the classification result of the karst cave, whether the covering layer has a soil layer which is easy to collapse and whether the karst cave is close to the building structure, different pile foundation construction methods are adopted and specifically comprise the following steps:

if the karst cave belongs to a small karst cave and a small soil cave with the cavity height of less than 3m, and a covering layer does not have an easily collapsed soil layer or slurry leakage occurs in the hole in the drilling process, processing by adopting a rubble and clay backfilling method;

if the karst cave belongs to a medium karst cave or a large karst cave, no easily collapsed soil layer exists in a covering layer or serious slurry leakage in the holes exists, and the rubble and clay backfill method is ineffective, plain concrete filling method is adopted for processing;

if the karst cave belongs to a small karst cave and a covering layer has a soil layer which is easy to collapse, a single-layer steel casing is adopted to follow up to 2.5m below the soil layer which is easy to collapse, but the single-layer steel casing does not enter a rock stratum for treatment;

if the karst cave belongs to a small soil cave with a cavity height of less than 3m and a covering layer with a soil layer which is easy to collapse, or a medium soil cave or a large soil cave with a cavity height of more than 3m, the karst cave is processed by adopting a method that a single-layer steel casing follows to a position 1m below the bottom of the soil cave but does not enter a rock stratum;

if the karst cave belongs to a small karst cave, a small bead-shaped karst cave or a medium karst cave which is close to a building structure and is a full-filling karst cave or a karst cave which is subjected to grouting pretreatment, a method that a single-layer steel casing follows to the bottom surface of a covering layer is adopted for treatment;

if the karst cave belongs to a medium karst cave, the karst cave is a half-filled or unfilled karst cave, the thickness of the top rock layer of the karst cave is less than or equal to 1m, or the karst cave belongs to a large karst cave and the thickness of the top rock layer of the karst cave is less than or equal to 1m, or the karst cave belongs to a full-filled medium karst cave adjacent to a building and the thickness of the top rock layer of the karst cave is less than or equal to 1m, and the karst cave is treated by adopting a method that a single-layer steel casing follows to the bottom of the karst cave;

if the karst cave belongs to a medium karst cave, the karst cave is a half-filled or unfilled karst cave, the thickness of the top rock layer of the karst cave is more than 1m, or the karst cave belongs to a large karst cave, the thickness of the top rock layer of the karst cave is more than 1m, or the karst cave belongs to a fully-filled medium karst cave adjacent to a building, and the thickness of the top rock layer of the karst cave is more than 1m, the karst cave is processed by adopting a double-layer steel casing following method, an outer layer steel casing follows to the bottom surface of a covering layer, and an inner layer steel casing follows to the bottom of the karst cave;

if the karst cave belongs to a medium-sized beaded karst cave and a large-sized beaded karst cave, the karst cave is treated by adopting a double-layer steel casing follow-up method, wherein the outer-layer steel casing follows up to the bottom surface of the covering layer, and the inner-layer steel casing follows up to the bottom of the lowermost karst cave.

Preferably, when the steel casing is adopted for follow-up, punching and hole expanding treatment are carried out by using a percussion drill, then the steel casing is vibrated by using a vibration hammer to sink to the bottom of the karst cave, and a plurality of sections of steel casings are spliced section by section and are applied section by section.

Preferably, the embedding of the steel casing penetrating through the covering layer is carried out by the following method:

a) a punch hammer with the diameter larger than that of the steel pile casing is adopted, and the diameter of a formed hole is ensured to be 0.1-0.15 m larger than the outer diameter of the pile casing; considering that slurry leakage easily occurs at the surface of the foundation rock, stopping footage when the distance between the base rock and the surface of the foundation rock is about 1.5m, checking holes and checking the diameter and the gradient of the holes;

b) the multi-section steel casing is spliced section by section and is applied section by section until the multi-section steel casing cannot fall down automatically, then a vibration hammer is adopted to apply the steel casing to a preset depth, and in the process of burying the steel casing, attention needs to be paid to the following steps: when the steel casing is spliced section by section, the straightness of splicing between the sections is well controlled to prevent bending; positioning an orifice, ensuring that the center of the opening of the steel casing is basically coincided with the center of the pile foundation, and then connecting and fixing the steel casing and the ground perforated steel casing by using a steel plate; strengthening the bottom edge of the steel casing;

c) after the casing is in place, clay and ballast are repeatedly backfilled near the surface of the foundation rock, cement is added, and the wall is impacted.

Preferably, when a rubble and clay backfilling method or a plain concrete pouring method is adopted for construction, the following pore-forming measures are adopted:

A) when the drill bit is 1m away from the top of the karst cave, putting rubble clay or concrete into the hole;

B) controlling the stroke of the percussion drill, slowly puncturing the karst cave through small-stroke fast-frequency impact, and extruding the rubble with clay or concrete into the karst cave; the small stroke is 1m-2m, and the fast frequency is 14m/s ² -16m/s ² ；

C) Once the karst cave is broken down, replenishing slurry into the hole in time, and continuously adding rubble-sandwiched clay or concrete into the hole;

D) and C, repeatedly flushing and smashing by using the method of the steps A to C, filling the karst cave, and extruding and compacting the protective wall until the liquid level of the slurry does not drop after the slurry smoothly passes through the karst cave.

Preferably, the grouting pretreatment is carried out by the following method:

in the grouting pretreatment, a single bearing platform is taken as a unit, grouting holes are arranged along the periphery of the bearing platform every 2m to form two grout stop walls;

grouting by using a phi 48X 4.5PVC pipe, wherein the top of the tunnel is provided with at least one exhaust hole in the grouting process;

detect the slip casting effect after handling the completion, specifically do:

estimating the diffusion radius of the slurry according to the injection amount of the slurry, and analyzing whether the grouting effect meets the design requirement or not to obtain a grouting effect detection result;

measuring the sound velocity, amplitude and attenuation coefficient of the rock mass before and after grouting by using the sound wave detector, judging whether the grouting effect meets the design requirement or not, and obtaining another grouting effect detection result;

and if any one of the two grouting effect detection results does not meet the design requirement, replenishing the drill hole and then grouting until the two grouting effect detection results meet the design requirement.

Preferably, the wall thickness of the steel casing is determined by adopting the following principle:

when the pile diameter is less than or equal to 1.6m, (1) the length of the steel casing is less than 10m, and the wall thickness of the steel casing is 8 mm; (2) the length of the steel casing is more than or equal to 10m and less than 20m, and the wall thickness of the steel casing is 10 mm; (3) the length of the steel casing is more than or equal to 20m, and the wall thickness of the steel casing is 12 mm;

when the pile diameter is larger than 1.6m, (1) the length of the steel casing is smaller than 10m, and the wall thickness of the steel casing is 10 mm; (2) the length of the steel casing is more than or equal to 10m and less than 20m, and the wall thickness of the steel casing is 12 mm; (3) the length of the steel casing is more than or equal to 20m, and the wall thickness of the steel casing is 14 mm.

Preferably, the inner diameter of the steel casing is determined by adopting the following principle:

when a single-layer pile casing is adopted, (1) the pile diameter is less than or equal to 1.6m, and the inner diameter of the pile casing is 20cm larger than the pile diameter; (2) the pile diameter is larger than 1.6m, and the inner diameter of the pile casing is 30cm larger than the pile diameter;

when a double-layer pile casing is adopted, (1) the pile diameter is less than or equal to 1.6m, the inner diameter of the outer layer pile casing is 50cm larger than the pile diameter, and the inner diameter of the inner layer pile casing is 20cm larger than the pile diameter; (2) the diameter of the pile is more than 1.6m, the inner diameter of the outer layer pile casing is 60cm larger than the diameter of the pile, and the inner diameter of the inner layer pile casing is 30cm larger than the diameter of the pile.

Preferably, welding a stiffening rib on the upper end opening, the lower end opening and the outer side of the middle part of the steel casing respectively; a40 cm x 40cm slurry overflow port is arranged 50cm below the top of the steel casing and is aligned with a drainage ditch leading to the slurry tank.

Compared with the prior art, the invention has the following beneficial effects:

(1) the invention classifies the karst cave in detail, and adopts different pile foundation construction methods according to whether the karst cave classification covering layer has a soil layer which is easy to collapse and whether the karst cave is close to the building structure or not: adopting a backfilling method for karst caves without easily collapsed soil layers; a steel casing follow-up method is adopted for the karst cave with soil layers prone to collapse, so that the construction of the karst cave bridge pile foundation is simple as far as possible, and the karst cave bridge pile foundation is more stable.

(2) The multi-section steel casing is spliced section by section and is applied section by section, so that the construction is easier.

(3) The invention strengthens the bottom edge foot of the steel casing to prevent edge rolling in the beating process.

Drawings

Fig. 1 is a process flow diagram of a karst bridge pile foundation construction process according to an embodiment of the invention;

FIG. 2 is a flow chart of a karst bridge pile foundation construction process according to yet another embodiment of the present invention;

FIG. 3 is a flowchart of the hole-forming measures taken during construction using a rubble and clay backfill method or a plain concrete fill method in accordance with an embodiment of the present invention;

FIG. 4 is a schematic diagram of a method for treating a small karst cave in which a collapsible soil layer exists in a covering layer, and a single-layer steel casing is used for following to a position 2.5m below the collapsible soil layer, but does not enter a rock stratum according to an embodiment of the invention;

FIG. 5 is a schematic view of a treatment method of a small soil cave with a cavity height of less than 3m and a cover layer with a soil layer prone to collapse or a medium-sized and large soil cave with a cavity height of more than 3m according to an embodiment of the invention, wherein a steel casing is adopted to follow to a position 1.0m below the bottom of the soil cave, but not enter a rock stratum;

FIG. 6 is a schematic illustration of one embodiment of the present invention for a small, small beaded cave or medium-sized cave in close proximity to a building structure, and for a fully filled cave or a cave that has been pre-treated with grouting, and away from the building structure, treated with a single layer steel casing following to the bottom surface of the cover layer;

FIG. 7 is a schematic diagram of a medium karst cave, which is a half-filled or unfilled karst cave, in which the thickness of the top rock layer of the karst cave is less than or equal to 1m, or the karst cave belongs to a large karst cave and the thickness of the top rock layer of the karst cave is less than or equal to 1m, or the medium karst cave is filled to the nearest building and the thickness of the top rock layer of the karst cave is less than or equal to 1m, and the medium karst cave is treated by adopting a single-layer steel casing to follow the bottom of the karst cave according to one embodiment of the invention;

FIG. 8 is a schematic diagram of an embodiment of the invention for a medium-sized karst cave, which is a half-filled or unfilled karst cave, and the thickness of the top rock layer of the karst cave is greater than 1m, or the karst cave belongs to a large-sized karst cave and the thickness of the top rock layer of the karst cave is greater than 1m, or the medium-sized karst cave is fully filled and is adjacent to a building and the thickness of the top rock layer of the karst cave is greater than 1m, and the medium-sized karst cave is processed by adopting a double-layer steel casing follow-up method, wherein an outer layer steel casing follows to the bottom surface of a covering layer, and an inner layer steel casing follows to the bottom of the karst cave;

FIG. 9 is a schematic diagram of a medium scale and large scale beaded caverns treated by a two-layer steel casing follow-up method, with the outer layer steel casing following to the bottom surface of the overburden and the inner layer steel casing following to the bottom of the lowermost cavern in accordance with an embodiment of the invention.

Detailed Description

The following detailed description of embodiments of the invention refers to the accompanying drawings.

1) combining geological drilling data of a construction site, and exploring the condition of a pile bottom karst cave by adopting an advanced drilling mode before construction for an approach bridge pile foundation; for a main bridge pile foundation, detecting the condition of a pile bottom karst cave by adopting a mode of detecting a pile of multiple holes and external pipe waves;

4) according to the classification result of the karst cave, whether the covering layer has a soil layer which is easy to collapse and whether the karst cave is close to the building structure or not, adopting different pile foundation construction methods:

and adopting a steel casing follow-up method for the karst cave with the soil layer which is easy to collapse, wherein the steel casing follow-up comprises single-layer steel casing follow-up and double-layer steel casing follow-up.

According to a specific embodiment of the invention, classifying the karst caves of the construction site according to the size, the forming reason, the filling state, the slurry leakage condition and the vertical number specifically comprises the following steps:

classifying the karst caves according to the karst caves whether to leak slurry or not, and dividing the karst caves into full slurry leakage karst caves, half slurry leakage karst caves and slurry leakage free karst caves;

classifying the karst caves according to the vertical number of the karst caves, and dividing the karst caves into single-layer karst caves, multi-layer karst caves and beaded karst caves;

according to a specific embodiment of the invention, according to the classification result of the karst cave, whether the covering layer has a soil layer which is easy to collapse and whether the karst cave is close to the building structure, different pile foundation construction methods are adopted, and the method specifically comprises the following steps:

if the karst cave belongs to a small karst cave and a covering layer has a soil layer which is easy to collapse, the single-layer steel casing is adopted to follow to 2.5m below the soil layer which is easy to collapse, but the single-layer steel casing does not enter a rock stratum for treatment;

if the karst cave belongs to a small karst cave, a small bead-shaped karst cave or a medium karst cave which is close to the building, is a full-filling karst cave or a karst cave which is subjected to grouting pretreatment and is far away from the building by at least 20m, processing by adopting a method that a single-layer steel casing follows to the bottom surface of the covering layer;

if the karst cave belongs to a medium karst cave, the karst cave is a half-filled or unfilled karst cave, the thickness of the top rock layer of the karst cave is less than or equal to 1m, or the karst cave belongs to a large karst cave, the thickness of the top rock layer of the karst cave is less than or equal to 1m, or the karst cave belongs to a full-filled medium karst cave adjacent to a building, and the thickness of the top rock layer of the karst cave is less than or equal to 1m, and the karst cave is processed by adopting a method that a single-layer steel casing follows to the bottom of the karst cave;

if the karst cave belongs to a medium-sized beaded karst cave and a large-sized beaded karst cave, the karst cave is treated by adopting a double-layer steel casing follow-up method, wherein an outer layer steel casing follows up to the bottom surface of a covering layer, and an inner layer steel casing follows up to the bottom of the lowest karst cave.

According to a specific embodiment of the invention, when the steel casing is used for follow-up, punching and hole expanding treatment are carried out by using a percussion drill, then the steel casing is vibrated and sunk to the bottom of the karst cave by using a vibration hammer, and a plurality of sections of steel casings are spliced section by section and discharged section by section.

According to a particular embodiment of the invention, the embedding of the steel casing through the covering layer is carried out by:

a) a punch hammer with the diameter larger than that of the steel pile casing is adopted, and the diameter of a formed hole is ensured to be 0.1-0.15 m larger than the outer diameter of the pile casing; considering that slurry leakage easily occurs at the surface of the foundation rock, stopping footage when the distance between the base rock and the surface of the foundation rock is about 1.5m, checking holes and checking the diameter and the gradient of the formed holes;

b) the multi-section steel casing is spliced section by section and is applied section by section until the multi-section steel casing cannot fall down automatically, then a vibration hammer is adopted to apply the steel casing to a preset depth, and in the process of embedding the steel casing, attention needs to be paid: when the steel casing is spliced section by section, the straightness of splicing between the sections is well controlled to prevent bending; positioning an orifice, ensuring that the center of the opening of the steel casing is basically superposed with the center of the pile foundation, and then connecting and fixing the steel casing with the ground perforated steel casing by using a steel plate; strengthening the bottom edge of the steel casing;

c) when the steel casing falls down by vibration, the total depth of the steel casing is controlled by referring to geological data, the blade of the steel casing is strengthened, after the steel casing is in place, clay and ballast are repeatedly backfilled near the bed rock surface, cement is added, and the wall is impacted.

According to a specific embodiment of the invention, when the construction is carried out by adopting a rubble and clay backfilling method or adopting a plain concrete pouring method, the following pore-forming measures are adopted:

A) when the hole is drilled to 1m away from the top of the karst cave, putting rubble-sandwiched clay or concrete into the hole;

C) Once the karst cave is broken down, the liquid level of the slurry in the hole is lowered, the slurry is supplemented into the hole in time, and meanwhile, the rubble-sandwiched clay or concrete is continuously added into the hole;

According to a specific embodiment of the invention, the grouting pretreatment is carried out by the following method:

the grouting pretreatment is to take a single bearing platform as a unit, and grouting holes are arranged along the periphery of the bearing platform every 2m to form two grout stopping walls;

grouting by using a phi 48X 4.5PVC pipe, wherein the top of the tunnel is provided with at least one exhaust hole in the grouting process, and the exhaust holes are additionally arranged when the distance is larger;

detect the slip casting effect after handling the completion, specifically do:

According to a specific embodiment of the invention, the wall thickness of the steel casing is determined by adopting the following principle:

According to a specific embodiment of the invention, the inner diameter of the steel casing is determined by adopting the following principle:

According to a specific embodiment of the invention, a stiffening rib is welded on the upper end opening, the lower end opening and the outer side of the middle part of the steel casing; a40 cm x 40cm slurry overflow port is arranged 50cm below the top of the steel casing and is aligned with a drainage ditch leading to the slurry tank.

Example 1

The karst bridge pile foundation construction process of the present invention is described in detail below, according to an embodiment of the present invention.

a backfill method is adopted for the karst cave without the easily collapsed soil layer;

Example 2

3) classifying the construction site karst caves according to the size, the forming reason, the filling state, the slurry leakage condition and the vertical number; the method specifically comprises the following steps:

4) according to the classification result of the karst cave, whether the covering layer has a soil layer which is easy to collapse and whether the karst cave is close to a building structure or not, different pile foundation construction methods are adopted, and the method specifically comprises the following steps:

Example 3

1) combining geological drilling data of a construction site, and exploring the condition of a pile bottom karst cave by adopting an advanced drilling mode before construction for an approach bridge pile foundation; for a main bridge pile foundation, a pile bottom karst cave condition is ascertained by adopting a mode of detecting a pile of multiple holes and additional pipe waves;

4) according to the classification result of the karst caves, whether the covering layer has the soil layer which is easy to collapse and whether the karst caves are adjacent to the building structure, different pile foundation construction methods are adopted, and the method specifically comprises the following steps:

if the karst cave belongs to a medium-sized beaded karst cave and a large-sized beaded karst cave, processing by adopting a double-layer steel casing follow-up method, wherein an outer layer steel casing follows up to the bottom surface of a covering layer, and an inner layer steel casing follows up to the bottom of the lowest karst cave;

when the steel casing is adopted for follow-up, firstly, a percussion drill is used for punching and reaming, then a vibration hammer is used for vibrating and sinking the steel casing to the bottom of the karst cave, and a plurality of sections of steel casings are spliced section by section and are discharged section by section;

the embedding of the steel casing penetrating through the covering layer is carried out by adopting the following method:

When a rubble and clay backfill method or a plain concrete pouring method is adopted for construction, the following pore-forming measures are adopted:

B) controlling the stroke of the percussion drill, slowly puncturing the karst cave through small-stroke fast-frequency impact, and extruding the rubble-sandwiched clay or concrete into the karst cave; the small stroke is 1m-2m, and the fast frequency is 14m/s ² -16m/s ² ；

D) and (D) repeatedly flushing and smashing by using the method of the steps A to C, filling the karst cave, and extruding and compacting the protective wall until the liquid level of the slurry does not drop after the slurry smoothly passes through the karst cave.

Example 4

The grouting pretreatment is carried out by adopting the following method:

detect the slip casting effect after handling the completion, specifically do:

Example 5

if the karst cave belongs to a medium karst cave, the karst cave is a half-filled or unfilled karst cave, the thickness of the top rock layer of the karst cave is more than 1m, or the karst cave belongs to a large karst cave, the thickness of the top rock layer of the karst cave is more than 1m, or the karst cave belongs to a fully-filled medium karst cave adjacent to a building structure, and the thickness of the top rock layer of the karst cave is more than 1m, the karst cave is processed by adopting a double-layer steel casing follow-up method, an outer layer steel casing follows up to the bottom surface of a covering layer, and an inner layer steel casing follows up to the bottom of the karst cave;

The wall thickness of the steel casing is determined by adopting the following principle:

The inner diameter of the steel casing is determined by adopting the following principle:

Welding a stiffening rib on the upper end opening, the lower end opening and the outer side of the middle part of the steel casing respectively; a40 cm x 40cm slurry overflow port is arranged 50cm below the top of the steel casing and is aligned with a drainage ditch leading to the slurry tank.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall fall within the protection scope of the present invention.

Claims

1. A karst bridge pile foundation construction process is characterized by comprising the following steps:

2. The karst bridge pile foundation construction process of claim 1, wherein classifying the karst caves of the construction site according to size, formation reason, filling state, slurry leakage condition and vertical number specifically comprises:

and classifying the karst caves according to the vertical number of the karst caves, and dividing the karst caves into single-layer karst caves, multilayer karst caves and beaded karst caves.

3. The karst bridge pile foundation construction process according to claim 2, wherein different pile foundation construction methods are adopted according to classification results of karst caves, whether a soil layer which is easy to collapse exists in a covering layer and whether the karst caves are close to a building structure, and the method specifically comprises the following steps:

if the karst cave belongs to a medium karst cave or a large karst cave, a covering layer does not have an easily collapsed soil layer or seriously leaks slurry in the holes, and when the rubble and clay backfilling method is ineffective, the karst cave and the large karst cave are treated by adopting a plain concrete filling method;

4. The karst bridge pile foundation construction process of claim 3, wherein when the steel casing is adopted for follow-up, a percussion drill is used for punching and reaming, then a vibration hammer is used for vibrating and sinking the steel casing to the bottom of the karst cave, and a plurality of sections of steel casings are spliced section by section and are applied section by section.

5. The karst bridge pile foundation construction process of claim 4, wherein the burying through the overburden steel casing is performed by the following method:

a) a punch hammer with the diameter larger than that of the steel pile casing is adopted, and the diameter of a formed hole is ensured to be 0.1-0.15 m larger than the outer diameter of the pile casing; stopping footage when the hole is punched to be about 1.5m away from the surface of the bedrock, checking the hole and checking the diameter and the gradient of the formed hole;

b) the multi-section steel casing is spliced section by section and is applied section by section until the multi-section steel casing cannot fall down automatically, then a vibration hammer is adopted to apply the steel casing to a preset depth, and in the process of embedding the steel casing, attention needs to be paid: when the steel casing is spliced section by section, the straightness of splicing between the sections is well controlled to prevent bending; ensuring that the center of the opening of the embedded steel casing is basically superposed with the center of the pile foundation, and then connecting and fixing the embedded steel casing and the ground perforated steel casing by using a steel plate; strengthening the bottom edge of the steel casing;

c) after the casing is in place, clay and ballast are repeatedly backfilled near the surface of the foundation rock, and cement is added to impact the wall.

6. The karst bridge pile foundation construction process of claim 5, wherein when the construction is carried out by adopting a rubble and clay backfill method or a plain concrete pouring method, the following pore-forming measures are adopted:

7. The karst bridge pile foundation construction process of claim 1, wherein the grouting pretreatment is performed by the following method:

detect the slip casting effect after handling the completion, specifically do:

8. The karst bridge pile foundation construction process of any one of claims 1-7, wherein the steel casing wall thickness is determined using the following principle:

9. The karst bridge pile foundation construction process of claim 8, wherein the inner diameter of the steel casing is determined by the following principle:

when a double-layer pile casing is adopted, (1) the pile diameter is less than or equal to 1.6m, the inner diameter of the outer layer pile casing is 50cm larger than the pile diameter, and the inner diameter of the inner layer pile casing is 20cm larger than the pile diameter; (2) the diameter of the pile is more than 1.6m, the inner diameter of the outer layer pile casing is 60cm larger than that of the pile, and the inner diameter of the inner layer pile casing is 30cm larger than that of the pile.

10. The karst bridge pile foundation construction process of claim 9, wherein a stiffening rib is welded to each of the upper and lower ports and the outer side of the middle part of the steel casing; a40 cm x 40cm slurry overflow port is arranged 50cm below the top of the steel casing and is aligned with a drainage ditch leading to the slurry tank.