CN110714459A - Construction method of cast-in-situ bored pile - Google Patents
Construction method of cast-in-situ bored pile Download PDFInfo
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- CN110714459A CN110714459A CN201810754481.3A CN201810754481A CN110714459A CN 110714459 A CN110714459 A CN 110714459A CN 201810754481 A CN201810754481 A CN 201810754481A CN 110714459 A CN110714459 A CN 110714459A
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- 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
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- E02D5/34—Concrete or concrete-like piles cast in position ; Apparatus for making same
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Abstract
The invention discloses a construction method of a cast-in-situ bored pile, and relates to the technical field of building construction. The method comprises the following steps: embedding a pile casing; after the drilling machine is in place, drilling by adopting a small-stroke hole; after confirming that the drilling depth exceeds the full height and the normal stroke of the drill bit, carrying out normal impact drilling; the drill bit of the drilling machine in the gravel soil rock layer adopts a cross-shaped drill bit, and the drill bit of the drilling machine in the sand clay, sand or sand gravel layer adopts a tubular drill bit; after confirming that the drilled hole reaches the designed elevation, cleaning sediments; hoisting a reinforcement cage and a guide pipe into the drilled hole after the sediment is cleaned, wherein the distance between the bottom of the guide pipe and the sediment surface at the bottom of the hole is 300-500 mm; cleaning the hole again according to the thickness of the sediment at the bottom of the hole until the thickness of the sediment at the bottom of the hole is not more than 100 mm; and pouring concrete into the drill hole. In the drilling process, the small-stroke hole drilling and normal impact drilling are adopted, so that the labor intensity of excavation is reduced, different drill bits are selected according to soil layers, hole cleaning is carried out twice, and the hole forming quality and the construction quality are improved.
Description
Technical Field
The invention relates to the technical field of building construction, in particular to a construction method of a cast-in-situ bored pile.
Background
The cast-in-place pile system is a pile formed by forming a pile hole in foundation soil through mechanical drilling, steel pipe soil extrusion or manual excavation and the like on an engineering site, placing a reinforcement cage and cast-in-place concrete in the pile hole, and the cast-in-place pile can be divided into a immersed tube cast-in-place pile, a cast-in-place pile and a cast-in-place pile according to different hole forming methods.
In the construction process of the cast-in-situ bored pile, attention is paid to how to improve the quality of formed holes. In the current construction scheme of the cast-in-situ bored pile, the drill bit of the drilling machine is determined to continuously drill, and the drilling speed cannot be correspondingly adjusted according to the drilled soil layer or rock stratum, so that the drilling efficiency is reduced. And after the reinforcement cage and the guide pipe are hoisted into the drill hole, concrete is directly poured into the drill hole, so that the construction quality cannot be ensured.
Disclosure of Invention
In view of this, the embodiment of the present invention provides a method for constructing a cast-in-situ bored pile, which can reduce the labor intensity of excavation, and improve the quality of hole formation and construction by selecting different drill bits and performing hole cleaning twice according to soil layers.
To achieve the above object, according to an aspect of an embodiment of the present invention, a method of constructing a cast-in-situ bored pile is provided.
The construction method of the cast-in-situ bored pile comprises the following steps: embedding a pile casing; after the drilling machine is in place, drilling by adopting a small-stroke hole; and, after confirming that the drilling depth exceeds the full height and the normal stroke of the drill bit, performing normal percussion drilling; wherein, the drill bit of the drilling machine in the gravel soil rock stratum adopts a cross-shaped drill bit, and the drill bit of the drilling machine in the sand clay, sand or sand gravel stratum adopts a tubular drill bit; after confirming that the drilled hole reaches the designed elevation, cleaning sediments; hoisting a steel reinforcement cage and a guide pipe into the drilled hole after sediment cleaning, wherein the distance between the bottom of the guide pipe and the sediment surface at the bottom of the hole is 300-500 mm; cleaning the hole again according to the thickness of the sediment at the bottom of the hole until the thickness of the sediment at the bottom of the hole is not more than 100 mm; and pouring concrete into the drill hole.
Optionally, the step of embedding the casing includes: excavating a probe hole, wherein the depth of the probe hole is at least 2 m; the central point of the pile position is released, and a control pile is embedded on an orthogonal cross line passing through the central point of 80-l 00cm outside the pile casing; digging a round pit 50-70 cm larger than the pile casing outside the control pile position, wherein the depth is at least 2m, and filling and tamping clay with the thickness of at least 20cm at the pit bottom of the round pit; symmetrically hoisting the pile casings into the round pits through steel wire ropes; finding out the pile position center of the control pile through control pile lofting, and moving the pile casing to enable the center of the pile casing to be superposed with the pile position center; after the protective cylinder is verified to be vertical through a level ruler or a suspension wire pendant, clay with specific water content is backfilled around the protective cylinder, and the protective cylinder is tamped in layers.
Optionally, before embedding the casing, the method further includes: respectively determining the inner diameter and the length of the casing according to the aperture and the underground water level; wherein the protective cylinder is made of a 5mm steel plate, and more than one stiffening rib is arranged on the outer side of the protective cylinder; the top end of the pile casing is provided with symmetrical hanging rings, and the upper part of the pile casing is provided with at least 2 grout overflow holes.
Optionally, the step of clearing the sediments after confirming that the drilled hole reaches the designed elevation comprises: after confirming that the drilled hole reaches the designed elevation, cleaning sediments through a cylindrical drill with a valve; wherein, under the condition that the mud skin deposition on the hole wall is thicker, the hole wall is swept up and down by a hole sweeping drill;
the step of cleaning the hole again according to the thickness of the sediment at the bottom of the hole comprises the following steps: and (5) confirming that the steel reinforcement cage and the guide pipe are successfully placed, and cleaning the hole by pouring the guide pipe in a reverse circulation mode until the thickness of the sediment at the bottom of the hole is not larger than 100 mm.
Optionally, the step of hoisting the reinforcement cage into the drilled hole after the sediment removal comprises: hoisting the reinforcement cage by a shoulder pole hoisting method, and vertically hoisting and welding the hoisted reinforcement cage section by section according to the serial number sequence; after the steel reinforcement cage was hung and is put to design elevation position, it constructs the post to hang and put the steel, wherein it inserts steel reinforcement cage length for 2m to construct the post.
Optionally, the step of pouring concrete into the borehole comprises: confirming that the sliding valve or the water-resisting plug is tightly attached to the water surface in the guide pipe; placing prepared cement mortar into a guide pipe and a funnel above a slide valve or a water stop plug; after confirming that the initial pouring amount is sufficient, pouring the first batch of concrete by cutting off an iron wire; wherein, the conduit is embedded into the concrete by more than 1.2m in the first batch of concrete; continuously pouring concrete, detecting the rising height of the concrete surface through a measuring hammer, and lifting or gradually disassembling the guide pipe according to the rising height of the concrete surface.
Optionally, before embedding the casing, the method further includes: determining the specification and quantity of the injected clean water, and injecting the specification and quantity of the clean water into the bentonite mixer with the rotating speed of at least 200 r/min; putting bentonite, confirming that the bentonite is completely dissolved, and uniformly putting carboxymethyl cellulose; a dispersant, a specific weight increasing agent and a water seepage preventing agent are added to obtain slurry for construction.
Optionally, the performance indicators of the mud include at least: the viscosity is at least 17, the relative density is 1.2-1.4, the sand content is 4-8%, the colloid rate is at least 90%, and the PH value is 7.0-8.0.
One embodiment of the above invention has the following advantages or benefits: after the drilling machine is in place, drilling by adopting a small-stroke hole; and after confirming that the drilling depth exceeds the full height and the normal stroke of the drill bit, performing normal impact drilling. Moreover, the drill bit of the drilling machine in the gravel soil stratum adopts a cross-shaped drill bit, and the drill bit of the drilling machine in the sand clay, sand or gravel layer adopts a tubular drill bit. Therefore, the method not only reduces the labor intensity of excavation, but also improves the hole forming quality by selecting different drill bits and drilling modes according to soil layers. And confirming that the drill hole reaches the designed elevation, cleaning the sediments, then cleaning the hole again according to the thickness of the sediments at the bottom of the hole, and improving the construction quality by cleaning the hole twice.
Further effects of the above-mentioned non-conventional alternatives will be described below in connection with the embodiments.
Drawings
The drawings are included to provide a better understanding of the invention and are not to be construed as unduly limiting the invention. Wherein:
fig. 1 is a schematic view of a main flow of a construction method of a cast-in-situ bored pile according to an embodiment of the present invention;
fig. 2 is a schematic view of an implementation of a construction method of a cast-in-situ bored pile according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a datum structure according to an embodiment of the present invention;
fig. 4 is a schematic view of a planar displacement small angle method monitoring.
Detailed Description
Exemplary embodiments of the present invention are described below with reference to the accompanying drawings, in which various details of embodiments of the invention are included to assist understanding, and which are to be considered as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. Also, descriptions of well-known functions and constructions are omitted in the following description for clarity and conciseness.
Fig. 1 is a schematic view of a main flow of a method for constructing a cast-in-situ bored pile according to an embodiment of the present invention, and as shown in fig. 1, the method for constructing a cast-in-situ bored pile according to an embodiment of the present invention mainly includes:
step S101: and embedding the pile casing. In this step, a probe hole is excavated, wherein the depth of the probe hole is at least 2 m. Then, the center point of the pile position is released, and the control pile is buried on the cross line passing through the center point of 80-l 00cm outside the pile casing. And digging a round pit which is 50-70 cm larger than the pile casing outside the control pile position, wherein the depth is at least 2m, and filling and tamping clay with the thickness of at least 20cm at the bottom of the round pit. And symmetrically hoisting the pile casing into the round pit through a steel wire rope, controlling pile lofting, finding out the pile position center of the control pile, and moving the pile casing to enable the center of the pile casing to coincide with the pile position center. And finally, after the protective cylinder is verified to be vertical through a level ruler or a suspension wire pendant, clay with specific water content is backfilled around the protective cylinder, and the protective cylinder is tamped in layers.
Before the steps, respectively determining the inner diameter and the length of the casing according to the aperture and the underground water level; wherein, the pile casing is made of a steel plate with the thickness of 5mm, and more than one stiffening rib is arranged on the outer side of the pile casing. The top end of the pile casing is provided with symmetrical hanging rings, and the upper part of the pile casing is provided with at least 2 grout overflow holes. In the embodiment of the invention, the inner diameter of the protecting cylinder is preferably larger than the aperture by 200mm, and when the underground water level is deeper, the length of the protecting cylinder is preferably 2 m. The pile casing is made of a 5mm steel plate, stiffening ribs are respectively added on the upper part, the middle part and the lower part of the pile casing, two lifting rings are welded at the top end, one lifting ring is used for lifting, the other lifting ring is used for binding a steel reinforcement cage hanging rod, the steel reinforcement cage is pressed to float upwards, four grooves are simultaneously orthogonally carved at the top end of the pile casing, so that a cross line can be hung, and the pile casing is prepared for being used for checking the pile casing and checking holes. 2 slurry overflow holes are arranged at the upper part of the device, so that the slurry can overflow conveniently and can be recycled.
Step S102: after the drilling machine is in place, drilling by adopting a small-stroke hole; and, after confirming that the drilling depth exceeds the full height and the normal stroke of the drill bit, performing normal percussion drilling; wherein, the drill bit of the drilling machine in the gravel soil stratum adopts a cross-shaped drill bit, and the drill bit of the drilling machine in the sand clay, sand or gravel stratum adopts a tubular drill bit.
Step S103: and (5) cleaning sediments after confirming that the drilled hole reaches the designed elevation. The step of clearing the sediments (first clearing) after confirming that the drill hole reaches the designed elevation comprises the following steps: after confirming that the drilled hole reaches the designed elevation, cleaning sediments through a cylindrical drill with a valve; wherein, under the condition that the mud skin deposition on the hole wall is thicker, the hole wall is swept up and down by the hole sweeping drill bit.
Step S104: and hoisting the reinforcement cage and the guide pipe into the drilled hole after the sediment is cleaned, wherein the distance between the bottom of the guide pipe and the sediment surface at the bottom of the hole is 300-500 mm. Hoisting a steel reinforcement cage into the drilling process after slag cleaning, hoisting the steel reinforcement cage by a carrying pole hoisting method, and vertically hoisting and welding the hoisted steel reinforcement cage section by section according to the serial number sequence; after the steel reinforcement cage is hung and is put to design elevation position, hang and put the steel structure post, wherein the steel structure post inserts steel reinforcement cage length and is 2 m.
Step S105: and cleaning the hole again according to the thickness of the sediment at the bottom of the hole until the thickness of the sediment at the bottom of the hole is not more than 100 mm. The step of cleaning the hole again according to the thickness of the sediment at the bottom of the hole (the second hole cleaning) comprises the following steps: and (5) confirming that the steel reinforcement cage and the guide pipe are successfully placed, and cleaning the hole by pouring the guide pipe in a reverse circulation mode until the thickness of the sediment at the bottom of the hole is not larger than 100 mm. In the first hole cleaning process, after the hole is drilled to the designed depth, the footage is stopped, the drilling tool is lifted slightly to be 10-20 cm away from the bottom of the hole, the normal circulation of the slurry is kept, the drilling disc is idled at regular time so that residual mud blocks at the bottom of the hole can be ground into the slurry to be discharged, and the hole cleaning time is about 30 minutes. In the second hole cleaning process, after the first hole cleaning, the drilling tool is lifted out, the hole depth is measured, then the reinforcement cage and the concrete guide pipe are placed in the holding time, and then the second hole cleaning is carried out, wherein the time is generally 0.5-1 hour. After the first and second hole cleaning, the hole depth and the hole bottom sediments are respectively measured. After the second hole cleaning, the thickness of the sediment at the bottom of the hole is less than or equal to 10cm, the index of the slurry is less than or equal to 1.15, the viscosity is 18-24 seconds, and the sand content is 4-8%. If the hole cleaning is not clean or secondary hole cleaning is not carried out, excessive sediment amount at the bottom of the pile can be caused.
Step S106: and pouring concrete into the drill hole. In this step, it is confirmed that the spool or the stopper is in close contact with the water surface in the pipe; the pre-formulated cement mortar is placed in the pipe and funnel above the slide valve or stopper. After confirming that the initial pouring amount is sufficient, pouring the first batch of concrete by cutting off an iron wire; wherein, the conduit is embedded into the concrete by more than 1.2m in the first batch of concrete. Continuously pouring concrete, detecting the rising height of the concrete surface through a measuring hammer, and lifting or gradually disassembling the guide pipe according to the rising height of the concrete surface.
Before embedding the pile casing, determining the specification and quantity of clear water, and injecting the specification and quantity of clear water into an bentonite stirring machine with the rotating speed of at least 200 r/min; putting bentonite, confirming that the bentonite is completely dissolved, and uniformly putting carboxymethyl cellulose; a dispersant, a specific weight increasing agent and a water seepage preventing agent are added to obtain slurry for construction. The performance indexes of the mud at least comprise: the viscosity is at least 17, the relative density is 1.2-1.4, the sand content is 4-8%, the colloid rate is at least 90%, and the PH value is 7.0-8.0.
For the embodiment of the invention, after the drilling machine is in place, the drilling machine firstly adopts small-stroke hole drilling; and after confirming that the drilling depth exceeds the full height and the normal stroke of the drill bit, performing normal impact drilling. Moreover, the drill bit of the drilling machine in the gravel soil stratum adopts a cross-shaped drill bit, and the drill bit of the drilling machine in the sand clay, sand or gravel layer adopts a tubular drill bit. Therefore, the embodiment of the invention not only reduces the labor intensity of excavation, but also improves the hole forming quality by selecting different drill bits and drilling modes according to soil layers. And confirming that the drill hole reaches the designed elevation, cleaning the sediments, then cleaning the hole again according to the thickness of the sediments at the bottom of the hole, and further improving the quality of the formed hole through cleaning the hole twice.
Fig. 2 is a schematic diagram of implementation of a construction method of a cast-in-situ bored pile according to an embodiment of the present invention. As shown in fig. 2, in the embodiment of the present invention, the air shaft may be constructed by an open-cut and sequential-construction method, a phi 800@1200 footing drilling cast-in-place pile + a prestressed anchor cable + a phi 800@1200 high-pressure jet grouting waterproof curtain is adopted above the weathered rock surface in the deep foundation pit and the shallow foundation pit enclosure, and a phi 25 ordinary mortar anchor rod jet grouting anchor support can be adopted below the rock surface. The waterproof curtain (Check the water curl) refers to a concept, which is a general term of a series of waterproof at the periphery of an engineering main body. The continuous water stopping body is used for preventing or reducing groundwater on the side wall of the foundation pit and the bottom of the foundation pit from flowing into the foundation pit and being adopted. Shotcrete-bolt support refers to reinforcing rock formations by the combined action of high-pressure shotcrete and metal bolts (which may be used individually depending on the geological conditions) driven into the rock formations, and is divided into temporary support structures and permanent support structures. The sprayed concrete can be used as the primary support of the surrounding rock of the cavern and can also be used as the permanent support. The spray anchor support is a system which enables an anchor rod, a concrete spray layer and surrounding rock to form a combined action, and prevents rock mass from loosening and separating. The surrounding rock with a certain thickness is converted into a self-supporting arch, and the surrounding rock is effectively stabilized. When the rock mass is broken, the small rock blocks between the anchor rods can be pulled and blocked by the silk screen, so that the concrete spraying layer is enhanced, and the spraying anchor support is assisted.
In the process of measurement and setting-out, the plane position of a pile hole is determined according to a measurement control pile point and a design drawing, a control net is established for accurate positioning by combining a conducting wire and triangulation, and meanwhile, a pile protection pile is longitudinally and transversely embedded by taking the center of the pile as an intersection point. When drilling, the center of the pile position is led to the periphery by a cross method and marked by short steel bars, and the reference point for measuring the hole depth can lead the elevation to the mouth of the protective cylinder or the steel bars at the periphery by a level gauge and marked by red paint. The retest is carried out frequently in the construction process, the measurement control pile points and the leveling points need to be specially protected, and the pile points can be recovered in time according to pile protection once being damaged.
The main materials for making the slurry comprise: A. bentonite: clay minerals mainly composed of montmorillonite; B. clay: the plasticity index IP is more than 17, and the content of clay particles smaller than 0.005mm is more than 50 percent. Is the main material of the slurry. The slurry of the embodiment of the invention is naturally made by adopting the original soil, and the properties of the slurry are shown in the following table:
in order to facilitate the complete dissolution of bentonite and carboxymethyl cellulose, a bentonite mixer is selected according to the required dosage of slurry, and the rotating speed is preferably more than 200 r/min. The order of adding the materials is to inject a predetermined amount of clear water, add bentonite while stirring, after the bentonite is almost dissolved, uniformly add carboxymethyl cellulose, then add the dispersant, and finally add the specific gravity increasing agent and the water seepage preventing agent. During construction, the mud surface in the pile casing should be higher than the underground water level by more than 1.0m, and when influenced by water level fluctuation, the mud surface should be higher than the highest water level by more than 1.5 m. For the requirement of circulating slurry, the performance indexes of the slurry injected into the orifice are as follows: the specific gravity of the slurry is not more than 1.10, and the viscosity is 18-20 s; discharge orifice slurry performance index: the specific gravity of the slurry is not more than 1.25, and the viscosity is 18-25 s. And in the hole cleaning process, the slurry is continuously replaced until underwater concrete is poured.
The pile casing has the functions of guiding drilling tools, controlling pile positions, isolating ground water leakage, preventing orifice collapse, raising static pressure water head in the hole, fixing a steel reinforcement cage and the like, and is to be buried carefully. Before the pile casing is buried, a probing hole needs to be excavated manually, and the probing hole depth is not less than 2 m. When embedding, firstly putting out the central point of a pile position, embedding a control pile on an orthogonal cross line which is 80-l 00cm outside the pile casing and passes through the central point, then digging a round pit which is 60cm larger than the pile casing and has the depth of 2.0m outside the pile position, filling clay with the thickness of 20cm at the bottom of the pit, tamping, symmetrically hoisting the pile casing into a hole by using a steel wire rope, finding out the center of the pile casing (the orthogonal cross line can be pulled), then lofting by controlling the pile, finding out the center of the pile position, moving the pile casing to ensure that the center of the pile casing is superposed with the center of the pile position, simultaneously checking the verticality of the pile casing by using a horizontal ruler (or a suspension line weight), backfilling the clay with the appropriate water content around the pile casing, tamping in layers, preventing the deflection of the pile casing during tamping, and checking the center deviation and the hole elevation of the pile casing by a quality worker and a supervision engineer after the pile casing is embedded. And after the central deviation meets the requirement, the driller can be in place to drill.
The pile casing is accurately and stably embedded, and the deviation between the center of the pile casing and the center of the pile position is not more than 5 mm. After calibration, the casing is fixed in the correct position, and the mouth of the casing should be 100mm above the ground. And the bottom is tamped by clay through layered backfilling along the periphery of the outer side of the pile casing, and direct grouting is adopted 20cm below the ground to reduce disturbance of the backfilling on the pile casing.
Before the drilling machine is in place, various preparation works before drilling are checked, including the checking and maintenance of main machine tools and equipment, and materials such as clay, rubbles, cement, steel casing and the like for treating the karst cave are required to be prepared sufficiently. After the drilling machine is installed in place, the base and the top end are stable and cannot be displaced or sunk, and the top end of the drilling machine is symmetrically tensioned by a guy rope. The deviation between the drill center and the center of the steel casing is not more than 5 cm. A cross-shaped drill bit is suitable for the crushed stone soil and rock stratum; tubular drill bits are preferably used in sand clay, sand or sand gravel layers.
When the drilling is started, a small-stroke hole is needed, and after the drilling depth exceeds the full height of the drill bit and the normal stroke is added, normal impact drilling can be carried out. During the drilling process, the rope should be loosened frequently and properly, and the air hammer cannot be knocked out; the drill bit is frequently impacted with fresh stratum due to frequent slag extraction. The rope loosening amount at each time is determined according to geological conditions, the drill bit form and the drill bit weight. The steel wire rope of the hanging drill bit must be twisted in the same direction, soft, high-quality, free of dead bend and broken wire, and the safety factor is not less than 12. A steering device is required to be arranged between the steel wire rope and the drill bit and is firmly connected, and the state and the rotation of the steel wire rope and the drill bit are always checked to be normal and flexible in the drilling process. When the main rope is lapped with the steel wire rope of the drill bit, the two rope diameters are the same, and the twisting directions are required to be consistent.
And (3) frequently paying attention to soil layer changes in the drilling process, fishing out slag samples when the drilling footage reaches 2m or at the soil layer change position, judging the soil layer, recording a drilling record table and checking the soil layer with the geological histogram. The operator must carefully fill in the drilling construction records, and when the shift is handed over, the operator needs to give a detailed view of the drilling situation of the shift and the matters needing attention of the next shift. During drilling, the height of a water head in the hole is kept to be 1.5-2 m, and foreign matters such as a wrench and the like are prevented from falling into the hole. The drilling operation must be kept continuous, the drill bit is lifted stably, and the drill bit cannot collide with a protective cylinder or a hole wall. In the drilling construction, the quality of the adjacent piles is not influenced, and the drilling can be started until the concrete compressive strength of the adjacent piles reaches 2.5MPa (generally after 24 hours of completion).
The pile hole forming quality detection method adopts a sound wave hole wall measuring instrument method, after each hole forming is finished, the circular hole measuring method is used for testing the pile hole forming quality, and in order to further ensure the engineering quality, a certain proportion of holes are extracted from the embodiment of the invention to be detected by a caliper (or a sound wave hole wall measuring instrument).
And for the first hole cleaning, cleaning sediments by using a cylindrical drill with a valve when the drill reaches the designed elevation, namely, cleaning the hole for the first time. When the mud skin on the hole wall is deposited thickly, the hole sweeping drill bit can be used for reciprocating up and down to sweep the hole wall. And for the second hole cleaning, after the pouring concrete guide pipe is placed, re-testing the hole depth, the hollow sediment, the mud proportion and the like. And if the thickness of the sediment at the bottom of the hole and the specific gravity of the slurry exceed the specifications, cleaning the hole by using a reverse circulation method by using a pouring guide pipe after the steel reinforcement cage and the guide pipe are well arranged, cleaning the hole for the second time for not less than 30min, measuring that the sediment at the bottom of the hole is less than or equal to 100mm, and stopping cleaning the hole. And (3) measuring the sediment at the bottom of the hole, testing by using a heavy hammer, wherein the reading of the measuring rope must be accurate, and correcting once by using 3-5 holes. The relative density of the slurry injected in the second hole cleaning process is about 1.05, the viscosity of the funnel is 18-22 s, and after the second hole cleaning process is carried out, the relative density of the slurry at the position 50cm away from the bottom of the hole is controlled to be about 1.15 and not more than 1.25. And after hole cleaning is finished, pouring concrete as soon as possible, wherein the interval time is not more than 30 min.
In the process of hoisting the steel reinforcement cage, the steel reinforcement cage is hoisted by adopting a shoulder pole hoisting method, hoisting points are arranged at the joint of the stirrups at the upper part of the steel reinforcement cage and the main reinforcement, and the hoisting points are symmetrical. Wherein, the steel reinforcement cage sets up 3 hoisting points to guarantee that the steel reinforcement cage does not warp when lifting by crane. When the steel bar cage is hung in the hole, the principle of 'one, two and three' is implemented, namely one person commands, two persons hold the steel bar cage and three persons are lapped, the hole position is aligned during construction, the hole position is kept vertical, the steel bar cage is lightly placed in the hole slowly, and the steel bar cage cannot rotate left and right. The length of the steel reinforcement cage is 10m, and the steel reinforcement cage is hoisted section by whole root processing. The spiral ribs and the main ribs are spot-welded, the stiffening ribs and the main ribs are spot-welded, and the stiffening rib joints are single-side welded for 10 d. And vertically hanging and welding the upper section cage and the lower section cage section by section according to the numbering sequence, aligning and correcting main ribs of the upper section cage and the lower section cage, symmetrically welding protective layer positioning steel plates at the reinforcing ribs according to the design drawing requirements, supplementing spiral ribs according to the drawing, and putting the cage into the furnace after the cage is qualified. Steel reinforcement cage length is 10m, and after steel reinforcement cage hoisted to design elevation position, the steel constructs the post to hoist, and the steel constructs the post and inserts steel reinforcement cage length and be 2 m.
The concrete strength of the underwater cast pile is prepared in a high-grade mode so as to ensure that the designed strength is achieved. The embodiment of the invention selects commercial concrete, the concrete pouring adopts a conduit underwater pouring method, and the used main machine comprises: a conduit for conveying concrete downwardly; a hopper for feeding the conduit; when the initial stock is large, a storage hopper is also required to be arranged; the first concrete is filled in the devices used for isolating the concrete of the guide pipe and the water in the guide pipe, such as a slide valve, a water stop plug, a bottom cover and the like; and lifting equipment for installing the guide pipe and the funnel, such as a perfusion platform and the like.
The top of the conduit is provided with a funnel. The funnel sets up the needs that the height should be suitable for the operation to should fill final stage, when filling in near the pile bolck position in particular, can satisfy the needs to the interior concrete column height of pipe, guarantee the filling quality of upper portion pile shaft. The height of the concrete column is at least 2.0m higher than the water level of the pile top when the pile top is lower than the water level in the pile hole, and is at least 0.5m higher than the pile top when the pile top is higher than the water level in the pile hole. The storage hopper should have sufficient capacity to store concrete (i.e., initial inventory) to ensure that the first fill of concrete (i.e., initial fill) can reach the required pipe-laying depth. The water-resisting plug is generally made of concrete and is preferably made into a cylinder shape, and the diameter of the water-resisting plug is preferably 20-25 mm smaller than the inner diameter of the guide pipe; the rubber gasket with the thickness of 3-5 mm is used for sealing, and the diameter of the rubber gasket is preferably 5-6 mm larger than the inner diameter of the guide pipe. The concrete strength is preferably C15-C20. The water-stop plug can also be made into a ball-shaped plug by using hardwood, a rubber gasket is nailed at the diameter of the ball, and lubricating grease is coated on the surface of the ball. In addition, the water-resisting plug can also be made of a steel plate plug, foam plastics, a bladder and the like. Regardless of the material, the plug should fall and be discharged smoothly when the concrete is poured. The slide valve is made of steel blades, and the lower part of the slide valve is provided with a sealing rubber gasket. The bottom cover is also made of concrete or steel.
When the conduit is hung into the hole, the rubber ring or the rubber pad is arranged completely and tightly to ensure good sealing. The position of the guide pipe in the pile hole is kept in the middle, so that the guide pipe is prevented from running, a reinforcement cage is prevented from being damaged by collision, and the guide pipe is prevented from being damaged. The height of the bottom of the conduit from the bottom of the hole (the sediment surface at the bottom of the hole) is 300-500 mm as high as the water-proof plug and the first batch of concrete can be discharged. And after the guide pipes are completely inserted into the holes, calculating the total length of the guide pipe column and the bottom position of the guide pipe, measuring the thickness of the sediment at the bottom of the holes again, and cleaning the holes again if the thickness exceeds the specification. The water-proof plug or slide valve is suspended on the water surface in the conduit by No. 8 iron wire. Before pouring the first batch of concrete, it is best to prepare 0.1-0.3 cubic meter of cement mortar, put it into the guide pipe and funnel above the slide valve (water-proof plug), then put the concrete, after confirming that the initial pouring amount is sufficient, it can cut off the iron wire, discharge the water in the guide pipe by the weight of the concrete, make the slide valve (water-proof plug) remain at the bottom of the hole, pour the first batch of concrete. The quantity of the first pouring concrete can meet the requirement that the guide pipe is buried in the concrete by more than 1.2 m.
After the first batch of concrete is normally poured, the concrete is continuously poured, and the shutdown is strictly forbidden. In the pouring process, a measuring hammer is often used for detecting the rising height of the concrete surface, and the guide pipe is lifted timely and detached step by step to keep the reasonable burial depth of the guide pipe. The detection times are generally not less than the number of the sections of the applicable guide pipes, and the height of the inner concrete surface and the outer concrete surface of each pipe is detected before the guide pipes are lifted each time. In special conditions (such as local serious overdiameter, diameter shrinkage, leakage position and pile hole with large pouring amount), the detection times are increased, and the water return condition is observed to correctly analyze and judge the conditions in the hole.
When the concrete is poured underwater, the minimum embedded depth of the guide pipe is strictly controlled according to actual conditions so as to ensure the continuity and uniformity of the concrete of the pile body, prevent the pile body from being possibly wrapped in floating slurry skins, soil blocks and the like on the concrete and prevent the phenomenon of pile breakage. The maximum buried depth of the conduit is determined by the initial discharge of concrete in the conduit along the smooth flow, which is convenient for lifting the conduit and reducing the auxiliary operation time of filling and lifting the conduit and detaching the conduit. The maximum depth of burial should not exceed the length of the lowest section of conduit. When the position close to the pile top is poured, the height of the funnel and the guide pipe should be strictly executed according to the regulations in order to ensure the quality of the concrete on the pile top.
The rising speed of concrete pouring is not less than 2 m/h. The pouring time must be controlled so that the concrete in the embedded duct does not lose its fluidity time. If necessary, proper amount of retarder can be added.
The filling elevation of the pile top is higher than the design elevation by more than 2.0m according to the design requirement so as to clear away the floating slurry slag layer on the pile top. After the pile top is poured, the actual elevation of the pile top surface is detected, and the concrete surface of the pile top is judged by detecting and sampling with a sampler consisting of a steel rod with a scale and a steel box with a valve capable of being opened and closed.
In order to prevent the reinforcement cage from floating upwards, the upper end of the reinforcement cage can be fixed at the orifice. In addition, the time for pouring concrete should be accelerated as much as possible to prevent the over-low fluidity of the concrete when the concrete enters the reinforcement cage. When the concrete in the hole approaches to the reinforcement cage, the buried pipe is kept deep, and the pouring speed is slowed down. After the concrete surface in the hole enters the reinforcement cage for 1-2 m, the guide pipe is lifted properly, the embedding depth of the guide pipe is reduced, the embedding depth of the reinforcement cage in the lower layer concrete is increased, and the reinforcement cage is prevented from floating upwards.
In the implementation process of the construction method of the cast-in-situ bored pile, monitoring work is carried out, and the monitoring work adopts the principles of integral arrangement and graded net arrangement in order to ensure the unification of all monitoring work, improve the precision of monitoring data and effectively guide the whole engineering construction. Firstly, a uniform monitoring control network is laid, and then monitoring points (holes) are laid on the basis. More than 3 stable elevation datum points are arranged outside the construction influence range, the elevation datum points and the construction elevation control points are jointly measured, the settlement deformation monitoring datum net takes the stable elevation datum points as starting points to form a leveling net for joint measurement, and the monitoring datum points can be jointly measured once every month.
Fig. 3 is a schematic structural diagram of a datum point according to an embodiment of the present invention, and as shown in fig. 3, the datum point and the working base point are embedded by manual excavation or drilling, and the embedding steps are as follows: excavating holes with the diameter of about 80mm and the depth of more than 1m on the soil surface by using a Luoyang shovel and a phi 80mm engineering drilling tool on the hard surface; tamping the bottom of the hole; removing residue soil, and injecting a proper amount of clear water into the hole for curing; pouring concrete with the mark number not lower than C20, and using a vibration machine to make the concrete poured densely, wherein the distance between the top surface of the concrete and the ground surface is kept about 5 cm; placing a steel bar mark with the length not less than 80cm in the center of the hole, and exposing the concrete surface by about 1-2 cm; a steel protective cover is additionally arranged on the upper part; maintaining for more than 15 days.
For the measurement of the vertical displacement of the monitoring points, according to the requirements of the second-class leveling standard of the building deformation measurement standard, the previous settlement deformation monitoring is to measure a leveling closed line through the connection between working base points, the elevation of each monitoring point is measured by the working points of the line, the initial elevation value of each monitoring point is continuously measured for three times (average for three times) in the early stage of the monitoring engineering, the difference of the current elevation minus the previous elevation of a certain monitoring point is the current settlement, and the difference of the current elevation minus the initial elevation is the accumulated settlement. In this process, it is noted that: when deep monitoring points are arranged, the deep monitoring points need to penetrate through a pavement structure hard shell layer; the settlement mark post is a phi 12mm screw-thread steel mark post, and the top of the settlement mark post is in a convex spherical shape; the settlement mark post should go deep into undisturbed soil by more than 60cm and keep vertical state; after the settlement mark post penetrates into the undisturbed soil, keeping the top of the settlement mark lower than the pipe cover by more than 5-10 cm, and reserving a sufficient measuring point uplift space; the inner diameter of the sleeve needs to ensure that the indium steel ruler can freely rotate in the sleeve and needs not less than 11 cm; the gap between the screw steel mark post in the protective sleeve needs to be backfilled by yellow sand.
And for the measurement of the horizontal displacement of the measuring point, an axis projection method or a small angle method is adopted for observation. The axis projection method adopts a total station instrument for observation, a stable reference point A, B is respectively selected from the distance of two ends of a certain measuring line, the total station instrument is erected at a point A, and a connecting line A, B is a datum line when a point B is oriented. During observation, a target is arranged at each monitoring point on the measuring line, the total station reads the vertical distance E from each monitoring point to an AB datum line on the target, the difference value of the current E value and the initial E value of a certain monitoring point is the accumulated displacement of the point, and the initial E value of each deformation monitoring point is an average value obtained twice.
Fig. 4 is a schematic view of monitoring by a plane displacement small angle method, as shown in fig. 4, the small angle method is to use a total station to monitor, and only one reference line PA is needed to be established, the measurement principle is that for a certain measuring point i, a horizontal angle β i and a horizontal distance Di are simultaneously measured by the total station, and then the plane rectangular coordinate (x i, y i) of the point can be calculated by using the observed values (β i, Di):
xi＝xP+Di·cos(αPA+βi),yi＝yP+Di·sin(αPA+βi)
wherein (x)p，yp) Is the coordinate of the base point P of operation, αPAIs the azimuth of the reference line PA, and the difference between the two observations (Δ x i, Δ y i) is the horizontal displacement of the point i. Wherein Δ x i is the north-south displacement value and Δ y i is the east-west displacement value.
The above-described embodiments should not be construed as limiting the scope of the invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions can occur, depending on design requirements and other factors. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (8)
1. A construction method of a cast-in-situ bored pile is characterized by comprising the following steps:
embedding a pile casing;
after the drilling machine is in place, drilling by adopting a small-stroke hole; and, after confirming that the drilling depth exceeds the full height and the normal stroke of the drill bit, performing normal percussion drilling; wherein, the drill bit of the drilling machine in the gravel soil rock stratum adopts a cross-shaped drill bit, and the drill bit of the drilling machine in the sand clay, sand or sand gravel stratum adopts a tubular drill bit;
after confirming that the drilled hole reaches the designed elevation, cleaning sediments;
hoisting a steel reinforcement cage and a guide pipe into the drilled hole after sediment cleaning, wherein the distance between the bottom of the guide pipe and the sediment surface at the bottom of the hole is 300-500 mm;
cleaning the hole again according to the thickness of the sediment at the bottom of the hole until the thickness of the sediment at the bottom of the hole is not more than 100 mm;
and pouring concrete into the drill hole.
2. The method of claim 1, wherein the step of embedding a casing comprises:
excavating a probe hole, wherein the depth of the probe hole is at least 2 m;
the central point of the pile position is released, and a control pile is embedded on an orthogonal cross line passing through the central point of 80-l 00cm outside the pile casing;
digging a round pit 50-70 cm larger than the pile casing outside the control pile position, wherein the depth is at least 2m, and filling and tamping clay with the thickness of at least 20cm at the pit bottom of the round pit;
symmetrically hoisting the pile casings into the round pits through steel wire ropes;
finding out the pile position center of the control pile through control pile lofting, and moving the pile casing to enable the center of the pile casing to be superposed with the pile position center;
after the protective cylinder is verified to be vertical through a level ruler or a suspension wire pendant, clay with specific water content is backfilled around the protective cylinder, and the protective cylinder is tamped in layers.
3. The method according to claim 1 or 2, further comprising, before embedding the casing:
respectively determining the inner diameter and the length of the casing according to the aperture and the underground water level; wherein the protective cylinder is made of a 5mm steel plate, and more than one stiffening rib is arranged on the outer side of the protective cylinder;
the top end of the pile casing is provided with symmetrical hanging rings, and the upper part of the pile casing is provided with at least 2 grout overflow holes.
4. The method of claim 1,
the step of clearing the sediments after confirming that the drill hole reaches the designed elevation comprises the following steps: after confirming that the drilled hole reaches the designed elevation, cleaning sediments through a cylindrical drill with a valve; wherein, under the condition that the mud skin deposition on the hole wall is thicker, the hole wall is swept up and down by a hole sweeping drill;
the step of cleaning the hole again according to the thickness of the sediment at the bottom of the hole comprises the following steps: and (5) confirming that the steel reinforcement cage and the guide pipe are successfully placed, and cleaning the hole by pouring the guide pipe in a reverse circulation mode until the thickness of the sediment at the bottom of the hole is not larger than 100 mm.
5. The method of claim 1, wherein the step of hoisting the reinforcement cage into the deslagged borehole comprises:
hoisting the reinforcement cage by a shoulder pole hoisting method, and vertically hoisting and welding the hoisted reinforcement cage section by section according to the serial number sequence;
after the steel reinforcement cage was hung and is put to design elevation position, it constructs the post to hang and put the steel, wherein it inserts steel reinforcement cage length for 2m to construct the post.
6. The method of claim 1, wherein the step of pouring concrete into the borehole comprises:
confirming that the sliding valve or the water-resisting plug is tightly attached to the water surface in the guide pipe;
placing prepared cement mortar into a guide pipe and a funnel above a slide valve or a water stop plug;
after confirming that the initial pouring amount is sufficient, pouring the first batch of concrete by cutting off an iron wire; wherein, the conduit is embedded into the concrete by more than 1.2m in the first batch of concrete;
continuously pouring concrete, detecting the rising height of the concrete surface through a measuring hammer, and lifting or gradually disassembling the guide pipe according to the rising height of the concrete surface.
7. The method of claim 1, further comprising, prior to embedding the casing:
determining the specification and quantity of the injected clean water, and injecting the specification and quantity of the clean water into the bentonite mixer with the rotating speed of at least 200 r/min;
putting bentonite, confirming that the bentonite is completely dissolved, and uniformly putting carboxymethyl cellulose;
a dispersant, a specific weight increasing agent and a water seepage preventing agent are added to obtain slurry for construction.
8. The method of claim 7, wherein the performance metrics of the mud include at least: the viscosity is at least 17, the relative density is 1.2-1.4, the sand content is 4-8%, the colloid rate is at least 90%, and the PH value is 7.0-8.0.
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