Construction method for anti-sloughing hole of strip-shaped pile foundation

Abstract

The invention discloses a construction method for preventing hole collapse of a strip-shaped pile foundation, which comprises the following steps of: adopting different protective measures according to the geological conditions of a construction area, underground structures and distribution conditions of the underground structures: if the geological conditions of the construction area belong to soft soil layer geology and no underground structures and overground structures exist nearby, taking the protective measures; guide walls are constructed at the design positions corresponding to the pile foundations; if the geological condition of the construction area belongs to soft soil layer geology and is close to a traffic lane, a protection measure of combining a steel sheet pile, a guide wall and a steel casing is adopted; if the geological condition of the construction area belongs to soft soil layer geology and is close to an underground pipeline or a riverway and the underground water level is high, a protection measure combining steel sheet piles, cement soil replacement and filling and guide walls is adopted; and if the geological condition of the construction area belongs to mucky soil, a heightened guide wall is adopted according to the thickness of the actually excavated silt layer. The method can effectively avoid hole collapse of shallow soil, and is suitable for soft geological conditions and conditions that pipelines are close to pile foundations.

Description

Technical Field

[0001] The present invention relates to the field of strip pile foundation construction, and more specifically, to a construction method for a strip pile foundation anti-collapse hole. Background Art

[0002] In the process of domestic bridge construction, round pile foundations are generally used for cast-in-place pile foundations, while in the process of bridge construction in Thailand, especially in the construction of municipal bridges, strip pile foundations are generally used. The pile foundation sizes are generally 1m×3m and 1m×3.8m. Compared with round piles, strip pile foundations have the advantages of large bearing capacity, less excavation times, and less environmental pollution. Taking the general pile length of 55m in this project as an example, the bearing capacity of a 1m diameter round pile is 510t, and the bearing capacity of a 1m×3.8m strip pile is 1500t. Strip pile construction also has the disadvantages of large earth excavation volume, easy hole collapse, and large ground disturbance. If the construction area is the green belt in the middle of the expressway, the pile foundation is close to the driving lane and is greatly disturbed by vehicle traffic; if the construction area is located in the old city, the geological conditions are poor, the groundwater is abundant, the underground pipelines are complex, and the outer side of the pipeline is generally protected by backfill sand. During the trenching process, it is very easy to cause a hole collapse due to the loss of backfill sand. Severe hole collapse causes the guide wall to deform and cannot continue excavation, which in turn causes concrete pouring over-square, increased costs, settlement of the adjacent road surface, deformation and cracking, mud upwelling, endangering driving safety, etc. Therefore, it is necessary to provide a construction method for preventing the hole collapse of strip pile foundations. During the pile foundation construction process, different protective measures are taken according to different underground conditions to solve the hole collapse problem during the trenching process. Summary of the invention

[0003] An object of the present invention is to solve at least the above problems and to provide at least the advantages which will be described hereinafter.

[0004] In order to achieve these purposes and other advantages according to the present invention, a construction method for a strip pile foundation anti-collapse hole is provided, comprising: conducting a geological survey on the construction area of ​​the pile foundation, and adopting different protective measures according to the geological conditions of the construction area and the distribution of underground structures and ground structures, specifically including: If the geological conditions of the construction area belong to soft soil layer and there are no underground structures or above-ground structures nearby, first construct the foundation pit in the construction area, and then construct the guide wall corresponding to the designed position of each pile foundation, and then carry out the pile foundation trenching, steel cage lowering and concrete pouring construction in the guide wall; If the geological conditions of the construction area belong to soft soil and it is close to the roadway, the steel sheet pile enclosure construction shall be carried out first in the construction area, and then the foundation pit and guide wall shall be constructed. After the pile foundation is excavated to a certain depth in the guide wall, the steel casing shall be installed in time, and then the pile foundation trenching, steel cage lowering and concrete pouring construction shall be continued; If the geological conditions of the construction area are soft soil and close to underground pipelines or close to rivers with high groundwater levels, steel sheet pile enclosure construction shall be carried out in the construction area first, and then the soil around the pipelines in the construction area shall be replaced with cement soil, and then the foundation pit and guide wall shall be constructed, and pile foundation trenching, steel cage lowering and concrete pouring shall be carried out in the guide wall; If the geological conditions in the construction area are silty soil, first construct a foundation pit in the construction area, and then construct a heightened guide wall for each pile foundation according to the actual thickness of the excavated silt layer, and carry out pile foundation trenching, steel cage lowering and concrete pouring construction inside the guide wall.

[0005] Preferably, if the geological conditions of the construction area belong to soft soil geology and the distance to the roadway does not exceed 2.5m, the length of the steel sheet pile enclosure should exceed 1.0m on both sides of the pile foundation, and the length of the steel casing should not be less than the depth of the soft soil.

[0006] Preferably, if the geological conditions of the construction area belong to soft soil and the distance to the underground pipeline is no more than 1m or it is close to the river and the groundwater level is high, cement is added to the replacement soil at a ratio of 100~200Kg / m³ and mixed evenly to form cement soil. The replacement area is at least 1.0m wider than the guide wall on each side, and the replacement depth is based on the actual excavation conditions on site until the silt soil and the backfill sand outside the pipeline are excavated.

[0007] Preferably, before the replacement begins, steel sheet piles are first used to surround the foundation pit to be excavated, and then a small excavation probe is used to clarify the pipeline boundary, and steel bars are used to mark the pipeline boundary line along the pipeline one by one. When the excavation reaches a pipeline burial depth of more than 0.5m, the actual boundary line of the pipeline is excavated manually before mechanical excavation continues. After excavation to the height of the pipeline top surface, a mechanical mixing method is used to mix cement soil with the soil 2.0m below the pipeline top surface. After mixing, the excavator grab is used for static pressure, and then the upper soil of the pipeline is replaced one by one.

[0008] Preferably, the guide wall comprises a guide wall body and a wing panel arranged on the top surface of the guide wall body, and the inner diameter of the guide wall is 0.05 m larger than the outer dimension of each side of the pile foundation.

[0009] Preferably, the guide wall body is a prefabricated structure; before installation, a 0.01m thick cushion layer of concrete is poured at the bottom of the foundation pit, and after the concrete reaches sufficient strength, the guide wall body is installed according to the designed coordinates; after the guide wall body is in place, the soil is backfilled symmetrically around it and compacted in layers; after the backfill is flush with the top surface of the guide wall body, the wing panel steel bars are tied and the wing panel concrete is poured.

[0010] Preferably, if the geological condition of the construction area is silty soil, the height of the guide wall body is increased according to the thickness of the actual excavated silt layer.

[0011] Preferably, an even number of sonic detection tubes are symmetrically arranged on the steel cage about its center, the bottoms of two sonic detection tubes on the same diameter are connected by a connecting tube, and the tops of the sonic detection tubes are set at an elevation of 1m above the pile top and are sealed.

[0012] The present invention has at least the following beneficial effects: 1. The construction method for preventing the strip pile foundation from collapsing provided by the present invention adopts different protective measures according to the causes of shallow collapse of the strip pile foundation, the geological conditions of the pile foundation construction area, and the distribution of underground structures and ground structures. During the construction of the pile foundation and the ground-connected wall, the collapse of the surface soil can be effectively avoided to ensure the safety of the carriageway. The implementation effect is good when the geological conditions are complex and the pipeline is close to the pile foundation.

[0013] 2. The construction method of the strip pile foundation anti-collapse hole provided by the present invention has the advantages of less excavation times, less environmental pollution and low noise, which meets the high requirements of nearby residential areas for environmental protection; low space requirements for the on-site construction area, construction can be carried out in a limited closed site, and continuous construction can be carried out without time restrictions without affecting traffic conditions, which can greatly solve the construction organization of limited construction sites; and effective protection of underground pipelines that cannot be relocated during construction.

[0014] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a structural schematic diagram of the construction method of the strip pile foundation anti-collapse hole of the present invention when steel sheet piles, steel casing and guide wall are used for protection at the same time; Figure 2 It is a structural schematic diagram of cement-soil replacement in the construction method of the strip pile foundation anti-collapse hole of the present invention; Figure 3 It is a structural schematic diagram of the guide wall described in the present invention. DETAILED DESCRIPTION

[0016] The present invention is further described in detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0017] It should be noted that the experimental methods described in the following embodiments are conventional methods unless otherwise specified, and the reagents and materials are commercially available unless otherwise specified; in the description of the present invention, the terms "lateral", "longitudinal", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0018] like Figures 1 to 3 As shown, the present invention provides a method for constructing a strip pile foundation anti-collapse hole, comprising: conducting a geological survey on the construction area of ​​the pile foundation, and adopting different protective measures according to the geological conditions of the construction area and the distribution of underground structures and ground structures, specifically including: If the geological conditions of the construction area belong to soft soil geology and there are no underground structures and above-ground structures nearby, a foundation pit is first constructed in the construction area, and then a guide wall 4 is constructed corresponding to the designed position of each pile foundation, and pile foundation trenching, steel cage lowering and concrete pouring construction are carried out in the guide wall.

[0019] The guide wall 4 is mainly used to provide guidance for the subsequent pile foundation trenching and the lowering of the steel cage to ensure the verticality of the trenching. The guide wall 4 includes a guide wall body 41 and a wing panel 42 arranged on the top surface of the guide wall body 41. Figure 3 As shown, the guide wall 4 is in the shape of "┒┎". The inner diameter of the guide wall 4 is 0.05m larger than the outer dimension of each side of the pile foundation. The top surface height of the guide wall 4 is 0.5m lower than the original ground. The guide wall body 41 is a prefabricated structure; before installation, a 0.01m thick cushion layer of concrete is poured at the bottom of the foundation pit, and after the concrete reaches the strength, the guide wall body 41 is installed according to the design coordinates; after the guide wall body 41 is in place, the soil is symmetrically backfilled around it and compacted in layers; after the backfill is flush with the top surface of the guide wall body 41, the wing panel steel bars are tied and the wing panel concrete is poured. After the wing panel concrete reaches the design strength, the trenching machine can perform trenching construction through the guide wall.

[0020] If the geological conditions of the construction area are soft soil and the distance to the road is no more than 2.5m, Figure 1 As shown, in the construction area, the steel sheet pile 2 enclosure construction is first carried out, and then the foundation pit and guide wall 4 are constructed. After the pile foundation is excavated to a certain depth in the guide wall 4, the steel casing 3 is installed in time, and then the pile foundation trenching, steel cage lowering and concrete pouring construction are continued.

[0021] The steel sheet piles 2 are used to form a separation zone between the pile foundation 1 and the lane to prevent the collapse from spreading to the bottom of the lane. The steel sheet piles are placed at the same position as the steel cofferdam of the cap as much as possible, and can be used as steel sheet piles for the cap foundation pit in the future. The steel sheet piles 4 should have a protection length that exceeds 1.0m on both sides of the pile foundation, and the length of the steel casing 3 should not be less than the depth of the soft soil.

[0022] If the geological conditions of the construction area are soft soil and the distance to the underground pipeline 6 is no more than 1m, Figure 2 As shown, the steel sheet pile 2 enclosure construction is first carried out in the construction area, and then the soil around the pipeline 6 in the construction area is replaced with cement soil, and then the foundation pit and guide wall 4 are constructed, and the pile foundation trenching, steel cage lowering and concrete pouring construction are carried out in the guide wall 4.

[0023] In view of the fact that pipeline 6 is close to the pile foundation and the geology of the adjacent location is poor and prone to collapse, cement soil is required to replace the soft soil. According to the groundwater level, cement is added to the replacement soil at a ratio of 100~200Kg / m³ and mixed evenly to form cement soil. Each side of the replacement area 5 is at least 1.0m wider than the guide wall. The replacement depth is based on the actual excavation conditions on site until the silt soil and the backfill sand outside the pipeline are excavated.

[0024] Before the replacement begins, use steel sheet piles 2 to surround the foundation pit to be excavated, then use a small excavation probe to clarify the pipeline boundary, use steel bars to mark the pipeline boundary line along the pipeline one by one, and when the excavation reaches the buried depth of pipeline 6 of more than 0.5m, use manual excavation to find the actual boundary line of the pipeline before continuing mechanical excavation. After excavation to the height of the pipeline top surface, use mechanical mixing to mix cement soil with the soil 2.0m below the pipeline top surface. After mixing, use the excavator grab static pressure, and then replace the upper soil of pipeline 6 one by one.

[0025] If the geological conditions of the construction area are soft soil and it is close to the river, and the groundwater level is high, after the steel sheet pile 2 enclosure construction is carried out in the construction area, the soil at a certain depth in the construction area is replaced with cement soil, and then the foundation pit and guide wall 4 are constructed.

[0026] If the geological conditions of the construction area are muddy soil, first construct a foundation pit in the construction area, then construct a heightened guide wall corresponding to each pile foundation according to the actual thickness of the excavated mud layer, and perform pile foundation trenching, steel cage lowering and concrete pouring in the guide wall. For the pile foundation at the location of abandoned ponds or sewage pipes, the soil is mainly muddy within a certain range. During the trenching process, shallow collapse holes are easily caused. The height of the guide wall body 41 can be increased according to the actual thickness of the excavated mud layer to ensure that the guide wall 4 is supported on a good soil foundation.

[0027] After the above-mentioned protective measures are completed, trenching can be carried out in the guide wall corresponding to each pile foundation 1 by means of a trenching machine; during the excavation progress of the trenching machine, the mud should be continuously circulated to maintain the mud level from dropping, so as to ensure the mud wall protection effect. The raw materials of the wall protection mud should be tested for the mix ratio of the mud according to the soil layer most prone to collapse based on the different geological conditions of each pier. Non-dispersible, low-solid phase, high-viscosity mud is used in trenching construction. In the event of excessive mud loss and insufficient mud supply, the progress should be stopped and the excavated drill cuttings and other materials should be used for backfilling immediately. If the excavated materials are insufficient, plain concrete should be used for backfilling.

[0028] After the trenching construction is completed, the steel cage is hoisted. The steel cage skeleton is made in sections in the steel processing yard in the back field, and the vertical steel bars of two adjacent sections of the steel cage are overlapped and connected. An even number of sonic detection pipes are symmetrically arranged on the steel cage about its center. The bottoms of two sonic detection pipes with the same diameter are connected through a connecting pipe. The top of the sonic detection pipe is set at an elevation of 1m above the pile top and is sealed. The sonic detection pipe is made of seamless steel pipe and connected by welding to ensure full closure. The sonic detection pipe is fixed to the steel bars of the steel cage with a U-shaped clip.

[0029] Before placing the steel cage, a hole test should be conducted on the pile foundation. This test should be conducted after debonding or replacing bentonite. And all working piles should be tested for hole wall to verify that the verticality of the hole wall and the pile length meet the specification requirements. After the steel cage is transported to the construction site, the first section of the steel cage is lifted and slowly placed into the groove. Note that the center line of the steel cage and the center line of the pile position are consistent. Before the steel cage is fully placed, two cross arms are placed on the guide wall to stabilize the first section of the steel cage. When the subsequent steel cage is lowered, the main reinforcement is aligned with the main reinforcement of the previous section of the steel cage, and each section is connected according to the corresponding marks.

[0030] After the steel cage is lowered into place, the pile foundation concrete pouring construction is carried out. The specifications and quantity of the conduit are determined according to the pile length, pile diameter and the amount of concrete poured per hour. The conduit connection adopts the quick bayonet connection method. The conduit should be subjected to a watertight test and a joint tensile test before the first use. The watertight test water pressure should not be less than 1.5 times the pressure of the water depth in the groove, nor should it be less than 1.5 times the maximum internal pressure that the conduit wall and weld may withstand when pouring concrete. Before the conduit is lowered, check whether each conduit is clean, unobstructed, has small holes, and the integrity of the water-stop "O" ring. The lower end of the lowest conduit cannot be in the form of a joint to avoid hooking the steel cage when lifting the conduit. The conduit is hoisted and extended section by section and lowered vertically until it is 20 to 40 cm from the bottom of the hole. During the lowering process, pay attention to keep it consistent with the center line of the pile foundation hole. When the conduit is extended, it is suspended by a movable card made of two I-beams.

[0031] The first bottom sealing of the cast-in-place pile is constructed by the plug-pulling method. Before pouring concrete, install a collection hopper on the guide tube, and install an eccentric plug at the bottom of the collection hopper to seal the collection hopper; concrete is transported into the collection hopper by a pump truck. When the concrete in the collection hopper is about 20cm away from the top of the hopper, pull out the eccentric plug of the collection hopper, and discharge the auxiliary hopper to the maximum speed while the concrete in the collection hopper falls, and add concrete into the collection hopper to ensure that the collection hopper does not leak before the bottom sealing concrete is poured.

[0032] After the bottom is sealed, the concrete should be poured continuously to ensure the continuity of the concrete pouring. When the buried depth of the conduit is more than 3m, the conduit should be raised by about 1m to ensure the smooth slurry of the concrete; when the buried depth of the conduit reaches 6m, the conduit should be removed in time to ensure that the buried depth of the conduit is between 2 and 6m. When the concrete pouring is discontinuous, the conduit should be lifted up and down every 15 minutes to ensure the normal slurry of the concrete. Before each pipe removal, the concrete surface must be measured, the buried depth of the conduit is calculated by the length of the conduit, and the length of the removed conduit is determined according to the buried depth of the conduit to ensure the pouring quality. When the concrete pouring is about to end, the conduit should be lifted up and down to ensure the compactness of the concrete on the top of the pile. The poured pile top elevation should be pre-added with concrete of not less than the design elevation of 1m to squeeze out the floating slurry on the pile top.

[0033] When the concrete of the strip cast-in-place pile reaches a certain strength, the pile head of the super-high part can be chiseled off to ensure the concrete strength of the pile head. Mark the design elevation line with red paint on the side of the strip pile body, and use a handheld circular saw to cut the pile body along the elevation line. The cutting depth should be appropriate without damaging the steel bars. Then use a pneumatic pick, steel chisel and steel chisel to peel out the main reinforcement of the pile head, and then chisel the pile head along the cutting line. Finally, use an excavator or crane to move the pile head out of the foundation pit. Straighten the steel bars of the pile head, trim the cross section, and clean the loose concrete of the pile head.

[0034] The ultrasonic detection test of the pile foundation is carried out through the ultrasonic detection tube. After the test, the bottom of the trench is grouting treated through the ultrasonic detection tube to ensure the bearing capacity of the pile end. Steps of grouting treatment of the bottom of the trench: (1) Clean water is injected into each group of acoustic detection tubes at the same time to clean the acoustic detection tubes. After the inspection is qualified, proceed to the next step; a group of acoustic detection tubes is two acoustic detection tubes with the same diameter, and the top of the two acoustic detection tubes is used as a water inlet and the other as a water outlet; (2) Inject clean water with a certain pressure into the acoustic detection pipe. When the pressure in the pipe reaches 4MPA, stop injecting water; (3) Pour cement slurry into the acoustic testing pipe at a speed not exceeding 5 liters / minute. Stop grouting when the pressure in the pipe reaches 6 MPA or the volume of cement slurry poured reaches 4 cubic meters. (4) Clean the acoustic detection pipe and complete the grouting at the bottom of the trench.

[0035] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes, and they can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the illustrations shown and described herein.

Claims

1. A construction method for a strip pile foundation anti-collapse hole, characterized in that: include: Conduct geological surveys on the construction area of ​​the pile foundation and adopt different protective measures according to the geological conditions of the construction area and the distribution of underground and above-ground structures, including: If the geological conditions of the construction area belong to soft soil layer and there are no underground structures or above-ground structures nearby, first construct the foundation pit in the construction area, and then construct the guide wall corresponding to the designed position of each pile foundation, and then carry out the pile foundation trenching, steel cage lowering and concrete pouring construction in the guide wall; If the geological conditions of the construction area belong to soft soil and it is close to the roadway, the steel sheet pile enclosure construction shall be carried out first in the construction area, and then the foundation pit and guide wall shall be constructed. After the pile foundation is excavated to a certain depth in the guide wall, the steel casing shall be installed in time, and then the pile foundation trenching, steel cage lowering and concrete pouring construction shall be continued; If the geological conditions of the construction area are soft soil and close to underground pipelines or close to rivers with high groundwater levels, steel sheet pile enclosure construction shall be carried out in the construction area first, and then the soil around the pipelines in the construction area shall be replaced with cement soil, and then the foundation pit and guide wall shall be constructed, and pile foundation trenching, steel cage lowering and concrete pouring shall be carried out in the guide wall; If the geological conditions in the construction area are silty soil, first construct a foundation pit in the construction area, and then construct a heightened guide wall for each pile foundation according to the actual thickness of the excavated silt layer, and carry out pile foundation trenching, steel cage lowering and concrete pouring construction inside the guide wall.

2. The construction method of the strip pile foundation anti-collapse hole according to claim 1, characterized in that: If the geological conditions in the construction area are soft soil and the distance to the road is no more than 2.5m, the length of the steel sheet pile enclosure should exceed 1.0m on both sides of the pile foundation, and the length of the steel casing should not be less than the depth of the soft soil.

3. The construction method of the strip pile foundation anti-collapse hole according to claim 1, characterized in that: If the geological conditions of the construction area belong to soft soil and the distance to the underground pipeline is no more than 1m, or it is close to the river and the groundwater level is high, cement is added to the replacement soil at a ratio of 100~200Kg / m³ and mixed evenly to form cement soil. Each side of the replacement area is at least 1.0m wider than the guide wall. The replacement depth is based on the actual excavation conditions on site until the silt soil and the backfill sand outside the pipeline are excavated.

4. The construction method of the strip pile foundation anti-collapse hole according to claim 3, characterized in that: Before the replacement begins, use steel sheet piles to surround the foundation pit to be excavated, then use a small excavation probe to clarify the pipeline boundary, use steel bars to mark the pipeline boundary line along the pipeline one by one, and when the excavation reaches a pipeline burial depth of more than 0.5m, use manual excavation to find the actual boundary line of the pipeline before continuing mechanical excavation. After excavation to the height of the pipeline top surface, use mechanical mixing to mix cement soil with the soil 2.0m below the pipeline top surface. After mixing, use the excavator grab static pressure, and then replace the soil on the upper part of the pipeline one by one.

5. The construction method of the strip pile foundation anti-collapse hole according to claim 1, characterized in that: The guide wall comprises a guide wall body and a wing panel arranged on the top surface of the guide wall body. The inner diameter of the guide wall is 0.05m larger than the outer dimension of each side of the pile foundation.

6. The construction method of the strip pile foundation anti-collapse hole according to claim 5, characterized in that: The guide wall body is a prefabricated structure; before installation, a 0.01m thick cushion layer of concrete is poured at the bottom of the foundation pit, and after the concrete reaches the required strength, the guide wall body is installed according to the designed coordinates; after the guide wall body is in place, the soil is backfilled symmetrically around it and compacted in layers; after the backfill is flush with the top surface of the guide wall body, the wing panel steel bars are tied and the wing panel concrete is poured.

7. The construction method of the strip pile foundation anti-collapse hole according to claim 6, characterized in that: If the geological conditions in the construction area are silty soil, the height of the guide wall body shall be increased according to the actual thickness of the excavated silt layer.

8. The construction method of the strip pile foundation anti-collapse hole according to claim 1, characterized in that: An even number of sonic detection tubes are symmetrically arranged on the steel cage about its center, the bottoms of two sonic detection tubes on the same diameter are connected by a connecting pipe, the top of the sonic detection tube is set at an elevation of 1m above the pile top and is sealed.

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