Deep foundation pit engineering field supporting system and construction method

Abstract

The invention discloses a deep foundation pit engineering site supporting system and a construction method, and belongs to the technical field of deep foundation pit construction, and the construction method comprises the following steps: surveying a site, preparing the site, measuring and positioning, excavating a foundation pit layer by layer, and performing supporting construction; according to the method, surface water can be effectively introduced into a drainage system by arranging drainage and dewatering construction, drainage ditches are reasonably arranged, smooth drainage is ensured, the safety of the foundation pit is prevented from being affected by accumulated water, dewatering wells are arranged in or around the foundation pit, the underground water level is reduced, and it is ensured that excavation and supporting construction of the foundation pit are not affected by underground water; when the dewatering well is constructed, parameters such as the well depth, the well diameter and the well casing quality are well controlled, the dewatering effect is ensured, and the construction effect and safety are greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of deep foundation pit construction, and in particular relates to a deep foundation pit engineering on-site support system and a construction method. Background Art

[0002] Deep foundation pit engineering refers to the earth excavation, support, and dewatering engineering of foundation pits (trenches) with an excavation depth of more than 5 meters (including 5 meters), or the earth excavation and support engineering of foundation pits (trenches) with an excavation depth of less than 5 meters but complex geological conditions, surrounding environment, and underground pipelines, or affecting the safety of adjacent buildings (structures). When carrying out deep foundation pit engineering construction, this construction method needs to be applied.

[0003] A Chinese patent discloses (CN117266182A) a deep foundation pit support system and construction method. The support system includes a retaining part located on the side wall of the foundation pit and a supporting part located in the foundation pit. The retaining part includes arranged inner supporting piles, outer supporting piles and a water-stop curtain. The supporting part includes an upper inner supporting beam and a lower inner supporting beam. A crown beam is arranged at the top of the inner supporting pile. The periphery of the upper inner supporting beam is connected to the crown beam. A waist beam is arranged in the middle of the inner supporting pile. The periphery of the lower inner supporting beam is connected to the waist beam. The upper inner supporting beam and the lower inner supporting beam are vertically connected with a plurality of column piles in the gravity direction. A driving trestle is arranged on one side of the upper inner supporting beam and the lower inner supporting beam. The construction method adopts a lowering auxiliary device. In view of the fact that the system method eliminates the use of inner supporting steel pipes, the lattice column guide device and the construction process are optimized at the same time, thereby reducing the foundation pit project cost and construction difficulty. Although the current construction method can also complete the construction, there is no targeted drainage and precipitation construction, which makes it impossible to effectively introduce surface water into the drainage system, ensure smooth drainage, avoid water accumulation, affect the safety of the foundation pit, and have poor actual application effects. It effectively solves the problem of limited site space in the foundation pit project and ensures the safety of surrounding buildings and underground pipelines. Summary of the invention

[0004] The purpose of the present invention is to propose a deep foundation pit engineering on-site support system and construction method to solve the problem that although the current construction method can complete the construction, there is no targeted drainage and precipitation construction, which makes it impossible to effectively introduce surface water into the drainage system, ensure smooth drainage, avoid water accumulation, affect the safety of the foundation pit, and have poor actual application effect.

[0005] In order to achieve the above object, the present invention adopts the following technical solution: a construction method of a deep foundation pit engineering on-site support system, comprising the following steps:

[0006] S1. Conduct site survey and site preparation;

[0007] S2, perform measurement and positioning;

[0008] S3, carry out layered excavation of the foundation pit;

[0009] S4. Carry out support construction;

[0010] S5, pull the anchor externally;

[0011] S6, grouting and inter-pile treatment;

[0012] S7. Carry out drainage and precipitation construction;

[0013] S8. Install the waist beam of the anchoring force transmission device;

[0014] S9. Carry out tensioning and anchoring.

[0015] As a further description of the above technical solution:

[0016] In S1, the site is surveyed and prepared, specifically, the site is surveyed, relevant survey data is recorded, the data is backed up, the construction site is cleaned, and the construction area is ensured to be barrier-free. At the same time, the machinery and materials required for construction are checked and prepared, and construction fences, safety warning signs, etc. are set up according to the construction drawings to ensure construction safety.

[0017] As a further description of the above technical solution:

[0018] In the S2, measurement and positioning are carried out, and the specific steps are: use a total station or theodolite to perform precise measurement and positioning according to the construction drawings to determine the foundation pit excavation line and the support pile position line. During the measurement process, ensure the measurement accuracy and avoid error accumulation. Set elevation control points at the construction site to ensure that the excavation depth and the elevation of the top of the support pile are accurate. Set elevation control points at the construction site to ensure that the excavation depth and the elevation of the top of the support pile are accurate. Regularly check and verify the elevation control points to ensure their accuracy.

[0019] As a further description of the above technical solution:

[0020] In S3, the foundation pit is excavated in layers, and the excavation principle is as follows: the first and second layers of the soil nail wall are excavated to a depth of 1.5-2m, and the third layer is excavated to a depth of 1-1.5m. The anchor cable part is excavated in 4 / 5 layers according to the designed number of anchor cable layers, with each layer being 2-2.5m, and each layer is excavated to 200mm below the designed elevation of the anchor cable. During the excavation process, over-excavation is strictly controlled to ensure timely construction of the supporting structure, and drainage is done well during the excavation process to avoid water accumulation affecting the construction progress and quality.

[0021] As a further description of the above technical solution:

[0022] In the S4, support construction is carried out. According to the foundation pit support plan, a suitable support structure is selected, which is one of mixing piles, rotary bored piles, and steel sheet piles. The support structure construction is strictly carried out in accordance with the construction drawings and plans to ensure the stability and safety of the support structure. After the support structure construction is completed, it is inspected and accepted to ensure that it meets the design requirements. If the mud wall protection process cannot form a hole and a casing drilling rig is required for construction, it is ensured that the casing is drilled ahead during the drilling process, and the advance depth is not less than 2.5m to prevent mud, sand and concrete of adjacent plain concrete piles from gushing out of the casing. When the drilling rig is in place and the first section of the steel casing is hoisted, two inclinometers are attached to the outer wall of the casing and the verticality of the casing is verified with a theodolite. The water-stopping effect of a single pile row is not good and needs to be coordinated with a water-stop curtain. The pile diameter of a single pile row is larger, and the composite external anchor can reduce the pile diameter of the pile row, control the horizontal displacement of the soil, and improve the hydraulic conditions and slope stability of the foundation soil more efficiently and effectively.

[0023] As a further description of the above technical solution:

[0024] In S5, external anchoring is performed, and its construction steps are: first, the pile top crown beam is constructed, then the first anchor cable is constructed, earthwork is excavated, and the second anchor cable is constructed; the cycle is repeated until the excavation reaches the bottom elevation of the foundation pit, and the foundation pit is excavated in sections and layers to facilitate the interlaced construction of earthwork and support. When drilling, the local pile body concrete is first broken according to the design requirements at the anchor cable positioning position, that is, the anchor cable working surface is reserved; then a water drill is used to drill a hole in the pile body, and a drilling machine is used to drill the hole after drilling. The inclination angle of the anchor cable is 10°-15°. When the unstable stratum or the stratum is disturbed and causes water and soil erosion, which will endanger the stability of the building, the casing wall is used for drilling. When it is greatly affected by the construction of adjacent anchor cables, the skipping mode is adopted. After drilling, the residual mud and other debris in the anchor cable hole are cleaned out by high-pressure water flow or high-pressure wind to achieve the purpose of cleaning. The grouting pipe is installed in the isolation bracket, and the grouting pipe and the steel strand are put into the hole at the same time.

[0025] As a further description of the above technical solution:

[0026] In S6, grouting and inter-pile treatment are carried out, cement slurry or cement mortar is used as the anchor grouting material, and secondary pressure grouting is used for anchor cable grouting. The grouting pipe is inserted to the bottom of the hole and grouting is performed from the bottom of the hole, and the distance from the end of the grouting pipe to the bottom of the hole is 100-200mm. During grouting and pipe pulling, the grouting outlet of the grouting pipe is always buried in the grouting liquid surface, and grouting is stopped after fresh slurry overflows from the hole mouth; after grouting, when the slurry level drops, grouting is performed, and between the supporting piles, rotary jet piles and other processes are used for reinforcement treatment to ensure the stability of the soil between the piles, and the parameters such as slurry ratio, injection pressure and injection speed are controlled during grouting to ensure construction quality.

[0027] As a further description of the above technical solution:

[0028] In S7, drainage and precipitation construction is carried out. A drainage ditch is set at the top of the foundation pit to introduce surface water into the drainage system. The drainage ditch is set reasonably to ensure smooth drainage and avoid water accumulation that affects the safety of the foundation pit. A precipitation well is set inside or around the foundation pit to lower the groundwater level and ensure that the foundation pit excavation and support construction are not affected by groundwater. When constructing the precipitation well, control the parameters such as well depth, well diameter and well pipe quality to ensure the precipitation effect.

[0029] As a further description of the above technical solution:

[0030] In the said S8, the waist beam of the anchoring force transmission device is installed: the waist beam is made of reinforced concrete beam or steel composite beam, the reinforced concrete waist beam is a trapezoidal cross-section with an inclined surface perpendicular to the axis of the anchor rod or a rectangular cross-section with an inclined surface only left at the anchor head, the concrete strength grade is not less than C25, the steel composite waist beam is made of double channel steel or double I-beam combination, the two steel sections are welded with a tie plate to form an integral structural member, the steel composite waist beam is set to an inclined surface with a wedge-shaped steel pad or an inclined seat is welded at the anchor head to achieve the verticality of the anchor rod axis and the pressure surface, and in the said S9, the grouting body strength is greater than 25Mp Before the anchor cable is formally tensioned, take 0.2 times the axial tension value of the anchor cable and pre-tension the anchor cable 1-2 times to make the contact of all parts close and the rod body completely straight; during formal tensioning, use a jack for tensioning, and it is advisable to over-tension it according to 1.1 times the standard value of the axial tension of the anchor cable. After holding the load for 5 minutes, lock it at 90% of the standard value of the axial tension. After the anchor cable is anchored, it is mechanically cut with an exposed length of not less than 50mm, and the anchor is sealed with fine stone concrete mortar or cement mortar of the same grade as the structure.

[0031] The invention also discloses a deep foundation pit engineering on-site support system, which is composed of pile anchors, waist beams, concrete retaining walls and support piles.

[0032] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0033] In the present invention, the method can effectively introduce surface water into the drainage system by arranging drainage and precipitation construction inside. The drainage ditch is reasonably arranged to ensure smooth drainage and avoid water accumulation affecting the safety of the foundation pit. Precipitation wells are arranged inside or around the foundation pit to lower the groundwater level and ensure that the foundation pit excavation and support construction are not affected by groundwater. During the construction of the precipitation wells, parameters such as well depth, well diameter and well pipe quality are controlled to ensure the precipitation effect, which greatly improves the construction effect and safety. At the same time, effective grouting and inter-pile treatment are carried out. After grouting, when the slurry level drops, grouting is carried out. Between the supporting piles, reinforcement treatment is carried out by adopting processes such as rotary jet piles to ensure the stability of the soil between the piles. During grouting, parameters such as slurry ratio, injection pressure and injection speed can be effectively controlled to ensure construction quality and further improve the actual application effect of the method. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The present invention is a flow chart of a deep foundation pit engineering on-site support system and construction method.

[0035] Figure 2 This is a schematic diagram of a deep foundation pit engineering on-site support system. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] Example 1

[0038] See also Figure 1 The present invention provides a technical solution: a construction method of a deep foundation pit engineering on-site support system, comprising the following steps:

[0039] S1. Conduct site survey and site preparation, specifically, survey the site, record relevant survey data, back up the data, clean up the construction site, ensure that the construction area is barrier-free, check and prepare the machinery and materials required for construction, set up construction fences and safety warning signs according to the construction drawings, and ensure construction safety;

[0040] S2. Conduct measurement and positioning. The specific steps are as follows: use a total station or theodolite to conduct precise measurement and positioning according to the construction drawings, determine the foundation pit excavation line and the support pile position line, ensure measurement accuracy and avoid error accumulation during the measurement process, set elevation control points at the construction site to ensure that the excavation depth and the support pile top elevation are accurate, set elevation control points at the construction site to ensure that the excavation depth and the support pile top elevation are accurate, and regularly check and verify the elevation control points to ensure their accuracy;

[0041] S3. Carry out layered excavation of the foundation pit. The excavation principle is as follows: the first and second layers of the soil nail wall are excavated at a depth of 1.5m, and the third layer is excavated at a depth of 1m. The anchor cable part is excavated in 4 / 5 layers according to the designed number of anchor cable layers, with each layer being 2m. Each layer is excavated to 200mm below the designed elevation of the anchor cable. During the excavation process, over-excavation is strictly controlled to ensure timely construction of the support structure. During the excavation process, drainage work is done well to avoid water accumulation affecting the construction progress and quality.

[0042] S4. Carry out support construction. According to the foundation pit support plan, select the appropriate support structure, which is a mixing pile. The support structure construction is strictly carried out in accordance with the construction drawings and plans to ensure the stability and safety of the support structure. After the support structure is completed, it is inspected and accepted to ensure that it meets the design requirements. If the mud wall protection process cannot form a hole and a casing drilling rig is required, ensure that the casing is drilled in advance during the drilling process, and the advance depth is not less than 2.5m to prevent mud, sand and concrete from adjacent plain concrete piles from gushing out of the casing. When the drilling rig is in place and the first section of the steel casing is hoisted, two inclinometers are attached to the outer wall of the casing and the verticality of the casing is verified with a theodolite. The water-stopping effect of a single pile row is not good and needs to be coordinated with a water-stop curtain. The diameter of the single pile row is larger, and the composite external anchor can reduce the diameter of the pile row, control the horizontal displacement of the soil, and improve the hydraulic conditions and slope stability of the foundation soil more efficiently and effectively.

[0043] S5, carry out external anchoring, and its construction steps are: first carry out the construction of the pile top crown beam, then the construction of the first anchor cable, earth excavation, and the second anchor cable; the cycle is carried out until the excavation reaches the bottom elevation of the foundation pit, and the foundation pit is excavated in sections and layers to facilitate the interlaced construction of earthwork and support. When drilling, the local pile body concrete is first broken according to the design requirements at the anchor cable positioning position, that is, the anchor cable working surface is reserved; then a water drill is used to drill a hole in the pile body, and a drilling machine is used to drill the hole after drilling. The inclination angle of the anchor cable is 10°. In unstable strata or when the strata are disturbed and soil erosion endangers the stability of the building, casing wall drilling is used. When it is greatly affected by the construction of adjacent anchor cables, a skipping mode is adopted. After drilling, residual mud and other debris in the anchor cable hole are cleaned out by high-pressure water flow or high-pressure wind to achieve the purpose of cleaning. The grouting pipe is installed in the isolation bracket, and the grouting pipe and the steel strand are put into the hole at the same time;

[0044] S6. Carry out grouting and pile treatment. Cement slurry or cement mortar is used as anchor grouting material. Secondary pressure grouting is used for anchor cable grouting. The grouting pipe is inserted to the bottom of the hole and grouting is carried out from the bottom of the hole. The distance from the end of the grouting pipe to the bottom of the hole is 100mm. During grouting and pipe pulling, the grouting outlet of the grouting pipe is always buried in the grouting liquid surface. Grouting is stopped after the fresh slurry overflows from the hole mouth. After grouting, when the slurry level drops, grouting is carried out. Between the supporting piles, rotary jet piles and other processes are used for reinforcement treatment to ensure the stability of the soil between the piles. During grouting, the parameters such as slurry ratio, injection pressure and injection speed are controlled to ensure the construction quality.

[0045] S7. Carry out drainage and precipitation construction. Set up drainage ditches at the top of the foundation pit to introduce surface water into the drainage system. The drainage ditches should be set reasonably to ensure smooth drainage and avoid water accumulation affecting the safety of the foundation pit. Set up precipitation wells inside or around the foundation pit to lower the groundwater level and ensure that the foundation pit excavation and support construction are not affected by groundwater. When constructing precipitation wells, control the parameters such as well depth, well diameter and well pipe quality to ensure precipitation effect;

[0046] S8. Install the waist beam of the anchoring force transmission device: the waist beam is made of reinforced concrete beam or steel composite beam. The reinforced concrete waist beam adopts a trapezoidal cross-section with the inclined surface perpendicular to the axis of the anchor rod or a rectangular cross-section with only the inclined surface left at the anchor head. The concrete strength grade is not less than C25. The steel composite waist beam adopts double channel steel or double I-beam combination. The two steel sections are welded with a tie plate to form an integral structural member. The steel composite waist beam is set into an inclined surface with a wedge-shaped steel pad or an inclined seat is welded at the anchor head to achieve the verticality of the anchor rod axis and the pressure surface.

[0047] S9. Prestressing and anchor sealing. Prestressing can only be carried out when the strength of the grouting body is greater than 25Mpa. Generally, prestressing is carried out 5 days after the grouting is completed. Before the formal tensioning of the anchor cable, take 0.2 times the axial tension value of the anchor cable and pre-tension the anchor cable once to make its various parts in close contact and the rod body completely straight. During the formal tensioning, use a jack for tensioning. It is advisable to over-tension the anchor cable by 1.1 times the standard value of the axial tension. After holding the load for 5 minutes, lock it at 90% of the standard value of the axial tension. After the anchor cable is anchored, it is mechanically cut with an exposed length of not less than 50mm, and the anchor is sealed with fine stone concrete mortar or cement mortar of the same grade as the structure.

[0048] The invention also discloses a deep foundation pit engineering on-site support system, which is composed of pile anchors, waist beams, concrete retaining walls and support piles.

[0049] In this embodiment, the method can effectively introduce surface water into the drainage system by arranging drainage and precipitation construction inside. The drainage ditch is reasonably arranged to ensure smooth drainage and avoid water accumulation that affects the safety of the foundation pit. Precipitation wells are arranged inside or around the foundation pit to lower the groundwater level and ensure that the foundation pit excavation and support construction are not affected by groundwater. When constructing the precipitation well, the parameters such as the well depth, well diameter and well pipe quality are controlled to ensure the precipitation effect, thereby greatly improving the construction effect and safety.

[0050] Example 2

[0051] See also Figure 1 The present invention provides a technical solution: a construction method of a deep foundation pit engineering on-site support system, comprising the following steps:

[0052] S1. Conduct site survey and site preparation, specifically, survey the site, record relevant survey data, back up the data, clean up the construction site, ensure that the construction area is barrier-free, check and prepare the machinery and materials required for construction, set up construction fences and safety warning signs according to the construction drawings, and ensure construction safety;

[0053] S2. Conduct measurement and positioning. The specific steps are as follows: use a total station or theodolite to conduct precise measurement and positioning according to the construction drawings, determine the foundation pit excavation line and the support pile position line, ensure measurement accuracy and avoid error accumulation during the measurement process, set elevation control points at the construction site to ensure that the excavation depth and the support pile top elevation are accurate, set elevation control points at the construction site to ensure that the excavation depth and the support pile top elevation are accurate, and regularly check and verify the elevation control points to ensure their accuracy;

[0054] S3. Carry out layered excavation of the foundation pit. The excavation principle is as follows: the first and second layers of the soil nail wall are excavated at a depth of 1.7m, and the third layer is excavated at a depth of 1.3m. The anchor cable part is excavated in 4 / 5 layers according to the designed number of anchor cable layers, with each layer being 2.3m. Each layer is excavated to 200mm below the designed elevation of the anchor cable. During the excavation process, over-excavation is strictly controlled to ensure timely construction of the support structure. During the excavation process, drainage work is done well to avoid water accumulation affecting the construction progress and quality;

[0055] S4. Carry out support construction. According to the foundation pit support plan, select the appropriate support structure, which is a mixing pile. The support structure construction is strictly carried out in accordance with the construction drawings and plans to ensure the stability and safety of the support structure. After the support structure is completed, it is inspected and accepted to ensure that it meets the design requirements. If the mud wall protection process cannot form a hole and a casing drilling rig is required, ensure that the casing is drilled in advance during the drilling process, and the advance depth is not less than 2.5m to prevent mud, sand and concrete from adjacent plain concrete piles from gushing out of the casing. When the drilling rig is in place and the first section of the steel casing is hoisted, two inclinometers are attached to the outer wall of the casing and the verticality of the casing is verified with a theodolite. The water-stopping effect of a single pile row is not good and needs to be coordinated with a water-stop curtain. The diameter of the single pile row is larger, and the composite external anchor can reduce the diameter of the pile row, control the horizontal displacement of the soil, and improve the hydraulic conditions and slope stability of the foundation soil more efficiently and effectively.

[0056] S5, carry out external anchoring, and its construction steps are: first carry out the construction of the pile top crown beam, then the construction of the first anchor cable, earth excavation, and the second anchor cable; the cycle is carried out until the excavation reaches the bottom elevation of the foundation pit, and the foundation pit is excavated in sections and layers to facilitate the interlaced construction of earthwork and support. When drilling, the local pile body concrete is first broken according to the design requirements at the anchor cable positioning position, that is, the anchor cable working surface is reserved; then a water drill is used to drill a hole in the pile body, and a drilling machine is used to drill the hole after drilling. The inclination angle of the anchor cable is 13°. In unstable strata or when the strata are disturbed and soil erosion endangers the stability of the building, casing wall drilling is used. When it is greatly affected by the construction of adjacent anchor cables, a skipping mode is adopted. After drilling, residual mud and other debris in the anchor cable hole are cleaned out by high-pressure water flow or high-pressure wind to achieve the purpose of cleaning. The grouting pipe is installed in the isolation bracket, and the grouting pipe and the steel strand are put into the hole at the same time;

[0057] S6. Carry out grouting and pile treatment. Cement slurry or cement mortar is used as anchor grouting material. Secondary pressure grouting is used for anchor cable grouting. The grouting pipe is inserted to the bottom of the hole and grouting is carried out from the bottom of the hole. The distance from the end of the grouting pipe to the bottom of the hole is 150mm. During grouting and pipe pulling, the grouting outlet of the grouting pipe is always buried in the grouting liquid surface. Grouting is stopped after the fresh slurry overflows from the hole mouth. After grouting, when the slurry level drops, grouting is carried out. Between the supporting piles, rotary jet piles and other processes are used for reinforcement treatment to ensure the stability of the soil between the piles. During grouting, the slurry ratio, injection pressure and injection speed and other parameters are controlled to ensure the construction quality.

[0058] S7. Carry out drainage and precipitation construction. Set up drainage ditches at the top of the foundation pit to introduce surface water into the drainage system. The drainage ditches should be set reasonably to ensure smooth drainage and avoid water accumulation affecting the safety of the foundation pit. Set up precipitation wells inside or around the foundation pit to lower the groundwater level and ensure that the foundation pit excavation and support construction are not affected by groundwater. When constructing precipitation wells, control the parameters such as well depth, well diameter and well pipe quality to ensure precipitation effect;

[0059] S8. Install the waist beam of the anchoring force transmission device: the waist beam is made of reinforced concrete beam or steel composite beam. The reinforced concrete waist beam adopts a trapezoidal cross-section with the inclined surface perpendicular to the axis of the anchor rod or a rectangular cross-section with only the inclined surface left at the anchor head. The concrete strength grade is not less than C25. The steel composite waist beam adopts double channel steel or double I-beam combination. The two steel sections are welded with a tie plate to form an integral structural member. The steel composite waist beam is set into an inclined surface with a wedge-shaped steel pad or an inclined seat is welded at the anchor head to achieve the verticality of the anchor rod axis and the pressure surface.

[0060] S9. Prestressing and anchor sealing. Prestressing can only be carried out when the strength of the grouting body is greater than 25Mpa. Generally, prestressing is carried out 6 days after the grouting is completed. Before the formal tensioning of the anchor cable, take 0.2 times the axial tension value of the anchor cable and pre-tension the anchor cable once to make its various parts in close contact and the rod body completely straight. During the formal tensioning, use a jack for tensioning. It is advisable to over-tension the anchor cable by 1.1 times the standard value of the axial tension. After holding the load for 5 minutes, lock it at 90% of the standard value of the axial tension. After the anchor cable is anchored, it is mechanically cut with an exposed length of not less than 50mm, and the fine stone concrete mortar or cement mortar of the same grade as the structure is used to seal the anchor.

[0061] The invention also discloses a deep foundation pit engineering on-site support system, which is composed of pile anchors, waist beams, concrete retaining walls and support piles.

[0062] In this embodiment, the method performs effective grouting and inter-pile treatment. After grouting, when the slurry level drops, additional grouting is performed. Between the supporting piles, reinforcement treatment is performed by adopting techniques such as rotary jet piles, which can ensure the stability of the soil between the piles. During grouting, parameters such as slurry ratio, injection pressure and injection speed can be effectively controlled to ensure construction quality and further improve the actual application effect of the method.

[0063] Example 3

[0064] See also Figure 1 The present invention provides a technical solution: a construction method of a deep foundation pit engineering on-site support system, comprising the following steps:

[0065] S1. Conduct site survey and site preparation, specifically, survey the site, record relevant survey data, back up the data, clean up the construction site, ensure that the construction area is barrier-free, check and prepare the machinery and materials required for construction, set up construction fences and safety warning signs according to the construction drawings, and ensure construction safety;

[0066] S2. Conduct measurement and positioning. The specific steps are as follows: use a total station or theodolite to conduct precise measurement and positioning according to the construction drawings, determine the foundation pit excavation line and the support pile position line, ensure measurement accuracy and avoid error accumulation during the measurement process, set elevation control points at the construction site to ensure that the excavation depth and the support pile top elevation are accurate, set elevation control points at the construction site to ensure that the excavation depth and the support pile top elevation are accurate, and regularly check and verify the elevation control points to ensure their accuracy;

[0067] S3. Carry out layered excavation of the foundation pit. The excavation principle is as follows: the first and second layers of the soil nail wall are excavated to a depth of 2m, and the third layer is excavated to a depth of 1.5m. The anchor cable part is excavated in 4 / 5 layers according to the designed number of anchor cable layers, with each layer being 2.5m. Each layer is excavated to 200mm below the designed elevation of the anchor cable. During the excavation process, over-excavation is strictly controlled to ensure timely construction of the support structure. During the excavation process, drainage work is done well to avoid water accumulation affecting the construction progress and quality;

[0068] S4. Carry out support construction. According to the foundation pit support plan, select the appropriate support structure, which is a mixing pile. The support structure construction is strictly carried out in accordance with the construction drawings and plans to ensure the stability and safety of the support structure. After the support structure is completed, it is inspected and accepted to ensure that it meets the design requirements. If the mud wall protection process cannot form a hole and a casing drilling rig is required, ensure that the casing is drilled in advance during the drilling process, and the advance depth is not less than 2.5m to prevent mud, sand and concrete from adjacent plain concrete piles from gushing out of the casing. When the drilling rig is in place and the first section of the steel casing is hoisted, two inclinometers are attached to the outer wall of the casing and the verticality of the casing is verified with a theodolite. The water-stopping effect of a single pile row is not good and needs to be coordinated with a water-stop curtain. The diameter of the single pile row is larger, and the composite external anchor can reduce the diameter of the pile row, control the horizontal displacement of the soil, and improve the hydraulic conditions and slope stability of the foundation soil more efficiently and effectively.

[0069] S5, carry out external anchoring, and its construction steps are: first carry out the construction of the pile top crown beam, then the construction of the first anchor cable, earth excavation, and the second anchor cable; the cycle is carried out until the excavation reaches the bottom elevation of the foundation pit, and the foundation pit is excavated in sections and layers to facilitate the interlaced construction of earthwork and support. When drilling, the local pile body concrete is first broken according to the design requirements at the anchor cable positioning position, that is, the anchor cable working surface is reserved; then a water drill is used to drill a hole in the pile body, and a drilling machine is used to drill the hole after drilling. The inclination angle of the anchor cable is 15°. In unstable strata or when the strata are disturbed and soil erosion endangers the stability of the building, casing wall drilling is used. When it is greatly affected by the construction of adjacent anchor cables, a skipping mode is adopted. After drilling, residual mud and other debris in the anchor cable hole are cleaned out by high-pressure water flow or high-pressure wind to achieve the purpose of cleaning. The grouting pipe is installed in the isolation bracket, and the grouting pipe and the steel strand are put into the hole at the same time;

[0070] S6. Carry out grouting and pile treatment. Cement slurry or cement mortar is used as anchor grouting material. Secondary pressure grouting is used for anchor cable grouting. The grouting pipe is inserted to the bottom of the hole and grouting is carried out from the bottom of the hole. The distance from the end of the grouting pipe to the bottom of the hole is 200mm. During grouting and pipe pulling, the grouting outlet of the grouting pipe is always buried in the grouting liquid surface. Grouting is stopped after the fresh slurry overflows from the hole mouth. After grouting, when the slurry level drops, grouting is carried out. Between the supporting piles, rotary jet piles and other processes are used for reinforcement treatment to ensure the stability of the soil between the piles. During grouting, the parameters such as slurry ratio, injection pressure and injection speed are controlled to ensure the construction quality.

[0071] S7. Carry out drainage and precipitation construction. Set up drainage ditches at the top of the foundation pit to introduce surface water into the drainage system. The drainage ditches should be set reasonably to ensure smooth drainage and avoid water accumulation affecting the safety of the foundation pit. Set up precipitation wells inside or around the foundation pit to lower the groundwater level and ensure that the foundation pit excavation and support construction are not affected by groundwater. When constructing precipitation wells, control the parameters such as well depth, well diameter and well pipe quality to ensure precipitation effect;

[0072] S8. Install the waist beam of the anchoring force transmission device: the waist beam is made of reinforced concrete beam or steel composite beam. The reinforced concrete waist beam adopts a trapezoidal cross-section with the inclined surface perpendicular to the axis of the anchor rod or a rectangular cross-section with only the inclined surface left at the anchor head. The concrete strength grade is not less than C25. The steel composite waist beam adopts double channel steel or double I-beam combination. The two steel sections are welded with a tie plate to form an integral structural member. The steel composite waist beam is set into an inclined surface with a wedge-shaped steel pad or an inclined seat is welded at the anchor head to achieve the verticality of the anchor rod axis and the pressure surface.

[0073] S9. Prestressing and anchor sealing. Prestressing can only be carried out when the strength of the grouting body is greater than 25Mpa. Generally, prestressing is carried out 7 days after the grouting is completed. Before the formal tensioning of the anchor cable, take 0.2 times the axial tension value of the anchor cable and pre-tension the anchor cable twice to make its various parts in close contact and the rod body completely straight. During the formal tensioning, use a jack for tensioning. It is advisable to over-tension the anchor cable by 1.1 times the standard value of the axial tension. After holding the load for 5 minutes, lock it at 90% of the standard value of the axial tension. After the anchor cable is anchored, it is mechanically cut with an exposed length of not less than 50mm, and the anchor is sealed with fine stone concrete mortar or cement mortar of the same grade as the structure.

[0074] The invention also discloses a deep foundation pit engineering on-site support system, which is composed of pile anchors, waist beams, concrete retaining walls and support piles.

[0075] In this embodiment, the method can effectively introduce surface water into the drainage system by arranging drainage and precipitation construction inside. The drainage ditch is reasonably arranged to ensure smooth drainage and avoid water accumulation affecting the safety of the foundation pit. Precipitation wells are arranged inside or around the foundation pit to lower the groundwater level and ensure that the foundation pit excavation and support construction are not affected by groundwater. When constructing the precipitation wells, parameters such as well depth, well diameter and well pipe quality are controlled to ensure the precipitation effect, which greatly improves the construction effect and safety. At the same time, effective grouting and inter-pile treatment are carried out. After grouting, when the slurry level drops, grouting is carried out. Between the supporting piles, reinforcement treatment is carried out by adopting techniques such as rotary jet piles to ensure the stability of the soil between the piles. During grouting, parameters such as slurry ratio, injection pressure and injection speed can be effectively controlled to ensure construction quality and further improve the actual application effect of the method.

[0076] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which are all covered by the protection scope of the present invention.

Claims

1. A construction method for a deep foundation pit engineering on-site support system, characterized in that: The steps include: S1. Conduct site survey and site preparation; S2, perform measurement and positioning; S3, carry out layered excavation of the foundation pit; S4. Carry out support construction; S5, pull the anchor externally; S6, grouting and inter-pile treatment; S7. Carry out drainage and precipitation construction; S8. Install the waist beam of the anchoring force transmission device; S9. Carry out tensioning and anchoring.

2. The construction method of a deep foundation pit engineering on-site support system according to claim 1, characterized in that: In S1, the site is surveyed and prepared, specifically, the site is surveyed, relevant survey data is recorded, the data is backed up, the construction site is cleaned, and the construction area is ensured to be barrier-free. At the same time, the machinery and materials required for construction are checked and prepared, and construction fences, safety warning signs, etc. are set up according to the construction drawings to ensure construction safety.

3. The construction method of a deep foundation pit engineering on-site support system according to claim 1, characterized in that: In the S2, measurement and positioning are carried out, and the specific steps are: use a total station or theodolite to perform precise measurement and positioning according to the construction drawings to determine the foundation pit excavation line and the support pile position line. During the measurement process, ensure the measurement accuracy and avoid error accumulation. Set elevation control points at the construction site to ensure that the excavation depth and the elevation of the top of the support pile are accurate. Set elevation control points at the construction site to ensure that the excavation depth and the elevation of the top of the support pile are accurate. Regularly check and verify the elevation control points to ensure their accuracy.

4. The construction method of a deep foundation pit engineering on-site support system according to claim 1, characterized in that: In S3, the foundation pit is excavated in layers, and the excavation principle is as follows: the first and second layers of the soil nail wall are excavated to a depth of 1.5-2m, and the third layer is excavated to a depth of 1-1.5m. The anchor cable part is excavated in 4 / 5 layers according to the designed number of anchor cable layers, with each layer being 2-2.5m, and each layer is excavated to 200mm below the designed elevation of the anchor cable. During the excavation process, over-excavation is strictly controlled to ensure timely construction of the supporting structure, and drainage is done well during the excavation process to avoid water accumulation affecting the construction progress and quality.

5. The construction method of a deep foundation pit engineering on-site support system according to claim 1, characterized in that: In the S4, support construction is carried out. According to the foundation pit support plan, a suitable support structure is selected, which is one of mixing piles, rotary bored piles, and steel sheet piles. The support structure construction is strictly carried out in accordance with the construction drawings and plans to ensure the stability and safety of the support structure. After the support structure construction is completed, it is inspected and accepted to ensure that it meets the design requirements. If the mud wall protection process cannot form a hole and a casing drilling rig is required for construction, it is ensured that the casing is drilled ahead during the drilling process, and the advance depth is not less than 2.5m to prevent mud, sand and concrete of adjacent plain concrete piles from gushing out of the casing. When the drilling rig is in place and the first section of the steel casing is hoisted, two inclinometers are attached to the outer wall of the casing and the verticality of the casing is verified with a theodolite. The water-stopping effect of a single pile row is not good and needs to be coordinated with a water-stop curtain. The pile diameter of a single pile row is larger, and the composite external anchor can reduce the pile diameter of the pile row, control the horizontal displacement of the soil, and improve the hydraulic conditions and slope stability of the foundation soil more efficiently and effectively.

6. The construction method of a deep foundation pit engineering on-site support system according to claim 1, characterized in that: In S5, external anchoring is performed, and its construction steps are: first, the pile top crown beam is constructed, then the first anchor cable is constructed, earthwork is excavated, and the second anchor cable is constructed; the cycle is repeated until the excavation reaches the bottom elevation of the foundation pit, and the foundation pit is excavated in sections and layers to facilitate the interlaced construction of earthwork and support. When drilling, the local pile body concrete is first broken according to the design requirements at the anchor cable positioning position, that is, the anchor cable working surface is reserved; then a water drill is used to drill a hole in the pile body, and a drilling machine is used to drill the hole after drilling. The inclination angle of the anchor cable is 10°-15°. When the unstable stratum or the stratum is disturbed and causes water and soil erosion, which will endanger the stability of the building, the casing wall is used for drilling. When it is greatly affected by the construction of adjacent anchor cables, the skipping mode is adopted. After drilling, the residual mud and other debris in the anchor cable hole are cleaned out by high-pressure water flow or high-pressure wind to achieve the purpose of cleaning. The grouting pipe is installed in the isolation bracket, and the grouting pipe and the steel strand are put into the hole at the same time.

7. The construction method of a deep foundation pit engineering on-site support system according to claim 1, characterized in that: In S6, grouting and inter-pile treatment are carried out, cement slurry or cement mortar is used as the anchor grouting material, and secondary pressure grouting is used for anchor cable grouting. The grouting pipe is inserted to the bottom of the hole and grouting is performed from the bottom of the hole, and the distance from the end of the grouting pipe to the bottom of the hole is 100-200mm. During grouting and pipe pulling, the grouting outlet of the grouting pipe is always buried in the grouting liquid surface, and grouting is stopped after fresh slurry overflows from the hole mouth; after grouting, when the slurry level drops, grouting is performed, and between the supporting piles, rotary jet piles and other processes are used for reinforcement treatment to ensure the stability of the soil between the piles, and the parameters such as slurry ratio, injection pressure and injection speed are controlled during grouting to ensure construction quality.

8. The construction method of a deep foundation pit engineering on-site support system according to claim 1, characterized in that: In S7, drainage and precipitation construction is carried out. A drainage ditch is set at the top of the foundation pit to introduce surface water into the drainage system. The drainage ditch is set reasonably to ensure smooth drainage and avoid water accumulation that affects the safety of the foundation pit. A precipitation well is set inside or around the foundation pit to lower the groundwater level and ensure that the foundation pit excavation and support construction are not affected by groundwater. When constructing the precipitation well, control the parameters such as well depth, well diameter and well pipe quality to ensure the precipitation effect.

9. The construction method of a deep foundation pit engineering on-site support system according to claim 1, characterized in that: In the said S8, the waist beam of the anchoring force transmission device is installed: the waist beam is made of reinforced concrete beam or steel composite beam, the reinforced concrete waist beam is a trapezoidal cross-section with an inclined surface perpendicular to the axis of the anchor rod or a rectangular cross-section with an inclined surface only left at the anchor head, the concrete strength grade is not less than C25, the steel composite waist beam is made of double channel steel or double I-beam combination, the two steel sections are welded with a tie plate to form an integral structural member, the steel composite waist beam is set to an inclined surface with a wedge-shaped steel pad or an inclined seat is welded at the anchor head to achieve the verticality of the anchor rod axis and the pressure surface, and in the said S9, the grouting body strength is greater than 25Mp Before the anchor cable is formally tensioned, take 0.2 times the axial tension value of the anchor cable and pre-tension the anchor cable 1-2 times to make the contact of all parts close and the rod body completely straight; during formal tensioning, use a jack for tensioning, and it is advisable to over-tension it according to 1.1 times the standard value of the axial tension of the anchor cable. After holding the load for 5 minutes, lock it at 90% of the standard value of the axial tension. After the anchor cable is anchored, it is mechanically cut with an exposed length of not less than 50mm, and the anchor is sealed with fine stone concrete mortar or cement mortar of the same grade as the structure.

10. A deep foundation pit engineering on-site support system according to claim 1, characterized in that: The deep foundation pit support system consists of pile anchors, waist beams, concrete retaining walls and support piles.

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