Coastal area combined type foundation pit supporting method and device

Abstract

The invention relates to the technical field related to deep foundation pit construction, in particular to a combined foundation pit supporting method and device in a coastal area. The silty-fine sand is used for soil descending construction; constructing fender posts; constructing a water curtain and a dewatering well; excavating a first layer of silty-fine sand, inserting ribs, and carrying out shotcrete-anchor support construction; a second layer of silty-fine sand is excavated, and shotcrete and anchor supporting Top beam grooves are excavated, and top beams are constructed; excavating a first layer of mucky silty clay, and shotcreting and supporting; pile body anchor cables and waist beams are constructed; excavating a second layer of mucky silty clay, and shotcreting and supporting; blasting and excavating basalt within the elevation of-3.100 to 5.900, and renovating a side slope; constructing a basalt anchor rod within the elevation of-3.100 to 5.900; blasting and excavating basalt within the elevation of-5.900-9.200, and renovating a side slope; constructing basalt anchor rods within the elevation of-5.900-9.200, and carrying out shotcrete anchor support; the water taking pool and the pump room deep foundation pit are constructed through the working procedures of foundation pit bottom closing, main body structure construction and the like, so that the problem that the construction period is long is effectively solved, and the safety of the construction process can be effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field related to deep foundation pit construction, and in particular to a combined foundation pit supporting method and device in coastal areas. Background Art

[0002] The foundation pit is an earth pit excavated at the foundation design location according to the base elevation and foundation plane dimensions. Before excavation, the excavation plan should be determined based on geological and hydrological data and the situation of nearby buildings on site, and waterproofing and drainage work should be done. If the excavation is not deep, the side slope can be used to stabilize the soil slope, and the slope size is determined according to relevant construction regulations. For deeper excavations and nearby buildings, foundation pit wall support methods and shotcrete wall protection methods can be used. Large foundation pits can even use underground continuous walls and column-type bored pile interlocking methods to prevent the outer soil layer from collapsing. If there is no impact on nearby buildings, the well point method can be used to lower the groundwater level and use slope open excavation. In cold areas, natural cold air freezing methods can be used for excavation, etc.

[0003] During the construction of sea foundation pit, it is necessary to support the foundation pit through supporting structures to ensure the overall strength of the foundation pit. However, the traditional deep foundation pit support structure construction method has the problems of long construction period, high safety risk during blasting construction and adverse effect of support replacement construction on the main structure. Therefore, the present invention proposes a combined foundation pit support method and device in coastal areas to solve the above problems. Summary of the invention

[0004] The object of the present invention is to provide a combined foundation pit support method and device in coastal areas to solve the problems raised in the above-mentioned background technology.

[0005] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: a combined foundation pit support method and device in coastal areas, the combined foundation pit support method in coastal areas comprising:

[0006] Fine sand soil reduction construction;

[0007] Construction of retaining piles;

[0008] Water curtain and dewatering well construction, soil nail wall is used on the upper part of the foundation pit, cantilever cast-in-place piles are used on the lower part, and an earthwork platform is reserved in front of the piles for support. Upper soil nail wall is used for local deepening, and bottom cast-in-place piles and anchor cables are used on the lower part. An earthwork platform is reserved in front of the piles for support. The water-stop curtain cuts off the connection between the groundwater inside and outside the pit, and drainage wells and open drainage for water collection are set up on the platform;

[0009] Excavation, reinforcement and shotcrete support construction of the first layer of fine sand;

[0010] Excavation of the second layer of fine sand and construction of shotcrete support;

[0011] Excavation of crown beam trench and construction of crown beam;

[0012] The first layer of silty clay is excavated and supported by shotcrete anchors;

[0013] Construction of pile anchor cables and waist beams;

[0014] The second layer of silty clay is excavated and supported by shotcrete anchors;

[0015] Basalt blasting, excavation and slope repair within the elevation range of -3.100 to 5.900;

[0016] Basalt anchor construction within the elevation range of -3.100 to 5.900;

[0017] Basalt blasting, excavation and slope repair within the elevation range of -5.900 to 9.200;

[0018] Basalt anchor construction and shotcrete support within the elevation of -5.900 to 9.200 are carried out by excavators at the bottom of the pit and blasting and drilling machinery, and then hoisted out of the foundation pit by crane;

[0019] The foundation pit is closed and the anti-floating anchor rods under the bottom plate are constructed simultaneously;

[0020] The main structure construction is carried out in two sections from north to south, and the concrete is poured vertically in four layers. After the water test of the water intake pool and the external anti-corrosion construction of the underground part are completed, the foundation pit is backfilled.

[0021] Preferably, during the basalt anchor construction and shotcrete support within the elevation of -5.900 to 9.200, three 220-type excavators are used to pour soil in steps during excavation. The first-level excavator is at the top of the foundation pit, and the soil pouring platform is set on the top of the crown beam; the second-level excavator is located at the bottom of the cantilever of the retaining pile, and the soil pouring platform is set at the bottom of the base plate; the third-level excavator is set at the bottom of the sinking section.

[0022] Preferably, during the construction of the retaining piles, two 360-degree rotary drilling drills are used for the construction of the retaining piles based on previous construction experience and investigations of similar surrounding projects, and then the site is leveled. After that, the technicians use instruments to measure and lay out the pile positions, and then lay out and locate the positions on site. The surface soil of the pile holes is excavated according to the pile positions, and the casing is buried. After the casing is buried, the pile positions are checked and laid out again. After ensuring that they are correct, the drilling rig is in place, and then the drill bucket is first put on the ground when drilling, and the zeroing operation is performed through the zeroing button on the display, and the original position of the drill bit of the drilling rig is recorded. At this time, the display shows the bar column and number of the current position of the drilling hole. The operator needs to monitor the actual working position of the drilling hole, the position of each footage, and the position of the hole depth through the display, so as to operate the drilling operation. After the drilling is completed, the hole is cleaned, and after the hole cleaning is completed, the hole is inspected;

[0023] Then, the steel cage is made. The steel cage is made in sections, and a butt joint structure is reserved at the end of the steel cage. To control the thickness of the protective layer, a positioning block is set every three meters on the main reinforcement of the steel cage, and four positioning blocks are symmetrically arranged around the steel cage. During the welding process, slag should be removed in time. The main reinforcement of the steel cage is connected according to the design requirements. The spacing between the main reinforcement joints is ≥35d, and the joints on the same section are not more than 50%. After the steel cage is in place, the grouting pipe is placed in the pile hole, and then grouting is carried out;

[0024] Commercial concrete is used in the grouting process, the slump should be controlled at 200±20mm, the concrete should be poured continuously, and the pile pouring time should be ≤8 hours. During the concrete pouring process, the minimum buried depth of the conduit should not be less than 2m. After the retaining piles are formed, the piles are tested and can enter the next process if qualified.

[0025] Preferably, the penetration speed is controlled according to the geological conditions during the drilling process: when drilling from a hard formation to a soft formation, the drilling speed is accelerated; when the soft formation becomes a hard formation, the drilling speed is slowed down; in formations that are prone to shrinkage, the number of hole sweeps should be increased to prevent shrinkage; high-speed drilling is used for hard plastic layers to improve drilling efficiency; and slow drilling is used for sandy layers, and the mud density and viscosity are appropriately increased.

[0026] Preferably, during the construction of the crown beam, firstly, the coordinates of the bored support piles are positioned, the eight corners of the crown beam of the support piles are determined, the crown beam contour line is laid out by spreading white lime, the pile head is sloped and excavated, and the excavation is carried out to 20 cm below the designed pile top elevation, and then the pile head is circumcised according to the designed elevation, the pile head is broken by a pneumatic pick, the pile head reinforcement is adjusted, and a 10 cm thick C15 concrete cushion layer is constructed in the range of the pile top crown beam to ensure that the pile top penetrates 10 cm into the crown beam, and then the corner points of the inner and outer walls of the crown beam are laid out, the template edge line is elasticated, and the reinforcement is tied and positioned, and then the reinforcement is processed according to the design drawings, and overlap welding is used when the reinforcement is extended, and then the template is installed;

[0027] During concrete pouring, the concrete must be fully vibrated during the pouring process. It is strictly forbidden to collide with the formwork during vibration to prevent the formwork from running. The formwork can be removed only after the strength of the concrete reaches 2.5Mpa. It is strictly forbidden to hit or pry hard during formwork removal to avoid damaging the edges and corners of the concrete. When removing the formwork, the bolts must be loosened manually and the tie rods must be pulled out. If they cannot be pulled out, they must be cut off with a grinding wheel saw blade. The removed formwork must be removed, cleaned, transported, and stacked at the same time. After the concrete strength of the crown beam reaches the design requirements, the slope on the outside of the crown beam should be backfilled.

[0028] Preferably, during the anchor cable construction process, the position of the anchor cable is accurately measured and placed on the slope surface according to the design drawings, and the anchor hole is constructed using the waterless dry drilling method. The design depth is drilled according to the design requirements. After the drilling reaches the design depth, the drilling cannot be stopped immediately, and steady drilling is required for 12 minutes. After the hole making is completed, the next process can be entered only after the supervisor has passed the acceptance inspection; the anchor cable is made of steel stranded wire or high-strength steel wire, and a guide cap should be installed at the bottom of the anchor cable before the anchor cable enters the soil, and the inside of the anchor hole should be grouted using suitable grouting equipment. The anchor hole grouting operation is generally preferably grouting by the bottom grouting method, and the grouting can be stopped only when the slurry overflows from the anchor hole or the exhaust pipe stops exhausting;

[0029] The anchor bar tensioning force should be applied in two tensioning operations. The first tensioning operation force is half of the designed tensioning force, and the second tensioning operation is until the tensioning force exceeds the set maximum tensioning load value. After the anchor bar is tensioned to the set maximum tensioning load value, the load should be maintained stable for 10 to 15 minutes, and then the load is unloaded for locking operation. After the anchor bar is locked, the remaining anchor bar must be cut mechanically. Arc burning is strictly prohibited, and 5 to 10 cm of exposed anchor bar should be left to prevent slipping. Finally, fill the gaps in the anchor plate and the anchor head with cement slurry, and seal the anchor according to the design requirements. It is advisable to seal it with concrete of not less than 20MPa.

[0030] Preferably, the anchor construction process includes:

[0031] Drill holes, set up simple steel pipe double-row scaffolding along the slope, lay bamboo springboards to form a working platform, and hammer anchor pipes into the soil or drill holes on the platform;

[0032] The rod body is made, and the anchor pipe is cut by a grinding wheel cutter. After the anchor pipe is processed in the processing plant, it is transported to the installation site. After the steel bar is processed, it is transported to the foot of the slope and transported for the second time by an excavator or loader.

[0033] Grouting and anchor construction adopts the method of first anchoring and then grouting, that is, the anchor pipe is first directly driven into the soil, and the grouting pipe is inserted to add grout to the hole until grout overflows from the hole mouth. The hole mouth of each hole is circulated and grouted every 1 to 2 hours to ensure its density;

[0034] The anchor rod is directly driven into the soil, using Φ22@1500 steel bars. A grouting hole is set every 500mm at the 1 / 2 section of the front end of the anchor rod, and a thin steel sheet or angle steel is welded to cover the hole to prevent it from being blocked by soil.

[0035] The anchor rods are aligned and welded to the reinforcing bars, locking bars, vertical grouting steel pipes, etc. on the slope surface;

[0036] The anchor rod grouting material uses P.042.5 cement paste with a cement water-cement ratio of 0.5-0.6. The cement paste must be mixed evenly and used immediately after mixing. The cement paste mixed once must be used up before initial setting. The anchor pipe uses pressure grouting with a grouting pressure of not less than 0.6MPa. The cement consumption of the anchor pipe is not less than 50Kg per linear meter on average.

[0037] The working surface of the soil nail wall is 500mm below each anchor pipe. When the surface is prone to collapse, it should be sprayed first and then drilled. The exposure time of the working surface after excavating each layer shall not exceed 8 hours. When excavating the soil nail wall, the slope footing should be measured layer by layer, and the slope rate should be strictly controlled according to the design. Reverse slope phenomenon is strictly prohibited.

[0038] Preferably, drainage facilities need to be set up during the construction of the deep foundation pit. This project adopts open ditch drainage, and a water cutoff is set on the top of the slope. Surface water is discharged into the foundation pit through the top of the slope, and groundwater in the slope is discharged through a drainage pipe;

[0039] The drainage pipe shall be made of PVC with a diameter of 50 mm. The length of the drainage pipe shall not be less than 1.0 m in the fill layer and not less than 0.5 m in other soil layers. The horizontal spacing shall not be greater than 1.50 m in the aquifer and not greater than 3.0 m in other layers. A drainage pipe shall be arranged at the bottom of the fill layer.

[0040] A hole must be left at the end of the drainage pipe that enters the soil, and a small pit must be dug in the soil and filled with crushed stone and other water filtering materials before burying to ensure the smooth flow of the drainage pipe; the drainage pipe mouth should be wrapped when spraying the surface concrete;

[0041] A drainage ditch 300m wide and 200m deep and a collection well 800x500x800 in size are set along the entire length of the slope foot, with a spacing of 20 to 30m.

[0042] A sedimentation tank should be set up between the foundation pit drainage facilities and the municipal pipe network interface; drainage ditches, water collection wells and sedimentation tanks should be unobstructed and silt should be cleared at any time when in use;

[0043] When unknown water sources such as leaking abandoned underground pipes are found on site, they must be diverted away or cut off outside the foundation pit.

[0044] Preferably, the main contents of the special monitoring of the construction site of the deep foundation pit construction include: surface settlement, horizontal displacement, vertical displacement, deformation of surrounding buildings and underground pipelines, groundwater level and soil pressure monitoring.

[0045] A combined foundation pit support device for coastal areas, which is used to implement the above-mentioned combined foundation pit support method for coastal areas. The combined foundation pit support device for coastal areas includes lower cantilever cast-in-place piles, high-pressure rotary jet piles, dewatering wells, bottom cast-in-place piles, anchor cables and anchor rods. The bearing strength of the foundation pit is ensured by the lower cantilever cast-in-place piles, high-pressure rotary jet piles and bottom cast-in-place piles, and the overall strength of the support device is ensured by auxiliary traction of the anchor cables and anchor rods.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] Through the construction of fine sand soil reduction; retaining pile construction; water curtain and water well construction; first layer of fine sand excavation, reinforcement insertion, shotcrete support construction; second layer of fine sand excavation, shotcrete support construction; crown beam groove excavation, crown beam construction; first layer of silty clay excavation, shotcrete support; pile body anchor cable, waist beam construction; second layer of silty clay excavation, shotcrete support; basalt blasting, excavation, edge Slope repair; basalt anchor construction within the range of -3.100 to 5.900; basalt blasting, excavation and slope repair within the range of -5.900 to 9.200; basalt anchor construction and shotcrete support within the range of -5.900 to 9.200; foundation pit bottoming and main structure construction and other processes are used to construct the deep foundation pit of the water intake pool and pump room, thereby effectively avoiding the problem of long construction period and effectively improving the safety of the construction process. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is the construction flow chart of the present invention;

[0049] Figure 2 This is a schematic diagram of the surface fine sand soil reduction of the present invention;

[0050] Figure 3 Construction drawings for retaining piles and water-stop curtains;

[0051] Figure 4 This is a schematic diagram of excavation of the first layer of fine sand;

[0052] Figure 5 This is a schematic diagram of the excavation of the second layer of fine sand and the crown beam;

[0053] Figure 6 This is a schematic diagram of the excavation of the first layer of silty clay;

[0054] Figure 7 This is a schematic diagram of the construction of pile anchor cables and waist beams;

[0055] Figure 8 This is a schematic diagram of the excavation of the second layer of silty clay;

[0056] Fig. 9This is a schematic diagram of blasting, excavation and slope modification of basalt above the bottom plate;

[0057] Fig.10 This is a schematic diagram of basalt anchor and shotcrete construction;

[0058] Fig.11 This is a schematic diagram of blasting, excavation and slope modification of weathered basalt in the sinking section;

[0059] Fig.12 This is a schematic diagram of the weathered basalt anchor and shotcrete construction in the sinking section;

[0060] Fig.13 This is a schematic diagram of the anti-floating anchor construction;

[0061] Fig.14 This is a schematic diagram of the main structure construction;

[0062] Fig.15 This is a schematic diagram of stone excavation;

[0063] Fig.16 It is the construction drawing of the retaining pile of the present invention.

[0064] In the figure: fine sand 1, silty silty clay 2, residual soil 3, strongly weathered basalt 4, moderately weathered basalt 5, lower cantilever cast-in-place piles 6, high-pressure jet jet piles 7, drainage well 8, bottom cast-in-place piles 9, anchor cables 10, and anchor rods 11. DETAILED DESCRIPTION

[0065] In order to make the purpose and technical solution of the present invention clearly and completely described, and the advantages more clearly understood, the embodiments of the present invention are further described in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are part of the embodiments of the present invention, rather than all of the embodiments, and are only used to explain the embodiments of the present invention, and are not used to limit 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.

[0066] In the description of the present invention, it should be noted that the terms "center", "middle", "upper", "lower", "left", "right", "inner", "outer", "top", "bottom", "side", "vertical", "horizontal" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "one", "first", "second", "third", "fourth", "fifth", "sixth" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0067] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0068] For the purpose of simplicity and illustration, the principles of the embodiments are mainly described by reference to examples. In the following description, many specific details are proposed to provide a thorough understanding of the embodiments. However, it is obvious that for those of ordinary skill in the art, these embodiments may not be limited to these specific details in practice. In some instances, known methods and structures are not described in detail to avoid making these embodiments unnecessarily difficult to understand. In addition, all embodiments can be used in combination with each other.

[0069] See also Figure 1-16 , the present invention provides the following preferred embodiments:

[0070] Embodiment 1

[0071] Combined foundation pit support method and device in coastal areas, the combined foundation pit support method in coastal areas includes fine sand soil reduction construction, the surrounding structure is constructed after the original ground is reduced to 4.000m, the slope of one layer is adjusted to 1:1.5, and the fine sand 1 grouting anchor pipe is cancelled except for one side of the substation. When the pile diameter is increased, the silty silty clay 2 between the piles cannot be stabilized, so the original pile diameter and the high-pressure rotary jet pile 7 between the piles are maintained for soil reinforcement. After the rock surface is excavated, it is determined whether the rock anchor can be cancelled according to the integrity of the rock mass;

[0072] Construction of retaining piles;

[0073] Water curtain and dewatering well construction, soil nail wall is used on the upper part of the foundation pit, cantilever cast-in-place pile 6 is used on the lower part, and earthwork platform support type is reserved in front of the pile. Upper soil nail wall is used for local deepening, bottom cast-in-place pile 9 and anchor cable are used on the lower part, and earthwork platform support type is reserved in front of the pile. Water-stop curtain cuts off the groundwater connection inside and outside the pit, and drainage well 8 and water collection open drainage are set at the platform;

[0074] Excavation, reinforcement and shotcrete support construction of the first layer of fine sand;

[0075] Excavation of the second layer of fine sand and construction of shotcrete support;

[0076] Excavation of crown beam trench and construction of crown beam;

[0077] The first layer of silty clay is excavated and supported by shotcrete anchors;

[0078] Construction of pile anchor cables and waist beams;

[0079] The second layer of silty clay is excavated and supported by shotcrete anchors;

[0080] Basalt blasting, excavation and slope repair within the elevation range of -3.100 to 5.900;

[0081] Basalt anchor construction within the elevation range of -3.100 to 5.900;

[0082] Basalt blasting, excavation and slope repair within the elevation range of -5.900 to 9.200;

[0083] Basalt anchor construction and shotcrete support within the elevation of -5.900 to 9.200 are carried out by excavators at the bottom of the pit and blasting and drilling machinery, and then hoisted out of the foundation pit by crane;

[0084] The foundation pit is closed and the anti-floating anchor rods 11 under the bottom plate are constructed simultaneously;

[0085] The main structure construction is carried out in two sections from north to south, with four layers of vertical concrete pouring. After the water test of the water intake pool is completed and the external anti-corrosion construction of the underground part is completed, the foundation pit is backfilled;

[0086] The groundwater level at the location of the water intake pool and pump house is 3.8m, and the strata include plain fill (0.5m thick), fine sand 1 (5m thick), silty silty clay 2 (3m thick), residual soil 3 (1m thick), strongly weathered basalt 4 (1m thick), and moderately weathered basalt 5 (3 to 6m into the rock).

[0087] Preferably, during the basalt anchor construction and shotcrete support within the elevation of -5.900 to 9.200, three 220-type excavators are used to pour soil in steps during excavation. The first-level excavator is at the top of the foundation pit, and the soil pouring platform is set on the top of the crown beam; the second-level excavator is located at the bottom of the cantilever of the retaining pile, and the soil pouring platform is set at the bottom of the base plate; the third-level excavator is set at the bottom of the sinking section.

[0088] Preferably, in the construction process of the retaining pile, first according to the previous construction experience and the investigation of similar surrounding projects, two 360-type rotary drilling drills are selected for the construction of the retaining pile, and then the site is leveled. After that, the technicians use instruments to measure and lay out the pile position, and then lay out and locate the position on site, dig out the surface soil of the pile hole according to the pile position, and bury the casing. 1 to 2 slurry holes are set on the upper part of the casing. The casing is used to fix the position of the pile hole, protect the hole mouth, prevent collapse, and guide the direction of the drill bit when drilling. After the casing is buried, the pile position is checked and laid out again. After ensuring that it is correct, the drilling rig is in place, and then the drill bucket is first put on the ground when drilling, and the zeroing operation is performed through the zeroing button on the display, and the original position of the drill bit of the drilling rig is recorded. At this time, the display shows the bar column and number of the current position of the drilling hole. The operator needs to monitor the actual working position of the drilling hole, the position of each footage and the hole depth position through the display, so as to operate the drilling operation, and clean the hole after the drilling is completed. After the hole cleaning is completed, the hole is inspected;

[0089] Then, the steel cage is made. The steel cage is made in sections, and a butt joint structure is reserved at the end of the steel cage. To control the thickness of the protective layer, a positioning block is set every three meters on the main reinforcement of the steel cage, and four positioning blocks are symmetrically arranged around the steel cage. During the welding process, slag should be removed in time. The main reinforcement of the steel cage is connected according to the design requirements. The spacing between the main reinforcement joints is ≥35d, and the joints on the same section are not more than 50%. After the steel cage is in place, the grouting pipe is placed in the pile hole, and then grouting is carried out;

[0090] Commercial concrete is used in the grouting process, the slump should be controlled at 200±20mm, the concrete should be poured continuously, and the pile pouring time should be ≤8 hours. During the concrete pouring process, the minimum buried depth of the conduit should not be less than 2m. After the retaining piles are formed, the piles are tested and can enter the next process if qualified.

[0091] Preferably, the penetration speed is controlled according to the geological conditions during the drilling process: when drilling from a hard formation to a soft formation, the drilling speed is accelerated; when the soft formation becomes a hard formation, the drilling speed is slowed down; in formations that are prone to shrinkage, the number of hole sweeps should be increased to prevent shrinkage; high-speed drilling is used for hard plastic layers to improve drilling efficiency; and slow drilling is used for sandy layers, and the mud density and viscosity are appropriately increased.

[0092] Preferably, during the crown beam construction process, the coordinates of the bored support piles are first positioned to determine the eight corners of the crown beam of the support piles, white lime is spread to lay out the crown beam contour line, the pile head is sloped and excavated, and the excavation is carried out to 20 cm below the designed pile top elevation. The pile head is then circumcised according to the designed elevation, and a pneumatic pick is used to break the pile head. The steel bars of the pile head are adjusted, and a 10 cm thick C15 concrete cushion layer is constructed in the crown beam range of the pile top to ensure that the pile top penetrates 10 cm into the crown beam. The corner points of the inner and outer walls of the crown beam are then laid out, the template edge lines are elasticated, the steel bars are tied and positioned, and then the design drawings are followed. Paper is used for steel bar processing. When the steel bar is extended, lap welding is used. The welding rod is E43 or E50. The lap length is not less than 10d (d is the diameter of the steel bar) for single-sided welding and not less than 5d (d is the diameter of the steel bar) for double-sided welding. The weld width is not less than 0.8d and not less than 8mm (d is the diameter of the steel bar). The weld thickness is not less than 0.3d and not less than 4mm (d is the diameter of the steel bar). Then the formwork is installed. The crown beam is constructed with steel formwork. The thickness of the formwork panel is 12mm. A12mm screws are used for tensioning. Double-jointed □48cm steel pipes are used as back ribs.

[0093] During concrete pouring, the concrete must be fully vibrated during the pouring process. It is strictly forbidden to collide with the formwork during vibration to prevent the formwork from running. The formwork can be removed only after the strength of the concrete reaches 2.5Mpa. It is strictly forbidden to hit or pry hard during formwork removal to avoid damaging the edges and corners of the concrete. When removing the formwork, the bolts must be loosened manually and the tie rods must be pulled out. If they cannot be pulled out, they must be cut off with a grinding wheel saw blade. The removed formwork must be removed, cleaned, transported, and stacked at the same time. After the concrete strength of the crown beam reaches the design requirements, the slope on the outside of the crown beam should be backfilled.

[0094] Preferably, during the anchor cable construction process, the position of the anchor cable 10 is accurately measured and placed on the slope surface according to the design drawings, and the anchor hole construction is carried out using the waterless dry drilling method. The design depth is drilled according to the design requirements. After the drilling reaches the design depth, the drilling cannot be stopped immediately, and steady drilling is required for 12 minutes. After the hole making is completed, the next process can be entered only after the supervisor has passed the acceptance inspection; the anchor cable 10 uses a steel stranded wire or a high-strength steel wire. Before the anchor cable 10 enters the soil, a guide cap should be installed at the bottom of the anchor cable 10, and grouting should be carried out inside the anchor hole using suitable grouting equipment. The anchor hole grouting operation is generally preferably grouting by the bottom grouting method, and the grouting can be stopped only when the slurry overflows from the anchor hole or the exhaust pipe stops exhausting;

[0095] The anchor bar tensioning force should be applied in two tensioning operations. The first tensioning operation force is half of the designed tensioning force, and the second tensioning operation is until the tensioning force exceeds the set maximum tensioning load value. After the anchor bar is tensioned to the set maximum tensioning load value, the load should be maintained stable for 10 to 15 minutes, and then the load is unloaded for locking operation. After the anchor bar is locked, the remaining anchor bar must be cut mechanically. Arc burning is strictly prohibited, and 5 to 10 cm of exposed anchor bar should be left to prevent slipping. Finally, fill the gaps in the anchor plate and the anchor head with cement slurry, and seal the anchor according to the design requirements. It is advisable to seal it with concrete of not less than 20MPa.

[0096] Preferably, the anchor construction process includes:

[0097] Drill holes, set up simple steel pipe double-row scaffolding along the slope, lay bamboo springboards to form a working platform, and hammer anchor pipes into the soil or drill holes on the platform;

[0098] The rod body is made, and the anchor pipe is cut by a grinding wheel cutter. After the anchor pipe is processed in the processing plant, it is transported to the installation site. After the steel bar is processed, it is transported to the foot of the slope and transported for the second time by an excavator or loader.

[0099] Grouting and anchor construction adopts the method of first anchoring and then grouting, that is, the anchor pipe is first directly driven into the soil, and the grouting pipe is inserted to add grout to the hole until grout overflows from the hole mouth. The hole mouth of each hole is circulated and grouted every 1 to 2 hours to ensure its density;

[0100] The anchor rod is directly driven into the soil, using Φ22@1500 steel bars. A grouting hole is set every 500mm at the front 1 / 2 section of the anchor rod 11, and a thin steel sheet or angle steel is welded to cover the hole to prevent it from being blocked by soil.

[0101] The anchor rods 11 are arranged in an aligned manner and are welded to the reinforcing ribs, locking ribs, vertical grouting steel pipes, etc. at the slope surface;

[0102] The grouting material of anchor rod 11 adopts P.042.5 cement paste, the cement water-cement ratio is 0.5-0.6, the cement paste must be mixed evenly and used immediately after mixing, and the cement paste mixed once must be used up before the initial setting; the anchor pipe adopts pressure grouting, the grouting pressure is not less than 0.6MPa, and the cement consumption of the anchor pipe is not less than 50Kg per linear meter on average;

[0103] The working surface of the soil nail wall is 500mm below each anchor pipe. When the surface is prone to collapse, it should be sprayed first and then drilled. The exposure time of the working surface after excavating each layer shall not exceed 8 hours. When excavating the soil nail wall, the slope footing should be measured layer by layer, and the slope rate should be strictly controlled according to the design. Reverse slope phenomenon is strictly prohibited.

[0104] Preferably, drainage facilities need to be set up during the construction of the deep foundation pit. This project adopts open ditch drainage, and a water cutoff is set on the top of the slope. Surface water is discharged into the foundation pit through the top of the slope, and groundwater in the slope is discharged through a drainage pipe;

[0105] The drainage pipe shall be made of PVC with a diameter of 50 mm. The length of the drainage pipe shall not be less than 1.0 m in the fill layer and not less than 0.5 m in other soil layers. The horizontal spacing shall not be greater than 1.50 m in the aquifer and not greater than 3.0 m in other layers. A drainage pipe shall be arranged at the bottom of the fill layer.

[0106] A hole must be left at the end of the drainage pipe that enters the soil, and a small pit must be dug in the soil and filled with crushed stone and other water filtering materials before burying to ensure the smooth flow of the drainage pipe; the drainage pipe mouth should be wrapped when spraying the surface concrete;

[0107] A drainage ditch 300m wide and 200m deep and a collection well 800x500x800 in size are set along the entire length of the slope foot, with a spacing of 20 to 30m.

[0108] A sedimentation tank should be set up between the foundation pit drainage facilities and the municipal pipe network interface; drainage ditches, water collection wells and sedimentation tanks should be unobstructed and silt should be cleared at any time when in use;

[0109] When unknown water sources such as leaking abandoned underground pipes are found on site, they must be diverted away or cut off outside the foundation pit.

[0110] Preferably, the main contents of the special monitoring of the construction site of the deep foundation pit construction include: surface settlement, horizontal displacement, vertical displacement, deformation of surrounding buildings and underground pipelines, groundwater level and soil pressure monitoring.

[0111] A combined foundation pit support device for coastal areas, which is used to implement the above-mentioned combined foundation pit support method for coastal areas. The combined foundation pit support device for coastal areas includes lower cantilever cast-in-place piles 6, high-pressure rotary jet piles 7, dewatering wells 8, bottom cast-in-place piles 9, anchor cables 10 and anchor rods 11. The bearing strength of the foundation pit is ensured by the lower cantilever cast-in-place piles 6, high-pressure rotary jet piles 7 and bottom cast-in-place piles 9, and the overall strength of the support device is ensured by auxiliary traction of the anchor cables 10 and the anchor rods 11.

[0112] Although the above describes the illustrative specific implementation methods of the present application so that technicians in this technical field can understand the present application, the present application is not limited to the scope of the specific implementation methods. For ordinary technicians in this technical field, as long as various changes are within the spirit and scope of the present application defined and determined by the attached claims, all application creations using the concept of the present application are protected.

Claims

1. Combined foundation pit support method in coastal areas, characterized by: The combined foundation pit support method in coastal areas includes: Fine sand soil reduction construction; Construction of retaining piles; Water curtain and dewatering well construction, soil nail wall is used on the upper part of the foundation pit, cantilever cast-in-place piles are used on the lower part, and an earthwork platform is reserved in front of the piles for support. Upper soil nail wall is used for local deepening, and bottom cast-in-place piles and anchor cables are used on the lower part. An earthwork platform is reserved in front of the piles for support. The water-stop curtain cuts off the connection between the groundwater inside and outside the pit, and drainage wells and open drainage for water collection are set up on the platform; Excavation, reinforcement and shotcrete support construction of the first layer of fine sand; Excavation of the second layer of fine sand and construction of shotcrete support; Excavation of crown beam trench and construction of crown beam; The first layer of silty clay is excavated and supported by shotcrete anchors; Construction of pile anchor cables and waist beams; The second layer of silty clay is excavated and supported by shotcrete anchors; Basalt blasting, excavation and slope repair within the elevation range of -3.100 to 5.900; Basalt anchor construction within the elevation range of -3.100 to 5.900; Basalt blasting, excavation and slope repair within the elevation range of -5.900 to 9.200; Basalt anchor construction and shotcrete support within the elevation of -5.900 to 9.200 are carried out by excavators at the bottom of the pit and blasting and drilling machinery, and then hoisted out of the foundation pit by crane; The foundation pit is closed and the anti-floating anchor rods under the bottom plate are constructed simultaneously; The main structure construction is carried out in two sections from north to south, and the concrete is poured vertically in four layers. After the water test of the water intake pool and the external anti-corrosion construction of the underground part are completed, the foundation pit is backfilled.

2. The combined foundation pit support method in coastal areas according to claim 1 is characterized in that: During the basalt anchor construction and shotcrete support within the elevation of -5.900 to 9.200, three 220-type excavators were used to pour soil in steps during excavation. The first-level excavator was at the top of the foundation pit, and the soil pouring platform was set on the top of the crown beam; the second-level excavator was located at the bottom of the cantilever of the retaining pile, and the soil pouring platform was set at the bottom of the base plate; the third-level excavator was set at the bottom of the sinking section.

3. The combined foundation pit support method in coastal areas according to claim 1 is characterized in that: During the construction of the retaining piles, two 360-degree rotary drilling rigs are used for the construction of the retaining piles based on previous construction experience and investigations of similar surrounding projects. The site is then leveled, and then the technicians use instruments to measure and lay out the pile positions. Then, they lay out and locate the pile positions on site, remove the topsoil of the pile holes according to the pile positions, and bury the casings. After the casings are buried, the pile positions are checked and laid out again. After ensuring that they are correct, the drilling rig is in place. When drilling, the drill bucket is first placed on the ground, and the zeroing operation is performed through the zeroing button on the display. The original position of the drill bit is recorded. At this time, the display shows the bar column and number of the current position of the drilling hole. The operator needs to monitor the actual working position of the drilling hole, the position of each advance, and the position of the hole depth through the display, so as to operate the drilling operation. After the drilling is completed, the hole is cleaned. After the hole is cleaned, the hole is inspected. Then, the steel cage is made. The steel cage is made in sections, and a butt joint structure is reserved at the end of the steel cage. To control the thickness of the protective layer, a positioning block is set every three meters on the main reinforcement of the steel cage, and four positioning blocks are symmetrically arranged around the steel cage. During the welding process, slag should be removed in time. The main reinforcement of the steel cage is connected according to the design requirements. The spacing between the main reinforcement joints is ≥35d, and the joints on the same section are not more than 50%. After the steel cage is in place, the grouting pipe is placed in the pile hole, and then grouting is carried out; Commercial concrete is used in the grouting process, the slump should be controlled at 200±20mm, the concrete should be poured continuously, and the pile pouring time should be ≤8 hours. During the concrete pouring process, the minimum buried depth of the conduit should not be less than 2m. After the retaining piles are formed, the piles are tested and can enter the next process if qualified.

4. The combined foundation pit support method in coastal areas according to claim 3 is characterized in that: During the drilling process, the penetration speed is controlled according to the geological conditions: when drilling from a hard formation to a soft formation, the drilling speed is accelerated; when the soft formation becomes a hard formation, the drilling speed is slowed down; in the formation that is easy to shrink, the number of hole sweeps should be increased to prevent the shrinkage; the hard plastic layer is drilled at a high speed to improve the drilling efficiency; the sand layer is drilled at a low speed and the mud density and viscosity are appropriately increased.

5. The combined foundation pit support method in coastal areas according to claim 3 is characterized in that: During the crown beam construction process, first locate the eight corners of the crown beam of the support pile according to the coordinates of the bored support pile, spread white lime to lay out the crown beam contour line, and carry out slope excavation of the pile head, excavate to 20 cm below the designed pile top elevation, then perform circumcision on the pile head according to the designed elevation, use a pneumatic pick to break the pile head, adjust the pile head steel bars, construct a 10 cm thick C15 concrete cushion layer in the crown beam range of the pile top to ensure that the pile top penetrates 10 cm into the crown beam, then lay out the corner points of the inner and outer walls of the crown beam, perform template edge line springing, and steel bar binding positioning, then carry out steel bar processing according to the design drawings, use lap welding when extending the steel bars, and then install the template; During concrete pouring, the concrete must be fully vibrated during the pouring process. It is strictly forbidden to collide with the formwork during vibration to prevent the formwork from running. The formwork can be removed only after the strength of the concrete reaches 2.5Mpa. It is strictly forbidden to hit or pry hard during formwork removal to avoid damaging the edges and corners of the concrete. When removing the formwork, the bolts must be loosened manually and the tie rods must be pulled out. If they cannot be pulled out, they must be cut off with a grinding wheel saw blade. The removed formwork must be removed, cleaned, transported, and stacked at the same time. After the concrete strength of the crown beam reaches the design requirements, the slope on the outside of the crown beam should be backfilled.

6. The combined foundation pit support method in coastal areas according to claim 5 is characterized in that: During the anchor cable construction process, the position of the anchor cable is accurately measured and placed on the slope according to the design drawings, and the anchor hole is constructed using the waterless dry drilling method. The design depth is drilled according to the design requirements. After the drilling reaches the design depth, the drilling cannot be stopped immediately, and steady drilling is required for 12 minutes. After the hole making is completed, the next process can be entered only after the supervisor has passed the acceptance inspection; the anchor cable uses a steel stranded wire or a high-strength steel wire. Before the anchor cable enters the soil, a guide cap should be installed at the bottom of the anchor cable, and the inside of the anchor hole should be grouted using suitable grouting equipment. The anchor hole grouting operation is generally preferably grouting by the bottom grouting method until the grouting overflows from the anchor hole or the exhaust pipe stops exhausting. The anchor bar tensioning force should be applied in two tensioning operations. The first tensioning operation force is half of the designed tensioning force, and the second tensioning operation is until the tensioning force exceeds the set maximum tensioning load value. After the anchor bar is tensioned to the set maximum tensioning load value, the load should be maintained stable for 10 to 15 minutes, and then the load is unloaded for locking operation. After the anchor bar is locked, the remaining anchor bar must be cut mechanically. Arc burning is strictly prohibited, and 5 to 10 cm of exposed anchor bar should be left to prevent slipping. Finally, fill the gaps in the anchor plate and the anchor head with cement slurry, and seal the anchor according to the design requirements. It is advisable to seal it with concrete of not less than 20MPa.

7. The combined foundation pit support method in coastal areas according to claim 6 is characterized in that: The anchor construction process includes: Drill holes, set up simple steel pipe double-row scaffolding along the slope, lay bamboo springboards to form a working platform, and hammer anchor pipes into the soil or drill holes on the platform; The rod body is made, and the anchor pipe is cut by a grinding wheel cutter. After the anchor pipe is processed in the processing plant, it is transported to the installation site. After the steel bar is processed, it is transported to the foot of the slope and transported for the second time by an excavator or loader. Grouting and anchor construction adopts the method of first anchoring and then grouting, that is, the anchor pipe is first directly driven into the soil, and the grouting pipe is inserted to add grout to the hole until grout overflows from the hole mouth. The hole mouth of each hole is circulated and grouted every 1 to 2 hours to ensure its density; The anchor rod is directly driven into the soil, using Φ22@1500 steel bars. A grouting hole is set every 500mm at the 1 / 2 section of the front end of the anchor rod, and a thin steel sheet or angle steel is welded to cover the hole to prevent it from being blocked by soil. The anchor rods are aligned and welded to the reinforcing bars, locking bars, vertical grouting steel pipes, etc. on the slope surface; The anchor rod grouting material uses P.042.5 cement paste with a cement water-cement ratio of 0.5-0.

6. The cement paste must be mixed evenly and used immediately after mixing. The cement paste mixed once must be used up before initial setting. The anchor pipe uses pressure grouting with a grouting pressure of not less than 0.6MPa. The cement consumption of the anchor pipe is not less than 50Kg per linear meter on average. The working surface of the soil nail wall is 500mm below each anchor pipe. When the surface is prone to collapse, it should be sprayed first and then drilled. The exposure time of the working surface after excavating each layer shall not exceed 8 hours. When excavating the soil nail wall, the slope footing should be measured layer by layer, and the slope rate should be strictly controlled according to the design. Reverse slope phenomenon is strictly prohibited.

8. The combined foundation pit support method in coastal areas according to claim 7 is characterized in that: During the construction of the deep foundation pit, drainage facilities need to be set up. This project adopts open ditch drainage, and a water cut-off is set on the top of the slope. Surface water is discharged into the foundation pit through the top of the slope, and groundwater in the slope is discharged through the drainage pipe; The drainage pipe shall be made of PVC with a diameter of 50 mm. The length of the drainage pipe shall not be less than 1.0 m in the fill layer and not less than 0.5 m in other soil layers. The horizontal spacing shall not be greater than 1.50 m in the aquifer and not greater than 3.0 m in other layers. A drainage pipe shall be arranged at the bottom of the fill layer. A hole must be left at the end of the drainage pipe that enters the soil, and a small pit must be dug in the soil and filled with crushed stone and other water filtering materials before burying to ensure the smooth flow of the drainage pipe; the drainage pipe mouth should be wrapped when spraying the surface concrete; A drainage ditch 300m wide and 200m deep and a collection well 800x500x800 in size are set along the entire length of the slope foot, with a spacing of 20 to 30m. A sedimentation tank should be set up between the foundation pit drainage facilities and the municipal pipe network interface; drainage ditches, water collection wells and sedimentation tanks should be unobstructed and silt should be cleared at any time when in use; When unknown water sources such as leaking abandoned underground pipes are found on site, they must be diverted away or cut off outside the foundation pit.

9. The combined foundation pit support method in coastal areas according to claim 8, characterized in that: The main contents of the special monitoring of the construction site of the deep foundation pit construction include: surface settlement, horizontal displacement, vertical displacement, deformation of surrounding buildings and underground pipelines, groundwater level and soil pressure monitoring.

10. A combined foundation pit support device for coastal areas, characterized in that: The combined foundation pit support device in coastal areas is used to implement any one of the combined foundation pit support methods in coastal areas of claims 7-9. The combined foundation pit support device in coastal areas includes lower cantilever cast-in-place piles 6, high-pressure rotary jet piles 7, dewatering wells 8, bottom cast-in-place piles 9, anchor cables 10 and anchor rods 11. The bearing strength of the foundation pit is ensured by the lower cantilever cast-in-place piles 6, high-pressure rotary jet piles 7 and bottom cast-in-place piles 9, and the overall strength of the support device is ensured by auxiliary traction of the anchor cables 10 and the anchor rods 11.

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