Double-row steel sheet pile cofferdam construction method

Abstract

The invention discloses a double-row steel sheet pile cofferdam construction method, which comprises the following steps of: before construction, measuring the original riverbed elevation of a cofferdam piling area, organizing steel pipes to enter a site according to a cross-section diagram and a construction sequence of a cofferdam, timely removing and recording if stone blocks and the like at the river bottom are measured in the measurement process, and before construction, checking and maintaining all mechanical equipment, so that the construction efficiency is improved. After entering the field, the steel pipes are stacked according to specifications, varieties and classifications, before pile conveying, the models and the number of the steel pipes used during construction are determined, and the steel pipes are arranged strictly according to the designed section. Compared with a construction scheme of adopting a Larsen steel sheet pile cofferdam and a temporary construction platform, the construction cost, the rental cost, the earthwork transportation cost, the earthwork compaction cost, the earthwork filling excavation filling cost and the like of temporary facilities can be saved, building construction is carried out in a water area needing a large area, the construction period is long, and the construction cost is low. The method is more economical and reasonable when being used for constructing structures in water under the conditions of high water level and the like.

Description

Technical Field

[0001] The invention relates to the technical field of cofferdam construction, and specifically relates to a double-row steel sheet pile cofferdam construction method. Background Art

[0002] A cofferdam is a temporary enclosure structure used to build permanent structures in hydraulic structures. Its function is to prevent water and soil from entering the construction site of the building, so that the water in the cofferdam can be drained, the foundation pit can be excavated, and the building can be built. In addition to being part of the formal building, the cofferdam is usually removed after use, and the height of the cofferdam is higher than the maximum water level that may occur during construction. The cofferdam method has the advantages of fast construction speed, safety, high efficiency, and low impact on the environment. It is widely used in construction fields such as water conservancy projects and underwater construction.

[0003] If underwater structures with a long construction period are to be constructed in a large area of ​​water with a high water level, the traditional Larsen steel sheet pile cofferdam plus temporary construction platform method will be difficult to construct, costly, have a great impact on the water environment, and pose a high risk to construction safety.

[0004] The geological conditions at the bottom of the water area may be complex and changeable, such as soft soil, silt, rock, etc., which will increase the difficulty of driving steel sheet piles. High water levels and large areas of water are usually accompanied by strong currents and waves. These natural conditions will increase the difficulty of construction and affect the stability of steel sheet piles and the construction of construction platforms. The structural stability of steel sheet pile cofferdams and temporary construction platforms is affected by natural conditions such as water flow and waves, and there is a risk of structural instability and collapse. After the construction is completed, the removal of steel sheet pile cofferdams and temporary construction platforms is complicated, especially in deep water areas, where removal is difficult and there are safety risks.

[0005] A double-row steel pipe pile cofferdam is used as a construction method for temporary support of underwater piers to avoid the construction of a large number of temporary structures in the water and change the original water operation to land construction. During the construction process, the deformation and water leakage of the steel pipe pile cofferdam are well controlled. Summary of the invention

[0006] The object of the present invention is to provide a double-row steel sheet pile cofferdam construction method to solve the problems raised in the above background technology.

[0007] To achieve the above purpose, the present invention provides the following technical solutions: a double-row steel sheet pile cofferdam construction method, before construction, the original riverbed elevation of the cofferdam piling area is measured, and steel pipes are organized to enter the site according to the cross-sectional diagram of the cofferdam and the construction sequence. If during the measurement process, it is determined that there are rocks on the riverbed, they must be removed in time and records are kept. Before construction, all mechanical equipment is inspected and maintained to ensure the normal operation of the mechanical equipment. After the steel pipes enter the site, they should be classified and stacked according to specifications and varieties. Before transporting the piles, the steel pipe models and quantities used in the construction are clarified, and the steel pipes are arranged strictly according to the designed sections.

[0008] S1 Lofting Positioning

[0009] Use GPS to determine the specific location of the cofferdam, set up control points on the river bank, drive steel pipes into the water at intervals of 50 to 60 meters as temporary positioning, and mark the elevation position on the steel pipe. The principle of advancing the positioning work is basically consistent with the construction sequence of steel pipe piles. The double-row steel pipe pile cofferdam ensures simultaneous driving. After the two piles of the same section are completed synchronously, the next section will be operated. The overall piling sequence of the cofferdam is the main cofferdam on the east side first, and then the water interception cofferdam on the west side. The construction sequence of the main cofferdam is: from west to east from the upstream to the downstream direction of the river at pier 4#, and the same process is used at pier 5#;

[0010] S2 Overwater Steel Pipe Pile Driving

[0011] When driving the steel pipe piles, they are driven from upstream to downstream and gradually closed. Try not to interrupt them to avoid excessive mud affecting the strength of the cofferdam. After determining the overall layout of the cofferdam, the auxiliary guide piles and corner piles are driven first. According to the position of the first steel pipe pile, the auxiliary guide piles are staked out: the auxiliary guide piles are hoisted with the clamp of the electric vibrating pile hammer of the pile driving ship, and two auxiliary guide piles are driven into the soil at the designed distance at the staked position. The depth of the soil is 7m or more. After the auxiliary guide piles are driven, guide devices are set on both sides of the auxiliary piles. The guide devices are composed of two thin steel wire ropes. Guide wire ropes are set on both sides of the three guide piles to perform linear control of the steel pipe pile driving.

[0012] After the auxiliary guide piles are driven, a directional spacing guide frame is set. The guide frame is welded with steel sections and has a height of 2m. The first steel pipe pile is clamped and lifted by the clamp of the driving and pulling machine, and the guide frame is inserted. The vibrating pile hammer is started and driven into the ground. The top surface elevation is controlled at +2.5m. After the first steel pipe pile is driven, the guide frame is dismantled and the auxiliary guide piles are pulled out.

[0013] After the layout, reset the direction spacing guide frame, lift the second steel pipe pile in the same lifting method as the first steel pipe pile, insert the guide frame, start the vibrating pile hammer, drive it into the ground, and control the top elevation at +2.5m to complete the second steel pipe pile driving construction. After the second steel pipe pile construction is completed, remove the temporary guide frame, and drive the remaining steel pipe piles according to the construction method of the second pile until all the steel pipe piles are driven. During the construction process, pay attention to the position of the corner piles, and the spacing cannot exceed the designed spacing;

[0014] When there is a concrete or mortar-laid block stone revetment on the river bank side, the cofferdam is connected to the revetment closure. At the upstream end of the outer side, 1.636m near the front edge of the retaining wall, a single row of steel pipe piles of the same specification is extended in parallel, with a spacing of 0.619m and a total length of about 10m. Geogrids and waterproof geotextiles are hung inside and then filled with soil to ensure that there is no leakage under the old revetment. When there is an earth revetment on the river bank side, the steel pipe piles are directly driven to the bank edge for natural connection;

[0015] S3 Geogrid and Geotextile Installation

[0016] After the steel pipe piles are driven for a certain distance, each row of piles exposed to the water All steel pipe piles are connected with 20# channel steel purlins. The channel steel and steel pipe piles are fixed by welding to ensure that each pile is firmly welded to the channel steel purlin and the single row of piles is connected as a whole.

[0017] After a certain number of steel pipe piles are constructed, geogrids and waterproof geotextiles can be hung. The width of the geotextile is 4m and the length is 50m, and the horizontal overlap width between each piece is 100cm. During construction, small stones are tied with lead wire at the bottom to ensure that the geomembrane does not fold and hangs vertically. The top of the geotextile is firmly tied to the steel pipe piles with lead wire. When filling the cofferdam, check the condition of the waterproof geotextile at any time and correct any abnormalities in time.

[0018] Use between two rows of steel pipe piles The steel wire rope wraps and tightens the steel pipe and two surrounding purlins (it can also be used The screw rod is used for pulling reinforcement) to form a stable skeleton structure for the whole dam body. When the wire rope is wound, a tensioner is needed to tighten the wire rope. After tightening, a U-shaped fixing card is installed at the cross node of the wire rope to prevent the tightened wire rope from loosening;

[0019] S4 Weir fill

[0020] After the steel pipe piles and waterproof geotextiles are constructed, the soil can be filled. The filling soil is made of cohesive soil with poor water permeability. The earth is dug into the steel pipe pile cofferdam by an excavator in the earth-pile area of ​​the bank at both ends of the cofferdam. The grab bucket must not collide with the steel pipe piles when putting the earth into the cofferdam.

[0021] The filling earthwork is transported to the vicinity of the cofferdam by ship and filled with earth by excavators. The cofferdam soil material is clay and silt filling is prohibited. The cofferdam soil needs to be backfilled in layers with a layer thickness of about 300cm. Because the cofferdam soil enters the water, the cofferdam settlement is large. Sufficient settlement must be reserved during construction. After the cofferdam soil is settled, the earthwork within the cofferdam range is filled as a whole;

[0022] During the entire construction period, the settlement and deformation of the cofferdam shall be monitored and the embankment shall be maintained. When the top surface elevation of the fill in the steel pipe pile is 5 cm lower than the design value, soil shall be piled up to maintain the design elevation. The deformation monitoring of the cofferdam structure is mainly carried out by combining visual inspection and instrument monitoring. The visual inspection mainly checks whether there are obvious cracks in the retaining soil at the foot of the steel pipe pile cofferdam slope, whether there are obvious landslides, soil gushing and water seepage, etc.

[0023] The buried monitoring points of steel pipe pile cofferdams should be selected in the position with large deformation amplitude and fast deformation rate, and laid out in principle to correctly reflect the deformation of the cofferdam. The longitudinal arrangement is a section every 30m. The monitoring points of steel pipe pile cofferdams should be laid out in sections horizontally, with 2 monitoring points laid out in each section. The monitoring point scale should be firmly combined with the deformed body and should be kept vertical during installation and burial. The steel pipe pile cofferdam scale is planned to be arranged on the steel pipe piles.

[0024] After the cofferdam is built, observations are carried out as soon as pumping begins. Initially, observations are carried out 1-2 times a day. After the weir is stable, the monitoring interval can be gradually enlarged. After it is stable, the cofferdam will be dismantled. If there are abnormal conditions such as the cofferdam tilting or excessive settlement, construction will be stopped immediately and the cofferdam will be reinforced. Construction can only be continued after it is stable.

[0025] S5 Weir Pumping and Drainage

[0026] After the cofferdam is built, water can be pumped out. The water level in the cofferdam needs to be lowered in layers. When the water level drops by 0.5-1m, pumping should be stopped, and the settlement and displacement of the cofferdam should be monitored. If the displacement of the cofferdam is greater than 10cm, the cofferdam should be reinforced. The water in the cofferdam should not be pumped out too quickly, and the water level should not drop by more than 1m per day. The soil out of the water should be compacted immediately. If water seepage is found, pumping should be stopped immediately, and the cofferdam should be reinforced in time to maintain the safety of the cofferdam. After pumping is completed, check whether each connection is firm and whether there is water seepage, and take timely measures to deal with it. During the construction period, a transport ship and a dredger are equipped to fill and maintain the cofferdam, and special personnel are arranged to inspect the cofferdam to deal with safety hazards in a timely manner.

[0027] S6 cofferdam intermediate acceptance

[0028] After the water is pumped out and the silt is removed from the cofferdam, the inner slope foot needs to be filled and reinforced. Technical requirements: During construction, it is necessary to dredge and backfill at the same time to prevent the lateral movement of the weir body due to the excessively low bottom of the pit. The filling height of the slope foot against the weir body is not less than 1.5m, and the slope ratio is 1:1. The outer side is connected to the bottom of the foundation pit, and steps are prohibited. The filling of the inner slope foot of the cofferdam needs to be carried out in layers, and the layered compaction thickness is about 30cm. The excavator is used to dig and backfill, and the filling is carried out from the river bottom to the top in sequence to the designed elevation. The backfill of the river channel is constructed according to the principle of "longitudinal segmentation, vertical layering, uniform symmetry, and continuous operation". The backfill is carried out in sections, and the fill is flattened by an excavator, and then rolled 3 to 4 times by the excavator to make it reach a certain density, and the surface must be flat, and all indicators meet the design requirements. When rolling, it should be rolled from low to high, and the travel speed should be controlled;

[0029] Each layer of backfill soil is reserved on the basis of vertical filling and compaction. The width of the step is not less than 2m, and the height is the same as the thickness of the filling layer. Before backfilling the river channel, always pay attention to the weather forecast and avoid rainy weather as much as possible to reduce the difficulty of construction. The filling material should meet the requirements. The filling material entering the site must not contain stones, gravel, ash and organic matter. The filling material must be inspected and qualified before entering the construction site, otherwise it must not be used for backfill construction;

[0030] S7 Daily maintenance during construction

[0031] S8 cofferdam removal

[0032] After the construction of the structure inside the cofferdam is completed, the materials, machinery and various residues inside the cofferdam are removed and then the cofferdam is dismantled;

[0033] When dismantling, all connections must be released first, and the purlins and wire ropes must be removed from bottom to top until all materials in the cofferdam are removed before pulling out the piles. During the construction process, all purlins and wire ropes must be collected on the pile transport ship and must not be left underwater. Before pulling out the piles, water must be poured into the cofferdam to ensure that the water surface inside and outside the cofferdam is level;

[0034] The water filling opening is initially selected near the main cofferdam and the revetment. First, the steel pipe piles and inner and outer earthworks of the shore structure are removed. At this time, river water will seep from the lower part. Then, the main cofferdam is cleaned to ensure that there is a 2-3m wide water opening. The entire water filling time lasts about 24 hours.

[0035] The depth of the opening should not exceed 1.5-2.0m below the water surface to prevent over-excavation from causing the base soil to be hollowed out and causing sliding hazards to the original revetment. Steel pipe enclosures should be set up, dense mesh should be hung, warning signs should be made, and irrelevant personnel should be prohibited from approaching to avoid accidents of falling into the water. At the same time, construction personnel must take safety measures. During the entire construction process, the stability and firmness of the personnel and mechanical working platforms must be ensured to prevent overturning;

[0036] Clamp the steel pipe pile with the clamp of the driving and pulling machine, start the vibratory pile hammer, and with the help of the continuous vibration of the vibratory hammer, reduce the friction between the pile and the soil, and directly pull the steel pipe pile out of the river channel and place it on the pile transport ship for transfer.

[0037] Preferably, during the construction of the cofferdam project, it is often encountered that the soil of the riverbed base in some local areas is hard, and the steel pipe piles are difficult to sink and it is difficult to reach the designed elevation. At this time, the piling condition is to continuously hammer the steel pipe piles for 10 minutes, and the sinking height of the pile body is less than 10 cm;

[0038] There are two ways to solve this problem;

[0039] By using large diameter steel pipes, the center distance between adjacent steel pipe piles can be appropriately increased to 750-800mm, and the elevation is still controlled at 2.5m. This can ensure the quality and safety of the cofferdam and ensure the normal construction progress of the cofferdam;

[0040] Alternatively, the steel pipes that exceed the design elevation shall be appropriately cut off, and the center distance between adjacent steel pipe piles shall remain unchanged. Regardless of the construction scheme adopted, the depth of steel pipe piles in the soil shall not be less than 7m in principle;

[0041] When the steel pipe piles need to be driven in sections, a positioning pile is driven every 5 meters to control the position and width of the cofferdam well, and then two piles are driven every 0.619m (center distance) until the driving is completed. Before driving, the pile-driving ship must be firmly fixed. When driving piles, the verticality and position of the steel pipe piles are adjusted through the guide frame until they are in place before driving. During the driving, the steel pipe piles are required to be hit lightly first. When the steel pipe piles are inserted into the soil for more than 1 meter, they can be hammered hard, and the verticality of the steel pipe piles can be adjusted at any time during the hammering process. In addition, from the perspective of environmental protection, it is advisable to use pile-driving ships with low construction noise to enter the construction site as much as possible.

[0042] Preferably, the settlement observation is carried out using a level, and the settlement amount of each monitoring point is calculated by measuring the elevation difference of each monitoring point twice, and the settlement amount is calculated accurately to millimeters.

[0043] Preferably, a total station is selected as the horizontal monitoring point, and the edge intersection method is used for observation. The horizontal displacement of each monitoring point is calculated and obtained by the data difference between two measurements, and the horizontal displacement is calculated accurately to millimeters.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] The construction process is simple and has a wide range of applications. The double-row steel pipe pile cofferdam technology is effective and feasible under complex hydrogeological conditions such as soft soil, silty soil layer, water-containing unstable soil layer, etc.

[0046] The construction period of double-row steel pipe pile cofferdam is fixed and easy to control, which can avoid safety problems such as water leakage and cofferdam deformation during the construction of structures inside the cofferdam;

[0047] Safe and reliable. Compared with the traditional Larsen steel sheet pile cofferdam plus temporary construction platform, the double-row steel pipe pile cofferdam is flexible in layout and does not need to form a closed whole. It has high structural stability, better water-stopping and water-isolating effects, is safe and reliable, has little impact on the surrounding environment, and the earthwork in the cofferdam can be cleaned and reduced, thereby reducing the excavation depth of the cap.

[0048] Resource conservation, less pollution to the water environment, small earth filling volume, less material usage, and the environmentally friendly materials used have little impact on the environment. The double-row steel pipe pile cofferdam method is a "green" construction method that conforms to the concept of environmental protection, energy saving and consumption reduction;

[0049] Economically reasonable, compared with the construction plan of Larsen steel sheet pile cofferdam plus temporary construction platform, it can save the construction cost of temporary facilities, rental costs, earthwork transportation costs, earthwork compaction costs, earthwork excavation and filling costs, etc. It is more economical and reasonable to use this method when constructing underwater structures in large areas of water, with long construction periods and high water levels. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 This is a schematic diagram of a specific embodiment of the method; DETAILED DESCRIPTION

[0051] 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.

[0052] See also Figure 1 The present invention provides a double-row steel sheet pile cofferdam construction method. Before construction, the original riverbed elevation of the cofferdam piling area is measured. According to the cross-sectional diagram and construction sequence of the cofferdam, the steel pipes are organized to enter the site. If during the measurement process, it is determined that there are rocks on the riverbed, they must be removed in time and records must be kept. Before construction, all mechanical equipment is inspected and maintained to ensure the normal operation of the mechanical equipment. After the steel pipes enter the site, they should be classified and stacked according to specifications and varieties. Before transporting the piles, the steel pipe models and quantities used in the construction are clarified, and the steel pipes are arranged strictly according to the designed sections.

[0053] S1 Lofting Positioning

[0054] Use GPS to determine the specific location of the cofferdam, set up control points on the river bank, drive steel pipes into the water at intervals of 50 to 60 meters as temporary positioning, and mark the elevation position on the steel pipe. The principle of advancing the positioning work is basically consistent with the construction sequence of steel pipe piles. The double-row steel pipe pile cofferdam ensures simultaneous driving. After the two piles of the same section are completed synchronously, the next section will be operated. The overall piling sequence of the cofferdam is the main cofferdam on the east side first, and then the water interception cofferdam on the west side. The construction sequence of the main cofferdam is: from west to east from the upstream to the downstream direction of the river at pier 4#, and the same process is used at pier 5#;

[0055] S2 Overwater Steel Pipe Pile Driving

[0056] When driving the steel pipe piles, they are driven from upstream to downstream and gradually closed. Try not to interrupt them to avoid excessive mud affecting the strength of the cofferdam. After determining the overall layout of the cofferdam, the auxiliary guide piles and corner piles are driven first. According to the position of the first steel pipe pile, the auxiliary guide piles are staked out: the auxiliary guide piles are hoisted with the clamp of the electric vibrating pile hammer of the pile driving ship, and two auxiliary guide piles are driven into the soil at the designed distance at the staked position. The depth of the soil is 7m or more. After the auxiliary guide piles are driven, guide devices are set on both sides of the auxiliary piles. The guide devices are composed of two thin steel wire ropes. Guide wire ropes are set on both sides of the three guide piles to perform linear control of the steel pipe pile driving.

[0057] After the auxiliary guide piles are driven, a directional spacing guide frame is set. The guide frame is welded with steel sections and has a height of 2m. The first steel pipe pile is clamped and lifted by the clamp of the driving and pulling machine, and the guide frame is inserted. The vibrating pile hammer is started and driven into the ground. The top surface elevation is controlled at +2.5m. After the first steel pipe pile is driven, the guide frame is dismantled and the auxiliary guide piles are pulled out.

[0058] After the layout, reset the direction spacing guide frame, lift the second steel pipe pile in the same lifting method as the first steel pipe pile, insert the guide frame, start the vibrating pile hammer, drive it into the ground, and control the top elevation at +2.5m to complete the second steel pipe pile driving construction. After the second steel pipe pile construction is completed, remove the temporary guide frame, and drive the remaining steel pipe piles according to the construction method of the second pile until all the steel pipe piles are driven. During the construction process, pay attention to the position of the corner piles, and the spacing cannot exceed the designed spacing;

[0059] When there is a concrete or mortar-laid block stone revetment on the river bank side, the cofferdam is connected to the revetment closure. At the upstream end of the outer side, 1.636m near the front edge of the retaining wall, a single row of steel pipe piles of the same specification is extended in parallel, with a spacing of 0.619m and a total length of about 10m. Geogrids and waterproof geotextiles are hung inside and then filled with soil to ensure that there is no leakage under the old revetment. When there is an earth revetment on the river bank side, the steel pipe piles are directly driven to the bank edge for natural connection;

[0060] S3 Geogrid and Geotextile Installation

[0061] After the steel pipe piles are driven for a certain distance, each row of piles exposed to the water All steel pipe piles are connected with 20# channel steel purlins. The channel steel and steel pipe piles are fixed by welding to ensure that each pile is firmly welded to the channel steel purlin and the single row of piles is connected as a whole.

[0062] After a certain number of steel pipe piles are constructed, geogrids and waterproof geotextiles can be hung. The width of the geotextile is 4m and the length is 50m, and the horizontal overlap width between each piece is 100cm. During construction, small stones are tied with lead wire at the bottom to ensure that the geomembrane does not fold and hangs vertically. The top of the geotextile is firmly tied to the steel pipe piles with lead wire. When filling the cofferdam, check the condition of the waterproof geotextile at any time and correct any abnormalities in time.

[0063] Use between two rows of steel pipe piles The steel wire rope wraps and tightens the steel pipe and two surrounding purlins (it can also be used The screw rod is used for pulling reinforcement) to form a stable skeleton structure for the whole dam body. When the wire rope is wound, a tensioner is needed to tighten the wire rope. After tightening, a U-shaped fixing card is installed at the cross node of the wire rope to prevent the tightened wire rope from loosening;

[0064] S4 Weir fill

[0065] After the steel pipe piles and waterproof geotextiles are constructed, the soil can be filled. The filling soil is made of cohesive soil with poor water permeability. The earth is dug into the steel pipe pile cofferdam by an excavator in the earth-pile area of ​​the bank at both ends of the cofferdam. The grab bucket must not collide with the steel pipe piles when putting the earth into the cofferdam.

[0066] The filling earthwork is transported to the vicinity of the cofferdam by ship and filled with earth by excavators. The cofferdam soil material is clay and silt filling is prohibited. The cofferdam soil needs to be backfilled in layers with a layer thickness of about 300cm. Because the cofferdam soil enters the water, the cofferdam settlement is large. Sufficient settlement must be reserved during construction. After the cofferdam soil is settled, the earthwork within the cofferdam range is filled as a whole;

[0067] During the entire construction period, the settlement and deformation of the cofferdam shall be monitored and the embankment shall be maintained. When the top surface elevation of the fill in the steel pipe pile is 5 cm lower than the design value, soil shall be piled up to maintain the design elevation. The deformation monitoring of the cofferdam structure is mainly carried out by combining visual inspection and instrument monitoring. The visual inspection mainly checks whether there are obvious cracks in the retaining soil at the foot of the steel pipe pile cofferdam slope, whether there are obvious landslides, soil gushing and water seepage, etc.

[0068] The buried monitoring points of steel pipe pile cofferdams should be selected in the position with large deformation amplitude and fast deformation rate, and laid out in principle to correctly reflect the deformation of the cofferdam. The longitudinal arrangement is a section every 30m. The monitoring points of steel pipe pile cofferdams should be laid out in sections horizontally, with 2 monitoring points laid out in each section. The monitoring point scale should be firmly combined with the deformed body and should be kept vertical during installation and burial. The steel pipe pile cofferdam scale is planned to be arranged on the steel pipe piles.

[0069] After the cofferdam is built, observations are carried out as soon as pumping begins. Initially, observations are carried out 1-2 times a day. After the weir is stable, the monitoring interval can be gradually enlarged. After it is stable, the cofferdam will be dismantled. If there are abnormal conditions such as the cofferdam tilting or excessive settlement, construction will be stopped immediately and the cofferdam will be reinforced. Construction can only be continued after it is stable.

[0070] S5 Weir Pumping and Drainage

[0071] After the cofferdam is built, water can be pumped out. The water level in the cofferdam needs to be lowered in layers. When the water level drops by 0.5-1m, pumping should be stopped, and the settlement and displacement of the cofferdam should be monitored. If the displacement of the cofferdam is greater than 10cm, the cofferdam should be reinforced. The water in the cofferdam should not be pumped out too quickly, and the water level should not drop by more than 1m per day. The soil out of the water should be compacted immediately. If water seepage is found, pumping should be stopped immediately, and the cofferdam should be reinforced in time to maintain the safety of the cofferdam. After pumping is completed, check whether each connection is firm and whether there is water seepage, and take timely measures to deal with it. During the construction period, a transport ship and a dredger are equipped to fill and maintain the cofferdam, and special personnel are arranged to inspect the cofferdam to deal with safety hazards in a timely manner.

[0072] S6 cofferdam intermediate acceptance

[0073] After the water is pumped out and the silt is removed from the cofferdam, the inner slope foot needs to be filled and reinforced. Technical requirements: During construction, it is necessary to dredge and backfill at the same time to prevent the lateral movement of the weir body due to the excessively low bottom of the pit. The filling height of the slope foot against the weir body is not less than 1.5m, and the slope ratio is 1:1. The outer side is connected to the bottom of the foundation pit, and steps are prohibited. The filling of the inner slope foot of the cofferdam needs to be carried out in layers, and the layered compaction thickness is about 30cm. The excavator is used to dig and backfill, and the filling is carried out from the river bottom to the top in sequence to the designed elevation. The backfill of the river channel is constructed according to the principle of "longitudinal segmentation, vertical layering, uniform symmetry, and continuous operation". The backfill is carried out in sections, and the fill is flattened by an excavator, and then rolled 3 to 4 times by the excavator to make it reach a certain density, and the surface must be flat, and all indicators meet the design requirements. When rolling, it should be rolled from low to high, and the travel speed should be controlled;

[0074] Each layer of backfill soil is reserved on the basis of vertical filling and compaction. The width of the step is not less than 2m, and the height is the same as the thickness of the filling layer. Before backfilling the river channel, always pay attention to the weather forecast and avoid rainy weather as much as possible to reduce the difficulty of construction. The filling material should meet the requirements. The filling material entering the site must not contain stones, gravel, ash and organic matter. The filling material must be inspected and qualified before entering the construction site, otherwise it must not be used for backfill construction;

[0075] S7 Daily maintenance during construction

[0076] S8 cofferdam removal

[0077] After the construction of the structure inside the cofferdam is completed, the materials, machinery and various residues inside the cofferdam are removed and then the cofferdam is dismantled;

[0078] When dismantling, all connections must be released first, and the purlins and wire ropes must be removed from bottom to top until all materials in the cofferdam are removed before pulling out the piles. During the construction process, all purlins and wire ropes must be collected on the pile transport ship and must not be left underwater. Before pulling out the piles, water must be poured into the cofferdam to ensure that the water surface inside and outside the cofferdam is level;

[0079] The water filling opening is initially selected near the main cofferdam and the revetment. First, the steel pipe piles and inner and outer earthworks of the shore structure are removed. At this time, river water will seep from the lower part. Then, the main cofferdam is cleaned to ensure that there is a 2-3m wide water opening. The entire water filling time lasts about 24 hours.

[0080] The depth of the opening should not exceed 1.5-2.0m below the water surface to prevent over-excavation from causing the base soil to be hollowed out and causing sliding hazards to the original revetment. Steel pipe enclosures should be set up, dense mesh should be hung, warning signs should be made, and irrelevant personnel should be prohibited from approaching to avoid accidents of falling into the water. At the same time, construction personnel must take safety measures. During the entire construction process, the stability and firmness of the personnel and mechanical working platforms must be ensured to prevent overturning;

[0081] Clamp the steel pipe pile with the clamp of the driving and pulling machine, start the vibratory pile hammer, and with the help of the continuous vibration of the vibratory hammer, reduce the friction between the pile and the soil, and directly pull the steel pipe pile out of the river channel and place it on the pile transport ship for transfer.

[0082] Preferably, during the construction of the cofferdam project, it is often encountered that the soil of the riverbed base in some local areas is hard, and the steel pipe piles are difficult to sink and it is difficult to reach the designed elevation. At this time, the piling condition is to continuously hammer the steel pipe piles for 10 minutes, and the sinking height of the pile body is less than 10 cm;

[0083] There are two ways to solve this problem;

[0084] By using large diameter steel pipes, the center distance between adjacent steel pipe piles can be appropriately increased to 750-800mm, and the elevation is still controlled at 2.5m. This can ensure the quality and safety of the cofferdam and ensure the normal construction progress of the cofferdam;

[0085] Alternatively, the steel pipes that exceed the design elevation shall be appropriately cut off, and the center distance between adjacent steel pipe piles shall remain unchanged. Regardless of the construction scheme adopted, the depth of steel pipe piles in the soil shall not be less than 7m in principle;

[0086] When the steel pipe piles need to be driven in sections, a positioning pile is driven every 5 meters to control the position and width of the cofferdam well, and then two piles are driven every 0.619m (center distance) until the driving is completed. Before driving, the pile-driving ship must be firmly fixed. When driving piles, the verticality and position of the steel pipe piles are adjusted through the guide frame until they are in place before driving. During the driving, the steel pipe piles are required to be hit lightly first. When the steel pipe piles are inserted into the soil for more than 1 meter, they can be hammered hard, and the verticality of the steel pipe piles can be adjusted at any time during the hammering process. In addition, from the perspective of environmental protection, it is advisable to use pile-driving ships with low construction noise to enter the construction site as much as possible.

[0087] Preferably, the settlement observation is carried out using a level, and the settlement amount of each monitoring point is calculated by measuring the elevation difference of each monitoring point twice, and the settlement amount is calculated accurately to millimeters.

[0088] Preferably, a total station is selected as the horizontal monitoring point, and the edge intersection method is used for observation. The horizontal displacement of each monitoring point is calculated and obtained by the data difference between two measurements, and the horizontal displacement is calculated accurately to millimeters.

[0089] Double-row steel pipe pile cofferdams are used for the construction of underwater structures. The main method is to use a pile-driving ship to drive double rows of steel pipes in the water according to the designed position, and then connect the steel pipes in the same row together. The soil between the two rows of steel pipes is wrapped with waterproof geotextile and geogrid to form a whole, which is used to resist the entry of lake water in all directions. After the water inside the cofferdam is pumped out, a temporary construction access road is built inside the cofferdam, and the construction on the water in the lake is changed to land construction. In this way, not only the closedness of the construction can be guaranteed, but also the pollution of the lake environment by mud, equipment oil, etc. can be avoided. It is worth mentioning that the sub-compartment construction of the cofferdam can not only speed up the construction progress and greatly reduce the construction cost, but also improve the construction safety factor.

[0090] Example

[0091] The inner filling of double rows of Φ219 (wall thickness 7mm) steel pipe piles is used as the main body of the cofferdam. The length of the steel pipe piles is 12m, the steel pipe piles enter the soil layer 7.5m, the center distance between adjacent steel pipe piles is 619mm, the cofferdam is more than 0.8m above the normal water level, the elevation of the cofferdam top is determined to be +2.5m, the distance between the double rows of steel pipe piles is designed to be 2.5m (middle to middle), and the outer side of the steel pipe piles is reinforced with two [20# channel steel purlins to connect the steel pipes in the same row together, and the steel pipes and purlins are wound and tightened with 12mm diameter steel wire ropes between the two rows of steel pipe piles (it can also be used Screw rods are used for tension reinforcement) to form a stable skeleton structure for the whole weir; 5mm waterproof geotextile and geogrid are fixed on the inner side of the steel pipe piles, and clay is filled in the middle to form a frame structure for the whole weir; this is used as the main body of the cofferdam, and the two weir corners on the water side are set to arc shape to play a diversion role, reduce the turbulence of the water flow and the scouring force of the water flow on the weir body.

[0092] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

[0093] The main materials include intermediate steel pipes, channel steel purlins, steel wire ropes, geogrids, waterproof geotextiles, backfill soil, etc. The main materials are as follows:

[0094] Main materials list

[0095]

[0096] Table of main construction machinery and equipment

[0097]

[0098]

Claims

1. A double-row steel sheet pile cofferdam construction method, characterized in that: Before construction, measure the original riverbed elevation of the cofferdam piling area, and organize the steel pipes to enter the site according to the cross-sectional diagram of the cofferdam and the construction sequence. If rocks are found on the riverbed during the measurement, they must be removed in time and recorded. Before construction, check and maintain all mechanical equipment to ensure the normal operation of the mechanical equipment. After the steel pipes enter the site, they should be classified and stacked according to specifications and types. Before transporting the piles, clarify the type and quantity of the steel pipes used in the construction, and arrange the steel pipes strictly according to the designed section. S1 Lofting Positioning Use GPS to determine the specific location of the cofferdam, set up control points on the river bank, drive steel pipes into the water at intervals of 50 to 60 meters as temporary positioning, and mark the elevation position on the steel pipe. The principle of advancing the positioning work is basically consistent with the construction sequence of steel pipe piles. The double-row steel pipe pile cofferdam ensures simultaneous driving. After the two piles of the same section are completed synchronously, the next section will be operated. The overall piling sequence of the cofferdam is the main cofferdam on the east side first, and then the water interception cofferdam on the west side. The construction sequence of the main cofferdam is: from west to east from the upstream to the downstream direction of the river at pier 4#, and the same process is used at pier 5#; S2 Overwater Steel Pipe Pile Driving When driving the steel pipe piles, they are driven from upstream to downstream and gradually closed. Try not to interrupt them to avoid excessive mud affecting the strength of the cofferdam. After determining the overall layout of the cofferdam, the auxiliary guide piles and corner piles are driven first. According to the position of the first steel pipe pile, the auxiliary guide piles are staked out: the auxiliary guide piles are hoisted with the clamp of the electric vibrating pile hammer of the pile driving ship, and two auxiliary guide piles are driven into the soil at the designed distance at the staked position. The depth of the soil is 7m or more. After the auxiliary guide piles are driven, guide devices are set on both sides of the auxiliary piles. The guide devices are composed of two thin steel wire ropes. Guide wire ropes are set on both sides of the three guide piles to perform linear control of the steel pipe pile driving. After the auxiliary guide piles are driven, a directional spacing guide frame is set. The guide frame is welded with steel sections and has a height of 2m. The first steel pipe pile is clamped and lifted by the clamp of the driving and pulling machine, and the guide frame is inserted. The vibrating pile hammer is started and driven into the ground. The top surface elevation is controlled at +2.5m. After the first steel pipe pile is driven, the guide frame is dismantled and the auxiliary guide piles are pulled out. After the layout, reset the direction spacing guide frame, lift the second steel pipe pile in the same lifting method as the first steel pipe pile, insert the guide frame, start the vibrating pile hammer, drive it into the ground, and control the top elevation at +2.5m to complete the second steel pipe pile driving construction. After the second steel pipe pile construction is completed, remove the temporary guide frame, and drive the remaining steel pipe piles according to the construction method of the second pile until all the steel pipe piles are driven. During the construction process, pay attention to the position of the corner piles, and the spacing cannot exceed the designed spacing; When there is a concrete or mortar-laid block stone revetment on the river bank side, the cofferdam is connected to the revetment closure. At the upstream end of the outer side, 1.636m near the front edge of the retaining wall, a single row of steel pipe piles of the same specification is extended in parallel, with a spacing of 0.619m and a total length of about 10m. Geogrids and waterproof geotextiles are hung inside and then filled with soil to ensure that there is no leakage under the old revetment. When there is an earth revetment on the river bank side, the steel pipe piles are directly driven to the bank edge for natural connection; S3 Geogrid and Geotextile Installation After the steel pipe piles are driven for a certain distance, each row of φ219 steel pipe piles exposed above the water surface are all connected with 20# channel steel purlins. The channel steel and steel pipe piles are fixed by welding to ensure that each pile is firmly welded to the channel steel purlin and the single row of piles is connected as a whole. After a certain number of steel pipe piles are constructed, geogrids and waterproof geotextiles can be hung. The width of the geotextile is 4m and the length is 50m, and the horizontal overlap width between each piece is 100cm. During construction, small stones are tied with lead wire at the bottom to ensure that the geomembrane does not fold and hangs vertically. The top of the geotextile is firmly tied to the steel pipe piles with lead wire. When filling the cofferdam, check the condition of the waterproof geotextile at any time and correct any abnormalities in time. Use φ12mm steel wire rope to wind and tighten the steel pipe and two surrounding purlins between two rows of steel pipe piles (φ20 screw rods can also be used for tension reinforcement) to form a stable skeleton structure for the entire dam body. When winding the steel wire rope, a tensioner needs to be used to tighten the steel wire rope. After tightening, install U-shaped fixing cards at the intersection nodes of the steel wire rope to prevent the tightened steel wire rope from loosening; S4 Weir fill After the steel pipe piles and waterproof geotextiles are constructed, the soil can be filled. The filling soil is made of cohesive soil with poor water permeability. The earth is dug into the steel pipe pile cofferdam by an excavator in the earth-pile area of ​​the bank at both ends of the cofferdam. The grab bucket must not collide with the steel pipe piles when putting the earth into the cofferdam. The filling earthwork is transported to the vicinity of the cofferdam by ship and filled with earth by excavators. The cofferdam soil material is clay and silt filling is prohibited. The cofferdam soil needs to be backfilled in layers with a layer thickness of about 300cm. Because the cofferdam soil enters the water, the cofferdam settlement is large. Sufficient settlement must be reserved during construction. After the cofferdam soil is settled, the earthwork within the cofferdam range is filled as a whole; During the entire construction period, the settlement and deformation of the cofferdam shall be monitored and the embankment shall be maintained. When the top surface elevation of the fill in the steel pipe pile is 5 cm lower than the design value, soil shall be piled up to maintain the design elevation. The deformation monitoring of the cofferdam structure is mainly carried out by combining visual inspection and instrument monitoring. The visual inspection mainly checks whether there are obvious cracks in the retaining soil at the foot of the steel pipe pile cofferdam slope, whether there are obvious landslides, soil gushing and water seepage, etc. The buried monitoring points of steel pipe pile cofferdams should be selected in the position with large deformation amplitude and fast deformation rate, and laid out in principle to correctly reflect the deformation of the cofferdam. The longitudinal arrangement is a section every 30m. The monitoring points of steel pipe pile cofferdams should be laid out in sections horizontally, with 2 monitoring points laid out in each section. The monitoring point scale should be firmly combined with the deformed body and should be kept vertical during installation and burial. The steel pipe pile cofferdam scale is planned to be arranged on the steel pipe piles. After the cofferdam is built, observations are carried out as soon as pumping begins. Initially, observations are carried out 1-2 times a day. After the weir is stable, the monitoring interval can be gradually enlarged. After it is stable, the cofferdam will be dismantled. If there are abnormal conditions such as the cofferdam tilting or excessive settlement, construction will be stopped immediately and the cofferdam will be reinforced. Construction can only be continued after it is stable. S5 Weir Pumping and Drainage After the cofferdam is built, water can be pumped out. The water level in the cofferdam needs to be lowered in layers. When the water level drops by 0.5-1m, pumping should be stopped, and the settlement and displacement of the cofferdam should be monitored. If the displacement of the cofferdam is greater than 10cm, the cofferdam should be reinforced. The water in the cofferdam should not be pumped out too quickly, and the water level should not drop by more than 1m per day. The soil out of the water should be compacted immediately. If water seepage is found, pumping should be stopped immediately, and the cofferdam should be reinforced in time to maintain the safety of the cofferdam. After pumping is completed, check whether each connection is firm and whether there is water seepage, and take timely measures to deal with it. During the construction period, a transport ship and a dredger are equipped to fill and maintain the cofferdam, and special personnel are arranged to inspect the cofferdam to deal with safety hazards in a timely manner. S6 cofferdam intermediate acceptance After the water is pumped out and the silt is removed from the cofferdam, the inner slope foot needs to be filled and reinforced. Technical requirements: During construction, it is necessary to dredge and backfill at the same time to prevent the lateral movement of the weir body due to the excessively low bottom of the pit. The filling height of the slope foot is not less than 1.5m on the side of the weir body, and the slope ratio is 1:

1. The outer side is connected to the bottom of the foundation pit, and steps are prohibited. The filling of the inner slope foot of the cofferdam needs to be carried out in layers, and the layered compaction thickness is about 30cm. The excavator is used to dig and backfill, and the filling is carried out from the river bottom to the top in sequence to the designed elevation. The river channel earthwork backfill is constructed according to the principle of "longitudinal segmentation, vertical layering, uniform symmetry, and continuous operation". The backfill is carried out in sections, and the fill is flattened by an excavator, and then rolled 3 to 4 times by the excavator to make it reach a certain density, and the surface must be flat, and all indicators meet the design requirements. When rolling, it should be rolled from low to high, and the travel speed should be controlled; Each layer of backfill soil is reserved on the basis of vertical filling and compaction. The width of the step is not less than 2m, and the height is the same as the thickness of the filling layer. Before backfilling the river channel, always pay attention to the weather forecast and avoid rainy weather as much as possible to reduce the difficulty of construction. The filling material should meet the requirements. The filling material entering the site must not contain stones, gravel, ash and organic matter. The filling material must be inspected and qualified before entering the construction site, otherwise it must not be used for backfill construction; S7 Daily maintenance during construction S8 cofferdam removal After the construction of the structure inside the cofferdam is completed, the materials, machinery and various residues inside the cofferdam are removed and then the cofferdam is dismantled; When dismantling, all connections must be released first, and the purlins and wire ropes must be removed from bottom to top until all materials in the cofferdam are removed before pulling out the piles. During the construction process, all purlins and wire ropes must be collected on the pile transport ship and must not be left underwater. Before pulling out the piles, water must be poured into the cofferdam to ensure that the water surface inside and outside the cofferdam is level; The water filling opening is initially selected near the main cofferdam and the revetment. First, the steel pipe piles and inner and outer earthworks of the shore structure are removed. At this time, river water will seep from the lower part. Then, the main cofferdam is cleaned to ensure that there is a 2-3m wide water opening. The entire water filling time lasts about 24 hours. The depth of the opening should not exceed 1.5-2.0m below the water surface to prevent over-excavation from causing the base soil to be hollowed out and causing sliding hazards to the original revetment. Steel pipe enclosures should be set up, dense mesh should be hung, warning signs should be made, and irrelevant personnel should be prohibited from approaching to avoid accidents of falling into the water. At the same time, construction personnel must take safety measures. During the entire construction process, the stability and firmness of the personnel and mechanical working platforms must be ensured to prevent overturning; Clamp the steel pipe pile with the clamp of the driving and pulling machine, start the vibratory pile hammer, and with the help of the continuous vibration of the vibratory hammer, reduce the friction between the pile and the soil, and directly pull the steel pipe pile out of the river channel and place it on the pile transport ship for transfer.

2. A double-row steel sheet pile cofferdam construction method according to claim 1, characterized in that: During the construction of the cofferdam project, it is often encountered that the soil of the riverbed base in some sections is hard, and it is difficult for the steel pipe piles to sink and reach the designed elevation. At this time, the piling condition is to continuously hammer the steel pipe piles for 10 minutes, and the sinking height of the pile body is less than 10cm; There are two ways to solve this problem; By using large diameter steel pipes, the center distance between adjacent steel pipe piles can be appropriately increased to 750-800mm, and the elevation is still controlled at 2.5m. This can ensure the quality and safety of the cofferdam and ensure the normal construction progress of the cofferdam; Alternatively, the steel pipes that exceed the design elevation shall be appropriately cut off, and the center distance between adjacent steel pipe piles shall remain unchanged. Regardless of the construction scheme adopted, the depth of steel pipe piles in the soil shall not be less than 7m in principle; When the steel pipe piles need to be driven in sections, a positioning pile is driven every 5 meters to control the position and width of the cofferdam well, and then two piles are driven every 0.619m (center distance) until the driving is completed. Before driving, the pile-driving ship must be firmly fixed. When driving piles, the verticality and position of the steel pipe piles are adjusted through the guide frame until they are in place before driving. During the driving, the steel pipe piles are required to be hit lightly first. When the steel pipe piles are inserted into the soil for more than 1 meter, they can be hammered hard, and the verticality of the steel pipe piles can be adjusted at any time during the hammering process. In addition, from the perspective of environmental protection, it is advisable to use pile-driving ships with low construction noise to enter the construction site as much as possible.

3. A double-row steel sheet pile cofferdam construction method according to claim 1, characterized in that: Settlement observations are carried out using a level. The settlement amount at each monitoring point is calculated using the elevation difference between two measurements of each monitoring point. The settlement amount is calculated with an accuracy of millimeters.

4. A double-row steel sheet pile cofferdam construction method according to claim 1, characterized in that: The horizontal monitoring points are selected by total station and the edge intersection method is adopted for observation. The horizontal displacement of each monitoring point is calculated by the data difference of two measurements and the horizontal displacement is calculated with an accuracy of millimeters.

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