the trench excavation depth in this contract section is about 4m. Because the construction area is located in the main street and the groundwater level is high. There are no conditions for slope excavation. It is planned to adopt the method of well point dewatering and driving steel sheet pile to support straight groove excavation for construction.
firstly, the structures, pavements and pavements within the pipeline line shall be removed. The old pavement and concrete structures are removed by machinery. The pavement slab shall be removed manually, and the old pavement slab shall be protected for reuse.
1. Construction of well-point dewatering
(1) Machines and tools:
①. Well-point pipe: φ6, seamless steel pipe or galvanized pipe with a wall thickness of 3.mm, with a length of about 6m
, one end of which is welded with a steel plate with a thickness of 4.mm, and a small circular hole with a diameter of φ15mm is drilled on the pipe wall within the range of 1.4m at this end.
② connecting pipe: the transparent pipe is connected with the well point pipe and the main pipe, and it is bound with No.8 lead wire, which should be tightened to prevent air leakage.
③. Main pipe: φ 1 ~ 12 steel pipe with a wall thickness of 4.mm, connected with flange and rubber gasket to prevent air leakage and water leakage.
④ pumping equipment: vacuum pump, unit fittings and water tank are equipped according to the design.
⑤. Water gun: φ6×5 seamless steel pipe, with a φ16 lance head nozzle welded at the lower end, and the upper end bent at a right angle, which extends out of the impact pipe and is connected with a high-pressure hose.
(2) Material:
Medium sand is not allowed for coarse sand, and fine sand is strictly prohibited to prevent clogging of the filter pipe network.
(3) technical preparation:
① refer to the engineering geological investigation report in detail to understand the engineering geological situation, analyze the technical problems that may occur in the precipitation process and take measures.
② Inspection of drilling equipment and pumping equipment.
(4) well point installation
①. Installation procedure: well point setting-out and positioning → installation of high-pressure water pump → drilling and installation of buried well point pipe → arrangement and installation of main pipe → connection between well point pipe and main pipe → installation of pumping equipment → trial pumping and inspection → formal operation of dewatering procedure.
② Burying of pipe at well point: according to the survey control points provided by the construction unit, determine the position of well point by surveying and setting out
, and then dig a small earth pit at the well location with a depth of about 5mm, which is convenient for collecting water when impacting the hole and filling sand when burying the pipe, and connect the pit with the sump with a ditch to drain excess water.
③ aim the steel pipe water gun at the well point, start the high-pressure water pump, and control the water pressure at .4 ~ .8 MPa. Under the impact of the high-pressure water jet of the water gun, the steel pipe begins to sink, and the steel pipe and the water gun are constantly lifted. Generally, the sand-bearing clay, according to experience, the steel pipe falls within 1 mm. Under the action of water injection and steel pipe punching, the well point pipe can sink about 5m within about 2 ~ 3 min. If it encounters thick pure clay, the pipe sinking time should be prolonged, and the pressure of high-pressure water pump can be increased at this time to accelerate the pipe sinking speed. The diameter of the impact hole should reach 1 ~ 15 mm, so as to ensure a certain gap between the pipe wall and the well point pipe, so as to facilitate the filling of sand and gravel.
The punching depth should be more than 5mm lower than the designed placement depth of the filter pipe, so as to prevent part of the soil from collapsing when the impact steel pipe is lifted
and make the bottom of the filter pipe have enough sand and gravel.
when the impact pipe moves up and down, it should be vertical, so as to keep the shaft wall of well point dewatering vertical. If large stones and bricks are encountered during impact, it will tilt, and the diameter of the hole should be kept consistent as far as possible.
after the impact forming of the borehole, the upper end of the well point pipe should be plugged with a cork, and a sand filter layer should be filled between the well point pipe and the borehole wall. Coarse sand must be used for sand and gravel to prevent the mesh of the filter tube from being blocked, and the filling quality of the sand and gravel filter layer directly affects the dewatering effect of light well points.
after the well point is filled with sand, 1.～1.5m below the wellhead shall be sealed and compacted with clay to prevent air leakage and reduce the dewatering effect.
④ Pipeline installation
First, along the outside of the well point pipeline, lay a water collecting capillary, and connect the main pipe with rubber gasket bolts. The main pipe is connected with the water tank pump, then unplug the cork at the upper end of the well point pipe, connect it with the main pipe with a rubber hose, and then tie it with 1# lead wire to prevent the pipeline from leaking and reducing the vacuum degree of the whole pipeline. The running water slope of the main road is 5‰ of the slope to the pump house, and the main pipe is padded with bricks. And do a good job in winter precipitation antifreeze and heat preservation.
⑤. Check the pipeline
Check whether there is air leakage at each joint of the rubber hose connected between the underwater collecting pipe and the well point pipe during the trial pumping. If it is found, it should be reconnected or blocked with grease, and the flange bolts and lead wires of the rubber hose should be tightened again until there is no air leakage. Before the formal operation of pumping, a trial pumping must be carried out to check whether the pumping equipment is operating normally and whether there is air leakage in the pipeline. Install a vacuum gauge on the water inlet pipe of the water pump and a pressure gauge on the water outlet pipe of the water pump. In order to observe the depth of precipitation and whether it reaches the required depth of precipitation in the construction organization design, an observation well point is set in the center of the foundation pit, so that the water level can be measured through the observation well point and the precipitation curve can be drawn < P >.
during the trial pumping, the vacuum degree of the whole pipe network should be checked, and it should reach 55mmHg(73.33kPa) before it can be put into pumping.
⑥. Pumping
Try pumping after all the light well point pipe networks are installed. When the pumping equipment runs normally, the whole pumping pipeline has no air leakage and can be put into normal pumping operation. Earthwork can be excavated after 3 days of precipitation.
2. Trench excavation
(1) The width of the trench bottom should be +.4m outside diameter of the pipe.
(2) During trench excavation, the elevation of the basement shall be strictly controlled, and the foundation surface shall not be overbreak or disturbed. When the excavator digs to 2cm away from the basement, it will continue to excavate manually until the elevation.
(3) The bottom of the tank shall not be soaked in water.
(4) quality standard of excavated trench:
1) loose soil, silt, large stones and other sundries at the trench bottom must be removed, and the trench bottom should not be soaked.
2) See the table for allowable deviation of groove:
Inspection method for allowable deviation of sub-projects
Number of range points
1. The elevation of groove bottom is -3mm; 3. Measure it with a level between two wells
2. The center line of groove bottom is not less than the specified ruler for 6 hanging center lines between two wells;
The width of each side is 3 points
3. The slope of groove is not steeper than the specified 6 times between two wells.
(2) the foundation shall be compacted tightly and the surface shall be smooth. The pipeline foundation is at the interface, and a groove should be reserved. So as to facilitate the interface operation. After the interface is completed, it will be filled with the same material.
(3) Quality standard of pipeline foundation
1) Pipeline foundation shall not be paved on silt or loose fill.
2) The pipeline foundation shall have a smooth surface and be straight between two wells.
3) The allowable deviation of pipeline foundation
is shown in the table:
Frequency inspection method for allowable deviation of sequential projects
Number of points in the range
1. The center line of foundation+1p>mm2 hanging ruler,
The width of each side is mm, and each side is counted as 1 point
2. The thickness of foundation+1mm2 ruler,
1 point on each side of-2mm
4. Pipe laying
(1) Pipe laying
1) Pipe joints to be used shall be inspected section by section according to product standards, and those that do not meet the standards shall not be used, and shall be marked and handled separately.
2) Generally, manual handling can be used for on-site handling of pipe joints, and it must be handled with care. It is forbidden to drag pipes on the ground.
3) Pipe laying can be done manually, and the ground personnel will pass the pipe to the trench bottom construction personnel. For large excavation groove, nonmetallic ropes can also be used to tie both ends of the pipe body, so as to keep the pipe body balanced and put it at a constant speed, so that the pipe can be placed in the groove smoothly. It is strictly forbidden to roll the pipe into the groove to the edge of the groove. When the crane runs the pipe, it should be fastened with nonmetallic ropes, and it is strictly forbidden to hoist the pipe in a string.
4) For pipes, it is advisable to install the socket in the direction of water flow and the socket in the direction of water flow, generally from downstream to upstream.
5) The pipe can be cut by hand saw according to the required length, and the fracture should be trimmed.
(2) Rubber ring interface
1) The rubber ring should be placed in the groove between the second and third ribs of the pipe socket.
2) when connecting, clean the inner wall of the socket, and apply lubricant on the inner wall of the socket and the rubber ring of the socket, and then align the central axis of the socket end.
3) interface method: one person hangs the socket of pipe B with cotton yarn rope, and the other person inserts it into the foundation obliquely with a long pry bar and leans against the horizontal file board at the center of the end of the pipe, and then slowly inserts the socket of pipe B into the socket of pipe A with force to the predetermined position.
4) After the pipeline interface, the elevation and straight line of the pipeline shall be rechecked to meet the design requirements.
5) quality standard of pipe laying and interface
①. The pipe should be straight, the slope of the pipe bottom should comply with the design, and there should be no falling water. See table for allowable deviation of pipeline laying line:
allowable deviation of sub-projects
1. centerline 2mm
2. pipe bottom elevation +2mm,-1mm
3. surface clearance between sockets <: 9mm
② There are two inspection methods for the rubber ring of the interface:
First, mark a certain position (generally about 23cm long) at the socket end, and check whether the mark line is in place during installation.
second, listen to the sound. Generally, when the socket is in place, it will make a collision sound when it contacts the socket.
quality standard for three-pound water inspection
pressure pipes must be inspected by pound water according to the design water pressure requirements. Pound water inspection shall be conducted by spot check.
5. Construction of inspection wells
(1) Brick masonry of sewage inspection wells must ensure that mortar is full and mortar joints are straight, and there can be no seam. Before wall treatment, surface dirt and floating ash must be removed. The launder and the shaft wall are built at the same time, and the height of the launder: the sewage well is flush with the pipe. The chute in the well should be smooth, and there should be no sundries such as construction waste. The inner wall of the well shall be plastered with 2mm thick 1: 2.5 cement mortar on the chute D/2+2mm(D: pipe diameter), and the above shall be jointing with 1: 2 waterproof cement mortar. In case of groundwater, the outer wall of the well shall be plastered with 2mm thick 1: 2 waterproof cement mortar to 5mm above the groundwater level. C3 concrete is used for the well ring. When the manhole cover and seat ring are installed, 1: 2 cement mortar is used to seat the slurry, and triangular ash is applied. The top surface of the manhole cover is flat with the road surface. Steel fiber manhole cover and seat ring must be intact, installed smoothly and located correctly. The manhole of this project adopts convergent type.
Mortar shall be mechanically mixed, and the mixing time shall not be less than 3 minutes. Mortar shall be used as it is mixed, and generally used up within 3 hours. Overnight mortar is strictly prohibited.
see the following table for the allowable deviation and inspection method of inspection wells:
allowable deviation of the project (mm) inspection frequency inspection method
borehole size 2 per seat /2 points
elevation difference between manhole cover and pavement is not 2 per seat /1 point
pavement 5
bottom elevation d ≤ 1mm. 1mm±15 each /1 point with a level
6. Closed water (sewage pipeline requirements)
Before the pipeline is installed and covered with soil, a closed water test shall be conducted according to the requirements of the construction acceptance specification, and the leakage can be covered and backfilled only after it is confirmed that it is within the allowable value of the specification. When the pipeline interface is soaked in water for 24 hours after the completion of the work, the water shut-off test can only be done if there is no obvious leakage by visual inspection, and it should be carried out before backfilling, so as to observe the leakage of the pipeline and interface and take plugging measures. In order to save the test work, several well sections can also be selected for water shut-off test together, but it is advisable to take one well in one section of pipe, and it is not advisable to just test the tube without well testing.
Carry out the test according to the technical requirements of closed water test, record the water seepage in time, observe the leakage point, and measure the water seepage for at least 3 minutes.
backfill immediately after passing the closed water test:
7. Trench backfilling
(1) Trench backfilling shall be carried out after the pipeline concealed works are accepted. Trench backfilling should be done in time to prevent the pipeline from being exposed for too long and causing losses.
(2) Trench backfilling shall comply with the following provisions:
1) Within 7cm of the pipe top, it must be backfilled manually, and it is forbidden to backfill with mechanical bulldozer.
2) Backfilling shall start from the joint between the bottom of the pipe and the foundation, and simultaneously backfill and tamp symmetrically in layers along both sides of the chest of the pipe. The height of each layer of backfill shall not exceed 2cm until it is 3cm above the top of the pipe. The quality of backfill materials shall meet the design requirements.
3) When rolling by the rolling machine, The thickness of the composite soil above the pipe top should not be less than 7cm.
(3) The density standard of the trench composite soil:
1) See the table for the dry weight of the trench backfill coarse sand:
Inspection method for the dry weight of the sequential project
Range points
1. For two wells with a chest part ≥16KN/m3, .7m steel bar is used for each layer. M3 two wells, each layer is set with ∮16 steel bars with a height of .7m
5mm(3 points) for free fall detection
2) Compactness of trench backfill:
①. Compactness of thoracic backfill under pavement: 95%
In other soil areas: 9%
②. Backfill above trench (pipe) top.
8. Pipes
(1) General provisions
1) Materials such as pipes and rubber rings shall conform to the current product standards, have product certificates and product performance specifications from the quality inspection department, and shall indicate the manufacturer, specifications and production date.
2) The rubber ring used for sealing the socket interface must match the specifications of the pipe.
(2) Quality of pipes
1) The pipes shall be consistent in appearance and color, and the inner wall shall be smooth and flat. There shall be no cracks in the pipe body, no more than 2 connection defects of tendons, and no defects such as breakage, crack and deformation at the nozzle.
2) The end face of the pipe shall be smooth and perpendicular to the central axis of the pipe, and the axis shall not be obviously bent. The dimensions and roundness of the outer diameter of the pipe socket and the inner diameter of the socket must conform to the provisions of the product standard.
3) The internal pressure strength and stiffness of pipes should meet the design requirements.
4) The performance and size of rubber ring for pipeline interface should meet the design requirements. The appearance of rubber ring should be smooth and level, and there should be no pores, cracks, wrinkles, damage, double skin and seams.
9. Loading, unloading, transportation and stacking
(1) Pipes and fittings should avoid collision during loading, unloading, transportation and stacking, and throwing is strictly prohibited.
(2) When pipes are transported in batches, sockets and sockets should be staggered in layers and tied firmly.
(3) Pipe stacking should be shaded, sockets and sockets should be arranged at intervals, and both ends should be securely plugged with wooden wedges.
(4) The rubber ring shall not be damaged during storage and transportation.
1. Dismantling of support
When dismantling the steel sheet pile support, the following requirements shall be met:
(1) The steel sheet pile cannot be pulled out until the backfill reaches the required height;
(2) The pile hole should be backfilled in time after the steel sheet pile is pulled out;
(3) When backfilling the pile hole, measures should be taken to fill it. When sand is used for filling, flushing can be used to assist sinking; When there are requirements for controlling ground subsidence, it is advisable to take measures of grouting while pulling out piles.
11. Repair of roads and track slabs
Pipe