This paper introduces the operation method, bit improvement and drilling construction technology of double-arm steel cofferdam construction platform, especially for different places.
The drilling methods under quality conditions are summarized.
Keywords: bored double-arm steel cofferdam for bridge pile foundation
China Library ClassificationNo.: U443 1 15 Document ID: B.
1 project overview
Hanjiatun Extra Large Capacity Expansion and Reconstruction Project of Jinyao Line in Dalian Railway Hub
The total length of the bridge is 603 m, and the superstructure is 32 m prestressed concrete with 18 holes.
Earth beam. This bridge is located in seawater, and its foundation is 1 125 m bored pile and pier.
There are 4 piers and 6 abutments, and the length of piles varies, with the longest pile reaching 29 meters.
It is 0/00 ~ 200m away from the coast/kloc-,with a water depth of 5 ~ 6m at high tide and 5 ~ 6m at low tide.
215 ~ 310 m. The geological surface layer is pebble soil with a thickness of 3 ~ 5 m, and the secondary layer is cohesive soil.
Soil, brownish red, hard plastic, containing a small amount of gravel. The bedrock is weathered limestone.
Different degrees, many ups and downs of bedrock surface, uneven bedrock, karst trough, karst trough,
Karst caves are rich in development. The deepest karst ditch and groove is 8 m, even in the same place.
Abutment and bedrock surface will also change greatly, and karst caves will develop and dissolve along the structural plane.
The holes are sometimes beaded, with 2 ~ 5 layers.
According to the construction characteristics and schedule requirements of this project, the substructure will be adopted.
The work is divided into 8 # ~ 16 # underwater pier and 0 # ~ 7 #, 17 #, 18 # pier abutment floodplain.
Two construction units. The underwater construction unit adopts double-walled steel cofferdam and ferry.
Transport scheme; The construction unit of the river beach adopts filling soil to build the island, and steel sheet piles are used to enclose the reclaimed land.
Ground construction scheme. The foundation of underwater construction unit is constructed by double-wall steel cofferdam.
Work, transported by temporary wharf user barge, 50 t ship crane with steel cofferdam.
Sucking mud and sinking, installing casing and construction platform, pouring back cover concrete and drilling holes.
Piling into holes, pumping and shoveling pile heads, and pouring pile caps. Foundation excavation of floodplain construction unit
Protect the island wall with mud, drill holes to design elevation, clean holes and hang steel bars.
Cage, pouring pile concrete. Steel sheet pile is used as the foundation of retaining wall for the pile cap, and it is chiseled.
Cast-in-place method, the steel is driven according to the design size outside the size range of the bearing platform.
Sheet pile: excavate the foundation pit with steel support, and then pour the pile cap.
2 Construction method
2 1 1 Double-wall steel cofferdam and drilling platform
According to the geometric size, water depth and geological conditions of the cap (6 12 m×5 17 m)
Under different conditions, the internal size of double-walled steel box is the size of cap.
Widen each side by 200 mm, and determine the height: h= water depth+cap bottom depth.
+Buried depth below box bottom+wave height+safety value = 2 19 1+
510+115+3199+10 =1315m, so the size of the container is determined as follows:
616m× 611m×13m, it is advantageous to make the upper opening bigger and the lower opening smaller during processing.
Take it apart and pull it out. The steel cofferdam is supported by wallboard, blade feet and internal truss, and suspended by sinking.
Grading. It is made and installed in two sections, the lower section is 5 meters long and the upper section is 5 meters long.
Main double-wall steel plate with length of 4 m and thickness of δ 1= 12 mm, steel blade angle steel plate.
Thickness δ2= 20 mm, steel blade angle length 1 150 m, double wall spacing.
1 10 m, a cross rib and I 12a I-beam are welded on the double wallboard every 0 18 m, and
Vertical ribs and double-deck plates shall be leveled with ∠75×75×8 angle steel.
Inclined connection to increase stability and make it uniformly stressed, steel blade foot position
The transverse rib and connecting rod are encrypted, and a transverse rib is set every 0 15 m to prevent sinking.
Due to excessive stress, the blade root is deformed. At the same time, the steel cofferdam is welded with the cross beam.
Four bearing steel plates are welded on the top surface of the bearing to prevent the steel cofferdam from sinking to the ground.
Due to the difficulty of sinking, the force applied by DZ60 vibrating hammer is uneven.
Deformation occurs. Double-walled steel cofferdam is assembled at wharf and installed with square barge.
Drag it to the designated dock. Anchor at the designated position, tighten the cable, and make technical cooperation.
The steel cofferdam is accurately positioned and installed, the exhaust sinks, and divers cooperate with underwater observation.
When sinking to the ground, use anchor cable to adjust the position for the second time, and then draw steel.
Add water to the compartment to keep the balance. Under the external force of DZ60 vibrating hammer.
Sink the pile cap to 1 15 m below the bottom. After in place, clean the foundation and install bored piles.
Casing, positioning frame and ship crane cooperate to hoist Bailey beam assembly platform, and pour and seal it.
Bottom concrete. Remove the positioning frame and lift the drilling equipment to reach the drill pipe.
Pieces.
Cofferdam construction is adopted for piers 0 # ~ 7 #, 17 # and 18 # on the floodplain.
Island, pumping and dredging, filling plain soil as a working platform. Construction elevation of offshore wharf
The platform is built on a steel cofferdam.
2 12 steel casing
Bored cast-in-place pile casing located in flood plain is rolled by 10 mm steel plate.
The length meets the requirement of passing through the silt layer, buried under the riverbed ≮ 2 m, and located in the water.
The steel casing of bored pile is made of 12 mm A3 steel plate, and the casing
The diameter is 20 cm larger than the pile diameter, and its length depends on the geology and buried depth of the borehole.
03
Of course. If drilling needs to be followed up, it needs to be extended on the platform.
2 13 mud wall protection
Large-area island building method is adopted for bored pile mud pit in flood plain.
It is suitable for circulating use of high drilling platforms and mud pools that are filled across.
During the construction of underwater pier pile foundation, the pulping pool and sedimentation tank are both set at the drilling elevation.
When on the drill floor, the mud circulation system is connected with 400 mm steel pipes, and the mud
Mud is pumped by a mud pump. It is planned to use high-quality clay to make slurry and put it into mud.
Add 16% bentonite, 0 1 15% CMC hydroxy cellulose and below.
Appropriate amount of quicklime powder is made into high-quality mud to strengthen the wall protection and prevent leakage and collapse.
Cave.
2 14 drilling
For gravel soil, pebble soil and breccia, it contains large particle size drift.
There are cracks, grooves and caves in the clay layer of stone, especially in limestone.
Impact drills are used for bored piles in the stratum, and cross deformation slopes are used for drill bits.
T-bit, but due to the long drilling length of the bridge crossing the dissolved rock stratum, the same
Sometimes there are gullies, troughs and caves, and the rock surface is extremely irregular, such as a cross.
I-shaped bit, two adjacent forks form a 90-degree angle. During drilling, the drill bit rotates and swings.
The moving angle is 30 ~ 40, so it is likely to get stuck, and because
When the rock layer is thick, hard rocks are bound to be encountered, so
Cross blades are easily damaged. Select the "3" bit, and the diameter of the bit is relatively designed.
The aperture is 3 cm smaller. In order to avoid sticking, an arc-shaped outer wall with an inclination of15 is adopted.
The bottom of the bit is flat, and the number of branches is two more than that of the cross bit.
Sample, in the process of drilling, as long as the rotary swing of the drill reaches 30, all
In order to strengthen the bit, achieve full-face drilling effect and avoid sticking.
The strength of contact with the rock surface, and the old rail is also used to weld each fork of the drill bit.
Four "blade heads" made on the back, 3 ~ 5 cm high, are used to hit the rock surface.
Achieve the effect of crushing the rock surface and reduce the wear on the drill bit.
Due to the karst development in this area, borehole data of different geology are collected.
Use different drilling methods:
1) There are rocks in the overburden, and the bedrock is inclined, such as the slope angle of bedrock.
Small stones or exploration stones invade the pile site in a large area, causing the phenomenon of "crooked hammer"
The slurry leakage at the contact between cylinder and bedrock surface or exploration stone is not serious, so "heavy hammer" can be used.
Knock "method for drilling. After the rock surface is leveled, drill holes normally. Otherwise,
First, backfill pebbles or pebbles with loess (1: 1), and compact them with a drill.
Form a retaining wall, and then drill a hole with a "heavy hammer tapping" method to cross the slope of the rock.
Or after the lowest point of rock exploration is 0 15 m, then drill normally.
2) In case of cracks and fissures, irregular cracks on the rock surface and fractured rocks,
When the inclination angle is large, it is easy to get stuck, and the backfill soil is higher than the bottom of the casing.
After 0 15 m pebbles, use the method of "heavy hammer percussion" to drill holes.
3) Cave phenomenon. For large caves with a layer thickness of 2 10 m, the bottom of casing should be protected.
When the stratum thickness between karst cave roof and karst cave roof is not large, casing should be used for follow-up.
Method, if the thickness is large and it is difficult to follow up the casing, the sleeve follow-up method is adopted.
4) When encountering beaded caves, the drilling data should be analyzed in detail.
Small caves can generally be made into holes. If the filling material is plastic clay or sand,
Class can be backfilled with clay and pebbles, and then rammed and drilled. if
Large sleeves are used for beaded caves that are not easy to form holes.
Small sleeve follow-up drilling method.
5) The living stone in the cave is treated, and sometimes the position of the cave will be judged when drilling.
Inaccurate, the heavy hammer still uses a high stroke to drill down, which is easy to cause the cave to go up.
The wall was suddenly difficult to break through, and the broken upper wall formed a big stone and fell into the solution.
The hole becomes a living stone in the hole. The drill bit rushed in and could not be taken because there were live stones.
Ballast, when this happens, take half soil and half stone.
Fill the cave before drilling.
2 15 hole inspection and hole cleaning
After drilling to the design elevation, the method specified by the supervision engineer shall be adopted.
Check the geometric dimensions such as hole depth, aperture and verticality. After passing the inspection,
Cleaning holes by slurry changing method.
Fabrication and installation of 2 16 reinforcing cage
Steel bars are coated with epoxy resin and processed according to the skeleton.
The rigidity and lifting capacity of the floating crane are divided into 10 ~ 15 m sections, and then they are released.
The epoxy resin coating is damaged, so it should be applied again before treatment.
2 17 underwater concrete pouring
Before pouring, re-measure the hole depth with a hammer to ensure that the sediment thickness at the bottom of the pile meets the requirements.
According to the specification and design requirements, concrete is poured by pumping, and should be connected when pouring.
Long catheter method, the diameter of the catheter is 30 cm and 35 cm, divided into 2 meters (another
Processing 1 section (1 m), which is connected by flange bolts and poured first.
Conduct air tightness test on the conduit and use it only after it is qualified. Back cover.
The volume of the funnel (i.e. the output of the first batch of concrete) shall meet the buried depth of the conduit at the time of back sealing.
1m. Self-made wooden balls are used as waterproof plugs between the funnel and the conduit, and used for back sealing.
Use the ball cutting method. After the back cover, remove the big funnel and replace it with a small funnel, next to the small funnel.
A storage tank is set, and the pumped concrete first enters the storage tank and then enters through the chute.
The small funnel can be lifted by a crane. Equipped on the construction site.
4 sets of 100 t jacks to prevent pile breakage or catheter failure.
Jack-up reinforcing cage or conduit. When grouting, the buried depth of conduit should be 2 ~ 6.
Meter (short for meter))
3 Conclusion
It is built in a special stratum with a lot of dissolved rocks and unstable overburden.
The foundation of punching cast-in-place pile is simple and safe.
At the same time, the construction progress has been accelerated and economic benefits have been achieved.
This improvement can provide reference for offshore karst geological pile foundation construction.
Resumption date: July 8, 2006
(Editor in Charge: White)
132006 10 Construction of Bridge Pile Foundation in Submarine Karst Stratum