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Special conditions of large diameter bored pile construction technology Deep

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1 Project Overview

Xingang Tianjin Binhai New Area on the 4th road tunnel is designed as dual ten lane viaduct piers and foundation due Jinbin Light effects , driveways not normally traverse . It is required to Tianjin - Binhai Viaduct 339 # ( brake pier ) and 340 # ( Shared pier ) pier for underpinning , underpinning φ2000mm using three and six φ1800mm bored bored . Where three φ2000mm bored pile length 90.00m, 6φ1800mm bored pile length 70.00m. Creepage piles located under the viaduct , viaduct bottom elevation of 10.00m ( Taku elevation , the same below ) , ground elevation of 3.00 ~ 3.50m. Just 7.00m clearance from about underpinning and 340 from the original 339 # # pier is only 7.50m ( see Figure 1 ) . After construction of self-balancing method to test pile bearing capacity testing, meet the design requirements .

1.1 site geotechnical conditions

According to the construction unit to provide drilling histogram . Site engineering geological formations are divided into nine layers :

① artificial fill soil (Qml)

② recently deposited soil (Q43Nal)

③ Section Ⅰ marine sedimentary layers (Q42m)

④ Section Ⅱ continental facies (Q41al)

⑤ Section Ⅲ continental alluvium (Q3eal)

⑥ Section Ⅱ marine sedimentary layers (Q3dmc)

⑦ Section Ⅳ continental alluvium (Q3cal)

⑧ Section Ⅲ marine sedimentary layers (Q3bm)

⑨ Section Ⅴ continental alluvium (Q3aal)

Site groundwater is mainly Quaternary pore water , still water depth of approximately 2.00m or so.

1.2 Design Requirements

According to information provided by the construction unit

1.3 engineering characteristics and difficulties

( 1 ) because at the basis of the original light rail viaduct close, never allow the emergence holes or wells collapse accident endangering the running rail .

( 2 ) due to the construction environment , restrictions on the existing rig equipment must be transformed , after the transformation of the construction equipment must meet the technical requirements .

( 3 ) vertical drilling requirements are particularly high , because since the static load test load balancing tank diameter φ0.60m, so in addition to the factors to consider reinforcing cage must be considered because the presence of the load box slurry pipe guide decentralization , increased difficulty . Load box location hole depth 60.00m, maximum diameter slurry pipe guide φ0.37m, the actual requirements of the vertical hole 1 /500 .

( 4 ) reinforcement cage fabrication and orifice docking, by limiting each section of the construction site of the effective length of the reinforcement cage 4.50m, a total of 20 ; reinforcement cage after docking vertical opening requirements ≤ 1/500. Orifice docking time as short as possible .

( 5 ) Since the soil is relatively soft, and the use of slag slurry wall , plus the multi-section steel cage orifice docking longer ( from mentioning slurry pipe drill pipe to guide decentralization finished about 60h), the first hole cleaning after the stability of the hole wall , the thickness of the sediment , mud high performance requirements .

( 6 ) due to heavy steel cage ( with test tube and testing facilities ) , theoretical weight 36.54t, affected by large cranes construction site can not be used , only use steel cage orifice rigs responsible for docking, decentralization .

2 construction equipment selection

According to the project and the bridge construction stratigraphy characteristics , selection after transformation, GW-25 drilling rig and GW-25B -type rig construction , the use of slurry wall positive cycle into a hole, reverse circulation hole cleaning , multi-section steel cage wellhead straight thread connection , guided underwater perfusion concrete slurry pipe pile process . After transformation, the GW-25 and GW-25B rig, torque 120kN · m, lift capacity 30t, rigs total height of 7.00m, the effective height of rigs 5.50m, machine drill a total height of 4.50m, after transformation of the equipment to meet the construction technology to

Requirements ( see Figure 2 ) . Other major equipment : 120kW generator sets ( alternate ); 750E air compressor ; φ300 catheter 200m; KE-200 inclinometer ; 16t crane and so on.

3 Construction Technology and Quality Control

3.1 Construction preparation

3.1.1 Surveying positioning, layout settlement observation points

Location pile up by the construction unit testing . To grasp the pile hole construction impact on the original piers , on both sides of the three piers were laid three settlement observation points , hole depth 40.00m once a day before the settlement observation , hole depth 40m twice daily after settlement observation , found that timely remedial action.

3.1.2 The selection of drill

To ensure the verticality of the pile hole , hole using a drill or hob counterweight alloy drill construction ( to the depth of the hole about 30m ) , use double belt comb -type alloy drill four wings to the final hole drilling .

3.1.3 hardened ground

As topsoil is relatively soft, capacity can not meet the rig construction requirements of the upper 1.5m deal for gravel cushion for filling , excavation beneath the overpass trough, length 15m, width 6m, 1.5m or so deep , gravel and laying sand cushion , capped with 30 cm thick C25 concrete , surrounded by grading , reserve position of orifice .

3.1.4 casings buried

The projects selected thickness 10mm casing , the diameter

Respectively, 2400mm, 2000mm, length of casing is not less than 3.00m. Casing laying note the following:

( A ) Casings centers should coincide with the center of the pile , the deviation is less than 50mm, less than 1% slope ;

( 2 ) casing surrounding layered clay compacted than surface casing height 200 ~ 300mm. Confirm pile hole location of underground pipes again when no openings .

3.2 Equipment installation and mud prefabricated

3.2.1 equipment installed in place

Before laying the rail and in the open area of the rig mounted on the rail , and then move on the rail alignment of the pile rig sites , drilling rig base firmly . Turntable rig horizontal ; pile sites turntable Center , Crane Center in the same vertical line .

3.2.2 slurry preparation

Prepared before opening a number of high quality slurry in order to ensure smooth drilling .

Slurry preparation and detection with the person responsible for strict control of performance indicators.

Mud formulations : sodium bentonite : 100kg/m3 ( mud )

Caustic soda : 1% by weight of bentonite mixed

CMC: 1% by weight of incorporation of bentonite

Mud Properties: Specific Gravity : 1.10 to 1.25

Viscosity : 22 ~ 28S

Colloidal rate:> 95%

Site preparation methods : first quantitative water injected into the mixer , will be calculated according to the provisions of bagged dry bentonite poured into water with stirring , while the already calculated according to the provisions of caustic soda and CMC incorporated therein , stir into the mud reserve pool can be.

3.3 Drilling into the hole

( 1 ) hole drilling using decompression , the project φ2000mm pile drill hole selection hob ( hob drill bit body length of 2.00m, weight about 6t), φ1800mm add weight piles using a double belt drill drilling. Ensure pile hole verticality.

( 2 ) Always check the process of drilling machines drill the vertical , horizontal turntable , ground subsidence and elevation casing situation , carefully observe the mud hole and slag , identify problems and timely treatment.

( 3 ) plus drill to drill before lift-off hole at the end of the drill bit 200 ~ 300mm, punching 10 ~ 20min or so, mention drilling plus drill pipe. Plus drill pipe drill pipe checked carefully before bending , welding flanges , pipe wear , etc. , to eliminate substandard drill down into the hole.

( 4 ) vertical drilling each hole measuring less than 3 times , hole depth 40m, 80m, final hole each time.

( 5 ) Mud index control : In the drilling process should be based on performance indicators to choose a different stratum of mud, mud -site configuration measuring instruments , measuring mud performance at any time .

Different formations mud performance indicators in the table below three .

( 6 ) the borehole collapse slight leakage of plasma and timely performance of the whole mud and mud during construction to maintain a good performance index .

( 7 ) If there is a serious accident plasma leakage , timely recharge mud, identify the reasons for re-treatment.

( 8 ) If there is a more serious collapse , first recharge mud, with a forklift backfilling , compacting backfill until then re- drilling.

3.4 once Chiang Khong

( 1 ) Drilling depth to meet the design after the first positive cycle Chiang Khong , the drill bit off the bottom of the hole about 200 ~ 300mm , reverse slow sweep times, the bottom of the hole and the drill mud massive crush on .

( 2 ) with a reverse circulation hole cleaning once a device based on an existing ( positive circulation drilling equipment ) homemade mixing chamber . Specific operation is as follows : ① the first cycle with a positive hole, and then drill the hole made ​​, the mixing chamber orifice add depth from a position of about 40m , plus the down pipe , while a good lashing hole duct ; ② check the air duct installation. First start recharging the pump , after opening the duct valves, air flow commissioning work ; ③ water hole to have someone responsible for the situation and ensure the mud head height ; ④ a mud hole cleaning performance requirements : Due to the reinforcement cage longer wellhead butt ( about 20 connectors , about 60 hours ) , to maintain the stability and bore hole wall thickness of sediment . Decentralized reinforcement cage should be kept before the mud following properties: density: 1.15 to 1.20 ; Funnel Viscosity : 20 ~ 22S; sand content : not more than 3%; PH value: 8-10 ; colloidal rate: 95% ; loss of water : 14 ~ 20ml; mud skin thickness : less than 2mm. Head height should be maintained while the hole .

3.5 steel cage production, docking place

3.5.1 Process selection reinforcement connections

φ2000mm pile reinforcement cage reinforcement 54D32, steel cage length 83.4m, to be made ​​of 21 , the orifice straight thread connections, each cage must 1134 section header ; φ1800mm pile reinforcement cage reinforcement 46D32, steel cage length 63.4 m, to be made ​​from 14 , to be 644 per cage section header .

Reinforcement quantity, spacing is small, the number of joints and more difficult to operate using welding or soldering , takes a long time , so the cage muscle tendons connected by straight thread connection. Each section has a length of 4m or 9m. Stiffener with added "△" type internal support , ultrasonic detector tube every pile 3 , the bottom block , ultrasonic detector tube inside and lashing in a cage with steel cage down into the hole.

3.5.2 reinforcement cage production

( A ) steel processing must be on level ground . Reinforcement cage machining program : reinforced steel test approach → → → single machining steel cage steel cage acceptance → forming → ​​Iguchi struck , fixed steel cage .

( 2 ) a single reinforcement processing: Feeding reinforced steel processing in a single front , by cutting, straightening , forming steel into line drawings , and then sub- models were stacked in the molding of reinforced dumps to prepare for access . Steel straightening , the surface can not have oil and rust .

( 3 ) In the same section joint reinforcement shall not exceed 50% , two joint spacing > 1120mm.

( 4 ) the required stiffening ribs bend round, wrapped around the ring after ring bars straightened back .

( 5 ) the reinforcement cage placed to be smooth , not a focal point uneven emergence cage body overhead bent.

( 6 ) Used φ8mm righting reinforced concrete cylinder made ​​of reinforced wear φ100mm , each 4m a group of six equally spaced welded reinforcement , making sure the cage center.

3.5.3 Butt steel cage

( A ) under the viaduct steel cage orifice docking , first remove the drill table .

( 2 ) Pre- assembled Technology: To overcome the straight thread connection process on the reinforcement length deviation and plane deviation of the special effects , to ensure the smooth docking port , so the steel cage to take pre- assembled production technologies.

( 3 ) in straight thread butt butt welded steel cage at the same test tube . Test tube welded parts can not enter into the mud , each finished welding a test tube , the tube is filled with water, the top of the block is good.

( 4 ) Positive reinforcement cage guide pads as required to weld .

( 5 ) Non- pier cage, hit the cage , twisted cage cages and anthropogenic pressure .

( 6 ) reinforcement cage positioning using four φ32 reinforced fixed .

( 7 ) Since the reinforcement cage large tonnage , and highly affected by the impact of light rail , using the rig dipping and developed using the unit hooks, both to ensure the decentralization of the reinforcement cage deformation, but also ensures the safety of the next cage . Specific operation is as follows:

Subject into the hole and the first hole cleaning work is completed, the rig turntable after the shift, and then a special plunger plate placed on the machine pillow to ensure plunger orifice center coincides with the center of the plate . Section steel cage skeleton first two-point lifting method into the hole until the first frame stiffening hoop down to the opening position, while the four plunger push the plunger fastened stiffening hoop to ensure the reinforcement cage skeleton vertical . Then the orifice for steel cage skeleton butt . Upon completion of the docking steel cage lifted out of the plunger , and then down to the second hole of the reinforcement cage skeleton , repeat the above steps. To ensure the reinforcement cage skeleton is inserted rod slipped from the end of the plunger is set to hook ; plunger to ensure the reinforcement cage can withstand the weight of the rear end portion of the plunger plunger sleeve .

3.6 Placement of slurry pipe guide

Lead slurry pipe diameter φ300mm, thickness 8mm, threaded connection .

( A ) To guide slurry pipe wall is smooth, inner diameter the same size, connected to a reliable , sufficient tensile strength and good sealing .

( 2 ) the guide tube pulp slurry prior to use as a guide tube sealing performance test , the pressure is not less than 1.2MPa, unqualified allowed slurry pipe down into the guide hole.

( 3 ) decentralized installation guide slurry pipe seal test must be numbered consecutively in the order bottom , indicating the length of slurry pipe guide , plus a good tighten the threaded ring , you can not mess with .

( 4 ) from the bottom of the hole at the bottom of the catheter 300 ~ 500mm.

( 5 ) people accountable guide slurry pipe cleansing and management.

3.7 perfusion secondary Chiang Khong before concrete

Since a long time lap steel cage , drilling deep holes thick sediment may ( subject to the specific measurement ) , with a positive cycle of Chiang Khong difficult to meet the design requirements , so the use of reverse circulation hole cleaning . See Figure 4 below .

( A ) the general down to the mixing chamber orifice 35.00m from around the catheter after the next , with a slurry pipe and duct down into the duct , the slurry pipe , duct and conduit with a cap on the slurry pipe , duct connected, then connect the catheter and catheter cap together , the surface of the slurry pipe , duct connected.

( 2 ) starting air compressor , hole cleaning to meet the requirements put out the slurry pipe , duct aside , put filling bucket .

3.8 concrete pouring

( A ) the amount of control the beginning of irrigation

According to " highway bridges and culverts technical specifications" , the first set of concrete should meet the minimum capacity required under the formula V:

V = h1 × 3.14d2 / 4 + Hc × 3.14D2 / 4

Where V- first set of concrete minimum capacity (m3)

Beginning of irrigation by calculating the amount of V = 10m3.

( 2 ) the amount of initial filling pressure the ball once used to mention cover method , which uses the ball once for isolation plug. Made a 3m3 of storage hopper , the infusion , the first hopper filled , to fill 8m3 concrete drive to the storage and filling bucket beside the hopper lift the cover at the same time , continuous release of concrete concrete car , in the middle without interruption . Ensure early catheter buried depth.

( 3 ) the infusion process, maintaining the continuity of perfusion concrete , on-site car spare concrete not less than two .

( 4 ) as measured with a fine wire rope . Person responsible for the detection of rising height of concrete , concrete time before extubation must detect rising height , keeping the catheter depth 2 ~ 6m, non- catheter removal concrete surface .

( 5 ) must be checked every car concrete concrete slump , slump unqualified strictly prohibited.

( 6 ) In order to prevent large coarse aggregate stuck pipe , mounted on the funnel 50mm × 50mm mesh sieve.

( 7 ) pile top elevation of Control: The last time control of concrete perfusion measurement height must be more than a few concrete surface points, while using homemade concrete overshot control.

4 Construction prone to problems and preventive measures

4.1 into the hole part

4.1.1 orifice collapse

Orifice near loads heavier, more loose soil , has long been immersed in water ; casing is too short, the bottom of the casing is not buried in the clay layer ( silty clay layer ) ; casings not fill compacting the soil around or casing too thin quilts soil squeezing variants .

Preventive measures: indeed protect the tube thickness not less than 10mm, bottom casing buried in the clay layer ( silty clay layer ) , retaining the barrel length not less than 3.00m. Casing filled with clay around the dense casing above the surface 200 ~ 300mm.

4.1.2 borehole collapse

Due to the larger diameter drilling , construction drilling a long time, plus the formation factor in the process of drilling hole collapse phenomenon often occurs ; construction prolonged power outage is caused by external reasons hole collapse .

Preventive measures: ① in the construction process to maintain the head height of the borehole , supervised mud , mud density greater than 1.15 , the funnel viscosity of greater than 20S; ② against sand , silt slurry preparation quality control footage speed ; ③ reserve a certain number of high-quality mud, found the hole dropout timely fill pulp. ④ forklift spare time backfill , standby diesel generator set to provide timely impetus.

4.1.3 Oblique

As drilling deeper , with the formation , the operation process , the bit precision, the bending of the drill pipe and other factors often make the vertical hole not meet design requirements .

Preventive measures: In addition to maintaining the construction into the hole drilling three-point line , keeping the drill pipe, drill vertical external should take the following measures: ① to improve the machining precision drill through tooling machining precision drill engineering methods . Bent down into the hole to prevent the drill pipe ; ② openings must take hob decompression drilling.

4.1.4 broken drill

Broken drill hole , in addition to the quality factor drill , drilling depth , hole resistance , long working hours , but also with the operating methods.

Preventive measures: ① the next drill , drill drill drill when carefully check the quality , substandard allowed to drill down into the drill hole ; ② carefully observe the drilling parameters , abnormal timely stop drilling, to drill check the hole drill , drill situation ; ③ based on past experience in construction, 40m meters deep in the hole , you must check the drill bit to drill , drill pipe in the hole usage simultaneously detect its verticality .

5 Conclusion

Tianjin Binhai New Area, in addition to light rail underpinning larger diameter piles , drilled deeper factors, due to space constraints , the construction more difficult and risky . Large diameter hole is bored hidden works , but many processes , quality accident occurred is difficult to remedy. The works in the construction process on the rig through the transformation , enhance quality control , careful study of new construction methods and process, strict quality control of the process to ensure the quality of bored piles , construction period and 340 339 # settlement of Pier volume less than 1mm, pile bearing capacity and quality to meet the design requirements , and achieved good economic and social benefits.