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Broken slip layer geological construction of large diameter bored piles

Broken slip layer geological construction of large diameter bored piles

(Summary description)Hangzhou to Lanzhou National Highway Traffic lines are "national key trunk road layout planning" key highway national road network " 13 vertical 15 horizontal" in a cross , is to connect China's eastern , central and southwestern regions of the important horizontal lines . Yunyang, Fengjie to Chongqing Expressway is a line in Chongqing , Hangzhou, Lanzhou important sections of the territory , but also the Chongqing Urban Planning of the " Ring 8 shooting " highway network, an important part. The construction of the project on improving the national trunk road network, improve traffic behind the Three Gorges reservoir conditions, implementation of the " western development " strategy is important.

Broken slip layer geological construction of large diameter bored piles

(Summary description)Hangzhou to Lanzhou National Highway Traffic lines are "national key trunk road layout planning" key highway national road network " 13 vertical 15 horizontal" in a cross , is to connect China's eastern , central and southwestern regions of the important horizontal lines . Yunyang, Fengjie to Chongqing Expressway is a line in Chongqing , Hangzhou, Lanzhou important sections of the territory , but also the Chongqing Urban Planning of the " Ring 8 shooting " highway network, an important part. The construction of the project on improving the national trunk road network, improve traffic behind the Three Gorges reservoir conditions, implementation of the " western development " strategy is important.


1 Project Overview

Hangzhou to Lanzhou National Highway Traffic lines are "national key trunk road layout planning" key highway national road network " 13 vertical 15 horizontal" in a cross , is to connect China's eastern , central and southwestern regions of the important horizontal lines . Yunyang, Fengjie to Chongqing Expressway is a line in Chongqing , Hangzhou, Lanzhou important sections of the territory , but also the Chongqing Urban Planning of the " Ring 8 shooting " highway network, an important part. The construction of the project on improving the national trunk road network, improve traffic behind the Three Gorges reservoir conditions, implementation of the " western development " strategy is important.

Plum River Bridge in Chongqing Fengjie to Chongqing Yunyang on a highway bridge, located in urban and rural areas of Chongqing Fengjie County territory in the northwest of the old town of Fengjie approximately 3.0km across the Plum River, Plum River Bridge beginning and ending mileage Stake for K76 +945.8 ~ K77 +766.8 m, bridge length 821m, span combination 190 (43 +147) +386 +190 (43 +147) +2 × 25m, main bridge towers and double cable planes PC girder cable-stayed bridge , in order to increase the overall stiffness of cable-stayed bridge , located on both sides of an auxiliary pier across the 190m side cross into (43 +147) m two cross . In secondary and transitional pier and pier beams are set on the next tower vertical supports , the structure of semi-floating system .

Approach using 2 × 25m prestressed concrete continuous box girder, at around two , single-box dual-chamber section , the use of stents in-situ .

Standard double girder cross-section main rib section , the full width 27.5m, main beam center height 2.6m, standard girder hanging basket cantilever construction segment are used , Cantilever segment length 6m. Cross- border use of stents in-situ , long 55.86m, divided into three pours. Sarasota using "H" type , reinforced concrete structure. Tower height 193m, of which the tower high 78.5m, the tower height 42m, tower under high 72.5m, are made of rectangular hollow section , set the radius of 0.5m square arc segment , the tower dimensions of 4.5m × 7.5m, the tower dimensions of 4.5m × 7.5m, 4.5m under the tower lateral variations in the end by the Ministry of size 9m, 7.5m vertical variation in the end by the Ministry of size 13.0m. As the next pylon resistance may ship direct impact, 36m above the solid segment set within 0.8m thick diaphragm for strengthened along the bridge and transverse to each one , the formation of the cross in the box bracket . In the tower anchor zone , set the cable anchor block tower wall , to balance the horizontal component of cable-stayed in the anchor zone emplaced within 15-12 circumferential prestressing tendons . Pylon total down two beams, prestressed concrete structures for the whole , the beam cross-section outline Dimensions Height 6m × width 7m, lower beam cross-section outline Dimensions Height 7m × width 6.5m, longitudinal prestressing anchorage in a tower outside . Sarasota pile length 24.8m × width 32m × height 6m. Main pier foundation pile diameter 2.5m, pile length 60m, arrangement of five rows of five , each pier 25 , a total of 50 full-bridge , are bored by friction pile design .

Two major technical indicators

1 road grade : two-way four-lane carriageway width 2 × 3.75m ( one-way ) , highway

(2) calculate driving speed : 80km / h

3 Deck Width : 24.5m; cable-stayed bridge deck width : 27.5m ( including anchor zone )

4 Design load: highway grade Ⅰ

5 Maximum longitudinal slope : ≤ 3%

6 Deck Cross Slope : 2%

7 design flood frequency : 1/300

8 navigation standards : the highest navigable water level 173.242m, meet four navigable waterway clearance and technical requirements

9 earthquake design intensity: basic intensity is Ⅵ degrees

3 bridge site area Natural geography

3.1 topography

Bridge site area of tectonic denudation - Erosion low mountain landscape. Bridge sites across the NNM Mei River downstream to the valley was "U" shape , the bottom is more wide and slow , longitudinal slope less than 1% ; surface water during that period because the strong erosion cutting, relatively steep terrain , relatively bridge site area elevation 200-350m. Overall slope of the hillside cross shore about 25-360 Fengjie , Yunyang shore about 26-390 .

3.2 Geologic Formations

Bridge site area is located in the hinterland of South paraplatform crust as a whole is relatively stable, the bridge site is located by the river Chu anticline axis , specifically the bridge located at the low angle of inclination Nancy monoclinic layer , occurrence Fengjie Shore 2250 ∠ 110, Yunyang shore 2250 ∠ 90, near the bridge toward the vertical axis and the strata .

Bridge site area than crushing rocks , joints , fissures .

3.3 lithology

According to engineering geological mapping and drilling results show that: both sides of the bridge district board is residual soil slope (Qel + dl) coverage , Plum Creek Valley alluvial soil distribution (Qal + pl), the underlying bedrock of Triassic system Badong group (T2b) of argillaceous limestone . The basic characteristics of geotechnical engineering geological layers from top to bottom :

1 Quaternary alluvial soil (Qal + pl):

Alluvial layer is only distributed in Plum River riverbed , mainly in the sallow gravel , pebble -based, loosely - Micronesia , thickness 2.5-5.0m.

2 Quaternary eluvial soil (Qel + dl):

Loam : yellow, with small amounts of breccia , wet, soft plastic . Thickness of less than 2.5m, local distribution .

Broken ( block ) Stone mixed loam : seen gentle slope surface area of argillaceous limestone gravel , marl , angular , sub- ribbed . Particle size of 2-8cm, content of about > 50 % gravel filling angle loam , slightly wet , loose - a little secret . Thickness of 3.5-6.0m.

Stone : local distribution , stone content of about 50-60 % , as argillaceous limestone , marl , angular shape , size 0.2-0.6m, filled with gravel and loam .

3 Triassic Badong system (T2b):

Argillaceous limestone , grayish green , microcrystalline structure , in a small amount of thick-bedded thin folder . Strongly weathered layer of rock joints , fractured rock is extremely broken , core mostly Chunky , RQD = 7.04-38.15%, uniaxial compressive strength limit saturated 14.7MPa, uniaxial compressive strength limit natural 28.9MPa; weak wind spend more complete core layers , short prismatic , blocky , RQD = 5.19-35.29%, limit saturated uniaxial compressive strength of 25.2MPa, uniaxial compressive strength limit natural 33.2MPa; breeze spend more complete core layer , was short column, long column , RQD = 14.27-45.63%, uniaxial compressive strength limit saturated 40.7MPa, uniaxial compressive strength limit natural 58.0MPa, cohesion 2.6MPa, internal friction angle 42.8 . .

3.4 adverse geological phenomena

Bridge site area of cross-strait steep slopes , rock weathering depths greater than rock crushing, after the Three Gorges reservoir water storage stability will weaken the role of the downhill , the Three Gorges water level below the Three Gorges reservoir bank slope stability is affected by alteration of greater impact, especially those located in the Three Gorges reservoir water level fluctuations within the band , rock cover thickness is larger and more broken cross toe area.

3.5 hydrogeological characteristics

Groundwater is mainly loose rock pore water and bedrock fissure water .

Diving loose rock voids occur in loose deposits of Quaternary gravel , angular gravel , stone kind of soil and weathered rock by meteoric recharge , generally poor rich water , groundwater runoff during rainfall speed, valley slope and slope excavation will have groundwater seeping on route adverse slope stability .

Size and distribution of bedrock fissure water uneven layer of hydrous and closed joints minimal, only the larger joints and splitting tensile shear joints ~ Zhang Fu water is relatively large. Overall lack of water along the bedrock fissure water .

3.6 meteorology, hydrology

Meixi warm subtropical monsoon climate , with a mild climate , abundant rainfall, four seasons, illumination suitable for long frost common dry winter , drought prominent feature . The average temperature in the region for many years 16.8 ℃, extreme maximum temperature 39.8 ℃, extreme minimum temperature -9.2 ℃. By early 2006, the reservoir water level of 154.742m run to 2009 hubs impounding water level is 173.242m. As encountered during construction in Chongqing hundred years of drought , the reservoir water level dropped , the actual reservoir level +140.0 m.

4 pile into the hole

4.1 the choice of drilling machinery

According to the bridge foundation construction of geological data and practical needs , the main pier on the pier every four YCJF-25 reverse circulation drilling rig hydraulic shocks and 2 10T positive cycle impact rig . The bridge to the impact of reverse circulation drilling rig mainly through proven : YCJF-25 full hydraulic percussion reverse circulation is more suitable for the construction of the bridge pile , and achieved good results. YCJF-25 full hydraulic percussion reverse circulation drilling rig main technical parameters: hole diameter 1.2-2.5m; drilling depth : 80m; Rated Drill Weight : 8.0T; drill stroke :0.1-1 .3 m; Main hoist lifting capacity : 100KN ; slagging mode: reverse Circulation : Main motor power : 75KW; weight : 19T.

4.2 laying casing

Wall reinforced concrete casing , made of hand-dug hole . Wall concrete and pile the same label , thickness 20cm, Wall each section height 1m, catchy diameter 2.7m, under the port diameter 2.9m, Wall laid φ8 steel mesh inside , horizontal and vertical spacing of 20cm, each section of the Wall vertical reinforcement using hooks connections so integrally connected vertically Wall . Casing above the top surface 30 cm above the ground , buried in the soil depth casing determined according to the actual situation , retaining the original cylinder bottom mouth buried below ground is not less than 2m, casing length 3-6m, casing and vertical plane position deviation deviation to meet the design and specification requirements.

4.3 mud circulation system settings mud circulation system consists of mud tanks, sedimentation tanks , mud , gravel pump , and the pump tube and other components. Due to space narrow , mud tanks, sedimentation tanks beside the direct use of pile hole casing .

4.4 Drilling 1 rig in place , should ensure a smooth base , in the drilling and operation should not result in the displacement and settlement . Rig lifting the top edge of the pulley , rope center and a pile hole in the center of the three should be the same vertical line, the deviation is less than 2cm.

2 holes drilled prior to the preparatory work for inspections drill hammer weight , diameter, alloy block welding quality ; rope and hammer is securely connected sets , whether serious wear and tear ; rope breaking force meet the construction needs by whether the wear is serious ; whether the performance of various machinery and equipment to meet the construction needs, is functioning properly ; whether salvage measures and equipment so as to ensure the smooth progress of construction drilling .

3 each hole before drilling design data plotted according geological sections , in order to check the actual geological .

4 in the open before drilling rig in place technical personnel checking deviations foundation is solid , with the drilling conditions, through quality inspection engineers and supervisory consent before drilling .

5 spud when the first pumped water or mud . Spud are slow when drilling, all drill into the formation to be only after the accelerated drilling.

6 drilling placement continuously, without interruption . In case of problems dealt with immediately .

7 large diameter bored piles are higher on the mud , drilling mud should be selected based on geological conditions , holes , drilling performance , mud materials, etc. OK. During the construction process , we must do mud performance indicators reasonable control .

8 stratigraphic drilling process and pay attention to changes in a timely manner to fish for residue samples to determine the geological category entered into the record of the table , and in contrast with the geological report , slag samples should be number saved for analysis . When the actual design drawings provided by geology and geological difference between the larger and geological cross checked in detail , a good collection of photos and other information, in a timely manner to the supervising engineer and design institutes reflect the final hole to determine a reasonable elevation and pile length .

9 drilling process technician timely completion of drilling construction records , consistent with the drilling progress , shift changes, explain the circumstances and the next one drilling precautions . Borehole logs to fill must be true , specification.

10 drilling process, according to the different strata choose the right stroke , mud performance indicators, as well as the appropriate method of mud circulation . Encountered clay layer , low stroke, dilute slurry is circulation drilling ; through the gravelly soil , the appropriate use of stroke ; regolith relatively strong crushing, drilling strongly weathered layer should be adopted in the stroke , and in the bottom of the hole to join adding clay or sawdust in the mud to play a role in plugging ; encounter Taku stone and weak breeze strata , should adopt a large stroke .

11 by observing the rope swing , and to check with the geological profile , when faced Put stone , caves, etc. UNEVEN junction formation at the time, adding rubble at the hole bottom , the surface pad level , prevent the occurrence of inclined holes or curved holes.

12 In order to correct the drills stroke, to keep abreast of drilling speed , on a wire and marked ; shock to the attention of evenly -release rope length , with special attention to prevent Matsunawa too small to form a " striking air hammer ."

13 reason to stop drilling, opening to add the cover and make sure there is enough head height of the hole , and often circulating mud , mud hole becomes soaked with water to prevent the hole wall , causing the collapse of the orifice . Non- drill hole left in order to prevent the emergence of the phenomenon of underground drilling .

14 during the drilling process should be timely checked drilling , casing inspection holes and deviations .

15 Troubleshooting :

( A ) . Drain syrup : adequate preparation before spud sawdust and clay plugging materials . When a minor leakage pulp , sawdust can be added in the hole , the cycle plugging. When severe plasma leakage , immediately proposed drill to the bottom of the hole to join 1-2m thick clay , and add water to the hole , ensuring the hole head height , plugging holes and then added to about 1m thick stone tablets , re- impact pushed the clay within the gap plugging.

( 2 ) the swap Drill : advance in the hammer at the top 1/3 of the position put salvage rope, reason out drilling , the use of decentralized immediate salvage rig or hoist hook , mud circulation at the same time , to prevent drilling residue buried hammer, if necessary underwater blasting, made after the hammer loose .

( 3 ) . Cards Hammer : In the drilling construction, especially drilled to elevation +116 m-+113.6 m segment strongly weathered rock , the rock easily broken , and there was a certain angle of inclination , the impact hammer footage , the hole wall broken loose layer prone to slippage occurs card drill phenomenon ; otherwise breeze when the drill bit to the rock , because rock breeze thick argillaceous limestone is a microcrystalline structure , easy chunks of rock crushing, drilling reaming coefficient smaller , and reverse circulation drilling rig drill hole bottom for the passive rotation , so reverse circulation drill rig into the hole in the course of this layer is also very prone to accidents hammer card .

To prevent the occurrence of the card hammer , drill base alloy ingot should be encrypted , and the bit retaining ring extending 1-2cm, and the retaining ring made of rib top sloping chamfer. When a card is hammer , keep mud circulation , along with a crane evenly around the hole wall decentralization four seamless ( carrying capacity of not less than 100t), welded steel bottom fishing hook, hanging on the drill bit retainer on the upper end of the bracket and wear welding through the orifice 2 * 2I50 tool steel, tool steel flat on the orifice , supported on the outside of the square wooden casing , each fishing hook 50t jacks through 2 sets of 8 units jack while jacking . When drilling in Broken slip layer , the need to bore and clay , sawdust, cement , etc., using the stroke impact process . Underwater concrete pouring when necessary , until the concrete reaches a certain intensity before drilling. The base of each pier pile drilling arrangement , first drill the four corners of the pile , in dealing with broken slippery layer, both before pouring concrete underwater drilling, completion of the four corners of the pile , the other piles drilled into the layer occurs when the card hammer, much less chance of missing a paddle .

4.5 Chiang Khong

Drilling in place, Chiang Khong before full hole depth range sweep up and down the drills holes , scraping mud hole wall thicker skin . After the final hole is used for slurry circulation drill hole cleaning method , reverse circulation rig pumping slurry method Chiang Khong , Chiang Khong whatever method is strictly prohibited ultra-deep into the hole in lieu of Chiang Khong , Chiang Khong process to ensure that there is sufficient the Chiang Khong time and repeated cycles , the hole of precipitation, suspended drilling residue and precipitate out the full replacement , hole cleaning after each performance index and the thickness of sediment pile must meet the technical specifications and requirements of design drawings .

2.5m diameter, large diameter bored piles for the high performance requirements of mud , in order to ensure the quality of concrete piles perfusion , perfusion guarantee smooth , high-quality construction made of clay and bentonite slurry and mixed with additives such as acrylamide , this the advantage of slurry is dispersed , low-solids , high viscosity .

Chiang Khong after mud performance indicators should meet the following requirements: the relative density of 1.06-1.20 , viscosity 17-20Pa.s, sand rate ≤ 2%, colloid rate of ≥ 98%. Rate , also known as colloidal stability rate is mud ballast grains remain in suspension performance is to detect mud sedimentation rate indicators as quality management point of control .

Chiang Khong to before reperfusion after a long time, in order to ensure uniformity of mud and perfusion quality, foundation piles must be performed before perfusion secondary Chiang Khong .

4.6 final hole inspection

1 drilling in place , check the pore size, pore shape and inclination , using the length of the pile diameter of 4 to 6 times higher than 10cm diameter steel cage reinforced inspection hole is hanging into the borehole testing.

(2) the center of the hole , diameter , inclination , hole depth , sediment thickness , hole cleaning after mud performance indicators must meet the design and construction technical specifications.

5 reinforcement cage fabrication and installation

5.1 Design of reinforcement cage length 62.5m, making three points , each section length 18-27m, 9m of rebar cut lengths are used . Steel connection : Strengthening the circle and positioning sided arc welding steel are used , mainly due to the reinforced single lengthening using flash butt welding , steel cage connection between the use of upsetting straight thread fittings.

5.2 After the final hole to timely reinforcement cage decentralization work . Multi-point lifting steel cage into a vertical position to prevent the steel cage in lifting and deformation during transit , transshipment bit slowly placed into the hole , the hole wall to prevent the collision . In the steel cage decentralization process should be timely detection of connected fittings and lashing ensure ultrasonic testing pipe joints tight , does not leak pulp, does not occur in the concrete construction shift . Decentralization in place , you must make steel cage center coincides with the center of the hole pile , and then welded four symmetrical U-shaped steel hooks , hooks and vertical reinforcement force welding firm .

6 pile pouring concrete piles to ensure the smooth progress of construction , the use of an inner diameter of 300mm, wall thickness of at least 4mm bayonet steel conduit . Catheter before use according to the construction specifications and requirements for watertight joints tensile test pressure test to check the catheter connector firmly and rigor to ensure that the concrete casting process safe, reliable , non-shedding , watertight. Concrete piles should be continuous perfusion , rapid manner , so that one go. After arrival strength concrete piles , concrete piles quality for ultrasonic testing. Pile test results consistent with the design and construction technical specifications .

7 Conclusion

In the early stage of drilling time , due to the complexity of the geological underestimated , inadequate preparation , such as plasma leakage occurs , swaps hammer, sticking and other difficulties are more construction progress is relatively slow. By problems , constantly analyze the causes , how to draw a set of prevention, effective measures to deal with the problem , regardless of the latter part of the construction progress and quality have achieved satisfactory results , while providing a reference for similar projects in the future experience .

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Key words: hield tool  Engineering tool  Wear-resistant heart

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