I. Project Overview:
(I) Project Characteristics:
Fulin? Jin Gui Liwan Phase II X standard (Cuizhuyuan) is located in XX City, education road and the south side of the intersection of the Wenshi Road, the site has convenient transportation, all construction machinery and equipment can be directly into the construction area. The site of the construction area is open and there are no buildings on the surface of the construction area.
(2) Design Overview:
The pile foundation of this project is hand-dug hole pile, the pile diameter is 800-1200mm, the strength grade of pile concrete is C30, the strength grade of retaining wall concrete is C25, the average thickness is about 175mm, the longitudinal reinforcement bar is 10Φ12 through-length, the helical hoop is φ8@200, and the reinforcing hoop is Φ12@2000, the holding layer is limestone, and the pile end is ≥500. The pile end is limestone, and the pile end enters into the holding layer ≥500.
(3) Geological condition:
(4) The lithology of the ground layer from top to bottom is as follows:
Artificial fill→powdery clay→limestone→charcoal tuff→mud tuff.
Surface water bodies in the site area are mainly concentrated in the surface water, and there are two layers of groundwater, the first layer is mainly in the upper stagnant water in the artificial fill and pulverized clay, and the second layer is in the limestone, which is karst fissure ~ cavern water. The depth of groundwater level is 78.95-80.55m.
(E) Geological condition analysis:
The geological condition of this project is more complicated, and the construction is more difficult, which is mainly manifested in the following aspects:
1. The depth of rock at the site is shallow.
2, weathered charcoal limestone is hard, compressive strength of 72.7Mpa, drilling is more difficult, slightly weathered limestone is even harder, compressive strength of 115Mpa, drilling is even more difficult, with the pickaxe can not be dug, you need to blast to loosen the hole dug into.
(F) the characteristics of the project, difficulties and countermeasures
1, the project workload, tight schedule
Countermeasures: into the well organization of 40 groups (80 people) of civilian workers at the same time excavation, can be excavated at the same time about 40 piles wells, the use of commercial concrete filling, and at the same time, to prepare 200Kw diesel generator set a standby, can be 24 hours to organize construction.
2, the swing space and approach road for the new filling area, and is in the rainy season
Countermeasures: approach road and concrete mixing station and reinforcing steel material storage and production workshop, pavement, ground must be hardened, the work must be carried out urgently.
3, the geological conditions of this project is extremely complex, the construction difficulty is mainly manifested in the following aspects:
a, the site groundwater level is high, the single well gushing water may be larger.
b, the holding layer is hard, the compressive strength of weathered charcoal chert reaches 72.7MPa, and the compressive strength of slightly weathered limestone reaches 115MPa, so it is difficult to dig in with a pickaxe, and the workload of entering the rock is large.
Countermeasures: using individual wells point precipitation, reduce the water table, using multi-hole small amount of loose blasting, accelerate the progress of the rock.
4, poor conditions of temporary workshops, personnel density, health care work is difficult
Countermeasures: site configuration full-time health cleaner, improve environmental hygiene, room windows, ventilation, regular disinfection, such as the prevention of SARS as the prevention of influenza, the site is equipped with a sufficient number of commonly used first aid items and medicines.
5, the construction of this project in the rainy season, and the pre-temperature is low, high humidity in the air, into the well construction workers every day from the inside out clothes are wet, every day have to take a shower and change clothes, and clothes in the natural conditions is very difficult to dry, this matter seems to be a small matter, but directly affects the health of the workers and the progress of the construction.
Response: the site is equipped with hot water pots, equipped with dehydration and drying machines, and arranged for special people responsible for drying clothes for the civilian workers to maintain combat effectiveness.
Two, construction preparation
(a) operating conditions
1, artificial hole pile hole, well wall support should be based on the soil characteristics of the region, groundwater distribution, the preparation of a practical construction program, the calculation and design of well wall support.
2, the site before excavation to complete the three passes and one leveling. Obstacles such as cables, pipelines, old buildings and equipment foundations on the ground and underground have been removed and dealt with. All temporary facilities, such as lighting, power, ventilation, safety facilities are ready.
3, familiar with the construction drawings and the site of the underground soil, hydrogeological data, so as to know.
4, according to the foundation plan, set the pile axis, positioning point: pile hole around the gray line. Determine the elevation level. After the completion of the release process, the pre-inspection procedures.
5, according to the design requirements of the steel cage made in sections.
6, before full excavation, selectively dig two test pile holes, analyze the soil quality, hydrology and other related conditions, so as to modify the original construction program.
7, in the area of high groundwater level, first lower the groundwater level to about 0.5m below the bottom of the pile.
8, the safety of manual digging operation is crucial, before excavation of the construction personnel to carry out a comprehensive safety and technical briefing; operation of the spreader before the safe and reliable inspection and testing to ensure the safety of construction.
9, prepare the concrete ratio.
(2) material requirements
1, cement: 32.5 grade or above ordinary silicate cement or slag silicate cement, with factory material certificate, retest report.
2. Sand: medium sand or coarse sand with mud content not more than 5%.
3, stone: pebbles or gravel, particle size 5 ~ 31.5mm, pile concrete can also be used in particle size of not more than 50mm stone, and the mud content is not more than 2%.
4, water: tap water or clean water without harmful substances.
5, reinforcing steel: reinforcing steel grade, diameter must meet the design requirements, factory certificates and retest reports, no old rust and oil on the surface.
6, pads: 1:3 cement mortar buried 22 fire wire prefabricated in advance or with plastic cards.
7, fire wire: specifications 18-20 iron wire burned.
8, additives, adulterants: factory material certificate, retest report.
(C) work equipment
Main work equipment: Miki hitch, winch set or electric hoist, wheelbarrows or dump trucks, picks, shovels, shovels, braziers, wire pendant, fixed pulley set, guided pulley set, concrete mixers, buckets, chute, conduit, vibrating rod, plug brazier, coarse hemp rope, steel wire rope, safety activities cover, waterproof lighting (low-voltage 36V, l00W), electric welding machine Ventilation and oxygen supply equipment, head pumps, wooden windlasses, movable ladders, safety belts and so on. Template: combined steel mold, arc tool type steel mold four (or eight) pieces of assembly. Clamps, hooks and spare parts. Wooden boards, wooden squares, No. 8 or No. 12 channel steel, etc..
Three, quality requirements
(A) Artificial hole filling piles (steel cage) quality requirements
1, the main control items
(1) the spacing of the main reinforcement: ± l0mm. foot check.
(2) Length: ±100mm. check by feet.
2, general items
(1) reinforcing steel material inspection: conform to the design requirements. Check the certificate of conformity and inspection report.
(2) hoop spacing: ± 20mm. foot check.
(3) Diameter: ±l0mm.
(2)Quality requirement of grouted pile
1.Main control items
1)Raw material and concrete strength of grouted pile must conform to design requirement and construction specification.
2)The actual amount of concrete poured is strictly prohibited to be less than the calculated volume.
3)The top elevation of the pile and the treatment of floating slurry after pouring concrete must conform to the design requirements and construction specifications.
2, general items
1)The thickness of virtual soil at the bottom of the hole should not exceed the provisions. The shape and size of the expanded bottom meet the design requirements. The pile bottom should fall on the holding soil layer, and the holding soil layer should not be damaged.
2)The deviation of pile position of grouted pile must comply with the following table:
Allowable deviation of plane position and verticality of grouted pile
Fourth, process flow
Laying down the line to set the pile position and elevation→excavating the earth of the first section of the pile hole→supporting the template of retaining wall to put the additional reinforcement→pouring concrete of the first section of the retaining wall→inspection of the pile position (center) axis→erecting the vertical transportation frame→ Installation of electric hoist (winch or wooden windlass) → Installation of bucket, lighting, movable cover, water pump, ventilator, etc. → Excavation and lifting of the second section of the pile hole earth (trimming) → First dismantling of the first section of the template, support of the second section of the retaining wall template (placing of additional reinforcement bars) → Pouring of the second section of the retaining wall concrete → Inspection of the pile position (center) axis → Cyclic operation downward by layer → Excavation of the bottom expansion part → Inspection and acceptance → Lifting and placing of the reinforcement cages → Placement of the concrete chute ( conduit)→pouring pile concrete (pouring and vibration)→pile top position.
V. Operation Technique
(1)Placement and Elevation
On the basis of three passes and one leveling of the site, according to the information of the building measurement control network and the foundation layout plan, determine the axial grid control network of the pile position and the elevation reference point. Determine the center of the pile position, take the midpoint as the center of the circle, and draw the upper part (i.e. the first step) of the circle circumference with the radius of the pile body plus the thickness of the retaining wall as the radius. The lime-scattering line is used as the pile hole excavation dimension line. After the pile line is set, it must be reviewed by the relevant departments and excavated after the pre-inspection procedures.
(2)Excavation of the first section of pile hole earth
Excavation of pile hole should be carried out layer by layer from the top to the bottom, first digging the middle part of the earth, and then expanding the periphery, to effectively control the cross-section size of the excavated pile hole. The height of each section should be determined according to the soil quality and operating conditions, generally 0.9m~1.2m is appropriate.
(C) support wall template additional reinforcement
1, in order to prevent the pile hole wall collapse, to ensure the safety of the construction, the formation of the hole should be set up reinforced concrete (or concrete) well ring. When the diameter of the pile hole is not large, the depth is shallow and the soil quality is good, the groundwater level is low, can also be used to spray concrete retaining wall. The thickness of the retaining wall should be determined by calculation according to the requirements of material, performance, rigidity, stability, easy operation and simple construction of the well ring, and according to the stress condition, with the soil side pressure and groundwater side pressure borne by the lowest section.
2, the retaining wall template using demolition on the section, support the next section of repeated turnover. Between the template with clamps, fasteners connected and fixed, but also in each section of the template on the lower end of each set an arc-shaped channel steel or angle steel made of internal steel ring as the inner support, to prevent deformation of the inner mold due to upward force. No horizontal support is provided to facilitate operation.
3, the first section of the retaining wall is 150~200mm above the ground level, it is convenient for retaining soil and water, the axis and elevation of the pile should be marked at the top of the first section of the retaining wall, and the thickness of the retaining wall is generally taken as 100~150mm.
(4)Pouring the first section of the retaining wall concrete
Pile holes should be poured with concrete after each section of the retaining wall concrete is dug. Manual pouring, manual pounding, concrete strength is generally C20, slump control in 80 ~ 100mm, to ensure the stability of the hole wall.
(E) check pile (center) axis and elevation
Each section of the pile hole retaining wall is done, the pile cross axis and elevation must be measured at the upper mouth of the retaining wall, and then use the cross line centering, hanging line pendant to the bottom of the well casting to check the vertical smoothness of the hole wall with a radius ruler rod. Followed by trimming, the depth of the well must be based on the datum point, root by root for the pilot test. Ensure that the pile hole axis position, elevation, section size to meet the design requirements.
(F) set up vertical transportation frame
After the first section of pile holes into holes, that is to start in the pile hole on the mouth of the vertical transportation bracket, requirements for the erection of stable, solid.
(VII) installation of electric hoist or winch
Installation of pulley block and electric hoist on the vertical transportation frame or through the wire rope of the winch, select the appropriate location to install the winch.
(H) Installation of bucket, lighting, movable cover, water pump and ventilator
1, when installing the pulley block and bucket, pay attention to make the bucket coincide with the center of the pile hole as the center line of intuitive control of the center of the pile position and the shielding wall support mold when digging.
2, the bottom of the well lighting must use low voltage power supply (36V, 100w), waterproof with the cover of the safety lamps and lanterns. Pile mouth on the fence.
3, when the pile hole is deeper than 20m, ventilation to the bottom of the well to strengthen air convection. Oxygen is delivered when necessary to prevent the harm of toxic gases. Operation of the upper and lower personnel rotation, pile hole on the personnel closely watch and observe the pile hole under the situation of the personnel, echo each other, and effectively prevent the occurrence of safety accidents.
4, when the amount of water under the ground is not big, the mud and water will be transported out by bucket with digging. Underground seepage is large, the bucket can not meet the drainage, first in the bottom of the pile hole digging catchment pits, with a high range pump sinking pumping, side of the precipitation side of the excavation, the specifications of the pump according to the amount of pumping to determine. To pumping day and night three shifts, so that the water level remains stable. When the groundwater level is high, it is necessary to use unified measures of precipitation before excavation.
5, pile hole mouth installation horizontal nudge movable safety cover, when pile hole someone digging, to cover the safety cover, to prevent debris fall down to hit people. Unrelated personnel shall not be close to the edge of the pile hole. When lifting soil, open the safety cover again.
(IX) excavation and lifting the second section of pile hole earth (trimming), starting from the second section, the use of lifting equipment to transport the soil, pile hole personnel should wear a helmet, ground personnel should be tied up with a safety belt. When the bucket leaves 1.5m above the hole, push the movable safety cover plate to cover the hole and prevent the soil, stones and other debris from unloading from falling into the hole and injuring people. After the bucket is unloaded in the trolley, open the movable cover and lower the bucket to load the soil.
After the pile hole is dug to the specified depth, the diameter of the pile hole and the arc of the wall are checked with the support pole, and the top and bottom should be vertical and smooth, and the wall of the hole is trimmed.
(10) first dismantle the first section of the second section of the support wall template (put additional reinforcement)
Sheathing wall template using demolition of the upper section of the next section of the support turnover use in turn. Template leaving a height of 100mm at the mouth of the concrete pouring mouth, the interface should be pounded solid, the strength of 1MPa demolding, demolding with concrete or brick blocking, cement mortar smoothing.
(XI) Pouring the second section of wall protection concrete
The concrete is delivered in a string bucket, poured manually, and pounded compactly by hand. The concrete can be mixed with early-strength agent determined by the laboratory to accelerate the hardening of the concrete.
(XII) Check the center axis and elevation of the pile
Take the positioning line of the pile hole mouth as the basis, and calibrate section by section.
(xiii) Cycle the work downward layer by layer, dig the pile hole to the design depth, remove the imaginary soil, check the soil condition, and the pile bottom should be supported on the holding layer specified in the design.
(XIV)Excavation of the bottom-expanding part
The bottom of the pile can be divided into two kinds of cases: bottom-expanding and non-bottom-expanding. Excavation of the pile to expand the bottom part of the pile body of the cylinder dug first, and then according to the size of the bottom part of the size, shape of the top-down chipping soil expansion into the requirements of the design drawings; such as the design of no clear requirements, expanding the bottom of the diameter of the general 1.5 ~ 3.0d, expanding the bottom of the size of the variant of the size of the bottom part of the 1:4.
(xv) inspection and acceptance
After the completion of the hole, must be the diameter of the pile, the size of the expansion of the head, the bottom of the hole Elevation, pile centerline, well wall vertical, virtual soil thickness for comprehensive determination, make construction records, for hidden acceptance procedures.
(16)Lifting and placing reinforcement cage
Before the cage is put into the cage, there is a φ20 earring on the main reinforcement every 3~4m or so as a positioning pad; when lifting and placing the cage, it should be aligned with the hole position, hang straight and hold it steady, sink slowly to avoid collision with the hole wall. When the cage is put into the design position, it should be fixed immediately. In case of two sections of reinforcing steel cage connection, single-sided welding should be used, and the number of joints should be staggered according to 50% to ensure that the position of the steel bar is correct and the thickness of the protective layer meets the requirements.
(XVII) Pouring pile body concrete
Pile body concrete can be used for stones with grain size not larger than 50mm, slump 80~100mm, and mechanically mixed. Use the chute plus string bucket to pour concrete into the pile hole. When the fall of concrete is more than 2m and the depth of pile hole is more than 12m, concrete conduit should be used for pouring. When pouring concrete, it should be carried out continuously and vibrated densely in layers. The first step is poured to the top surface of the expanded bottom part, and then the upper part of the concrete is poured. Layers of height according to the vibration of the tool but not more than 1.5m.
(xviii) concrete pouring to the top of the pile, should be appropriate to exceed the top of the pile design elevation, generally 20-30mm, to ensure that in the removal of floating slurry, the top of the pile elevation in line with the design requirements.
(XIX) Finished product protection
1, has dug the pile hole must be covered with wooden board or scaffolding board, reinforcing steel mesh, to prevent the soil, debris, personnel fall. Strictly prohibit the use of straw bags, plastic sheeting false cover.
2, the pile hole has been dug in time to put the reinforcing cage, timely pouring of concrete, the interval shall not exceed 4h, to prevent collapse. Groundwater pile holes should be dug, checked, and placed with the reinforcing cage, at any time the concrete will be poured to avoid groundwater immersion.
3. The outer ring of the upper mouth of the pile hole should be a good retaining platform to prevent flooding and falling soil.
4. Protect the formed reinforcement cage, do not twist, loose and deformed. When lifting into the pile hole, don't touch the hole wall. String bucket should be placed vertically to prevent the concrete from impacting the hole wall obliquely, destroying the soil layer of retaining wall and causing soil entrapment.
5. Don't contaminate the reinforcing cage with mud: when pouring concrete, fix it firmly at the top of the reinforcing cage to limit the uplift of reinforcing cage.
6, pile hole concrete pouring is completed, to review the pile position and pile top elevation. Hold the main bar at the top of the pile upright and surround it with plastic sheet or grass curtain to prevent the concrete from shrinkage and dry cracking.
7, the construction process to properly protect the site of the axis of the pile, level points. Shall not crush the pile head, bending steel.
(XX) quality problems to pay attention to
1, the vertical deviation is too large: due to the excavation process is not in accordance with the requirements of each section of the verification of verticality, resulting in digging after the vertical super deviation. After digging each section, according to the axis on the pile hole mouth must be lifted straight, trimming, so that the hole wall arc to keep straight up and down.
2, hole wall collapse: because of the pile soil quality is not good, or groundwater seepage and make the hole wall collapse. Before excavation, we should grasp the site soil condition, stagger the pile excavation, shorten the height of each section, observe the soil loosening situation at any time, if necessary, we can use bricklaying at the collapsed holes, steel sheet piles, sheet piles sealing: the operation process should be compact, do not leave intervals between the gaps, to avoid collapsed holes.
3, the bottom of the hole residual virtual soil is too much: into the hole, trimming after more virtual soil, broken bricks, not seriously removed. Before and after the release of reinforcing steel cage should carefully check the bottom of the hole, remove the virtual soil debris. If necessary, use cement mortar or concrete to seal the bottom.
4, the bottom of the hole appeared water: when the groundwater seepage faster or rainwater inflow, pumping and drainage is not timely, there will be water. Excavation process at the bottom of the hole to dig water collection well pit, timely pumping under the pump. If there is a small amount of water, pouring concrete can be used in the first plate of semi-dry hard concrete, a large amount of water is difficult to remove for a while, it is necessary to use the conduit underwater pouring of concrete to ensure the quality of construction.
5, the pile body concrete quality is poor: necking, hollowing, clamping soil and other phenomena. Before pouring concrete two must do a good job of operation and technical advice, adhere to the layered pouring, layered vibration, continuous operation. If necessary, with iron pipes, bamboo poles, steel brazier artificial auxiliary insertion pounding, in order to supplement the mechanical vibration is insufficient.
6, steel cage distortion and deformation: steel cage processing and production of spot welding is not secure, did not take the support of strong steel, transportation, lifting and placing of deformation and distortion. Reinforcement cage should be processed on special platform, the main bar and hoop bar spot welding is firm, the support reinforcement measures should be reliable, lifting should be vertical, so that it can be put into the pile hole smoothly and keep the skeleton intact.
(XXI) safety precautions
1, daily before the start of work should be detected in the well with or without hazardous gases and unsafe factors, the hole depth is greater than 10m as well as humus soil layer is thicker, there should be a special air supply equipment, the air volume should not be less than 25L/s, to the pile hole in the work surface to send fresh air. After blasting under the pile hole, air must be sent to the pile hole, or evenly spray water to the pile hole, so that all the smoke is excluded or cohesion after sinking, before the pile hole operation. When the pile hole in the soil layer contains harmful gases and organic substances more in addition to strengthening the ventilation, should also strengthen the monitoring of harmful gases.
2, pile hole mouth should be strictly managed. Pile hole should be set above the ground 200mm of the guard plate, to prevent the ground stones or other debris is spoiled pile hole. Ground hole must be surrounded by guardrail, height of not less than 800mm. unrelated personnel shall not be close to the pile hole mouth, pile hole mouth machinery operators are not allowed to leave their posts. No objects (such as keys, pens, pocket watches, lighters, small tools, playthings, etc.) shall be placed in the pockets to prevent falling into the pile hole.
3, pile hole operators must wear a good helmet, wear good insulating shoes, pile hole and the lower part of the operator should have reliable contact facilities. If the pile hole management disorder, the pile hole should immediately stop the operation back to the ground. The ground operator should wait for the underground operator to come up before leaving the post.
4. When pouring pile concrete by conventional method (including the method of sealing the bottom first), the upper opening of the pile hole must be sealed (only the funnel opening is left), and its maximum clearance shall not exceed 3m, and the sealing plate and square wood shall be strong enough to ensure the safety of the lower working personnel. The skewer should be reinforced with No.8 galvanized iron wire, and the lower mouth of the skewer should be pulled temporarily to prevent the skewer from swinging and hurting people. After sealing, the air should be strengthened to be sent to the pile hole, or a vent with a height of more than 1m should be preset on the sealing platform of the pile hole.
5. Hanging ladder should be set on the pile hole opening and lengthened with the depth of the pile hole, so that the personnel can go up and down smoothly in case of accident. Under normal condition, the operator should take the basket or special bucket to go up and down. The operator should be specialized and licensed to start the machine and pay attention to all the dynamics in the pile hole, and the electrical switch should not be left in the hand. The hook should have a spring-type decoupling device to prevent turning over the bucket, turning over the basket, decoupling and other malicious accidents, it is strictly prohibited to stand on the edge of the slag bucket up and down. Vertical transportation equipment and devices, must be equipped with automatic clamping insurance device.
6, slag bucket, basket, bucket up and down with electric hoist, up and down should be aligned with the center of the pile hole.
7, in any case is strictly prohibited lifting equipment overloading operation, on and off before the lifting frame and track should be checked, work found abnormalities should immediately stop work, find out the cause, seriously overhaul, not allowed to operate with disease.
8, lifting steel into the pile hole, should be tied tightly fastened (the lower mouth should be pocketed with an iron plate), to ensure that do not slip off the fall. Should wait until the steel bar lifting into the bottom of the hole, before the next person into the pile hole unhooked.
9, in the pile hole binding steel skeleton, operation platform square wood must be placed in the solid (can be placed on the concrete retaining wall protruding surface or reinforcing steel skeleton reinforcing ring), and nailed to the platform planks, to prevent the square wood sliding displacement, the platform fell.