I. Site preparation
The plane size of drilling site should be determined according to the plane size of pile foundation design, the number of drilling rigs and the plane size of drilling rig base, the displacement requirements of drilling rigs, the construction method and the layout of other construction machinery and facilities.
The height of the construction site or working platform should be 2.0m higher than the construction water level or tidal water level.
Second, the rig and other equipment preparation
1, impact drilling rig
Impact drilling rigs can be roughly divided into two categories: one is impact drilling rigs, equipped with drilling rigs and complete sets of lifting and impact equipment. The other is a simple percussion drilling tool composed of a double-barrel winch with a clutch, and its drilling frame and equipment are designed and assembled by the construction unit according to the site conditions. The simple percussion drill driven by winch has a 30~ 150KN double-barrel winch with clutch, a simple drill frame, a steering device, a slag bucket and a drill bit.
2. Stamping cone
The impact cone consists of cone, blade foot and steering device. The cone provides the necessary gravity and impact kinetic energy for the impact cone, and the blade foot is located at the bottom of the impact cone, which is a component that directly impacts and breaks the earth and stone; The steering device is located at the top of the cone and connected with the lifting wire rope, which is the key part to make the impact cone impact into a round hole. Its total weight shall not exceed the lifting capacity of the hoist. The cutting edge of the root of the conical blade should be welded with a wear-resistant layer with high-quality covered electrode, especially strengthened. There are four-wing (cross-shaped), five-wing and six-wing drills, and five-wing drills are mostly used at present.
3. Steering gear
In order to obtain a complete cylindrical hole, the punch cone needs to rotate by an angle at each impact. Therefore, it is necessary to set a steering device at the top of the cone. The commonly used steering device is alloy sleeve, also called tungsten-gold sleeve. When the stamping cone is cast, a steel wire rope hole and a sleeve hole are left at the top of the cone, a section of steel wire rope passes through the hole, is pulled out from the side of the sleeve hole, and then passes through the steel sleeve with the tapered hole. Disassemble and clean this end of the steel wire rope, hook each scattered steel wire head and put it into the steel sleeve. Then the molten mixed metal (such as lead, aluminum, tin and other alloys) is poured into the steel sleeve, cooled to form the alloy sleeve, and the alloy sleeve is put into the sleeve hole.
Three, drilling technical parameters requirements
1, gasket
The casing has a fixed pile position to guide the direction of the drill bit, isolate the surface water from flowing into the space, protect the orifice from collapsing, ensure that the water level (mud) in the hole is higher than the groundwater or construction water level by a certain height, form hydrostatic pressure (water head), and protect the hole wall from collapsing.
1), general requirements
(1) the buried lining made of steel plate should be firm and waterproof; When the pile casing is buried deeply, methods such as weighting, vibration, hammering or removing the soil in the pile casing should be adopted to sink. The casing inner diameter is slightly larger than the pile diameter: when the casing length is in the range of 2~6m, the casing inner diameter of the drill pipe-guided reverse circulation rotary drilling rig should be 20 ~ 30cm； larger than the pile diameter; The inner diameter of casing of impact drilling rig should be 30 ~ 40cm； larger; The inner diameter of the pile casing in deep water should be 40 cm larger than the pile diameter. Height of casing top: when percussion drilling is used, the casing top should be higher than the groundwater level 1.5m~2.0 and 0.3m above the ground.
2), liners production
Steel lining is generally made of steel plate with a thickness of 4~6mm in general working occasions and small and medium aperture conditions. In order to increase rigidity and prevent deformation, reinforcing ribs can be welded on the upper, lower and middle outer sides of the shell.
3) Embedding of the gasket
The burying of casing is the beginning of bored pile construction. Whether the plane position and verticality of the pile casing are accurate, and whether the periphery of the pile casing and the foot of the pile casing are tight and watertight have great influence on the quality of hole-forming and pile-forming. When buried, the central axis of the pile casing should correspond to the center of the marker pile to be measured, and the deviation of the inclination of the pile casing should be no more than 5cm, and the deviation of the inclination of the pile casing should be no more than 65438 0%. If required by the design, it must meet the design requirements and strictly maintain the vertical position of the liners.
2. Mud
The main properties of mud are: relative density, viscosity, fine shear force, sand content, colloid rate, water loss rate, PH value and mud skin thickness.
1), relative density: the relative density of mud is the ratio of the mass of mud to the mass of water with the same volume at 4℃. When the relative density of mud increases, the pressure on the hole wall increases correspondingly, and the more stable the hole wall is, the greater the ability to suspend and carry cuttings. However, the mud with relatively high density also increases water loss and mud skin on the hole wall, which increases the consumption of mud raw materials and brings difficulties to hole cleaning and concrete pouring.
2) Viscosity: Viscosity refers to the friction between molecules or particles when liquid or mixed liquid moves. The mud with high viscosity produces thick mud skin on the hole wall, which is beneficial to prevent sand turning and plugging, and has strong ability to carry drilling slag in suspension. However, if the viscosity is too high, it will be easy to "paste drilling", which will affect the normal work of the mud pump, increase the difficulty of mud purification, and then affect the drilling speed. The viscosity is too small, the drilling residue is not easy to suspend, and the mud skin is thin, which is not conducive to preventing sand turning and sand leakage.
3) Fine shear force: Fine shear force is the minimum force required for static mud to start flowing under the action of external force. The fine shearing force of mud should be appropriate. If it is too large, the flow resistance will be large, and the drilling residue in the mud flowing to the sedimentation tank will not be easy to precipitate, which will affect the purification speed, make the relative density of mud too high and slow down the drilling speed. If it is too small, the effect of suspending and carrying drilling slag will be poor, and the drilling speed will also decrease.
4) Sand content: Sand content is the volume ratio of sand and clay particles contained in mud. When the sand content of mud is high, it will reduce the viscosity and increase the sedimentation, which will easily damage the mud pump.
5) Colloidal rate: Colloidal rate refers to the degree to which clay particles in suspended state are separated from water after the mud is still, expressed as a percentage. Mud with high colloid rate is not easy to precipitate clay particles, but has high ability to suspend drilling slag, and vice versa.
6) Water loss rate: Water loss rate, also known as water loss or permeability, is the amount of water that mud penetrates into the formation within a certain period of time under the action of head pressure difference between inside and outside the borehole, and the unit is ml/30min.
7) PH value: expressed by PH value, with PH value equal to 7 as neutral mud, less than 7 as acidic mud and more than 7 as alkaline mud.
3. Preparation of mud
1), selection of clay and preparation of common mud.
It is best to use bentonite with fast hydration, strong pulping ability and high viscosity or clay that has been frozen and thawed near the surface, but local materials should be used as much as possible. Through field identification, the soil with the following characteristics can meet the above requirements as raw materials for mud preparation.
After natural air drying, it is not easy to move and crush by hand; When cut with a knife, the section is smooth and the color is dark; After soaking in water, it feels sticky and slippery. Mud paste is formed after adding water, and it is easy to knead into a slender mud strip of1mm. When you twist it with your fingers, you feel that there is not much gravel. It can expand greatly after being soaked in water. Generally speaking, clay with plasticity index greater than 25, particle size less than 0.005 mm and particle content accounting for more than 50% of the total can be used for pulping. When there is a lack of suitable clay, slightly poor clay can be used, and 30% clay with plasticity index greater than 25 can be mixed; If cohesive soil is used, its plasticity index should not be less than 15, and the particles larger than 0. 1mm should not exceed 6%. The selected clay should not contain gypsum, lime or calcium compounds.
2), mud modulation
Before pulping, the clay blocks should be broken as much as possible, so that it is easy to form slurry when mixing, shortening the mixing time and improving the mud quality.
There are two methods for pulping: mechanical stirring and bit stirring. When drilling with forward and reverse circulation rotary drilling rig, it is best to make slurry outside the well because of the requirement of high mud quality. Drilling tool stirring is to throw clay raw materials into the bottom of the hole when impacting to form a hole, and then impact and stir them into mud with an impact drill.
4, mud circulation and purification treatment
1), impact positive circulation drilling
Mud circulation system is mainly composed of mud pool, mud pump, mud outlet pipe and mud proximity pipe.
Mud enters the mud pool from the orifice through the slurry outlet pipe, and is sent back to the bottom of the hole by the mud pump through the slurry inlet pipe after purification. The mixture of mud and drilling slag turns from the bottom of the hole to the orifice and enters the mud pool through the slurry outlet pipe. Through mud circulation, the drilling residue is precipitated in the mud pool, and then the drilling residue is removed to achieve the purpose of slag removal.
2) Drilling and construction in dry land with positive and negative circulation rotary drilling rig.
The pulping pool, the pulp storage pool and the sedimentation pool can be arranged and connected through the circulating pool. The specifications of sedimentation tank, circulating tank and circulating tank in the circulating system should be determined according to the drilling volume and the model and specification of sand pump. The volume of the circulating pool should not be less than 1.2 times of the actual volume of the pile hole; The volume of sedimentation tank is generally 6~20m3. When the diameter of pile hole is less than ∮80cm, take 6m3; when it is less than ∮ 150cm, take12m3; Be chosen. If it exceeds ∮ 150cm, choose 20m3；; The capacity of sedimentation tank depends on mud capacity and mud purification method; A slurry storage tank shall be specially set up at the site, and its volume shall not be less than 1.2 times of the actual volume of the pile hole. Generally, the size of the pulping pool is 3m×8m, and the depth is about1m.. There are two pulping tanks, one for soaking clay and the other for stirring pulping, which are used alternately.
3) Water quality and equipment requirements for mud preparation
(1) require the use of water that meets the requirements of the specification. When tap water cannot be used, the water quality should be checked in advance to ensure the mud quality;
(2) To clean machinery and equipment, water supply facilities with a diameter of 25mm and a flow rate of 50l/min should be prepared;
③ In order to reuse the mud in the borehole, a water pump and a storage station should be prepared; In order to treat the wastewater produced by cleaning machinery, it is necessary to set up drainage ditches and caissons; The waste mud shall be transported to the treatment site by tank car for treatment, and shall not be discharged on the site. Drilling slag should be sent to the designated slag yard.
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