Rotary drilling shoring drilling construction process features and principles of introduction?

①Overcome the problem of shrinkage of the hole wall in the process of rotary drilling soft soil drilling, and it is easy to generate negative pressure in the hole in soft soil. The contact surface between rotary drilling rig drilling barrel and soil is relatively large, if the drilling footage is large in soft soil, the bucket lifting process is prone to negative pressure, which increases the weight of the rotary drilling rig while the stability of the borehole wall is adversely affected, and it is prone to form the borehole wall shrinkage. As the shield adopts the full-following type shield to protect the wall, avoiding the situation of hole wall shrinkage. ②Full-following barrel rotary drilling is faster than other drilling rigs. As the rotary drilling rig construction relies on the cylinder drill bit with a flap at the bottom to rotate and break the rock and soil, and directly loads it into the drilling bucket to elevate and transport to the ground, no need to stir up the rock and soil by the slurry to return to the outside of the hole, and the average footage can reach about 50cm per minute. The construction efficiency can be increased 5 to 6 times in the suitable stratum compared with the drilling and punching pile rig. ③ Rotary drilling in the process of drilling machine, the center of the shroud and the drilling machine drilling center position overlap. At the same time, check with a level or plumb ball to make the steel shroud vertical. Ensure that the pile is straight and smooth. Compared with percussion drilling, positive and negative circulation rotary drilling to form the verticality of the pile foundation is effectively controlled.2 Scope of applicationThis method is applicable to the construction of pile foundation for soft foundation, narrow site and short construction period. Especially when the geological situation is more complicated and the surface water system is developed, it is more suitable to use this method.3 Technological PrincipleThe full follow up of the shield is the construction process according to the analysis of the ground survey data and the design of the pile length of the drawing of the Tonghe Special Bridge. Steel barrel (to prevent the hole soil and particles collapse, falling barrel facilities) generally have three roles: ① pile center and barrel center positioning, drilling process to ensure that; ② surface geology is easy to collapse hole strata, play the role of the wall; ③ elevation control, according to the surveyor to determine the elevation of the barrel barrel to control the depth of the hole. Mud is a suspended liquid of clay dispersed in water, which is used to protect the wall and cool the flushing fluid of drilling tools when drilling. Mud according to a variety of drilling rigs using different mud specific gravity and viscosity requirements, slurry materials, if in the clay scarcity areas expensive, and the construction of profitability goals. The whole follow up type shield instead of mud to play the effect of wall protection. And because of the river with the river bridge is in the river with the section, according to the survey data surface water system developed. Ordinary percussion drilling, positive (reverse) circulation rotary drilling rigs in the drilling process surface water can not be blocked to meet the mud wall effect, easy to cause hole expansion, hole collapse phenomenon. Due to the small site and tight construction schedule, other drilling rigs will not be considered. In order to ensure the integrity of the mechanical platform, the site should be leveled. The pile holes are mainly formed by hydraulic rotary excavator, and the double-walled steel pipe ensures the stability and accurate location of the pile holes. ② The first section of the barrel is equipped with a boot at the lower end of the barrel and cutting teeth arranged in a circular pattern, so that the barrel can be quickly and easily placed into concrete and strata with a high degree of compactness. (iii) The shroud is connected to the shroud pusher of the full shroud drilling rig, and the rig operator places the first section of double-walled steel shroud into the guide wall at a precise location. (iv) A liquid bubble level was used to check and adjust the longitudinal position of the shoring before the double-walled shoring was pressed into place by rotating the power head of the drilling rig. After the sheath is pressed into the ground a few meters, use the level meter to test the vertical level of the sheath again, the transverse center axis of the sheath and the longitudinal center of the location of each test need to be calibrated, and the deviation of the verticality of the sheath is permitted to be determined in accordance with the relevant regulations and the actual situation.4 Construction process 4.1 Construction process. Site layout → construction measurement → steel sheath burial → drilling rig in place → digging hole → hole → inspection and allowable deviation → clearing hole → installation of reinforcing cage → second clearing hole → underwater concrete pouring → conduit removal → concrete filling elevation determination. 4.2 Construction method. 4.2.1 Measurement and sampling, steel sheath burial. After the measurement class of the project department puts out the pile position, the work class immediately buries the cross guard piles, which are 3m away from the pile position, and fixes the center point of the pile position. After controlling the positioning, bury the steel shield and fix it, control the center of the pile with two-way cross line and correct the steel shield with the center of the measured pile to see if it is off position. When digging and burying, between the shield and the pit wall is filled with clay without water leakage. The deviation of plane position is less than 50mm, the deviation of inclination is less than 1%, and the deviation between the center of shroud and the centerline of pile position is ≤50mm.4.2.2 Drilling rig in position, digging to form hole. The drilling rig is positioned according to the pile line placed on the platform beforehand. The base of the drilling rig should be stable and firm when it is in place. In the process of drilling, the drilling rig shall not produce displacement and subsidence. In the process of drilling, the construction record must be filled in time, and the slag samples should be taken at the change of soil layer, so as to check the soil layer with the geological profile, and after reaching the design surface, the samples should be taken in time for identification; the slag samples should be taken every 2m, and the slag samples should be taken once when encountering the geological change, the slag samples should be taken once for the foundation of the piles under each platform, and the slag samples should be taken once for every 0.5m when the geological change is intensive or not in conformity with the design; the slag samples should be collected with a sealing bag each time, and should be placed in the slag sample box. The slag samples are collected in sealed bags every time and placed neatly in the slag sample box, labeled with information such as part, pile number and number of meters drilled. Fig. 1 When making holes, we should control the feeding speed according to the soil layer, in order to ensure that the verticality of the holes meets the design requirements, we must keep the piling machine level, strengthen the inspection, and inspect and correct the holes diligently.4.2.3 Inspection and permissible deviation. After clearing the hole, installation of reinforcement cage, and removal of the second clearing rig, use cage hole checker to check the hole diameter, hole slope and hole depth, the outer diameter of cage hole checker should be the same as the designed pile diameter, the length of cage hole checker should be 4~5 times the designed pile diameter and should not be less than 6m, the two ends of which are made into a cone, and the height of the cone should not be less than the radius of the hole checker. The deviation of pile diameter ±50mm, the permissible deviation of pile position is not more than 100mm, and the permissible deviation of perpendicularity is less than 1%, and the company can only enter the next process after passing. The hole clearing method of rotary drilling adopts slag emptying method and slurry exchange method. It is strictly prohibited to use over-drilling instead of hole cleaning. Reinforcing steel cage according to the vertical every 2m set a protective pad, each one along the circumference of the arrangement of 4, the thickness of the protective layer of steel 80mm; reinforcing steel cage installation process must ensure that the center of the cage and the center of the pile shall not be more than 20mm deviation. second section of reinforcing steel cage and the first section of reinforcing steel cage main reinforcement and spot welded, and then use a single-sided lap welding of the main reinforcement, the welded length of 10D. the number of joints on each cross-section is not more than 50%. more than 50%. After the conduit lowering is completed, the depth of the hole and the thickness of slag at the bottom of the hole are tested again, if the thickness of slag exceeds the standard, the hole should be cleaned again using the method of slag pulling, until the standard is reached after the completion of the hole (less than 10cm).4.2.4 Establishment of the height of the underwater concrete casting, conduit dismantling and concrete pouring. Underwater concrete pouring should be prepared before the following: ① should test the thickness of slag, mud function indicators, the bottom of the conduit mouth elevation, into the hole bottom elevation. ② should check the construction machinery, understand the situation of the operating personnel, operating machinery and personnel should meet the highest filling volume standards. ③ Spray the concrete transportation pipeline and hopper wet with water, but there should not be obvious water accumulation. ④ Check whether there is any abnormality in the chopping equipment. The material storage hopper used for underwater concrete pouring should be made of steel material, which should be in line with the actual demand of the pouring process, and the structure size is scientific and appropriate, which is convenient for lifting. The storage hopper and the conduit used for underwater concrete pouring should be connected by clips, and when connected by flanges, the connection should be stable and the shape should be kept unchanged, and when connected by sockets, anti-locking devices should be set up. Underwater concrete pouring to use the hopper specifications should be consistent for concrete storage needs. The number of underwater concrete conduits arranged in the plane and the distance between two conduits should be determined according to the function of each conduit and the size of the pile bottom. The inner side of the conduit should be kept smooth, with the same inner diameter and tight joints; the diameter can be 20 to 30cm, the length of the middle section should be kept at 2m, and the length of the lowest section can be determined as 4m; the conduit with a length of 1m can be used under the funnel. Before application, the pressure should be tested to ensure that there is no water leakage, and mark the scale from bottom to top; after the installation of the conduit, the axis deviation should be ≤ 0.5% of the depth of the hole, and at the same time, ≤ 10cm; in the process of assembling, and the bolt connected to the nut should be located in the upper part; test pressure should be determined as the value of the bottom of the hole static hydrostatic pressure of 150%. The length of the conduit can be specified according to the depth of the hole and the height of the working platform at the mouth of the hole, etc. The distance between the bottom of the funnel and the mouth of the hole should be longer than 1 section of the intermediate conduit. The conduit should be in the center of the hole, before pouring concrete should be implemented to lift the experiment, the performance of the conduit lifting and lifting facilities should be consistent with the total amount of all the conduits filled with concrete and friction, and do a good job of safety. In order to ensure the continuous operation of concrete filling, there must be enough concrete tankers before the concrete operation, and ensure that the mixing plant will not be interrupted due to any factor. The mix used for underwater concrete should meet the relevant standards. The preparation ratio and setting time of the concrete can be specified by means of tests. The easy properties, slump and hardness of the concrete should correspond to the requirements of the piles to be poured. After the first batch of underwater concrete is poured, the depth of the conduit should be ≥1 m, and it should be ≤3 m. During the process of conduit elevation, it should be ensured that the axis is vertical, in the center position, and slowly elevated, so as to avoid the conduit connecting position affecting the reinforcing cage. During the underwater concrete pouring, the speed should be kept uniform, and the quantity of concrete pouring should be calibrated throughout the process, so that the height of concrete pouring is always consistent with the design. During the pouring period when the conduit is not fully filled with concrete, the back should focus on controlling the concrete pouring rate, to prevent excessive pressure in the conduit, resulting in conduit destruction, and even cause harm to people, concrete pouring should be often detected during the height of the concrete surface, and at any time on the depth of the conduit buried in order to adjust. The buried depth of the conduit should be controlled between 2 and 6 m, at any time to maintain the minimum buried depth ≥ 1 m. When the pouring rate is relatively fast, the conduit is more stable and has lifting performance, you can appropriately increase the depth of burial, but it should be controlled at 8 m or less. Concrete pouring using the traditional conduit lifting method for pouring. The intermittent length of conduit dismantling should be reduced as much as possible, and the pouring length of a pile should not be too long, and it should be poured within the initial setting time of concrete. In order to ensure the concrete quality of the pile head, the top of the pile concrete more than 1m, underwater concrete pouring period, especially in the region of high and low tide and pressurized groundwater, should pay attention to maintain the height of the water in the hole. In the critical completion of pouring, the number of concrete pouring should be proofread, so as to make clear whether the tested concrete pouring height is accurate or not.5 ConclusionThe full-cell grouting pile has the advantages of fast speed of hole formation, good quality of hole formation, short operation time and low investment cost in operation, and the application of it in the construction of pile foundation of the bridge effectively avoids the troubles brought by the bad geology such as shrinking diameter and collapsing holes, etc., and accelerates the progress of the construction. Meanwhile, the quality of pile foundation is ensured by the principle of "technically feasible, economically reasonable, safe and reliable", which provides reference for similar drilled piles in the same geological conditions.

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