Construction technology of punching cast-in-place pile

Construction of punching cast-in-place pile \x0d\ 1, preparatory work (1) Installation of hoist: ① The distance between hoist and pile hole should be controlled at about15m, not too far. If the distance is too large, the steel wire rope will swing too much during impact, which will cause great impact energy loss and be unsafe. At the same time, it affects the line of sight, and it is difficult to control the height of the hammer, especially at night, which is easy to empty the hammer and cause accidents. (2) The drum of the hoist should be aligned with the notch of the ground pulley to prevent the wire rope from being twisted out of the groove and causing danger. (3) A ground anchor must be set behind the hoist, which is connected with the hoist to pull the hoist to prevent it from moving forward. (2) Connection of impact system: \x0d\ ① Connection of steering ring and hammer: Pass the prepared connecting ring (round steel with a diameter of 50mm and a length of about1/kloc-0 ~120cm) through the lower end of the steering ring, and then weld the two feet of the connecting ring firmly with a hammer. The weld length is not less than 30 cm. \x0d\ ② Connection between the hoist and the impact hammer: One end of the main wire rope is fixed on the hoist, and the other end is connected with the upper end of the steering ring through the ground pulley and the top pulley. In order to increase the stress radius of the wire rope in the bending part and prolong the service life of the wire rope, a special groove-shaped iron guard is installed in the bending part of the wire rope. The first buckle of the consolidated wire rope should not be screwed too tightly, so as to avoid the wire rope being injured and broken here after being stressed. Generally, three buckles are used, and the spacing between the buckles should not be less than 6 times the diameter of the wire rope. \x0d\ (3) Buried bucket: \x0d\ ① Excavation: the excavation depth is 0.5 ~1m. The barrel mouth must be at least 50 cm above the ground to keep the water level in the hole higher than that outside the hole or on the ground, to increase the water pressure in the hole and to protect the hole wall from collapse. After the foundation pit is dug, put the bucket. \x0d\ ② Backfilling: firstly, pad the bottom of the outer periphery of the barrel with clay (rake mud) with a thickness of about 20cm, and tamp it with your feet. Then, build loess straw bags, stack them alternately, build a layer of straw bags, and then lay a layer of clay. After stepping on it, cover the second straw bag, spread a layer of clay, and step on it to make it slightly lower than the barrel mouth. Loess straw bags and clay must be compacted layer by layer, which can not only prevent the river from infiltrating, but also fix the bucket. \x0d\ ③ Preparation of retaining wall materials: If the surface is soft soil, flaky, crushed stone and loess are added into the bucket, with a ratio of about 3: 1: 1. If the surface is gravel, only pebbles (small gravel) and loess are added in the bucket, and the ratio is roughly 1: 1. All these jobs should be finished before drilling. \x0d\ 2。 Middle hole \x0d\ (1) drilling: in the drilling stage, the drilling progress should not be too fast. Generally, the footage of the console should be within 1 m, accordingly, the height of the hammer should be smaller, and the impact times should be more (see the table below), so that the impact force generated is smaller, and the hole wall is gradually squeezed and compacted by horizontal force. \x0d\ Height of soil lifting hammer (cm), impact times (times/minute), mud concentration \x0d\ Soil 40 ~ 6020 ~ 251.4 ~1.5 \ x0d \ Gravel 40 ~ 6020 ~ 25/kl. Therefore, the drilling progress should be strictly controlled and the hole wall should be strengthened in the drilling stage. It is required to protect the hole wall as firmly as possible in the range of hole depth and 3 ~ 4 meters below the bucket bottom, and then it is not easy to collapse when entering normal drilling. \x0d\ (2) Normal drilling: After the light impact drilling stage is over, normal drilling will be accelerated. The height of the hanging hammer can be increased to more than 1.5 ~ 2 meters, and the mud concentration is correspondingly reduced, which is roughly below 1.5. In general, the drilling footage per shift is about 1 ~ 1.5m, sometimes more. \x0d\ (3) Bored rock stratum: The surface of rock stratum is mostly uneven or inclined, so \x0d\ is most likely to produce eccentric holes when drilling just enters the rock stratum. Therefore, special care should be taken when drilling holes to contact rock strata. Usually, flaky with a diameter of 20 ~ 30 cm is thrown at the bottom of the hole to fill the inclined plane and uneven place of the rock stratum. Then tighten the rope and impact quickly with a low hammer, so as to form a relatively compact platform to support the impact hammer, uniformly stress and prevent the hole from being eccentric. However, it should be noted that the hammer cannot be lifted before the inclined protruding part of the rock stratum is leveled, and the hammer can be hammered with a high hammer after the rock stratum is basically leveled, so as to speed up the drilling process. \x0d\ After rushing into the rock stratum, the mud concentration will be reduced to about 1.2 to reduce the resistance and hammer jam, but it should not be too small, otherwise the stone slag will not float up, and it is difficult to remove the slag. \x0d\ 3。 In the process of dredging and punching, a part of the stone slag and mud broken are squeezed into the gap of the hole wall, and most of them are removed by the slag bucket. In the opening stage, in order to make the stone slag mud and stones squeeze into the pores around the hole wall as much as possible to strengthen the hole wall, the stone slag is not removed during the impact process, and it is removed once after reaching 4 ~ 5 meters to reduce the mud concentration. In the normal stamping stage, slag should be removed in time, otherwise the resistance is too great, which is not conducive to impact. Generally, the slag is removed once per machine shift, and 4-5 barrels of stone slag mud are taken out at a time. However, two points should be paid attention to when cleaning slag: \x0d\ (1) Add water to the hole in time to keep the water level in the hole at a necessary height to prevent the hole from collapsing due to the decrease of water pressure. \x0d\ (2) After the stone slag is removed, the wall protection material should be added to the hole immediately to restore the mud to normal concentration. Such cyclic replacement can ensure the smooth drilling. As for rushing into the rock stratum, it is usually once per machine shift, and 5 ~ 6 barrels of slag slurry are pulled out at a time. \x0d\ 4。 Lower the reinforcing cage \x0d\ In order to facilitate the hoisting of the reinforcing cage, the reinforcing cage should not be too long, and every 8 ~10m is saved. Therefore, the length of the reinforcing cage can be bound by sections according to the depth of the pile hole and its total length, and in order to increase the hoisting rigidity of the reinforcing cage, temporary measures can be taken to use logs with a diameter of about 15 cm, which is the length of the reinforcing cage. \x0d\ According to the height of the tripod and the length of the reinforcing cage, the following methods shall be adopted for hoisting: \x0d\ The reinforcing cage shall be hoisted in sections, but a single-leg boom shall be erected at the upper end of the tripod to increase the hoisting height, and the first reinforcing cage shall be hoisted into the hole and hoisted, that is, the second section shall be hoisted. The first section shall be welded properly, and the facilities for hoisting the reinforcing cage shall be dismantled after welding, and then proceed. \x0d\ When lifting and lowering the reinforcing cage, control the lifting speed. Hoisting should be slow and even, so that the reinforcing cage can slowly rise along the tripod feet and gradually stand up. Excessive lifting may deform the reinforcing cage. After the reinforcing cage is hoisted and erected, it should be lowered slowly in a straight line to prevent the reinforcing cage from swinging in the hole. Collision with the hole wall, resulting in hole collapse. \x0d\ 5。 Hole cleaning \x0d\ After the reinforcement cage is laid, hole cleaning shall be carried out. \x0d\ (1) Install hole cleaner: \x0d\ Assemble two sections of hole cleaning conduit near the orifice to form several large sections. Connect the lower intake pipe and install the upper nozzle elbow. Then use the top pulley of the hanger to lift it in turn. Hang the bottom section into the hole first, and then hang it in the right position. Then, hang the second section for connection, and so on until the whole catheter is installed. The conduit should be 3 ~ 4 meters above the ground, and the nozzle should be aligned with the outlet. In order to prevent the catheter from rotating, two logs should be used to clamp the catheter, that is, to control the direction of water spraying and to hold the catheter down. At the same time, connect the water source. After hole cleaning, water should be poured into the hole to keep the water level in the hole and avoid hole collapse. \x0d\ (2) Hole cleaning: \x0d\ Air compressor and water pump are started at the same time. The air pressure of the air compressor is not less than 6 ~ 7kg. According to the general principle of the sand blower, the air compressor continuously delivers high-pressure air into the conduit, and a generally powerful high-pressure airflow runs upward in the conduit. The stirred sludge flows upward with the high-pressure airflow and is ejected from the nozzle (as shown in the following figure) until clear water is ejected from the orifice. In this way, pebbles generally smaller than the diameter of the hole cleaning pipe can be removed, and only a few pebbles larger than the diameter of the hole cleaning pipe remain at the bottom of the hole, which is harmless to the quality of concrete. \x0d\ According to practical experience, it is considered that this hole cleaning method can basically meet the requirements. \x0d\ 6。 Pouring underwater concrete \x0d\ (1) Installation conduit: \x0d\ ① At the same time of hole cleaning, the preparation for pouring concrete should be carried out, which is required to be ready before the hole cleaning is completed. After hole cleaning, remove the hole cleaning equipment, take out the hole cleaner, and then lift the concrete conduit. The concrete conduit must be pre-assembled, divided into several sections and arranged in turn for hoisting. Requirements for conduit: it must be straight, without uneven bending, so as not to hinder the falling of water polo; The bolts connecting the flange of the conduit shall be tightened to avoid water leakage and slurry leakage. \x0d\ ② Lift the concrete conduit with a tripod and place it. \x0d\ ③ The conduit shall be placed in the center of the pile hole and fixed. The lower outlet is 30 ~ 40 cm away from the bottom of the hole, not too big. The diameter of the conduit used here is 30 cm, and the waterproof ball of concrete is also large, so the outlet of the conduit is far from the bottom of the hole, so the concrete that flows out at first is washed with heavy water. The diameter of the conduit should be 20 or 25 cm, and the size of the waterproof ball should be reduced, so that the distance between the conduit mouth and the bottom of the hole is controlled within 30 ~ 35 cm, and the concrete scouring phenomenon can be reduced. The top of the conduit is 3 ~ 4 meters above the ground or water surface, and the water isolation ball is suspended below the water surface (as shown in the following figure). \x0d\ (2) Concrete pouring: \x0d\ ① The fluidity of concrete should not be too large, and its slump is generally controlled at around 18 ~ 20cm. \x0d\ ② Sufficient concrete must be reserved before cutting the ball, and the concrete shall be buried in the conduit for 50 ~ 60cm. After the ball is cut, the concrete must be continuously lowered into the funnel to avoid interrupting the concrete in the conduit. \ x0d \ (3) Control the depth of the conduit buried in concrete. Generally, when the lower part of the conduit is buried in concrete for 2 ~ 2.5m, it is necessary to lift the conduit. Care must be taken to prevent the conduit from being lifted out of the concrete, so that the lower end of the conduit is still buried in the concrete by about 100cm, so as to avoid frost boiling accidents. If buried too deep, it will be difficult to lift the pipeline. \ x0d \ (4) After concrete pouring, dismantle the bucket.