Original title: Hole guiding scheme of down-the-hole hammer Pile Foundation Project of Plot 1-02 of Xinghe Legend Garden Construction scheme of pile-sinking with down-hole hammer According to the geological survey report and site survey, when the construction of prestressed pipe pile in Block 1-02 of Xinghe Legend Garden crosses the gravelly clay layer, some areas will encounter moderately weathered and slightly weathered spheres or interlayers, which will cause pile breaking or cracking, and it is difficult to sink into the bearing stratum, so it is necessary to use large-diameter pneumatic down-the-hole hammer to cross the moderately weathered and slightly weathered spheres or interlayers. Therefore, a special scheme for down-the-hole hammer guiding hole is prepared. I. Technology and Parameter Analysis of Pile Sinking with Dth Hammer (I) Pile-sinking process with down-the-hole hammer Pneumatic down-the-hole hammer is also called pneumatic impactor. Under the action of air compressor, the large-diameter down-the-hole hammer uses compressed air as the power medium to drive its work, and carries out high-frequency crushing and impact on hard rock; In the process of pneumatic Dth hammer drilling, high-pressure air drives the piston in the impactor to do high-frequency reciprocating motion, and the kinetic energy generated by the motion is continuously transmitted to the drill bit, so that the drill bit can obtain certain impact work. Under the action of the impact energy, the drill bit continuously impacts the rock at the bottom of the hole. Under the action of the impact energy, the rock is crushed in volume. At the same time, the compressed air generated by the air compressor is also used as the well flushing medium to carry the rock debris crushed by the down-the-hole hammer out of the hole. The large diameter Dth hammer has achieved good results in the drilling of block stone, boulder, moderately weathered and slightly weathered hard rock strata,rock drilling tools, which meets the smooth pile formation of prestressed pipe piles. The hole guiding technology of large diameter pneumatic Dth hammer is to combine Dth hammer construction technology with prestressed pipe pile hole guiding technology to solve the problem of pile sinking in complex strata. The process flow of pile sinking construction in this project is shown in the following figure: A. Dth hammer leading hole; B. Down-the-hole hammer drilling with casing; C. Prestressed pipe pile sinking; D. Prestressed pipe pile sinking to the bearing stratum. ① Lead the pile driver in place to ensure the verticality of the pile driver, and lower the down-the-hole hammer drilling tool (as shown in Fig. 1-a); ② The guide hole penetrates the gravel layer. Start the air compressor and drill with the down-hole hammer until the pilot hole passes through the moderately weathered or slightly weathered sphere (as shown in Fig. 1-b); Expand the full text ③ Pile driver is in place. Pull out the drilling tool, install the pipe pile and conduct the pile sinking operation (as shown in Fig. 1-c); ④ Drive and send piles to the highly weathered mudstone layer, and stop hammering according to the standard (as shown in Fig. 1-d). 2. Machines and equipment: According to the process requirements, the following supporting equipment shall be selected to realize the construction of large diameter pneumatic down-the-hole hammer: Pneumatic Dth hammer and drill bit (Φ560): 2 sets of QZ26 type; ② 30m ³/min Ingersoll Rand medium air compressor: 2 sets; II) Analysis on technical parameters of down-the-hole hammer At present, the Dth hammer is mainly used below 300 mm in China, and the hole larger than 300 mm belongs to the scope of large diameter Dth hammer drilling. There are two main parameters in pneumatic Dth hammer drilling technology: air pressure and air volume. These two parameters mainly meet the requirements of two aspects: 1. Meet the requirements of rock breaking power of driving impactor; 2. The rock debris in the hole shall be discharged out of the well to avoid repeated crushing. Different hydrogeological conditions,dth hammer bit, borehole structure, borehole depth and borehole diameter parameters have different requirements for air volume and air pressure. The parameters of Dth hammer can be determined according to the following methods. Selected: (1) Air volume. The rated air volume of the impactor selected in this project is 30 m ³/min. With the increase of hole depth and hole diameter, it is necessary to ensure the discharge of rock debris at the bottom of the hole and reduce the repeated crushing of rock powder to achieve ideal drilling efficiency. Generally, it is required that the upward return velocity of air volume in the hole is ≥ 15m/s. At this time, the airflow velocity is greater than the suspension velocity of rock debris. The air volume can be calculated according to the following formula according to the conditions such as the diameter of the drill hole, the outer diameter of the drill pipe, and the upward return air speed on the slag discharge channel: Q=47.1K1K2（D2 -d2 ）V Where: Q — — air supply volume m ³/min; K1 — — correction coefficient of hole depth K1 = 1 ~ 1.1; K2 — — Gushing water system in the hole K2 = 1 ~ 1.5; D — — drilling diameter; D — — outer diameter of drill pipe; V — — Upward wind speed (15 ~ 25m/s). According to the formula, the air return velocity at the orifice is 15 m/s, the borehole correction coefficient of borehole depth is K1 = 1.0, and the water inflow coefficient in the borehole is K2 = 1.5; (2) Wind pressure. QZ26 Dth hammer is a low pressure Dth hammer, the required wind pressure is 0. 5 ~ 0. 7 MPa, but the drilling efficiency is directly affected by the wind pressure, mining dth bit ,mining dth bit, the greater the wind pressure, the greater the impact power, and the higher the rock breaking efficiency. Therefore, to complete the large-diameter pneumatic down-the-hole hammer drilling, first of all, the working pressure of the impactor should be met to make it work at full load, and at the same time, the pressure along the way (0.0015 MPa/m) brought by the increase of the drilling depth should also be met to overcome the water column pressure below the water level and the pressure difference for removing the debris in the hole. II. Treatment of Main Technical Problems in Hole Guide Construction (I) Insufficient air volume of guide hole Countermeasures: According to the requirements of the borehole diameter and the air volume of the selected air compressor, the down-the-hole hammer and casing drilling process shall be used to guide the hole. According to the guide hole diameter capacity and casing specification met by the air compressor. Through practical application, Dth hammer drilling with casing solves the problem of insufficient air volume, and the ideal effect is obtained in the construction process. (II) Rock debris perforation Countermeasures: The reason why the cuttings are drilled in series is that the distance between the two pilot holes is small. Under the action of high-pressure air, the high-pressure air passes through the pores in the formation, and the boreholes are connected with each other, resulting in the reduction of high-pressure air pressure. In the construction process of prestressed pipe pile Dth hammer leading hole, because of the problem of rock debris string hole, the air volume at the leading hole outlet is less than 15m/s, which can not achieve the purpose of debris removal, so that rock debris enters another hole through the pore, and a certain thickness of sediment is formed in the adjacent hole. Through research and analysis, it is found that the sediment in the hole has little influence on the sinking of prestressed pipe piles, and there are two main reasons: On the one hand, because the sediment particles in the hole are small and the structure is loose, it has little influence on the resistance of pile sinking. On the other hand, the sediment in the hole forms a saturated sand layer under the action of water in the hole, and the saturated sand layer produces sand liquefaction under the action of vibration force during the construction of the pipe pile, so that the sediment in the hole has little influence on the pile sinking. Therefore, in the construction process, no special treatment was carried out on the pile-hole guide hole. Through the actual construction, it was found that the rock debris string hole phenomenon did not have a greater impact on the pile-hole guide pile sinking. (III) How to control the verticality of guide hole Countermeasures: Start the air compressor to drive the Dth hammer to start drilling. During the initial drilling, the drilling speed shall be low, the verticality of the drill pipe shall be rechecked frequently, and it shall be adjusted in time. The down-hole hammer and casing drilling technology is used to guide the hole, which not only solves the problem of insufficient outlet air volume, but also controls the verticality of the guide hole. III. Guarantee of construction period of down-the-hole hammer There are about 200 prestressed pipe piles to be drilled in the concentrated area of weathered and slightly weathered spheres or interlayers in this project. Two down-the-hole hammer drills are arranged to enter the site for construction. Each down-the-hole hammer drill can drill about 5 piles every day. The drilling operation of about 10 piles is completed every day. The drilling work in this area is completed within 20 days. After this part of hole guiding operation is completed, a down-the-hole hammer drill is left as a standby, and hole guiding operation is carried out when the remaining pipe pile construction area needs hole guiding. After receiving the Letter of Acceptance from Party A, immediately organize the mobilization of mechanical equipment and pipe pile materials. This project plans to arrange 2 down-the-hole drills for pipe pile hole guiding operation. During the construction process, the number of hole guiding equipment can be adjusted and increased according to the actual situation, so as to ensure the realization of the total construction period target. END Source: Baidu Library We are committed to protecting the copyright of the author, the source of the content has been marked,down the hole bit, only for the dissemination and sharing of knowledge. No other commercial profit, if there is infringement, please contact us to delete. Push Return to Sohu to see more Responsible Editor:. wt-dthtools.com