Percussion drilling is employed when auger or wash boring is not possible in very stiff soil or rock. It also can be used in most soil types.
Here the advancement of a hole is achieved by alternatively lifting and dropping a heavy cutting or hammering bit that is attached to a rope or cable that is lowered into an open hole or inside a temporary casing (casings are hollow cylindrical pipes used for borehole stability and to prevent the loss of drilling fluid through the boreholes).
Usually a tripod is used to support the cable. The stroke of bit varies according to the ground condition. The major disadvantage of this method is that it is not possible to get good-quality undisturbed samples. In very hard rock (and especially fractured hard rock), down-the-hole (DTH) drilling can be employed. In this case the hammer, applying repeated percussive pressure, is located just behind the drill bit inside the hole, unlike the open percussion drilling, where the hammer is on top of the drilling string.
The drilling string provides the necessary force and rotation to the hammer and bit, as well as compressed air or fluids to the hammer and for the flushing of cuttings.
This arrangement also allows for much deeper percussion drilling. However, the DTH drills are typically more expensive.
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According to the “Notice of the Ministry of Finance on the Approval of the Budget for the 2013 National Major Scientific Instruments and Equipment Development Special Project Budget†issued by the Ministry of Finance (Caijiao [2013] No. 301), the Ministry of Finance plans to issue a special fund of RMB 19.9 million to the company.
The project was led by the company, and five other organizations including Wuhan University and the Chinese Academy of Sciences Nanhai Institute of Oceanography participated in the implementation. The starting and ending time of the project is from October 2013 to October 2017. The special funds for the project will be allocated to the company's account in part by the fiscal period. The funds will be transferred by the company according to the tasks and funds invested by other participating units.
Recently, the company received the third phase of this project's special fund of 5 million yuan, of which the company received 21.19 million yuan, and the remaining 2.88 million yuan will be transferred from the company to other participating unit accounts. Up to now, the Ministry of Finance intends to allocate the company's special funds for the project amounting to RMB 19.9 million.
(Original title: Wuhan Fangu won the third-phase budget appropriation for the National Major Scientific Instrument Development Project)
[China Instrument Network Instrument Research and Development] announced on the evening of February 16 that Wuhan Fangu Company and Wuhan University, the Chinese Academy of Sciences Nanhai Marine Institute, China Shipbuilding Heavy Industry Zhongnan Equipment Co., Ltd., Fujian Ocean Forecasting Station, and the State Oceanic Administration East China Sea Forecast The 2013 national major scientific instrument development special project “Development and Application of Dual Frequency All-digital High-frequency Ocean Sounder†jointly undertaken by the Center has been officially approved by the Ministry of Science and Technology.