Application And Technology Study Of The DTH Hammer Pilot Drilling

Prestressed anchor is more and more wildly used in hydropower projects because of its reasonable price, convenient and significantly reinforcing effect, it is instant and widespread attention in hydropower projects by using more extensive.In hydropower projects, the prestressed anchor reinforcement is firstly used in the dam, such as Fengman Hydropower Dam 8MN prestressed reinforced . Gradually, it is applied to the slope protection.the horizontal prestressed cable was used to reinforce the slope of the Three Gorges Permanent ship lock and its vertical wall of the chamber . To drill hole is the first process of prestressed anchor construction, but it have a high-precision in the Three Gorges permanent ship lock of the cable layout, According to the requirements for Hydraulic architecture of the permanent ship lock and avoid stress excessive concentration. The design of horizontal Anchor hole of the permanent ship lock have to achieve the following request : the depth of terminal bolt hole is less than 2% of the depth of the hole, The depth of crossing bolt is not more than 1% of the one of the hole (according to the ministerial standards ,the depth is not more than 3% of the one of hole).To meet the design requirements and avoid deviating an anchor hole, we must find out the reasons for deviation of anchor hole and the various factors affecting anchor hole deviation. Taking corresponding measures prevent it.The factors to lead to the horizontal anchor hole deviation:1.The impact of the formation nature . Rock is the direct target of drilling hole, the rigidity, weathering state, the integrity, the structural cracks , other rock surface composition of the space and the homogeneity of rock have a direct impact on the pilot and borehole deviation. The Three Gorges project is located at the medium to coarse grained diorite intrusive Precambrian granite-plagioclase. served in a number of the anchor hole of the permanent ship lock are most among at the granite breeze, the rock is mostly hard, complete and homogeneity, This will help anchor hole pilot; But the Local band of black mineral enrichment is soft, so it have some difficult to drill hole and control hole ramps because of the individual fracture zones.2.The impact of machinery and equipment . The d rill rig is DKM-1, it is sufficient to consider the Three Gorges working conditions and the development of technical requirements, having some feature: working steadily, and facilitate adjustment exact location. Besides, the speed, direction and pressure can meet the demands of high-precision pore. In practice, it should apply to lower speed and pressure in the premise meeting the requirements of highly effective rock-breaking.The working wind for DTH impactor is provided by VHP-700 air compressor (or VHP-700E electric). It's air pressure, air volume are determine whether DTH can work efficiently and normally.The accuracy and efficiency of pore-forming are governed by many factors including the performance of the DTH, the drill bit is new or old and the precision of drill stem and joints.In many factors about equipment, the choice and use to drilling guide is often most critical, It can remove all obstacles and dilution factor.3) Operational factors. In the course of the construction, it is important and complex that both of technology capability and operation factor of site operation staff. The whole of advanced equipment and technology are required by the operators to achieve. Establishing sophisticated w operational procedures and forming fine work style is one factor to ensure that the bored can be lank.The deflection of horizon anchor hole can be resolve into vertical direction and horizontal direction. In general, the standard anchors hole is downward deflection in the vertical direction but right side in the horizontal direction. The deflection in the vertical direction was caused by gravity, However, it is caused by drilling stem, drilling rod and drilling stem generates right rotating at the bottom of the hole in horizontal direction.In order to overcome the deflection of an anchor hole in the vertical direction. It would be drill by the ideal direction ,when the under side of drilling bit keep suspension or make it touch the upward appropriate of hole if necessary, besides, it should be upward appropriately. To achieve this purpose, installing a guide device, which diameter is similar to the bore (between the drilling stem of DTH and drilling rod). Then the weight of impactor can be balance with the weight of drilling rod backend by use of guided device located in the pivot. When the weight of drilling rod is more than the weight of impactor, the latter will upswept. Then drilling direction of DTH will accord with theoretic direction.The deflection in the horizontal direction of standard anchor hole is caused by rotation of the drilling stem and drilling rod. Before installing guided device, the drilling bit is suspended in support of the next semicircle on the hole, it is rolling in underside of hole wall, meanwhile, a right thrust will brought because of clockwise rotation. Expressed in formulas, the thrust is f=k×N. Where K-- the friction coefficient between brazing alloy and rock, k=0.5 N—- positive pressure to the wall brought by the drilling bit.The right thrust inevitably lead to deflection: the right and downward in the vertical direction. The combination of these two skewed orientation, it is just a reason why the boreholes often skewed to the lower-right panel in the DTH drilling construction uninstalled guided device. This is Consistent with a large amount of observations.The adjustment and correction to the standard anchor hole drilling direction, is mainly depend on adjusting fulcrum correcting device, the diameter of drilling rod correcting device and the spacing of two. The different diameter result in the different leap in the horizontal direction, and decide on the deflection in the horizontal direction when drilling; The spacing of two correcting device decided the upswept force of the drilling stem, decided the touch which upper limb or lower limb to hole wall and thereby determined the deflection in the vertical direction,Under the direction and extent of deviation drilling, drilling will adjust and correct for the deviation by combining with the fulcrum correcting device different diameter and different drilling rod correcting devices by using different distances.DKM-1 standard cable rigs and cedar technology were developed aimed at the horizontal anchor hole with high-precision in the Three Gorges permanent ship lock construction, overcoming the deflection in the horizontal anchor hole successfully by adopting theory about pivot guide pilot theory, meanwhile, some difficulties in construction were resolved, such as rig relocation, dusting and deviational survey. Therefore, making sure the construction of permanent ship lock anchor hole can go with a swing, achieving good economic and social benefits.Under the direction and extent of deviation drilling, ABM now will be the fulcrum for different diameter drill pipe and is guided by different devices using a mix of distance, Drilling will adjust and correct for the deviation,Construction rig relocation and resolve the difficulties, many construction dust and inclinometer problem Construction of the permanent ship lock anchor hole so smoothly and have achieved good economic and social benefits.