Craftwork Design And Application Of Pneumatic DTH Spiral Drilling In Deep Foundation Excavation Support

Combining engineering theory and practice, this paper discusses applications of rotary drilling technique in deep foundation excavation support. Anti-sliding pile with anchor cables support is used in deep foundation excavation support of Chongqing IFC project. Total length of anchor is more than36,000meter and anchor cables construction plays a large proportion in deep foundation excavation support. It is the key distribution project in deep foundation excavation support. Anchor cables hole is the pivotal in anchor cables construction. Anchor cables must penetrate gravelly backfill soil of depths up to40meter which is loose and hole-collapse, and it is difficult to be pore-forming. Anchor hole has three kinds of hole diameter:110mm,130mm and150mm. Design angle is-5～40°and the depth into the bedrock is7-12m. Because of special construction conditions, it is high cost and pore-forming difficult by use of conventional anchor hole drilling construction. Though contrasting with Conventional bare fluid hole drill, drilling fluid with the tube, Pneumatic DTH drilling, Pneumatic DTH eccentric drilling eccentric and spiral drilling, the paper summarize drilling theory of spiral drilling and Pneumatic DTH drilling, and establishes the composite pattern of Pneumatic DTH spiral drilling rod BHA. It analyzes the technological parameter of Pneumatic DTH spiral drilling and suggests the method of determining the diameter of spiral drilling pipe. At last, it used the technological parameter of Pneumatic DTH spiral drilling for Chongqing IFC deep foundation excavation support construction. After analyzing Pneumatic DTH spiral drilling technology and practical application, we get following conclusions:(1) Pneumatic DTH damages the rock by attack and rotation. It overcomes the shortcoming in normal digging method which cut the rocks only, loss of fluid during digging and hole collapse issues. Pneumatic DTH spiral drilling rod has the advantage of both advantage of DTH and spiral drilling rod. It can drill effectively, evacuate the dregs well and work efficiently in all kinds of lands with low cost. It also improves cohesion number between mortar and gneis and increases the friction and anti-pull strength of anchor segment.(2) Spiral drilling rod pull the dregs out of anchor hole progressively with its rotating blades. So it is beneficial for loose strata of air leakage. Replacing general drill pipe by spiral drill pipe what can combine high-pressure air with dust and automatic discharge cuttings of spiral drilling rod, it can drill efficiency and reduce the amount of wind and wind pressure.(3) Pneumatic DTH spiral drilling uses air as cyclic medium without flushing fluid which can avoid hole-collapse because of fluid into the rock cracks or loose soil. It not only gives full play to the role of retaining wall of the spiral drill pipe, but also decreases the probability of hole-collapses because of high-speed airflow.(4) Putting lower demand on order parameter of drilling technique, It is allowed to choose drilling rig and air compressor with lighter weight and smaller drilling load. Machine can be placed on the far stability ground for facilitating the construction on the bench.(5) Construction results show that DTH spiral drilling rod design and analysis of process parameters is a reasonable choice. DTH drilling obtain obtains good pore-forming effect, drilling high efficiency, low cost of construction, outstanding overall performance in deep foundation excavation support of Chongqing IFC.