Construction Technology of Rapidly Forming Holes in Hard Rock Formation of Zhongcha Beijing DTH Drilling and Rotary Drilling Rig

In recent years, with the continuous development of China's engineering construction, there are more and more foundation pit support and pile foundation engineering. Rotary drilling rig is a new equipment emerging in the construction of bored piles in recent years. Its hole forming speed is fast and construction is convenient. With a high degree of civilization, it has gradually replaced the traditional rotary drilling rig and punching pile drill. However, in the stratum with high rock stratum strength, the construction speed of the rotary drilling rig is slow, and even it is impossible to drill, and it is difficult to fully exert its characteristics. In this paper, in combination with the borehole piles of the vertical shaft retaining structure of the Longdong Station to Kemulang Station of the Guangzhou Metro Line No. 6 in the process of forming a hole in the weathered and slightly weathered rock strata of the granite, the submerged hole drilling is used to effectively solve the problem of the rotary drilling rig in the hard rock formation. Hole puzzle.

I. Project Overview

The hard rock section of Longdong Station-Kemuyu Station is excavated by mining method. The mine tunnel enters the construction through construction shaft and cross channel. The clearance of the shaft is 7m×9m and the depth is 28.738m. The shaft is constructed by open cut method. The wellbore of the soil layer adopts φ800 bored pile + φ600 jet grouting pile to stop water, and the ring frame beam is supported inside. The rock stratum well body adopts anchor spray support. The distance between the bored piles is 1m, a total of 40, the design pile length is 17.75m, and the pile bottom is embedded in the medium weathered granite not less than 1m.

Second, engineering geology

The preliminary survey geological report shows that the top-down stratum of the bored pile is artificial fill layer, plastic residual soil layer, hard plastic residual soil layer, fully weathered granite layer and medium weathered granite layer. The maximum rock strength is about 30 MPa.

Third, construction machinery selection

After analyzing the geological conditions, combining with the site and construction period, the bored piles are drilled and drilled into holes. Rotary drilling rig is a new equipment for bored pile construction in recent years. Compared with traditional drilling rig construction, it has the following advantages:

1 into the hole speed. Compared with the traditional circulating drilling rig, the advantages are obvious, which effectively ensures the progress of the project, saves the construction period and reduces the construction investment.

2 The formation has strong adaptability. From weak muddy soil to moderately weathered rock with a strength of more than 30Mpa.

3 outstanding environmental features. The traditional method of processing hard rock is to drill holes into impacts. It is necessary to set up mud ditch and slag on site, which has poor civilized construction and high noise.

4 pile hole alignment is convenient and accurate.

Fourth, there are problems

According to the preliminary survey geological report, the bottom of the bored pile is located in the middle weathered granite stratum, and the maximum rock strength is about 30 MPa. However, during the process of rotary drilling and hole formation, it is found that the rock layer is hard and cannot be holed. In the later stage, the four corner points of the shaft are re-investigated, and the height difference of the middle weathered granite in the 8m*10m shaft is 4.5m. The borehole pile in the northeast corner of the shaft has entered the micro-weathered stratum with a rock strength of 63MPa. Construction has brought great difficulties.

Five, the solution

Because some of the bored piles need to enter the middle and slightly weathered strata, the piles grow into the middle weathered rock stratum 6m, the rock strength reaches 63MPa, and the rotary drilling rig can't drill into the hole.

If the traditional hole drilling rig is used to carry out the hole formation, the construction site is small and the mechanical efficiency is extremely low, which has a great impact on the whole construction period.

After analysis and research, combined with the on-site rock strength, the MDL-135D submerged hole drilling rig was used to crush the medium hard rock, and then the rotary drilling rig was used to form the hole. According to the depth and strength of each borehole pile, the number and arrangement of drill holes in the downhole drilling rig are different.

Among them, MDL-135D type down-the-hole drilling rig has the advantages of easy vertical control, large mechanical power, suitable for hard rock drilling construction, difficult to drill, good construction effect and high speed.

Sixth, on-site progress indicators

The hard rock layer is drilled first by the down-hole drilling rig, the hard rock is reduced to zero, the overall strength of the rock is reduced, and then the hole is drilled by the rotary drilling rig. The shaft has a total of 40 piles, and the piles are all grown into the middle weathered rock layer 6m, the total construction period For 40 days, the progress indicator for pile formation is 1/day.

If the hole is drilled by a traditional punching rig, the impact of the hard rock layer is about 1m/day, and the pile is about 1/6 days. Considering the on-site construction conditions, even if two punching pile machines are used, the construction period will take 120 days.

Seven, summary

The rotary drilling rig has the advantage of quick construction in the soft soil layer, and has gradually replaced the traditional rotary drilling machine and punching drilling rig. However, the rotary drilling rig cannot be constructed in the medium hard rock formation, which limits its wider application. Sex.

The project uses the down-the-hole drill to advance the hard rock into zero, and then drills with the rotary drilling rig, which solves the problem of difficult hole formation in the medium hard rock, and the work efficiency is higher than that of the impact drill construction, and the civilized construction conditions are good and the noise small. In the future municipal engineering, it can be widely used for the construction of supporting piles with complex surrounding environment, high civilized construction requirements and tight construction period.

However, due to the drilling process of the down-the-hole drilling rig, the verticality of the drilling position is difficult to ensure, and the string hole is prone to occur during the construction process, which makes it difficult to ensure the verticality of the pile during the drilling process of the later drilling rig. For the bridge pile foundation and enclosure The applicability of the structure and structure of the main structure needs to be further verified.

Produce capacity: 10000pcs/monty
Brand: zowo
New o rebult: 100% new
Warranty: high quality, fully tested and 12 month warranty