The Construction Method of Self Drilling Anchor Bolt in Sandy Gravel Deep Excavation

Time:2015-10-22View:

Introduction

With the rapid expansion of urban underground spaces and the construction of large-scale underground retail spaces, deep excavation projects have become increasingly common. Traditional deep excavation retaining methods often struggle to meet the stability requirements of these extensive underground structures. This issue is particularly pronounced in the sandy cobble stratum, where the ratio of finishing gas holes is low, leading to higher pressures during grouting and anchoring processes, ultimately driving up construction costs.

self-drilling-rock-bolt-of-sinorock

In response to these challenges, the introduction of the self-drilling anchor bolt technique from foreign countries has proven to be a game-changer. This innovative rock-soil anchoring method excels in complex geological conditions, especially in weak soil and sandy cobble stratum. Moreover, successful examples of its application in domestic railway construction further testify to its reliability and effectiveness.

Features of the Construction Method

The self-drilling hollow injection anchor bolt system is a cutting-edge technology comprising a hollow anchor bar, nut, plate, coupler, drill bit, centralizer, and the anchor bar that can be cut and lengthened by coupling according to specific project requirements. This anchor system integrates drilling, grouting, and anchoring functions while ensuring robust anchoring in even the most challenging ground conditions.

Key features of the self-drilling anchor bolt system include

1. Safety, reliability, and time-saving benefits.
2. Simple installation and operation procedures.
3. Versatility with a range of drill bits available for various ground conditions.
4. Synchronized grouting during or after drilling to effectively fill fractures.
5. Flexibility with anchor bars that can be cut and lengthened, ideal for narrow spaces.
6. Enhanced bonding stress compared to smooth steel pipes, thanks to continuous R-thread and T-thread technology.

An Application Case: Beijing Subway Line 4

A prominent example of the successful application of the self-drilling anchor bolt system can be found in the construction of Beijing Subway Line 4, situated in Dongzhuang Park, Fengtai District. This ambitious project commenced on November 30, 2005, with the South Underground Station designed to integrate seamlessly with the Beijing South Railway Station. The metro station, spanning the second and third floors underground, measures 150.3 meters in length, 125 meters in width, and approximately 10 meters in height. The total excavation depth reaches about 30 meters, encompassing a construction area of around 32,203 square meters. In this vast project, the self-drilling anchor bolt system covered an impressive area of 3,200 square meters and successfully supported the sandy cobble stratum during construction.

Detailed Construction Process

1. Site Assessment and Analysis

Before the implementation of the self-drilling anchor bolt system, a comprehensive site assessment and geological analysis was conducted to understand the ground conditions fully. Detailed surveys were carried out to identify potential risks and challenges associated with the sandy cobble stratum.

2. Design and Planning

Based on the site assessment data, a specialized design and construction plan were developed. The self-drilling anchor bolt system was chosen for its compatibility with complex geological conditions and its ability to offer stable support during excavation.

Parameter Design

Rows	Supporting Form	Length (m)	Aperture (mm)	Distance (mm)	Model of Main Reinforcement	Slope Rate
First Row	Soil Nailing	15	110	1500	Ф28	0.3
Second Row	Soil Nailing	15	110	1500	Ф28
Third Row	ZB40/20 Self drilling anchor bolt	13		1500	seamless steel pipe
Fourth Row	ZB40/20 Self drilling anchor bolt	12		1500	seamless steel pipe
Fifth Row	ZB40/20 Self drilling anchor bolt	10		1500	seamless steel pipe
Six Row	>ZB40/20 Self drilling anchor bolt	8		1500	seamless steel pipe

3. Installation of Self-Drilling Anchor Bolt System

The installation process commenced with drilling holes using the self-drilling anchor bolt system, which involved simultaneous drilling and grouting. The grout effectively filled any fractures in the ground, enhancing the overall stability of the stratum.

subway-construction-site

4. Monitoring and Quality Control

Throughout the construction process, a rigorous monitoring and quality control system was in place. Data on the self-drilling anchor bolt system's performance, ground movement, and stability were continuously collected and analyzed to ensure the effectiveness of the support system.

5. Results and Conclusions

Based on practical application, measurement, and monitoring data, the self-drilling anchor bolt system showcased exceptional performance in stabilizing the foundation pit. The successful completion of Beijing Subway Line 4's construction using this system stands as a testament to its feasibility and reliability in challenging sandy cobble strata.

Conclusion

The construction of Beijing Subway Line 4 serves as an excellent example of the effectiveness and benefits of the self-drilling anchor bolt system in deep excavation projects, particularly in sandy cobble stratum. The integration of drilling, grouting, and anchoring functions ensures a safe, reliable, and time-efficient construction process, ultimately reducing costs and improving project outcomes. As the demand for underground spaces continues to rise, the self-drilling anchor bolt system represents a valuable tool for stabilizing large-scale underground structures in various geological conditions. Its successful application in the Beijing Subway Line 4 project highlights its potential to revolutionize the future of deep excavation construction.

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