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

With the exploitation of the underground space in cities and the large scale construction of the underground retail spaces, the deep excavation projects is becoming more and more. The traditional deep excavation retaining method can not meet the requirement of the stabilization of large-scale underground buildings. Especially in sandy cobble stratum where the ratio of finishing gas hole is very low, it must lead to high pressure for the grouting and anchoring later and increase the construction cost.

The technique of self drilling anchor bolt, which is introduced from foreign countries, is a new kind of rock-soil anchoring technique to apply for the projects in complicated geological conditions and construction environment especially in the weak soil and sandy cobble stratum. There are also the successful examples in domestic railway constructions.

The Feature of Construction Method

Self-drilling hollow injection anchor bolt is an advanced anchor system, which is composed by hollow anchor bar, nut, plate, coupler, drill bit, centralizer and anchor bars can be cut & lengthened by coupling according to your demands. This anchor system can be integrated with the functions of drilling, grouting and anchoring. It also can ensure the anchoring for complex ground conditions.

▪ It is safe, reliable, and time saving.

▪ Installation & operation are simple.

▪ Choice of drill bits for different ground conditions.

▪ Grouting works synchronize with drilling or after drilling. Grout can fill fractures effectively.

▪ Anchor bars can be cut and lengthened according to your demands. It applies to narrow spaces.

▪ It provides higher bonding stress than smooth steel pipe depending on continuous wave and T-thread.

An Application Example——the Line No. 4 of Beijing Metro

The Line No.4 of Beijing Metro is located in the Dongzhuang Park in Fengtai District. The project was started on November 30 in 2005. South Underground Station was designed to combine with the Beijing South Railway Station, the metro station is situated in the second floor and third floor underground. The Line No.4 of Beijing Metro is in the second floor and is 150.3m long, 125m wide and about 10m high. The total depth of the excavation is about 30m, and the total construction area is about 32203 square meters. While the area to use self drilling anchor bolt has been up to 3200 square meters. This project applied it successfully in large scale to support the sandy cobble stratum during construction.

Parameter Design

Rows Supporting Form Length
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

According to the practical application, measurement and monitoring data, this shoring of foundation pit is reasonable, and it also illustrates the application of the self drilling anchor bolt is entirely feasible.

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