Common Types and Layout Form of Pipe Roof

What is Pipe Roof

A pipe roof is a group of steel pipe structures set in the surrounding stratum of the tunnel, and through the effective combination with the steel arch frame, a shed frame is formed. So as to stabilize the excavation surface and the surrounding rock in front of it, and form pre-support. The application of the pipe roof can carry the load of the upper rock mass, and further strengthen the broken surrounding rock by grouting into the stratum, thereby improving the stability and ensuring the progress of the construction.

The pipe roofing method is widely used in some strata with high water content and weak and broken surrounding rock, which can effectively control surface subsidence and prevent the occurrence of stratum collapse.


Pipe Roof Types

1. Classified by construction method

The construction method of the pipe roof is classified according to the different ways of driving the steel pipe into the soil.

a. The Drilling method is a widely used method. It mainly uses a drilling machine to form holes, and then pushes the steel pipes one by one. In actual situations, problems such as hole collapse and pipe sticking may occur. Drilling and pipe inserting is carried out at the same time.

b. The Rammed Pipe method is mainly used in some soft soils, and the steel pipe is directly rammed into the soil through some tools to form a pipe roof.

c. The Pipe Jacking method is to directly push the steel pipe into the stratum through the jacking technology to achieve the purpose of installing the pipe roof. 

2. Classified by steel pipe layers

The pipe roof can be divided according to the number of layers of steel pipe arrangement. There are single-layer and double-layer pipe roofs.

When the overlying load of the tunnel is not large, in order to reduce unnecessary waste of pipes, the single-layer pipe roof is often used.

If the tunnel is located in a complex condition, or the overlying load is relatively large, double-layer pipe roofs can be used.

In the actual situation, combined with the characteristics of the project, double-layer pipe roofs can be selectively set up in some weak parts, and single-layer pipe roofs can still be used in other parts with sufficient bearing capacity. 

3. Classified by the length of steel pipes

Short pipe roof: Pipe roof with a length of single circulating steel pipe less than 6m.

Long pipe roof: Pipe roof with a length of single circulating steel pipe more than 6m.

4. Classified by the diameter of the steel pipes

The pipe roofs can be divided into three categories according to the different diameters:

Small pipe roofs: steel pipe diameter less than 129mm;

Large pipe roofs: steel pipe diameter greater than 300mm;

Middle pipe roof: steel pipe diameter between 129~300mm.

In actual engineering, 89mm, 108mm, and 159mm are used more.

5. Classified by grouting or not

a. The pipe roof without grouting:

Only needs to drive the steel pipe into the stratum, without grouting reinforcement of the rock and soil around the tunnel, but only fill the steel pipe, so as to improve the strength performance of the steel pipe. The filler is generally mortar or concrete.

b. The grouting pipe roof can be divided into two types according to the grouting sequence:

(1) First, install the steel pipe in the stratum. After the installation is completed, grouting can be carried out for reinforcement.

(2) First, grouting to the surrounding rock, and then the steel pipe is inserted to ensure the supporting performance and improve the overall bearing capacity.

The Layout Forms of Pipe Roof

The arrangement of the pipe roof is an important part of tunnel construction design. The common arrangement ways are as follows:

1. Fan-shaped distribution

It is mainly used when the surrounding rock condition of the tunnel is relatively good. And the tunnel arch is the weak link of the bearing capacity of the upper part of the tunnel, and the stability of the surrounding rock is poor.

Fan-shaped arrangements of pipe roof

2. Semicircular distribution

It belongs to the expansion form of fan-shaped distribution and is mainly used in the case of unstable upper strata, in order to fully control the displacement of the rock mass.
Semicircular distribution

3. Door-shaped distribution

It is mainly used when the basic level of the surrounding rock is relatively low. During the tunnel excavation process, not only the upper surrounding rock is indifferent, but the surrounding rock displacement on both sides is also relatively large.
Door-shaped distribution

4. Whole-circumferential distribution

It is used in the surrounding rock that is weak, broken, expansive and has a lot of groundwater, in order to fully control the stability of the tunnel during construction.
Door-shaped distribution

5. Unilateral distribution in the upper half

When the tunnel is located in a sloping terrain and its force is biased, this type of reinforcement is often used.
Unilateral distribution in the upper half

6. In-line distribution

When the tunnel needs to pass through some railways, highways, or other structures, and the distance is relatively close, this form is often used.
In-line distribution

7. Double-layer distribution

When the geological condition of the tunnel is poor and the upper part needs to carry a large load, this form is usually used to control the deformation of the surrounding rock after the tunnel is excavated.

Double-layer distribution



Pipe roofing is mainly used in tunnel projects with soft and broken surrounding rock, such as highway and railway tunnels, subways, hydropower station tunnels, and other underground projects. Traditional pipe roofs generally are seamless steel pipes. Hole collapse may occur during construction in the weak surrounding rock, which makes it difficult to insert pipe roof, so the casing is required.

The self-drilling pipe roof system consists hollow anchor bar, coupling, and drill bit, which can be drilled and grouted at one time. The self-drilling pipe roof system can replace traditional pipe roofs in a variety of easily collapsed formations, and common specifications are R51, T76, T103, etc. If you have any interest in self-drilling pipe roof or self-drilling anchor bolt system, welcome contact us.

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