The laying and jointing of concrete pipes must be done with high precision and efficiency to achieve a leak-free and robust joint between two concrete pipes. The joining of pipes is usually rigid unless it is specified that a flexible joint may be provided.
In this article, we discuss the procedure of jointing of concrete pipes by rigid type and flexible type.
1. Excavation of Trenches
- The excavation of the trench for laying of pipes and the point where the joining of two pipes is required shall be excavated as described in the plan and estimation.
- The width and the depth of the excavation shall include the working space and depth of bedding material (if required), respectively.
- In the case where the pipe is directly laid over the soil, the bottom of the excavation shall be suitably rounded to fit the lower part of the pipe.
- The cost of rounding of soil shall be included in the rate for laying the pipe itself.
2. Laying of Concrete Pipes
- The handling of the pipe shall be such as to avoid impact at the time of loading, transporting, and unloading.
- Mechanical appliances (chain pulley block) are recommended for unloading and lowering of pipes into the trenches carefully.
- The pipes shall be laid starting from the upgrade of the slope and shall be true to line and grade as specified.
- In the case where loose collars are to be used for the jointing of pipes, the collars shall be installed in the adjacently laid pipe before laying the next pipe.
- The socket end of the pipe shall be kept on the upstream wherever spigot and socket type of jointing is prescribed.
- In special conditions, where the pipes are to be laid in close proximity of trees, manholes, or foundation of a building, the pipe shall be encased with cement concrete of 1:5:10 or compacted sand or gravel all around of thickness 150mm.
- In the places where the soil is inadequate to carry the load of pipe, the pipe must be laid either in concrete cradle supported on a proper foundation.
- The depth of the concrete cradle shall be in the range of 100mm to 300mm or at least a quarter of the internal dia of the pipe.
- The cradle concrete at the side of the pipe shall include extent up to a quarter of the outside diameter of pipes 300 mm and over in dia.
- It must be made sure that the pipe is laid in the cradle concrete bedding before the concrete has set.
- In the case where the pipe is laid in hard rock clay, shale, or other hard material, the portion of the earth below the pipe shall be excavated and replaced with an equalizing bed of concrete, sand, or compacted earth.
- Under no circumstances, the pipe shall be laid directly on any hard material.
- When the pipe is to be laid above the ground, the pipe shall be supported with a rigid foundation at intervals. The supports shall be placed as far as possible close to the joints.
3. Jointing of Concrete Pipes
The jointing of concrete pipes is carried out by two methods, namely, rigid and flexible. Generally, all the jointing are of the rigid type, unless until mentioned as flexible type.
The different types of joints made in the concrete pipe are described below:
1. Rigid Spigot and Socket Joint
This is a commonly preferred type of joints in the concrete pipes, as this is easy to install. The spigot of the pipe is slipped inside the socket of the previously laid pipe and adjusted in the correct position, as shown in figure 2. The joint shall be filled with a 1:2 cement mortar mixture of stiff consistency, which shall be rammed with a caulking tool. The excess cement mortar shall be removed, and the joint shall be cured.
2. Rigid Collar Joint
The rigid collar joint is made by joining two adjacent pipes with butt to butt position and adjusted in the correct position, as shown in figure 3. A collar is used to cover the joint equally on both pipes. The void space in between the pipe and collar shall be fixed with a 1:2 cement mortar and rammed with a caulking tool. The excess cement mortar shall be removed, and the joint shall be cured.
3. Semi-Flexible Spigot and Socket Joint
The mechanism involved in the joining of pipes is the same as that of rigid spigot and socket joint. The difference is that a rubber ring is placed on the spigot, which shall be slipped into the socket of the adjacent pipe, as shown in figure 4. The remaining gap is filled with a stiff mixture of cement mortar 1:2 and rammed with a caulking tool.
4. Semi-Flexible Collar Joint
The ends of both pipes are fitted with a rubber ring, which is further compressed in between the spigot and the collar which seals the joint, as shown in figure 5. The remaining gap is filled with a stiff mixture of cement mortar 1:2 and rammed with a caulking tool.
5. Internal Flush Joint
As the name suggests, the joint is flushed with both inside and outside with the pipe wall. The ends of both the pipe are specially shaped to form a self-centering joint with an internal jointing space 1.3 cm wide, as shown in figure 6. The joint space is then filled with 1:2 cement mortar, compacted using trowel or rammer, and cured. This joint is generally used for culvert pipe of 60cm dia and over.
6. External Flush Joint
This type of joints is preferred for pipes that are too small for jointing from inside. The ends of both pipes are butt-joined against each other and adjusted in the correct position, as shown in figure 6. The joint space is then filled with 1:2 cement mortar, compacted using trowel or rammer, and cured.
The different types of joints made in the concrete pipe are Rigid Spigot and Socket Joint, Rigid Collor Joint, Semi-Flexible Spigot and Socket Joint, Semi-Flexible Collar Joint, and Internal and External Flush Joint.
The commonly used joint for concrete pipe is Rigid Spigot and Socket Joint, as this joint does not require machinery and is easy to work with.
The internal flush joint is generally used for culvert pipe of 60cm dia and over.
The external flush joint is used for pipes that are too small for jointing from inside.