Stoneware pipes are generally preferred over other types of pipes for sewer and drain works as they are much more effective where acid effluents or acid sub-soil conditions are likely to be encountered.
In this article, we discuss trenching, laying, jointing, testing and refiling of stoneware pipe.
- The trench for laying of stoneware pipes shall be excavated to the required alignment and required depth.
- When the pipeline is under a roadway, a minimum cover of 90mm is recommended.
- The trench shall be so shored and drained in such a way that the workmen can work therein safely and efficiently.
- The discharge of the trench de-watering pumps shall be conveyed either to drainage channels or to natural drains.
- The excavation shall be carried out with manual labor or with suitable mechanical equipment as approved by the engineer.
- Unless otherwise specified by the engineer, the width at the bottom of the trenches for different diameters of pipes laid at different depths shall be as given below
- For all diameters, up to an average depth of 120 cm, the width of the trench in cm = diameter of pipe + 30 cm.
- For all diameters for depths above 120 cm, the width of trench in cm = diameter of pipe + 40 cm.
- Notwithstanding (1) and (2), the total width of the trench shall not be less than 75 cm for depths exceeding 90 cm.
Laying of Stoneware Pipes
- All pipes shall be laid on a bed of cement or lime concrete with thickness and mix as specified, projecting on each side of the pipe to the trench’s specified width.
- The pipes with their crown level at 1.20 m depth and less from the ground shall be covered with a 15 cm thick concrete.
- The concrete above the pipe’s crown shall be sloped off to meet the outer edges of the concrete to give a minimum thickness of 15 cm all-around the pipe, as shown in figure 2.
- The pipes laid at a depth greater than 1.20 m at the pipe’s crown shall be sloped off from the edges to meet the pipe tangentially.
- The pipe shall be carefully laid to the alignments, levels, and gradients shown on the plans and sections.
- Great care shall be taken to prevent sand etc. from entering the pipes.
- The pipes between two manholes shall be laid in a straight line without vertical or horizontal undulation.
- The pipes shall be laid with a socket up the gradient.
- The pipe’s body shall rest entirely on an even bed of concrete, and places shall be excavated in the concrete to receive the socket of the pipe.
- Where pipes are not bedded on concrete, the trench floor shall be left slightly high and carefully bottomed up as pipe laying proceeds, so that the pipe barrels rest on firm and undisturbed ground.
- If the excavation has been carried too low, the desired levels shall be made up of concrete 1:5:10 (1 cement: 5 fine sand: 10 graded stone aggregate 40 mm nominal size) for which no extra payment shall be made.
- If the trench floor consists of rock or very hard ground that cannot be easily excavated to smooth surface, the pipe shall be laid on a leveling course of concrete as desired.
- When stoneware pipes are used for stormwater drainage, no concreting will normally be necessary. The cement mortar for jointing will be 1:3 (1 cement: 3 fine sand).
Jointing of Stoneware Pipes
- The tarred gasket of hemp yarn soaked in thick cement slurry shall first be placed around the spigot of each pipe, and the spigot shall then be slipped into the socket of the previously laid pipe.
- The pipe shall then be adjusted and fixed in the correct position, and the gasket caulked tightly to fill not more than 1/4th of the socket’s total depth.
W = D+X
D is the external diameter of the pipe.
X = 300 up to trench depth of 1200
400 trench depth more than 1200
T = 100 for pipes under 150, ¼th internal dia
Subject to a min. of 150 and max. 300 for pipes more than 1500 dia.
MWL = Maximum water level
3. The socket’s remainder shall be filled with a stiff mixture of mortar in the proportion of 1:1 (1 cement: 1 fine sand).
4. When the socket is filled, a fillet shall be formed around the joint with a trowel forming an angle of 45 degrees with the pipe’s barrel.
5. After a day’s work, any extraneous material shall be removed from the inside of the pipe.
6. The newly made joint shall be cured for at least seven days.
Testing of Joints of Stoneware Pipe
- The stoneware pipes used for sewers shall be subjected to a test pressure of 2.5 m head of water at the highest point of the section under test.
- The test shall be carried out by suitably plugging the lower end of the drain and the ends of the connection, and filling the system with water.
- A knuckle bend shall be temporarily jointed in at the top end and a sufficient length of vertical pipe jointed to it so as to provide the required test head, or the top may be plugged with a connection to a hose ending in a funnel which could be raised or lowered till the required head is obtained and fixed suitably for observation.
- If any leakage is visible, the work’s defective part shall be cut out and fixed.
- A slight amount of sweating, which is uniform, may be overlooked, but excessive sweating from a particular pipe or joint shall be watched for and considered as a defect and the jointing procedure shall be redone.
- Any joint found leaking or sweating shall be rectified or embedded into a 15 cm layer of cement concrete (1:2:4) 30 cm in length, and the section retested.
Refilling of Stoneware Trenches
- In cases where pipes are not bedded on special concrete, care shall be taken in refilling trenches to prevent the displacement and subsequent settlement at the surface resulting in uneven street surfaces and dangers to foundations, etc.
- The backfilling shall be packed by hand and rammed with a shovel and light tamper.
- This method of filling will be continued up to the top of the pipe.
- The refilling shall be carried out simultaneously on both sides of the pipe up to 60 cm without disturbing the pipe.
- No tamping should be done within 15 cm of the top of the pipe.