Providing good quality and quantity of water is duty of any state so is a measure of level of development of it’s people. Modern states are engaged in planning and executing water projects on large scales. Lengths of pipelines are running in hundreds of kilo meters and diameter of pipes in excess of a few meters. Pipe lines are running through Jungles, deserts, cross country terrains, water submerged areas, busy city roads etc. Pipe lines are being laid underground with depths varying from shallow to large; and over the ground supported on RCC or MS structures/supports.

Use of RCC in a judicious way is very integral to success of any water supply project.

  • Thrust Blocks are used to counter any thrust on the pipe line caused by unbalanced vertical or horizontal forces arising due to change of direction of flowing water in the pipe line. Unbalanced forces are countered by weight of thrust blocks. Proportioning of sizes of thrust block should be such that Centre of Gravity of the thrust block and that of unbalanced forces match as much as possible suiting the side conditions, so that least moments arise on the block. Quantity of reinforcement provided is generally minimum catering to temperature shrinkage and expansion stresses only.
  • When pipes are laid over the ground, they are often supported by RCC supports. When height of the support is not very high, supports are designed as pedestal columns and often referred as pedestal. Moments due to temperature and contraction are not very significant and the pedestal is only designed for the vertical compressive forces caused due weight of water and pipe. There is a minimum requirement of reinforcement here too.
  • When height of the support is relatively high, supports may need to be designed as regular columns short or long, resisting the vertical compressive forces caused due weight of water and pipe and also moments caused due horizontal forces resulting from temperature expansion and contraction of metallic pipes. Type of foundation may be open or piles depending upon the strata. Piles are being used where bearing capacity of the sub strata is very weak or supports are provided in the water flowing Nallahs/ rivers/ ponds etc. Piles may be rested on the hard strata where nature of flowing water is only flashy and the hard stratum is encountered. It is always advantageous to anchor the piles in the base for one to two meters, whatever practically possible. This helps to counter immeasurable forces arising when flowing debris, trees etc entangle in between the piles during high flow of water. When strata is relatively weak full depth piles i.e 1.2 x (High flood level- Max scour depth) should be provided.
  • Pipe line is often supported on the columns without any bearing, paper tar bearing, metallic bearing etc. Coefficient of friction due to each type decreases by one fifth to one tenth respectively, which in turn decreases the horizontal forces and moments on the supporting columns. When expansion joints are used horizontal forces are limited to manageable values and so are the moments. If size and reinforcement of the columns are sufficient to resist these forces, use of bearings should be avoided as this at one hand is not economical and on the other hand raises maintenances issues in the future. Use of metallic bearing should be resisted to the rarest of rare cases.
  • As transfer of large amount of surface water is being taken up to large populated cities, large size pipes are being laid under busy city roads. Presence of already under laid underground utilities has often necessitated laying of water pipe line in the main carriage ways. Presence of sewer lines, already existing water pipe lines, electrical cables, telephone cables often restricts cover below one meter. It is often seen that use of plain cement concrete is made for such sites. PCC at maximum prevents transfer of any concentrated/point load transferring to pipe lines. But if heavy traffic loads are plying over the road and cover is not proper, loads may get transferred to pipes causing heavy damages. In such case proper designed RCC culverts should be used to encase the pipe. The gap between the top of the pipe and bottom of the top slab should be filled with clean sand. Special care should be taken when pipe lines are crossing the main carriage ways.
  • Because of the circular shape of the pipes and limited time available in case of busy roads, compaction is always a tricky issue. Roads witness large depression and consolidation over a period of time, which in turn cause heavy deflections in the pipe line. The use of underground thrust blocks and RCC culverts demand special precautions during laying of pipe line. These lumped masses may cause differential settlements of the adjacent parts of the pipes, which in general cause welding joints at the top of the pipes to open up. This phenomenon is aggravated in winters more because of pipe being in tension. It is therefore suggested that proper compaction practices should be adopted especially at such locations where heavy lumped masses of loads are created on the pipe lines in form of thrust blocks or RCC culverts.
About The Author
Deepak Sharma
An M. Tech from MNIT, Jaipur. Working as Assistant Engineer in PHED, Rajasthan. A large number of structural project to his credit. Have penchant for innovative design & aesthetic aspects of structural designs