Article
Joint Restraint vs. Thrust Blocks
February 13, 2006
•Article: Joint Restraint vs. Thrust Blocks
The question often arises "Can you really eliminate thrust blocks using joint restraint?" This report is an attempt to provide you with the information needed for you to realize the answer to that question is "yes". For many years, thrust blocks have been successfully used in distribution systems all over the world. Thrust blocks, however, are not without limitations.
It has been argued that thrust blocks are the cheapest form of pipeline restraint. When all of the costs such as labor, forming time, and waiting for concrete to be poured and cure are added to the price of the concrete, the thrust block is not as cheap as originally thought.
A thrust block prevents separation of joints and pipe movement by transferring the resultant thrust force at a bend to the undisturbed soil behind the thrust block. The bearing strength of the soil is expressed in pounds per square foot. Therefore, the area behind the thrust block must engage enough soil area to resist the resultant thrust force at a change in direction.
A properly designed thrust block involves much more than "dumping" a load of concrete behind a bend. The design involves consideration of undisturbed soil, soil bearing strength, test pressure, pipe size, fitting configuration, and trench depth to determine the bearing area of the thrust block. It is then a matter for the installer to form up and pour the proper block. Care needs to be taken to prevent the concrete from covering the joints at fittings, the weep holes in hydrants, and operating mechanisms of valves. Once the thrust block has been properly designed and properly formed, a concrete truck must be called to the site to pour the concrete. Now the waiting begins. Only after the concrete has cured can the pipeline be charged with water and tested. This procedure addresses horizontal fittings. When complicated bend combinations, vertical downbends, parallel lines, dead ends, and future excavation possibilities become involved , the use of thrust blocks become very problematic. This report does not begin to explore the combinations involved with thrust blocks in locations with poor soil conditions.
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•Article: Joint Restraint vs. Thrust Blocks
SOURCE: EBAA Iron Sales, Inc.
