Update to the Improved Approach for the Design of Thrust Blocks in Buried Pipelines

In 2011, the ASCE Task Committee on Thrust Restraint Design of Buried Pipelines (Task Committee) presented a paper detailing an improved approach to the design of thrust blocks and thrust restraint systems to improve current practice. This paper presented two rational approaches, "standard" and " simplified", for the design of thrust blocks for all pipe materials, by considering the tolerable movement of the pipe, the structural integrity concerns of the adjoining pipe segments and joints, the characteristics of the soil, and an appropriate factor of safety. It has been noted that the simplified version of the improved approach presented in ASCE (2011) still required analytical representation of the flexure of the pipe in response to the movement of the bend and to the lateral resistance of the soil, particularly with respect to the first piece of pipe adjacent to the pipe bend. Such analytical representation is usually more involved than a design engineer is willing to use for a simple thrust block design. Considering this, the Task Committee has further simplified the assumptions used in the 2011 simplified approach and assumes that the first piece of pipe moves rigidly, with the pipe joints on either end behaving as connections free to slide axially and to deflect transversely. This simplification allows the " simplified" analysis to use simpler equations using readily available parameters such as bend angle, length of the first piece of pipe, ultimate soil bearing resistance, and the available extension and deflection capability of the joint. This paper presents the revised simplified approach, documenting the justifications and limitations for the assumptions made, and an example of its use for a common thrust block application.