Sustainable Construction for Large Diameter Steel Pipeline on the Integrated Pipeline Project

After nearly four years of construction on several sections of the integrated pipeline (IPL) project in north Texas consisting of approximately 60 mi of 108-in steel pipeline using imported granular embedment, the existing soil conditions in IPL Sections 10 and 11 provided the contractor the opportunity to use native excavated material for a sustainable construction solution to importing embedment material. Most of the these completed sections of the IPL project were constructed in soils that were not conducive for use as pipe embedment without extensive screening and processing in the form of controlled low strength material (CLSM) for fat clay soils or crushing and screening of limestone. IPL Sections 10 and 11 which consists of approximately 12.5 mi of 84-in raw water steel pipeline in Ellis, Johnson, and Tarrant Counties partly runs through sandy soils that can be processed and mixed with cement to make cement stabilized sand (CSS). IPL Sections 10 and 11 begins in fat clay soils in the south and ends in the north and west in sandy soils. There are several sand borrow sites in the area including one that the pipeline runs through. This sand borrow site was active prior to construction of the pipeline. The contractor proposed using the native sandy soil excavated along the pipe alignment for CSS in lieu of gravel embedment. This paper highlights the steps taken to evaluate the use of the native sand for making CSS for pipe embedment: triaxial testing to determine Young’s modulus properties of various CSS sand mixes ranging from 1% to 5% cement content; determine modulus of soil reaction, E', values for each CSS mix design to confirm it’s suitability for a standard trench width; and require contractor to demonstrate that CSS could be produced from a pug mill with consistent quality that had optimum moisture determined as part of the triaxial testing process. By using native sandy soils excavated along the pipeline for producing CSS for the pipe embedment, the contractor was able to greatly reduce the number of embedment deliveries to the project site and reduce the amount of spoil material that had to be hauled off. This directly reduced the impact to existing roads and the environment.