NATIVE SOIL FLOWABLE FILL INVESTIGATION FOR THE IPL

The Tarrant Regional Water District (TRWD) and the City of Dallas Water Utilities (DWU) are currently engaged in the planning, design, and implementation of a 350 MGD raw water transmission system. The approximately 150 mile pipeline will run across north central Texas from Lake Palestine to Lake Benbrook. The program developed by TRWD to accomplish these improvements is called the Integrated Pipeline Project (IPL). To reduce the project costs and the impact on the environment, project management is investigating construction methods that re-use as much of the native soil as possible. One approach is to use native soils to make flowable fill for the pipeline embedment. Laboratory trial mixes of soils from along the alignment demonstrated that the various soil formations have the potential for use in flowable fill using either Portland cement or Class C flyash. Field trials were then conducted to evaluate the potential of making flowable fill using typical construction equipment and methods with the native soils. While laboratory mixes are conducted under controlled conditions with exact amounts of material, the field trials were used to see if the laboratory procedures can be adapted for actual construction methods. The flowable fill field trials demonstrated that soil shredders can process the various native materials, showed how commercial mixing of materials can make flowable fill, and verified that native flowable fill can be used for pipe embedment. The soils were mixed with either Portland cement or Class C flyash to meet a target strength of 40 to 80 psi.