Title: Soil-Cement Slurry Pipe Embedment
Author(s): A. K. Howard
Publication: Symposium Paper
Appears on pages(s): 97-110
Keywords: compressive strength; construction; pipelines; pipes (tubes); placing; slurries; soil cement; soils; tests; Construction
Soil-cement pipe embedment has been used by the Bureau of Reclamation for about 25 years. The ingredients of the soil-cement can vary, but typically it is a combination of soil, portland cement, and water. In most cases, the pipe trench is trimmed so that a semicircular excavation is created that is only slightly larger than the pipe diameter. The soil-cement is used to fill the gap between the pipe and the in situ soil. Thus, the native trench material must be able to provide adequate supporting strength to the pipe. The consistency of the soil-cement can vary from a fluid (slurry) to a mixture of about 25-cm (10-in.) slump, depending on the placement requirements. The consistency, ingredients, and placement dimensions can all vary as long as two basic requirements are met: 1) The material must be placed so that there is complete contact between the pipe and the in situ soil; and 2) The unconfined compressive strength of the hardened material is at least 700 kPa (100 lb/in. 2) at 7 days. The most suitable soil to use is a silty sand with the fines content not exceeding about 30 percent. This allows native soils from the trench excavation or from nearby the construction site to be used. Fly ash has been used in place of cement, and bentonite has been added to improve pumping characteristics. The versatility and consistent mixing and placement characteristics of soil-cement slurry have made it a popular choice for contractors.