Soil-cement slurry used in buried pipe installations has become an increasing popular choice for contractors. Flexible pipe, including PVC and RPM, as well as rigid pipe are being installed using this technique. The ingredients of the soil-cement can vary, but typically is a combination of soil, portland cement, and water. In most cases, the pipe trench is trimmed to a semicircular shape 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. Accordingly, 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 with a 25 cm 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. 2. The unconfined compressive strength of the hardened material is at least 700 kN/m2 (100 1b/in2) 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. Cementitious fly ash has been used in place of cement and bentonite has been added to improve pumping characteristics.