Blasting was used successfully in many projects for soil improvement. Buried, time-delayed explosive charges are used to densify granular soils.
The sands and gravels must be essentially cohesionless with a maximum of 15 percent of their particles passing the No 200 sieve size and 3 percent passing 0.005 mm size. The moisture condition of the soil is also important, for surface tension forces in the partially saturated state, limit the effectiveness of the technique. Sometime prewetting the site is required via the construction of a dyke and reservoir system.
The process involves the detonation of explosive charges such as 60% dynamite at a certain depth below the ground surface in saturated soil. The lateral spacing of the charges varies from about 3 to 9 m. Theoretically, an individual charge densifies the surrounding adjacent and soil beneath the blast. It should not lift the soil situated above the blast. Charge delays should be timed carefully to achieve uniform densification from bottom up. Three to five successful detonations are usually necessary to achieve the desired compaction. Compaction (up to a relative density of about 80%) up to a depth of about 18 m over a large area can easily be achieved by using this process. Usually, the explosive charges are placed at a depth of about two-thirds of the thickness of the soil layer desired to be compacted. The uppermost part of the stratum is always loosened, but this can be surface compacted by vibratory rollers.
References
- Das, B. M. (2011). Principles of foundation engineering(7th ed.). Boston, MA: Cengage Learning.
- Bowles, J. E. (1984). Physical and geotechnical properties of soils(2nd ed.). New York: McGraw-Hill.
- Murthy, V.N.S. (1974). Principles of soil mechanics and foundation engineering (5th Ed.). New Delhi: UBSPD.