Due to commercial land scarcity in Sri Lanka, people have to look into soft grounds such as marshes for building and other constructions.These soft grounds need to be improved for bearing capability. Engineering geologists along with geotechnical engineers play an important role in understanding the subsurface conditions in such soft ground improvement designs. Therefore, the role of the geologists in soft ground improvement industry throughout the world including Sri Lanka is significant.
This article introduces a soft ground improvement method “Deep cement mixing (DCM)” which is suitable for deep foundations where a binder material, typically cement, is injected into the ground for soft ground stabilization and land reclamation. In ground stabilization applications, it is typically used to obtain a better load bearing capability of the existing soil, e.g. in order to bear buildings and other structures. This method consists of soft in-situ soil mixing with cement slurry to produce soil / cement columns with high strength and low compressibility. The column size is 0.5 m. (500 mm) diameter and maximum depth of a pile that can be drilled is 21m. Construction of various structures on compressible, saturated soils like soft clay, of low bearing capacity and excessive settlement conditions are common problems to deal with. The ground improvement technique using DCM is one of the most suitable methods to overcome this problem. The sole purpose of DCM is to improve the shear strength of the soil by in-situ mixing of the soil with cement grout. Application of ground improvement by using DCM method allows excavation works without collapse, construction of embankments for highways, reservoirs, construction of large a water tank and use the soil foundation system in the soft soil environment.
The Machinery/Equipment
40 Ton Weight Single auger, Crawler SOIL MECH machine with 23 m shaft ; Typical Auger Drive of Rotation Speed 14-28 rpm with penetration speed of 0.5-10 mtr. per minute; Fully Electric Grout Pump of Capacity – 950 ltr. at a flow rate of 50-270 ltrs / minute to attain 40-115 bar pressure. The Machine is equipped with complete computerized touch screen cabin for checking the verticality of the pile and accuracy of mixing cement from bottom to top equally.
ADVANTAGES OF THE DCM PILE
1. Cost is very low comparing with the precast pile and in-situ cast pile.
2. This is more suitable for construction of group of piles for improvement of the
ground.
3. In this technique shear strength parameter of the soil is increased.
4. Reduce the permeability of soil.
5. Uniaxial compression Strength can beachieved minimum 5 to maximum 12
MN/m2
6. The verticality of the pile, mixing of cement proportion and pile integrity is uniform.
7. Complete data and details of the pile during and after completion can be obtained from
the data logger.
8. Speed in construction of piles is the most advantage in this machine. Normal speed is
1.0 m /1 minute downwards and 1.0m /2 minute upwards
