INTRODUCTION
The purpose of deep soil mixing (cement column) is to improve the load carrying capacity and reduce anticipated settlement of the foundation subsoil for construction purpose. i.e. embankment construction. This technique involves the introduction and mechanically mixing of in-situ soft/weak with a cementitious compound (cement). The range of soils applicable spans over soft cohesive deposites, expansive clays, loose granular soils, and pulverized fuel ash. The technology is primarily used to reduce subsidence and increase bearing capacity of the composite soil mass. The installed columns can also act as drain to accelerate the consolidation process, hence reduce construction time for projects.
The purpose of deep soil mixing (cement column) is to improve the load carrying capacity and reduce anticipated settlement of the foundation subsoil for construction purpose. i.e. embankment construction. This technique involves the introduction and mechanically mixing of in-situ soft/weak with a cementitious compound (cement). The range of soils applicable spans over soft cohesive deposites, expansive clays, loose granular soils, and pulverized fuel ash. The technology is primarily used to reduce subsidence and increase bearing capacity of the composite soil mass. The installed columns can also act as drain to accelerate the consolidation process, hence reduce construction time for projects.
Figure 1: Construction of cement column in progress
PREPARATION FOR WORKING PLATFORM (SAND BLANKET)
Generally the ground is very soft and is unable to support any construction equipment. For this reason, the top vegetation and very soft top soil were excavated and replaced with a sand with a minimum thickness of 1.0m so as to form a platform. This platform has the following three functions: i) to provide a stable working platform for the heavy equipment. ii) to assist in transferring the load to the cement column. iii) to allow for the drainage of the pore water which is being drained by the columns.
Generally the ground is very soft and is unable to support any construction equipment. For this reason, the top vegetation and very soft top soil were excavated and replaced with a sand with a minimum thickness of 1.0m so as to form a platform. This platform has the following three functions: i) to provide a stable working platform for the heavy equipment. ii) to assist in transferring the load to the cement column. iii) to allow for the drainage of the pore water which is being drained by the columns.
Granular material for sand blanket shall be clean, hard, durable and inert and naturally occurring material. The material shall have the grading 14 mm - 63 µm.
INSTALLATION SET-UP
A typical DSM set consists of an installation rig and a track- mounted batching plant. The area of treatment is first pegged out based on prepared shop drawings showing locations of all cement columns, each of which has its own ID-designation.
Figure 2: Typical DSM set-up
Figure 3: Cement columns pegged out based on shop drawings
INSTALLATION PROCEDURES
The drilling rod of the LC-machine is placed in the position of the columns with high precision and is probed or directed towards the intended inclination by means of a special indication device. The mixing tool is drilled down to firm ground or the designed depth. Output and mixing of binder agent in the soil are affected by the tool being screwed upwards by the same time as the binder agent is pushed out at the top of the tool. The binder agent has been mixed in the machine's storage tank and is then fed out into the pressure pipe with speed controlled feeders synchronized with the upward movement of the drilling rod and mixing tool. The output agent can be adapted to varying needs both in terms of amount and mixing proportion.
Figure 4: The drilling rod of the LC-machine is placed in the position of the columns
Figure 5: The shaft which as a cutting and mixing blades at the lower end is rotated down to design depth or stiff layer through weak soils and then withdrawn by simultaneous rotation mixing of the binder with the existing soil.
p/s: Credit to Ariffin for this useful article. Thank you very much.
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