ECONOMIC DESIGN FOR BUILDING FOUNDATION IN WEAK SOIL
Lalit Kumar R.
Experienced Site QAQC Manager proficient in regulatory compliance and technical documentation. Certified QMS ISO 9001:2015 Lead Auditor (CQI and IRCA).
DID YOU KNOW RI?
Rigid inclusion is a ground improvement method using high deformation modulus columns constructed through compressible soils to reduce settlement and increase bearing capacity. Ground improvement efficiency depends on the stiffness relationship between the soil and the columns
TECHNICAL ASPECT
?This technique consists in installing rigid vertical inclusions (generally concrete), which mobilize the skin friction and tip resistance of the soil. In addition, a Load Transfer Platform (LTP) or load distribution layer is designed and placed on top of the CSC(controlled stiffness column is a method of vibration free technique for soil reinforcement) grid to ensure transferring the surface loads through arching effects in the columns. As a result, settlements are significantly reduced and the soil bearing capacity is increased.
When applied for slab as it is the case for this project, the rigid inclusions are installed with a uniform grid and are designed to act as a group and with a LTP. Load is transferred to the head of rigid inclusions by arching effect through the transfer layer. RI efficiency is increased as additional load is transferred from weak soil to upper part of the inclusions by mobilization of negative skin friction. In the lower part of the inclusions, load is then transferred back to competent soil by mobilization of positive skin friction and tip resistance.?
The transition plane between negative skin friction and positive skin friction is called the neutral plane or plane of equal settlement (between the soil and the inclusion). This is where the internal stress of rigid inclusion reaches its maximum.
STEPS INVOLVED
MATERIAL FOR RIGID INCLUSION
The material used for Rigid inclusions ready-mix concrete with grade C25 after 28 days. The concrete will be supplied from a local Approved ready-mix plant. Additive such as a plasticizer may be used to speed up or slow down the setting process as per the site situation which best suits the project. Mix consistency shall also be adapted to ensure pumpability with our equipment.
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POST TESTING
I.??????????????????? Plate Load Test (PLT)
Single RI column will be tested by means of Plate Load Test using 0.76m dia plate with testing load up to 1.5 times the allowable bearing pressure. The load will be applied on top of RI head after installation of the LTP. Three Plate Load Tests on randomly selected RI columns are proposed.
II.??????????????????? Zone Load Test (ZLT)
The complete system as it is designed and on which the raft foundation will be casted is to be tested by means of a Zone Load Test (2.50mx2.50m) steel plate, with testing load up to 1.5 times the allowable bearing pressure, and maximum holding time not exceeding 12 hrs. One Zone Load Test performed on top of LTP and located above 4 columns at a randomly selected location is proposed.
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