Innovations in the Improvements of Soft Bangkok Clay using Prefabricated Vertical Drains and Deep Cement Mixing (DCM)

Abstract

Soft ground improvement techniques such as Prefabricated
Vertical Drains (PVD) and Deep Cement Mixing (DCM) are the
most practical and popular methods to increase soil strength, soil
stiffness and reduce soil compressibility of soft clays. PVDs are
artificial drainage paths to vertically drain the pore water
squeezed out from the soft clay due hydraulic gradient generated
by preloading. DCMs are piles formed by mixing cement with soft
clays. This paper focuses on innovations and comparative
performances of PVDs using surcharge, vacuum and heat
preloading as well as the cement-admixed clay of DCMs and
Stiffened DCM (SDCM) methods for the improvement of soft
Bangkok clays. The Vacuum-PVD can increase the horizontal
coefficient of consolidation, Ch, resulting in faster rate of
settlement at the same magnitudes of settlement compared to
Conventional PVD. Moreover, the new methods of Thermal PVD
and Thermal Vacuum PVD can increase further the coefficient of
horizontal consolidation, Ch, with the associated reduction of
kh/ks values by reducing the drainage retardation effects in the
smear zone around the PVD which resulted in faster rates of
consolidation and higher magnitudes of settlements. A new kind
of reinforcing method, the SDCM pile consists of DCM pile
reinforced with precast reinforced concrete (RC) core pile. The
simulation results using PLAXIS 3D indicated that the surface
settlements decreased with increasing lengths of the RC core
piles. In addition, the lateral movements of the embankment
decreased by increasing the lengths (longer than 4 m) and, the
sectional areas of the RC core pile