Soil Consolidation

During the construction of highway, embankments, bridge approaches, dykes, dams, tanks, buildings, and other structures on soft compressible soil, considerable settlement may occur. This is due to the consolidation of soil under the superimposed load.

The consolidation of soil can be done in three various ways, viz surcharging (or preloading), vertical drains (or band/wick drains) and staged construction. In case a saturated soil experiences a steady pressure due to the weight of overlying soil or pre-loading from an embankment, its volume will decrease with time.

Soil particles, as well as the water in the voids being almost incompressible at the pressure, encountered, any change in volume can only occur if the water between the voids is forced out. This reduces the size of the voids enabling the solid particles to become wedged closer together.

The consolidation is highly recommended to avoid serious and potentially expensive problems due to such settlement. The consolidation is desirable to occur at the outset of the project and in the shortest possible time during the construction period. Construction of a facility on top of a soft soil foundation will normally be delayed until there is an assurance that it will not be damaged by the settlement that occurs during subsequent consolidation.

In order to monitor the progress of consolidation and the stability of the foundation, suitable instrumentation is recommended. Instrumentation is used to monitor the progress of consolidation beneath a single-stage embankment, a surcharged embankment or staged construction so that construction schedules can be determined.

When vertical drains are installed, the instrumentation will normally be used to evaluate whether it is effective in accelerating consolidation. Instrumentation may also be installed to provide a warning of any instability, thereby allowing remedial measures to be implemented before critical situations arise.

Encardio Rite Vibrating Wire Piezometers can be installed well before the start of filling, to define the pre-construction groundwater pressure regime, including any perched or artesian water. Settlement measurements may also be required to establish pre-construction settlement behaviour by using surface settlement markers, borehole extensometer and inclinometers. Instrumentation data allows schedules to be determined for surcharge removal and for placement of stages during staged construction along with an evaluation of the effectiveness of vertical drains.

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