soil improvement layer (a simple approach) by structural engineer ayyappadhas

7/31/2019 Soil Improvement Layer (A simple approach) By Structural Engineer Ayyappadhas

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SOIL IMROVEMENT LAYER: A SIMPLE APPROACH

An Overview By: N.Ayyappadhas(Structural Engineer)

INTRODUCTION:

Most of the construction is done on soil, but the nature and properties of soil is not

always adequate for the desired construction. When such inadequacy occurs, the

engineer could redesign the structure according to the capacity of the soil - which is

generally not preferred, go for a very deep foundation depreciating the economy of the

project, or improve the properties of the ground before the commencement of

construction.

The most common and workable way to upgrade the ground is Densification. By

densification, not only can we achieve improvement in ground behavior such as

strength and stiffness, but we could also eliminate its vulnerability to volume

compression, even in the long run. In the construction of high raised structures with raft

foundations, one of the ways to achieve densification of the ground is to provide an

improvement layer on the ground before laying the foundation raft of the building.

Fig. 1: An image illustrating the ground improvement executed at site.


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METHODOLOGY:

The provision of the imprmethod of soil improveme

layer and replacing it with

done by laying an artificial

coarse aggregates. The c

cohesive soil, the rubber-ti

compaction.

The detailed procedure be

depth, considering a 1 m

foundation. The excavate

aggregates and the availab

layers of 15 cm or 30 cm d

Fig. 2: P

After each layer is sprea

rubber-filled roller or any

Compaction may be prolon

Site cleaning

Finalizing the levels

Excavating soil upto a

desired depth

Excavation

ovement layer is based on the removnt. This method involves removal of th

structural fill during grading operations.

cushion or a natural cushion formed u

shion layer requires adequate compact

red roller or the vibratory roller is most

ins with the excavation of the weak soil

hick improvement layer additional to th

area should be re-filled with a mix

le soil from the excavation. This re-fill s

pending upon the compaction effectiven

rocedure for laying the improvement laye

d, compaction should be implemented

suitable compaction machine for a co

ged in some cases in accordance with th

40 mm Course

Aggregates

Excavated Soil

Water if required

Material for

Re-fill In laAd

Total

afte

al and replacemente compressible soil

The grading can be

sing 40 mm granite

ion. In case of non-

commonly used for

own to the required

e desired depth the

of 40 mm course

ould be executed in

ess.

r.

using vibratory or

nsiderable duration.

e density of soil and

yers of 15 - 30 cm.

quate compaction

fter each layer

l achieved thickness

r compaction - 1m

Re-fill Process


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the required bearing capacity. If and when required, water can be used for compaction.

The process should continue until the total depth of the layer reaches 1 m. An engineer

at site is mandatorily required to monitor the whole process with caution.

CONCLUSION & RECOMMENDATION:

The introduction of the improvement layer below laying the foundation is gradually

gaining popularity in our country, even though it has been a popular practice in certain

other parts of the world for a long time now. In recent times, Indian engineers being very

open to the reception of innovative ideas and construction techniques, and more widely

accepting this method which is a very efficient alternative compared to providing

uneconomical foundation design or redesigning of the entire structure.

The improvement layer has additional advantages which are listed below:

Increases shear strength

Reduces permeability

Reduces compressibility

Cheap and easily achieved, when compared to other soil improvement methods.

IS 1893(Part1) recommends under section 6.5.3.2, that appropriate methods of

compaction is a possible alternative when the soil deposits consist of submerged loose

sand. Studies indicate that the primary settlement, which is a major concern in the case

of silty soil, can be resisted to a great extent by such densification methods. Hence, the

use of improvement layer is highly recommended, particularly in construction sites of

high raised structures having raft foundation.

soil improvement layer (a simple approach) by structural engineer ayyappadhas

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