Boring Methods of Exploration of Soil

BORING METHODS OF EXPLORATION OF SOIL
The boring methods are used for exploration at greater depths where direct methods fail.
These provide both disturbed as well as undisturbed samples depending upon the method of
boring. In selecting the boring method for a particular job, consideration should be made for
the following:
 The materials to be encountered and the relative efficiency of the various boring
methods in such materials
 The available facility and accuracy with which changes in the soil and ground water
conditions can be determined
 Possible disturbance of the material to be sampled
The different types of boring methods are:

(i) Auger boring.
(ii) Auger and shell boring.
(iii) Wash boring.
(iv) Percussion boring.
(v) Rotary boring.
(I) AUGER BORING

Augers are used in cohesive and other soft soils above water table. They may either be
operated manually or mechanically. Hand augers are used up to a depth up to 6 m.
mechanically operated augers are used for greater depths and they can also be used in
gravelly soils. Augers are of two types: (a) spiral auger and (b) post-hole auger. Samples
recovered from the soil brought up by the augers are badly disturbed and are useful for
identification purposes only. Auger boring is fairly satisfactory bar explorations at shallow
depths and for exploratory borrow pits.
(II) AUGER AND SHELL BORING
Cylindrical augers and shells with cutting edge or teeth at Lower end can be used for making
deep borings. Hand operated rigs are used for depths up to 25 m and mechanised rigs up to 50
m. Augers are suitable for soft to stiff clays, shells for very stiff and hard clays, and shells or
sand pumps for sandy soils. Small boulders, thin soft strata or rock or cemented gravel can be
broken by chisel bits attached to drill rods. The hole usually requires a casing.
(III) WASH BORING
Wash boring is a fast and simple method for advancing holes in all types of soils. Boulders
and rock cannot be penetrated by this method. The method consists of first driving a casing
through which a hollow drilled rod with a sharp chisel or chopping bit at the lower end is
inserted. Water is forced under pressure through the drill rod which is alternatively raised and
dropped, and also rotated. The resulting chopping and jetting action of the bit and water
disintegrates the soil. The cuttings are forced up to the ground surface in the form of soil-
water slurry through the annular space between the drill rod and the casing. The change in
soil stratification could be guessed from the rate of progress and colour of wash water. The
samples recovered from the wash water are almost valueless for interpreting the correct geo-
technical properties of soil.
(IV) PERCUSSION BORING

In this method, soil and rock formations are broken by repeated blows of heavy chisel or bit
suspended by a cable or drill rod. Water is added to the hole during boring, if not already
present and the slurry of pulverised material is bailed out at intervals. The method is suitable
for advancing a hole in all types of soils, boulders and rock. The formations, however, get
disturbed by the impact.
(V) ROTARY BORING
rotary boring or rotary drilling is a very fast method of advancing hole in both rocks and
soils. A . Drill bit, fixed to the lower end of the drill rods, is rotated by a suitable chuck, and
is always kept in firm contact with the bottom of the hole. A drilling mud, usually a water
solution of betonies, with or without other admixtures, is continuously forced down to the
hollow drill rods. The mud returning upwards brings the cuttings to the surface. The method
is also known as mud rotary drilling and the hole usually requires no casing. Rotary core
barrels, provided with commercial diamond-studded bits or a steel bit with shots, are also
used for rotary drilling and simultaneously obtaining the rock cores or samples. The method
is them also known as core boring or core drilling. Water 15 circulated down drill rods during
boring.

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BORING METHODS OF EXPLORATION OF SOIL

The different types of boring methods are:

(I) AUGER BORING

(IV) PERCUSSION BORING

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