Sub surface exploration part 2

101
Saw-tooth bits,
• the cutting edge comprises a series of teeth.
• The teeth are faced and tipped with a hard metal
alloy such as tungsten carbide to provide wear
resistance and thereby increase the life of the bit.
• These bits are less expensive but normally used to
core overburden soil and very soft rocks only.
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102
Common types of drilling bits

103

104
Open-holing
Bits for rotary open holing
Fixed rock bits

105
Open-holing
The formation of a hole in the subsoil
without taking intact samples is known
as ‘open-holing’.
carried out in a number of ways, but in
site investigation a commonly used tool
is the ‘tricone rock roller bit’ (or roller
core bit) (Fig.).
In site investigation such methods are
usually used to drill through soft
deposits, which have been previously
sampled by light percussion or auger
rigs.

106
Sampling during open-holing is usually limited
to collecting the material abraded away at the
bottom of the borehole, termed ‘cuttings’, as
it emerges mixed with ‘flush fluid’ at the top
of the hole

107
Coring
Double-tube swivel type core barrel
with face discharge bit
Double tube core barrel is that the inner tube is
mounted on anti-friction bearings and remains
virtually stationary while the outer barrel and
bit rotate. There is less tendency to grind core
with swivel type barrels.
The swivel type - double tube core barrel is the
generally accepted tool for obtaining core in
fractured, broken formations. It gives high
recovery when used properly.

108
Schematic representation of double – tube
swivel type core barrels with various bit types

109
(a) Core barrels to which (b) coring bits
are attached to obtained rock cores

110
Coring
Rotary coring in ground investigations is used to
obtain intact samples of the rock being drilled, at the
same time as advancing the borehole
In the rotary drilling method a cutter bit or a core
barrel with a coring bit attached to the end of a
string of drill rods is rotated by a power rig.
The rotation of the cutting bit shears or chips the
material penetrated and the material is washed out
of the hole by a stream of water just as in the case
of a wash boring

111

112
ROTARY DRILLING
Rotary drilling uses a rotary action combined
with downward force to grind away the
material in which a hole is being made
may be applied to soil or rock, but are
generally easier to use in strong intact rock
than in the weak weathered rocks and soil

113
Rotary drilling consists of a number of elements
(Fig.): ‘rotary rig’ , at the ground surface, which
delivers torque and thrust;
a flush pump, which pumps flush fluid down the hole,
in order to cool the mechanical parts and lift the
‘cuttings’ of rock to the ground surface as drilling
proceeds;
a ‘string’ of hollow drill rods, which transmit the
torque and thrust from the rig, and the flush fluid
from the flush pump to the bottom of the hole; and
a core barrel, which grinds away the rock, and in
addition may be designed to take a sample.

114
Bit at the end of drill rod
rotated and advanced
Soil/rock cuttings removed by
circulating drilling fluid
Common drilling fluid;
bentonite in water with slurry
density 68-72pcf
Air may be used as drilling
fluid
Rotary Drilling

115

116

117
Figure : Split Barrel Sampler: (a) Open sampler with soil sample and cutting
shoe; (b) Sample jar, split-spoon, Shelby tube, and storage box for transport
of jar samples.

118
Split spoon sampler

119
A ball check valve incorporated
in the sampler head facilitates
the recovery of cohesion less
materials.
This valve seats when the
sampler is being withdrawn
from the borehole, thereby
preventing water pressure on
the top of the sample from
pushing it out.
If the sample tends to slide out
because of its weight, vacuum
will develop at the top of the
sample to retain it.

120
Split spoon sampler
Driven in the soil by hammering action
When the Area Ratio is 10% or less, the sample is generally
considered to be undisturbed
Samples are generally taken at intervals of about 1.5 m
Spring core catcher is added when samples from sand are
required

121
Split- Barrel Sampler

122
Split barrel sampler
inserts
Standard Split Barrel Sampler

123
Sample catchers.

124
Scraper Bucket
When soil deposit is mixed with sand and pebbles
Pebbles prevent spring core catcher from closing
Scraper bucket driven down in the soil and rotated
Scrapping from side fall into bucket
Highly disturbed sample

125
Thin Wall Tube (Shelby Tubes)
The system is used to
sample soils that are
particularly sensitive to
sampling disturbance as it
has a very low wall
thickness-to-sample area
ratio.
This sampler is usually
only suitable for cohesive
soils up to a firm-to-stiff
consistency and free from
large particles.
It is not suitable for
granular non-cohesive soils.

126

127
Piston
Sampling
For obtaining undisturbed samples
from soft soils

128

129
Piston Sampling

130

131
Common Rotary Sampling methods
Sample by rotary core drilling by
rotating drill bits and cylindrical
core barrel i.e single, double, triplesingle, double, triplesingle, double, triplesingle, double, triple
core barrel.core barrel.core barrel.core barrel.
Drilling fluid pump down
through drill rod to lubricate drill
bits and flushes cuttings/drill
debris up the borehole.
Drill hole normally supported
by casing to avoid collapse.
Flushing media : water, air, foamwater, air, foamwater, air, foamwater, air, foam
or drilling mudor drilling mudor drilling mudor drilling mud

132
Rotary Core Samples
Single Tube Core Barrel
Rotary coring by portable
electric drill,
Hand portable single
tube
core barrel, without
protection between sample &
flushing medium useful for
checking mass concrete /
masonry retaining wall
thickness, geometry and
filling materials

133
Rotary Core Samples
Double-tube core barrel
T2-101 (Ø) = 101mm
Core = 84mm,
T2 76/ TNW (Ø) = 76mm
T2 / TNW Core = 62 /61

134
Double Tube Core barrel

135
Triple-tube core-barrel

136

137

138
Block Sample Sampling Method
Trial PitsTrial PitsTrial PitsTrial Pits
and Trenchesand Trenchesand Trenchesand Trenches
Block sample collectionBlock sample collectionBlock sample collectionBlock sample collection

139
Field Samples Storage / Delivery

140
Handling samples
Proper Storage
Ensure sample test data
representative
Avoid storing samples in heated up
area
Preserve original moisture contents
Store up in sealed container
Use wax as sealer

141

142

143

144

145

146

147
Block Sample
Sample Packing
Sample collected
by hand dug from
Trial Pit or Trial
Trench，
Record the
position, depth
and orientation of
the sample
collected。

148
Field Samples Storage / Delivery
Field samples kept
in core boxes for
delivery and storage.
Disturbed jar
samples
Rock cores - H
sizes

149

150

Sub surface exploration part 2

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Sub surface exploration part 2