Types of Field Testing

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CHAPTER III

CASE STUDY

3.1 Introduction

A project site at Durian Tunggal, Melaka is used as a case study mainly to

highlight the importance of anticipating the presence of hard materials on site and the

associated problems if hard materials are detected during construction work. The study

was undertaken alongside the remained hilly terrain.

The original hills have been leveled down to the required reduced level and the

site is now bounded by half completed cut platform. ithin the e!cavation site, the dig"

able and rip"able material of the hills cover was seen to have been stripped off and

removed, leaving e!posed the rock mass.

The project site is located about # km east of Alor $ajah. %t is accessible from

the &antai 'elimbing(Durian Tunggal road and along an earth road over the )orth"

*outh +!pressway. The site location plans and site photographs are attached as per &late.

-rom visual observation, the project site contains many protruded coarse"

grained granite stones. The protruded ground face formed an outcrop of boulders of

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grey color coarse"grained to medium biotite granite. Most of it is located along the hill

slopes. The surrounding earth is made up of reddish brown, sandy silt with some gravel.

ith reference to past e!perience and information derived in the literature study,

the project site is believed to contain granite bedrock at depth.

3.2 Types of data otained fro! fie"d

This case study involved a number of field investigations and measurements as

mentioned below0

. Total *tation survey for e!isting ground profile and topography.

. Mackintosh &robe is used to provide a profile of penetration resistance with

depth to give an assessment of the variability of in-situ materials on site.

1. *eismology instruments equipped with wave detection i.e. geophone, wave

recorder i.e. for displaying seismograph, a sledge hammer and steel plate for

beating. These instruments are meant for seismic refraction tests to detect the

presence of hard materials at depth below the ground surface.

/. A &ercussion 2ig 'oring 3ash 'oring4 consists of a derrick, power"winch

and a set of drilling tools are used to drive through the overburden soil layers

and coring bits are being used during core"drilling to recover the rock cores.

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3.2.1 Tota" Station Instru!ent

Total *tation instrument is being used to carry out the e!isting ground profile

and cross section survey. Total *tation instrument consists of the prism, tripod and level

staff. &late indicates the Total *tation instrument used for this case study.

3.2.2 #ac$intos% Proe

6ne of the most common types of probing is Mackintosh &robe. The

Mackintosh prospecting tool consists of rods which can be threaded together with barrel

connectors and which are normally fitted with a driving point at their base, and a light

hand"operated driving hammer at their top. The tool provides a very economical method

of determining the thickness of soft deposits such as peat. &robing is carried out rapidly,

with simple equipment. %t produces simple results, in terms of blows per unit depth of

penetration, which are generally plotted as blow"count(depth graphs.

3.2.3 Seis!ic Refraction Test E&uip!ent

%n order to detect the presence of hard materials at depth below ground surface,seismic refraction tests are being adopted. &late 1 depicts the seismograph equipments

for seismic wave test. Amongst the equipment used to carry out these tests are as

follows0

. *eismograph set for the recording of seismic wave data.

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. $eophone for detecting the seismic waves.

1. *ledge 8ammer and metal plate for the beating to create shock waves.

/. Measurement tape for measuring distance.

3.2.' (orin) Tests

A &ercussion 2ig 'oring 3ash 'oring4 consists of a derrick, power"winch and

a set of drilling tools are used to drive through the overburden soil layers and coring bits

are being used during core"drilling to recover the rock cores. &late / depicts the pictures

taken for the recovered core samples, photographs taken during coring works and steel

casings used for the case study.

3.3 Sur*eyin) +or$s

The longitudinal profile and cross section for e!isting ground levels were taken

at project site. *urvey work is carried out to determine the limit of case study. 'esides

this, survey work is carried out to determine the datum for the whole area in preparingcontour mapping of area involved. This will make it easier to draw the cross section of

case study area. During surveying work, it is bound to come across obstacles and thus

shifting of alignment could not be avoided.

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The total station equipments are being used to carry out surveying work at

project site to determine the coordinates and reduced levels of each designated tests.

&late 5 shows the surveying work being carried out at site.

%n determining the hori:ontal profile, surveying work using trevass method has

been adopted to produce the bearing and distance of case study area. The reduced levels

are determined by use of trigonometry method. -or this case study, total station

equipment used is T6&;6) type where the data collected are using T6&;6) -;5

Data ;ollector.

3.3.1 Deter!inin) t%e presence of Hard #ateria" and ,*erurden

%n order to determine the volume of sub"surface soil and presence of hard

material underneath, data from the measurement of cross section survey needs to be

analy:ed and plotted first. To obtain a more accurate volume, a few cross section survey

needs to be carried out. The more cross section survey is taken, the more accurate will

be the volume.

The datum and coordinates for the respective bore holes carried out shall form

part of grid survey for more accuracy in determining the calculation of volume and

reduce having to resort to interpolation.

-rom the site investigation carried out i.e. using seismic reflection and wash

boring methods, the thickness of sub"surface soil and presence of hard material at

respective tests could be determined.

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-or calculation in terms of volume for the sub"surface soil and hard material of

whole area, two methods being frequently used are Trape:oidal method and *impson

method. &rior to calculating the volume, the area for each cross section profile must be

obtained first. 8ence, each cross section survey shall be in uniform distance apart. This

is essential in order to apply the Trape:oidal or *impson formulas to obtain the volume

directly. The calculation of respective cross section survey will determine the thickness

of sub"surface soil.

*impson

?olume, V = d/3[A1 + A5 + 2 x A3 + 4 x (A2 + A4)] " *impson


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Fi. 1. Typical Trape:ium and *impson


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pulled out of the soil using a lifting(driving tool. 'ecause of the light hammer weight

the Mackintosh probe is limited in the depths and materials it can penetrate.

3.- Seis!ic Refraction Tests

*eismic 2efraction tests are possibly the most important and commonly used

supplementary methods in site investigation. The purpose is to detect the presence of

hard materials at depth below the ground surface.

3.-.1 Preparation of Seis!ic Refraction Tests

Amongst the equipments used for seismic refraction tests are0

. *eismograph for measuring seismic waves

. $eophone for detecting seismic waves

1. *ledge 8ammer and metal plate for knocking and producing source of energy.

orks to affi! the geophone for the transmission of seismic waves were carried

out upon completion of surveying works. This is to ensure convenience in installing the

equipment in straight alignment and also the results obtained could be plotted in straight

line as well. During these periods when tests are being carrying out, the equipments are

required to be fi!ed at the designated locations determined earlier by the surveying

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works. -or this purpose, the geophone is fi!ed at the designated locations at a distance

of 5.m c(c along the alignment of case study area.

A total of / geophone equipments were used and placed alongside the

alignments mentioned above. All the geophones were connected to the seismograph

with wiring whereby the seismograph will read, measure and plot out the waves

detected by the geophones.

The geophones used in this case study are fi!ed vertically upright above firm

ground levels. 8owever, at areas where the ground conditions are weak and when

strong wind is encountered, geophone equipments were planted a few center meters

below ground surface. This is to avoid unnecessary disturbance during the event of

testing being carrying out. The geophone equipment is also forbidden to be placed on

the surface containing roots. %n surrounding the geophone equipments, ensure it is kept

clean from grass, soil and sand for reasons to avoid disturbance against the wave signals

received by the geophones as mentioned above. During the course of carrying out tests,

the seismograph equipments are to be placed as far as possible apart and away from the

geophone locations for effective results.

%n order to produce seismic waves, a sledge hammer is used to generate energy.

The sledge hammer is to knock onto a piece of metal plate on the ground surface to

generate energy or wave noise. The wave will move through layers of soil beneath the

earth surface and subsequently refracted back to earth surface whereby it is detected viageophones. The sledge hammer is connected to seismograph with wiring. The

ma!imum distance apart between sledge hammer and last geophone equipment 3nearest

to the knocking metal plate4 is between 1 to 5 times more than the depth of hard

materials beneath the location of knocking.

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A metal plate for knocking to produce energy or wave sound, measuring in si:e

of #mm ! #mm and thickness of 5mm is suitable. A smaller plate si:e will not be

effective as it will sink into earth surface upon the impact of knocking to dissipate

energy distribution. Moreover, smaller late is difficult to carry out knocking.

3.-.2 I!p"e!entation of Seis!ic Refraction Tests

=pon fi!ing the geophone and seismograph, the metal plate for knocking is

placed on firm earth surface appro!imately 5.m away from the nearest geophone no..

eak ground surface and wild grass surrounding the plate for knocking must be

removed earlier to produce ma!imum energy impact when knocking by the sledge

hammer carried out.

*witch on the seismograph equipment and reset the readings to :ero prior to

carrying out the test. %t is utmost important to ensure no disturbance to the geophone

and no one else walking past or cause any movement adjacent to testing location e!cept

the knocking sound produced by the sledge hammer only. This is due to geophone

equipment is very sensitive and it capture any reading of any kind be it produced by

human movement or whatever it is. The readings produced will be affected by the wind,

passing traffic and miscellaneous.

Thereafter, instruct the operator to carry out knocking with the sledge hammer

on the metal plate. During the process of carrying out knocking with the sledge

hammer, ensure that the operator knocks the metal plate accurately and also to make

sure the sledge hammer does not knock the metal plate more than once which is as

required.

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%n order to obtain a good result, the more test taken the better result will be.

8owever, time and cost is another contributing factor to limit the number of tests taken.

Therefore, a total number of / seismic refraction tests were conducted.

3. (orin)

The equipment for &ercussion 2ig 'oring 3ash 'oring4 consists of a derrick,

power"winch and a set of drilling tools. A percussion method is used, whereby the tool

assembly is raised by the winch to about m above the bottom of the hole and then

allowed to fall under its own weight, thus driving the cutting tool into the soil. hen the

tool becomes full of soil, it is raised to the surface, where disturbed samples may be

taken from its contents. The most usual borehole diameter is 5mm, but others up to

1mm can be drilled> the ma!imum depth of e!ploration, although dependent on soil

type to some e!tent, is around 5"7 m.

%n compact cohesion"less soils, or where boulders or cobbles are encountered,

the !"is#$is used to break up hard materials> fragments and slurry are then removed

using the bailer. %n wet conditions and in loose soils, and for very deep holes, a !asin

must be installed near the surface. This usually consists of steel tubes, screwed together

in as many lengths as appropriate, and jacked or knocked into the drilled hole as drilling

proceeds. They can be hauled out after completion of drilling or left in place if furtherobservations are required.

%n stiff soils and rocks power"operated !%-d&i$$s are used, consisting of small"

diameter hollow tube, fitted at the lower end with a !%&in 'it. The core barrel is rotated

at speeds ranging between 7 and rpm, a controlled pressure applied and water

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circulated through the bit. The fragments removed in the annular cut are brought to the

surface with the circulating water as the core fills the barrel. A drilling run of "1 m is

usually made before raising the barrel and removing the core. The more usual standard

si:es of core barrel used in site investigation range between 1 and mm 3hole

diameter4, although larger"diameter equipment is available for special uses.

3..1 Reco*ered Core Sa!p"es

The presence of discontinuities reduces the overall strength of a rock mass and

their spacing and orientation govern the degree of such reduction. 8ence, the spacing

and orientation of the discontinuities are of paramount importance as far as the stability

of structures in jointed rock masses is concerned i.e.

BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB

Description *pacing of discontinuities 2ock mass grading

BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB

?ery wide 6ver 1 m *olid

ide to 1 m Massive

Moderately close .1 to m 'locky(seamy

;lose 5 to 1 mm -ractured

?ery close =nder 5 mm ;rushedBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB

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3..2 Sa!p"es ,ser*ations

a4 -resher core samples with higher 2CD values could be recovered at

depth, especially in :one where less fracture occurs.

b4 -ractures are caused partly due to the wobbling drilling rods and core

barrel alignment and in most cases the enormous pressure concentrated

on the drilling surfaces.

c4 Most of the fractured surfaces observed showed prominent secondary

infilling of joint, failures or minor faulted :ones.

d4 The granite is homogeneous throughout the depth of boreholes.

e4 A deeper coring using a higher speed and bigger capacity drill plant

could penetrate and recover better 2CD.

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Types of Field Testing