45
CHAPTER V
CONCLUSION
5.1
Discussion
One of the major problems associated with the foundation construction phase is
rock excavation. In general, rock excavation is much more expensive than soil
excavation. Excavation of rock by blasting is not only expensive but may not be
accepted if it is likely to induce adverse effect on nearby structures or general
environmental conditions such as water supply, noise, etc. Field investigation for
detecting the presence of rock in project site is necessary because of the following
possible reasons:
1. that the foundation rests directly on rock
2. excavation of the rock is necessary during construction (i.e. the cost for
rock excavation may be many times that for ordinary soil)
3. the rock formation may be subject to weathering effects (e.g.
disintegration, expansion) during construction
4. variations in the rock stratum (e.g. flaws or fractures, variation in
characteristics and formations, elevations)
46
Among the relevant data obtained from various methods discussed in Section
2.3, rock sampling is commonly done via a core drill for a minimum depth of 3.0m. The
depth may vary, however, and greater depths are common if such variation is detected
in the rock formation within the site during the coring operations, or if voids (e.g. coalmine voids, limestone sinkholes) may be present. In such cases the strength and
soundness of the rock strata above the voids may be of paramount importance in the
assessment of the ability of the rock formation to bridge over these voids and support
the superstructure.
It is relatively difficult to determine the spacing and number of borings prior to
the commencement of the drilling work because so much of such planning is tied to the
underlying soil conditions, which are usually unknown at the time of planning. Hence, it
is common practice to proceed with a rather skimpy preliminary investigation, and then
follow up with a more structured plan.
The preliminary borings usually lack of detailed sampling. Instead, drill cuttings
or disturbed samples and water table information usually suffice. The follow-up borings
are planned as complements regarding the type, method, depth, and amount or
frequency of sampling.
For relatively light structure, the preliminary phase may be sufficient if the soil
strata are good and appear uniform throughout the site. Frequently a comparison of the
design data and performance history of an adjoining structure, if one is available, and
then this becomes useful tool for establishing the need for a more detailed investigation.
On the other hand, for heavy and important structures, and for cases where the
stratification information is doubtful or inconclusive, there is little choice but to proceed
47
with the more comprehensive survey. This should be done with due care to extract only
samples and perform only tests as required.
Table 5.1 below is a summary of those site investigation methods that can be
used to detect the presence of hard materials on site.
Table 5.1: Summary of Site Investigation Methods used for Detecting the Presence of
Hard Materials on Project Site
Methods of site
Data related to detection of hard materials on site
investigation
1. Total Station Survey
Establish existing ground profile and topography
2. Mackintosh Probe
Provide variability of in-situ sub-strata materials and
depth of hard materials manually
3. Seismic Refraction
Determine soil stratum boundaries and depth of hard
materials geophysically
4. Wash Boring
Recovered core samples to determine RQD, joint
spacing and weathering grade relating to degree of
excavatability
48
5.2
Conclusion
From the case study, it is calculated that the thickness of overburden varies from
19.5m to 35.0m. The quantity of overburden is 717.65m3 and the volume of hard
materials detected at within the study area is 978.55m3.
Notwithstanding the above-mentioned, it is concluded that the methods adopted
in this case study i.e. total station survey, seismic refraction tests and wash borings are
appropriate to detect the presence of hard materials at depth and as well to determine
the quantity of overburden and volume of rock mass for a project site prior to
commencement of any construction work.
The seismic refraction tests were implemented to detect the type of rock at depth
in referring to seismic refraction velocity data. This could be carried out in comparison
with test results against the refraction velocity shown manually in assuming the types of
hard materials underneath the earth surface.
However, not depending on the convenience of one method adopted, there
bound be weakness existed. Amongst them were seismic refraction test where no
disturbances are permitted at all. This is due to geophone equipments are very sensitive
and will produce wrong readings if affected by any slight movement.
Nevertheless, this method is proven as the best for preliminary investigation due
to its convenience and readily available results obtained immediately after seismic
refraction test. It is thus concluded that the above-mentioned methods adopted fulfill the
followings:
49

From literature review there are several specific site investigation methods that
can be used to detect the presence of hard materials on site.

Based on the case study, there are three (3) appropriate methods that can be used
to detect the presence of hard materials i.e. Boreholes, Seismic Refraction and
Topographic Survey and also supplementary methods like Mackintosh Probe.

Useful data and information on the hard materials in the case study site (e.g.
RQD results, weathering zones, volume and depth) are adopted as guidelines in
recommending the suitable methods of investigation that are appropriate for
acquiring optimum information for preparation of tender document on
earthwork.

The project site at Durian Tunggal, Melaka will now be used as a bench mark
for future references if any research team were to carry out review tests for
detecting the presence of hard materials on site prior to commencement of
construction work.
50
References
Attewell, P.B. (1993), The role of engineering geology in the design of surface and
underground structures, Comprehensive Rock Engineering, Hudson, J.D. (ed.),
Pergamon Press, Oxford Vol. 1 p. 111-154.
Bell F.G. (1983), Engineering Properties of Soils and Rocks, Butterworth & Co. (pub)
Ltd, ISBN 0-408-01457-1, UK, 656p.
Bickel J.O. & Kuesel T.R. (1982), Tunnel Engineering Handbook, Van Nostrand
Reinhold Co. (pub), ISBN 0-442-28127-7, London, 670p.
Caterpillar Performance Handbook (1991), 22nd edition Caterpillar Inc., SEB D0333,
Illinois; USA.
Cernica J.N. (1995), Geotechnical Engineering Soil Mechanics, ISBN 0-471-30884-6,
John Wiley & Sons, Inc., 185p.
Clayton C.R.I., Simons N.E. & Matthews M.C. (1995) Site Investigation, 2nd Edition,
Granada (pub.), 999p.
Hunt, R.E. (1984) Geotechnical Engineering Investigation Manual, McGraw-Hill,
ISBN 0 07 031309 1, New York.
51
ISRM (1985), Suggested Method For Determining Point Load Strength, Working
Group on Revision of the Point Load Method, Int. Journal Rock Mechanics Mining
Science & Geomechanics Abstract, Vol. 22 No.2, pp. 51-60.
ISRM (1981), Rock Characterisation Testing and Monitoring, ISRM Suggested
Methods, Commission on testing methods, International Society of Rock
Mechanics, Brown E.T. (ed.), Pergamon Press, ISBN 0 08 027309 2, Oxford,
211p.
McLean A.C. & Gribble C.D. (1980), Geology for Civil Engineers, George Allen &
Unwin, ISBN 0 04 624002, London, 310p.
Mohd For Mohd Amin & Eddy Tonnizam Mohamad (2003), Technical Report on
Excavatability of Hard Materials, Projek Cadangan Membina dan Menyiapkan
Institut Latihan Perindustrian Mersing,Uni Technologies Sdn Bhd, Johor, UTM
Skudai, Johor.
Mohd For Mohd Amin (1992), Technical Report on Petrographic Study of Rock Sample
from Eng Seng Quarry, Kluang, Johor, UTM Skudai, Johor.
Pettifer, G. S. & Fookes, P.G. (1994), A revision of graphical method for assessing the
excavatability of rock, Quarterly Journal of Engineering Geology, V.27, The
Geological Society, pp 145 – 164.
Witlow Roy, Basic Soil Mechanics, Longman Group Limited (1995) 3rd Edition, ISBN
(1995) 0-582-23631-2, 559p.