Geotechnical Report - Presscane (Factory Site)

THE POLYTECHNIC
CIVIL ENGINEERING DEPARTMENT
GEOTECHNICAL TECHNICAL REPORT FOR THE PROPOSED
NEW FACTORY SITE AT PRESCANE LTD, CHIKWAWA
MALAWI
PREPARED BY: ISHMAEL NG’OMA
Email: ishmaelngoma@poly.ac.mw
Cell: 0888528690
August 2015
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1.0
INTRODUCTION
1.1
General
PRESSCANE LIMITED contacted The Malawi Polytechnic, Civil Engineering
Department to conduct geotechnical investigation surveys on soils at the
Proposed New Factory Site close to the weighbridge at Presscane Ethanol
Distillery Complex in Chikwawa District of Malawi.
Site reconnaissance, in situ (on site) testing and soil sampling were carried out
on 09th August 2015. Laboratory testing proceeded immediately at the
Malawi Polytechnic, Civil Engineering Laboratory in Blantyre.
1.2
Project Description
It is our understanding that the project involves the construction of new
factory buildings at Presscane Ethanol Distillery Complex in Chikwawa District.
It is also our understanding that the structures to be built will be ground level
structures with no storeys and that the structures will be mainly load bearing
walls resting on standard mass concrete strip footings.
1.3
Objectives of the Soil Investigation Survey
The purpose of the geotechnical exploration exercise was:
1. To determine the subsoil conditions under the proposed new site for the
construction of factory buildings.
2. To determine the engineering properties of the soil.
3. To comment on the type of foundation to be adopted.
4. To assess the bearing capacity of the soil in line with standard strip
footings of the width 690mm.
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2.0 SOIL SAMPLING AND TESTING
Three trial pits for soil sampling and measurement of insitu strength of soils by
DCP (Dynamic Cone Penetrometer) were dug around the proposed site. The
trial pits were dug in order to reveal the soil profile and get samples for
laboratory testing. Location for the three trial pits were agreed with Richard
Dikamdima of PressCane. The trial pits were approximately 2.0m deep and
two (2) samples were collected from each trial pit at 1.0m and 2.0m depths.
Samples collected were taken to Polytechnic Laboratory and tested for
Atterberg Limits (Plasticity Index), Particle Size Distribution (Wet Sieve Analysis)
and Linear Shrinkage.
It was NOT possible to collect undisturbed samples for triaxial testing because
the soils were loose to medium dense making it impossible to penetrate the
soil sampling tubes for undisturbed sample extraction. Therefore, due to the
nature of the soils, triaxial tests were NOT done.
3.0 OBSERVATIONS AND DISCUSSIONS
Observations on all the pits namely; Pit #1, Pit #2 & Pit #3 indicated that the
soils were basically loose sand near the surface and medium dense silty sand
soils of non plastic beyond 0.5m which was relatively difficult to excavate.
Basically the surface of the ground to about 0.3m deep was very weak made
up mainly of loose sand. Below 1.0m it was difficult to do the DCP penetration
tests because the soils were made of medium dense silty sand.
For Trial Pit #1 and Trial Pit #2, DCP test results indicated a Penetration Index
of less than 8mm/blow (approximate CBR of 22%) and computing to
approximate Safe Bearing Pressure of 210kPa which means the ground is
strong and very stable.
For Trial Pit #3, DCP test results indicated a Penetration Index of 13mm/blow
(approximate CBR of 13%) and computing to approximate Safe Bearing
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Pressure of 165kPa which means the ground is relatively weaker compared to
the other pits i.e. Pit#1 & Pit #2 (Sketch Map attached to the summary of
results sheet).
The Natural Moisture Content (insitu) ranges from 2.5% - 5.9% with the
Atterberg Limits (Plasticity Index) showing that the soils are Non Plastic (NP).
Where necessary, materials excavated from all the three trial pits can be
used as fill provided that they are compacted to their Maximum Dry Density
(MDD) at their Optimum Moisture Content (OMC).
4.0 TRIAL PITS
Loose sand soils were observed to a depth of about 0.3m from all the three
trial pits as shown below;
Trial Pit #1; Loose Sand Soils to less than 0.3m deep
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Trial Pit #2; Loose Sand Soils to less than 0.3m deep
Trial Pit #1; Medium Dense Silty Sand Soils of Non Plastic beyond 1.0m deep
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Trial Pit #3; Medium Dense Silty Sand Soils of Non Plastic beyond 1.0m deep
Trial Pit #1; Difficult to excavate layer after 1.0m deep
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Trial Pit #2 with Soil Profile similar to Trial Pit #1 as shown above
Trial Pit #3 with Soil Profile similar to Trial Pit #s1 & 2 as shown above
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Trial Pit #3; DCP Penetration Test in progress
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5.0 RECOMMENDATIONS
It can be noted that the proposed site is dominated loose to medium dense
silty soils which overlay the hard to cultivate material beyond 1.0m deep.
Where necessary, materials excavated from all the three trial pits can be
used as fill provided that they are compacted to their Maximum Dry Density
(MDD) at their Optimum Moisture Content (OMC).
The recommendation is based on the field and laboratory test results. From
field observations and findings, the soils at the proposed site are adequate to
support normal strip footing foundation.
The design of any foundation base, considers the permissible Bearing Pressure
on the ground that corresponds to a service stress and its maximum value
that can be supported without excessive deformation taking place.
Therefore, the type and shape of the loading determines the shape of the
foundation.
The maximum expected load from the factory buildings is NOT known.
However the foundation can be erected at the ranges of between 1.5m 2.0m deep. The approximate Bearing Pressure of the soil on a proposed
factory site ranges between 165kPa - 210kPa.
6.0 REFERENCES
Barnes G, E (2000). Soil Mechanics: Principles and Practice. 2nd Ed.
MacmillianPressLtd, London
BS 1377, 1990 Methods of Testing for Soils for Civil Engineering Purposes
Clayton C.R.I. (1999). The standard Penetration test (SPT); Method and Use.
CIRIAreport no. Report/CP/7 Great Britain
Craig R.F (2004). Soil Mechanics.7th Ed. Spon Press. London
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7.0 APPENDICES (Attachments through email & hard copies)
1. Particle Size Distribution test results - 3 pits (6 copies)
2. DCP test results - 3 pits (3 copies)
3. Linear Shrinkage test results (1 copy)
4. Moisture Content test result (1 copy)
5. Sketch Map (1 copy)
6. Table showing summary of the results & the Sketch Map (1 copy)
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