Download - Soil Investigation
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Soil classification
• From an engineering viewpoint,
the ground beneath a site can
conveniently be divided into the
categories, which are based upon
generalizations of its expected
behaviour in construction works.
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SOIL STRATUM
• 2 layers
– Top soil
– Ground soil
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Top soil
• 150-300mm from soil surface
• Contains vegetation, rubbish & rotten
materials
• Not suitable in supporting
foundation/structure
• Usually the top soil will be cart away
before construction
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GROUND SOIL
• Situated between top soil & rock layer
• The thickness of the soil varies
depending on the rock formation
• This layer are compacted naturally
which occasionally can support light
construction
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GEOTECHNICAL SYSTEM
• Soil used to be rock, which was tuned
into soil by weathering, chemical and
mechanical forces.
• Nature recycles the soil to rock, that
this takes millions of years.
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NATURAL RECYCLING OF
SOIL TO ROCK
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Metamorphic rock
Sedimentary rock
Igneous rock
Residual soil
Sediments
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SOIL…
• Three main size groups :
Sand (0.05 to 2.00 mm)
Silt (0.002 to 0.05 mm)
Clay ( less than 0.002 mm
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HORIZONS
• Surface horizon is usually referred to
as the O layer.
• It consists of loose organic matter such
as fallen leaves and other biomass.
• Below is the A horizon, containing a
mixture organic mineral materials and
organics.
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HORIZONS
• Next is E horizons, layer from which clays, iron and aluminum oxides have been lost by leaching process
• Below horizons E is B, which most of the iron, clays, and other leached materials have accumulated.
• After that is C horizons consisting of partially weather bedrock
• And last is R horizons of hard bedrock
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SOIL CHARACTERISTICS
• Color,
• Texture,
• Aggregation,
• Porosity,
• Ion content and
• pH all important to soil characteristics
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COLOR
• Soils come in a wide range of colors.
• Shades of brown, red, orange, yellow,
gray and even blue or green.
• A dark color usually indicates the
presence of organic matter.
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TEXTURE
• A soil texture depends on its content of
the three main mineral components of
the soil, sand ,silt and clay.
• Very fine textured soils may be poorly
drained.
• Medium texture and a relatively even
proportion of all particle sizes are most
versatile
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AGGREGATION
• Individual soil particles tend to be
bound together into lager units referred
to as aggregates or soil pads.
• Aggregation occurs as a result of
complex chemical forces acting an
small soil components in soil act as
glue binding particles together.
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POROSITY
• Part of the soil that is not solid is made
up pores of various sizes and shapes
• Porosity greatly affects water
movement and gas exchange.
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ION CONTENT
• Particularly the clay, hold groupings of
atoms known as ions.
• These ions carry a negative charge.
• Like magnets, these negative ions
(anions) attract positive ions (cations)
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pH
• Another important chemical measured
is soil pH.
• Refers to the soil acidity or alkalinity.
• A greater concentration of hydrogen
results in a lower pH, meaning greater
acidity
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Categories of soil
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Soil and rock description
• Soil and rock description is to a certain
degree subjective. In order to minimise the
subjective element a systematic
examination should be carried out using a
standard terminology, whether the material
be in a natural exposure, trial pit face or
samples recovered from a borehole.
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Soil and rock description
• The use of a standardised scheme of description ensures that:
• (i) all factors are considered and examined in logical sequence
• (ii) no essential information is omitted
• (iii) no matter who describes the sample, the same basic description is given using all terms in an
• identical way
• (iv) the description conveys an accurate mental image to the readers
• (v) any potential user can quickly extract the relevant information.
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Soil description
• Samples must be described in a
routine way, with each element of the
description
• having a fixed position within the
overall description:
• a) consistency or relative density;
• b) fabric or fissuring;
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Soil description
• c) colour;
• d) subsidiary constituents;
• e) angularity or grading of principal soil type;
• f) PRINCIPAL SOIL TYPE (in capitals);
• g) more detailed comments on constituents
or fabric;
• h) (geological origin, if known) (in brackets);
and
• i) soil classification symbols (optional).
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Soil description
• Descriptions should be simple, since very detailed comments on all aspects of a soil lead to confusion.
• Some examples are given below:
• Very stiff fissured dark grey CLAY (London clay)
• (a) (b) (c) (f) (h)
• Loose brown very sandy sub-angular coarse GRAVEL with pockets of soft grey clay
• (a) (c) (d) (e) (f) (g)
• Firm laminated brown SILT and CLAY
• (a) (b) (c) (f) (f)
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Soil types
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Soil type
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SOIL CHARACTERISTIC IN RELATION
TO CHOICE OF FOUNDATIONS
• Soil have different attribute when load
implied on them. The characteristic
are:
– Compressibility
– Permeability
– Plasticity
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• Foundation-
• the interface of a building structure with the ground
• Shallow Foundation- a type of foundation that is used when the earth directly beneath a structure has sufficient bearing capacity to sustain the loads from the structure
• Deep Foundation- a type of foundation that is used when the soil near the ground surface is weak
• The bearing capacity- is the capacity of soil to support the loads applied to the ground.
• The bearing capacity of soil is the maximum average contact pressure between the foundation and the soil which should not produce shear failure in the soil.
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CHOICES OF FOUNDATION
Solid chalk, sands and gravels or sand and
gravels with only small proportions of clay,
dense silty sands
Shallow strip or pad footings as appropriate
to the load bearing members of the building
Uniform, firm and stiff clays
-Where vegetation is insignificant
-Where trees and shrubs are growing or to be
planted close to the site
-Where trees are felled to clear the site and
construction is due to start soon afterward
-Bored piles and ground beams, or strip
foundations at least 1m deep
-Bored piles and ground beams
-Reinforced bored piles of sufficient length
with the top 3m sleeved from the surrounding
ground and with suspended floor
Soft clays, soft silty clays Strip footing up to 1m wide if bearing capacity
is sufficient, or raft
Peat Bored piles with temporary steel lining or
precast or insitu piles driven to firm strata
below
Mining and other subsidence area Thin reinforced rafts for individuals houses
with load bearing walls and for flexible
building
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CN Tower
KLCC Tower
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SOIL INVESTIGATIONS
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SPECIFICALLY RELATED TO
THE SUBSOIL BENEATH THE
SITE UNDER INVESTIGATION
AND COULD BE PART OF OR
SEPARATE FROM THE SITE
INVESTIGATION
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• A well designed soil
investigation can often lead to
project cost savings in the long
term by allowing contractors to
foresee potential problems.
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PURPOSE
1. Determine the suitability of the site for
the proposed project.
2. Determine an adequate and economic
foundation design.
3. Determine the difficulties which may
arise during the construction process
and period.
4. Determine the occurrence and/or cause
of all changes in subsoil conditions.
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SOIL SAMPLES
Disturbed Soil Samples
• Soil samples obtained from boreholes
and trial pits. The method of extraction
disturbs the natural structure for visual
grading, establishing the moisture
content and some lab tests. Disturbed
soil samples should be stored in
labelled air tight jars.
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SOIL SAMPLES
Undisturbed Soil Samples
• Soil samples obtained using coring tools which preserve the natural structure and properties of the subsoil. The extracted undisturbed soil samples are labelled and laid in wooden boxes for dispatch to a lab for test. This method of obtaining soil samples is suitable for rock and clay subsoils but difficulties can be experienced in trying to obtain undisturbed soil samples in other types of subsoil.
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DEPTH OF SOIL INVESTIGATION
• Before determining the actual
method of obtaining the required
subsoil samples, the depth to
which the soil investigation should
be carried out must be
established.
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DEPTH OF SOIL INVESTIGATION
• Factors that should be considered:-
1. Proposed foundation type;
2. Pressure bulb of proposed
foundation;
3. Relationship of proposed
foundation to other foundations.
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SOIL INVESTIGATION METHODS
• Method chosen will depend on several
factors:
1. Size of contract;
2. Type of proposed foundation;
3. Type of sample required;
4. Type of subsoils which may be
encountered.
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SOIL INVESTIGATION METHODS
• As a general guide the most suitable methods in terms of investigation depth are:
1. Foundations up to 3.000d – trial pits;
2. Foundations up to 30.000d – borings;
3. Foundations over 30.000d – deep boring and in-situ examination from tunnels and/or deep pits.
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TYPES OF INVESTIGATION
• Generally the following soil investigation
techniques are employed for the majority of
projects:
• Trial Pitting
• Window sampling and Dynamic Probe
Testing
• Cable Percussive Boreholes
• Rotary Drilled Boreholes
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• Results of site investigations
can be presented as either
factual or interpretive reports
with recommendations relating
to both geotechnical and
environmental considerations
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TRIAL PITTING
• Trial pitting can be carried out by a
variety of methods from hand dug pits
to machine excavated trenches.
• Trial pitting is generally carried out to a
maximum depth of 4.5m with standard
excavation plant and, depending on
soil conditions, is generally suitable for
most low rise developments.
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TRIAL PITTING
• All trial pit investigations are
supervised by experienced engineers
with a thorough understanding of
geology and soil mechanics.
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• Shallow investigation by the
excavation of trial pits ideally suited to
smaller scale projects, especially
housing; also used for soak away
testing and extensively on
contaminated sites where direct
observation of the ground conditions
in-situ is often invaluable.
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WINDOW SAMPLING
• Window sampling is carried out by
either tracked percussive samplers or
hand held pneumatic samplers.
• Samples are retrieved in seamless
plastic tubes for logging by a suitably
qualified engineer. Window sampling is
particularly suited to restricted access
sites, contamination investigations,
and where disturbance must be kept to
a minimum.
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WINDOW SAMPLING
• The track mounted equipment is also
capable of carrying out dynamic
penetrometer testing.
• This is a continuous soil test procedure
which enables the relative density or
strength of the ground to be assessed
to depths of 10m or more.
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CABLE PERCUSSIVE
BOREHOLES
• Suitable for most projects, cable
percussive boreholes are a common
method of site investigation.
• Using a land rover towed rig or a
specialist cut down rig suited to
restricted access locations most sites
can be investigated
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• The preferred method for deeper
investigation in soft or marginal
ground, where sufficient information
cannot be obtained from trial pits.
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CABLE PERCUSSIVE
BOREHOLES
• In-situ testing techniques including
Standard Penetration Testing,
Permeability Testing, Borehole Vane
Testing and Packer Testing can all be
carried out in the boreholes in order to
provide information for geotechnical
design
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CABLE PERCUSSIVE
BOREHOLES
• Disturbed and undisturbed samples
are retrieved from the boreholes for
inspection and logging by engineers
and subsequent testing in a
laboratories.
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A standard cable percussion
drilling rig
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Operation of cable percussion rig for
working in areas of restricted access or
with restricted headroom
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ROTARY DRILLED
BOREHOLES
• Rotary drilling techniques are
employed where boreholes are
required into very dense gravel or
bedrock.
• Samples of bedrock are recovered in
seamless plastic tubes for subsequent
logging by a suitably qualified engineer
and for laboratory testing
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ROTARY DRILLED
BOREHOLES
• Most of rotary coring work relies on the
use of drilling rigs which can also
obtain continuous samples of soils
using dynamic sampling equipment.
• The rigs are suitable for limited access
works.
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rotary drilling techniques on
a jackup platform
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OTHER EXAMPLES…..
• Drilling in restricted areas…
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• Working on
Escarpments
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• Working on slopes….
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It can be anywhere……