SOIL

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.

SOIL STRATUM

• 2 layers

– Top soil

– Ground soil

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

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

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.

NATURAL RECYCLING OF

SOIL TO ROCK

Metamorphic rock

Sedimentary rock

Igneous rock

Residual soil

Sediments

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

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.

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

SOIL CHARACTERISTICS

• Color,

• Texture,

• Aggregation,

• Porosity,

• Ion content and

• pH all important to soil characteristics

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.

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

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.

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.

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)

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

Categories of soil

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.

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.

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;

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).

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)

Soil types

Soil type

SOIL CHARACTERISTIC IN RELATION

TO CHOICE OF FOUNDATIONS

• Soil have different attribute when load

implied on them. The characteristic

are:

– Compressibility

– Permeability

– Plasticity

• 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.

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

CN Tower

KLCC Tower

SOIL INVESTIGATIONS

SPECIFICALLY RELATED TO

THE SUBSOIL BENEATH THE

SITE UNDER INVESTIGATION

AND COULD BE PART OF OR

SEPARATE FROM THE SITE

INVESTIGATION

• A well designed soil

investigation can often lead to

project cost savings in the long

term by allowing contractors to

foresee potential problems.

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.

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.

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.

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.

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.

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.

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.

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

• Results of site investigations

can be presented as either

factual or interpretive reports

with recommendations relating

to both geotechnical and

environmental considerations

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.

TRIAL PITTING

• All trial pit investigations are

supervised by experienced engineers

with a thorough understanding of

geology and soil mechanics.

• 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.

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.

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.

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

• The preferred method for deeper

investigation in soft or marginal

ground, where sufficient information

cannot be obtained from trial pits.

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

CABLE PERCUSSIVE

BOREHOLES

• Disturbed and undisturbed samples

are retrieved from the boreholes for

inspection and logging by engineers

and subsequent testing in a

laboratories.

A standard cable percussion

drilling rig

http://www.geositesurveys.co.uk/images/cablepercussive2.jpg

Operation of cable percussion rig for

working in areas of restricted access or

with restricted headroom

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

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.

rotary drilling techniques on

a jackup platform

OTHER EXAMPLES…..

• Drilling in restricted areas…

• Working on

Escarpments

• Working on slopes….

It can be anywhere……

THANK YOU…….

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