CHAPTER 1SOILAl-Hafzan Abdullah Halim

DEFINITION

The simplest classification of geological deposits falls generally into two major classes to provide engineers and others with basic information which is:

“ROCK”- which refers mainly to a hard rigid and strongly cemented deposit, and

“SOIL”- which refers to the soft, or loose and cemented deposis

IMPORTANCE

For construction purposes Structure implementation Foundation choices Reduce the risk of soil/foundation failure

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

SOIL FORMATION

3 types of formation Transported soil Residual soil Organic soil

TRANSPORTED SOIL

E.g. – gravel, sand, silt and clay Produce by the formation of wind and

water Dust flown by wind

RESIDUAL SOIL

E.g. – top soil & laterite weathering action on rock fragments

which breaks and crushed and becomes smaller pieces

ORGANIC SOIL

E.g. – top soil and peat Produce by the formation of rotten

vegetation and animals

ROCK FORMATION

Divided into 3 major groups: Igneous rocks Sedimentary rocks Metamorphic rocks

IGNEOUS ROCK

E.g. – basalt & granite Formed by solidification of molten

materials which has ascended towards the surface from the hot lower levels of the earth crust

SEDIMENTARY ROCKS

E.g.-sandstone, shale, limestone Formed by deep fissures and swallow

holes which are cavities formed at some time by the passage of water through soft rock.

METAMORPHIC ROCKS

E.g.-slates, quartzite, marble These rocks include any sedimentary

deposit or igneous rock which, after consolidation, has become altered by heat or pressure

TYPES OF SOIL

2 types of soil Non-cohesive soils Cohesive soils

COHESIVE SOILS

• Fine grained particles are closely integrated and stick together

• Particle size ranges between 0.06mm or less• The level of cohesiveness depends on the size, shape

and water level• When its wet, it is soft and when its dry it becomes

hard• Has a high level of moisture content• Always experiences shrinkage and extension process• The increasing of water level can caused soil

strengths to differ• Therefore the depth of the foundation should be

constructed at least 1m from the earth surface

High level of water content can caused difficulty in earth excavation which will flood the construction site

E.g- clay,silt, peat and laterite

NON-COHESIVE SOIL

The soil particles are not sticking to each other

The particle size ranges between 0.06mm-200mm

Non-cohesive soils has a high value for a construction site

Water are easy to flow out because of its hollow particle

E.g- gravel, sands

CLASSIFICATION OF SOILS

Soil classification can be done by: Grain size-divided into several sizes

Coarse grain non-cohesive Fined grained cohesive Organic soilCan be done by sieving and sedimentation

technique- Sieving : for non-cohesive soil such as gravel

and sand- Sedimentation : for cohesive soil such as clay

and silt

Moisture contentMoisture content classification for

cohesive soil such as clay and siltCan be classified by moisture content

test or plastic limit/liquid limit test. Refer to BS 1377:1975

GROUND WATER

Usually refer to the ground water level Water usually come from rain and water

penetration into the earth opening which can penetrates until 12000m

Water content depends on: Surface slopes/gradients Vegetation Weather Soil opening and penetration

- Ground water content will influence construction works where it involved the stabilization and strength of the soil.

- Usually high level of water content require a much more complicated foundation system.

- It will also make more difficult when water penetrates into excavation work and will obstruct workers and machineries.

- Water proof retaining wall needed in such cases

SOIL CHARACTERISTIC IN RELATION TO CHOICE OF FOUNDATIONS Soil have different attribute when load

implied on them. The characteristic are: Compressibility Permeability Plasticity

CHOICES OF FOUNDATIONSolid 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