BU3102: CONSTRUCTION TECHNOLOGY III

BU3102: CONSTRUCTION TECHNOLOGY III Q3: DISCUSS SOIL CHARACTERISTICS & THEIR RELATION TO FOUNDATION SELECTION WITH CASE STUDIES

General Classification ofSoil BU3102: CONSTRUCTION TECHNOLOGY III • Large variety of soil and rock types. • Enable the engineers to draw some useful conclusions from the type of soil available

BU3102: CONSTRUCTION TECHNOLOGY III Soil Types • Comparatively soft, loose & uncemented deposits with the voids between the particles. • Described and defined by the size of the particles.

BU3102: CONSTRUCTION TECHNOLOGY III Classification of Soil TYPES OF SOILS NON COHESIVE COHESIVE ORGANIC SILTS COBBLES PEAT BOULDERS CLAY GRAVEL SAND Soil encountered at site is in a mixture of few types of soils.

BU3102: CONSTRUCTION TECHNOLOGY III Characteristics of Soil Types NON COHESIVE SOIL SAND GRAVEL • consist of angular & mainly siliceous products of rock weathering. consist of rock fragments & usually sandy material.

BU3102: CONSTRUCTION TECHNOLOGY III Characteristics of Soil Types COHESIVE SOIL CLAY SILTS Finest siliceous & aluminous products of rock weathering Natural sediment of material Possesses some plasticity & cohesion, when dry Smooth & greasy to touch. Shrink appreciably and considerable strength when dry.

BU3102: CONSTRUCTION TECHNOLOGY III Characteristics of Soil Types TYPES OF SOILS ORGANIC PEAT Made up of fibrous particles of decayed vegetable matter.

BU3102: CONSTRUCTION TECHNOLOGY III Soil Testing • Assess the behavior of soil masse under imposed conditions • Natural material that is more variable than man-made building materials • Indicates the suitability of a site and the various design alternatives for a foundation.

BU3102: CONSTRUCTION TECHNOLOGY III Soil Testing TYPES OF SOILS Consolidation Test Shear Strength Test Compaction Test Compressibility characteristics Optimum moisture content & corresponding maximum density. 3 types of triaxial are: Undrained Consolidated-undrained Drained Apparatus used known as oedometer.

BU3102: CONSTRUCTION TECHNOLOGY III GEOLOGY OF SINGAPORE • Bukit Timah Formation • Jurong Formation • Old Alluvium Formation • Kallang Formation

BU3102: CONSTRUCTION TECHNOLOGY III (1) Bukit Timah Granite GEOLOGY OF SINGAPORE • Mainly distributed in the central part of the island • Residual soil, which consists mainly of sandy clayey soil • Ideal bearing stratum • Shallow foundation may be adopted if the level of the bedrock is near to the ground level. • High bearing capacity

BU3102: CONSTRUCTION TECHNOLOGY III (2) Jurong Formation GEOLOGY OF SINGAPORE • Western and southern coastal areas • The bearing stratum for shallow and deep foundations • Resting of pile into the sandstone • Hardness of the rocks, properties and depth of the overburden soil decide the type and length of pile to use.

BU3102: CONSTRUCTION TECHNOLOGY III (3) Old Alluvium Formation GEOLOGY OF SINGAPORE • Northern, north-eastern part & north-western part of Singapore island • Possesses good shearing strength and low compressibility. • Has high value in friction • Provides sufficient pile bearing capacity

BU3102: CONSTRUCTION TECHNOLOGY III (4) Kallang Formation GEOLOGY OF SINGAPORE • 2 layers:the upper and lower marine clay • Average shear strength of 10 kN/m² and 40kN/m² for the upper and lower marine member, respectively • The MC of the upper marine member is high, about 70% to 100% and this layer has high compressibility

BU3102: CONSTRUCTION TECHNOLOGY III FOUNDATION • Part of the substructure designed & constructed to be in direct contact with and transmitting loads to the ground. • Spread the load from the superstructure • Can be broadly classified into shallow and deep foundations

CLASSIFICATION OF FOUNDATION SYSTEMS FOUNDATION SYSTEM DEEP FOUNDATION SYSTEM SHALLOW FOUNDATION SYSTEM DISPLACEMENT SYSTEM REPLACEMENT SYSTEM CASISSON PRECAST PILES DRIVEN CAST IN PLACE BORED PILE DROP HAND DUG & MACHINE BORED TIMBER STEEL RC PERCUSSION BORED ROTARY BORED FLUSH BORED

BU3102: CONSTRUCTION TECHNOLOGY III FOUNDATION DISPLACEMENT SYSTEM • Consist mainly of piles such as precast reinforced concrete piles, steel piles and timber piles • A pile, which, being install in the ground, displaces its own volume of soil, • Transmission of load can be achieved through end bearing, skin friction or a combination of both

BU3102: CONSTRUCTION TECHNOLOGY III DISPLACEMENT SYSTEM A) PRECAST RC PILES • Used when a high resistance to lateral forces is required or when the soil conditions are unfavorable to cast-in-place piles. • Driven by drop hammers or vibrators using a pile-frame, a crane and leaders, or a pile driving rig.

BU3102: CONSTRUCTION TECHNOLOGY III DISPLACEMENT SYSTEM B) STEEL PILES • Do not cause large displacement of the soil. Used in situation where loose or medium dense sand. • In Singapore, H-pile or universal steel beam is the most popular form of steel pile. • Care must be taken in the welding of joints. Provision of adequate driving heads to protect the end of the steel sections.

BU3102: CONSTRUCTION TECHNOLOGY III REPLACEMENT SYSTEM • Installed by first removing the soil by drilling process, then constructing the pile by placing concrete or some other structural element in the drilled hole. • 2 main types : bored and cast in places piles and drilled tubular (caisson) piles.

BU3102: CONSTRUCTION TECHNOLOGY III REPLACEMENT SYSTEM A) BORED PILES • Cast-in-situ concrete piles. 3 main types: percussion, rotary and flush bored piles. • Soil profile & the general changes in soil layers can be made. • Temporary metal casing and the usage of bentonite slurry prevent the collapsing of soil, especially very soft clay, loose and water bearing sand.

BU3102: CONSTRUCTION TECHNOLOGY III REPLACEMENT SYSTEM B) CAISSONS • A boxlike structure, round or rectangular, which is sunk from the surface of either land or water to some desirable depth. • To enable structural loads to be taken down through deep layers of weak soil on to a firmer stratum • Suitable for multi-storey buildings and heavy civil engineering works

BU3102: CONSTRUCTION TECHNOLOGY III REPLACEMENT SYSTEM B) CAISSONS • Box caissons • Hand-dug / machine-bored / drilled caisson. • Pneumatic Caisson • Buoyancy Rafts & Basements (Box Foundations)

BU3102: CONSTRUCTION TECHNOLOGY III Factors Affecting The Selection of Foundations • Site Conditions • Ground Conditions • Structural Factors • Relative Costs • Working Conditions

BU3102: CONSTRUCTION TECHNOLOGY III Site Conditions That Affect The Selection of Foundations • Location of site • Environment surrounding site • Adjacent buildings • Presence of trees and how root systems will affect the foundation • Noise, vibration and air pollution during construction phases

BU3102: CONSTRUCTION TECHNOLOGY III Ground Conditions That Affect Foundation Type • Soil characteristics (bearing capacity) • Sufficient geological studies must be conducted for: • Horizontal and vertical variations in soils and rocks • Groundwater • Compressibility and bearing capacity of different strata

BU3102: CONSTRUCTION TECHNOLOGY III Ground Conditions That Affect Foundation Type (cont.) • Permeability of strata for excavation and construction methods • Soft bed implies relatively high compressibility and low bearing capacity • Firm bed implies relatively low compressibility and high bearing capacity

BU3102: CONSTRUCTION TECHNOLOGY III Selection of Foundation According to Soil Type

BU3102: CONSTRUCTION TECHNOLOGY III Structural Factors/ Types of Structures to be Supported • The nature and structure of the building to be supported will affect the foundation type • The characteristics of the superstructure are relevant to the selection of foundation types

Independent Reinforced Concrete Footings Steel Grillages and Predestals Raft Foundations Piles and Piers Goal is uniform settlement BU3102: CONSTRUCTION TECHNOLOGY III Type of Foundations Employed For Tall Buildings

BU3102: CONSTRUCTION TECHNOLOGY III Factors to be Considered with Spacious Buildings • Lateral Thrust- arises from both vertical loads and wind loads • Uplift- wind loads will affect spacious buildings since they are relatively light

BU3102: CONSTRUCTION TECHNOLOGY III Relative Costs/ Cost Restraints • Foundation type may also be affected by economic factors • Foundation design must be the best technical solution as well as the best economical solution when related to contractor’s expertise

BU3102: CONSTRUCTION TECHNOLOGY III Working Conditions • Working conditions include weather conditions, ground conditions, etc. • Any work below ground level must take into account the effect the condition of the ground can have on the method employed • In wet conditions with a site of low bearing capacity, pile driving may a better choice

BU3102: CONSTRUCTION TECHNOLOGY III Causes of Defects in Foundations • Shrinkage of Clays • Swelling of Clays • Climatic Factors • Effects of Vegetation • Water Seepage and Surface Erosion • Ground Movements Due to Vibrations • Hillside Creep

BU3102: CONSTRUCTION TECHNOLOGY III Causes of Defects in Foundations (cont.) In the design of foundations these factors must be considered in order to prevent defects • Deepening the depth of foundations to ground that is not susceptible to movement • Special forms of construction which will allow appreciable movement without damaging the structure

BU3102: CONSTRUCTION TECHNOLOGY III Causes of Defects in Foundations (cont.) • Ground movements can occur • In the design of foundations these factors must be considered in order to prevent defects • Deepening the depth of foundations to ground that is not susceptible to movement • Special forms of construction which will allow appreciable movement without damaging the structure

BU3102: CONSTRUCTION TECHNOLOGY III Shrinkage of Clays Causes of Defects in Foundations • May be due to seasonal moisture changes or absorption of water by plants • Seasonal effects may be cumulative over a period of years • Both horizontal and vertical shrinkage may be experienced

BU3102: CONSTRUCTION TECHNOLOGY III Swelling of Clays Causes of Defects in Foundations • Fundamentally related to shrinkage • Dominant factor under certain conditions with some clays • High capacity for shrinkage and swelling is generally associated with high montmorillonite content • Degree of movement depends on the proportion of the mineral present and amount of exchangeable bases

BU3102: CONSTRUCTION TECHNOLOGY III Climatic Factors Causes of Defects in Foundations • 2 factors that necessitate special methods of foundation design • Wind difference in seasonal rainfall • Soil temperature conditions • Development of cracks is progressive from season to season • In hot climates swelling may be due to thermosmotic transfer of moisture towards the zone of lower temperature

BU3102: CONSTRUCTION TECHNOLOGY III Effects of Vegetation Causes of Defects in Foundations • Roots of trees and shrubs • Heave of foundations may result on sites which have been cleared of trees and hedges • Settlement in existing structures may be affected by growing trees or planting of new trees • Special considerations and preventive measures must be taken around growing trees

BU3102: CONSTRUCTION TECHNOLOGY III Water Seepage and Surface Erosion Causes of Defects in Foundations • Trouble with water seepage and surface erosion normally occur in sandy soils • Soil erosion and loss of ground from beneath foundations may lead to collapse of structures • Surface erosion is a result of loss of material due to strong winds or erosion by flowing water

BU3102: CONSTRUCTION TECHNOLOGY III Ground Movements Due to Vibrations Causes of Defects in Foundations • ??? • Damages to existing structures resulting from pile driving vibrations are not uncommon • Precautions must be taken against these effects in sands adjacent to existing structures

BU3102: CONSTRUCTION TECHNOLOGY III Ground Movement Due to Hillside Creep Causes of Defects in Foundations • Construction operations may have a serious effect on slope stability • Terracing of the slope may change the state of stress in both cut and fill areas • It is best to avoid building in such areas • Design foundations so that the whole structure will move as one unit

CASE STUDY: THE DBS BUILDING INTRODUCTION • Located between Shenton Way & Robinson Road, i.e., in the Financial District and houses the HQ of the DBS. • A 50-storey block and two side podiums. • Started in 1970 and was completed in 1974.

CASE STUDY: THE DBS BUILDING SOIL CHARACTERISTICS • Constructed on reclaimed land • Encountered varied greatly from the fill material on top of soft marine clay and alternating layers of stiff clay and medium dense to dense sand • Fresh rock behind the exposed surface was in a “dust-dry” condition which may indicate a low water table.

CASE STUDY: THE DBS BUILDING FOUNDATION TYPE • The podiums is supported on 20-36 m long bored piles + driven precast concrete piles about 31 to 61 m long. • The Tower Block is supported on four 7.3 m diameter caissons. Varied from 39.6m to 64.0m. The design load is about 200MN • Linked to a common raft or caisson cap 3.1 m think and 30m x 35m in area.

CASE STUDY: THE DBS BUILDING FOUNDATION TYPE WHY CASSION ?? • Very high weight of the tower • Soil conditions • Use of hand excavation for the construction would reduce noise and vibration

CASE STUDY: THE DBS BUILDING CONSTRUCTION OF CASSION • Upper part of the caissons was lined with contiguous bored piles down. These were braced laterally by reinforced concrete compression rings • When the required depth was achieved by excavation the bottom of the caisson was cleaned and concreting was started.

CASE STUDY: THE DBS BUILDING CONSTRUCTION OF CASSION • The smallest caisson was concreted continuously while the other ones were concreted in stages. • Concrete was poured up to 12.2 m below ground level. Then the raft was built.

BU3102: CONSTRUCTION TECHNOLOGY III