Week 01 Preliminaries Works, Soil Investigate & Ground Water Control

SITE PREPARATIONS

Site Investigation Soil Investigation Ground Water Control Preliminaries Works

Prepared by:

Mr. Syamsul Hendra Mahmud

Faculty of Built Environment, UTM

Introduction

Every site are different? Why? What are the difference between site

investigation and soil investigation? Please give some examples?

Why we need to have site and soil investigation?

Site Investigation

Aim is to collect systematically and record all the necessary data which will be needed or will help in the design and construction processes of the proposed work.

Site investigation includes the overall investigation of the site and it may consists of roads and access analysis, pipes and services analysis, location, development costs and environment analysis, plans etc.

It also consists of soil investigation which covers the analysis of the existing soil.

Site Investigation

Stages of site investigation– Desk study– Visiting analysis– Topography and hydrology analysis– Construction progress analysis

Follows BS 5930 : 1981 “Code of Practice for Site Investigation”

Soil Investigation

Specifically related to the subsoil beneath the site under investigation and could be part of or separate from the site investigation.

Objectives:– Determine the suitability of the site for the proposed

projects.– Determine an adequate and economic foundation design.– Determine the difficulties which may arise during the

construction process and period.– Determine the occurrence and/or cause of all changes in

subsoil conditions.

Soil Investigation

How: in a fully annotated and dimensioned plans and sections.

Includes: any elements on adjacent sites which may affect the proposed works or conversely anything appertaining to the proposed works which may affect an adjacent site should also be recorded.

Soil Investigation

Soil samples:– Disturbed soil samples: these are soil samples

obtained from boreholes and trial pits. The method of extraction disturbs the natural structure of the subsoil but such samples are suitable for visual grading, establishing moisture content and some laboratory test. Disturbed samples should be stored in labelled air tight jars.

Soil Investigation

Soil samples:– Undisturbed soil samples: these are 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 laboratory for testing. This method is suitable for rock and clay subsoils but difficulties can be experienced in trying to obtain undisturbed samples in other types of subsoil.

Soil Investigation

Methods– Trial pits– Hand or mechanical auger– Mechanical auger– Sampling shells– Wash boring– Mud rotary drilling– Core drilling

Soil Investigation

Soil assessment and testing– Are designed to evaluate the density or shear

strength of soils and are very valuable since they do not disturb the soil under test.

– Type of tests: Standard penetration test Vane test Unconfined compression test

Ground Water Control

Water can be classified by its relative position to or within the ground.


Problems of water in the subsoil:– A high water table could cause flooding during

wet period.– Subsoil water can cause problems during

excavation works by its natural tendency to flow into the voids created by the excavation activities.

– It can cause an unacceptable humidity level around finished building and structures.


Control of ground water always referred to temporary and permanent exclusion.– Temporary exclusion: lowering of the water table

and within the economic depth range of 1500mm using subsoil drainage methods, for deeper treatment a pump or pumps are usually used.

– Permanent exclusion: the insertion of an impermeable barrier to stop the flow of water within the ground.



Temporary exclusion– Simple Sump Pumping– Jetted Sumps– Wellpoint Systems


Simple Sump Pumping– Suitable for trench work and/or where small

volume of water are involved.



Jetted Sumps– Almost the same with simple sump methods of

dewatering.– A borehole is formed in the subsoil by jetting a

metal tube into the ground by means of pressurised water to a depth within the maximum suction lift of the extract pump.

– The metal tube is withdrawn to leave a void for placing a disposable wellpoint and plastic suction pipe.

– The area surrounding the pipe is filled with coarse sand as filtering media.



Wellpoint systems– This is a method of lowering the water table to a

position below the formation level to give a dry working area.

– Jetting into the subsoil a series of wellpoints which are connected to a common header pipe which then connected to a vacuum pump.

– Commonly use in trench excavation.– If the proposed formation level is below the

suction lift capacity of the pump a multi-stage system can be employed.





Permanent exclusion– Thin Grouted Membranes– Contiguous Piling– Diaphragm Wall– Precast Concrete Diaphragm Walls– Grouting Methods– Ground Freezing Techniques


Thin Grouted Membranes– Work as permanent curtain or cut-off non

structural walls or barriers inserted in the ground to enclose the proposed excavation area.

– Suitable for silts and sands and can be installed rapidly but they must be adequately supported by earth on both sides.

– The only limitation is the depth to which the formers can be driven and extracted.



Contiguous Piling– Forms a permanent structural wall of interlocking

bored piles.– Alternate piles are bored and cast by traditional

methods after which the interlocking piles are bored using a special auger or cutter.

– Suitable for most types of subsoil and has the main advantages of being economical on small and confined sites; capable of being formed close to existing foundations and can be installed with the minimum of vibration and noise.


Contiguous Piling– To ensure a complete interlock of all piles over

the entire length may be difficult therefore the exposed face of the piles is usually covered with a mesh or similar fabric and face with rendering or sprayed concrete.

– Suitable for structures such as basements, road underpasses and underground car parks.



Diaphragm Wall– Are structural concrete walls which can be cast in-

situ or using pre-cast concrete methods.– Suitable for most subsoil and their installation

generates only a small amount of vibration and noise.

– The high cost of these walls makes them uneconomic unless they can be incorporated into the finished structure.

– Normally use for basements, underground carparks and similar structures.



Pre-cast Concrete Diaphragm Wall– Have some applications with in-situ concrete

diaphragm walls.– Lack in design flexibility.– The panel or post panel units are installed in a

trench filled with a special mixture of bentonite and cement with a retarder to control the setting time.

– This mixtures ensures that the joints between the wall components are effectively sealed.

– To provide stability, the panels of posts are tied to the retained earth with ground anchors.



Grouting Methods– Are used to form a curtain or cut-off wall in high

permeability soils where pumping methods could be uneconomic.

– The curtain walls formed by grouting methods are non-structural therefore adequate earth support will be required and in some cases this will be a distance of at least 4m from the face of proposed excavation.


Grouting Methods– Grout mixtures are injected into the soil by pumping

the grout at high pressure through special injection pipes inserted in the ground.

– The pattern and spacing of the injection pipes will depend on the grout type and soil conditions.

– Grout types:Cement groutsChemical groutsResin grouts



Ground Freezing Techniques– Suitable for all types of saturated soils and rock

and for soils with a moisture content in excess of 8% of the voids.

– The basic principle is to insert into the ground a series of freezing tubes to form an ice wall thus creating an impermeable barrier.

– Takes time to develop and the initial costs are high.


Ground Freezing Techniques– The freezing tubes can be installed vertically for

conventional excavations and horizontally for tunneling works.

– Normally using magnesium chloride and calcium chloride with a temperature of -15 to -25 degree Celsius which takes 10 to 17 days to form an ice wall 1m thick.

– Liquid nitrogen could be used as the freezing medium to reduce the initial freezing period if the extra cost can be justified.


Preliminaries Works

What is preliminaries work? The reason of having preliminaries works? Is there any difference between preliminaries items

for different projects? Why? Example of preliminaries items that is needed for a

project.

Education

Week 01 Preliminaries Works, Soil Investigate & Ground Water Control