Embed Size (px)
DESCRIPTION
foundation
Citation preview
UNIVERSITI TEKNOLOGI MALAYSIA PSZ 19:16 (Pind.1/07)
DECLARATION OF THESIS / POST GRADUATE PROJECT PAPER AND COPYRIGHT
Author’s full name : MEGAT ZAHARI BIN MEGAT JAAFAR
Date of birth : 20th April 1966
Title : Semi Top Down and Bottom Up Construction Work in
Deep Basement of Tall Building in Kuala Lumpur.
Academic Session : 2009/2010
I declared that this thesis is classified as :
CONFIDENTIAL (Contains confidential information under the Official Secret Act 1972)*
RESTRICTED (Contains restricted information as specified by the Organization where research was done)*
OPEN ACCESS I agree that my thesis to be published as online open access (full text)
I acknowledged that Universiti Teknologi Malaysia reserves the right as follows:
1. This thesis is the property of Universiti Teknologi Malaysia.
2. The library of Universiti Teknologi Malaysia ha the right to make copies for the purpose
of research only.
3. The library has the right to make copies of the thesis for academic exchange.
Certified by:
SIGNATURE
SIGNATURE OF SUPERVISOR
660420-02-5567
NEW IC NO.
ASSOCIATE PROFESSOR DR. A.AZIZ SAIM
NAME OF SUPERVISOR
Date : Date :
NOTES : * If the thesis is CONFIDENTIAL or RESTRICTED, please attach with the letter from
the organization with period and reasons for confidentiality or restriction
“ I hereby declare that I have read this project report and in my
opinion this project report is sufficient in terms of scope and quality for the
award of the degree of Master of Engineering (Civil-Structure)”
Signature : ………………………………………
Name of Supervisor : Associate Professor Dr. A.Aziz Saim
Date :
SEMI TOP DOWN AND BOTTOM UP CONSTRUCTION WORK IN DEEP
BASEMENT OF TALL BUILDING IN KUALA LUMPUR.
MEGAT ZAHARI BIN MEGAT JAAFAR
A project report submitted in partial fulfilment of the
requirements for the award of the degree of
Master of Engineering (Civil-Structure)
Faculty of Civil Engineering
Universiti Teknologi Malaysia
NOVEMBER 2009
ii
I declare that this project report entitled “Semi Top Down and Bottom Up Construction
Work in Deep Basement of Tall Building in Kuala Lumpur” is the result of my own
research except as cited in the references. The project report has not been accepted for
any degree and this is not concurrently submitted in candidature of any degree.
Signature : ………………………………….…
Name : Megat Zahari Bin Megat Jaafar
Date :
iii
Special dedication to my beloved wife (Noorleha Lee Jung-hee) who has fully given
encouragement and moral support towards accomplishment my study and to my
dearest daughter (Wan Noorlily).
……….. for everlasting love and cares………
iv
ACKNOWLEDGEMENT
I would like to thank Associate Professor Dr.A.Aziz Saim of the Faculty of Civil
Engineering, Universiti Teknologi Malaysia who has reviewed and given commitments,
comprehensive and generous advice towards accomplishment of this project report.
Great thank to all personnel of both projects who have contributed thoughts and
information during my field study.
v
ABSTRACT
This project report is to present underground basements construction work in tall
building constructed with bottom up method and semi top down method. Bottom up
method is normally carried out in area with fewer plant facilities to operate. Semi top
down method is carried out in urban area with compact surround area to reduce
construction period and cost. Three floors underground basement founded on same type
underground limestone from two projects of 30-storey building are investigated. The
excavation for both basement substructures is varied from 14m to 18m below existing
ground level. The work methodology in the basement construction work is presented.
Excavation works, slope stabilization, retaining systems, site instrumentations and
under ground water table are those parameters influenced in substructure works. All the
parameters from both methods are compiled during substructure work then assessed and
evaluated in view of technical aspect. Contrary to bottom up method, in semi top down
method, the retaining wall system and pre installed temporary stanchion are required,
however shot-crete in slope stabilization, steel strutting system and earth backfilling are
eliminated. It appears that in basements works using semi top down method has
offered more advantages compare with bottom up method in view of shorter
construction period and cost effective. The suggestions proposed for preliminary study
in three floors basement work are rate completion time are 16.3m2/day and 13.2m2/day
and for construction cost at sub-contractor price are RM1,556.92/m2 and
RM1,758.76/m2 for semi top down method and bottom up method respectively.
vi
ABSTRAK
Lapuran projek ini mengupaskan kerja-kerja besmen bawah tanah dalam
pembinaan bangunan tinggi mengunakan cara kerja bawah ke atas dan cara kerja separa
atas ke bawah. Cara kerja bawah ke atas dijalankan di kawasan yang tidak memerlukan
penggunaan banyak jentera. Cara kerja separa atas ke bawah pula dijalankan di kawasan
yang padat sekelilingnya dengan mengambilkira penjimatan kos dan masa pembinaan.
Pembinaan dua bangunan setinggi 30 tingkat dengan tiga besmen bawah-tanah di atas
tanah batu-kapur dikajisiasat. Kerja-kerja mengorek tanah untuk sub-struktur di kedua-
dua besmen bangunan tersebut adalah di sekitar 14m sehingga 18m kedalamannya dari
aras sediaada. Tata kerja dalam pembinaan besmen tersebut dibentangkan. Kerja-kerja
pengorekan tanah, kesetabilan cerun, sistem penghadangan, alat-alat pengukuran tapak
bina dan aras air bawah tanah adalah pembolehubah yang mempengaruhi kerja-kerja
substruktur. Semua pembolehubah dari kedua-dua cara kerja disusunkan semasa kerja-
kerja substruktur, selepas itu ditentukan dan dinilaikan dari sudut teknikal. Berbeza dari
cara kerja bawah ke atas, didapati cara kerja separa atas ke bawah memerlukan sistem
dinding penghadang dan tiang pasang siap, walaubagaimana pun pelindungan shot crete
dalam kesetabilan cerun, sistem besi jermang sadak (steel strutting system) dan timbus
balik tanah tidak diperlukan. Kerja-kerja besmen menggunakan cara kerja separa atas ke
bawah didapati memberi kelebihan berbandingkan cara kerja bawah ke atas dari sudut
masa pembinaan yang singkat dan penjimatan kos kerja. Cadangan yang diutarakan
untuk kajian permulaan dalam pembinaan tiga besmen bawahtanah adalah kadar masa
pembinaan ialah 16.3m2/hari dan kadar harga subkontraktor ialah RM 1,556.92/m2 bagi
cara kerja separa atas ke bawah. Manakala bagi pembinaan mengikut cara kerja bawah
ke atas, kadar masa pembinaan ialah 13.2m2/hari dan kadar harga subkontraktor is RM
1,758.76/m2
vii
TABLE OF CONTENTS
CHAPTER TITLE PAGE
DECLARATION ii
DEDICATION iii
ACKNOWLEDGEMENT iv
ABSTRACT v
ABSTRAK vi
TABLE OF CONTENTS vii
LIST OF TABLES x
LIST OF FIGURES xi
1 CHAPTER 1 - Introduction
1.1 Introduction 1
1.2 Problem Statement 3
1.3 Aim and Objective 3
1.4 Scope of Project Study 4
2 CHAPTER 2 - Construction Of Basement In Tall Building
2.1 Introduction 5
2.1.1 Soil Investigation 6
2.1.2 Ground Water 8
2.1.3 Raft and Piled Raft 9
2.1.4 Retaining Wall 10
viii
2.2 Criteria in Deep Basement Work 11
2.2.1 Dilapidation Survey of Adjacent Structures 12
2.2.2 Instrumentation and Monitoring Program 13
2.2.3 Supervision and Construction Control 15
2.3 Bottom Up Method in Deep Basement Work 18
2.4 Semi Top Down Method in Deep Basement Work 20
3 CHAPTER 3 - Methodology
3.1 Introduction 23
3.2 Project Study Case 23
4 CHAPTER 4 – Project 1: Bottom Up Method in Deep Basement Work
4.1 Introduction 26
4.2 Substructure Construction Planning Sequences 28
4.3 Erection of Contiguous Bored Pile 31
4.4 Foundation Bored Pile 32
4.5 Earth Excavation 33
4.6 Instrumentation and Monitoring 36
4.7 Raft Basement Construction 38
4.8 Erection of Strutting and Bracing 41
4.9 Construction Basement Floors to Ground Floor 44
4.10 Backfilling with Suitable Material 45
5 CHAPTER 5 – Project 2 : Semi Top Down Method in Deep Basement Work
5.1 Introduction 48
5.2 Basement Construction Planning Sequences 50
5.3 Contiguous Bored Pile 51
5.4 Foundation Bored Pile 53
5.5 Pre-installed Column Stanchion 56
5.6 Top Down Work 57
5.7 Floor Casting and Top Down Work 60
ix
5.8 Foundation Base Casting and Bottom Up Work 62
6 CHAPTER 6 – Data Analysis
6.1 Introduction 66
6.2 Parameter Activities 67
6.3 Design Parameter 67
6.4 Time and Cost Completion Work 72
7 CHAPTER 7 - Conclusion and Suggestion
7.1 Introduction 77
7.2 Conclusion 77
7.3 Suggestion 78
REFERENCES 80
x
LIST OF TABLES
TABLE NO. TITLE PAGE
2.1 Common types of instrument for basement construction works
14
6.1 Parameter in bottom up excavation method in
underground basement work 69
6.2 Parameter in semi top down method in underground
basement work 70
6.3 Parameter designs influenced in bottom up and semi top
down method of underground basement work 71
6.4 Actual work completion of bottom up method for Project
1 75
6.5 Actual work completion of semi top down method for Project 2
76
xi
LIST OF FIGURES
FIGURE NO. TITLE PAGE
1.1 Tall buildings in Kuala Lumpur 2 2.1 Typical arrangement of soil investigation using
percussion borins (a) percussion boring rig, (b) boring rod and chisel
7
2.2 Typical sump arrangement 8 2.3 Propped piled wall (a) stage 1, (b) final stage 10 2.4 Plan view of contiguous bored pile with skin wall 11 2.5 Open excavation with slope protection 15 2.6 Open excavation with braced wall (a) internally strutting
to wall, (b) wall with ground anchor 16
2.7 Closed excavation with braced wall in full top down
method 16
2.8 Semi top down work 17 2.9 Open excavation in deep basement work 18
2.10 Bottom up method in deep basement 19
2.11 Lateral force acting in deep basement
20
2.12 Semi top down method in deep basement 21
xii
3.1 Methodology flowchart of project study 24
4.1 Layout plan of retaining system 27
4.2 Site observation method chart 29
4.3 Basement work planning in stages 30
4.4 Contiguous bored pile at perimeter site boundary 31
4.5 Foundation bored pile in dry condition 32 4.6 Excavation work in stages 33 4.7 Exposed slope with shotcrete 34
4.8 Progress of excavation work 35
4.9 Proper trimming work at base 36 4.10 Typical installation detail for inclinometers 37
4.11 Installation inclinometer behind wallperimeter bored pile 38
4.12 Rebar installation for raft base in progress 39
4.13 Raft foundation concreting work is being in progress 40
4.14 Raft foundation curing with polystyrene sheet cover on
top surface 41
4.15 Typical installation of temporary inclined steel strutting
with reinforced concrete corbel support integrated to raft foundation
42
4.16 Temporary strutting structure and excavation work in
progress 43
4.17 Temporary strutting structure to support retaining wall
(sheet pile and contiguous bored pile) 43
4.18 Basement floor in sequences casting work 44
xiii
4.19 Basement work at construction joint 45 4.20 Gap between basement wall and open slope 46
4.21 Backfilling to required level 47
5.1 Layout plan of semi top down site 49
5.2 Basement work planning in stages 50
5.3 Contiguous bored pile work in progress 52 5.4 Cut off contiguous bored pile to required level 53 5.5 Soil investigation (SI) works are being in progress at
each column position 54
5.6 Lowering down rebar cage in wet hole bored pile 55 5.7 Pre-installed steel stanchion column in bored pile 56 5.8 Ground floor formwork in progress 57
5.9 Top down work in progress 58 5.10 Excavation work to expose pre-installed steel stanchion
column 59
5.11 Excavation work to formation level carried out at center of building downward
60
5.12 Top view of top down work at perimeter building 61 5.13 Bottom up work at center of building 62 5.14 Bottom up area with basement raft work in progress 63
5.15 Bottom up work for center building structure 64 6.1 Actual cost and time completion for semi top down
method and bottom up method without pile foundation 73
CHAPTER 1
INTRODUCTION
1.1 Introduction
In Malaysia, tall buildings with deep basements have been extensively
constructed mainly in the expensive and congested urban area. Basements effectively
serve as underground space for car park and other usage in extensive scheme. The
excavation of the deep basement requires much attention of structural and geotechnical
engineers as well as contractor itself. The considerations involved in design and
planning contributed to safety and economical aspect which should be emphasized at
early stage. The execution of the deep basement construction work can be either carried
out with method of bottom up or top down, however it is subject to site local geology
condition and location of the building itself. The hybrid of both methods which is called
semi top down method may look more viable to give influences in saving of both time
and economical construction aspect.
In Kuala Lumpur area, as metropolitan city, development of tall building with
underground basement rapidly being in progress recently, refer Figure 1.1. Demand on
2
luxurious standard living in town area with ease infrastructure has caused land usage is
fully utilized. The development gives challenging to engineers and contractors to think
intensively in designing and method of construction while maintaining client objectives
to suit with functional of building itself. Based on local experience, construction of
basement required more attention in economical aspect in finding accurate method to
construct deep basement in safely manner.
Figure 1.1 : Tall buildings in Kuala Lumpur
3
1.2 Problem Statement
In construction of deep basements, the major concerned is safety and
economical aspect. This matter is not only implies to project itself but also influence to
surround existing building as well. Safety is mainly influenced by proper sequence
activity in construction system which being implementing at the present of time.
Economical is cost effective contributes to move the construction activity influenced by
operation and monitoring activity. Settlement in soil contributed to ground movement is
due to excavation, presence of ground water, vibration in piling works, stability system
in bracing and strutting as well as others activity in basement construction works. The
proper knowledge of sequence activity in excavation work executed plays important
role to eliminate such consequence defects to existing adjacent structures or building. In
cost estimating of underground structures, methodology of basement construction work,
cost operation and time completion contributed in many type of construction method. In
each method, there are certain limits influenced bound with the pros and cons of the
system activity. Reviewing past project is able to give guideline decision to support
estimation cost and time analysis for basement construction works.
1.3 Aim and Objective
The aim of the project study is to get comparison sequence activity, time and
cost completion in basement work in tall building executed using two types deep
basement construction method i.e (a) Bottom Up Construction Method and, (b) Semi
Top Down Construction Method.
4
Through these two basement construction methods, the objectives of this project study
are encompassed in:-
i. Investigation of sequence activity in construction basement work of tall
building.
ii. Comparison in cost and time construction basement work of tall building.
1.4 Scope of Project Study
In capturing the above aim and objectives, field investigation is to be carried out
from two selected tall building projects in Kuala Lumpur area which are:-
(i) Project 1:One (1) block 30-storey building with 3 floors basement at Jalan
Ampang, Kuala Lumpur which basement work is carried out with Bottom Up
Method, and
(ii) Project 2:One (1) block 30-storey building with 3 floors basement at Jalan
Tuanku Abdul Rahman, Kuala Lumpur which basement work is carried out with
Semi Top Down Method
Project 2 is commenced after one year late from Project 1. Both projects are founded
on similar underground Kenny Hill Formation underlain by Kuala Lumpur Limestone.
CHAPTER 2
CONSTRUCTION OF BASEMENT IN TALL BUILDING
2.1 Introduction
Construction of basement in tall building is expensive due to nature of
soil condition and ground water problems. The substructure basements are designed and
produced by taking considering underground earth, water pressure and all vertical loads.
The method of construction should be well planned and analysed in safety manner and
economical aspect during preliminary stages of development work. Most of the people
who work with underground project consider that a study of the past projects can
provide some general idea as to trends in the future marketplace cost of the underground
cost [1].
In engineering aspect, the excavation will induce stresses in the ground mass around the
excavation changes. The most common changes in stresses in the retained side are the
stresses relieve on the excavation face resulting in horizontal ground movement and
follows by vertical movement for equilibrium. It increases vertical stress due to
6
lowering water table resulting in both immediate and consolidation settlement of the
ground. Ground settlement due to soil movement is observed influencing towards defect
such as cracks to non-suspended slab [2] and other main structure element of surround
existing building when new construction of underground basement takes place nearby.
Improper sequence of excavation is contributed preliminary failure in collapse to
adjacent property [3].
Contractually, substructure construction integrated with temporary support system shall
be the contractor’s responsibility not withstanding any suggestions given by the
consultant engineer who may reject the use of any system he seems unsafe. It is
imperative that basic principle of design and construction should be fully understood by
all directly concerned and particularly by the resident engineer and the contractor’s site
staff. The lack of communication between concerned parties can lead to
misunderstanding that could have serious consequences.
Generally, basement construction work mainly influenced by (a) soil investigation, (b)
ground water, (c) foundation system – raft and piled raft and, (d) retaining wall
2.1.1 Soil Investigation
Soil investigation (SI) is required to be thoroughly carried out in tall building
work. Basically, it is to get information of subsoil profile with respect to subsoil
properties, shear strength and ground water condition. The principal objects [4] of the
investigation are; (a) to determine the sequence, thickness and lateral extent of the soil
strata and, where appropriate, the level of bedrock; (b) to obtain representative samples
7
of the soil (and rock) for identification and classification and, if necessary for use in
laboratory tests to determine relevant soil parameter; (c) to identify the groundwater
conditions.
SI is executed with a few methods [5] such as (a) trials pits, (b) hand auger borings,
mechanical auger borings, (d) light cable percussion borings, (e) rotary open hole
drilling, (f) wash borings, (g) wash probings, (h) dynamic cone penetration tests, (i)
static cone penetration tests, (j) vane shear tests, (k) pressuremeter tests, (l) dilatometer
tests and (m) plate bearing tests. Typical arrangement of SI using percussion boring is
shown in Figure 2.1
Figure 2.1 [4] : Typical arrangement of soil investigation using percussion borings
(a) percussion boring rig, (b) boring rod and chisel
8
2.1.2 Ground Water
In order to carry out construction work below surface levels it is normally
necessary for the working area to be reasonably free from standing water. The water
flow must be either be blocked or carried away from the area. In selecting the proper
method of dealing with ground water it is influenced by the type of soil height of water
table, the depth of excavation and its shape. The purpose of de-watering is to lower the
water table in the vicinity of an excavation to provide a relatively dry and stable
working area. Water can be removed by pumping, isolated from the works by providing
a barrier or drainage to a sump. Pumping from well/sump positioned outside the
excavation boundary is usually preferred technique. The system of pumping from an
open sump (Figure 2.2) is popular because the cost installation and maintenance of the
equipment are relatively low compared to those for wells, and because the system is
applicable to most soils [6].
Figure 2.2 [6] : Typical sump arrangement
9
2.1.3 Raft and Piled Raft
The chief function of a raft is to spread the building load over as great an area of
ground as possible and thus reduce the bearing pressure to minimum. Raft provides a
degree of rigidity that reduces differential movements in the superstructures. The
settlement of a raft foundation does not depend on the weight of the building supports.
Rather settlement depends on the difference between this weight and the weight of the
soil that is removed prior the construction of the raft, provided the heave produced by
the inconsequential. A raft can be built at a sufficient depth so that the weight of soil
removed equals the weight of the building. Such rafts are referred to as buoyancy,
compensated, floating or semi-floating foundation. The success of this type of
foundation structure in overcoming difficult soil conditions has led to the use of deep
raft and rigid frame basements for high buildings on clay soils.
Piled rafts [7] are used as a means of supporting tall buildings on a various types of soil.
It would appear that the basement has a marked influence on the load displacement
within a piled raft foundation. During the initial stages of construction, up lift forces
resulting from the removal of soil can induce initial pressures on the base of a raft,
together with tensile forces in the piles. Subsequent downward loading imposed by the
structure slowly increases contact pressures and gives rise to a comparatively rapid
build-up in compressive pile loads. The load distribution between the piles and the raft
at any stage of construction depends on the ration of uplift force to vertical structural
load. The long-term effect of consolidation is to increase the load carried by the piles
and to decrease the raft contact pressures.
10
2.1.4 Retaining wall
Deep basement work frequently shoring. The choice of method depends upon
technical factors. There are such as depth of the basement foundation, the available
space, the nature and permeability of the soil, the depth of water table and economic
considerations related to the period excavation must be left open, the availability of
labour, plant and materials and the construction program. The cheapest method is to
prop from the base of the excavation as shown in Fig 2.3 [6]. It is obviously can be
progressively carried out as the excavation is deepened, if excessive cantilevering is to
be avoided.
Figure 2.3 [6] : Propped piled wall (a) Stage 1, (b) Final Stage
11
Cost of shoring can be reduced when support system is designed as part of permanent
works. Method involved the use of in situ bored pile cast to form a continuous wall.
The row contiguous bore pile could be given a facing of reinforced concrete wall (skin
wall) to improve of the surface appearance and water tight feature, refer Figure 2.4.
Figure 2.4 [6] : Plan view of contiguous bored pile with skin wall
2.2 Criteria in Deep Basement Work
The common selections criteria for deep basement subject to retaining wall type
and support system [2] made usually on the basis of the followings:-
a. Foundation of adjacent properties and services,
b. Designed limits on wall and retained ground movements
c. Subsoil conditions and ground water level
d. Working space requirement and site constraints
e. Cost and time in construction
f. Flexibility of the layout of the permanent works
g. Local experience and availability of construction plant
h. Maintenance of the wall and support system in permanent condition.
12
Based on the above criteria, the construction of deep basement apparently required
involvement of design engineer, geotechnical engineer together with contractor hand in
hand closely supervise the construction at site. The monitoring work at site is to review
the performance of retaining structure and compare to design requirement and
predictions. The necessary action in immediate time is solution to ensure the occurrence
of critical limit state like large displacement of wall causing damage to nearby
structures or services eliminated.
There are three major considerations being taken during construction deep basement [7]
work in Malaysia, such as dilapidation survey of adjacent structures, instrumentation
and monitoring program and supervision and construction control.
2.2.1 Dilapidation Survey of Adjacent Structures
In Malaysia, for deep excavation work, the dilapidation survey of adjacent
properties is necessary to prevent unnecessary contractual conflict or even lawsuit.
Dilapidation survey also forms part of the requirement by local authorities and serves as
reference report in lawsuit. It should be carried out prior to any construction activities at
the site.
During the excavation, the earth movement is expected. It induces stresses in both
vertical and horizontal soil properties towards influenced defect to adjacent properties
as well. The survey should be thoroughly carried out, with owner permission, in all
angles at various locations at external and internal structure of the adjacent properties.
13
Photographs should be taken together with the measuring equipments and included in
report.
2.2.2 Instrumentation and Monitoring Program
Instrumentation plays an important role in the underground basement
construction activities. It is to monitor any soil movements or any changes in soil stress
condition around the excavation zones and also the behaviour of retaining system and
adjacent properties during excavation to ensure the safety of excavation and satisfactory
performance. Proper planning of instrumentation program and qualified interpretation
of monitoring results by competent geotechnical engineer are essential in ensuring the
effectiveness of the monitoring system, the accuracy/validity of the monitoring results
and proper action in preventing possible damage. The knowledge and experience in
common type of instrument are the successful for safety control in underground
basement construction works, Table 2.1.
14
Table 2.1 [8] : Common types of instrument for basement construction works.
Types
Instruments
Purposes
Related Problem
Water Standpipe Change in groundwater level
Seepage and ground subsidence
Groundwater Table/ Piezometric Pressure Piezometer Change in piezometric
level Consolidation settlement,
uplift or weakening of soil
Lateral movement
Inclinometer Lateral ground movement and deflection of retaining walls
Instability of retaining system and adjacent structures
Vibrating Wire Stain Gauge
Stress along strut member
Load Cell Axial load of strut
Over-load of struts
Bar Stress Transducer
Stress in rebar of concrete retaining structure
Over-load of reinforcing bars
Stress/Load
Earth Pressure Cell
Earth pressure distribution on retaining wall
Over-stress of earth retaining wall
Surface Settlement Point
Ground surface settlement Movements of surrounding ground and damage to existing utilities
Building/Utility Settlement Point
Settlement of adjacent building and utilities
Settlement Gauge Continuous settlement of Structures
Instability of structures
Heave Gauge Elastic heave in soft clay Soil weakening and instability of excavation
Extensometer Vertical ground movements in various depth zone
Deep ground movements
Settlement /Heave Settlement /Heave
Automatic Tunnel Monitoring Device
Movement of MRT tunnels Ground heave, subsidence and lateral movement
Tiltplate/Tiltmeter Tilting of structures Instability of structures
Tilt/Crack
Crackmeter Cracks on structure surface Uneven settlement of structures
Vibration Vibration sensor Vibration effect to adjacent properties
Disturbance to foundation soils and structures
15
2.2.3 Supervision and Construction Control
A competent Resident Engineer is required for site supervision and construction
control. The work methodology through conceptual sequences in stages at various types
of basement construction works is significant important for monitoring purposes. It
contributed the unexpected circumstances can be predicted at early stage and recurrence
of same incident can be immediately reduced or eliminated. A few methods of
conceptual deep basement works in tall building have been practicing, however the
most significant types work adopted in modern practice in Malaysia are as follows:-
1. Open excavation with slope protection or with braced wall
2. Closed excavation with braced wall.
Figure 2.5 : Open excavation with slope protection
The open excavation concept as Figure 2.5, is classical method implementing in tall
building. It is generally carried out in wide area where surround is not constraint. The
cost operation is not expensive, however construction period needs longer time to
complete mainly due to earth excavation activity.
16
Figure 2.6 : Open excavation with braced wall (a) internally strutting to wall, (b) wall with ground anchor
In town and congested area, open excavation in deep basement is able to be carried out.
However, permanent wall supported with bracing and anchor is required, as shown in
Figure 2.6. The cost induced by the bracing system is expensive.
Figure 2.7 : Closed excavation with braced wall in full top down method
In constraint working area, execution of full top down method as shown in Figure 2.7,
with closed excavation enable the substructure work in deep basement and building
17
superstructure can be concurrently constructed without obstruction. This method is look
viable when the building required early occupying. However, more heavy machineries
are required made cost incurred in basement work has been proof not economical
compared with construction time.
Figure 2.8 : Semi top down work
In few occasional, in constraint working area, semi top down excavation is carried out
for deep basement work. The conceptual method is hybrid of open excavation and top
down method. It is illustrated as Figure 2.8
18
2.3 Bottom Up Method in Deep Basement
Bottom up method, refer to Figure 2.9 and Figure 2.10, is normally carried out
in site area with fewer plant facilities to operate. In deep basement work, retaining wall
structure is required. It may form permanent or temporary elements integrated with
building structure. The excavation is carried out within the wall parameter. In absence
of retaining wall structure, the excavation area is appeared bigger in size due to
elimination of slope sliding. Generally, slope ratio is made 1 : 1.5 in vertical and
horizontal respectively but subject to soil geology of the working area.
Figure 2.9 : Open excavation in deep basement work
As the excavation proceeds, horizontal support using strut frame, bracing system or
other shoring are to be installed in order to counteract the lateral pressure on wall due to
19
newly exposed cut [9]. Temporary appropriate dewatering provisions to suit geological
or neighboring environment should be incorporated to keep the pit safe and free from
the entering of ground water. The movement of soil in horizontal and vertical monitored
using instrumentation gauges.
Figure 2.10 : Bottom up method in deep basement
Foundation rafts, pile caps or ground beam are constructed on base formation level. It is
constructed from the lowest basement level up wards. The basements work is repeated
until reach the ground level. The temporary strut and brace members are released and
dismantled at suitable stages as the basements are completed gradually, then backfilling
with suitable material is carried out until finished formation level.
20
2.4 Semi Top Down Method in Deep Basement Work
In urban area with congested, constraint adjacent building surround and
complicated underground infrastructure, the bottom up method for deep basement work
tall building is found not viable and cause more time spent merely contributed costly in
money value. Semi top down method is looks more advantage as solution.
In semi top down method, perimeter retaining wall structure is required at early stage.
Generally, diaphragm wall or contiguous bored pile as retaining wall structure is more
effective for deep ground. Temporary column usually at the same position of the
permanent column and the form of steel stanchions as to support the basement structure
is required to construct from the top level downward [9]. It always executed by
inserting the steel stanchion in bored pile while concrete is still in green. The steel
stanchion in bored pile is carried out at perimeter bay slab basement, as center portion
remain to follow bottom up method.
Figure 2.11 : Lateral force acting in deep basement
21
In actual design, there is lateral force induced by earth pressure, hydrostatic and
surcharge. The force acting on diaphragm wall is taken by slab as deep beam in
horizontal then transferred to vertical steel column. The vertical steel column shall be
designed in such away that able to eliminate the lateral force action. It is shown in
Figure 2.11
Figure 2.12 : Semi top down work in deep basement
Casting work is starting from perimeter bay ground slab level as to form diaphragm
action to support perimeter retaining structure, refer Figure 2.12. Excavation is
performed from center portion of building downward. The intermediate temporary strut
or bracing system is optionally constructed where it is required. The next below
basement is cast and excavation carried out similarly. The process is repeated until
reaching the required level at base formation where raft foundation, pile caps and
22
ground beams are constructed. The temporary column is encased and cast to form
permanent column. Temporary dewatering system is provision to keep site free from
underground water. The movement in horizontal and vertical is monitored using
instrumentation gauges. The center portion of basement is constructed upwards using
bottom up method. In general, there is no significant backfilling is required.
CHAPTER 3
METHODOLOGY
3.1 Introduction
A desk study is performed by establishment of data search methodology as
shown in Figure 3.1. A well planned flow chart is drawn up in expectation that the
requirements in study search will be no loop hole left out when search to be carried out
from a study project. Time frame is set up for 14 weeks made to complete the overall
study case from record compilation, assessment data, finding on analysis,
conclusion/suggestion and project report write up is considered adequate in time.
3.2 Project Case Study
A few tall projects with basement underground within Kuala Lumpur area have
been approached not only directly to main contractor and subcontractors on site but also
directly consulting the project Client and consultants. Most of responses and feedback
24
from them are good. However most of those tall buildings are found with basement
works have been earlier completed and documents compilation are inadequate for this
study case. Among the inadequacies are the availability of documents is limited in term
of authorization to access the compilation records, commitment and restricted approval
due to company regulation within their organization; Client, Consultants and
Contractors.
Figure 3.1 : Methodology flowchart of project study
Out of the projects approached, two projects are found have sufficient requirements for
this study case. The selected projects mentioned, are based on criteria that underground
basement work method meets the study case, accessibility and availability of project
25
data such as work methodology, photos, drawings, cost work and time planning from
the project itself and commitment from client, consultant and main
contractor/subcontractor.
CHAPTER 4
PROJECT 1 : BOTTOM UP METHOD IN DEEP BASEMENT WORK
4.1 Introduction
The project is located at Jalan Ampang, Kuala Lumpur, Malaysia. It comprises
3-storey basement which serves as underground parking area and 30-storey floors tower
block for mixed development of hotel, residential and office floor.
The site is originally refurbishment of petrol kiosk with flatten platform. Neighboring
buildings located adjacent to project, as shown in Figure 4.1, at west side is existing 6-
storey building and shop lot which foundations are supported on pile. At south-west
side is 43-storey building with 3-basement founded on pile foundation and at south side
is 38-storey building with 3-basement also founded on pile foundation. At north side is
open ground parking area and at east is public road.
The building footprint is 5,163.75m2. The depth of basement excavation varied from
13m to 17m. Owing to the variation in subsoil condition and cost consideration, a
27
combined retaining system is adopted. The combined retaining system included open
excavation with temporary closed berm slope protection using shotcreting, internal
horizontal strutting with inclined-struts-and berm systems to support the earth retaining
walls consisting of contiguous bored pile of size 750mm diameter and temporary sheet
pile.
Figure 4.1 : Layout plan of retaining system
28
4.2 Substructure Construction Planning Sequences
The site geologically lies in the Kenny Hill residual deposits overlying
Limestone Bedrock. A total of 12 number of borehole in soil investigation (SI) is
carried out to identify the soil profile of the site. Geotechnical engineer has identified
and confirmed that there is no limestone bedrock was encountered. In general, the site
soil stiffness increases with depth based on Standard Penetration Test (SPT) value
recorded from the SI. The raft foundation is adopted for the building. However, at
center of building which houses lift core area, integrated bored pile with raft foundation
is designed for construction.
The bottom up excavation for sub-structure basement is adopted by considering the
availability of local expertise in open excavation work in using fewer plants to operate.
The soil and structure behavior monitored to confirm the safe excavation works during
basement construction are assured. The site observational method proposed by Ikuta
et.al [10] as shown in Figure 4.2 is used to modify and optimize the retaining wall
system. It is used to revise and confirm the design assumption and to predict the precise
behaviour of the subsequent stages.
29
Figure 4.2 [10] : Site observation method chart
30
Figure 4.3 : Basement work planning in stages
The basement work is planned for construction in stages as shown in Figure 4.3. The
work methodologies approached are based on sequences of planning work as below.
a. Erection of contiguous bored pile
b. Foundation bored pile
c. Earth excavation
d. Instrumentation and monitoring
e. Raft Basement Construction
f. Erection of Strutting and Bracing
g. Construction basement floors to ground level
h. Backfilling with suitable material
31
4.3 Erection of Contiguous Bored Pile
Contiguous bored piles (CBP) retaining wall is adopted. The CBP construction
work is carried out along building perimeter boundary at location as shown in layout
plan in Figure 4.1. Progress work of CBP retaining wall is shown in Figure 4.4. The
permanent reinforced concrete skin wall is cast in-situ integrated to contiguous bored
pile as a better finish and water tight structure for basement area.
Figure 4.4 : Contiguous bored pile at perimeter site boundary
At the side of project which is parallel to open ground parking area and Jalan Tun
Razak, bare open excavation is carried out. However in restricted space area, a low
temporary cantilever wall is adopted during the basement excavation.
32
4.4 Foundation Bored Pile
Based on soil properties at lift core, bored pile foundation is recommended by
geotechnical engineer. It is integrated with thick raft foundation. The load at the area is
high compared with other portion. The design load consideration is induced by lateral
force as well as gravity load.
Figure 4.5 : Foundation bored pile in dry condition
The drilling work is carried out in dry hole, as shown in Figure 4.5. No bentonite agent
to strengthen soil wall in the hole is required. All piles at the area are designed mainly
in friction capacity more than end bearing capacity. The depth of piles from raft bottom
33
base is 6m and rock socket is not required. It is only 45 nos. of bored pile have been
installed as design requirement at lift core area.
4.5 Earth Excavation
The excavation work needs proper planning to avoid time waste which
contributing to cost and to control slope stabilization in safety aspect. It has been carried
out in stages as shown in Figure 4.6.
Figure 4.6 : Excavation work in stages
The access to and from site has been made in gentle slope to enable transporting earth
and sand carried out without disruption. Proper silt trap to discharge water out off site is
34
located at one place. A few temporary earth drain streams are adjusted to suite site
ground water condition to flow water to the silt trap.
As excavation proceeds further down, the contiguous bored piles retaining wall is
exposed further and left the upper part acting as cantilever. At the open cut area, the
slope is stabilized with cut berm as to follow design requirement. The run off water at
surface is protected from penetration into the slope by ensuring the exposed slope
covered up with shotcrete, otherwise failure due to erosion may occur. It is shown in
Figure 4.7.
Figure 4.7 : Exposed slope with shotcrete
During the excavation work, ground water is kept pumping out of the excavation area
by providing earth drain and sump. The location of silt trap sump and earth drainages
system is not fit at one place. It is flexible and subject to progress of excavation work as
shown in Figure 4.8.
35
Figure 4.8 : Progress of excavation work
Excavation is completed when it is carried out reaching to require level in both bottom
base of raft and lift pit. The base is then trimmed to proper required level, as shown in
Figure 4.9 and laid with lean concrete.
36
Figure 4.9 : Proper trimming work at base
4.6 Instrumentation and Monitoring
A comprehensive instrumentation and monitoring adopted in construction of
retaining wall is to ensure the performance of the retaining and basements structures as
envisaged in the design. Main important instrumentation is inclinometer. The typical
detail inclinometer is shown in Figure 4.10.
37
Figure 4.10 [8] : Typical installation details for inclinometer
A numbers of inclinometer are installed within the sheet pile behind retaining wall as
shown in Figure 4.11. It is to monitor retaining wall and ground movement. The
standpipe piezometers are installed behind the wall to monitor the groundwater level.
38
Figure 4.11: Installation Inclinometer behind wallperimeter bored pile
Data collected are verified to design assumption as to ensure that the effects of the
construction on adjoining structures are minimised. The soil and structure behaviour are
often monitored to confirm that the safety of excavation works during construction are
assured. There are advantages to use monitoring data to optimize the design with back-
analyses of excavation made during construction.
4.7 Raft Basement Construction
Reinforcement rebars are laid on lean concrete. Mechanical water pumps are
kept working 24 hours daily. The base is ensured free of underground water. The
39
sequence in basement casting should be given priority from the deepest area as shown
in Figure 4.12. Lift core area with lift pit sump is earlier cast, later it is used as sump to
cumulate underground water flow in and discharge off site.
Figure 4.12 : Rebar installation for raft base in progress
Since casting is to be carried out in bulk concrete, pump concrete is used. It is shown in
Figure 4.13. The output of concrete pump, based on site experience with normal site
congestion and traffic in Kuala Lumpur, is approximately 25m3/hour. For massive
quantity of concrete, low heat concrete is used. The slow hydration reaction in low heat
concrete is able to reduce and even eliminate crack.
40
Figure 4.13 : Raft foundation concreting work is being in progress
Curing is kept to minimum seven days using polystyrene sheet cover on top surface as
shown in Figure 4.14. At the expose side of raft foundation, chemical spraying curing
is applied. Temperature is measured in raft foundation using thermocouple at different
level of height. The differential temperature of raft foundation and ambient temperature
is monitored and it should within allowable limit as design code of practice
requirement.
41
Figure 4.14 : Raft foundation curing with polystyrene sheet cover on top
surface.
4.8 Erection of Strutting and Bracing
The inclined-struts-and-berm system is introduced and two rows of inclined
strutting are proposed. The support of inclined struts is designed as reinforced concrete
corbel and integrated with raft foundation [11]. The typical illustration shall be referred
to Figure 4.15.
42
Figure 4.15 : Typical installation of temporary inclined steel strutting structure with reinforced concrete corbel support integrated to raft foundation
The site is first excavated with temporary berm to foundation level for the construction
of raft foundation. After completion of the raft foundation, the first row of inclined prop
is installed followed by partial excavation at the earth berm for the installation of the
second level of strutting. The last part of the earth is removed upon the installation of
the lowest row prop. Figure 4.16 shows the constructions of inclined-struts-and-berm-
system and excavation work.
43
Figure 4.16 : Temporary strutting structure and excavation work in progress
The temporary strutting work is adopted to prop contiguous bored and sheet pile. It is
shown in Figure 4.17.
Figure 4.17 : Temporary strutting structure to support retaining wall (sheet pile and contiguous bored pile)
44
4.9 Construction Basement Floors to Ground Level
Construction of basements is carried out in stages. Work planning is more
concern on progress with required capacity of concrete volume which able to be
achieved. The sequences of casting until construction joint is planned to avoid
disruption and clashing of consuming tower on site, refer Figure 4.18. Any rebar
lapping provided shall be at engineer requirement and proper planning rebar bending
schedule able to reduce rebar waste simultaneously. Normally, core wall is maintained
constructed three to four floors above floor level.
Figure 4.18 : Basement floors in sequences casting work
The basement raft foundation shall be cast at required construction joint, refer Figure
4.19. Once the retaining wall integrated with basement floors completed with casting
45
and concrete is already achieved required strength, the temporary steel strutting and
bracing are dismantled. Any opening on wall or slab due to access of dismantled
strutting column or beam is then cast subsequently.
Figure 4.19 : Basement work at construction joint
4.10 Backfilling with Suitable Material
Upon completion of basement floor to ground floor, backfilling with suitable
earth is required to cover up gap between basement floor wall or retaining wall and
exposed slope. It is to form the base of road and drainage as shown in Figure 4.20.
46
Figure 4.20 : Gap between basement wall and open slope
The backfilling work shall be carried out in layers and compact properly to fill any void
and hole behind the wall as shown in Figure 4.21. Normally sand is used. Sand
backfilling method can be either with direct pour and compact using compactor or using
pressure pump and water then compact using compactor. The base formed shall be
monitored and any further minor settlement compared to required level shall be touch
up later.
47
Figure 4.21 : Backfilling to required level
CHAPTER 5
PROJECT 2 : SEMI TOP DOWN METHOD IN DEEP BASEMENT WORK
5.1 Introduction
The project is located at Jalan Tuanku Abdul Rahman, Kuala Lumpur, Malaysia.
It comprises 3-storey basement which serves as underground parking area and 30-storey
floors tower block for mixed development of hotel, office floor, training center and
business center.
The site is originally located 8-storey building which has been demolished.
Neighbouring buildings located adjacent to project, Figure 5.1 shows that at west side
is existing 26-storey building with 3-basement founded on pile foundation. At north-
west side is 27-storey building with 3-basement founded on pile foundation and at north
is 32-storey building with 3-basement also founded on pile foundation. At south side
and east side are public roads. There is an existing 600mm thick diaphragm wall facing
to existing 26-storey building at the west side.
49
Figure 5.1 : Layout plan of semi top down site
The building footprint is approximately trapezium shape at area of 4,925.43m2. The
depth of basement excavation varied from 12m to 17m. Since the building is to be built
at constraint area couple with limestone subsoil underneath, semi top down method is
adopted. The contiguous bored pile of size 750mm diameter is built surround perimeter
boundary attached to the existing diaphragm wall. The top down area is executed at
perimeter bay and at center is executed with bottom up method. Thus, bracing work and
backfilling work are able to be eliminated.
50
5.2 Basement Construction Planning Sequences
The site geologically lies in the Kenny Hill residual deposits overlying
Limestone Bedrock. Cavity area is expected within the site. Thus, every column point
has been earlier carried out with SI to identify soil properties and underground
limestone bedrock. Foundation is designed to use bored piles at specified depth based
on the SI integrated with 2.2m thick raft foundation
Figure 5.2 : Basement work planning in stages
The work sequences are shown in stages as Figure 5.2 above. The basement work is
carried out with site observational method as in Figure 4.2 to modify and optimize the
retaining wall system. It is used to revise and confirm the design assumption and to
predict the precise behaviour of the subsequent stages. The work methodologies in
semi top down method are listed below.
a. Erection of contiguous bored pile
b. Foundation bored pile
c. Pre-installation of column stanchion
d. Top down work
51
e. Excavation
f. Bottom up work
5.3 Contiguous Bored Pile
The perimeter wall is required surrounding the boundary. In choosing the type
of retaining scheme, the following factors are taken for considerations [12].
a. the site constraint
b. the condition of the soil/ground, total excavation depth and area.
c. The control on ground movement
d. The importance of water tight as the location of ground table is high.
e. The availability of machines and contractor’s experience in the local market to
construct the proposed structures
f. The construction feasibility, monitoring and control during construction
After considering the factors as listed above, contiguous bored pile (CBP) size 750mm
diameter is found feasible as the basement retaining system and adopted. Each CBP is
carried out from existing ground level and end length approximately 2m depth anchored
into sound rock. It is carried on perimeter boundary attached to existing diaphragm wall
as shown in Figure 5.3.
52
Figure 5.3 : Contiguous bored pile work in progress
CBP are cut to required level with reinforcement rebar, as shown in Figure 5.4, are left
protruded. Capping beam is constructed on top of CBP to cap all CBPs together.
53
Figure 5.4 : Cut off contiguous bored pile to required level
5.4 Foundation Bored Pile
In preliminary soil investigation (SI) and history of adjacent building
development in previous work, it is recorded that limestone area is laid within range of
cavity underground. Geotechnical engineer has advised that every column foundation
should have proper SI to be carried out on column location directly. There are five SI
machineries have mobilized to site area for SI works. The intensive SI works, as shown
in Figure 5.5, have been carried out prior bored pile work can take placed. The record,
54
analysis and result of the SI are used to finalize the length of bored pile should be bored.
Each completed SI hole is then grouted up to original ground level.
Figure 5.5 : Soil investigation (SI) works are being in progress at each column position.
The varies bored pile ranging of 1000mm φ to 1800mm φ are designed based on
column load capacity. It needs to be rock socketed at minimum total length of 7 x pile
diameter. The pile lengths are varies from 35m depth to 47m depth from ground
surface. The ground water is recorded at average of 6m to 10m depth from existing
ground level. Bored pile works are carried out in wet hole, as shown in Figure 5.6.
Each hole is required temporary steel casing to be used for 12m depth. Bentonite to
strengthen soil wall in the hole is need to be used.
55
Figure 5.6 : Lowering down rebar cage in wet hole bored pile
A total of four bored pile machines with two lifting cranes are used in this work. When
bored hole completed, the reinforcement rebar cage is lower down and it is ready for
concreting. Casting work is carried out at night time. Concrete tremie II is used for
underground concreting in presence of underground water. The cut off pile level is
measured to projected 1000mm above raft base.
56
5.5 Pre-installed Column Stanchion
Steel used as stanchion column in this project is universal column (UC). In
design, the column stanchion is analyzed on the capacity to withstand primary
horizontal and vertical loads during excavation works. Most of the steel column is
installed at column point and later will act also as permanent column.
Figure 5.7 : Pre-installed steel stanchion column in bored pile
The stanchion installation method is usually selected by the piling contractor. The
method adopted is based on the installation depth, size of stanchion and size of bored
pile [13]. The pre-concreting method is used in this project. The sequence installation of
steel stanchion column in bored pile is illustrated in Figure 5.7 above. In this method,
steel stanchion is installed after completion of drilling work and lowering of pile
reinforcement. Then, concrete is poured until cut off pile level. The guide frame located
on top casing of bored is used to position steel stanchion vertically. It is important in
achieving positional accuracy.
57
5.6 Top Down Work
The excavation is carried out to required level for scaffolds stand on ground
base to support ground beam and slab formwork, as shown in Figure 5.8. The protruded
stanchion column is ensured securely joint to floor slab by providing welded square
steel plate. The slab reinforcement is lapped on top and bottom of the steel plate. At
steel stanchion column, rebar is welded with allowable lapping length into slab.
Figure 5.8 : Ground floor formwork in progress
Excavation is carried out simultaneously to lower basement from center area. The
disturbance to cast area should be definitely avoided. Once, the cast ground floor has
sufficient concrete strength, the formwork is dismantled. The construction of top down
is carried out at the perimeter building where the area is pre-installed with steel
stanchion. Column with steel stanchion used as permanent column, need to properly
58
clean from soil. The reinforcement rebar using mechanical coupler is used to joint both
top and bottom ends, refer Figure 5.9. Later, formwork is fabricated and the column is
cast as usual as in normal practice.
Figure 5.9 : Top down work in progress
The basement excavation work is carefully carried out. At early stage, heavy excavators
are operating from ground slab area, as shown in Figure 5.10. As such, the perimeter
slab is designed to take loads of accommodating heavy machineries and trucks on it.
The slab thickening and more reinforcement rebar than normal are among parameter
required in the slab and beam during construction period which is designed as
permanent element. The exposed steel stanchion column should be cleaned and free
from any agent which protected concrete from bonding to it.
59
Figure 5.10 : Excavation work to expose pre-installed steel stanchion column
As the excavation has to go down deeper and deeper, excavators required for excavation
are directly located on basement area. In this project as shown in Figure 5.11, three
excavators are placed at the basement for ground excavation work. From the open area,
the excavator needs to enter the underneath top down area which completed with cast
slab and beam for earth excavation work. The tendency of excavator arm to hit beam
and slab soffit at the area is very large. The work has to be performed in safely and
carefully manner. When the excavation reached to second basement area, ground water
starts to come out from the ground. The temporary of earth drains and sump are needed
to be established immediately. Mechanical pumps at sufficient capacity are provided at
sump area. Any contamination in water should be filter through silt trap. As authority
requirement, clean water is discharged out of area into the nearby surface drain to the
river.
60
Figure 5.11 : Excavation work to formation level carried out at center of building downward.
One excavator, operating from ground slab is accommodated with long arm shover. It
has to take earth from the bottom basement and load into the truck at ground slab area.
The process of excavation is continuously carried out until all earth have been
excavated to form raft base at required level
5.7 Floor Casting and Top Down Work
The floor casting is identified by dividing the area into zones. Each zone is
terminated at pre-installed steel stanchion column by forming construction joint. The
61
concrete of each zone is ensured adequate to be handled for approximately 6 to 8 hours
per casting activity at night time. Otherwise construction joint has to be immediately
rescheduled form for the next casting work.
Figure 5.12 : Top view of top down work at perimeter building
As shown in Figure 5.12, all perimeter zone areas from ground level downward to raft
foundation are carried using top down method. No bottom up structure is designed to be
simultaneously constructed on perimeter area during the top down work in this project.
The column at top down area has been analyzed and designed to execute loading
induced in ground floor to basement activity only.
62
5.8 Foundation Base Casting and Bottom Up Work
At center area of building, once the excavation has reached raft base, lean
concrete is laid to make working area neat and clean for reinforcement rebar work.
Ground water is avoided to enter the working area by ensuring sump is constructed at
nearby area. Temporary earth drain is built and ground water is ensured flow along it by
gravity into to the sump. The water is discharged out of site using mechanical pumps
which are kept running continuously.
Figure 5.13 : Bottom up work at center of building
As shown in Figure 5.13, rebar work for the raft foundation at bottom up area is
fabricated until construction joint. The special joint for raft base is designed to have
water stop. The jointing method of water stop at the area is carried out according with
63
specialist advice and follow technical requirement from manufacturer. Reinforcement
rebar is ensured left spanning outside from face of construction joint area at required
lapping length for subsequent casting. Formwork is fabricated at construction joint face
in both vertical and horizontal alignment props. The strengthening to the formwork prop
is required whenever raft depth cast is too high. However, in this project, the thickness
of raft 2.2m is considered normal and generally use in construction practice in
Malaysia.
Figure 5.14 : Bottom up area with basement raft work in progress
At columns point where pile foundations are used, lapping from bored pile
reinforcement rebar with sufficient length is anchored into raft base. Beams are cast
64
homogeneously with the raft and also act as tie beams spanning from column to
column, as shown in Figure 5.14. At slab area, since the thickness of raft is 2.2m, the
top rebar is required to hold in its upper position on support rebar chair which specially
designed to ‘U’ shape. Concreting in massive quantity is continuously cast using pump
method. It is properly poured in order to avoid occurrence of cold joint.
Figure 5.15 : Bottom up work for center building structure
Upon completion of raft foundation at lowest base, columns, shear walls, lift core walls
and skin wall at perimeter building which located at basements are cast bottom up. As
normal bottom up working activity in vertical elements, reinforcement rebar are
installed to its position then formwork is fabricated to required size. In this project,
65
since it is located in town area, casting is inevitably carried out mainly at night time.
The process of bottom up method at the center portion of this project is carried out until
ground level and further upper for superstructure work until roof level as shown in
Figure 5.15.
CHAPTER 6
DATA ANALYSIS
6.1 Introduction
All data collected from both of bottom up excavation method and semi top down
method on field study required for objective of this project report are properly
compiled. The proper attention are given to followings aspects in view of construction
considerations with sound understanding in design of underground work,
a) Tabulation of parameter activities
b) Design consideration should take place during activity work
c) Time and cost taken to complete each activity.
67
6.2 Parameter Activities
The deep excavation work in underground basement has been mostly influenced
by work methodology itself. Data are collected by recording all circumstances incurred
during the work. The comments and advices from both consultant and contractor are
information encountered during work being carried out. It needs to be recorded and
compared with earlier predictable element during design and planning work. The
tabulation parameter of bottom up construction method is listed in Table 6.1,
meanwhile semi top down method is in Table 6.2
6.3 Design Parameter
The site observation method adopted in both basement works is used by
geotechnical and structural engineer to analyse result on field work. The analysed
results are then used to satisfy the assumptions envisaged in design office, otherwise the
revised design is required immediately.
The summary of basement work activity from both methods is tabulated. The awareness
of the activity monitoring in any circumstances has enabled both geotechnical and
structural designers classified what to do rather than depends solely on contractor trial
on error work on site.
In actual site work, the excavation work caused most others parameter changes
simultaneously in presence with underground water. Ground movement may contribute
vertical and horizontal deformation in retaining structure element. It causes more
problem arises when the next course of action late to resolve. The forecast problem such
68
as slope erosion and collapse should be monitored closely by Resident Engineer. With
the presence of tabulated parameter as shown in Table 6.3, Resident Engineers are
easily identified the right person to consult, subsequently coordination with all parties
concerned is able to hold in order to resolve whatever matter arised smoothly.
69
Table 6.1 : Parameter in bottom up excavation method in underground basement work
Item
Activity
Description
Comments
1. Foundation Bored Pile and Raft Base
• Pile foundation integrated with raft foundation based on underground soil properties to reduce differential settlement.
2. Retaining structure Contiguous bored pile
and reinforced concrete skin wall
• Form part of building structure at parameter building adjacent to existing building from basement up to ground floor.
• 3. Excavation Open excavation with
shotcrete slope protection. At localized area with stiff slope need temporary sheet pile.
• To avoid excessive erosion and collapse to exposed slope. Sheet pile installed at toe slope by maintaining open cut slope with shotrete protection on exposed surface.
4. Dewatering work Temporary silt trap and earth drainage/sump
• To discharge underground water from basement working area
• To ensure base is free of water at concreting work area.
5. Strutting and Bracing
Temporary work propping to retaining wall structure.
• Acting as temporary structure and dismantle upon completion of basement.
• To ensure retaining wall structure capable to retain lateral forces due to adjacent building load, hydrostatic pressure and surcharge during excavation work.
6. Instrumentations Inclinometer,
piezometer, and tiltmeter
• To monitor the horizontally, verticality structure levelling and underground water table during construction work
7. Concreting Basement structure concreting work
• To cast all column, beam, slab, core wall, skin wall etc which at basement area
• 8. Backfilling Backfilling with
suitable material • To cover up all open excavation at
exposed slope to form base for road and drainage work
70
Table 6.2 : Parameter in semi top down method in underground basement work
Item
Activity
Description
Comments
1. Foundation Bored Pile and Raft Base
• Pile foundation integrated with raft foundation based on underground soil properties to reduce differential settlement.
2. Retaining structure Contiguous bored pile
and reinforced concrete skin wall
• Form part of building structure at parameter building adjacent to existing building from basement up to ground floor.
3. Stanchion column
Pre-installed steel column
• Install during piling foundation work in bored pile and formed as permanent column.
• Able to take vertical and horizontal load by ensuring basement floor slab acting as diaphragm beam transferred load to it during basement work
4. Excavation Basement excavation
• Excavation performed from the
center of building downward to basement.
5. Dewatering work Temporary silt trap and
earth drainage/sump
• To discharge underground water from basement working area
• To ensure base is free of water at concreting work area.
6. Instrumentations Inclinometer,
piezometer, and tiltmeter
• To monitor the horizontally, verticality structure levelling and underground water table during excavation work
7. Concreting Basement structure
concreting work • To cast all column, beam, slab, core
wall, skin wall etc which at basement area
71
Table 6.3
: Pa
ram
eter
des
igns
infl
uenc
ed in
bot
tom
up
and
sem
i top
dow
n m
etho
d of
und
ergr
ound
bas
emen
t wor
k
STRUCTURAL DESIGN
INVOLVEMENT
Item
ACTIVITY
REMARKS
BUM
STDM
STEEL
R.C
GEO.
1.
Foun
datio
n
•
Dep
end
on s
oil p
rope
rtie
s an
d de
sign
ed to
tran
smit
load
s in
to h
ard
stra
ta u
nder
neat
h.
√ √
√
√
2.
Ret
aini
ng
wal
l st
ruct
ure
•
Tak
e la
tera
l and
ver
tical
for
ces.
Des
igne
d to
cou
nter
act
load
s in
duce
d fr
om n
eigh
bour
ings
bui
ldin
gs a
nd
surc
harg
e.
√ √
√ √
√
3.
Stan
chio
n st
eel
colu
mn
•
desi
gned
to w
iths
tand
ver
tical
and
hor
izon
tal f
orce
at
prel
imin
ary
wor
k an
d a
ncho
rage
into
pile
fou
ndat
ion.
√
√
4.
Ear
th e
xcav
atio
n
•
desi
gned
at a
llow
able
slo
pe a
nd b
erm
gra
dien
t.
√ √
√
5.
Slop
e pr
otec
tion/
shot
cret
e
•
desi
gned
to s
tabi
lise
slop
e fr
om e
rosi
on a
nd c
olla
pse.
√
√
6.
Tem
pora
ry
stru
ttin
g/br
acin
g
•
stee
l st
ruct
ure
to p
rop
reta
inin
g w
all
form
ed b
y sh
eet
pile
or
cont
iguo
us b
ored
pile
.
√
√
√
7.
Inst
rum
enta
tions
•
site
m
onito
ring
ga
uges
to
m
onit
or
defo
rmat
ion
in
vert
ical
and
hor
izon
tal d
urin
g ex
cava
tion
wor
k.
√ √
√
8.
Tem
pora
ry
dew
ater
ing
syst
em
•
to
ensu
re
site
fr
ee
from
un
derg
roun
d w
ater
an
d
infl
uenc
e gr
ound
set
tlem
ent.
√
√
√
9.
Bac
kfil
ling
wit
h su
itabl
e m
ater
ial
•
to f
orm
bas
e fo
r ro
ad,
drai
nage
and
gro
und
area
with
al
low
able
deg
ree
of c
ompa
ctio
n.
√
√
√ =
app
licab
le, B
UM
= B
otto
m U
p M
etho
d, S
TD
M =
Sem
i Top
Dow
n M
etho
d, R
.C =
Rei
nfor
ced
Con
cret
e, G
EO
= G
eote
chni
cal
72
6.4 Time and Cost Completion Activity
In both methods, refer Table 6.4 and Table 6.5, costs at completion of basement
work are based on specialist price which mean from direct local sub-contractors of these
two projects. The main contract cost of project is not viable to consider since Project 1
is under private development meanwhile Project 2 is under government development.
Thus it is not under the same development case.
Pile foundation activity in both projects should not be considered influenced the
basement work activity in construction stages as it is able to be carried out
independently. Determination of the use bored pile as foundation is designed solely
based on soil properties. It is to transfer building loads vertically to hard strata
underneath.
In Project 1 which basement works are carried out by bottom up method, the building
foundation is designed as raft foundation. However, pile foundation of 45 nos. bored
pile is designed to support core wall which located at center of building. Core wall is
designed as main braced element in tall building as to take both forces from lateral wind
load and vertical (gravity) building load.
By referring Table 6.4, with absence of pile foundation activity, the basement work
completion is still remains at 392 days. Hence, total completion cost should be
00.800,081,900.000,56500.800.646,9 RMRMRM =− . The footprint area Project 1 is
275.163,5 m . Thus, based on working area for three stories basement work, the cost rate
is 22
76.758,1
75.163,5
00.800,080,9
m
RM
m
RM=
Meanwhile in Project 2 which basement works are carried out by semi top down
method, the pile foundation is designed as building foundation. As to simulate the
costing of basement work, the costing of Project 2 by referring Table 6.5, should be
73
assessed in absence of pile foundation. The time still remains at 303 days to complete
the basement work. Hence, total completion cost is
00.500,668,700.000,750,200.500,418,10 RMRMRM =− . The footprint area Project 2
is 243.925,4 m . Based on working area for three stories basement, the cost rate is
22
92.556,1
43.925,4
00.500,668,7
m
RM
m
RM=
Figure 6.1 : Actual cost and time completion for semi top down method and bottom up method without pile foundation
The analysis of cost and time of both methods is tracked from operations in Table 6.4
and Table 6.5. It is superimposed into one graph as shown in Figure 6.1. From the
graph, at the first of starting project until 3.8 months, cost operation of both methods is
likely same. However for the period of 3.8 months to 7 months, the operation cost of
74
semi top down method is seems less than bottom up method. Contrary, at the 7 months
towards 10 months i.e at the end of completion progress of semi top down method, cost
operation of semi top down method is seen more than cost operation of bottom up
method. However, semi top down method is finished three months earlier than bottom
up methods with less cost.
75
Table 6.4
: A
ctua
l wor
k co
mpl
etio
n of
bot
tom
up
met
hod
for
Proj
ect 1
76
Table 6.5
: A
ctua
l wor
k co
mpl
etio
n of
sem
i top
dow
n m
etho
d fo
r Pr
ojec
t 2
CHAPTER 7
CONCLUSION AND SUGGESTION
7.1 Introduction
In tall building with underground basement, completion on time is one critical
item vital to the owner, the consultants and the contractor. Close coordination and
cooperation between all parties concerned, together with the use of latest technique and
a reliable and diligent workforce had ensured the completion of the building on
schedule.
7.2 Conclusion
The justification for the both of semi top down and bottom up methods has been
made in both 30-storey tall building with three basements construction for Project 2
78
which is commenced one year late from Project 1 based on field compiled data and
analysis result.
Thus, the followings have been concluded,
1. The work methodology and activity on site are depend on construction
parameter which influenced both completion cost and time both method of
basement works.
2. Semi top down method requires simultaneously preinstalled column
stanchion and retaining wall element.
3. Elimination of strutting structure, earth backfilling work and shorten time in
excavation work due to reduction in excavation volume, is seems influenced
semi top down method completed work earlier with cost saving compared
with bottom up method.
Eventhough, the cost rates in both project activities are based on present time of price
from local expertise, semi top down method has given more benefit in term of reduction
construction time and competitive cost saving. However performance in each activity is
solely depend on reliable local expertise with availability of modern equipment and
machinery to carry out the underground basement work.
7.3 Suggestion
.
In tall building with underground basement, the effectiveness and suitably
method of construction to carry out basement work is needed to study from a few
similar projects within same type of geological area. The construction cost budget in
79
three basements underground of tall building to be built is related to time completion of
each project which mainly contributed by method in work implementation. In feasibility
study, cost and time referred should be based on records of completed project within the
same conceptual designed and work method.
Based on field study which is carried out from these two projects, the rate of
construction time and rate cost at subcontractor price is suggested for preliminaries
study in three basements work of tall building could be summarized as below,
1. Rate of completion time for semi top down method is 16.3m2/day and for bottom
up method is 13.2m2/day.
2. Rate of construction cost at sub-contractor price for semi top down method is RM
1,556.92/m2 and for bottom up method is RM 1,758.76/m2.
The above suggestion is exclusive of pile foundation contribution.
80
References :
1. Don, R. (1991), Cost Estimating For underground Structures. R.S.Sinha (Ed.).
Underground Structures Design and Construction (pp.480-515). U.S : Elsevier
Science Publishers B.V.
2. Gue, S.S. & Tan.Y.C. (1998), Design and Construction Considerations For Deep
Excavation. SSP Geotechnics Sdn. Bhd, Selangor Darul Ehsan, Malaysia. from
www.sspsb.com.my.
3. Narong Thasnanipan, Aung Wing Maung & Pornpot Tangseng (2006), Important of
Temporary Works and Construction Sequence – Lessons from Collapse of an Inlet
Shaft During Excavation, International Symposium on Underground Exacavation
and Tunnelling, 2-4 February 2006, Bangkok, Thailand from
http://www.itaaites.org/cms/fileadmin/filemounts/general/pdf/ItaAssociation/Organi
sation/Members/MemberNations/Thailand/T-31Thasnanipan.pdf.
4. Craig, R.F. (1983), Soil Mechanics (3rd Ed.), United Kingdom:Van Nostrand
Reinhold.
5. Tomlinson, M.J. (1995), Foundation Design and Construction (6th. Ed.), United
Kingdom: Longman.
6. Harris, F. (1994), Modern Construction and Ground Engineering Equipment and
Methods (2nd Edition), United Kingdom:Longman.
7. Bell, F.G. (2004), Engineering Geology and Construction, London : Spon Press.
8. Kong, S.K. (2003), Application of Geotechnical Instrument For Safety Control in
Basement Construction works, Moh and Associated (S) Pte. Ltd, Singapore from
www.maa.com.tw/common/publications/2000/2000-063.pdf
9. Wong, W. M. (2008), A Review on Common Technology Employed for The
Construction of Building in Hong Kong, Division of Building Science and
Technology, City University of Hong Kong from
Personel.cityu.edu.hk/~bswmwong/pp/cbpaper/cbright.html.
10. Ikuta, Y., Marouka, M., Aoki, M. And Sato, E. (1994), Application of The
Observational Method to A deep Basement Excavation Using Top-Down Method,
Geotechnique 44, No.4, pp 655-664.
81
11. Lim, C.S., Tan, S.M. & Hiew, L.C. (1999), A Basement Excavation Using Tie Back,
Internal Horizontal Strutting and Inclined-struts-and–berm system, SSP.
Geotechnics Sdn. Bhd, Selangor Darul Ehsan, Malaysia from www.sspsb.com.my
12. Sofiana Talha (2000), Deformation Behaviour of a Retaining Wall for a Deep
Basement Excavation with Semi-Top Down Method, SSP Geotechnics Sdn. Bhd,
Selangor Darul Ehsan, Malaysia from www.sspsb.com.my.
13. Narong Thasnanipan, Aung Wing Maung & Zaw Zaw Aye (2000), Practical
Installation of Stanchion For Top Down Construction in Bangkok Subsoil,
Development in Geotechnical Engineering, Thailand, pp 337-346 from
www.seafco.co.th/RDpaper/BP-10.pdf.
