Basement

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BASEMENT

DCQ3043 CONSTRUCTION

TECHNOLOGY 3

TOPIC: BASEMENT

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Syllabus Content :

2.1 Understand the construction of basement.

2.1.1 Explain methods of excavation for the construction of

deep and huge basement.

2.1.2 Explain usage of waterproofing system in basement

construction.

2.1.3 Identify clauses in Uniform Building By-Laws for

basement construction.

2.1.4 Describe construction of earthwork support system.

2.1.5 Justify the purpose of earthwork support system.

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BASEMENT

Definitions:

1. A storey with a floor that at

some point is

more than 1.2m

below the highest level of

ground adjacent to the outside

wall.

2. A storey of a building

constructed wholly or partly

below ground level

exposed to

soil, water and/or water

vapour pressure.

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Types of Basement:

1. Semi-basement

Single storey with only one, two or three

wall fully or partially below ground

level.

2. Residential basement

A shallow or semi-basement providing

space for storage and/or accommodation,

associated with housing.

3. Shallow basement

Not more than one storey wholly below

ground level.

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Types of Basement (cont’d):

4. Deep basement

More than one storey wholly

below ground level.

5. Cellar basement

Used for storage, heating plant

and for purpose other than

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Basement Requirements:



Primary functional requirements

of basement /wall below ground

may be summarized as follows:

1. Structural stability

2. Durability

3. Moisture exclusion

4. Buildability

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Basement Grades:



Basements are graded according to BS8102 depending on their specific

performance requirements.

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METHOD OF EXCAVATION FOR THE

CONSTRUCTION OF DEEP & HUGE BASEMENT

Classification of Excavation:

Excavation may be classified in the following manner:

1. Shallow

excavation –

up to 1.5m deep.

2. Medium

excavation –

1.5m to 3.0m deep.

3. Deep

excavation –

over 3.0m deep

.

Factors that Affect Excavation Work:

Method of excavation depends on:

1. Nature of the subsoil

- to determine the type of plant or hand tools and the type

of earthwork supports.

2. Purpose of the excavation

- to determine the sizes, depth and volume of

excavation.

3. Presence of ground water

- to determine dewatering techniques.

4. Location and surrounding condition

- needs permit from local authorities such

as JKR, DBKL, etc. and impose certain restrictions and precautions.

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METHOD OF EXCAVATION FOR THE

CONSTRUCTION OF DEEP & HUGE BASEMENT

Method of Excavation:

There are 3 method of excavation for the construction of Deep and

Huge Basement that can be used:

1. Excavation with sloping sides / Open excavation.

2. Excavation with temporary support.

3. Excavation with permanent embedded retaining walls to deep

basements.

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1. Excavation with sloping sides /

Open excavation



Excavation basement on an open site can

be carried out by cutting the perimeter

back to the natural angle of repose of the

soil.



This method required sufficient site space

around for the over excavation and to

allow for the creation of a stable slope to

sides of the excavation.



No temporary or permanent earth support

so saving the cost of excavation but

increase in volume of back filling.

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2. Excavation with temporary support



Suitable where the space around the

excavation is insufficient for open excavation.



Very economical compare with permanent

support such as contiguous piles, secant piles

or diaphragm walls.



Temporary support elements such as

Steel

Sheet Piles, Cross-lot bracing, Rakers and

Tiebacks.



Temporary support are placed within the

ground around the perimeter of the intended

area to be excavated.



When the earth is done excavate, the void will

become the basement area.



Permanent basement walls are than

constructed and after completion the

temporary support is removed.

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Temporary Support

Elements:-a) Steel Sheet Pile

 Sheet piling is an earth retention and excavation support technique that retains soil, using steel sheet sections with

interlocking edges.

 The interlocked sheet piles reduced groundwater inflow.

 Vibratory hammers are used to install sheet piles. If soils are too hard or dense, an impact hammer can be used to

complete the installation. At certain sites where vibrations are a concern, the sheets can be hydraulically pushed into the

ground.

 Sheet piles are also a sustainable option since recycled steel is used in their

construction, and the piles can often be reused.

Hydraulic vibratory hammer

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b) Cross-lot Bracing

 Cross-lot bracing using steel sheet piles or I-beam as waler that are driven into the earth.

 As the earth is excavated down around the sheeting (waler), tiers of horizontal bracing struts, usually of steel are added to support walers, which are beams that span across the face of the sheeting.

 Where the excavation is too wide for cross-lot bracing, sloping rakers are used instead, bearing against heel blocks or other temporary footings.

Steel sheet pile or I-beam

Horizontal bracing

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A closer view of the cross-lot bracing supporting excavation.

Horizontal Bracing Support

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c) Raker

 For very wide excavations, raker bracing is used.

 The support for the rakers are installed at the bottom of the excavation.

 Construction of the soil support and removal of the remainder of the excavation then begins.

 The bottom ends of the rakers are braced against the central part of the building foundation slab.

 The excavation was carried to full depth at the center first so that the foundation slab could be placed.

 Prior to installation of the rakers, the lower part of the slurry trench concrete wall was supported by an earth berm.  The earth berm remains at the far side of

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d) Tiebacks

 To minimize wall movement and ground settlement, tieback anchors are designed to achieve the highest stiffness.

 Tieback capacity depends on the vertical and horizontal spacing of anchors and on surcharge conditions.

 Typical tieback spacing ranges from 2m to 4m in the vertical, and from 1.5m to 4.5m in the

horizontal direction.

 First drilling a hole with an auger and then placing a bar (tendon) in the hole, concrete is then poured in the hole and the connection with wall is made.

 Different types of augers are used to drill the tieback holes. The choice of the drilling method depends on the soil/rock conditions on the site.  Drilling should be done carefully since

inadequate procedures can cause significant soil losses.

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3. Excavation with permanent embedded

retaining walls to deep basement



The construction of deep basement walls

can be costly if traditional excavation and

construction techniques are used.



Limitation on access to most commercials

sites also restrict the possibility of such an

approach.



The most common options available for the

formation of deep basement wall

(permanent embedded retaining walls) are:

a)

Contiguous piles

b)

Secant piles

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• Piles are installed at centers generally 150mm greater

than their diameter therefore leaving gaps in the structural

wall where soil is exposed during excavation.

• This option is suitable where the retained soil is usually

firm to stiff (not generally granular) and where the

ground water table is below the level of the maximum

excavation.

• This is the most economic option and normally the fastest

method to construct.

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b) Secant Pile RW

• Similar to the contiguous bored pile wall but the gap

between piles is filled with an unreinforced

cement/bentonite mix (1 to 2N/mm2) for the hard/soft

wall and weak concrete (in the order of 10N/mm2) for

the hard/firm wall.

• Construction is carried out by installing the primary piles

(A) and then the secondary piles (B) are formed in

reinforced concrete, cutting into the primary piles.

• By using this form of construction the ingress of water to

any subsequent excavation can be substantially reduced.

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c) Diaphragm Walling



This method need to construct a R.C. retaining wall along the area

of work.



The wall is designed to reach very great depth and sequence of

work includes:

a) Construct a guide wall

b) Excavation of the trench using bentonite slurry

c) Placement of reinforcements and pumped out bentonite slurry

d) Concrete casting

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• The excavation of the deep trenches for segments of the

diaphragm wall can be achieved by means of hydraulic

grabs, by means of hydro fraise or by means of rotary

auguring.

• Overlapping holes are drilled to form a wall section as

opposed to individual pile holes.

• Traditionally, as the spoil is removed from the excavation

it is replaced by material called ‘bentonite’ slurry.

• This can be used to support the walls of the excavation

shaft in order to prevent collapse as the excavation

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• Once the excavation of a particular section of walling is

complete, a reinforcement cage may be placed into the

slurry and concrete placed using a tremie pipe.

• Diaphragm walls of 450mm to 1.0m thick can be formed

by hydraulic grabs and hydro fraise, whereas thicknesses

of up to 1.50m can be achieved using rotary methods.

• Diaphragm walls can be

constructed to depths of up to

50.00m.

• Once the diaphragm walls are

placed and completed, the deep

excavation work can proceed

virtually unobstructed.

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• Some degree of lateral support is normally required to

resist the bending stresses that are set up by soil and

water pressure as before since a diaphragm wall is not

normally intended to act as a pure retaining wall.

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Installation of rebar cage and concreting of panel

Excavation of panel and installation of rebar cage

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Waterproofing Work



Apart from the structural design of

basement walls and floor,

waterproofing presents the greatest

problem in basement construction.



There are 3 types of basement wall

structure:

1. Tanked / Membranes

2. Waterproof / Monolithic

Structures

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Tanked / Membranes:



Tanked / Tanking / Membranes is a thin

material placed either on the external or

internal face of a basement wall or floor to

provide the resistance to passage of moisture

to the inside of the basement.



Membrane material can be applied

externally (external tanking) during

construction process meanwhile membrane

also can be applied to the interior face of the

walls after construction (internal tanking).



Membrane materials such as fibre-reinforced

bituminous felt, polythene sheet,

polyisobutylene plastic, epoxy resin

compounds, bituminous compounds and

mastic asphalt.

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Mastic Asphalt Tanking

Asphalt in tanking work is laid in 3 coats to the total thickness of not less than 30mm on horizontal surfaces and not less than 20mm on vertical faces. All internal angles (angle fillet) are reinforced by means of a fillet 50mm on the face, formed in 2 coats.

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Waterproof / Monolithic Structures:



Basement of dense reinforced concrete

using impervious aggregates for the wall

and floor to form the barrier to water

penetration.



Its considered as ‘structurally integrated

protection’ where the waterproofing is

provided by the structural wall & floor

themselves.



Shrinkage cracking can largely be

controlled by forming construction

joints at regular intervals.



Structural joints normally incorporate

water stops made from materials such as

neoprene, rubber water bar, PVC etc.

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Drained / Drained Cavities:



Cavity drain structures make allowance for

the small amount of water that may pass

through the external wall.



The basement is constructed with 2 wall

forming a void between the external and

internal wall and cavity is formed in the

walls around the basement and below the

floor.



Traditionally cavities were formed with

floor tiles which created void and two

separate wall of masonry walling.



Any water that penetrates through the

external wall or floor is guided to drainage

channels to a sump pit and remove by

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In-situ Concrete:

Construct the basement using in-situ reinforced concrete and tradition

formwork system:



The basement structure can be constructed upon the completion of the

excavation with the basement pit properly formed and supported.



Usually this is done in a bottom-up arrangement using in-situ reinforced

concrete formed by traditional timber formwork.



However, all the works are to be done in the congested underground

environment inside the basement pit with a lot of lateral supporting

frame and work in confined space.



Special attention including accurate construction planning and spatial

design to allow room for the erection of the formwork as well as for the

placing in of the required materials and equipments, safe access etc.

should be provided.

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2. Prepare perimeter walling

5. Complete excavation work 6. Waterproofing at basement

9. Concreting wall & column 10. Placing grd flr reinf. 1. Before start of work

7. Placing basement flr reinf.

3. Bulk excavation 4. Excavation almost complete

8. Concreting basement floor

11. Concreting ground floor 12. Finish work

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Sequence of Constructing Huge Basement

1. Driven sheet pile & bulk excavation

2. Excavation, ramming bottom of excavation & bracing earthwork support

3. Lean concrete & horizontal tanking

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7. Reinforcement & waterproofing 8. Reiforcement

10. Preparing formwork for wall 11. Wall complete

9. Concreting

12. Formwork & reinforcement for next level

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13. Constructing the superstructure 14. Ditto

16. Constructing the superstructure till it gets finished

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CLAUSES IN UNIFORM BUILDING BY-LAWS FOR

BASEMENT CONSTRUCTION

72. (1) In the design of basement wall and similar underground

structures, provision shall be made for the lateral pressure of

adjacent soil due allowance being made for possible surcharge

from fixed on moving loads.

(2) When a portion, or the whole of the adjacent soil in below a

free water surface, computations shall be nased on the weight

of the soil diminished by bouyancy plus full hydrostatic

pressure.

(3) In the design of basement floors and similar structures

underground, the upward pressure of water, if any, shall be

taken as the full hydrostatic pressure applied over the entire

area.

(4) The hydrostatic head shall be measured from the underside of

the construction.

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CONSTRUCTION OF EARTHWORK SUPPORT SYSTEM



When applying the principles of

permanent embedded retaining

walls, two common construction of

earthwork support system, there are:

1. Bottom-up Construction

2. Top-down Construction

1. Bottom-up Construction



Figure shown the sequence of

operation where the diaphragm

walls formed using bentonite.



Retaining walls can from

contiguous pile, secant pile and steel

sheet pile.

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Bottom-up Construction (cont’d)



First stage in this process is to form perimeter walls.



This will become the structural walls of the basement.



Bulk excavation then take place to the desired depth (lower level

of basement).



The next stage is to form sub-structure such as foundation,

column, basement floor up to super-structure as work proceeds.



Advantages using Bottom-up Construction Method are:

a) Speed construction

b) Save cost

c) Stability of the ground around

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Construction of basement using Bottom-up approach

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The overall excavation and lateral support system for a typical large-scale

basement construction project (with cut-off wall on the sides, lateral supporting frame and other temporary

work stations/platform)

Excavation carried out using excavator and rock breaker

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2. Top-down Construction



Top-down construction attempts to

make use of the perimeter elements

of the construction works to

provide rigidity and bracing against

loadings from the ground.



Figure shown the sequence of

operations for top-down

construction.



First stage the formation of the

permanent retaining walls to the

perimeter of the basement area.



Retaining walls can from either

contiguous pile, secant pile or

diaphragm wall.

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Top-down Construction (cont’d)



Next stage is the creation of the foundation

that will support the columns of the

building structure at internal location.



These columns will provide intermediate

support for the floors of the basement and

the building superstructure as work

proceeds.



In the most cases the foundations to these

columns will take the form of CFA piles

with columns attached using pile caps or

increasingly in the case of steel framed

buildings, using the ‘plunge’ method.



Excavation then take place to remove earth

from beneath the slab through appropriate

holes in the slab.



The process is then repeated until the base

slab is reached.

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Construction of basement using Top-down approach.

 Suitable for basement of very large size with complex environment.

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Removal of Soil

 There will have great amount of excavated soil produced during the process of excavation.

 Suitable planning for the removal of the excavated material should be made in

advance in order not to cause disruption to work and incur extra costs. Soil removal can be done by the following ways.

i. Using manual method, by wheel barrow.

ii. Using bucket and lift to ground level by crane.

iii. Using hoist rack (opening has to be provided in the basement/excavation pit first).

iv. Using gantry crane (opening has to be provided in the basement/excavation pit first).

v. Using conveyor belt

vi. Using excavating machine to removal spoil, may be in stepped position in case of very deep pit.

vii. Using dump truck but access provision has to be provided in advance (such as a temporary ramp or the permanent vehicular access into a basement)

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Excavating machine to take up spoil from bottom

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Hoisting machine is provided for removing spoil from basement

Using of a gantry crane for spoil removal

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The use of a material hoist for the removal of spoil from the basement interior

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References:

http://personal.cityu.edu.hk/~bswmwong/contents/ebook/construction_technology/2e.pdf – Excavation & Basement Construction http://www.cv.titech.ac.jp/~courses/atce2/Lesson5.pdf– Excavations and Excavation Supports

http://ebooks.narotama.ac.id/files/Deep%20Excavation;%20Theory%20and%20Practice/Chapter%203%20%20Excavation%20Method s%20And%20Lateral%20Supporting%20Systems.pdf– Excavation Methods and Lateral Supporting System

http://constructionduniya.blogspot.my/2012/02/top-down-construction.html– Top Down Construction Part 1

http://constructionduniya.blogspot.my/2012/05/structural-members-required-for-top.html– Top Down Construction Part 2 https://www.youtube.com/watch?v=9DBNLAJ-bxk– Video Botton Up Construction

https://www.youtube.com/watch?v=vDvyOLD5n5w – Video Top Down Construction https://www.youtube.com/watch?v=jRgxiQSw48U– Video Top Down Construction https://www.youtube.com/watch?v=sboDavo84gc– Video Top Down Construction https://www.youtube.com/watch?v=wUlQyiHfex0– Diaphragm wall construction https://www.youtube.com/watch?v=li6N6t09J-c– Diaphragm wall construction