This document discusses technical education and underpinning foundations. It begins with definitions of technical education and underpinning. Reasons for underpinning include new construction, structural issues, soil instability, and excavation. Common underpinning methods discussed include conventional pit method, jet grouting, micropiles, needle beams, cantilever needle beams, and underpinning railway bridges. The document emphasizes that underpinning requires expert design and execution to safely renovate structures and protect surrounding buildings.

1. ASSIGNMENT QUESTION
YOUR COLLEGE IS HOSTING AN
INTERNATIONAL EXPO ON
TECHNICAL EDUCATION IN
ZIMBABWE.PREPARE A
POWERPOINT PRESENTATION
BASED ON UNDERPINNING OF
FOUNDATIONS.YOUR
PRESENTATION SHOULD HAVE
CLEAR & INFORMATIVE
ILLUSTRATIONS & SHOULD
FOLLOW THE FOLLOWING
FORMAT:
(a) DEFINITIONS
(b) REASONS FOR UNDERPINNING
(c) PROCEDURE USING THE
FOLLOWING MATERIALS:
i. CONCRETE
ii. BEAMS
iii. MINI PILES

2. UNDERPINNING
CHAKAMBA J

3. UNDERPINNING
OBJECTIVES
• Define the term underpinning.
• Describe underpinning,when it is
needed and how it is done.
• State the reasons for underpinning.
• State the methods of underpinning a
structure.

4. UNDERPINNING OF BUILDINGS.

5. INTRODUCTION
Whenever a new building is to be built especially
in urban areas,it is quite common to have the
foundations lower than the foundations of
adjacent buildings.
It is therefore essential that the stability of the
existing building(s) is safeguarded by performing
underpinning as well as shoring.`that care and
forethought should be undertaken if these
operations are to be successfully carried out.
Only highly skillied and experienced personnel or
companies should perform these operations.

6. DEFINITIONS
TECHNICAL EDUCATION
• It is academic and vocational preparation of students for jobs
involving applied science and modern technology.
• It is also understood to include the theoretical & practical scientific
knowledge and skills that permit a person receiving such education
to solve production engineering and economic problems in his
speciality.(encyclopedia2, the freedictionary).
UNDERPINNING
• It is a broad term to describe the process of modifying
an existing foundation by adding support.
• It can also be described as the installation of temporary
or permanent support to an existing foundation to
provide either additional depth or an increase in
bearing capacity.(Nemati 2007).

7. DEFINITIONS Cont
• Underpinning can also be reffered to as a process of
strengthening the foundation of an existing building or
other structure(wikipedia,the free encyclopedia).
REASONS FOR UNDERPINNING
 Construction of a new project with a deeper
foundation adjacent to an existing building.
 To enable the foundations to be deepened for
structural reasons e.g to construct a basement or
addition of another storey to the building.

8. REASONS cont
To support a structure that is sinking or tilting due to
poor soil or instability of the superstructure.
Change in use of a structure.
 As a safeguard against possible settlement of a
structure when excavating close to or below its
foundation level.
To support a structure while making alteration to its
foundations or main supporting members.
To increase the width of a foundation to permit
heavier loads to be carried e.g when increasing the
height of a building with new levels.
To enable a building to be moved bodily to a new site.

9. REASONS Cont
The original foundation is simply not strong or
stable enough.
The properties of the soil supporting the
foundation may have changed possibly through
subsidence or were mischaracterized during
design stages.
Settlement of an existing structure.

10. UNDERPINNED FOUNDATIONS

11. SOME CAUSES OF SETTLEMENT ON A
BUILDING
 Lowering of the water table due to tidal fluctuations,wells
for a water district etc.
 Lowering of the water table can then cause tops of timber
piles to decay overtime and will require remedial
underpinning.
 Rising of the water table in some soils can effect a
decrease in bearing capacity of the soil causing settlement
on the building which will then require underpinning.
 Construction of buildings on unsuitable bearing material or
over compressible layer e.g peat,organic silts or poorly
compacted backfill may also cause settlement.
 Earthquakes,floods or other natural causes can cause the
structure to move thereby requiring stabilisation of
foundation soils or footings.

12. DETERMINING THE NEED FOR
UNDERPINNING
 Underpinning as a direct support of an existing building
foundation provides the opportunity to preload i.e jacking to
limit settlement and improve poor foundations.
 When a structure starts showing signs of settlement or distress,
it is of utmost importance to precisely monitor the settlement
or movement by a professional on a daily,weekly or monthly
basis.
 Data collected or readings will indicate if the movements are
decreasing or increasing.
 Analyzing the results will also tell whether underpinning is
required or not to safeguard the structure e.g cracks or any
other weaknesses
 Before the beginning of any excavation on a new structure a
professional must examine all the structures in close proximity
to the construction site so as to determine whether
underpinning is also necessary.Nash 1988:146.

13. PROCEDURES INVOLVED WHEN
USING PILES FOR UNDERPINNING
 The piles are formed of precast concrete sections.
 Each section has a steel-linked hole running through it.
 The steel lining helps the locating of the sections and ensures
that they are all in line.
THE PROCESS
 A hole is dug below the existing foundation of the structure.
 The first section which has a pointed steel toe-piece to make
penetration into the ground easier is placed into position below
the foundation .
 A bearing plate is then positioned between the jack and the
foundation.

14. PROCESS cont
The jack is then put between the first section and the
bearing plate and the first section is forced
downward by the hydraulic jack powered by a pump
outside the excavation.
When the top of the first section is almost flush with
the ground,the jack is removed and the process is
repeated with the second and subsequent sections.
As each section is added,a length of steel tube is
inserted into the hole and grouted into position to
make an effective joint between the sections.
The operation is continued until the pressure gauge
indicates sufficient penetration resistance to ensure
adquate bearing capacity.

15. THE PROCEDURES INVOLVED WHEN
UNDERPINNING BUILDINGS cont.
The wall to be underpinned must be carefully inspected for
any cracks or weaknesses and these carefully noted.
The wall should then be divided into a convenient number
of working bays,generally not exceeding about
1.5m,depending on the quality and stability of the
wall.These working bays should have sufficient room to
enable a person to work inside them.
A batten should now be fixed along the face of the wall
throughout its length to act as a datum.
A sequence of working which will often be determined by
the conditions on the site and the accessibility of the
working area adjacent to the wall should now be carefully
outlined.

16. PROCEDURE cont
No two adjacent bays must be excavated at the
same time. If consecutive bays have to be worked
in,it is essential that the first bay is fully
completed and allowed to harden before work is
begun on the second bay.
Each bay excavated in turn,usually by hand.The
earth is taken out at the front of the bay which
allows support to be given to the foundations for
as long as possible,while this excavation is being
dug.
The earth is then dug out from underneath the
foundations until new level is reached.

17. PROCEDURE cont.
The ground is now levelled and thoroughly rammed.
The projection of the foundations is cut off so that it is
flush with the face of the wall.
The foundation concrete is laid to the required
thickness,provided there is adquate projection on both
side of the wall.Any water in the excavation should be
pumped out first.
The brickwork is then built up in the working bay with
good quality bricks and cement mortar usually 1:3 or 1:4.
The work should be thoroughly pinned up to the concrete.
The gap behind the new wall can be filled in with hardcore
or weak concrete as the new wall is built.Nash 1988:146

18. UNDERPINNING OF FOUNDATIONS
UNDERPINNED STRUCTURE CONVENTIONAL PIT METHOD

19. UNDERPINNING METHODS
o The means and methods of supporting a
structure foundation depends on some of the
following factors:
Foundation Loads: static and dynamic,permanent and
temporary.
Type and magnitude of allowable structural movement i.e
deformations.
Subsurface soil conditions.
Subsurface ground water conditions.
Access and mobility to the foundations.
Potential for environmental hazards.
Seismic loading.

20. WAYS OF ACHIEVING UNDERPINNING
 It can be done by :
i. Load transfer
ii. Soil treatment or
iii. A combination of the above two mechanisms
LOAD TRANSFER
 This literally take structural loads and transfer them to an
underlying stratum that is more suitable for support.
SOIL TREATMENT
 This changes the physical properties of the ground to
make it stronger and more supportive ,often without any
change to existing foundations.
 In some cases, ground treatment can be utilized to
strengthen the ground while also acting as a load transfer.

21. UNDERPINNING METHODS
 There are numerous methods that can be used
when underpinning.
 Each methods having its own specific soil and
loading conditions where its application is most
effective.
 In some cases constructability can also determine
the system to be used.
 Each method have also its own advantages and
disadvantages depending on the specific
characteristics of the project.

22. 1. CONVENTIONAL PIT METHOD
o It consists of enlarging and or deepening existing foundations by
removing soil from beneath the foundations and replacing it with
concrete,reinforcements and a grout material.
o The structure can also be temporary shored to prevent settlement.
DISADVANTAGES OF THE PIT METHOD
i. It often results in moderate deformation of the structure.
ii. Unsafe working conditions.
ADVANTAGES OF THE PIT METHOD
i. Simplicity of the engineering.
ii. Low cost of labour to produce the result.
iii. There is continuity of the structure’s uses during construction.

23. 2. JET GROUTING
 It is a load transferring system for the underpinning,often
also serving as an excavation support and ground water
control system.
 It is an in-situ method of construction undertaken beneath
foundations.
 High velocity injection of fluids,often enclosed in air erodes
the soils and replaces the soil with and engineered
grout,forming a cementations product known as SOILCRETE
that is capable of attaining unconfined compressive
strengths in excess of 70.3 kg/cm2.
 Groups of 1 to 1.2m diameter soilcrete columns are
constructed to transfer foundation loads to underlying
suitable bearing material.

24. USE OF JET GROUTING METHOD
IT IS A LOAD TRANSFERRING SYSTEM FOR THE UNDERPINNING.
SERVING AS AN EXCAVATION SUPPORT AND GROUND WATER CONTROL
SYSTEM.

25. ADVANTAGES OF JET GROUTING
i. Work is accomplished safely above grade and
sequenced so that little or no structural
deformation occurs.
ii. It is most widely used for underpinning historical
and sensitive structures.
iii. Can also be used to construct deep foundations,in
site gravity wall structures and groundwater cut off
structures.

26. 3.MICROPILES
 It is used to stabilize or upgrade existing foundation by
installing micropiles through pre-drilled holes
determined by load characteristics.
 Micropiles are described as small diameter piles that
can be installed in almost any type of soil and that can
carry loads up to 500 tonnes depending on the type of
it.
 These micropiles are steel reinforced placed into a
small diameter hole and scaled to the ground by grout
injections under relatively high pressure.
 Micropiles are widely recognized as a common
remedial option for underpinning structures having
foundations problems after completion or during
service period.

27. ADVANTAGES OF MICROPILES
i. They have high carrying capacity.
ii. Less site constraint problems.
iii. Low noise and vibration.
iv. It is a self –sustained operation.
v. It can be designed to have very low settlement.
DISADVANTAGES OF MICROPILES
i. Higher cost as compared to other pilling systems.

28. TYPES OF MICROPILES
 Pile and Beam.
 Pile and Cantilever Beam.
 Knuckle pile.
 Piled raft.
 Angle pile.
 Cantilever Ring Beam.
 Twin pile.
 Jack Down piles.

29. METHODS OF UNDERPINNING
1.NEEDLE BEAM 2.NEEDLE WALL

30. UNDERPINNING METHODS
3.CANTILEVER NEEDLE BEAM 4.UNDERPINNING RAILWAY BRIDGE.

31. UNDERPINNING METHODS
FOUNDATION UNDERPINNING FOUNDATION UNDERPINNING

32. CONCLUSION
• Finally it is important to note that underpinning
works require experts in the design and execution
levels.
• Because of its complexity and specially the
dangerousness for the renovation building and
the buildings around it,safe working practices
should be undertaken.

33. REFERENCES
http://encyclopedia2.the
freedictionary.com|Technical Education.
Accessed on 06/01/2014.
http://courses.washington.educ|cm420/underpi
nning.pdf
Accessed on 06/01/2014.
Nash,W.G.(1988).Brickwork 3 revised third
edition.Essex.Anchor Press Ltd.