Ground Movement.qxd - Building Products Index

GROUND
MOVEMENT
THE CORDEK SOLUTION
C E L L C O R E
•
C L AY M A S T E R
•
C E L L F O R M
Introduction
Ground movement and its associated problems are well known
to Engineers and Contractors. It is caused by the rehydration of
clay or expansive shale soils, overburden recovery resulting
from deep excavations or, in certain parts of the world,
permafrost heave.
The amount of movement will depend on a number of factors including:
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●
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The plasticity of the soil and the degree of dessication
The extent to which vegetation and trees have been removed or planted
The excavation depth
Analysis of the site investigation should indicate the
expected amount of movement. Valuable guidance is
supplied in the NHBC document ‘Building Near Trees’
(Chapter 4.2) and the BRE.
CELLCORE
Cordek have developed a number of products to prevent
ground movement damaging the integrity of commercial
or residential buildings.
CELLFORM
They are fully proven on major projects throughout the UK and overseas.
CLAYMASTER
Cellcore
The Cellcore range has been developed to minimise the effects of ground movement
on the foundations of buildings and is extensively used on major projects both in the
UK and overseas.
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Fully proven and tested
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Agrément and NHBC approved
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Made in a wide range of designs
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Water resistant and does not degrade
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Backed by quality engineering and
production teams
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Inert and contains no CFCs or HCFCs
Performance
All grades of Cellcore and Cellform work on established
engineering principles and performance, unlike other antiheave products, does not rely on material degradation.
At the pre-determined load above the SAFE LOAD,
which is known as the FAIL LOAD, the legs will buckle
and collapse and allow the ground to move upwards.
Each grade is designed to support a given thickness of
concrete plus a live load allowance of 1.5kN/m2 with
negligible creep compression during a 16 hour curing
period (THE SAFE LOAD).
The slab, beam or pile cap must be designed to accept the
difference between its self weight and the fail load (see
design examples on page 5).
There are three types of Cellcore:
Type CC
Polypropylene
sheet
Type CF
Heavy duty polypropylene
sheet
Type CC and CF are used beneath piled beams. Cellform also acts as permanent
formwork. Both are supplied to the correct beam width.
Type CP
High density
EPS
Type CP usually used beneath the
ground floor slabs and pile caps.
Cellcore Plus
On the Type CP, the thickness of the
EPS top can be increased to provide
better insulation.
The table opposite shows the
improved thermal properties.
Thickness Thermal Resistance
(mm)
m2c/w
50 (Standard)
1.40
75
2.08
100
2.78
125
3.47
150
4.17
1
Cellcore
The standard grades incorporate drainage slots to
alleviate water pressure.
Standard Grades of Cellcore
Table 1
Concrete Depth and Load characteristics
Cellcore
Grade
Maximum
Concrete
*Thickness
Cellcore
Type
Beams Slabs
-
CP
Safe Load
kN/m2
Fail Load
kN/m2
8
12
8/12
270mm
10/15
350mm
CC
CP
10
15
15/22
550mm
CC
CP
15
22
20/30
770mm
CC
CP
20
30
*Allows for 1.5kNm2 Live Load
When concrete thickness exceeds 770mm please contact our Technical Services
Department
Cellcore Grades are available for concrete thicknesses up to 2 metres
Standard Depths for Cellcore
Table 2
Compression characteristics
Cellcore Type
Compression
at Fail Load
mm
Type CC
Depth mm
Type CP
Depth mm
100
150
55
175
225
100
200
250
125
300
350
200
The depth of Cellcore selected will depend on the predicted
amount of ground movement at the Fail Load
The thickness of the EPS top can be increased to improve the
insulation value (Cellcore Plus).
Selection of Cellcore
Table 3
Ground movement and void characteristics
Results
of
Soil
Analysis
Plasticity
Index
NHBC
Category
Predicted Ground
Movement, or
BRE/NHBC
requirement
Depth of Cellcore
required to achieve
‘Equivalent Void’
Shrinkage
Potential
Void
dimension (mm)
Type CC
Type CP
10-20
Low
50
100mm
150mm
20-40
Medium
100
175mm
225mm
40-60
High
150
250mm
300mm
200
300mm
350mm
Above 60
Very High
This category is applicable when potential ground movement exceeds
the NHBC range
2
Sizes
Standard Panel:
2.44m x 1.22m
Beams:
Manufactured to width in 2.44m
lengths
For non standard sizes, please contact
our Technical Services Department
On-site information
Delivery
All products are delivered in polythene packaging.
Packaging material is kept to an absolute minimum.
The packs are easily manually off loaded and handled.
Storage and Handling
The panels are all relatively light and should be weighted down
to prevent damage from the wind. Apart from that, no special
storage conditions are required as all products are unaffected
by water.
Note:
Most damage is caused during off loading, storage and handling,
so sensible precautions should be taken.
Installation
The procedure is straightforward but the following points are important:
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Ensure that Cellcore and Cellform are placed on a firm level surface.
Concrete or sand blinding will often be required.
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Where necessary seal the joints with a formwork tape which can be
obtained from Cordek.
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Do not overload with steel or surcharge with concrete.
If you have any doubts please contact our Sales Support team on 01403 799601.
3
Claymaster
The original compressible expanded polystyrene. Coloured pink, so
that it can be readily identified, Claymaster is Agrément approved
and water resistant.
Claymaster is used on the inside of piled
beams to reduce the effect of lateral
movement.
Typical PIled
Ground Beam
Claymaster does not compress significantly until loads exceed 20kN/m2.
A load of 40kN/m2 is needed to produce 50% compression. Therefore,
its use is not recommended under ground floor slabs, piled beams or
pile caps.
Whilst deep trenchfill is a typical type of house foundation, it is now less
used because of improvements in piling techniques and health and safety
considerations.
Selection of Claymaster
Table 4
lateral ground movement and void characteristics
Shrinkage
Potential
Predicted lateral movement
NHBC recommended void
Low
Zero
Zero
Medium
25mm
50mm
High
35mm
75mm
*Very High
60mm
100mm
* This category is recognised by the BRE
4
Claymaster thickness
for ‘equivalent void’
Sizes
Standard sheet sizes are 2.4 x 1.2m with
thicknesses ranging from 50 - 300mm.
Cordek supplies Claymaster cut to beam
depth at no additional charge. You only
pay for the waste which is kept to a
minimum.
Design Examples
Cordek’s Technical Department are always available to supply design advice to the specifier.
DESIGN EXAMPLE - For a beam
DESIGN EXAMPLE - For a slab
Beam (500 mm deep)
Light Slab (200mm thick)
- Assume the soil survey showed a plasticity index of 14
- Table 3 on page 2 shows soil heave potential is low shrinkability
- BRE/NHBC data recommends a clear Void of 50mm.
- Assume the soil survey showed a plasticity index of 31.
- Table 3 on page 2 shows the potential for ground movement
is medium
- BRE/NHBC data recommends a clear Void of 100mm.
1. Total deadweight/downward load is
Self weight of 500mm concrete beam:
0.5m x 24kN/m3
=
+ Live load allowance =
TOTAL LOAD
=
12.0kN/m2
1.5kN/m2
13.5kN/m2
2. Table 1 on page 2 shows the next SAFE LOAD value is 15kN/m2
(Fail Load of 22kN/m2 )
The appropriate Cellcore grade = 15/22
3. 100mm of ground movement is predicted and Table 3 on page 2
shows that,
The Cellcore depth to accommodate this = 175mm
So, the full product specification = Cellcore 175 CC 15/22
Table 1 on page 2 shows this Cellcore specification has a
FAIL LOAD of 22kN/m2
The beam must therefore accommodate a Residual Upward
Force derived as follows:
Cellcore Fail Load - Self weight of beam =
22.0
-
12.0
=
Residual Upward Force
10kN/m2
Typically two modes of failure should be considered at this point.
i) Lifting the beams off the top of the piles
ii) Failure of the beam in bending or shear due to the uplift forces
Note: Table 4 on page 4 shows the recommended void for lateral
movement in medium shrinkability soils is 25mm and that a 50mm thick
Claymaster grade would be required to accommodate the lateral
movement if the design incorporates any perimeter downstand beams.
1. Total deadweight/downward load is:Self weight of 200mm concrete slab:
0.20m x 24kN/m3
=
4.8kN/m2
+ Live load allowance =
1.5kN/m2
+ No blinding screed required
TOTAL LOAD
=
6.3kN/m2
2. Table 1 on page 2 shows the next SAFE LOAD value is 8kN/m2
(Fail Load of 12kN/m2 )
The appropriate Cellcore grade = 8/12
3. A maximum 50mm of ground movement is predicted and Table 3 on
page 2 shows that,
The Cellcore depth to accommodate this in CP form = 150mm
So, the product specification = Cellcore 150 CP 8/12
Table 1 on page 2 shows this Cellcore specification has a
FAIL LOAD of 12kN/m2
The slab must therefore accommodate a Residual Upward Force,
derived as follows:
Cellcore Fail Load - Self weight of slab = Residual Upward Force
12.0
-
4.8
=
7.2kN/m2
Typically two modes of failure should be considered at this point.
i) Lifting the slab off the foundations
ii) Failure of the slab in bending or shear due to the uplift forces
Note : The table 4 on page 4 shows that no void is required for lateral
movement in low shrinkability soils, so there is no Claymaster
application for this design.
5
For our detailed literature on these other Cordek Solutions,
please call our technical sales on: 01403 799601
Formwork Solutions
For a range of construction applications
Trough & Waffle Moulds
For forming ribbed concrete floors
Piling Accessories
A range of product solutions and systems
Corform
For constructing Bridge Decks
Groundform
A formwork system for in-situ ground beams and pile caps
Correx® & Seekure
For temporary protection
Tipform
A system for constructing steep sided landfill sites
Filcor EPS
For voidforming, fill and a range of other applications
Creative Solutions
For a range of design led applications
Gas Protection
If the contents of this brochure do not point to a solution for a
particular application, we urge contractors and specifiers to call our
Technical Sales line on 01403 799601.
Our reputation is built on innovation and we have a wealth of
problem solving experience for you to call on.
For venting hazardous gases from under buildings
Cordek Limited
Spring Copse Business Park
Slinfold
West Sussex
RH13 0SZ
England
Telephone 01403 799600
Facsimile 01403 791718
e-mail
info@cordek.com
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May 2010
and may not be reproduced without permission.