4. Impact of Cavities
Technical considerations
Stability of heavy machines.
Concrete Over-consumption.
Tight Schedule.
Middle East Concrete & PMV Live ExhibitionNov. 2014
9. GYPSUM DISSOLUTION
Gypsum is a highly soluble rock and under suitable groundwater flow
conditions it can dissolve forming caves and karstic features
including collapse.
Middle East Concrete & PMV Live ExhibitionNov. 2014
11. How the cavities were formed?
Ground Water + Carbon Dioxide = Weak Carbonic Acid Solution
The acid solution dissolves the crystalline gypsum in the flowing groundwater
through rock joints, fractures or bedding planes and forming voids or even
continuous channels.
Geophysical and
Geotechnical Findings of
the Site
Middle East Concrete & PMV Live ExhibitionNov. 2014
12. Seismic effects included in working loads (UBC 1997).
Potential cavity collapse and
corresponding down drag forces
accounted for.
Design Aspects
No skin friction considered above
-10.0 m NADD.
Reduced lateral soil resistance above
-10.0 m NADD.
Friction piles, end bearing component
neglected.
Existing Ground Level
(-10.00)
Weak Rock
With
Potential
Cavities
Competent
Rock
Middle East Concrete & PMV Live ExhibitionNov. 2014
13. Middle East Concrete & PMV Live Exhibition
Design Procedure
Column
loads as given by the consultant
Load
Combinations
(70 SLS& 60 ULS)
Max. Column Loads
Design Loads of piles for
SLS and ULS
GeotechnicalDesign
Structural
Design
Soil Pile friction
Effect of Cavities
Check of Wedge Failure
Settlement of a single pile
Settlement of PileGroup
PileGroup Effect
Lateral Analysis
Check of Buckling
Crack Width Control
Check of tensile stress
Main Reinforcement
Shear Reinforcement
Nov. 2014
14. Middle East Concrete & PMV Live Exhibition
Column Load Combinations
BS EN1991-1_2002 Eurocode 1
For UltimateLoad combinations
UBC
For Working Load Combinations
4.1/)3.03.0(75.00.1
4.1/)3.03.0(75.00.1
0.10.13
0.10.10.12
0.10.11
MyEyMxExQkGkSeismicY
MyEyMxExQkGkSeismicX
WGkSLS
WQkGkSLS
QkGkSLS
MyEyMxExQkGkSeismicY
MyEyMxExQkGkSeismicX
WGkULS
WGkULS
WQkGkULS
QkGkULS
3.03.06.00.1
3.03.06.00.1
Dead)l(Beneficia4.10.14
Dead)(Adverse4.14.13
2.12.12.12
6.14.11
Resulted in 70Load CombinationsResulted in 60Load Combinations
AnalysesforEach Pile
Cap
+
Load Combinations (SLS & ULS)
Nov. 2014
15. Middle East Concrete & PMV Live Exhibition
Pile Working & Ultimate Loads
22
y
yM
x
xM
n
Q
P xy
p
Mx, My: Moment about x and y axes
x, y: Distance from y and x axes to any pile
x2, y2: Group moment of inertia
n: Number of piles
Ultimate load combinations 4 critical cases considered for structural design:
• Maximum Compression + corresponding moment and lateral load.
• Maximum Tension + corresponding moment and lateral load.
• Maximum moment + corresponding axial and lateral load.
• Maximum lateral load + corresponding axial and bending moment.
• Transformation of Loading Orientation:
Global Pile Cap Local
• Calculation of Pile Loads
Nov. 2014
16. Geotechnical Design
Ultimate pile-rock unit skin adhesion (R.G. Horvath, 1978).usu qf .15.0.27
Working friction capacity of pile, Fs = 2.0
susocketsf
s
sf
a
fLDQ
F
Q
Q
...
W
F
fLD
Q
s
susocket
uplifta
...
)(
Working uplift capacity, Fs = 3.0
Soil Pile Friction, working capacity
Middle East Concrete & PMV Live ExhibitionNov. 2014
17. Geotechnical Design
Factor of safety against wedge failure:
t
cohesion
F
FW
SF
cos.
..
W: Total weight of the wedge (pile Wp, pile cap Wr, and soil/rock Ws)
FCohesion is the rock cohesion resistance over the wedge surface.
A minimum safety factor of 1.1 against probable wedge failure is ensured.
Check of Wedge Failure - Uplift
Wp
Wr
Ws
(a) (b)
tF tF
Middle East Concrete & PMV Live ExhibitionNov. 2014
19. Structural Design
Rotational Stiffness k:
Spansofnumberx
L
IE
k crc
4
Lateral Analysis using ALP
Lateral pile-soil interaction
Bending moments
Shear forces
Middle East Concrete & PMV Live ExhibitionNov. 2014
20. Middle East Concrete & PMV Live Exhibition
Structural Design
Structural Capacity
Check
Crack width
assessment
Nov. 2014
21. Pile Tests and Design Validation
Sonic Logging almost 1800 piles
75 Working Pile Load Tests
13 Instrumented Non-Working Pile
Load Tests (conventional +
bidirectional O-cell)
(250% of the working loads)
Caliper logging tests
LONGITUDINAL SECTION
BHT-36
Middle East Concrete & PMV Live ExhibitionNov. 2014
23. Impact of Cavities
Technical considerations
Stability of heavy machines.
Concrete Over-consumption.
Tight Schedule.
Middle East Concrete & PMV Live ExhibitionNov. 2014
24. Classification of Cavities
Existing Ground Level varies from +7.00 to +16.50 NADD
(-10.00 NADD)
Shallow Cavities
(Within 8m from Ground)
Cavities above -10.0 NADD
-Permanent Casing
-Lean Mix
Cavities below -10.0 NADD
-Concrete Overbreak
90% of suspected cavities
are situated above
-10.0 NADD
Middle East Concrete & PMV Live ExhibitionNov. 2014
27. Probing Logs
Analysis of Probing Records
Spreadsheets GIS Model
Middle East Concrete & PMV Live ExhibitionNov. 2014
28. Probing Logs
Analysis of Probing Records
Spreadsheets GIS Model
Middle East Concrete & PMV Live ExhibitionNov. 2014
29. Cavity (500 psi) Soft Zone
(or cavity filled with loose materials 250 psi)
2D and 3D distribution of cavities using ArcGIS
Analysis of Probing Records
Middle East Concrete & PMV Live ExhibitionNov. 2014
30. Probing Conclusion
Based on the results of probing, recommendations were issued by our technical engineers to tackle:
1. For shallow cavities - either to fill or detour around it.
2. For cavities above El -10.00 NADD - use permanent
casing in pile construction, fill the cavity with lean mix
prior to pile construction, or allow for concrete over
consumption.
3. Deep cavities below El -10.00 NADD - we elected to
use self compacting concrete in order to insure that all
cavities are properly filled.
Middle East Concrete & PMV Live ExhibitionNov. 2014
42. ACHIEVEMENTS
-Complete piling construction on time with maximum production rate of 46 piles/
day consuming about 2000m3/day.
-Cost Saving for the client by proposing Lean Mix Concrete for plugging
suspected cavities instead of using permanent casings.
Estimated Cost of all permanent casings: 109 million Dirham
Estimated Cost of Combination of Lean mix + Permanent Casings: 34 million
Dirham
Saving of approximately 65 million Dirham
- The numbers of deep wells required for dewatering are reduced to 45 nos. after
conducting various stages of de-watering optimization trials .
Middle East Concrete & PMV Live ExhibitionNov. 2014