Presentation on centrifuge modelling for building tilt correction

1. Centrifuge Modelling test for Correction of Building
Tilt
Presented By
Vivek Prakash Mani
Centrifuge Modelling 1

2. Table of Content
Introduction 3 to 4
Fundamental Principles 5 to 7
Principle Application 8 to 10
Building tilt Correction-
Introduction
11
Test Setup 12 to 13
Effects of soil extraction
and comparison
14 to16
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3. Introduction
 Developed by Phillips in Paris,1896
 Ranked 5th most important development in Geotechnics in past 50 yrs. – British
Geotechnical Society,1999.
Contd.
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4.  First Geotechnical centrifuge was built in china by Yangtze Water Conservancy
Institute, 1988.
 Adopted to simulate Geophysical events and processes by Ramberg,1968.
 Main Objective- Increasing self weight of small scale model by introducing
centrifuge.
 Helps in improving understanding of complex Geotechnical problems.
 Validating Numerical analysis/estimation.
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5. Fundamental Principles
• Samples A & B
• CSL – Critical State Line
• NCL – Normal Compression Line
 Sample A sheared under low confining
Stresses.
 Sample B of same density sheared under
high mean effective stress.
 Sample A – Dilates
 Sample B – Contracts
Thus, It is vital to simulate the stress level of
soil correctly.
Contd.
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6. Fundamental Principles Contd.
 Recreate Prototype Stress condition
 Increasing n-times gravitational acceleration in 1/n scale model
 Achieved by provided by centripetal acceleration, ng=r𝜔2
 Thus it is suitable for modelling stress dependent geotechnical problems
 And Scaling laws are generally derived through
 dimensional analysis
 Governing equations for a phenomena, or
 Principles of mechanical similarity between model and prototype.
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7. Some Common Scaling Factors are-
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8. Principal applications of centrifuge modelling
1. Modelling of prototype:
 Direct application of the centrifuge modelling technique.
 To simulate and tackle actual engineering problems.
 Slope instability, pile capacity and the effect of excavation on adjacent existing underground
structures are some common applications.
2. Investigation of new phenomena:
 It is applied to study various unusual phenomena that are not well understood and are extremely
difficult to study.
 Typical examples are plate tectonics, various earthquake-induced events and soil liquefaction.
 Behaviour of loose-fill slopes subjected to various rainfall and earthquake conditions can also
be investigated.
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9. Principal applications of centrifuge modelling contd.
3. Parametric studies:
To design and manufacture the first model, while the actual testing and small variations in the model
are relatively easily performed.
By varying some model parameters (geometry, loading and boundary conditions, rainfall intensity or
soil type), the sensitivity of test results to these variations can be evaluated.
 The most critical parameters can be identified.
Examples include bearing capacity of footings on slopes, critical design parameters in flow processes,
and capacity of laterally loaded pile groups.
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10. Principal applications of centrifuge modelling contd.
4. Validations of numerical methods:
Any modelling technique, either physical or numerical, demands the acceptance of simplifications and
assumptions.
Numerical techniques are limited to 2D problems for various reasons, but centrifuge modelling does not
impose this restriction.
It is often easier to simulate a 3D than a 2D plane strain problem in a centrifuge.
It would be ideal to perform both numerical analyses and centrifuge model tests.
The results from these two techniques can then be compared and verified.
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11. Correction of building tilt by in-flight soil extraction
1. Introduction:
Building tilt is encountered where ground is not homogeneous or there are adjacent underground
constructions conducted.
The Italian engineer Terracina in 1962 proposed method to correct building tilt .
 Soil was extracted through inclined boreholes from the less settled side of the leaning tower at Pisa.
Vertical soil extraction is generally simpler than an inclined extraction.
Generally, vertical boring is less effective than inclined boring.
To investigate the effectiveness of vertical soil extraction, in-flight vertical boring adjacent to an
initially tilted building was simulated, by the four-axis robotic manipulator.
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12. Test Setup/Model preparation:
 The test was conducted at 30g.
 The simulated building have the base area as 5.4m*5.4m which was 9 storeyed and produced an
average bearing pressure of 89 KPa on the ground (in prototype).
 The soil in model ground was prepared with unsaturated completely decomposed granite with average
initial water content of 15.3% and dry unit weight of 13 KN/m3.
 Here soil is being extracted using a hollow cylinder of external dia. 30 mm.
 The movements of the buildings were measured using linear variable differential transformers (LVDT)
and laser displacement transducers.
 The performance was monitored by 5 different cameras.
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13.  When the centrifuge was spun at 30g, the building was initially tilted at 1/27.
 To correct the tilted building two series of bore holes were drilled in order to extract out the soil
from the opposite direction.
 The holes were 160 mm deep and 100 mm away from the building (in model).
 When converted into prototype they measure as 4.8 m deep and 3 m away from the building.
Plan view
Elevation View
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14. Effects of soil extraction on building tilt:
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15.  The above figure shows the development of building tilt during soil extraction
 Here the calculated value of building tilt by the theoretical elastic solution is also included for the
comparison.
 The measured results shows that drilling of 1st series of holes (1-4) caused 1.5% reduction in the
building tilt whereas when second series of holes are drilled (5-9) it caused more 0.7% reduction in
building tilt.
 When using the Mindlin’s equation Ng and Xu derived an elastic solution which showed the similar
trend of decrease in tilt.
 But in the case of calculation value the value is 45% of Measured value.
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16. Two main reasons for this under estimated value is :
1. Solution was derived from the vertical boring of a single hole. And so any influence from the
previous boring was not taken into account.
2. Yielding and plastic deformation of the soil were not considered.
So, the correct construction sequence and plastic deformation must be taken into account when
predicting the correction of building tilt.
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17. Centrifuge Modelling 17
Reference
 The state-of-the-art centrifuge modelling of geotechnical problems at
HKUST
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering)
ISSN 1673-565X (Print); ISSN 1862-1775 (Online)
www.zju.edu.cn/jzus;
www.springerlink.com
E-mail: jzus@zju.edu.cn

18. Thank You
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