use of dmt in geotechnical design with emphasis on liquefaction assessment
Post on 13-Apr-2017
44 Views
Preview:
TRANSCRIPT
USE OF DMT IN GEOTECHNICAL
DESIGN WITH EMPHASIS ON
LIQUEFACTION ANALYSIS
Presented By: Muhammad Ali Rehman
Overview
Introduction
Data Interpretation
DMT Correlations
Liquefaction
Liquefaction Assessment
Case Study
Conclusions
References
DMT
Equipment Layout
Test Procedure
INTRODUCTION
Dilatometer Test (DMT)
Developed by Professor Silvano
Marchetti (Italy).
Published test procedure &
correlations in 1980.
DMT measures the lateral deflection
of soil.
Equipment Layout
Fig: General Layout of DMT
Test Procedure
DMT in-situ testing involves expanding membrane
by using nitrogen gas.
The primary way of using DMT results is to
interpret them in terms of common soil
parameters.
DATA INTERPRETATION
Dilatometer Test Parameters
Primary parameters of DMT.
Material Index
ID = (p1 – p0) / (p0 – u0)
Horizontal Stress Index
KD = (p1 – p0) / σ´v0
Dilatometer Modulus
ED = 34.7 (p1 – p0)
Pore-pressure Index
UD = (p2 – u0) / (p0 – u0)
• DMT parameters, ID, KD, and ED are used in
subsequent soil analysis.
DMT CORRELATIONS
Correlations
Soil Behavior
Over-consolidation
Relative Density
Undrained Shear Strength
Constrained Modulus
Compression Ratio
Settlement Prediction
Skin friction of Driven Piles
SPT N-value and Dilatometer Modulus
1. Behavior of Soil
Soil behavior chart introduced by Marchetti et al.
(1980).
ID<0.6 : Clays
0.6≤ID≤1.8 : Silts
ID>1.8 : Sands
2. Over-Consolidation Ratio (OCR)
Original correlation proposed by Marchetti et al.
(1980):
OCRDMT = (0.5 x KD)1.56
Confirmed by a comprehensive collection of data
by Kamei & Iwasaki (1995) for clays.
Finno (1993)
Over-Consolidation Ratio (OCR)
Kamei & Iwasaki (1995) Finno (1993)
3. Relative Density
Reyna & Chameau (1991)
and
Tanaka & Tanaka (1998)
Robertson & Campanella
4. Undrained Shear Strength
Marchetti et al. (1980):
cu = 0.22 σ'v0 (0.5 KD)1.25
Undrained Shear Strength
Comparison of undrained shear strength by DMT
and other tests, at National Research Site,
Bothkennar (UK):
Nash et al. (1992)
5. Constrained Modulus : MDMT
Obtained by applying correction factor RM to ED
MDMT = RM . ED
RM is the function of material index (ID) and
horizontal stress index (KD).
Increases with KD while ID has lesser effect on the RM
value.
Generally varies from 1 to 3.
6. Compression Ratio
Marchetti et al. (1980)
Pre-consolidated Clays
M = σ’p (2.3/CR)
Normally Consolidated Clays
M = σ’v (2.3/CR)
7. Settlement Prediction
Predicting the settlement of shallow foundations
(particularly for Sands) is one of the best
applications of DMT.
Calculated by means of expression:
S = [ Δσv/MDMT ] ΔZ
Totani, Marchetti, Monaco &
Calabrese (2001)
8. Skin Friction for Driven Piles in Clay
Powell et al. (2001 b), developed a method for the design of piles driven in clay.
Method predicts pile skin friction qs, from ID and (p1
- p0):
ID < 0.1 : qs /(p1 - p0 ) = 0.5
0.1 < ID < 0.65 : qs /(p1 - p0 ) = -0.73077 ID + 0.575
ID > 0.65 : qs /(p1 - p0 ) = 0.1
9. SPT N-value & ED
Mayne & Frost
Introduction
Liquefiable Soils
Liquefaction Assessment
LIQUEFACTION
Liquefaction
“Transformation of coarse grained soil from a solid state into a liquid state”
Excessive hydrostatic pressure build-up & reduction of effective stress
sudden shock
cyclic loading.
Devastating effects of structure:
Tilting of high rise buildings
Ground subsidence
Surface rupture
Collapse
Liquefiable Soils
Loose granular soils are potentially susceptible to
liquefaction.
Fine grained soils (such as silts and clays) are non-
liquefiable.
Andrews & Martin (2000) suggested:
Potentially Liquefiable: soils having, CF < 10% & LL <
32%
Non-Liquefiable: soils having, CF > 10% & LL ≥ 32%
Liquefaction Assessment
Glaser and Chung (1995):
Loose granular soils densify on sampling.
Laboratory measurements demonstrate higher cyclic strength
In-situ testing is preferred.
“Simplified Procedure” for liquefaction assessment,
proposed by Seed & Idriss (1971).
To evaluate the loading to a soil caused by an earthquake (by
CSR)
To evaluate the resistance of a soil to triggering of
liquefaction (by CRR)
Liquefaction Assessment
Factor of Safety against the occurrence of
liquefaction is defined as:
FS = CRR7.5 /CSR7.5
If FS < 1, liquefaction will be triggered.
Cyclic Stress Ratio (CSR)
CSR is the measure of intensity of cyclic loading during an earthquake.
Obtained by formula, developed by Seed & Idriss(1971):
CSR 7.5 = 0.65 (amax / g) . (σv0 / σ’vo) . rd
amax is the peak horizontal ground acceleration generated by the earthquake.
rd is the stress reduction factor.
Cyclic Stress Ratio (CSR)
Seed & Idriss porposed:
rd is the function of stratigraphy and depth.
Has a value of 1.0 at ground surface, tends to reduce
with depth.
Seed and Idriss (1971)
Cyclic Stress Ratio (CSR)
Youd et al. (2001)
rd = [1.0 – 0.00765z] (z ≤ 9.2m)
rd = [1.174 – 0.0267z] (9.2 < z ≤ 23m)
rd = [0.744 – 0.008z] (23 < z ≤ 30m)
rd = 0.5 (z > 9.2m)
Cyclic Resistance Ratio
In-situ test Procedures:
Standard Penetration Test
Cone Penetration Test
Shear wave velocity test
Dilatometer Test
DMT Based CRR Evaluation
Include:
Marchetti (1980)
Roberstson & Campnella (1986)
Reyna & Chameau (1991)
Monaco et al. (2005)
Grasso & Maugeri (2006)
Monaco & Marchetti (2007)
Tsai et al. (2001, 2009)
DMT Based CRR Evaluation
Marchetti (1980) proposed the basic correlation:
CRR = (KD/10)
Refined by Monaco et al. (2005):
CRR7.5 = 0.0107KD3 − 0.0741KD
2 + 0.2169KD – 0.1306
Grasso & Maugeri (2006) further updated Monaco
et al. (2005) model into:
CRR7.5 = 0.0908KD3 − 1.0174KD
2 + 3.8466KD – 4.5369
DMT Based CRR Evaluation
Curves for CRR (Reyna & Chameau
1991)
Clean sand is safe against liquefaction for following KD
values:
Non seismic areas:KD > 1.7
Low seismicity areas :KD > 4.2
Medium seismicity areas: KD > 5.0
High seismicity areas:KD > 5.5
Performance of DMT Based Liquefaction
Evaluation of Chi-Chi Earthquake, Taiwan (1999)
by Tsai et al. (2001)
Case Study
Chi-Chi Earthquake
21 September 1999, at 1:47 am,
an Earthquake hit Taiwan.
7.6 magnitude
Epicenter near Chi-Chi (town in
Nantou County)
2400 deaths, 8373 Injuries
Damage of US$30 billion.
Extensive field investigation after
earthquake was conducted by
NCREE.
In-situ SPT & CPT were performed.
Collection of SPT Data
Liquefaction sites:
Wufeng, Nantou, Yuanlin & Zhangbin
Total 31 SPT Cases
24 liquefied
7 non-liquefied
Collection of SPT Data
Area Test NumberTriggering of
Liquefaction
Wufeng SPT9 Yes
1 No
Nantou SPT7 Yes
1 No
Yuanlin SPT8 Yes
5 No
SPT Based Method
Seed et al. established chart for estimating SPT
based CRR7.5 :
Seed et al. (1985)
SPT Based Method
The CRR7.5 curves were further modified by Youd et al. (2001) and formulated as:
CRR7.5 = 𝟏
𝟑𝟒− (𝑵𝟏)𝟔𝟎+
(𝑵𝟏)𝟔𝟎
𝟏𝟑𝟓+
𝟓𝟎
(𝟏𝟎 (𝑵𝟏)𝟔𝟎 + 𝟒𝟓)𝟐−
𝟏
𝟐𝟎𝟎
Valid for (𝑵𝟏)𝟔𝟎 < 30
Sandy soils are considered to be non-liquefiable for (𝑵𝟏)𝟔𝟎 > 30.
Idriss and Boulanger (2006) proposed a new equation:
CRR7.5 = Exp(𝑵𝟏)𝟔𝟎
14.4+
(𝑵𝟏)𝟔𝟎
126
2−
(𝑵𝟏)𝟔𝟎
23.6
3+
(𝑵𝟏)𝟔𝟎
25.4
4− 2.8
DMT Based Method
DMT parameters, KD and ED are used to develop
DMT based CRR7.5 boundary curves.
Two boundary curves, CRR7.5-KD & CRR7.5-ED were
established by Tsai et al. (2001), following the
existing CRR7.5-(N1)60 curve.
Tsai et al. (2001) established the following
correlations to develop DMT based CRR7.5 curves.
(N1)60-KD
(N1)60-ED
DMT Based Method
Tsai et al. (2001):
(𝑵𝟏)𝟔𝟎 = 0.185KD3 − 2.75KD
2 + 17KD – 15
(𝑵𝟏)𝟔𝟎 = 0.00022ED3 − 0.02ED
2 + 0.9ED – 3
DMT Based Method
Based on above correlations, Tsai et al. (2001)
developed the DMT based CRR7.5 boundary curves.
CRR7.5 = Exp𝑲𝑫
8.8
3−
𝑲𝑫
6.5
2+
𝑲𝑫
2.5− 3.1
CRR7.5 = Exp𝑬𝑫
49
3−
𝑬𝑫
36.5
2+
𝑬𝑫
23− 2.7
DMT Based Method
DMT Based Method
CRR curves proposed by Monaco
(2005), Grasso & Maugeri (2006)
and Tsai (2009)
CONCLUSION
Conclusion
DMT is relatively quick in-situ method which estimates a number of parameters, that can be effectively used in geotechnical design.
DMT is capable of taking into account the soil structure, aging and consolidation effects, which generally influence the liquefaction potential of soil (Tsai et al. 2001).
Tsai et al. (2001) study shows that the accuracy of DMT based CRR7.5 curves for Liquefaction assessment is satisfactory.
Liquefaction assessment is relatively fast and reliable as compared to SPT, which takes longer time to supplement SPT with lab testing.
Conclusion
However, it is desirable to directly conduct DMTs in
the liquefied and non-liquefied areas of
earthquake to obtain more KD and ED data of soils
for further validating the developed DMT-based
liquefaction evaluation method although the results
of this study are preliminarily satisfactory
REFERENCES
References
Marchetti, S. (1980). "In Situ Tests by Flat Dilatometer." J. Geotech. Engrg. Div., ASCE, 106, No.GT3, 299- 321.
G. Totani, S. Marchetti, P. Monaco & M. Calabrese. Use of Flat Dilatometer Test in Geotechnical Design, Intl. Conf. on In-situ Measurement of Soil Properties (2001)
Monaco, P., Marchetti, S., Totani, G. and Calabrese, M. (2005). “Sand liquefiability assessment by Flat Dilatometer Test (DMT).” Proc. XVI ICSMGE, Osaka, 4, 2693-2697
Robertson, P.K., and R.G. Campanella, [1986]. “Estimating liquefaction potential of sands using the flat plate dilatometer. Geotech. Testing J., Vol. 9, No. 1, pp. 38–40.
Tsai, Tung and Lee (2001) . Performance of DMT based liquefaction evaluation method on case history of Chi-Chi Earthquake
Bambang Setiawan,(2011) “Assessing Liquefaction Potential of Soils Utilizing In-situ Testing” M.Sc Thesis
top related