ground types sin - srmeg.org.sg ground types are ground (rock masses) ... ground types tbm segmental...
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DETERMINATION OF GROUND PROPERTIES
and
DEFINITION OF GROUND TYPES
2Short Course Singapore 11 Klima, Schubert
Ground types
OBJECTIVES
■ Physical and geometrical parameters of the ground are required for various purposes:
□ Assessment of potential failure modes□ Estimation of stresses and displacements□ Evaluation of required support□ Selection of excavation method□ Estimation of water inflow□ Estimation of tool wear and progress rate□ etc.
Necessary for any analytical or numerical design approach.
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STRATEGY
■ Get overview on the geological/geotechnical conditions of the project
■ Distinguish engineering-geological units, with emphasis on lithological and structural characteristics
■ Describe the characteristics of each unit and make a sketch of a representative volume, preferably in 3D
■ Identify characteristic features of each unit, eg intact rock strength, anisotropy, shear strength of discontinuities, etc.
■ Determine the degree of acceptable simplification; a simplified model should still allow capturing characteristic behaviours
■ Split units into Ground Types, if variation of properties is large; determine relevant parameters for each GT
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Determination of properties
■ Which properties do we need?
■ What do we use them for?
■ Whenever possible, try to use direct methods for an estimate of the ground parameters
■ Using empirical methods cannot be completely avoided.
■ When using empirical methods for the determination of parameters check their plausibility
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GROUND TYPES
■ Definition: Ground Types are ground (rock masses) with similar properties (of a geotechnically relevant volume)
■ Definition of geotechnically relevant parameters – key parameters
■ Evaluation of the parameter values and ranges
■ Classification into Ground Types
■ Description of Ground Types shall contain
□ Rock/soil type□ Verbal description of composition and condition□ Sketch of representative volume□ Properties of intact rock and discontinuities□ Properties of rock mass (range); in case of anisotropy
properties in different directions
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Parameter representative value/range
Engineering geological unit
Limestone (limestone, and marble)secondary: dolomite
LithologyGrey and sometimes dark grey limestone with transitions to marble ot to domomite (marble), limestone breccia (cemented)
UCS [MPa] 30 - 80 (50 - 120*)
c [MPa] 8 - 18 (12 - 20*)
45 ± 6
mi [-] 20 ± 6 (15 ± 2*)
Braz. [MPa] 1,4 - 2,9 (range of lab results)
E [GPa] 20 - 60 (40 - 80*)
ν [-] 0,18 ± 0,07 (0,2*)
Abrasivity (low) abrasive CAI [-] 0,9 - 1,8
General descriptionPartially bedded with spacing in a cm range, partially karst along jointsTeilweise with openings of mm to some cm (signs of weathering)
Foliation / bedding, spacing
bedded and thinly laminated; bedding only partially mechanically relevant
foliation spacing
6 - 20 (partially <6 bzw. >20)
φsf [°] 35 - 45
φsf, rest [°] 30 - 40
sizedom.: 2 - 20 cmsec.: 20 - 60 cm
geometry generally blocky
φK,H [°] 35 - 45
φK,H, rest [°] 30 - 40
GSI-classificationJoints and bedding are dominating, blocks show size of cm to some dm, rough discontinuities
GSI [-] 40 - 55
UCSRM [MPa] 14,3 (6,6-25,5)
cRM [MPa] 3,8 (1,9-6,3)
φRM [°] 34,4 (31,1-37,5)
νRM [-]
Elastic properties ERM [GPa] 15,8 (6,4-32,7)
Remarks concerning grouting
Remarks concerning swelling
Dis
co
nti
nu
ity
Foliation / bedding, conditions
Strength propertiesthe rock mass strength is generally dominated by the discontinuities. Isotropic to slightly anisotropic
Joints, block size and goometry
manily narrow jointing and very narrow secondary jointing (incomplete healing); rarely medium jointing
dom.: stepped to planar, rough partially oxidated (karstic joints)sec..: planar /rough to smooth; rarely clayey (sl)
Joints / slickensides, conditions
Interpretation of laboratory results, filed data and core logging
Ground Type 4b Limestone and Marble (Permomesozoic), moderately to heavily fractured
Short descritption Limestone and marble,moderately to heavily fractured
Detailed rock mass description
Inta
ct r
ock
Mechanical propertiesIsotropic to low anisotropic rock with high intact rock strength
Gouting is possible up to a certain level (along joints), locally high grouting volumes possible due to open karst discontinuities
planar to wavy, rough, partially oxidations, partially minor clay fillings
Ad
dit
ion
al
da
ta
no swelling potential
Ro
ck
ma
ss
Representative core photos:
Sketch:
KB 17/07: limestone, bedded, with joints, fractrued, with karst
KB 06/08: Limestone marble, tectonized, fractured
Die dargestellte Gefügeneigung ist beispielhaft. Die tatsächliche Gefügeorientierung zum Bauwerk kann davon stark abweichen.
Remarks:
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Case study:Evaluation of Construction Methods for the Mae Ngad – Mae Kuang Project
Alfred Fasching & Wulf Schubert, 3G
Alois Vigl, viglconsult
Chinda Sutiwanich, Panya
8Short Course Singapore 11 Klima, Schubert
Ground types
The Project
■ The Mae Kuang Dam Inflow Augmentation Project in theChiang Mai province includes a 23.1 km distribution tunnelwith approximately 5 m diameter, connecting the Mae Ngad and Mae Kuang reservoirs.
■ Client: Royal Irrigation Department
■ Feasibility and alignment studies were carried out in theprevious years, including geological investigations. In 2005 the alignment was fixed, and the tender designstarted.
■ Construction start is planned for this year
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INTAKE
ADIT #5
ADIT #6
OUTLET
Several alignments were studiedwith emphasis on minimizing risksassociated with tunnelling.
Site installations are possible at theadits 5 and 6, and at the outlet
Adit #5 required during operationfor depletion of tunnel
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Longitudinal section
quartzitic sandstoneshale and siltstone
intercalations
sheared shalechert and sandstone
limestone blocksquartzitic sandstone with shale intercalations
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Method of evaluation
■ Rock mass characterization
□ Determination of Rock Mass Types (RMT)□ Assignment of physical parameters to each RMT□ Divide alignment into evaluation sections
■ Evaluation of rock mass behaviour
□ Evaluate response of rock mass to excavation underconsideration of rock mass type, stresses, ground water, tunnel size and orientation for each section
■ Assign construction measures
□ Appropriate excavation and support methods for eachbehaviour type
■ Evaluation of System Behaviour
■ Assignment of time and costs
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Distribution of Ground Types
0
1
2
3
4
5
6
7
8
9
0 5.000 10.000 15.000 20.000
station
RM
T
0
500
1000
1500
2000
2500
3000
ove
rbu
rde
n
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Ground types
Distribution of Behaviour Types
0
1
2
3
4
5
6
7
8
9
10
11
0
5000
100
00
150
00
200
00
station [m]
Be
ha
vio
ur
Typ
e
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
ove
rbu
rden
, w
ate
rtab
le (
m)
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Options studied
ADIT 6ADIT 5
INTAKE OUTLET
D&
B
TBM
D&
B
D&B D&B D&B D&B
OPTION 1
ADIT 6ADIT 5
INTAKE OUTLET
D&
B D&
BTBM D&B TBM
OPTION 2
ADIT 6ADIT 5
INTAKE OUTLETTBM TBM
D&
B
D&B
OPTION 3
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Tunnelling methods
■ Drill & blast
□ 4 excavation & support classes□ Round lengths from 1,0 to 3,0 m□ Support from spot bolting to full shotcrete lining with bolts
■ TBM
□ Double shield TBM chosen□ Open TBM considered earlier in the project was ruled out due
to the requirement of smooth lining, and the existence of several fault zones
□ Two segment types considered (standard + strong)
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D&B tunnel support
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Ground types
D&B tunnel support
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Ground types
Typical section adits
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Support Adits
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TBM segmental lining
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Ground types
Discontinuity controlled block fall
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Ground types
Finite element model TBM
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Ground types
Axial forces
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Bending moments
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Time & cost estimate
■ Advance rates and costs estimated based on:
□ Rock type (strength, abrasivity)□ Rock mass behaviour (assignment of excavation and support types,
TBM performance, etc.)□ Ground water treatment, probing ahead, drainage, grouting etc.,
correlated to ground behaviour□ Special measures & events
□ Machine costs□ Material and labor costs□ Site installation, etc.
■ Uncertainty in rock mass quality was considered by evaluating time and costs for three different rock mass qualities (low, average, high strength)
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Time schedule excavation & supportOPTION 2 m
0
10
20
30
40
50
60
0 5000 10000 15000 20000 25000
station (m)
mo
nth
s
0
500
1000
1500
2000
Lining D&B
D&B
TBM
TBM
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Ground types
Time schedule excavation & supportOPTION 3 m
0
10
20
30
40
50
60
0 5000 10000 15000 20000 25000
station (m)
mo
nth
s
0
500
1000
1500
2000
Lining D&B
D&B
TBMTBM
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Cost Comparison
0%
20%
40%
60%
80%
100%
low RQ average RQ high RQ
Option 1
Option 2
Option 3
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Conclusion
■ Systematic geological modelling and rock masscharacterization in combination with a consistentevaluation of rock mass and system behaviour allows to objectively compare different construction methods in terms of feasibility, time and costs.
■ For the Mae Ngad – Mae Kuang project option 1 with thehighest share in labor intensive drill & blast due to relatively low labor costs showed to be economicallyadvantageous. Risk of delays and cost overruns due to multiple headings minimized