1804
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
retained side. In the site charactirization stage, a total of 105
consolidated undrained (CU) triaxial tests, with pore water
pressure measurement, were carried out. Soil design parameters
for the fill, CDG and HDG were determined based on this
testing program.
Ho et al. (2013) used two methods to design the wall. One
method is the traditional method used in Hong Kong. The other
is the CIRIA C580 method. Use of the C580 design approach
netted 10 % overall cost savings over what the wall would have
cost if designed using the traditional method. This represented
an amount of HK$ 9.6 million saving on this project. This case
history illustrates that geotechnical engineering still relies on
design methods that may be too conservative, and that savings
can be significant when more recent knowledge is put into use.
Merrifield et al. (2013) review the history of and difference
in current practice of design and testing of ground anchors in
Europe. Ground anchors were first used in rock applications,
but found their way into soil retention systems in the 1950s.
Ground anchors are routinely used in connection with
embedded (cantilevered) walls and may be viewed as enablers
of this type of retaining wall, which would otherwise be
prohibitively expensive.
Merrifield et al. (2013) discuss the differences between the
treatment of anchors in European national codes and provisional
(draft) prescriptions in Eurocode (EN-1997:2004). Prescriptions
must address the two primary limit states: an ultimate limit state
that will prevent pullout of an anchor under the maximum
expected load it will be subjected to during its service life and a
serviceability limit state related to deflections, which may be
stated in terms of loss of load or creep (in fact, an anchor is
likely to both move or deform and see a degradation in the load
it carries over its service life).
The authors call attention to an important, if not universally
recognized, detail concerning definition of limit states for walls:
serviceability limit states develop with retaining wall movement
that is typically not sufficient to develop active or passive
pressures historically assumed to act behind or in front of the
wall. As a consequence, serviceability limit states must be
defined separately from ultimate limit states. From the point of
view of anchor design, anchor resistance must be sufficient to
carry loads transferred to it by either serviceability or ultimate
limit states, and the draft provisions do account for that as well.
In part because of the empirical basis for anchor design,
proof loading has always been part of ground anchor design and
installation practice. Again, each country handles testing and
proof loads differently, a point that Merrifield et al. (2013)
discuss in detail.
7 SUMMARY AND CONCLUSIONS
Safety and serviceability are the requirements that any
geotechnical design must meet. These requirements are met
through risk management, specific design checks and proper
construction. The design checks are calculations that show that
no limit state is achieved or exceeded. One of the main tasks of
the geotechnical designer is to properly identify applicable limit
states and then produce a design that keeps the probabilities of
their occurrence below threshold levels. Guidance on
identification of limit states and specific checks to be done in
connection with these limit states are often prescribed by codes.
Recent codes, such as the Eurocode and LRFD codes attempt to
anchor the design process the notion of an acceptable
probability of failure, which depends on the problem and
consequences of achievement of a specific limit state. In the
absence of specific guidance, definition of what these limiting
probability values are sometimes must also be defined by the
designer.
The papers submitted to the XVIII ICSMGE illustrate the
complexity of probabilistic limit-states based design and
encapsulation of it in design codes. Much work still remains for
researchers and code development agencies to produce codes
and methods of analysis that will enable engineers to produce
designs that achieve safety and serviceability in an optimal and
economical manner.
8 REFERENCES
Basu, D. and Salgado, R. 2012. "Load resistance factor design of drilled
shaft in sand from soil variables."
Journal of Geotechnical and
Geoenvironmental Engineering
, ASCE 138(12), 1455–1469.
Christian, J. T. (2004). “Geotechnical engineering reliability: How well
do we know what we are doing?” 39
th
Terzaghi Lecture, Journal of
Geotechnical and Geoenvironmental Engineering, 130(10), 985-
1003.
Christian, J. T., Ladd, C. C., and Baecher, G. B. 1994. “Reliability
applied to slope stability analysis.”
J. Geotech. Eng. Div.
, 120(12),
2180-2207.
CIRIA (Construction Industry Research and Information Assocation).
2003. Embedded Retaining Walls – Guidance for Economic Design
(C580),
CIRIA
.
Cornell, C. A. 1971. “First-order uncertainty analysis of soils
deformation and stability.” Proc. 1
st
international Conference on
Applications of Probability and Statistics in Soil and Structural
Engineering, Hong Kong, 129-144.
European committee for standardization, CEN. 2004.
EN 1997-1
Eurocode 7: Geotechnical design.
Brussels: European committee
for standardization.
Foye, K. C. and Salgado, R. 2005. “Soil Characterization for Consistent
Reliability in the Load and Resistance Factor Design of Pile
Foundations.” International Symposium on Frontiers in Offshore
Geotechnics. Perth, Western Australia, Australia.
Foye, K. C., Prezzi, M., and Salgado, R. 2011 “Resistance Factors for
Design of Piles in Sand: Tools to Understand Design Reliability.”
3rd International Symposium on Geotechnical Safety and Risk.
Munich, Germany.
Foye, K. C., Prezzi, M., and Salgado, R. 2011 “Developing Resistance
Factors for Design of Piles in Sand.” GeoRisk 2011. Atlanta,
Georgia.
Ho, A., Wright, M. and Ng, S. 2013. "Deep Excavation in Hong Kong –
Cantilever Bored Pile Wall Design Using CIRIA Report No.
C580."
XVIII International Conference on Soil Mechanics and
Geotechnical Engineering, September, Paris, France.
Katzenbach, R., Bohn, C. & Wehr, J. 2013. "Comparison of the safety
concepts for soil reinforcement methods using concrete columns."
XVIII International Conference on Soil Mechanics and
Geotechnical Engineering, September, Paris, France.
Kim, D.W. and Salgado, R. 2012a. "Load and resistance factors for
external stability checks of mechanically stabilized earth walls."
Journal of Geotechnical and Geoenvironmental Engineering
,
ASCE 138(3), 241–251.
Kim, D.W. and Salgado, R. 2012b. "Load and resistance factors for
internal stability checks of mechanically stabilized earth walls."
Journal of Geotechnical and Geoenvironmental Engineering
,
ASCE, 138(8), 910-921.
Kim, J., Salgado, R., and Yu, H. S. 1999. "Limit analysis of soil slopes
subjected to porewater pressures."
J. Geotech. Geoenviron. Eng.,
125(1), 49-58.
Kim, J., Salgado, R., and Lee, J. 2002. "Limit analysis of complex soil
slopes."
J. Geotech. Geoenviron. Eng.,
128(7), 546-557
.
Länsivaara, T. & Poutanen, T. 2013. "Slope stability with partial safety
factor method."
XVIII International Conference on Soil Mechanics
and Geotechnical Engineering, September, Paris, France.
Larsson R., Bergdahl U., Eriksson L. 1984. Evaluation of shear strength
in cohesive soils with special reference to Swedish practice and
experience. SGI Inf. Linköping. No. 3, 1-32
Lechowicz, Z & Wrzesiński, G. 2013. "Assessment of embankment
stability on organic soils using Eurocode 7."
XVIII International
Conference on Soil Mechanics and Geotechnical Engineering,
September, Paris, France.
Lee, J. and Salgado, R. 1999. "Determination of pile base resistance in
sands."
Journal of Geotechnical and Geoenvironmental
Engineering
, ASCE, 125(8), 673-683.
Loehr, J.E., Bowders, J.J., Rosenblad, B.L., Luna, R., Maerz, N.,
Stephenson, R.W., Likos, W.J. & Ge, L. 2013. "Implementation of
LRFD Methods to Quantify Value of Site Characterization
Activities."
XVIII International Conference on Soil Mechanics and
Geotechnical Engineering, September, Paris, France.
