Geoscience Reference
In-Depth Information
TheHDPEexperimentshavethreeprincipalresults.First,theydemonstratetheflexibility
andductilityofHDPEpiping.Maximummeasuredtensilestrainswereonly8%at1.2m
ofoffset,wellbelowtheultimatestraincapacityofthepipe.Theaxialloadinthepipeline
decreased by 40% within 2h after ground rupture. Because HDPE is visco-elastic, it has
thebeneficialeffectofreducingtheloadwithtimeatanchoragesoutsidethegroundrup-
ture zone. Second, the laser profiling shows significant ovaling and some torsion in the
pipeline. The deformation of the pipeline therefore needs to be modeled as a cylindri-
cal shell for an accurate representation of its behavior. Models based on beam-column
deformation forthistypeofHDPE pipe willbeapproximate. Third, the soildeformation
zone is 3-D, as illustrated in the figure. It develops during ground rupture progressively
as a series of nonlinear soil rupture zones that increase in size longitudinally along the
pipeline and are confined to a distance of approximately 9-10 pipe diameters on either
side of the soil rupture plane.
This latter observation is significant. The 3-D soil-pipeline deformation differs sub-
stantially from the 2-D deformation in the central zone of landslide and lateral spread
movement depicted in Figure 17.3, and generates p-y interaction with less lateral force
andlargerrelativedisplacementthanisapplicableforthe2-Dconditions.Measurements
pertaining to these 3-D conditions are being performed with tactile force sensors manu-
factured by Tekscan, Inc. These devices consist of a matrix of pressure sensitive trans-
ducers, embedded in a fabric that covers all or part of the surface of the experimental
pipeline. Preliminary results indicate that peak lateral forces per unit length of pipeline
in partially saturated soil near the ground rupture plane are about 40%-50% of those
measured for2-Dconditions.
7. Concluding remarks
Soil-structure interaction under extreme loading conditions includes performance dur-
ing earthquakes, floods, landslides, large deformation induced by tunneling and deep
excavations, and subsidence caused by severe dewatering or withdrawal of minerals and
fluids during mining and oil production. Such loading conditions are becoming increas-
inglymoreimportantastechnologies aredeveloped tocopewithnaturalhazards, human
threats, and construction in congested urban environments.
This paper examines extreme loading conditions with reference to earthquakes, which
are used as an example of how extreme loading influences behavior at local and geo-
graphically distributed facilities. The paper covers performance from the component to
the system-wide level to provide guidance in developing an integrated approach to the
application of geotechnology over large, geographically distributed networks. Specific
topicscoveredincludegeotechnicalearthquakeloading,lifelineresponsetoearthquakes,
large-scale tests of ground rupture effects, and soil-structure interaction during ground
failure.
Permanent ground deformation (PGD) is the most damaging consequence of an earth-
quake for underground facilities, including regional distribution networks for water and
