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EXTERNAL STABILITY OF VERTICAL EXCAVATIONS IN SOFT
CLAY WITH SELF-SUPPORTED DMM WALLS
Ala'a El Nahas and Jiro Takemura
ABSTRACT: Six centrifuge tests were conducted to study the possible failure
mechanisms for open excavations in soft clay with DMM self-supported
walls, and the pre-failure soil and wall behavior, as well as the effect
of some parameters on the wall external stability. In the tests,
in-flight excavation was conducted until failure. The DMM wall was
modeled by a wall made from aluminum and acrylic plates, which were
instrumented with pressure cells to measure the active and passive earth
pressures, and the base contact pressure of the wall during excavation.
Upper bound analysis was conducted to verify the efficiency of the
current used design method, and to identify the main parameters which
affect the external wall stability.
It was found that the failure of the excavations with by the DMM
self-supported walls floating in the clay, took place suddenly without
marked pre-failure soil and wall movements. The main parameters which
affect the wall stability are the wall dimensions, the soil strength
profile, the adhesion between the wall surfaces and the surrounding
clay, the strength anisotropy, and the surcharge on the clay surface.
The soil strength profile and the adhesion between the wall surfaces and
the clay were found to be the most important parameters.
Keywords: open excavation, soft clay, DMM, self-supported wall,
stability, deformation, centrifuge test, and upper bound calculation. (IGC:
H2)
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