| Summary: | 碩士 === 國立中央大學 === 土木工程學系 === 84 === Dynamic consolidation method has a lot of merits such as
shortduration,low cost and has no pollution. Moreover, it needs
only simpleequipments and iseasy to implement with a vast range
of application. Italso has distinct impro-vement effect and can
be applied in large area ofsubsoil improvement exclusively.
Despite of having a lot of merits , thedesign and construction
of this me-thod depend on a semi-experimentalapproach. So far a
complete design system isstill unavailable. After alarge amount
of real practice in field for many years, many countries inthe
world begin to pay attention to the research of
dynmicconsolidationmethod in laboratory. In this research,
the triaxial tests,cylindrical shape tank tests,and half-
cylindrical shape tank tests were used to investigate the
variation of pore water pressure, consolidation settlement,the
volume change and the strength improvement of soil after the
treatment ofdynamic consolid-ation method for clayey or sandy
ground. Further more, thisstudy investigatedthe wave speed of
motion and behavior at the moment of impact in sandy ground with
different relative density, the relationship betweenthe
impactpressure at soil surface and the dynamic stress at a
certain depth,the settlement and deformation models of soil
under the print and the depthof crater due to impact in order to
understand and control the improvement effects and mechanical
mechanism. According to the results of these tests,it is
known that the consolid-ation settlements of soil reached the
maximum value at the moment of impact, and it increases with the
magnitude of impact pressure. This result matchedwith the
function of complete major consolidationsettlements in short
timeas dynamic consolidation method . For the excess porewater
pressure in theclay sample induced by the impact, the
dissipation time needed is much longerlonger than that for the
sandy sample. For saturated co-hesive ground in field, the
elapsed time after impact of each impact phase should be longer
to obtainto obtain a better improvement effects by impact. After
the treatment of impact, the strength of soil increases distinct
with the impact pressure, but the increment of impact pressure
has a limit which depends on the value of theconsolidation
pressure on the soil body and the degree of absorbing impact
energy. Under the same impact condition, the improvement effects
for shallow ground soil is evident superior to that of thedeep
ground. The strength increment of soil decreases with respect to
the depth. According to the mathematical formula, the factor of
concentration υ can be obtained by the dynamic stress which are
measured under the conditionof different weight and radius
ofhammer. Once the value of υ is decided, we can find the
dynamic stress in the depth Z under the soil surface by
measuringthe dynamic stress of surface duet o impact without
really measurement. The depth of crater increases with the
number of impact, but it would bereach to aconstant value when
the number of impact has reached a certain value that is called
"the best number of impact". At that time the best improvement
effects will be obtained. The effective depth of improvement
increases directly with single impact energy. It also has a
close relationship with the properties of soil（such as relative
density）and thenu mber of impact. In a word, if the major
factors such as impact energy, impact number and elapsed time
after impact of each phase can be controled well, both clayey
and sandy soil may obtain good improvement of strength in short
duration by using dynamic consolidation method. In this way we
can also take the mechanical mechanism ofsoil into our own hands
effectively.
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