Utilizing GDS unsaturated triaxial apparatus and pressure plate extractor, the tensile crack propagation depth of
unsaturated expansive soils is studied. A linear elastic solution of the tensile crack propagation depth is presented and
reduced coefficient of effective cohesion is defined. Expressions for critical matrix suction at the ground surface, and the
crack propagation depth with no influence of the depth of the groundwater level are derived from the equation of crack
propagation depth. Relationships with influencing factors are compared, such as effective cohesion, reduced coefficient
of effective cohesion, effective internal friction angle, Poisson's ratio, matrix suction at the ground surface and the depth
of the groundwater level. Based on above, the influences of tensile cracks on tension zone depth are analyzed,
considering three typical matrix suction profiles along the depth, that is, constant, linear and parabolic distributions.
Vegetation includes all plant communities that cover the earth surface. And vegetation cover is the most important
index to scale the status of the vegetation of the region, so the vegetation is the composition and the function body of
ecological system. Vegetation cover in different districts of Wuhan were calculated based on remote sensing images (TM
images and ETM+ images) in 1988, 1991, 1996 and 2002 by employing NDVI method for dimidiate pixel model, and
the vegetation cover maps of different periods were generated to analysis the temporal change of vegetation cover of
Wuhan area. The results showed that, the vegetation cover changed much from 1988-2002; the average vegetation cover
of the whole area was decreased from 58.41% to 50.45%, especially in Jiangxia district and the central district. From
1996 to 2002 is the period which vegetation cover decreased the most sharply in this period. From 1991 to 1996 the
vegetation cover was lightly increased in the whole study area. Analyzing spatial changing characteristics in the whole
study area we can see that, the whole area was in the decreasing moment, especially in Jiangxia district and the central
district, this was the result of urban development, and led to the huge development of the environment, worthy of all
aspects of attention.
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