A study of landslide deformation fieldwith digital correlation method
2016
Landslides are one of the main geological disasters that persist
in the reservoir after the completion and dynamic water storage of
the Three Gorges Dam, and it is a threat to the safety of the residents
along the river and shipping. The increase of landslides around the
reservoir is affected by the yearly cycle of impoundment and flood
water discharged from the dam, and precipitation, etc. Hence, monitoring
the reservoir accurately and timely is one of the essential means
for preventing disasters like landslide in the Three Gorges. In this
work, we apply the photogrammetry method to the field of landslide
monitoring on the basis of previous methods. We develop a solving
method of landslide displacement field based on the image gray feature
matching. First, image capture equipment like camera, vidicon is utilized
to photograph the dynamic and static fields or movement process so
as to obtain the time series images. Then kinematic variables like
position, velocity, acceleration and deformation variables like displacement
and strain are calculated by analyzing the images with digital correlation
method. The essential idea of the image gray feature matching method
is based on the viewpoint of statistics. Images in this method are
treated as two-dimensional signals for searching corresponding match
between signals by using correlation method. We can match two images
around the same site before and after the landslide and obtain the
displacement of this point. The Woshaxi landslide of Zigui County,
Hubei Province is chosen as the study object, and we obtain the displacement
field over time and the displacement vector of the landslide. The
overall displacement is up to 50 cm, and the value and direction of
regional displacement of the landslide surface are not completely
the same. The overall landslide surface move rightward in the horizontal
direction, and slid downward to the river in the direction vertical
to the flow direction of the river. The vertical displacement is relatively
larger in comparison with the horizontal displacement. Therefore,
landslide movement is a non-uniform and non-rigid body motion. By
integrated use of the speckle method, gray feature search and other
related serial methods, we succeed in dealing with landslide problems
like small deformation relationship and large displacement movement.
As a new observation method, this method also solves problems, such
as the registration of collected images and the peering of gray level.
We calculate the variation and direction of displacements of all points
on the landslide and obtain the distribution map of the landslide
displacement. The error in the indoor calibration test was within
the acceptable range, which verified the validity of this method.
The measuring method of the landslide displacement field proposed
in this work possesses advantages of whole field, non-contact and
flexible monitoring range like the traditional photogrammetry, as
well as other advantages such as large deformation measuring range,
good adaptability of environment, etc. Compared with the traditional
point measurement method, this method may not only obtain displacement
data of more landslide points, but also monitor the global deformation
of the landslide and observe and predict the whole movement behavior
of the landslide. This method bounds the observation range to every
specific landslide, has higher displacement resolution, and is unconstrained
by weather condition, attitude angle and flight cycle relative to
the photogrammetry based on satellite images. More importantly, the
cost of data acquisition is relatively low in this method. We can
set up cameras at landslide points and realize unattended data acquisition
and analysis, i.e., autonomic monitoring and early warning of landslide
displacement. Consequently, this method has a good application prospect.
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