The 3-D Facies and Geomechanical Modeling of Land Subsidence in the Chaobai Plain, Beijing
L. Zhu, H. Gong, Y. Ke, Y. Pan, X. Li
College of Resource Environment and Tourism, Capital Normal University,
Beijing Key Laboratory of Resource Environment and Geographic Information System, Beijing, China
Z. Dai
College of Construction Engineering, Jilin University, Changchun, China
A. Franceschini, M. Ferronato, P. Teatini
Dept. of Civil, Environmental and Architectural Engineering,
University of Padova, Padova, Italy
R. Wang
Beijing Institute of Hydrogeology and Engineering Geology, Beijing, China
The hydrogeologic systems of alluvial fan are characterized by a heterogeneous distribution
of various lithological units/facies. The structure (integral scale and volumetric proportion)
of the hydrofacies distribution and the values of the hydrogeomechanical parameters of each
facies can play a major role on the system response to groundwater withdrawal in term of land
subsidence. We propose a novel approach where stochastically simulated hydrofacies distributions
are coupled with 3-D finite element groundwater flow and geomechanical simulations to characterize
land subsidence and horizontal movements due to groundwater withdrawal under a statistical framework.
The integrated approach is applied on the Chaobai alluvial plain, China, an area of about 1,100 km2
where the main wellfields supplying water to Beijing are located. Groundwater pumping from the 1960s
to now caused a land subsidence larger than 1 m and the present subsidence rate peaks to 70 mm/year.
A Monte Carlo simulation with 100 hydrofacies generations is used. The model outcomes highlight how
the heterogeneous structure of the hydrofacies fan reflects into the computed displacement fields.
The standard deviation associated to the mean displacement field amounts up to 1/10 of the
displacement components. The larger coefficient of variation (CV up to 0.5) is associated to the
zone characterized by longer integral scale and with localized groundwater withdrawals. The computed
variability of the subsidence rate, in the range of 1 to 3 mm/year, reflecting the intrinsic
heterogeneous nature of an alluvial fan, corresponds to the short-distance variability of land
subsidence measured by persistent scatterer interferometry.
