Abstract
Groundwater is an important factor of slope stability, and 90% of slope failures are related to the influence of groundwater. In the past, free surface calculations and the prediction of water inflow were based on Darcy's law. However, Darcy's law for steady fluid flow is a special case of non-Darcy flow, and many types of non-Darcy flows occur in practical engineering applications. In this paper, based on the experimental results of laboratory water seepage tests, the seepage state of each soil layer in the open-pit slope of the Yanshan Iron Mine, China, were determined, and the seepage parameters were obtained. The seepage behaviour in the silt layer, fine sand layer, silty clay layer and gravelly clay layer followed the traditional Darcy law, while the gravel layers showed clear nonlinear characteristics. The permeability increases exponentially and the non-Darcy coefficient decreases exponentially with an increase in porosity, and the relation among the permeability, the porosity and the non-Darcy coefficient is investigated. A coupled mathematical model is established for two flow fields, on the basis of Darcy flow in the low-permeability layers and Forchheimer flow in the high-permeability layers. In addition, the effect of the seepage in the slope on the transition from Darcy flow to Forchheimer flow was considered. Then, a numerical simulation was conducted by using finite-element software (FELAC 2.2). The results indicate that the free surface calculated by the Darcy–Forchheimer model is in good agreement with the in situ measurements; however, there is an evident deviation of the simulation results from the measured data when the Darcy model is used. Through a parameter sensitivity analysis of the gravel layers, it can be found that the height of the overflow point and the water inflow calculated by the Darcy–Forchheimer model are consistently less than those of the Darcy model, and the discrepancy between these two models increases as the permeability increases. The necessity of adopting the Darcy–Forchheimer model was explained. The Darcy–Forchheimer model would be applicable in slope engineering applications with highly permeable rock.
Highlights
In China, from 1949 to 2011, even the most conservative estimates of the deaths from landslides exceed 25 000 people, which was a death toll of more than 400 people each year, and the average annual pecuniary loss was $50 million dollars [1]
The position of the free surface has a great effect on the slope stability; the stability safety coefficient of a soil slope gradually decreases with the continuous increase in the free surface area, until slope sliding occurs [9]
The velocity reaches a maximum value of 3 mm s−1 at the outlet of the slope surface; this value is approximately equal to the measured velocity of 2.3 mm s−1
Summary
In China, from 1949 to 2011, even the most conservative estimates of the deaths from landslides exceed 25 000 people, which was a death toll of more than 400 people each year, and the average annual pecuniary loss was $50 million dollars [1]. To investigate the influence of the drawdown on the slope stability and pore water pressure, Wang et al [7] performed some laboratory physical model tests. According to different theories and methods, including Darcy theory and non-Darcy theory, the results of these studies are sometimes very different
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