The basal entrainment of debris flows play a significant role in its amplification and the final volume of deposition could be several to hundred times of its initial volume. In this paper, the ...shallow water equations coupled with basal material entrainment applied in debris flows have been given to demonstrate the amplification. A new basal entrainment model taking advantage of both Coulomb and Voellmy frictional laws are proposed, providing a unified formula to simulate the stop-and-go process of debris flows. Both time and space second-order MacCormack-TVD finite difference method is suggested to solve the coupled equations. Numerical comparisons with USGS flume experiment and Hongchun gully debris flow in Wenchuan earthquake-induced area are carried out to prove its effectiveness. It is established that the momentum exchange term between the flows and the basal materials has a significant influence on the dynamic characteristics and the entrainment effects are essential to model the dynamic process of debris flows in an earthquake-induced area.
•A new entrainment model which satisfies the momentum jump condition is proposed.•The coupled mass and momentum conservation equations on erodible beds are derived and solved.•The modeling of flume experiments and Hongchun debris flow are well calculated.
A series of laboratory tests were performed to assess the effects of confining pressure on the mechanical properties and fatigue damage evolution of sandstone samples subjected to cyclic loading. Six ...levels of confining pressure (2.0, 10.0, 20.0, 30.0, 40.0 and 50.0MPa) were applied during axial cyclic loading at a 1.0Hz frequency using a MTS-815 Rock and Concrete Test System. Results from the cyclic dynamic loading tests indicated that the level of confining pressure had a significant influence on the cyclic dynamic deformation and fatigue damage evolution of the sandstone samples tested. With increasing confining pressure, the axial strain at failure increased, as did the residual volumetric strain at the initiation of dilatancy. The residual axial strains of sandstone samples obtained at a confining stress state can be described as three deformational stages, namely, the initial phase, uniform velocity phase and accelerated phase. Both the residual strain method and the axial secant modulus method proposed here could be used to describe the initial fatigue damage and degradation process of sandstone samples subjected to fatigue loading under a confining stress state; however, the latter also considers the influence of stress level on fatigue damage evolution when fatigue loads are applied. At a constant confining pressure, the shear fracture plane can form under static and cyclic dynamic loading conditions, and the higher the confining pressure, the wider the shear fracture planes become under cyclic dynamic loadings.
► Axial cyclic dynamic loading tests were conducted on rock samples at confined stress state. ► Confining pressure affects the cyclic dynamic deformation, fatigue damage of rocks greatly. ► With the increasing confining pressure, the axial strain at failure increases. ► The axial secant modulus method proposed can consider the influence of level stress. ► The axial secant modulus method proposed can describe fatigue damage evolution well.
We study the 2D Navier–Stokes equations linearized around the Couette flow
(
y
,
0
)
t
in the periodic channel
T
×
-
1
,
1
with no-slip boundary conditions in the vanishing viscosity
ν
→
0
limit. ...We split the vorticity evolution into the free evolution (without a boundary) and a boundary corrector that is exponentially localized to at most an
O
(
ν
1
/
3
)
boundary layer. If the initial vorticity perturbation is supported away from the boundary, we show inviscid damping of
both
the velocity
and
the vorticity associated to the boundary layer. For example, our
L
t
2
L
y
1
estimate of the boundary layer vorticity is
independent of
ν
, provided the initial data is
H
1
. For
L
2
data, the loss is only logarithmic in
ν
. Note both such estimates are false for the vorticity in the interior. To the authors’ knowledge, this inviscid decay of the boundary layer vorticity seems to be a new observation not previously isolated in the literature. Both velocity and vorticity satisfy the expected
O
(
exp
(
-
δ
ν
1
/
3
α
2
/
3
t
)
)
enhanced dissipation in addition to the inviscid damping. Similar, but slightly weaker, results are obtained also for
H
1
data that is against the boundary initially. For
L
2
data against the boundary, we at least obtain the boundary layer localization and enhanced dissipation.
This study aimed to develop an integrated model of the runoff-generated debris flow that considers the initial conditions, movement mechanisms, and entrainment effect. The study focused on the ...formation and propagation processes of debris flow within a catchment, and the process is divided into three stages: rainfall infiltration, runoff, and debris flow routing. Soil saturation, rainfall, and entrainment are the main factors that influence the debris flow formation and propagation processes. Existing models for each stage, including Richards’s equations, shallow water equations, and two-phase debris flow equations, were coupled. The tridiagonal matrix algorithm and finite volume method were applied to solve these equations. Finally, several experimental cases and the 2010 debris flow event in the Hongchun catchment in China were simulated by using the proposed model. The results showed that the proposed model could effectively describe the behaviours of each stage during the debris flow formation and propagation processes. Although several aspects of the model require further improvement, the physical-parameter-based prediction of runoff-generated debris flows from formation to propagation is effectively performed by the model.
The 2010 Mount Meager landslide generated strong seismic waves. We used seismic signals generated by a smaller landslide that occurred within 2 min of the end of the main landslide as the empirical ...Green's function (EGF) with which to obtain landslide dynamics from high‐frequency signals. We then obtained the apparent force‐time function of the landslide based on the EGF by inverting the higher‐frequency seismic signals. The apparent force‐time function shows that the source material of the main landslide came from four collapses and that the second collapse involved multiple small collapses. We also used the EGF to simulate the vertical seismogram recorded at one station and found that the synthesized seismogram fits the response of the bulk mobilization of the sliding materials remarkably well. Our study demonstrates that the use of the EGF can significantly broaden quantitative insights into landslide dynamics.
Plain Language Summary
Seismic records reflect the effects of landslide dynamics and the path of seismic waves through the Earth. Because the calculation of the high‐frequency component of the effect of a wave's path through the Earth requires a detailed characterization of the velocity and attenuation structure, the effects of landslide dynamics can only be estimated by inverting the long‐period seismic signals. To study the high‐frequency seismic signals generated from the Mount Meager landslide, we considered the seismic signals generated by a smaller landslide as the effects of the path of seismic waves. We used the seismic signals generated by the smaller landslide to simulate the signal generated by the main landslide to overcome the effects of a potential overlap in the frequency domain between signals from the bulk and those from smaller particles. Our results show that the seismic signals generated by a small landslide can be used to improve our understanding of those generated by the main landslide.
Key Points
The empirical Green's function was used to invert the apparent force‐time function of a landslide
The dynamic properties of the landslide were estimated from high‐frequency signals
The potential overlap in the frequency domain between signals from the bulk and those from smaller particles was analyzed
•Baffles system can reduce the deposit area of rock avalanches by more than 13.5%.•Shape changing (cylindrical to arc-shaped) will up-regulate the fragment blockage degree; the following avalanches ...will take place close to the avalanche deposition, leading to a huge dissipation of kinetic energy.•Arc-shaped baffle system showed competitive blocking ability when Sc=3.5 and Sr=4.5.•The number of rows mainly affects the avalanches deposit area and the baffles blocking capacity.•Baffles’ spacing Sc mainly affects its blocking efficiency.
To reduce the flow energy of rockfall in rmountain area, a baffle array is set up in the protection zone. The optimized design can enhance the efficiency of hazard source energy dissipation project. In the present study, the arc-shaped baffles were studied as compared with the conventional baffles (square baffles and cylindrical baffles) based on practical engineering. The comparison of three types of baffles was discussed in detail by experimental studies, which primarily focused on the blocking ability and effectivity. In particular, by determining the optimal case using those different types of baffles, the effects of the optimization of baffle system column spacing, row spacing and Ld (distance between first baffle row and chute terminal) were investigated. According to the results, the arc-shaped baffle is the best case among those three types of baffle, i.e. the deposit area and runout are all shorter than those of any other cases with the same value of Sr. Shape changing (cylindrical to arc-shaped) will up-regulate the fragment blockage degree; the following avalanches will take place close to the avalanche deposition, leading to a huge dissipation of kinetic energy. Moreover, by comparing deposition, dimensionless velocity (U*) and velocity reduction ratio (VRR), arc-shaped baffle system showed competitive blocking ability when Sc=3.5 and Sr=4.5. With the rise in the Ld, the energy dissipation efficiency can be enhanced through the particle collision and particle friction during the geo-disaster movement. Furthermore, it can effectively narrow the deposit area and reduce deposit depth and deposit width. The results obtained from this study are useful for facilitating design of baffles against rock avalanches.
The material point method (MPM) has been widely used in the simulation of large deformation problems involving hydromechanical coupling recently. Here, an explicit stabilized formulation of ...hydromechanically coupled two-phase MPM with zero air pressure for both saturated and unsaturated conditions is presented, and to avoid numerical instability when low-order MPM is applied to hydromechanically coupled problems, techniques including low-order shape functions based on the Hu-Washizu multi-field variational principle, the B-bar matrix, and the reduced integration are implemented in the algorithm of MPM. The accuracy of the formulation is verified through numerical examples involving the consolidation problem and Liakopoulos drainage test, and then, two cases, the unsaturated slope failure under rainfall infiltration as well as the Yanyuan landslide, are performed. The simulation results further demonstrate the capability of the present formulation to capture the hydromechanical behavior as well as the failure and post-failure stages when modelling hydromechanical large deformation problems.
Construction solid waste (CSW) landslides are always characterized by high mobility, and thus pose much danger to surrounding residents and buildings. In this study, a back in situ analysis of the ...catastrophic CSW landslide occurred in Shenzhen in December 2015 is presented, in which the motion-accumulation evolution process of the landslide and damage to structures are reproduced, and reasonable agreement between the simulation and actual conditions is obtained. In landslide process modeling, a depth-averaged model that can undergo dilation and contraction during deformation is adopted to simulate the behavior of the landslide assuming different conditions of initial solid volume fraction. The results show that a small initial solid volume fraction of a water-laden landslide undergoes small resistance caused by dilatancy. On the basis of landslide process analysis, the fluid–solid interaction is decoupled and considered to be a one-way action of the landslide on structures, which is reflected in the form of impact force. Structural response is evaluated by 3D finite element modeling. The failure process presents a type of plastic hinge formation at the beam–column connection positions, followed by local destruction of the impacted columns, and final structural failure is the cumulative result of this damage over time. This integrated approach could be implemented in quantitative risk assessment procedures pertaining to landslides.
•A depth-averaged model considering dilatancy effect is adopted to describe the high mobility of CSW landslide.•The failure analysis of structure is based on landslide movement process, which indicates the time effect of damage.•Reasonable agreement between simulation and observed conditions is obtained.
This study aimed to investigate the formation and propagation processes of a landslide-generated debris flow within a small catchment while considering the effects of vegetation. This process is ...divided into three stages: rainfall infiltration, slope failure, and debris flow routing, according to their different mechanisms. Existing models that involve the effect of vegetation for each stage, including Richards’s model, infinite slope stability model, and the enhanced two-phase debris flow model (Pudasaini
2012
), were coupled. The tridiagonal matrix algorithm and finite volume method were applied to solve these equations, respectively. Finally, the approach was tested by application to the 2018 debris flow event in the Yindongzi catchment, China. The results showed that the proposed comprehensive model could effectively describe the behaviors of each stage during the formation and propagation processes of landslide-generated debris flows in vegetated area. The roles of vegetation on each stage, such as root water uptake and root soil reinforcement, were also analyzed by performing several scenarios.
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