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Dynamic Analyses of Rock Avalanche Focusing on the Effects of Block Size and Block ShapeBased on Discontinuous Deformation Analysis〇Changze LI, Gonghui WANG
1. Introduction
Rock avalanches are massive, extremely rapid, far-models with the same volume but different block sizes
or rock shapes are conducted using 3D DDA.

reaching landslides originating from the abrupt

Table 1. Parameters in muti-block rockfall model.

rockfalls and rockslides. Rock avalanches involve thedestruction and posing a significant threat to bothParameter
Density (kg/m3)
Poisson’s ratio
Young’s modulus E(GPa)Friction ϕ (°)
Model for size/shapeCOR

people and infrastructure. Heim's observation in 1932

Figure 1 and Figure 2 demonstrates the geometry

revealed that as the volume of a rock avalanche

parameters of rockfall model and the definition of theincreases, its mobility also increases. This phenomenon

models’ name, respectively. The size of rockfall model

was characterized by plotting the ratio of its pre-fallfor block shape analysis is magnified by a factor of two.

height to the farthest horizontal runout distance (H/L).

The differences in runout distance, velocity, and theHowever, the complex nature of the dynamic processes

H/L ratio during the movement are discussed.

disintegration of initially intact rock masses during
descent, creating highly fragmented debris that spreads
over vast areas within minutes. Their travel velocities
can exceed 10 meters per second, leading to widespread

Rock Mass
2500
0.2

Base Block/
0.2

1.0

1.0

25/30

25/15

0.925~0.928

0.925~0.928

and the challenges in observing or replicating rockavalanches have resulted in a limited understanding ofthe behavior and deformation patterns of rockavalanches from experiments and field studies.
Consequently, the scientific literature still contains
ongoing challenges on this topic. In this study, weemploy the 3D Discontinuous Deformation Analysis(3D DDA) to simulate multi-block rockfalls, with theaim of analyzing the impacts of the block size, andFigure 1. (a) Rockfall numerical model (volume is 1

block shape on runout distance, collision frequency,m3) in 3D DDA (Okura et al., 2000) and (b) geometry

and the H/L ratio of rock avalanche.

parameters of rockfall model.

2. Method and numerical models
Numerical modelling methods can overcome some ofthese limitations in experimental and field studies andprovide a more feasible method for simulating rockavalanches. Among these numerical methods, 3D DDA
is a powerful technique for modelling the movement ofrockfall. In this study, to unravel the dynamic behaviorsof rockfall, dynamic analyses of multi-block rockfall

Figure 2. Number of pieces in Ln×Dn×Hn sides forblock shape analysis (volume is 8 m3).

3. Results and discussions

compared to length.

The effect of block size on the H/L ratio, denoted asf, is investigated, as shown in Figure 3. It is observedthat f decreases with an increasing number of sides(equivalently, a decrease in block size), indicating alonger runout distance. As for fg, it decreases with theincreasing size number when size number is lower than
3 and then increases when the size number is larger than
3. Additionally, simulations reveal that the back-tofront relative positions of the blocks remain largely
consistent with the downflow direction during
movement. Moreover, blocks initially located in themiddle part tend to experience more collisions

Figure 4. Relation curves of f = H/L and r fg = Hg/Lg

throughout the rockfall process.

with respect to slice number in each direction of side.
Summary
The effects of block size and shape on the rockavalanche were studied by simulating the muti-blockrockfall models based on 3D DDA. It was found that:
1)With the decrease of block size, f decreases,
indicating a longer runout distance.

2)

fg decreases with the increasing size number whensize number is lower than 3 and then increases
when the size number is larger than 3.

3)
Figure 3. Relation curves of equivalent coefficient offriction f = H/L and gravity-center fg = Hg/Lg withrespect to side number.

Blocks initially located at middle part experience
more collisions during the rockfall process.

4)

f decreases rapidly while fg decreases slightly withthe decreasing length, width and heigh of block.

In the analysis of a rockfall model with varying block
shapes, simulations were conducted for models withdimensions 6×6×6, 9×6×6, 12×6×6, 6×9×6, 6×12×6,6×6×9, and 6×6×12, corresponding to aspect ratios of
1:1:1, 3:2:2, 2:1:1, 2:3:2, 1:2:1, 2:2:3, and 1:1:2,respectively.

The results, presented in Figure 4,

Acknowledgments
Financial support for this study was provided by theJST SPRING (Grant Number JPMJSP2110). The
financial supports are gratefully acknowledged.
References

reveal that as the number of slices in each side direction

Okura, Y., Kitahara, et al., 2000. The effects of rockfall(Ln, Dn, and Hn defined in figure 2) increase, thevolume on runout distance. Engineering Geology

equivalent coefficient of friction f decreases rapidly

58(2): 109-12

while the equivalent coefficient of friction at gravity

Chen Guangqi, Zheng Lu, et al., 2013. Numericalcenter fg shows a slight decrease. Moreover, thesimulation in rockfall analysis: a close comparison ofsimulations indicate that the width and height of each

2-D and 3-D DDA. Rock Mechanics and Rockblock have a more significant impact on the value of fEngineering.;46(3):527-541.