On the energy budgets of fragmenting rockfalls and rockslides: Insights from experiments

Abstract

The travel lengths of rockfalls and rockslides can be difficult to predict due to complex interactions of numerous physical processes, such as fragmentation of the rock mass and its effect on the energy dissipation through basal and internal friction. Previous studies have shown that the front of the rockslide deposits travels farther with increased fragmentation. However, little is known about the displacement of the center of mass, which is the relevant parameter for studying the energy budget, leaving open the question whether fragmentation acts as an effective sink or source of energy. Taking advantage of a newly developed rock analogue material, we perform a total of 109 experiments to study the effect of fragmentation on the displacement of the center of mass and the energy budget of experimental rockslides. To determine the degree of fragmentation, we define a characteristic fragment size from the total mass of the experimental sample and the mass of the largest fragment. The degree of fragmentation is seen to depend linearly on the aspect ratio of the experimental sample and as a power law on its cohesion. Similar to the previous studies, our results show that the travel distance of the front of the deposits increases with the degree of fragmentation. In contrast, displacement of the center of mass is reduced with the degree of fragmentation, suggesting increased energy consumption, consistent with the assumption that fragmentation acts effectively as an energy sink.

Contributions of Rock Mass Structure to the Emplacement of Fragmenting Rockfalls and Rockslides: Insights From Laboratory Experiments

“…According to our additional 60 friction tests of sliding masses on matte paper, the variation in the friction coefficient caused by recurrent friction between the experimental materials and matte paper is very small and negligible during our 36 experiments. The sliding distance of the materials on the inclined slab (L) is 2 m. This kind of experimental model is similar to those used in previous slab experiments (Davies & McSaveney, 1999; Manzella & Labiouse, 2009; Bowman et al, 2012; Haug et al, 2016; Zhao et al, 2017, 2018), which allows us to compare our results with those from previous studies.…”

“…Such events can cause many casualties and economic losses due to their great destructive power, unusually high velocity and unpredictable runout (Erismann & Abele, 2001; Evans et al, 2006; Legros, 2002; Pudasaini & Miller, 2013). Many efforts, such as field investigations (Dufresne et al, 2016; Voight, 1978; Weidinger et al, 2014), laboratory experiments (Davies & McSaveney, 1999; Haug et al, 2016; Manzella, 2008; Shea & Benjamin, 2008; Valentino et al, 2008), and numerical simulations (Pudasaini & Hutter, 2007: Pirulli, 2009; Cagnoli & Piersanti, 2017; Zhao et al, 2017), have been made over a hundred years. Although some advancements have been made, the prediction of the travel distance and the risk area of rockfalls and rockslides, especially rock avalanches, is still challenging.…”

“…In rock avalanching, some researchers consider that fragmentation is an energy sink, as the new surface area increases with energy consumption, which eventually shortens the travel distance (Crosta et al, 2007; Haug et al, 2016; Locat et al, 2006); others insist that fragmentation may introduce different mechanical processes that can lead to higher mobility or at least increase the distance of the distal edge of the deposit (Bowman et al, 2012; Davies et al, 1999; Davies & McSaveney, 2009, 2016; De Blasio & Crosta, 2015; Zhao et al, 2017). Haug et al (2016) proved that the displacement of the center of mass decreases with the degree of fragmentation, suggesting an energy sink during fragmentation in rockfalls and rockslides. However, Davies et al (2019) stated that only a small portion of energy is consumed as fracture surface energy in creating new surface area following fragmentation, and the main part of the energy is possibly converted into an elastic body wave.…”

Dynamic Fragmentation of Jointed Rock Blocks During Rockslide‐Avalanches: Insights From Discrete Element Analyses

“…Rock avalanches are always associated with dynamic rock fragmentation (Davies & McSaveney, 1999;De Blasio & Crosta, 2015;Locat et al, 2006), together with high spreading velocities, long runouts, and energy release, affecting the overall mobility and destructive power of rock avalanches (Agliardi & Crosta, 2003;Perinotto et al, 2015;Ruiz-Carulla et al, 2017). The related research has been performed by means of field observations in real rock avalanche deposits (Crosta et al, 2007;Dunning, 2006;Locat et al, 2006;Strom, 2006) and physical and numerical modeling (Bowman et al, 2012;Giacomini et al, 2009;Haug et al, 2016;Imre et al, 2010;Zhao et al, 2017). During the dynamic fragmentation, cracks propagate within the rock mass under compressive or tensile loading, together with the transmission and reflection of stress waves at impact (Crosta et al, 2007;Thornton et al, 1996).…”

“…Notwithstanding these advancements, a thorough understanding of the physical processes responsible for rock avalanche motion and dynamic fragmentation is still needed. In recent studies, Bowman et al (2012), Bowman and Take (2015), and Haug et al (2016) investigated the fragmentation of a small brittle block, sliding along an inclined plane, against a slope break. These studies have been considered as reasonable initial proxies to study rock fragmentation and propagation (De Blasio & Crosta, 2015).…”