Ejected Rocks Research Articles

Spalling characteristics of sandstone containing rectangle hole with gradient cavity height: An experimental and DEM numerical study

Spalling failure commonly exists during the progressive excavation of underground engineering, and the stepped excavation of underground mining stope is rarely simulated in previous studies. Therefore, the biaxial compression test is finished by sandstone samples containing rectangular hole (with different cavity heights), and the corresponding numerical simulation is conducted by the discrete element method. Based on the mechanical, optical and acoustic data captured during the test, the main results and conclusions are as follows: 1) There are two paths to activate the typical spalling failure, the first way is caused by the rapid energy release (manifested as sudden AE burst), and the second way is that the released energy accumulates to a threshold over a long period and finally causes large-scale damage. 2) The relatively larger cavity height delayed the initiation of central tensile failure in the roof & bottom surrounding rocks and the spalling failure in sidewalls. 3) The relatively larger confining pressure contributes to the early construction of the spalling failure and limits the extension of the central tensile crack bands. 4) The construction of spalling failure is very fast, the ejected rock plates are caused by several rounds of spalling failure, and the final V-shaped groove is built by the spalling failure and internal crushing failure.

Evaluation of the performance of yielding rockbolts during rockbursts using numerical modeling method

The assessment of yielding rockbolt performance during rockbursts with actual seismic loading is essential for rockburst supporting designs. In this paper, two types of yielding rockbolts (D-bolt and Roofex) and the fully resin-grouted rebar bolt are modeled via the “rockbolt” element in universal distinct element code (UDEC) after an exact calibration procedure. A two-dimensional (2D) model of a deep tunnel is built to fully evaluate the performance (e.g., capacity of energy-absorption and control of rock damage) of yielding and traditional rockbolts based on the simulated rockbursts. The influence of different rockburst magnitudes is also studied. The results suggest that the D-bolt can effectively control and mitigate rockburst damage during a weak rockburst because of its high strength and deformation capacity. The Roofex is too “soft” or “smooth” to limit the movement of ejected rocks and restrain the large deformation, although it has an excellent deformation capacity. The resin-grouted rebar bolt can maintain a high axial force level during rockbursts but is easy to break during dynamic shocks, which fails to control rapid rock bulking or ejection. Three types of rockbolts cannot control the large deformation and mitigate rockburst damage effectively during violent rockbursts. The rockburst damage severity can be significantly reduced by additional support with cable bolts. This study highlights the effectiveness of numerical modeling methods in assessing the complex performance of yielding rockbolts during rockbursts, which can provide some references to improve and optimize the design of rock supporting in burst-prone grounds.

A steeply-inclined trajectory for the Chicxulub impact

The environmental severity of large impacts on Earth is influenced by their impact trajectory. Impact direction and angle to the target plane affect the volume and depth of origin of vaporized target, as well as the trajectories of ejected material. The asteroid impact that formed the 66 Ma Chicxulub crater had a profound and catastrophic effect on Earth’s environment, but the impact trajectory is debated. Here we show that impact angle and direction can be diagnosed by asymmetries in the subsurface structure of the Chicxulub crater. Comparison of 3D numerical simulations of Chicxulub-scale impacts with geophysical observations suggests that the Chicxulub crater was formed by a steeply-inclined (45–60° to horizontal) impact from the northeast; several lines of evidence rule out a low angle (<30°) impact. A steeply-inclined impact produces a nearly symmetric distribution of ejected rock and releases more climate-changing gases per impactor mass than either a very shallow or near-vertical impact.

Phobos LIFE (Living Interplanetary Flight Experiment).

The Planetary Society's Phobos Living Interplanetary Flight Experiment (Phobos LIFE) flew in the sample return capsule of the Russian Federal Space Agency's Phobos Grunt mission and was to have been a test of one aspect of the hypothesis that life can move between nearby planets within ejected rocks. Although the Phobos Grunt mission failed, we present here the scientific and engineering design and motivation of the Phobos LIFE experiment to assist with the scientific and engineering design of similar future experiments. Phobos LIFE flew selected organisms in a simulated meteoroid. The 34-month voyage would have been the first such test to occur in the high-radiation environment outside the protection of Earth's magnetosphere for more than a few days. The patented Phobos LIFE “biomodule” is an 88 g cylinder consisting of a titanium outer shell, several types of redundant seals, and 31 individual Delrin sample containers. Phobos LIFE contained 10 different organisms, representing all three domains of life, and one soil sample. The organisms are all very well characterized, most with sequenced genomes. Most are extremophiles, and most have flown in low Earth orbit. Upon return from space, the health and characteristics of organisms were to have been compared with controls that remained on Earth and have not yet been opened.

Degradation of 100‐m‐Scale Rocky Ejecta Craters at the InSight Landing Site on Mars and Implications for Surface Processes and Erosion Rates in the Hesperian and Amazonian

AbstractRocky ejecta craters (RECs) at the Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) landing site on Elysium Planitia, Mars, provide constraints on crater modification and rates for the Hesperian and Amazonian. The RECs are between 10 m and 1.2 km in diameter and exhibit five classes of preservation. Class 1 represents pristine craters with sharp rims and abundant ejected rocks. From Classes 2 to 5, rims become more subdued, craters are infilled, and the ejecta become discontinuously distributed. High‐Resolution Imaging Science Experiment digital elevation models indicate a maximum depth to diameter ratio of ~0.15, which is lower than pristine models for craters of similar size. The low ratio is related to the presence of a loosely consolidated regolith and early‐stage eolian infill. Rim heights have an average height to diameter ratio of ~0.03 for the most pristine class. The size‐frequency distribution of RECs, plotted using cumulative and differential methods, indicates that crater classes within the diameter range of 200 m to 1.2 km are separated by ~100 to 200 Myr. Smaller craters degrade faster, with classes separated by &lt;100 Myr. Rim erosion can be entirely modeled by nonlinear diffusional processes using the calculated timescales and a constant diffusivity of 8 × 10−7 m2/year for craters 200 to 500 m in diameter. Diffusion models only partly capture depth‐related degradation, which requires eolian infill. Depth degradation and rim erosion rates are 10−2 to 10−3 m/Myr, respectively. The rates are consistent with relatively slow modification that is typical of the last two epochs of Martian history.

Independent analyses of cutting and friction forces applied on a single polycrystalline diamond compact cutter

This paper presents an analysis of the excavation forces involved in the cutting action and in the friction of a cutter/rock contact. A vertical lathe-type device provided data on the forces applied on a single cutter under dry excavation conditions. A cutting device was used to perform cutting experiments with unworn and worn cutters. A tribometer was used to perform friction tests on the cutters wear flat previously realized with the vertical lathe. The experiments display results conform to the literature as the non-dependence of the cutting coefficient to the rock properties. Then, this study focuses on the cutting forces and explains that these forces include a component of rock shearing and impact friction. The impact friction is induced by the interaction between ejected rock particles and the cutting active area. The evidence of this impact friction is then brought by the formation of an eroded zone on the cutting active area.

Impact-driven planetary desiccation: The origin of the dry Venus

The fate of surface water on Venus is one of the most important outstanding problems in comparative planetology. Although Venus should have had a large amount of surface water (like the Earth) during its formation, the current water content on the Venusian surface is only 1 part in 100 000 of that of the mass of Earth's oceans. Here a new concept is proposed to explain water removal on a steam-covered proto Venus, referred to as “impact-driven planetary desiccation”. Since a steam atmosphere is photochemically unstable, water vapor dissociates into hydrogen and oxygen. Then, hydrogen escapes easily into space through hydrodynamic escape driven by strong extreme ultraviolet radiation from the young Sun. The focus is on the intense impact bombardment during the terminal stage of planetary accretion as generators of a significant amount of reducing agent. The fine-grained ejecta remove the residual oxygen, the counter part of escaped hydrogen, via the oxidation of iron-bearing rocks in a hot atmosphere. Thus, hypervelocity impacts cause net desiccation of the planetary surface. I constructed a stochastic cratering model using a Monte Carlo approach to investigate the cumulative mass of nonoxidized, ejected rocks due to the intense impact bombardment. The ejecta mass after each impact was calculated using the π-group scaling laws and a modified Maxwell's Z model. The effect of projectile penetration into the ground on the ejecta mass was also included. Next, an upper limit on the total amount of removed water was calculated using the stoichiometric limit of the oxidation of basaltic rocks, taking into account the effect of fast H2 escape. It is shown that a thick steam atmosphere with a mass equivalent to that of the terrestrial oceans would be removed. The cumulative mass of rocky ejecta released into the atmosphere reaches 1 wt% of the host planet, which is 10 000 times of the current mass of the Earth's atmosphere. These results strongly suggest that chemical reactions between such large amounts of ejecta and planetary atmospheres are among the key factors required to understand atmospheric mass and its composition, not only in the Solar System but also in extrasolar systems.

Maskelynite in asteroidal, lunar and planetary basaltic meteorites: An indicator of shock pressure during impact ejection from their parent bodies

Maskelynite is a diaplectic glass that forms from plagioclase at shock pressures of ∼20–30GPa, depending on the Ca concentration. The proportion of maskelynite-rich samples in a basaltic meteorite group correlates with the parent-body escape velocity and serves as a shock indicator of launching conditions. For eucrites (basalts widely presumed to be from Vesta; vesc=0.36kms−1), ∼5% of the samples are maskelynite rich. For the Moon (vesc=2.38kms−1), ∼30% of basaltic meteorites are maskelynite rich. For Mars (vesc=5.03kms−1), ∼93% of basaltic meteorites are maskelynite rich. In contrast, literature data show that maskelynite is rare (∼1%) among mare basalts and basaltic fragments in Apollo 11, 12, 15 and 17 soils (which were never ejected from the Moon). Angrites are unbrecciated basaltic meteorites that are maskelynite free; they were ejected at low-to-moderate shock pressures from an asteroid smaller than Vesta.Because most impacts that eject materials from a large (⩾100km) parent body are barely energetic enough to do that, a collision that has little more than the threshold energy required to eject a sample from Vesta will not be able to eject identical samples from the Moon or Mars. There must have been relatively few impacts, if any, that launched eucrites off their parent body that also imparted shock pressures of ∼20–30GPa in the ejected rocks. More-energetic impacts were required to launch basalts off the Moon and Mars. On average, Vesta ejecta were subjected to lower shock pressures than lunar ejecta, and lunar ejecta were subjected to lower shock pressures than martian ejecta.H and LL ordinary chondrites have low percentages of shock-stage S5 maskelynite-bearing samples (∼1% and ∼4%, respectively), probably reflecting shock processes experienced by these rocks on their parent asteroids. In contrast, L chondrites have a relatively high proportion of samples containing maskelynite (∼11%), most likely a result of catastrophic parent-body disruption 470Ma ago.

Observation of rock fragment ejection in post-failure response

Rockburst is a dynamic energy phenomenon accompanying the failure of hard rock in the form of brittle fractures [1–3]. Surplus energy is released when the accumulated elastic strain energy of rock is greater than the consumptive energy required for fracturing during its quick post-failure. This freed energy often takes radiant forms, such as acoustic energy, electromagnetic energy, and thermal energy [2,4,5], as well as physical forms, such as fragments being thrown in the laboratory, or an ejective rockburst in the field [6–11]. Of these types of releases, the fragments with kinetic energy always result in dangerous engineering accidents due to their abrupt impacts at high speeds [12–17]. To reduce bursting disasters in underground engineering, a great deal of effort has been put forth to explain the rockburst mechanism, predict ejection behavior, and design corresponding protective support techniques, etc. [18–24]. Conventional wisdom indicated that knowledge of the ejection velocity of the burst rock fragments is the key to further predicting rockburst risks and designing a corresponding protective support system [25–28]. For example, Kaiser and Cai underlined that rock ejection with a velocity of up to 3 m/s required a specially integrated yielding support system [28]. Simulated rockburst experiments in an underground tunnel in South Africa were successfully conducted to measure the ejection velocity of rock fragments directly. The results indicated that the in situ rock fragments were ejected from the tunnel wall with velocities in the range of 0.6 m/s to 2.5 m/s, thereby providing useful clues for rockburst's prevention technique in deep mining [29,30]. As expected, high experimental costs, rigorous site requirements (i.e., hard rock and high geostress) and complicated preparatory work for such field experiments have limited the application of in-situ rockburst measurements. Laboratory observations of rock ejections serve as a convenient and reasonable alternative method [31–33]. Petukhov noted that violent fracture of rock specimen in a compression machine could represent a laboratory simulation for dynamic rock failure during a burst in the field [32,34]. Visual observations of fragment ejection velocity in a laboratory are important not only to understand further the outbreak behavior of fragments in post-failure of hard rock but also to assess the bursting properties of rock in actual engineering. High-speed filming, which records instantaneous behavior by taking successive photographs over a short time interval, has been used in dynamically mechanical experiments as an accurate tool for observing impact failure [33,35,36]. Unfortunately, the highspeed camera has few applications in the documentation of ejection performance rock specimens under quasi-steady compression conditions. As a result, these filming methods warrant further research. In this article, we present a method to observe the ejection velocity of rock fragments under laboratory uniaxial compression tests with the help of a high-speed camera. Also shown in this article is an algorithmic program developed to calculate the initial speed and throwing angle of ejected rock fragments. This work

At what depths do magma‐water eruptions breach the surface?

When magma ascends upward in the Earth's crust, it can react violently with groundwater, leading to underground explosions or even full‐fledged eruptions. If they breach the surface, these phreatomagmatic eruptions leave debris that falls concentrically around the crater or cone. Previously, researchers have sought to determine the depth within the vent from which the eruption originated by looking at the types of ejected rocks and their original positions beneath the volcanoes, but Valentine et al. found that these two factors are not necessarily directly related.

Multi-geohazards of Ende city area

http://dx.doi.org/10.17014/ijog.vol2no4.20073The Ende City is a steep mountainous area, of which the height of their peaks are above 1500 m asl. It has the limited extent of plain places, without coastal plains. Due to this condition, large parts of the area are vulnerable to mass-movements mainly debris flows, rock-falls and shallow translational and rotational landslides. On the other hand, Flores Island is a segment of the Banda Arc that contains eleven very active volcanoes and numerous inactive volcanic cones. Two of them, Mount Iya and Mount Kelimutu are included to Ende Regency. The northern foot of Mount Iya is only about 1 km away from the southern outskirts of Ende city. But the presence of Mount Meja and Mount Roja as the barrier, and the orientation of the active crater (K2), the highly explosive eruption of Iya Volcano may not directly endanger the city of Ende. Most pyroclastic flows of previous eruptions and other eruptive material emplaced into the sea, but due to a short horizontal distance between Mount Iya and Ende City, the ejected rock fragments can endanger the city of Ende especially its southern parts. A crack has developed around the active crater (K2) of Iya Volcano. It seems that the crack indicates a major weakness within the volcano, which could result in a giant landslide, entering the sea in future eruptions of Iya Volcano. The kinetic energy which is transmitted through the water may probably generate a tsunami. The Ende City also experienced significant damages in the 1992 earthquake. Luckily this city is located on a solid rock instead of alluvial sediments which can potentially undergo liquefaction.

Lithopanspermia in Star-Forming Clusters

This paper considers the lithopanspermia hypothesis in star-forming groups and clusters, where the chances of biological material spreading from one solar system to another is greatly enhanced (relative to action in the field) because of the close proximity of the systems and lower relative velocities. These effects more than compensate for the reduced time spent in such crowded environments. This paper uses approximately 300,000 Monte Carlo scattering calculations to determine the cross sections <sigma(cap)> for rocks to be captured by binaries and provides fitting formulae for other applications. We assess the odds of transfer as a function of the ejection speed v (eject) and number N(.) of members in the birth aggregate. The odds of any given ejected meteoroid being recaptured by another solar system are relatively low, about 1:10(3)-10(6) over the expected range of ejection speeds and cluster sizes. Because the number of ejected rocks (with mass m > 10 kg) per system can be large, N (R) approximately 10(16), virtually all solar systems are likely to share rocky ejecta with all of the other solar systems in their birth cluster. The number of ejected rocks that carry living microorganisms is much smaller and less certain, but we estimate that N (B) approximately 10(7) rocks can be ejected from a biologically active solar system. For typical birth environments, the capture of life-bearing rocks is expected to occur N (bio) asymptotically equal to 10-16,000 times (per cluster), depending on the ejection speeds. Only a small fraction (f (imp) approximately 10(4)) of the captured rocks impact the surfaces of terrestrial planets, so that N (lps) asymptotically equal to 10(3)-1.6 lithopanspermia events are expected per cluster (under favorable conditions). Finally, we discuss the question of internal versus external seeding of clusters and the possibility of Earth seeding young clusters over its biologically active lifetime.

Cratering model of asteroid and comet impact on a planetary surface

Summary A discrete model of crater formation describing the ejection of rock fragments from a crater has been developed. This model takes into account elastic-plastic behavior of media, energy transfer by radiation, contact boundaries, thermal and force interaction of gas and fragments of ejected rock. The results obtained in the course of computational experiments demonstrate versatility and flexibility of the developed model in application to different variants of problems on impact and explosive cratering. They will be presented in a second part of the paper.

Stratigraphy of Ejecta from the Lunar Crater Aristarchus

Ejecta from lunar crater Aristarchus consist of mappable units that have different surface characteristics, lithologies, and geneses. Photogeologic mapping demonstrates that these units can be ordered into a stratigraphic succession representing stages in the emplacement of ejecta during a single impact event. Four main ejecta units are recognized: (a) a highly fractured rim unit consisting of an overturned flap of country rock, (b) a continuous ejecta blanket, (c) a zone of bright discontinous ejecta outside the continuous ejecta blanket associated with numerous secondary impact craters, and (d) a group of ejecta deposits on the rim which are genetically related to each other and include hummocky material (the hummocky rim unit), blocky lobes, and smooth flows. Other units, such as the ridged and leveed flows and the dark “lakes” or “playas,” are relatively younger than the ejecta and are only briefly discussed. The continuous ejecta blanket lies stratigraphically above the rim unit. To the east and south, the ejecta blanket has been stripped off the overturned rim unit by outward flowage from the crater during ejecta production, leaving parts of the rim eroded bare. Fall of large missiles to form the secondary craters and bright ejecta preceded the emplacement of the continuous ejecta. The general asymmetry of the continuous ejecta-blanket distribution appears to be related to the Aristarchus Plateau boundary fault, which may have controlled the way material was excavated. The hummocky rim unit only occurs on the northern and western rim and may be an overturned flap of premare Aristarchus Plateau bedrock not present near the surface on the southern and eastern rim of the crater. Blocky lobes and smooth flows mainly associated with the hummocky rim unit are interbedded, arguing that the smooth flows are part of the sequence of ejected rocks and are not younger volcanic flows.