Boulder Volume Research Articles

Lessons Learned from NASA’s DART Impact about Disrupting Rubble-pile Asteroids

We present a series of numerical simulations using a shock physics smoothed particle hydrodynamics code, investigating energetic impacts on small celestial bodies characterized by diverse internal structures, ranging from weak and homogeneous compositions to rubble-pile structures with varying boulder volume packing. Our findings reveal that the internal structure of these rubble-pile bodies significantly influences the impact outcomes. Specifically, we observe that the same impact energy can either catastrophically disrupt a target with a low boulder packing (≲30 vol%), or result in the ejection of only a small fraction of material from a target with the same mass but high boulder packing (≳40 vol%). This finding highlights the pivotal role played by the rubble-pile structure, effectively acting as a bulk shear strength, which governs the size and behavior of the resulting impact. Consequently, understanding and characterizing the internal structure of asteroids will be of paramount importance for any future efforts to deflect or disrupt an asteroid on a collision course with Earth.

Stochastic modeling for offshore risk assessment of pile refusal triggered by the presence of boulders

A 3D stochastic model is developed for the spatial distribution of seafloor and subsurface boulders. Boulder interception data from borings recovered from a European wind farm is presented and statistically analyzed. The proposed model is applied to simulate the boulder fields over the domain of an entire wind farm site and the simulated boulder fields were found to be consistent with field observations from boreholes (i.e., boulder interception by borehole), quantitatively validating the capability of the proposed method to reconstruct the boulder field based on data obtained from site investigation. A general relationship between the fraction of borehole interception and the fraction of boulder volume is defined and can be used for rapid estimation of the number of boulders at a site based on borehole data. This 3D boulder model can be easily incorporated into pile driving risk analysis to estimate the probability of pile refusal at a site or used to calculate the amount of necessary excavation work for shallowly embedded cable routes. Results calculated from a case study using the developed stochastic model and the boring data collected from the Beatrice wind farm show that the average pile refusal rate is 6.3% with significant dependence on the spatial location.

Monitoring of Coastal Boulder Movements by Storms and Calculating Volumetric Parameters Using the Volume Differential Method Based on Point Cloud Difference

The measurements of boulder volume and axial length play significant roles in exploring the evolution of coastal boulder deposition, which provides a theoretical framework to examine the hydrodynamics of extreme wave events. At present, the application of structure-from-motion (SfM) to unmanned aerial system (UAS) imagery is one of the most used boulder surveying techniques. However, the monitoring of boulder movement and the accurate measurement of boulder morphometrics are rarely investigated in combination. In this study, UAS surveys were used to monitor moving boulders and measure boulder volumes using the volume differential method based on the differences of dense point clouds. This was undertaken at a site on the rocky shoreline of northwest Ireland in three repeated UAS surveys conducted in 2017, 2018, and 2019. The results from UAS monitoring and mapping of the distribution of 832 moving boulders in the study area over the 3-year period showed that boulders located in different zones of the coast vary significantly in their mobility. The main findings reveal that the theoretical error of the volume, obtained using the volume differential method, was estimated as 1–3.9%, which is much smaller than that of the conventional method of estimating volume using a tape measure.

Safety level assessment of shield tunneling in water rich sandy pebble strata with large particle size

Shield tunneling method is widely used in urban metro construction. The construction stability is closely related to the engineering geological conditions. Sandy pebble strata have a loose structure and low cohesion, resulting in great engineering-induced stratigraphic disturbance. Meanwhile, the high water-abundance and strong permeability are extremely detrimental to construction safety. It is of great significance to evaluate the dangerousness of shield tunneling in water-rich pebble strata with large particle size. In this paper, risk assessment of engineering practice is carried through with Chengdu metro project in China as a case study. Referring to the special engineering situations and assessment workload, seven evaluation indices, including compressive strength of pebble layer, boulder volume content, permeability coefficient, groundwater depth, grouting pressure, tunneling speed and tunnel buried depth are selected to establish an evaluation system. A complete risk assessment framework is established based on the cloud model, AHP and entropy weight method. Further, the measured surface settlement is taken as the risk degree characterization to verify the results. This study can provide reference for method selection and evaluation system establishment in the risk assessment of shield tunnel construction in water-rich sandy pebble strata, and contribute to proposing safety management in similar engineering projects.

Monitoring Coastal Erosion Using Remote Images: Comparison between Physically and Remotely Acquired Data on a Limestone Coast

Boulder-sized clasts on rocky coasts are considered as erosional signatures of extreme wave events and boulder attributes are often used in numerical models to estimate wave characteristics. The use of unmanned aerial vehicle (UAV) technology and related software has facilitated the monitoring of coastal areas, by generating models from which 2D and 3D measurements can be derived. However, the reliability and preciseness of such measurements is still to be determined. This study seeks to analyse the accuracy of boulder measurements by comparing the dimension data obtained through in-situ measurements with ex situ data generated from digital models, based on UAV images. The study area is a bouldered sloping coast located on the southeast coast of Malta (Central Mediterranean) that has developed into multiple limestone dipped strata with a fractured and heavily jointed morphology. The dimensions of c. 200 boulders in different morphological settings, such as clusters or ridges, have been statistically compared. The results show a very strong correlation between the two datasets, both in 2D and 3D; however some notable differences were observed at the individual boulder level. For the majority of boulders analysed, the A and B axes dimensions varied by ±10% to 20%. The C axis proved to be harder to measure accurately and showed a wider range of difference. Boulder volume results in the majority of cases varied from 0% to ±40%. Some tested methods of volume calculation may be more accurate and realistic than others depending on the boulder position in relation to other clasts and shore morphology. An automated digital analysis of the terrain surface to identify the boulder extents may offer possibilities for a more accurate estimation of boulder attributes.

Holocene Hurricane Deposits Eroded as Coastal Barriers from Andesite Sea Cliffs at Puerto Escondido (Baja California Sur, Mexico)

Previous studies on the role of hurricanes in Mexico’s Gulf of California examined coastal boulder deposits (CBDs) eroded from limestone and rhyolite sea cliffs. Sedimentary and volcanic in origin, these lithotypes are less extensively expressed as rocky shores than others in the overall distribution of gulf shores. Andesite that accumulated as serial volcanic flows during the Miocene constitutes by far the region’s most pervasive rocky shores. Here, we define a subgroup of structures called barrier boulder deposits (BBDs) that close off lagoons as a result of lateral transport from adjacent rocky shores subject to recurrent storm erosion. Hidden Harbor (Puerto Escondido) is the most famous natural harbor in all of Baja California. Accessed from a single narrow entrance, it is commodious in size (2.3 km2) and fully sheltered by outer andesite hills linked by two natural barriers. The average weight of embedded boulders in a succession of six samples tallied over a combined distance of 710 m ranges between 74 and 197 kg calculated on the basis of boulder volume and the specific gravity of andesite. A mathematical formula is utilized to estimate the wave height necessary to transport large boulders from their source. Average wave height interpreted by this method varies between 4.1 and 4.6 m. Input from fossil deposits and physical geology related to fault trends is applied to reconstruct coastal evolution from a more open coastal scenario during the Late Pleistocene 125,000 years ago to lagoon closure in Holocene time.

Digital mapping of coastal boulders – high‐resolution data acquisition to infer past and recent transport dynamics

AbstractCoastal boulder fields provide clues to long‐term frequency‐magnitude patterns of coastal flooding events and have the potential to play an important role in coastal hazard assessment. Mapping boulders in the field is time and labour‐intensive, and work on intertidal reef platforms, as in the present study, is physically challenging. By addressing coastal scientists who are not specialists in remote sensing, this contribution reports on the possibilities and limitations of digital applications in boulder mapping in Eastern Samar, Philippines, where recent supertyphoons Haiyan and Hagupit induced high waves, coastal flooding and boulder transport. It is demonstrated how satellite imagery of sub‐metre resolution (from Pléiades and WorldView‐3 imagery) enables efficient analysis of transport vectors and distances of larger boulders, reflecting variation in latitudes of both typhoon tracks and approaching angles of typhoon‐generated waves. During the investigated events, boulders with a‐axes of up to 8 m were clearly identified to have been shifted for up to 32 m, mostly along the seaward margin of the boulder field. It is, however, hard to keep track of smaller boulders, and the length of a‐axes and b‐axes including their orientation is often impossible to map with sufficient accuracy. Orthophotographs and digital surface models created through the application of an unmanned aerial vehicle and the ‘Structure from Motion’ technique provide ultra‐high‐resolution data, and have the potential to not only improve the results of satellite image analysis, but also those from field mapping and may significantly reduce overall time in the field. Orthophotographs permit unequivocal mapping of a‐axes and b‐axes including their orientation, while precise values for c‐axes can be derived from the respective digital surface models. Volume of boulders is best inferred from boulder‐specific Structure from Motion‐based three‐dimensional models. Battery power, flight speed and altitude determine the limits of the area covered, while patches shielded by the boulders are difficult to resolve. For some tasks, field mapping remains mandatory and cannot be replaced by currently available remote sensing tools: for example, sampling for rock type, density and age dating, recording of lithological separation of boulders from the underlying geological unit and of geomorphic features on a millimetre to decimetre‐scale, or documentation of fine‐grained sediment transport in between the boulders in supratidal settings. In terms of future events, the digital products presented here will provide a valuable reference to track boulder transport on a centimetre to decimetre‐scale and to better understand the hydrodynamics of extreme‐wave events on a fringing reef coastline.

Intertidal boulder-based wave hindcasting can underestimate wave size: Evidence from Yorkshire, UK

Large boulder-size clasts can represent important archives of high energy erosional wave activity at the coast. From tropical coral reefs to high-latitude eroding cliffs, boulders have been used to hindcast the frequency and magnitude (height) of waves produced by both storms and tsunami. Such reconstructions are based on the balance between the hydrodynamic forces acting on individual boulders and the counteracting resistive forces of friction and gravity. We test published models on over 900 intertidal boulders on the coast at Staithes in North Yorkshire, U.K., using repeat high-resolution topographic survey data. We quantified the predicted versus actual rates of boulder movement in the field over a 7-year period (2007–2014). We assessed the degree to which local geomorphology and biology may affect the resistive forces inhibiting transport. We found that 84% of intertidal boulders predicted to be mobile remained stationary over 7 years, suggesting that in some contexts boulder movement may be significantly less than predicted, regardless of boulder volume, shape or location. In situ cementation of boulders to the substrate by marine organisms appears to play a key role in retarding or preventing boulder transport. The implication is that boulder characteristics may not always provide a reliable estimation of wave height on the coast and reliance solely on hindcasting relationships may result in under prediction of the frequency and magnitude of past storm wave activity. We suggest here that more field studies that consider boulder movement are needed, set within specific site contexts, and that these data are used to improve the applicability and robustness of boulder transport models.

Prediction of blast boulders in open pit mines via multiple regression and artificial neural networks

The most important objective of blasting in open pit mines is rock fragmentation. Prediction of produced boulders (oversized crushed rocks) is a key parameter in designing blast patterns. In this study, the amount of boulder produced in blasting operations of Golegohar iron ore open pit mine, Iran was predicted via multiple regression method and artificial neural networks. Results of 33 blasts in the mine were collected for modeling. Input variables were: joints spacing, density and uniaxial compressive strength of the intact rock, burden, spacing, stemming, bench height to burden ratio, and specific charge. The dependent variable was ratio of boulder volume to pattern volume. Both techniques were successful in predicting the ratio. In this study, the multiple regression method was superior with coefficient of determination and root mean squared error values of 0.89 and 0.19, respectively.

Numerical simulations to account for boulder movements on Lanyu Island, Taiwan: tsunami or storm?

Boulders that originated from the Holocene coral terrace and coral reef are distributed on the coral terrace or talus on the shore of Lanyu Island, Taiwan. We employed numerical simulation of storm waves and estimated whether the boulders could be moved by storm waves with a return period of 50 years, by larger storm waves with return periods of hundreds of years, or by tsunamis. The coral boulders are distributed between 36 and 128 m from the shoreline at elevations of 2.7 to 9.3 m. The sizes of the boulders are in the range 0.3 to 6.4 m. The boulder volume and a-axis length versus distance from the shore show weak and moderate correlation (r = 0.21 and 0.48), respectively. We reproduced the runup of waves using the equation of continuity for a two-dimensional non-compressive fluid and the Navier-Stokes formula. In order to handle the free surface of the fluid, the volume of fluid method was applied. For the flow velocity to move the boulder, we employed the theoretical formula for the transport of boulders. We used the wave height for a return period of 50 years and set the height of the input wave to 13.1 m. The results show that all the large boulders on Lanyu Island could be moved by storm waves with a return period of 50 years. Moreover, the computations show that most of the boulders could not have been transported by tsunamis generated by the Mw8.7 earthquakes. The ages of two boulders indicate that they were transported after 340 and 6,330 years ago. If these boulders were moved by tsunamis several hundred years ago, they would have been relocated subsequently by storm waves.

Three‐dimensional modeling of coastal boulders using multi‐view image measurements

ABSTRACTCoarse clastic sediments (boulders) on coastlines have seen a groundswell in geomorphic research interest over recent years, associated in part with the potential of boulder evidence for interpreting characteristics of high‐energy wave processes. Yet, the fundamental property of boulder volume is normally difficult to measure accurately owing to complex clast morphology and irregular surface texture. To tackle this problem, this paper concentrates on creating precise, measurable and textured three‐dimensional (3D) models of coastal boulders without physical contact with the object, based on multi‐view image measurement techniques. This method has several advantages over traditional measurements that are inaccurate or alternative solutions using costly techniques such as terrestrial laser scanning. Our methods propose the use of low‐cost equipment (digital cameras) that can be used in various coastal environments to easily acquire numerous images of the object of interest. Initial results can be rapidly assessed in the field for immediate quality control. Resulting 3D models, built from overlapping multi‐view digital photographs, allow the reconstruction of realistic‐looking and textured boulder surfaces. A particular interest in this task is the family of algorithms known as structure from motion (SFM). The work presents analysis of SFM techniques by examining 3D models of boulders observed at a coastal field site on Lu Dao Island in south‐eastern Taiwan. Copyright © 2013 John Wiley & Sons, Ltd.

Runout analysis of a large rockfall in the Dolomites/Italian Alps using LIDAR derived particle sizes and shapes

ABSTRACTLiDAR data were used to quantify and analyse a rockfall event which occurred in 2003 in the Western Dolomites (Italian Alps). In addition to previously existing airborne laserscanning (ALS) data, high resolution terrestrial laserscanning (TLS) data were collected. By using the original point clouds, the volume, axial ratio and runout length of single boulders as well as the surface roughness in the runout zone of the rockfall were derived. The total volume of the rockfall event of approximately 10 000 m³ was estimated by a reconstruction of the pre‐event surface at the detachment zone. The analysis of the laser scanning data of the accumulation zone revealed a power law scaling for boulder volumes larger than 8 m³. The dependence of runout length on boulder volume is complex; it is moderated by particle sphericity.In addition, we used ALS and TLS data to derive the spatial distribution of surface roughness on the talus cone. TLS allow for more accurate roughness mapping than ALS data, but for most applications the point density of ALS data seems to be sufficiently high to derive measures of roughness. Different sampling approaches for plane fitting on the scale of 5 m did not show significant effects besides the computational time. The results of our analyses provide important perspectives for rockfall modelling and process understanding with potential applications in both ‘applied’ (natural hazards) and ‘pure’ geomorphological research. Copyright © 2012 John Wiley & Sons, Ltd.

Bonaire's boulder fields revisited: evidence for Holocene tsunami impact on the Leeward Antilles

Supralittoral boulders and blocks are prominent sedimentary features along rocky shorelines worldwide. In most cases, their deposition is attributed to high-energy wave events (tsunamis, severe storms). Even though tsunami waves are expected to have higher transport capacities compared to storm waves, megaclasts of up to 100 t were observed to have been moved laterally by the latter waveform. The deduction of certain extreme wave events (tsunamis, severe storms) from the boulder record thus remains a major challenge in palaeo-event research; the debate on their differentiation is ongoing. At the eastern coast of Bonaire (Leeward Antilles) in the southern Caribbean, numerous limestone blocks and boulders (up to c. 130 t) are distributed on top of a 3–6 m a.s.l. (above mean sea level) palaeo-reef platform. Disagreement exists among a number of authors concerning the transport processes involved in the formation of the boulder fields. In this paper, state-of-the-art modelling approaches of coastal boulder entrainment and transport were applied in order to provide new and more reliable data to support/challenge the working hypothesis of tsunami deposition. To improve the reliability of the boulder transport model, more realistic input parameters were provided by new DGPS measurements of the boulder dimensions and the calculation of bulk densities by taking into account the heterogeneity of the reef-rock boulders. Existing hydrodynamic equations were modified to allow for the irregular shape and real dimensions of the boulders. The results indicate that (i) boulder weight and dimension, and thus (ii) calculated wave energy and wave heights were overestimated in most of the previous studies, where calculations of boulder volume were based on multiplication of the main axes. The results of this study and wave heights observed during recent severe tropical cyclones seem to rule out storm-generated waves for the dislocation of the largest blocks. However, the majority of coarse-clast deposits may have been generated by periodic hurricane swells. The results underline the significance of more realistic field data in modelling boulder transports by waves.

Geological controls on boulder production in a rock coast setting: Insights from South Wales, UK

We investigate some of the geological controls on boulder size, using a heterogeneous outcrop of Blue Lias limestone. Discontinuity and predicted boulder size data were collected on different layers of Blue Lias limestone on a shore platform in Wales, United Kingdom. Significant differences in joint spacing were found between the four layers examined and significant differences in the predicted boulder size were found between many of the ten stratigraphic layers examined. Predicted boulder size ranged from 0.18 to 4.00 m measured on the longest axis. These data demonstrate that the shape and size of boulders liberated from the platform is dependent on which layer of limestone is at the surface. Since the size of boulders varies between layers depending on the thickness of beds and joint spacing, the magnitude of wave energies required to detach, entrain and transport boulders must vary. Boulder erosion is therefore geologically contingent and highly variable through time and space. This variability requires us to develop methods to predict where boulder-scale erosion is likely to occur and what wave conditions are required to add these materials to the sediment supply. We therefore considered the reliability of predictions of boulder size. For two layers examined (layers 19 and 24), predicted boulder sizes were compared with boulders recently detached by storm waves (i.e. within 2.5 months of detachment) from the same layer. Results show that boulder volume was statistically similar between predicted and actual boulders, and either the long or intermediate axis measurements were statistically similar. Variations between predicted and actual boulder axis lengths are attributed to the sampling design for measuring predicted boulders, variable detachment processes and the rapid breakdown of rock masses post-detachment. Our results demonstrate that in locations where repeated entrainment, transport and boulder breakdown are observed, loose boulder size may not be a reliable means of reconstructing wave energies required to detach, entrain and transport boulders.

Some Proposals on the Construction of Man-made Tide Pool Aiming at Coexistence with Marine Organisms

The purpose of this study is to clarify the best habitable conditions for marine organisms in a tide pool. From this view point, field observations on marine organisms andtheir life environment are conducted in the tide pools located at the both natural lagoonand man-made one.It is found that the number of species of marine organisms in the tide pools located at natural lagoon is larger than that at man-made one. This depends on the roughness of side and bottom, the water depth and total volume of boulders scattered in the tide pool.

Field Investigation on the Construction of Tide Pool Aiming at Coexistence with Marine Organisms

The purpose of this study is to clarify the best habitable conditions for marine organisms in a tide pool. Field observation on marine organisms and the sea water auality are conducted in the eleven tide cools located at natural lagoon. It is found that the diversity index on marine organism is changed with the size variation and total volume of boulders scattered in the tide pool. The number of species of marine organisms in the tide pool located at natural lagoon is larger than that at man-made one.

Statistical Model of Boulder Size and Fraction

The presence of boulders in a soil stratum could pose problems during construction and affect satisfactory performance of a geotechnical system. Statistical description of boulders can be useful in assessing the reliability of satisfactory geotechnical performance and in decision making. Statistics of boulder size and volume fraction may be inferred from boring logs. However, the dimension of each boulder recorded in a boring log does not necessarily represent its diameter (assume spherical boulder); moreover, larger boulders are more likely to be encountered. Bayesian method is applied to treat this censored sampling problem, with the objective of determining the distribution of the in-situ boulder population from the observed chord length of boulders intercepted by borings. The spatial variation characteristic of the fraction of boulder volume across a given site can also be inferred from the boring logs at scattered locations. A method for updating these statistics established for a macro region with additional local data in a specific construction site is developed. The technique is applied to a site in Singapore where a large number of borings through a boulderous stratum has been reported.