Surface and Subsurface Damage Caused by Bullet Impacts into Sandstone

The shift of armed conflicts to more urbanised environments has increased the risk to cultural heritage sites. Small arms impacts are ubiquitous in these circumstances, yet the effects and mechanisms of damage caused are not well known. A sandstone target was shot under controlled conditions to investigate surface and subsurface damage. A 3D model of the damaged block, created by structure from motion photogrammetry, shows that internal fracturing was at least as extensive as the visible surface fractures. Backscatter electron imaging of the damaged surface shows a shift from intragranular fracturing and grain size reduction at < 5 mm from the impact point to primarily circumgranular fracturing and grain ‘plucking’ at 20 mm from the impact point. Internal fracture intensity decreased with distance from the centre of the crater. Volumes around the impact point are therefore at greater risk of subsequent weathering deterioration, but significant damage extends to the periphery of the target, rendering whole blocks vulnerable. The surface crater, despite being one of the most conspicuous aspects of conflict damage, has many times less area than internal and surface fractures.

Study on the Acoustic Emission Characteristics of Different Rock Types and Its Fracture Mechanism in Brazilian Splitting Test

In order to investigate the relationship between rock microfracture mechanism and acoustic emission (AE) signal characteristic parameters under split loads, the MTS322 servo-controlled rock mechanical test system was employed to carry out the Brazilian split tests on granite, marble, sandstone, and limestone, while FEI Quanta-200 scanning electron microscope system was employed to carry out the analysis of fracture morphology. The results indicate that different scales of mineral particle, mineral composition, and discontinuity have influence on the fracture characteristics of rock, as well as the b-value. The peak frequency distribution of the AE signal has obvious zonal features, and these distinct peak frequencies of four types of rock fall mostly in ranges of 0–100 kHz, 100–300 kHz, and above 300 kHz. Due to the different rock properties and mineral compositions, the proportions of peak frequencies in these intervals are also different among the four rocks, which are also acting on the b-value. In addition, for granite, the peak frequencies of AE signals are mostly distributed above 300 kHz for granite, marble, and limestone, which mainly derive from the internal fracture of k-feldspar minerals; for marble, the AE signals with peak frequency are mostly distributed in over 300 kHz, which mainly derive from the internal fracture of dolomite minerals and calcite minerals; AE signals for sandstone are mostly distributed in the range of 0–100 kHz, which mainly derive from the internal fracture of quartz minerals; for limestone, the AE signals with peak frequency are mostly distributed in over 300 kHz, which mainly derive from the internal fracture of granular-calcite minerals. The relationship between acoustic emission signal frequency of rock fracture and the fracture scale is constructed through experiments, which is of great help for in-depth understanding of the scaling relationship of rock fracture.

Flow partitioning in partially saturated fracture networks: Relation between dispersive properties and internal fracture geometry

&lt;p&gt;Modeling of of infiltration and recharge dynamics in fractured-porous aquifers remain an extremely challenging task due to the formation of preferential pathways along fracture networks and hence deviation from classical diffuse Darcy-type percolation patterns. In contrast to soil systems the vadose zone of consolidated rock systems often reaches depths of several tens to hundreds of meters which limits the accessibility and complicates the application of moisture measurement techniques. Under partially-saturated conditions flow through percolating fracture networks contribute to the fastest spectrum of infiltration velocities. At fracture intersections flow is often fragmented into a vertical and horizontal component which controls the dispersive properties of the infiltrating fluid front. As hydraulic information in consolidated aquifers is often only available at boreholes or springs, we explore how internal fracture network geometries can potentially be reconstructed from external boundary information, e.g., the dispersive properties of discharge (groundwater level fluctuations). In order to relate boundary information, e.g. discharge measured at the water table within boreholes, to internal properties such as geometry of the fracture network and fluid-solid interaction properties we derive an approximate analytical solution for flow through a cascade of simple fracture intersections with the help of parallalized smoothed particle hydrodynamics simulations [1]. Via linear response theory we derive expressions for the non-dimensional bulk flow velocities and dispersion coefficient to characterize the fracture network in terms in the dimensionless time scales of the vertical and horizontal fracture components. We demonstrate that the dispersion coefficient converges towards a universal value for a realistic range of fluid and solid properties and recover a characteristics Washburn-type scaling for the dimensionless velocity.&lt;/p&gt;&lt;p&gt;[1] Kordilla, J., Tartakovsky, A. M. and Dentz, M. (2020): Numerical and analytical modeling of flow partitioning in partially saturated fracture networks, Earth and Space Science Open Archive, pp. 44, doi:10.1002/essoar.10504345.1&lt;/p&gt;

A Retrospective Study of Dogs with Osteomyelitis Secondary to Fractures (2016-2020)

The purpose of this work was to evaluate the role of surgical procedures and the effectiveness of antimicrobial therapy in dogs with osteomyelitis secondary to fractures repair.Medical records between 2016 and 2020 were analyzed. Clinical data including signalment, affected bone segment, fracture type, isolated microorganisms, antimicrobial susceptibility profiles, applied therapeutic management and fracture healing time were documented.Eleven cases were confirmed with exogenous osteomyelitis of long bones secondary to fractures repair. The most common microorganisms isolated were Staphylococcus spp., Streptoccocus spp., and Escherichia coli. Amoxicillin and clavulanate potassium followed by ceftriaxone were the most effective drugs. High-resistance rates were documented for penicillin and clindamycin. All 10 cases undergoing surgical revision were cured in 10-17 weeks.Simultaneous debridement with implant removal, reduction, and rigid internal fracture fixation is a satisfactory method for revision surgery in treatment of long bones fractures complicated with osteomyelitis.

A modelling resin material and its application in rock-failure study: Samples with two 3D internal fracture surfaces

The mechanism of fracture propagation, interaction and coalescence inside rock masses is a highly concerned issue in geotechnical engineering. But as it is difficult to manufacture 3D internal pre-fractures and observe directly the failure evolution process inside real rocks or their opaque similar materials, most previous studies have been limited to 2D conditions. The experiment investigation on 3D rock failure is still in a preliminary stage. In this study, a resin material has been developed by extensive formula tries. It is absolutely transparent and the ratio of tension–compression strength (brittleness value) can be 1/6.6 at −10 to −15℃. It is much more brittle and rock-like than analogous materials used by former scholars. A set of preparation, casting mould, and post-processing technologies were established and specimen-making with multiple pre-fractures is enabled. In the designed scheme, specimens are made with two parallel internal fracture surfaces yet of four different stagger separations. Uniaxial tests were carried out and the stress–strain relationship is analysed. It is shown that the specimen has gone through four stages as the traditional rock test before failure. Many diverse forms of secondary fractures, such as wrapping wing crack, petaloid crack, and giant quasi-wrapping fracture surface, which were not found in 2D conditions have appeared and their evolutions were clearly seen in each stage.

Dispersion in small-scale discrete fracture networks with internal fracture roughness: Challenges for site-scale modelling

&lt;p&gt;There is a need for improved understanding of the mechanisms controlling solute transport in fractured crystalline rocks in order to address long-term safety analysis of repositories for spent nuclear fuel. In this contribution, flow and transport in three-dimensional discrete fracture networks with internal heterogeneity in aperture and permeability is investigated using a numerical DFN model. The fracture networks are obtained using field data of sparsely fractured crystalline rock from the Swedish candidate repository site for spent nuclear fuel. Then, heterogeneity textures with different correlation length and variance are created and mapped to each individual fracture of the network to represent internal fracture roughness. We demonstrate how the structure and variability of textures on the scale of individual fractures leads to different transport and dispersion behaviour at the scale of the network. Key thresholds for cases where flow dispersion is controlled by single-fracture heterogeneity versus network-scale heterogeneity are identified. Furthermore, we highlight enhanced flow channelling for cases where small-scale structure continues across intersections in a network, and highlight challenges for extension to large scale and site-specific modelling.&lt;/p&gt;