Wall Slope Research Articles

ANALISIS KESTABILAN LERENG DINDING AKHIR DI PIT BARATLAUT PADA PENAMBANGAN BATUBARA DI PT. PUTERA BARA MITRA , KECAMATAN MENTEWE, KALIMANTAN SELATAN

PT. Putera Bara Mitra used open mining system for mining operation, Yet the completion of study on the end wall slope stability that undertaken by geotechnical PT. Putera Bara Mitra in Northwest Pit and the occured a failure in the low wall on the 1st June 2012 led to the need for analysis and design the overall slope at the mine site. To analyze and design the overall slope, used value of the recommended minimum safety. The value was based on company for single slope SF ≥ 1.2 and SF ≥ 1.3 for overall slope. The calculation used Bichop method with the help of software slide v 5.0. Geometry improvements was done at the low slopes that originally single wall with a 30 m bench height and a slope 70° with SF = 0.781, into 4 levels with SF = 1.305. The analysis explained the factors that affect the stability of the low wall included the mining slope geometry, unfavorable drainase system, material stockpiles and seismicity factors. It was necessary to do prevention efforts to maintain the stability of the slope included the redesign to slope geometry, handling surface and subsurface water in a way to control slopes draining groundwater, vegetation stabilization using and monitoring slope using Total Station with Prism and Crackmeter to determine the movement of cracks visible on the surface.

Probabilistic and Geotechnical Modeling of an Excavation in the Outskirts of Qaen

Summary An excavation operation for the building purposes is a high-risk activity, which is done for different reasons, such as achieving an appropriate level of the earth for foundation or construction of basements. In this paper, using the Slide 6.0 program the stability of a pit wall in the outskirts of Qaen is investigated at first and then the pit wall stability after using soil nailing with various patterns is analyzed. Using back analysis, sensitivity analysis, and probabilistic analysis, this study presents a comprehensive model for analyzing pit walls, and will be useful for excavation operation in neighboring areas as well. Finally, several pit designs with acceptable safety factors have been proposed for pit excavation. Introduction Due to the growing trend of urban populations, the construction activities are increasing in central and marginal areas of cities. One of the basic concerns in these constructions is the stability of the excavated pit wall. The basic rule of judgment about the stability of a pit wall is the standard safety factor. In the traditional deterministic approach of safety factor calculation, any error or uncertainty in the soil parameters is directly reflected in the results. In recent years, the use of the probabilistic approach that provides additional measures related to the probability of failure and risk rate has become popular. In the probabilistic approach in addition to the mean safety factor, the probability of failure and reliability index are also obtained. Methodology and Approaches To perform a probabilistic analysis of a pit wall, strength properties of the soil layer and the soil density were defined as variable inputs. The coefficients of variation of these parameters according to laboratory experiments were selected. Normal and log-normal statistical distributions were used for the input variable parameters as recommended by USACE. For the efficient performance of the probabilistic analysis, Monte Carlo simulation was used. This way, and using the Slide 6.0 program, the stability of a pit wall in the outskirts of Qaen is investigated with various patterns of soil nailing as the supporting system. Results and Conclusions According to the results of this study, the soil is unstable for excavation operation and employing soil nailing technique and reducing the pit wall slope angle are appropriate steps to achieve a secure condition. Several safe pit designs have been proposed for excavating the pit.

Fluid flow in a spiral microfluidic duct

We consider the steady, pressure driven flow of a viscous fluid through a microfluidic device having the geometry of a planar spiral duct with a slowly varying curvature and height smaller than width. For this problem, it is convenient to express the Navier–Stokes equations in terms of a non-orthogonal coordinate system. Then, after applying appropriate scalings, the leading order equations admit a relatively simple solution in the central region of the duct cross section. First-order corrections with respect to the duct curvature and aspect ratio parameters are also obtained for this region. Additional correction terms are needed to ensure that no slip and no penetration conditions are satisfied on the side walls. Our solutions allow for a top wall shape that varies with respect to the radial coordinate which allows us to study the flow in a variety of cross-sectional shapes, including trapezoidal-shaped ducts that have been studied experimentally. At leading order, the flow is found to depend on the local height and slope of the top wall within the central region. The solutions are compared with numerical approximations of a classical Dean flow and are found to be in good agreement for a small duct aspect ratio and a slowly varying and small curvature. We conclude that the slowly varying curvature typical of spiral microfluidic devices has a negligible impact on the flow in the sense that locally the flow does not differ significantly from the classical Dean flow through a duct having the same curvature.

Influence of Non-linear Radiation Heat Flux on Rotating Maxwell Fluid over a Deformable Surface: A Numerical Study

Mathematical model for Maxwell fluid flow in rotating frame induced by an isothermal stretching wall is explored numerically. Scale analysis based boundary layer approximations are applied to simplify the conservation relations which are later converted to similar forms via appropriate substitutions. A numerical approach is utilized to derive similarity solutions for broad range of Deborah number. The results predict that velocity distributions are inversely proportional to the stress relaxation time. This outcome is different from that observed for the elastic parameter of second grade fluid. Unlike non-rotating frame, the solution curves are oscillatory decaying functions of similarity variable. As angular velocity enlarges, temperature rises and significant drop in the heat transfer coefficient occurs. We note that the wall slope of temperature has an asymptotically decaying profile against the wall to ambient ratio parameter. From the qualitative view point, temperature ratio parameter and radiation parameter have similar effect on the thermal boundary layer. Furthermore, radiation parameter has a definite role in improving the cooling process of the stretching boundary. A comparative study of current numerical computations and those from the existing studies is also presented in a limiting case. To our knowledge, the phenomenon of non-linear radiation in rotating viscoelastic flow due to linearly stretched plate is just modeled here.

An Assessment of Regional Variations in Martian Modified Impact Crater Morphology

AbstractImpact craters on Mars have been extensively modified by ancient geologic processes that may have included rainfall and surface runoff, snow and ice, denudation by lava flows, burial by eolian material, or others. Many of these processes can leave distinct signatures on the morphometry of the modified impact crater as well as the surrounding landscape. To look for signs of potential regional differences in crater modification processes, we conducted an analysis of different morphometric parameters related to modified impact craters located in the Margaritifer Sinus, Sinus Sabaeus, Iapygia, Mare Tyrrhenum, Aeolis, and Eridania quadrangles, including depth, crater wall slope, crater floor slope, the curvature between the interior wall and the crater floor slope, and the curvature between the interior wall and surrounding landscape. A Welch's t test analysis comparing these parameters shows that fresh impact craters (Type 4) have consistent morphologies regardless of their geographic location examined in this study, which is not unexpected. Modified impact craters both in the initial (Type 3) and terminal stages (Type 1) of modification also have statistically consistent morphologies. This would suggest that the processes that operated in the late Noachian were globally ubiquitous, and that modified craters eventually reached a stable crater morphology. However, craters preserved in advanced (but not terminal) stages of modification (Type 2) have morphologies that vary across the quadrangles. It is possible that these variations reflect spatial differences in the types and intensity of geologic processes that operated during the Noachian, implying that the ancient climate also varied across regions.

Influence of the shape, thermal radiation, and variable properties on the turbulent buoyancy-driven airflow inside cavities with Trombe wall geometry

ABSTRACTThe effects of the radiative heat transfer and the influence of air variable properties on the natural convection flows in cavities with Trombe wall geometry are numerically investigated. The influence of considering surface-radiative effects on the differences reached for the Nusselt number and the mass flow rate obtained with several heating intensities is studied. The effects of the shape change consisting of varying slope angle of the heated wall is also analyzed. The influence of the thermal radiation on the appearance of the burnout phenomenon becomes particularly relevant. Important changes in the thermal and dynamic flow patterns are observed for high enough values of the wall slope angle.

A unified description of oblique waves in ideal and non-ideal steady supersonic flows around compressive and rarefactive corners

According to classical gas dynamic theory, if a steady supersonic parallel flow encounters a sudden change in the wall slope, two very different phenomena may occur. If the flow expands around a sharp corner, the well-known isentropic Prandtl–Meyer fan is observed. Conversely, a shock wave occurs if the flow is compressed: for wedge angles smaller than the detachment value, which depends on the uniform upstream state, an oblique shock originates at the corner; at larger deviation angles, a detached shock is formed. A unified description of these flows is presented here to extend the validity of the common $$\beta $$ – $$\vartheta $$ (shock angle–deflection angle) diagram for shocked non-isentropic flows into the realm of isentropic expansions. The new graph allows for a straightforward identification of the wave angles for self-similar flow fields around compressive and rarefactive corners. Besides, it clarifies the relation between shock waves and rarefaction fans in the neighbourhood of the $${\vartheta =0}$$ axis, where shock waves are weak enough to be fairly well approximated by isentropic compressions. At $${\vartheta =0}$$ , indeed, shock and rarefaction curves are demonstrated to be first order continuous. This result is interpreted in view of the bisector rule for oblique shock waves. Exemplary diagrams are reported for both ideal-gas flows, dilute-gas flows and non-ideal flows of dense vapours in the close proximity of the liquid–vapour saturation curve and critical point. The application of the new diagram is illustrated for the textbook case of the supersonic flow past a diamond-shaped airfoil.

Evaluation of stable and safe pit wall slope design for underground extraction of mineral reserves under Kamagan open pit mine bottom

Evaluation of stable and safe pit wall slope design for underground extraction of mineral reserves under Kamagan open pit mine bottom

Numerical study on overtopping performance of a multi-level breakwater for wave energy conversion

Overtopping wave energy converter (OWEC) is capable of converting the unstable wave energy into the relatively stable potential energy in its reservoir. The small wave height and the large tidal range in China will cause a lower efficiency of the traditional single-level overtopping device especially at the lower tidal level. The design of the multi-level reservoirs may be a solution to improve the overtopping performance, which can be integrated in the sloping-ramp breakwater. In this study, a multi-level breakwater for wave energy conversion, consisting of two reservoirs with sloping walls at different levels, is proposed. A numerical wave tank based on the VOF model is established in ANSYS-Fluent® 12.0 for the OWEC's performance investigation. The numerical model on predicting the overtopping process and time-averaged discharges is validated by corresponding experimental data. Effects of the opening width of the lower reservoir, sloping angles of two reservoirs and the gap height between the reservoirs on the dimensionless overtopping discharges are studied numerically. It is found that a smaller opening width, larger height ratio, and two sloping angles of 30° have positive effects to improve the overtopping performance of the device.

Advancing electrochemical jet methods through manipulation of the angle of address

Electrochemical jet processing techniques have traditionally been considered to be limited to planar interactions with the electrolyte jet being maintained normal to the workpiece surface. In this study, the viability and resultant effects of articulating the nozzle relative to the work were investigated for the first time. Two machining conventions were defined, normal, where the jet is maintained perpendicular to the traverse direction, and push/pull, where the nozzle is rotated with respect to the direction of travel. It was found, with the normal convention that a range of differing resultant profile surface geometries could be created; unique to this process. This was demonstrated by the changing resultant side wall slopes found through the rotation of the head with up to 80% difference between the slopes of the cut walls. The adjacent wall to the nozzle slope decreasing as the jet angle approaches 90° whilst the opposite side wall slope increases. Predictable ratios of the differing slopes of the striation side walls were then able to be defined. The push/pull convention demonstrated that deeper, sharper cuts are possible due to the highly localising current density effect of nozzle inclination achieving a 35% increase in depth without requiring additional energy. Also, that resultant surface finish could be greatly improved, reducing the profile roughness (Ra) from 0.2 μm in the pull mode to 0.04 μm in the push mode achieving a mirror-like finish. The mechanics of these phenomena are investigated and defined. The influence of nozzle jet speed variation combined with inclining the jet was also studied. This was found to have no noticeable influence on the resultant profile when the nozzle is inclined. In contrast, when the nozzle is normal to the surface, jet velocity is seen to have a direct influence due to polarisation effects relating to the poor clearance of machining debris and the formation of oxides. It is shown that through variation of the angle of jet address an extra level of flexibility and performance is possible within electrochemical jet processes.

Experimental study on multi-level overtopping wave energy convertor under regular wave conditions

A multi-level overtopping wave energy converter was designed according to the large tidal range and small wave heights in China. It consists of two reservoirs with sloping walls at different levels. The reservoirs share a common outflow duct and a low-head axial turbine. The experimental study was carried out in a laboratory wave-flume to investigate the overtopping performance of the device. The depth-gauges were used to measure the variation of the water level in the reservoirs. The data was processed to derive the time-averaged overtopping discharges. It was found that the lower reservoir can store wave waters at the low water level and break the waves which try to climb up to the upper reservoir. The upper sloping angle and the opening width of the lower reservoir both have significant effects on the overtopping discharges, which can provide more information to the design and optimization of this type of device.

A numerical study of the wall effects for Newtonian fluid flow over a cone

The effect of blockage ratio i.e. ratio of diameter of cone, d and flow channel, D on the drag coefficients due to Newtonian fluid flow over cone is studied numerically by solving the CFD equations in Ansys FLUENT. The drag coefficients (CD) as a function of Reynolds number (Re) and d/D are reported in the range of Re: 0.01–30,000 and d/D: 0.0015–0.9. The obtained CD values are higher for confined flow (high d/D) than unconfined flow. Validity of CDRe2=constant is ascertained for the confined Newtonian fluid flow over the cone. The variations of angle of separation and its effect on the drag coefficients are examined and justified. The comparative studies among the drag coefficients of sphere, cylinder and cone are carried out in terms of wall effect, re-circulation length and slope of axial velocity profile. The observations revealed the order of CD as cylinder > cone > sphere. The hydrodynamic interactions between wall and fluid medium are presented with the help of velocity contour plots. More asymmetric flow is observed around the particle at higher Reynolds number and for higher wall effect. The simulated results presented herein for unconfined flow are in good agreement with the literature data.

The impact of building massing on net-zero achievability for office buildings

The simultaneous impact of massing on both energy consumption and renewable energy production potential is studied by taking the case of office buildings in Washington D.C. A Baseline design with a square footprint is compared with eleven massing alternatives: three rectangular parallelepiped designs with aspect ratios of respectively 2, 3, and 4, along the east-west orientation; three rectangular parallelepiped designs with aspect ratios of respectively 2, 3, and 4, along the north-south orientation; two H-shaped designs; one cross-shaped design; and two pyramidal buildings with wall slopes of respectively 86° and 83°. With differences between the best performing massing alternative and the worst performing massing alternative of more than 10% in terms of energy consumption, and more than 20% in terms of renewable energy production, massing is found to significantly impact both energy use and energy production. Consideration of both energy consumption and renewable energy production potential suggests that, for temperate climates such as Washington D.C., buildings with H-shaped footprints, buildings with crossshaped footprints, and buildings with high aspect ratio footprints are preferable when targeting net-zero energy status.

Application of geotechnical monitoring tools for deformation analysis in the vicinity of the Dębina salt dome (Bełchatów mine, Poland)

The presence of the Dębina salt dome (DSD) entails new challenges for the exploitation of the Bełchatów lignite (brown coal) deposit. Poland is the 5th largest world lignite producer (63.1 Mt). The Bełchatów open-pit mine provides more than a half of the brown coal production capacity in Poland. The geological structure of the Bełchatów area is complex due to tectonic and sedimentation processes, as well as to the presence of the DSD, which determines rather unique geological conditions in comparison to other brown coal mines. Halokinetic processes connected with rising of the DSD contributed to shaping the present lignite seams form. Brown coal extraction in such a complex environment endangers stability of pit wall slopes. The long-term mining of the Bełchatów coal field and relaxation processes are factors that influence the development of both vertical and horizontal displacements. Of particular concern is the stability of the Bełchatów western pit wall slope, outlining the necessity of a comprehensive geotechnical monitoring effort. A geodetic network aimed at measuring vertical displacements was installed above the salt dome. In order to measure horizontal displacements, borehole inclinometers were also installed on several mine benches. The analysis of vertical displacements revealed that the eastern part of the dome has been uplifted, while the southern, south-eastern and northern parts have undergone subsidence. Our study of horizontal displacements indicated zones of potential shear movements. The deformations were primarily connected with changes in geometry and steepening of the Bełchatów western pit slope. However, relaxation processes caused a change in the primary stress conditions of the DSD and may have triggered the halokinetic salt movement.

STABILITY ANALYSIS AND FAILURE MECHANISMS OF OPEN PIT ROCK SLOPE

Rock mass in nature tend to be unideal, for it is heterogeneous, anisotropic and has discontinuity. The discontinuity makes anisotropic strength and stress in the rock mass, and also controls the changing of the elastic properties of rock mass. This condition results to disruptions in the rock mass strength balance, and finally drives the slopes to collapse. This study aims to determine the slope failure mechanisms in the area of case study, as well as its variations based on the Rock Mass Rating (RMR), Geological Strength Index (GSI), Slope Mass Rating (SMR), kinematic analysis, numerical analysis and monitoring approach slope movement in a coal mine slope applications. The site investigations were implemented to obtain information about slope collapse. Prior to the collapse, the slope inclination was 38° with of 94 meters height, strike slope of N 245 E and direction of slope surface of 335°. After the collapse, the slope was became 25º; and after the collapse materials were cleared, it was 35º. The discontinuity mapping obtained 5 sets of discontinuities, and the data were developed to obtain the value of RMR. The result of piezometer measurements was that at occurrence of collapse, slope elevation was 44.40m. Displacement value from monitoring SSMR showed that when the slope was collapsing in two stages, the first stage value was 70.61cm (a more critical condition, the value was rounded down to 70cm to the implementation in modelling) and the second stage value was at 124.25cm. The value of RMR89 in this study was greater than the value of GSI and SMR. As for the average value, it was obtained 34.67 for RMR89 value and 29.67 for GSI value, these rocks then can be classified into Poor Rock class number IV. The result of kinematic analysis found that sliding planar failure at dips 36°, and wedge failure at dips 36°, 35° and 34°. Acquisition SMR value obtained at 25, 27, 28 and 29. The SMR values classified the rock mass quality into class number IV, the description of the rock mass was relatively poor, the slope stability was low or unstable and the collapse manifold was planar or wedge failure. The result from the analysis of the model with its criteria obtained was that un-collapse conditions at angle 29°. It is recommended to use 29° angle to repair the slopes, and also recommended for overall high wall slope angle. Type of collapse that occurred on the slope failure mechanisms in all of the analysis that has been done, it is known that the mechanisms involved are complex types (combine of wedge failure, planar failure, and step-path failure) or classified into large scale rock slope failure surface.

Axisymmetric active lateral earth pressure for c- soils using the stress characteristics method

The slip line or Stress Characteristics Method (SCM) is used to analyze the active lateral earth pressure in the axisymmetric case. In this paper, in addition to the retaining walls in the axisymmetric and plane strain conditions that studied in the past, a new model of the retaining wall in the axial symmetry is considered, which widely used in the design of grain silos, buildings and road constructions. The effects of the various parameters, including cohesion and friction angle of the soil, wall and backfill slopes and soil-wall interface adhesion and friction angle on the lateral earth pressure have been evaluated for all cases of the retaining walls. Based on the proposed theory, a computer code has been developed for the plane strain and axisymmetric cases. Also, finite element modelling is used to verify the results of the SCM. Comparison of the results indicated the accuracy of the proposed method. Furthermore, the effect of the plastic critical or tension crack depth has been evaluated and indicated that neglecting the plastic critical depth is not conservative.

Small lunar craters at the Apollo 16 and 17 landing sites - morphology and degradation

New analysis and modeling approaches are applied to high-resolution images and topography of the Apollo 16 and 17 landing sites to investigate the morphology and estimate degradation of small lunar craters (SLCs; 35 to 250 m diameter). We find SLCs at the two sites are mostly degraded with an average depth-diameter ratio (dD)<0.1, resulting in a landscape dominated by shallow, inverted cone-shaped craters. An improved standardized morphological classification and a novel set of quantitative shape indicators are defined and used to compare SLCs between the two sites. Our classification methodology allows morphological class populations to be designated with minimal (and measurable) ambiguity simplifying the study of SLC degradation at different target regions. SLC shape indicators are computationally obtained from topography, further facilitating a quantitative and repeatable comparison across study areas. Our results indicate that the interior slopes of SLCs evolve faster and through different processes relative to larger craters ( > 500 m). Assuming SLCs are formed with large initial depth-to-diameter ratio (dD≥0.2), our observation that even the fresher SLCs are relatively shallow imply that a faster mass wasting process post-formation stabilizes the crater walls and eventually slows down degradation. We also found that the Apollo 16 Cayley plains have a higher percentage of fresh craters than the Apollo 17 Taurus Littrow (TL) plains. A combination of a less-cohesive target material and/or seismic shaking resulting from moonquakes or the impact of Tycho crater secondaries was likely responsible for a higher degradation rate in the TL-plains compared to the Cayley plains. This study explores the relationship between the symmetry and probability densities of key morphological traits like dD, mean wall slope and rate of degradation. We show that the shape of dD probability density function of SLCs in a study area encodes their rate of degradation. Comparison of power-law fitting and probabilistic modeling of depth-diameter relations shows that probabilistic methods complement regression models and are necessary for robust prediction of SLC depths from diameter (and vice versa) for different geological targets.

Limit resistive forces from ice frozen to concrete-revetment interface of an inclined dam wall

To estimate ice loads on concrete panel revetments of inclined dam walls, a series of simple shear tests were conducted to investigate adfreezing (freezing adhesion) behaviors of freshwater ice to concrete panel. Experimental results indicated that the adfreezing strength increases generally as the temperature decreases from −2°C to −10°C, and is impacted insignificantly by the loading/displacement rate. The adfreezing strength for coarse interface (surface roughness (SR)=4.2mm) is greater by 30%–40% than that for smooth interface (SR=0.3mm). Field investigations in a reservoir in northeastern China and theoretical discussions on ice-dam interactions indicated that the ice-dam bond is the strongest restraint on ice cover movement for a sloped dam wall. The adfreezing strength of ice-dam bond limits the restraining force during ice-push events, usually damaging dam walls or shoreline revetments. Limiting ice loads are estimated using the present adfreezing strengths under various ice failure scenarios induced by typical patterns of water level changes. The highest loads are generated when the water level keeps constant or drops quite slowly especially after large drops and/or ice push events. The estimates of ice loads are in the range of values derived from previous field observations.

Flow between two rectangular inclined plane walls

Problem of two dimensional, steady and viscous fluids in a rectangular converging (diverging) plane walls is studied here. Rectangular coordinate system is considered in which x is representing axial direction and y is normal to it. Walls are situated at y=±(mx+h0) where m is the slope of channel walls and ± h0 are y-intercepts or 2h0 is gap between walls when x=0. The free stream at center of channel is inversely proportional to mx+h0. Flow phenomena have been characterized by non-dimensional parameters Re (Reynolds number) and slopes of walls m. The governing equations are reduced to a set of ordinary differential equations by using appropriate transformations for velocity components and pressure. These ordinary differential equations have been solved for different values of m and Re subject to relevant boundary conditions. Effects of parameters on velocity and pressure distributions have been studied. Three types of solutions are discussed here: perturbation solution, numerical solutions and a solution obtained by collocation method. Also these results are matched with classical models. For reasonable values of parameters, excellent agreement among solutions is also found.

Relative depths of simple craters and the nature of the lunar regolith

We assessed the morphologies of more than 930 simple impact craters (diameters 40m–10km) on the Moon using digital terrain models (DTMs) of a variety of terrains in order to characterize the variability of fresh crater morphology as a function of crater diameter. From Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) DTMs, we determined depth-to-diameter (d/D) ratios for an extremely fresh set of these craters with diameters less than 400m and found that their d/D ratios range from 0.11 to 0.17. Using both NAC and Kaguya Terrain Camera DTMs, we also determined the d/D ratios for the set of fresh simple craters larger than 400m in diameter. The d/D ratios of these larger craters are typically near 0.21, as expected of gravity-dominated crater excavation. Fresh craters less than ∼400m in diameter, on the other hand, exhibit significantly lower d/D ratios. Various possible factors affect the morphologies and relative depths (d/D ratios) of small strength-dominated craters, including impactor and target properties (e.g., effective strength, strength contrasts, porosity, pre-existing weaknesses), impact angle and velocity, and degradation state. While impact conditions resulting from secondary impacts can also affect crater morphologies, we found that d/D ratio alone was not a unique discriminator of small secondary craters. To investigate the relative influences of degradation and target properties on the d/D ratios of small strength-dominated craters, we examined a subset of fresh craters located on the geologically young rim deposits of Tycho crater. These craters are deeper and steeper than other craters of similar diameter and degradation state, consistent with their relative freshness and formation in the relatively coherent, melt-rich deposits in this region. The d/D ratios of globally distributed small craters of similar degradation state and size range, on the other hand, are relatively shallow with lower average wall slopes, consistent with crater excavation in a weak or poorly cohesive layer. The widespread predominance of these small, shallow craters is consistent with the pervasive, poorly cohesive upper regolith.