Rock Piles Research Articles

Solving problem of encountering a huge cavern in a TBM drive for water diversion tunnel project in Northern Thailand

AbstractA huge cavern in a zone of thrusted and sheared clastic sedimentary rocks was encountered during drill and blast (D&B) and tunnel boring machine (TBM) excavation of water transfer tunnel in Thailand. The cavern floor made of thick and loose pile of fallen rock blocks hampered the advance of the TBM through it. Because the size of the cavern was large (50 m × 40 m) and the extent of the thickness of the pile of rock blocks could not be precisely determined, the adopted ramification was to solidify a zone of loose rock fragments around the tunnel alignment. This measure is to allow a safe TBM excavation passing the cavern and ensure the long‐term function of the segmented concrete‐lined tunnel to convey water without problem of loss from subsidence damage. The scheme of the solidification consisted of staged grouting that began with polyurethane (PU) foam grouting to form a bottom barrier of the intended cement grout zone. It was followed large void filling by flowable concrete and then cement injection for the remaining smaller voids. The work that took 8 months to complete started with the excavation of a bypass adit to the front of TBM cutterhead as an access to the cavern and the installation of dewatering and ventilation systems to the cavern so that the grouting work could be made.

Mechanical Characterization of Coarse-Grained Waste Rocks Using Large-Scale Triaxial Tests and Neuroevolution of Augmenting Topologies

Mining operations produce large quantities of waste rocks, which are usually disposed of in waste rock piles, but can also be valorized in mine haul roads. The engineering performance of these haul roads significantly depends on the mechanical characteristics of the materials used for the construction. However, available experimental studies on coarse-grained waste rocks are relatively limited, mainly because of their large grain size and the scarcity of adapted testing equipment. In this study, a series of repeated load and monotonic triaxial tests (specimens 300 mm in diameter and 600 mm in height) were carried out to evaluate the resilient modulus, permanent deformation, and shear strength of coarse-grained waste rocks (up to 60 mm in diameter) with different gradations. Results showed that an increasing in maximum particle size and compaction effort resulted in a larger resilient modulus and shear strength and smaller permanent deformation. The optimal gravel-to-sand ratio to maximize resilient modulus and shear strength was around 5. Permanent strain was relatively constant when the gravel-to-sand ratio was between 1 and 5, but it decreased significantly when the ratio increased to 8. The impact of fines content and water content on the mechanical properties was relatively limited. Also, the MR-θ model and Rahman and Erlingsson model showed good fitting performance for resilient modulus and permanent strain, respectively. Finally, neuroevolution of augmenting topologies (NEAT) was used to develop a machine learning model for predicting the resilient modulus of waste rocks, based on 265 data sets. The model showed reliable accuracy, simple topology, and high generalizability capacity. The findings described in this article should be beneficial for the valorization of waste rocks in pavement engineering.

Construction and Calculation Analysis of Mechanical Model of Crushed Rock Pile Treatment of Foundation Earthquake

In recent years, earthquakes have occurred frequently at home and abroad, causing huge losses to the local society. Therefore, it is important to study the mechanical response of foundations under earthquakes. In this paper, firstly, gravel piles are selected as soft ground improvement materials, and A single bulk material pile section and a peripile soil section within the influence of a single pile are considered as a study unit, and the pore water discharge from the consolidation process is equal to the volume reduction of the unit, considering the consolidation deformation of the pile body, the composite foundation consolidation equation is derived, and the consolidation equation is solved by the separation variable method through the isostrain assumption and initial boundary conditions, and the average superporous water pressure of the soil between the body and the pile is obtained. Then, a more realistic non-uniform ground motion input method is adopted, and the seismic fluctuations are converted into equivalent loads on artificial boundary nodes through the Matlab program, and the equivalent loads are applied to the established viscoelastic artificial boundary by OpenSees software to realize ground motion input. Finally, a mechanical analysis model is established by hypothesis, and with the help of mode orthogonal theory and Hilbert yellow transform, the calculation method of ground seismic mechanical response based on non-uniform ground motion input is obtained. The results show that the effect of gravel pile encryption can reduce the accumulation rate and peak of super-static pore pressure during vibration, and the surface settlement of the site is reduced by 40–50% and the surface lateral shift is reduced by 30–50% after encryption; the drainage effect has a significant effect on reducing the accumulation rate of super-static pore pressure and the post-earthquake dissipation time of the soil during vibration, and the surface settlement is reduced by about 10–20% and the lateral shift is reduced by about 30–40% after increasing the drainage effect.

Pile tip bearing capacity in rock masses: analytical and numerical analysis comparison

This paper researches the different approaches to calculate the ultimate bearing capacity at the pile tip embedded in a homogenous rock mass characterized by the modified Hoek and Brown failure criterion. The main objective is to analyze the performance of the novel Discontinuity Layout Optimization method (DLO), which directly calculates the limit load, instead of using a load convergence scheme, being first applied here to the complex problem of piles in rock. The DLO results are validated against the available analytical solution and the Finite Difference Method (FDM) results, for wide range of geometric and geotechnical parameters. Perfect plasticity, plane strain conditions, associated flow rule, the modified Hoek and Brown failure criterion, and weightless rock media are considered in all models. The comparison between solutions is expressed by a percentage difference considering the analytical solution or the numerical solution as a reference. Results relative to DLO and FDM differences against the analytical solutions point towards some limitations of the analytical solution and that the numerical model does not reproduce exactly the analytical solution hypotheses. From the analysis, DLO demonstrates to be a very efficient and accurate tool to address the tip-of-pile bearing capacity, presenting considerable advantages over other methods.

Calculation Model of Vertical Bearing Capacity of Rock-Embedded Piles Based on the Softening of Pile Side Friction Resistance

Rock-socketed pile is widely used in coastal wharf, Marine bridge, and Marine power engineering, and the end bearing function is considered more in the design process. However, the lateral friction resistance of rock-socketed piles is an important bearing part, and the load transfer mechanism of the pile–soft rock interface is an important research focus. In this paper, a comparative analysis was adopted in the test, and ten groups of test specimens were made, including five groups of natural and saturated mudstone specimens, respectively. The characteristics of interfacial load transfer were analyzed through the shear test of a pile–mudstone interface. A calculation model for the vertical bearing capacity of rock-socketed piles based on the softening of lateral friction resistance was established, and the effects of interface relative displacement, lateral positive pressure, pile length, and pile stiffness on the vertical bearing capacity of rock-socketed piles were analyzed. The results show that the shear strength of the pile–rock interface is lower than that of the mudstone interface, and the interfacial shear strength shows the characteristics of “first increasing, then decreasing, and finally flattening with the increase of shear displacement”. The vertical ultimate bearing capacity and residual bearing capacity under saturation were 89.49% and 89.73% of the natural state, respectively. With the increase of pile side pressure, the proportion of pile side friction resistance increased by 39.96%, and the pile side friction resistance was fully exerted. With the increase of pile length, the vertical ultimate bearing capacity of pile foundation increased, and the residual bearing capacity change value increased from 6.80% to 16.97%. However, the increase in pile stiffness had little effect on the vertical bearing capacity. The calculation model can provide a certain reference for the design and calculation of rock-socketed piles in soft rock areas.

Influence of competition on root architecture and root anchorage of young hybrid poplar plantations on waste rock slopes

ABSTRACT Root systems are crucial to tree and soil stability in terms of mechanical support, but are rarely considered in revegetation studies. This study aimed at determining the effect of planting density and herbaceous hydroseeding on the root architecture and mechanical resistance to uprooting of planted hybrid poplars on waste rock piles. The study took place at an open pit gold mine in the Canadian boreal zone where a hybrid poplar plantation was established in 2013 on soil-covered waste rock slopes (33%). Four treatments were randomly distributed in three replicated blocks: 4 × 4 m, 2 × 2 m, 1 × 1 m between trees and 2 × 2 m + h, corresponding to trees spaced at 2 × 2 m with hydroseeding. Lateral uprooting tests of four-year-old hybrid poplars were conducted in the direction of the slope. Maximum resistance to the uprooting force was observed in the 2 × 2 m treatment. Root systems were more symmetrical, deep, branched, and had higher root diameters in the 2 × 2 m and 4 × 4 m treatments. In contrast, the treatments with greater intra- or interspecific competition showed shallower, asymmetrical root systems with smaller roots. Therefore, competition significantly reduced tree anchorage.

Spectral element formulation for rock-socketed mono-pile under horizontal dynamic loads

The current study entails a thorough investigation of the dynamic response of a mono-pile foundation in homogeneous soil and varied layered soil–rock conditions under horizontal dynamic loads. A sequence of visco-elastic springs linked along its length represents the mono-pile immersed in elastic half space. The frequency dependent stiffness and damping of a mono-pile foundation embedded in layered elastic half space are developed using spectral element formulation. The variations in stiffness and damping with frequency for various soil–rock systems are demonstrated. The dynamic response characteristics of the pile were found to be influenced by the depth of the rock-socketed pile. The presence of the underlying layer of stiffer layer of rock enhances the overall stiffness of the system. The frequency versus amplitude responses of a mono-pile supported heavy mass block for both horizontal translation and rocking motion are calculated using the stiffness and damping of the mono-pile under various soil rock conditions. The horizontal amplitude of the pile decreases with increasing pile rock socketing depth. The resonant amplitudes for rocking motion increases as the pile’s rock socketing depth increases. Finally, the changes in natural frequency and peak amplitudes with varied pile slenderness ratios are investigated for diverse pile–soil–rock conditions.

Implications of New Geological Mapping and U‐Pb Zircon Dating for the Barrovian Tectono‐Metamorphic Evolution of the Lepontine Dome (Central European Alps)

AbstractThe Barrovian metamorphism of the Lepontine dome is manifested by isograds that cross‐cut tectonic nappe contacts, which is commonly interpreted as metamorphism that occurred after nappe emplacement. However, the pervasive mineral and stretching lineation in amphibolite facies, associated with top‐to‐foreland shearing, suggests that peak Barrovian conditions are coeval with nappe‐overthrusting. Here, we combine mapping and U‐Pb zircon dating to better constrain the relation between metamorphism and overthrusting. Metamorphic zircon rims show two age populations at 31–33 and 22–24 Ma. The younger population is locally observed in post‐foliation dikes (and associated metasomatism) likely sourced from deep‐migmatites exhuming along the Alpine backstop. The older population occurs regionally and is found in syn‐kinematic migmatites which occur along a crustal‐scale shear zone. Below this shear zone, magmatic and detrital zircon cores suggest that the Cima Lunga unit, previously interpreted as a tectonic mélange with Mesozoic fragments, was a pre‐Variscan metasedimentary sequence intruded by Permian granitic sills, now orthogneisses. This unit was strongly sheared along the top of the Simano nappe during overthrusting of a rock pile here‐termed Maggia‐Adula nappe. This large‐scale nappe emplacement imprinted the regional lineation and peak temperatures until 31–33 Ma. Péclet (1–10) and Brinkman (0.002–1.8) numbers, estimated for the overthrusting, suggest an advection‐dominated heat transfer caused by rock exhumation, with some diffusion (conduction) during nappe emplacement. Diffusion contributed to Barrovian isograds discordant to the thrust. Shear heating was important if stress times shearing rate >∼5·10−6 W·m−3 within the nappe. The thermal evolution after overthrusting was spatially heterogeneous until ca. 22 Ma.

Moving towards sustainable mine waste rock management through automated mineral and geochemical analysis

Mining activities generate vast amounts of waste rock (WR); if this waste is sulphide- and sulphosalt-bearing, it can pose a risk to ecosystems due to contaminated mine drainage. Strategic long-term planning is necessary to prevent and mitigate adverse environmental impacts. This study includes a detailed characterization of WR from a mine in northern Canada and defines the diameter of physical locking of sulphides and sulphosalts (DPLS) that can be used to separate the WR into two fractions according to the geochemical reactivity. An automated mineralogy system (QEMSCAN®) and computed tomography (CT) were used to quantify the liberation degrees of acid-generating (sulphides) and neutralizing minerals (carbonates). Chemical and mineralogical analysis indicated that sulphides, mostly pyrite (FeS2) and gersdorffite (NiAsS) (dominant sulphides), were enriched in the fine- to mid-sized fractions compared to the coarse fractions. These minerals were more liberated within the fine fractions and their liberation degree was considered negligible at sizes >2.5 mm. Consequently, 2.5 mm was defined as the critical diameter of sulphide reactivity (DPLS) for the studied WR. Furthermore, kinetic tests using humidity cells were conducted to confirm this result and to assess the geochemical behaviour of the total fraction (< 10 mm), the coarse fraction (> 2.5 mm) and the fine fraction (< 2.5 mm). Sulphides associated with the coarse fraction were not significantly exposed to weathering conditions; sulphides were associated with non-sulphide gangue minerals, which was confirmed by QEMSCAN® and computed tomography. Moreover, mineral weathering occurred primarily in the fine fraction (< 2.5 mm) due to the higher available exposed surface area of the minerals. The geochemical analysis of humidity cells leachate revealed that the pH values remained within the range of 7.07 and 8.61, and that the instantaneous metal concentrations (Fe, Cu, and Ni) were consistently below environmental limits during the154- day test period. However, As concentrations from fine and total fractions exceeded environmental standards. Sample reactivity showed that the fine fraction controlled the geochemical behaviour of the studied WR, where the fine fraction was 1.5 times more reactive than the total fraction and 10 times more reactive than the coarse fraction which represents about 60 wt% of the total sample. Consequently, screening waste rock in accordance with the DPLS could prove to be an effective method for managing WR to prevent contaminated drainage. This approach may allow a reduction in the amount of WR to be stored in surface piles (which need to be managed) and will reduce the costs associated with the reclamation of waste rock piles.

Dissolved thiolated arsenic formed by weathering of mine wastes

Aqueous thiolated arsenic (As) species play an important role in the biogeochemical cycling of As in wetlands and hydrothermal systems. Although mine wastes such as tailings ponds and waste rock piles may harbor similarly sub-oxic and neutral to alkaline conditions that favor the formation and mobility of thio-As species, quantitative data on their existence in these systems is lacking. We conducted laboratory column experiments under contrasting redox conditions with waste rock from the Antamina mine, Peru, and processed tailings from Montague, Nova Scotia, Canada. Dissolved As concentrations between 1 and 7000 μg/L were recorded in drainages across these mine waste types, with up to 13 μg/L As present in thiolated form, predominantly monothioarsenate. Higher percentages of thio-As species (up to 5%) were observed in drainages from enargite-rich materials compared to arsenopyrite-bearing materials (<0.5%). The lower abundance of dissolved thio-As in the arsenopyrite-rich mine waste samples is attributed to their partially oxidized nature and reduced mineral reactivity under the experimental circumneutral drainage pH, the difference in S [-II/0]-to-As molar ratios compared to the enargite-rich mine waste samples, as well as the oxidation of di- and tri-thiolated As species by dissolved Fe. Overall, our results demonstrate that aqueous thiolated As species may occur in mine wastes with different As-bearing minerals and could play an important role in governing the mobility and fate of As in these systems.

Assessing the importance of drainage layers over geomembrane liners within engineered cover systems: Seven years of field monitoring at three mine waste rock piles

Geomembrane liners are commonly subject to defects that can allow water leakage through these openings and significantly undermine their performance. While defects are difficult to prevent and characterize, minimization of potential leakage can still be attained with appropriate lateral drainage over the liner. The objective of this study is to assess the performance of different drainage layer materials within HDPE-lined cover systems at three mine waste rock piles (WRPs) in the Sydney Coalfield, Nova Scotia, Canada. Natural soil, clean gravel and a geocomposite net were employed at the Summit, Victoria Junction and Franklin WRPs, respectively. Extensive field monitoring of precipitation (PPT), moisture content within the cover materials, and head of water above the liner, was performed. The head of water and moisture was consistently high at Summit throughout the year, while consistently low at Victoria Junction and Franklin, with the geocomposite net being just as effective as the gravel layer. Using typical assumptions of defect size/number, leakage rates at Victoria Junction and Franklin remained very low due to limited water head and flow gradient. Therefore, while the prevention of defects is highly challenging at HDPE-lined cover systems, potential defect leakage can be proactively controlled during cover system design with the implementation of adequate drainage layers above the liner.

An Application of Spherical Cavity Expansion Theory in Soft Rock Pile-Base Resistance

The failure mode should be taken into account in the analytical solution for pile base resistance. In order to determine the pile’s failure pattern in soft rock, the graphical model test method is used. That the compression zone below the pile base in soft rock is compatible with the spherical cavity expansion is shown. An improved calculation model for the ultimate base resistance may be developed by considering the force balance of the rigid cone under the pile-end in the ultimate stress state and the limit pressure required to expand a spherical cavity. To account for the influence of socket length, the limiting pressure for the spherical cavity expansion in infinite space is adjusted to that in semi-infinite space. The ultimate resistance of a base is computed by factoring in the length effect. The normalization of the base resistance-displacement relation is provided based on the findings of pressure chamber experiments on pile load-settlement, which are independent of socket length and overburden pressure. This semi-empirical technique is verified via the use of pressure chamber experiments and field testing of piles in soft rock.

Ecological-niche modeling reveals current opportunities for Agave dryland farming in Sonora, Mexico and Arizona, USA.

For centuries, humans occupying arid regions of North America have maintained an intricate relationship with Agave (Agavoideae, Asparagaceae). Today Agave cultivation, primarily for beverage production, provides an economic engine for rural communities throughout Mexico. Among known dryland-farming methods, the use of rock piles and cattle-grazed areas stand out as promising approaches for Agave cultivation. Identifying new cultivation areas to apply these approaches in Arizona, USA and Sonora, Mexico warrants a geographic assessment of areas outside the known ranges of rock piles and grasslands. The objective of this study was to predict areas for dryland-farming of Agave and develop models to identify potential areas for Agave cultivation. We used maximum entropy (MaxEnt) ecological-niche-modeling algorithms to predict suitable areas for Agave dryland farming. The model was parameterized using occurrence records of Hohokam rock piles in Arizona and grassland fields cultivated with Agave in Sonora. Ten environmental-predictor variables were used in the model, downloaded from the WorldClim 2 climate database. The model identified potential locations for using rock piles as dryland-farming methods from south-central Arizona to northwestern Sonora. The Agave-grassland model indicated that regions from central to southern Sonora have the highest potential for cultivation of Agave, particularly for the species Agave angustifolia. Results suggest that there are many suitable areas where rock piles can be used to cultivate Agave in the Sonoran Desert, particularly in the border of southeastern Arizona and northwest Sonora. Likewise, cattle-grazing grasslands provide a viable environment for cultivating Agave in southern Sonora, where the expanding bacanora-beverage industry continues to grow and where different Agave products (e.g., syrups, fructans, saponins, and medicinal compounds) can potentially strengthen local economies.

Pueblo Resistance and Inter-Ethnic Conflict: The 1540–1542 Vázquez de Coronado Expedition to the Middle Río Grande Valley, New Mexico

The expedition led by Francisco Vázquez de Coronado from west-central Mexico into the American Southwest from 1540 to 1542 had a profound and lasting impact on everybody involved. The exploration sought an overland route to Asia and to establish trade relations. The enterprise was also the first major contact between foreigners/others and Indigenous peoples of northern Mexico and the American Southwest. Research at Piedras Marcadas Pueblo, an ancestral village of the Southern Tiwa in central New Mexico, has material evidence and artifact patterns reflecting the cultural groups on the exploration and those with whom the expeditionaries ultimately fought. Geophysics surveys and metal detection have found evidence of a major battlesite at the pueblo. Specific artifact types, such as European metal items, slingstones hurled by their Mexican allies, and piles of rocks thrown back by Pueblo defenders all attest to the conflict and the hard-fought Tiwa resistance.

Calculation of Bored Piles in Rock Under a Compressive Axial Load

Calculation of Bored Piles in Rock Under a Compressive Axial Load

О ФОРМИРОВАНИИ ПРЕДОХРАНИТЕЛЬНОЙ ПОДУШКИ ПРИ ОТРАБОТКЕ ПОДКАРЬЕРНЫХ ЗАПАСОВ ТРУБКИ "УДАЧНАЯ" СИСТЕМАМИ С ОБРУШЕНИЕМ

Rational methods of creating protective cushion for isolating underground mining operations from open pit during the mining of sub-pit reserves of the Udachnaya kimberlite pipe with caving have been determined. The optimal operating order and ore drawing mode are recommended. It is shown that when ore drawing under rock pile, the actual protective cushion thickness is determined by the maximum amount of dilution and will be more than required under the conditions of mining safety.

Predicting displacements of ore body boundaries in generation of blasted rock pile

Predicting displacements of ore body boundaries in generation of blasted rock pile

Geochemical controls on mobilization of metals from a 100-year-old waste rock pile and implications for selection of cover amendments

Reclamation of mine waste rock piles typically consists of constructing a cover with amendments to improve conditions for vegetation. However, cover amendments have potential to mobilize metals in waste by introducing new chemicals and altering pH and redox conditions. This study evaluates metal phases in a 100-year-old waste rock pile with high metals content (3.5% lead by weight, 0.8% zinc, and 0.75% copper) and the potential for these metals to be mobilized by several cover materials and amendments (topsoil, spent brewery grain, biochar, compost, commercial soil media, and phosphate). Laboratory testing indicates that metals have weathered from their initial metal sulfide phases (galena, sphalerite, chalcopyrite), and are now also present as sulfates, phosphates, carbonates, and phases associated with manganese/iron oxides. Sequential extraction tests demonstrated that the largest extractable fraction of metals is associated with manganese/iron oxides (37% of lead by weight, 22% of copper, and 26% of zinc), suggesting an environmental risk should geochemically reducing conditions develop and mobilize metals in the pile after cover construction. Testing of specific cover materials demonstrated that metals mobilization also occurs from low pH (as with spent brewery grain), formation of stable aqueous metal–organic complexes (as with spent brewery grain and compost), and ligand exchange (as with phosphate amendment). Results of this study demonstrate the importance of identifying metal phases present in a waste rock pile prior to selecting cover amendments.

An Experimental Study on the Socketed Pile in Soft Rock

Pile foundation systems are used in India in many projects such as metro and railways, flyovers, and multi-story buildings. The pile transfers superstructure load to the substructure, i.e. to rock layers by means of skin resistance and end-bearing resistance. In this study, an attempt is made to observe the performance of socketed piles in soft rock. A series of socketed small-scale model pile load laboratory studies have been conducted using the loading frame. Load tests were performed on a model steel pile to calculate its axial load-bearing capability at various socket depths. An unconfined compression test was performed on pseudo-rock variations to find out the properties of the soft rock used. The results showed the ability of the drilled pile to enhance the strength of the pseudo rock. An attempt was also made to calculate the optimum depth for the socketed pile in soft rock.

The Influence of Crest Width and Working States on Wave Transmission of Pile–Rock Breakwaters in the Coastal Mekong Delta

The coastline of the Ca Mau and Kien Giang provinces in the Vietnamese Mekong Delta has been severely eroded in recent decades. Pile–Rock Breakwaters (PRBWs) are among the most widely adopted structures for controlling shoreline erosion in this region. These structures are effective for wave energy dissipation, stimulating sediment accumulation, and facilitating the restoration of mangrove forests. These breakwaters are generally considered to be the best-engineering practice; however, there is currently insufficient scientific evidence with regard to specific structural design aspects. This can lead to PRBW structures being compromised when deployed in the field. This study used a physical model of a PRBW in a laboratory to investigate several design parameters, including crest width and working states (i.e., submerged, transition, and emerged), and investigated their relationship with the wave transmission coefficient, wave reflection coefficient, and wave energy dissipation. To investigate these relationships further, empirical formulas were derived for PRBWs under different sea states and crest widths to aid the design process. The results showed that the PRBW width had a significant influence on the wave energy coefficients. The findings revealed that the crest width of the breakwater was inversely proportional to the wave transmission coefficient (Kt) under the emerged state. The crest width was also proportional to the wave reduction efficiency and wave energy dissipation in both working states (i.e., the submerged and emerged states). The front wave disturbance coefficient (Kf) was found to be proportional to the wave reflection coefficient, and the wave height in front of the structure was found to increase by up to 1.4 times in the emerged state. The wave reflection coefficient requires special consideration to reduce the toe erosion in the structure. Lastly, empirical equations including linear and non-linear formulas were compared with previous studies for different classes of breakwaters. These empirical equations will be useful for understanding the wave transmission efficiency of PRBWs. The findings of this study provide important guidance for PRBW design in the coastal area of the Mekong Delta.