Rock Depth Research Articles

Investigation on the mechanism and control methods for roof collapse caused by cable bolt shear rupture

Roof collapse of mining roadways has always been key in the studies of the surrounding rock control. One of the critical factors lies in the roof separation and horizontal displacement which led to the cable bolt shear rupture, resulting in the roof fall. This study investigates the roof collapse accident that occurred at the No.15028 tailgate of XinJing coal mine in China. In-situ observations, numerical simulation and laboratory test are conducted to analyse the gradual deterioration of the roof strata. The field observation of the fractures, separations, pretension load and rock bolts loading are conducted during the process of separation. The analysis results indicate that owing to the torque value of rock bolts below 150 N·m (pretension load was 29 kN) and incompatibility of reinforcement fittings of rock bolts, the pretension load failed to solidify the surrounding rocks effectively. Obvious separations were identified at rock depths ranging from 0 to 2.6 m. Simulation results revealed that different flexural deflections caused horizontal displacement in rocks, which is positively correlated with the vertical separation. In weak interlayers of rocks, the severe horizontal displacements led to shear fracture of cable bolts, resulting in roof collapse. An increasing rock bolt pretension load can reduce the horizontal displacement of the rock stratum beyond the anchorage zone, which can lower the shear force of cable bolts by 30% and reduce the shear fracture risk of the cable bolts. Mechanical compatibility tests of the surrounding rock support system are conducted to develop a practical and reasonable reinforcement fittings to increase the pretension load of the rock bolts. Based on the research, a series of control methods are developed to enhance the roof stability. The field tests proved that the newly proposed methods can effectively improve the stability of the roof and eliminate roof collapses.

Quantification of dynamic damage and breakage in granite under confined indentation

Understanding of indentation rock damage and breakage under confining stress is necessary for underground engineering applications, as both loading rate and in-situ stress can affect the failure behaviour and mechanism. A triaxial apparatus capable of applying both static lateral confinement and dynamic loading is utilised to experimentally investigate the influence of both loading rate and confinement on rock indentation failure. The force-displacement relationships and energy evolution were determined for different dynamic loading and confinement conditions, while digital reconstruction of indented rock samples was achieved for crater depth and damage volume measurements. The failure mechanisms at microscale are studied using the optical microscopy and Synchrotron-based X-ray Computed Tomography (CT). The relationship between the incident energy and indentation force is correlated with the crater depth and volume of rock removed. The crater depth increases linearly with increasing force and incident energy, while the volume increases exponentially. The biaxial confinement controls the propagation of radial cracks, which propagate in the direction of major confining stress, while impact velocity dominates the crater depth and lateral crack formation beneath the crater. The formation of chipping during indentation is reflected on both the force-displacement relationships and X-ray CT measurements. Different minerals within the rock also affect the propagation and coalescence of cracks, harder mineral such as quartz has better resistance to crushing, whereas biotite deflects and terminates cracks.

Evaluation of Uncertainties in Site Response Analysis of Deep Soil Profiles in South Carolina Coastal Plain

ABSTRACTThe South Carolina Coastal Plain consists of deep soil sediments over basement bedrock. The depth of basement bedrock varies from being present at the surface to a depth of more than 1200 m at the southern tip of the state. A large variation exists in the thickness of the sediment, which impacts the seismic site response analyses of the Coastal Plain, particularly in areas where the availability of deep shear-wave velocity profiles is limited. This study evaluates the impact of variations in the shear-wave velocity profiles for two sites in the South Carolina Coastal Plain. The shear-wave velocity profiles were measured using different geophysical methods, including a combined multichannel analysis of surface waves and microtremor array measurement (MASW-MAM) method and P–S suspension logging. The equivalent-linear site response analyses were conducted by applying a synthetic earthquake motion at the depth of the B–C boundary (a depth of competent rock in which the shear-wave velocity is 760 m/s). The results are presented in terms of the amplification factor and its standard deviation. Results show that the average shear-wave velocity at the first 30 m (VS30), the shear-wave velocity contrast at the interface of the base layer and the B–C boundary, and the depth to the B–C boundary have a significant impact on the amplification factor and its variability, particularly for the amplification factor at periods higher than 0.1 s. The MASW-MAM method provided significantly lower VS30 values than the P–S suspension logging method at one of the two sites. Consequently, an additional peak in the amplification factor was observed for the site that had a low VS30, and the corresponding period was close to the resonant period of the loose, surface deposit.

Tracking C-O-H fluid-rock interactions in reworked UHT granulite: Tectonic evolution from ca. 990 Ma to ca. 500 Ma in orogenic interior of Eastern Ghats Belt, India

A suite of high-grade granulite rocks occurring close to one of the earliest reported ultra-high temperature rocks (“Paderu” rocks) from the central part of the Eastern Ghats Belt, India has been studied. Here we present a detailed pressure-temperature-time-fluid history of the suite of aluminous granulite and associated gneisses from a single exposure, which were injected by granitic aplite veins at a high angle at a ductile depth of the host gneissic rocks. Detailed studies of the sapphirine-spinel-quartz-bearing aluminous granulite reveal a peak metamorphic condition of ~1000 °C at ~8 kbar. Porphyroblastic garnet and quartz in the peak assemblage have mono-phase, high-density, CO2-rich primary fluid inclusions (~1 g/cm3). Orthopyroxene-garnet-sillimanite forming corona textures in the aluminous granulite and the presence of cordierite-K-feldspar-quartz intergrowths imply post-peak cooling and subsequent decompression down to ~6 kbar. Secondary fluid inclusions in quartz grains of the aluminous granulite have the signature of bi-phase CO2-H2O fluids with a comparatively low estimated density (0.8 g/cm3). The CO2 isochore plots suggest a pressure drop from 7 to 8 kbar to 4–5 kbar (simultaneous or after the cooling from 1000 °C to 800 °C). Texture-constrained monazite dating using U-Th-total Pb EPMA technique reveals that there are strong peaks at ~940 Ma, ~900 Ma, and ~ 800 Ma with several smaller and younger peaks. On the other hand, the UPb SHRIMP dating of zircon from the same rock reveals discordant ages with upper and lower intercepts at ~1700 Ma and ~ 990 Ma. Late pegmatite dykes and aplite veins were emplaced cutting across the dominant structural fabric of this litho-assemblage at a high angle. The asymmetric dragging of the foliation of the host leptynite possibly implies a shear-induced intrusion. The fluid inclusion study of the aplite reveals that the quartz grains contain numerous primary and pseudosecondary fluid inclusions (CO2 monophase to biphase). The calculated density is in the range of 0.71–0.82 g/cm3, suggesting the entrapment of carbonic fluid at <3 kbar. Monazite dating yields a strong single peak at 497 ± 4 Ma, one of the rare dates from the orogenic interior of the Eastern Ghats Belt. The studied suite of deep crustal granulites with aplite veins preserves a history of at least two events of fluid-rock interactions during its residence at the extremely hot deep crustal level until its exhumation to shallower levels where a magmatic fluid is trapped, through a time corridor between the Grenvillian and Kuunga orogenies.

Quantitative evaluation of lateral sealing of extensional fault by an integral mathematical-geological model

To evaluate the lateral sealing mechanism of extensional fault based on the pressure difference between fault and reservoir, an integral mathematical-geological model of diagenetic time on diagenetic pressure considering the influence of diagenetic time on the diagenetic pressure and diagenetic degree of fault rock has been established to quantitatively calculate the lateral sealing ability of extensional fault. By calculating the time integral of the vertical stress and horizontal in-situ stress on the fault rock and surrounding rock, the burial depth of the surrounding rock with the same clay content and diagenesis degree as the target fault rock was worked out. In combination with the statistical correlation of clay content, burial depth and displacement pressure of rock in the study area, the displacement pressure of target fault rock was calculated quantitatively. The calculated displacement pressure was compared with that of the target reservoir to quantitatively evaluate lateral sealing state and ability of the extensional fault. The method presented in this work was used to evaluate the sealing of F1, F2 and F3 faults in No.1 structure of Nanpu Sag, and the results were compared with those from fault-reservoir displacement pressure differential methods without considering the diagenetic time and simple considering the diagenetic time. It is found that the results calculated by the integral mathematical-geological model are the closest to the actual underground situation, the errors between the hydrocarbon column height predicted by this method and the actual column height were 0–8 m only, proving that this model is more feasible and credible.

Geochemical Characteristics and Oil Source Correlation of Minfeng Area, Dongying Depression, China

The identification of the oil-source correlation plays a significant role in petroleum exploration and development. In this study, we identify the oil-source correlation by a hierarchical cluster analysis method combined with traditional methods. The results shed light on the oil-source correlation in Minfeng area and revealed the oil migration and accumulation process. The crude oil in different structural belts and different horizons has different geochemical characteristics. According to the four types of crude oil and their planner distribution, it was considered that the crude oil mainly migrates along with favorable sand bodies and unconformity surfaces in the lateral direction and then charged and accumulated in the glutenite of Sha3 and Sha4 members since the area from sag to Yan Jia Oil and the gas field was lacking of oil source faults. Further analysis shows that the traps of fault blocks in Yong’anzhen are formed in the same phase, while the crude oil generated in the early stage is charged and accumulated in the fault block of the near source. Along with increasing of the buried depth of source rocks, the overlying source rocks gradually entered into the hydrocarbon generation phase, when crude oil started to charge in the fault blocks farther away.

Impact generated porosity in Gale crater and implications for the density of sedimentary rocks in lower Aeolis Mons

Sedimentary rocks in Gale crater record important information about the climatic history and evolution of Mars. Recent gravity measurements and modeling indicate strata encountered by the Curiosity rover have a very low density (1680 ± 180 kg m−3) and thus unusually high porosity. Missing in these models, however, is the role of deeper crustal porosity on the observed gravity signatures. Here we simulate the impact formation of Gale crater and find that impact generated porosity results in a negative gravity anomaly that decreases in magnitude with distance from the basin center. Incorporating this expected post-impact gravity signature into models for the bulk density of strata in lower Mt. Sharp, we find a best-fit density of 2300 ± 130 kg m−3 for an impact into a target with no pre-impact porosity. Models incorporating pre-impact porosity result in densities that are up to 200 kg/m3 lower. These revised densities increase the maximum potential burial depth of rocks along the rover traverse, allowing for the possibility Gale crater may once have been filled with sediment.

Sealing mechanisms in volcanic faulted reservoirs in Xujiaweizi extension, northern Songliao Basin, northeastern China

Distribution of volcanic reservoirs in Xujiaweizi half graben is controlled by both faults and sealing layers where their integrity could have been compromised. This paper documents the distribution of sealing units of the Denglouku and Yingcheng Formations based on seismic and well-log data to delineate all of the reservoirs with proper cap rocks within the volcanic Yincheng Formation via the relationship between the fault system and reservoir rocks. Based on the regional sealing effect of Denglouku Formation, two hydrocarbon traps are identified: the lower primary and upper secondary gas reservoirs where the formation with a mudstone percentage of more than 50% within the second member seals the primary reservoirs. The upper secondary trap is controlled by faults that have been activated during the structural reversal phase, causing the regional sealing layers in the Denglouku Formation to get displaced with a cap rock juxtaposition thickness of less than 35 m. This has created a series of fault-seal, dual-control reservoirs. The local seals within the Yingcheng Formation consist of mudstone, tight volcanic rock, and clayey breccia covering each volcanic eruption cycle. These local seals separate the volcanic gas reservoirs with a minimum thickness of 20 m. The local top seals in this tectonically active zone were placed on the hanging wall via the juxtaposition of the reservoir and overlying mudstone and/or clayey breccia. It was concluded that gas has migrated vertically through the faults and accumulated in the fault-controlled traps where sharp changes in the lithology (juxtaposition) form the seal, whereas the gas-water contact is controlled by the depth of the reservoir rock. Finally, this study concludes that the primary reservoirs are distributed in a sinusoidal configuration around the fault zone because of the dolphin effect of the Xuzhong strike-slip fault system that has connected the source and reservoir rocks.

Geothermal signature of basaltic flows using aeromagnetic data, west Cairo area, Egypt

Tertiary volcanics in Egypt are basaltic flows. These are recorded in the subsurface of Nile Delta and west Cairo in the Khattatba and Abu Roash regions but exposed on Gabal Qatrani. Such flows and structure trends made west Cairo the focus of geothermal exploration. The present study aimed to discover the geothermal resource and its relation with basaltic flows and subsurface structures in the area. To achieve these aims, aeromagnetic data (TMI) map, scale 1:500,000, was used. The source parameter imaging technique was used to calculate the depth of basement rocks. The results indicated that depth to the basement varies from 700 m at Khattatba and Abu-Roash regions to 4400 m southward and at G. Muqattam in the extreme eastern parts. These results are verified by subsurface data of three drilled deep wells. The detected major structure trends run in three directions: east-west, northeast-southwest, and northwest-southwest. The Curie point depth (CPD), geothermal gradient (GG), and heat flow (HF) were all calculated using the spectral analysis technique. CPD values range from 14 km in the eastern parts of the area to 34 km in the south-west. The GG values range from 15 to 33 °C/km. The HF values range between 38 and 86 mW/m2. The high GG and HF values recorded at Khattatba and Abu-Roash are due to the basaltic flows in the subsurface. The two regions are considered reservoirs that were promising for geothermal energy. Increase in thickness of the sedimentary cover to 4000 m southward indicates the possibility of hydrocarbon occurrences.

Resource potential of the Jurassic gas system, northern margin of the Qaidam Basin, northwestern China

The main source rocks, hydrocarbon generative subbasins, hydrocarbon generation periods, resource potential, and the relationship between the trap evolution history and hydrocarbon generation history are important problems associated with oil and gas exploration. In this study, we develop a three-dimensional geological model with respect to the Mesozoic and Cenozoic strata of the northern margin of the Qaidam Basin based on the most recent geological data. Using this model, the burial depth, temperature, maturity, and gas generation history of the source rock, the plane diagram of the source-rock current maturity, the gas generation intensity map, and the amount of gas generation during each geological period and within different subbasins can be obtained. Based on the obtained maps, we can state that the maturity of the source rock controls the distribution of natural gas (i.e., natural gas is located within and in the vicinity of mature and highly mature source rocks). We also observed the following: (1) the Lower Jurassic section is the main gas source rock; (2) the Yibei subbasin is the main hydrocarbon generative subbasin, followed by the Kunteyi, Pingdong, and Lenghu subbasins; (3) the main gas generation period is after the upper member of the lower Ganchaigou Formation deposition, with maximum gas generation occurring during the upper Ganchaigou Formation deposition and gradually decreasing thereafter—the majority of the structures in the inner basin are formed after lower Youshashan Formation deposition, demonstrating the tectonic activity coincided with periods of natural gas formation; and (4) the amount of natural gas resource becomes 1.23 trillion cubic meters. From these analyses, we can demonstrate that the late tectonic belts formed in the four gas-generating subbasins exhibit considerable promise for exploration.

Profiles of Near‐Surface Rock Mass Strength Across Gradients in Burial, Erosion, and Time

AbstractRock mass strength is recognized as an important control on landscape morphology and evolution. However, the controls on rock strength in mountainous topography remain poorly characterized, in part because strength remains challenging to quantify at spatial scales relevant to geomorphology. Here we quantify the mechanical properties of rock masses using subsurface S‐wave velocities, Schmidt hammer hardness values, and Geological Strength Index (GSI) observations. We produce shallow depth profiles of rock mass shear strength using intact rock hardness as measured from a Schmidt hammer, and assessment of the structure and surface conditions of fractures using GSI. We apply these techniques to the Western Transverse Ranges, southern California, USA, where gradients in stratigraphic age and erosion rate allow us to evaluate our methodology. We resolve strength differences of 200 kPa to ∼5 MPa that appear to be related to diagenetic changes associated with the maximum burial depth of young clastic sedimentary rocks. For rocks of the same lithologic type, stratigraphic age, and inferred burial histories, we resolve smaller differences in strength (300 kPa–1.5 MPa) that appear to be positively correlated with mean erosion rates. We suggest that the increase in strength with increasing erosion rate reflects decreased residence time in the weathering zone for ranges experiencing faster fault slip rates. These findings demonstrate up to an order of magnitude variability in strength with respect to burial, erosion, and time for lithologically similar rocks. As such, lithology alone is unlikely to adequately capture the role of rock strength in landscape evolution.

Deep-sea submarine erosion by the Kuroshio Current in the Manila accretionary prism, offshore Southern Taiwan

The Kenting Plateau is characterized by unusual low relief surfaces that straddle the topographic crest of the northern Manila accretionary prism off southern Taiwan at 400–700 m water depth. Multibeam bathymetric data, reflection seismic data, Acoustic Doppler Current Profiler (ADCP) data, surface grab samples, and sediment cores were collected in and around the Plateau to identify evidence of erosion in the Kenting Plateau and understand how the morphological evolution has been influenced by submarine erosion over geological time scales. The most distinctive feature on the Kenting Plateau is a 3 km × 7 km bean-shaped flat elevated platform (Kuroshio Knoll) revealed by multibeam bathymetry. Seismic data show almost no reflections beneath the seafloor and erosional truncations at the seafloor, especially in the Plateau's eastern half, evidencing widespread erosion. The P-wave velocity of the gravels recovered from the top of the Plateau ranges from 2.2 to 4 km/s. After comparing the velocity with the borehole data from nearby basin the burial depth of the parent rocks was found to be around 2 to 4 km below the seafloor, indicating that the parent rocks have been uplifted and gravels were formed due to erosion of the Plateau. The truncation of the seafloor shown on seismic sections suggests significant erosion on the Plateau. Sand content of the sediment cores decreases away from the Plateau, suggesting that sediment transport is effective in this area with high energy deposition, thereby accumulating coarse sediments on the Plateau and removing fine particles away from it. The presence of a dune field migrating northward of the Plateau, parallel to the Kuroshio Current also evidences active sediment transport in the area. Flow velocity of the Kuroshio Current observed from the ADCP data is very high, reaching up to 1.8 m/s on top of the Kuroshio Knoll (SE domain). We thus interpret that the observed intense erosion is caused by the Kuroshio Current, while the uplift of the Kenting Plateau is partially due to isostatic rebound caused by sediment removal through erosion and compression of the accretionary wedge. The higher sedimentation rate and coarser in grain size during sea level lowstand (20,000–12,000 yrs. BP) suggests that the erosion was more intense during the glacial period compared to that of deglacial period (< 12,000 yrs. BP) as seen from the MD97–2145 core. Submarine erosion is predominant throughout the Plateau, and it controls the geomorphology of the Plateau, especially the Kuroshio Knoll.

Magnetometric Identification of Sub-basins for Hydrocarbon Potentialities in Qattara Ridge, North Western Desert, Egypt

The present work aims to detect the Phanerozoic sedimentary sub-basins and their hydrocarbon potentialities within the Qattara Ridge in the northern Western Desert, Egypt, through the interpretation of high-resolution land magnetic data. The in-depth relations between observed magnetic anomalies and the magnetic mineralogy of the underlying rocks and the associated chemical reactions are essential to understanding the hydrocarbon potentialities. A high-resolution land magnetic survey has been conducted covering an area of 3600 km2, and several filters have been applied to the measured total field including reduction to pole, normalized source strength, tilt-depth and 3D Euler deconvolution with un-prescribed structural index, to accomplish the goals. Regularized focused inversion was applied to six selected profiles on the total magnetic intensity field to model variations in subsurface magnetic susceptibilities and to study the relation with hydrocarbon reservoirs in the area. Results show perfect structurally controlled sub-basins, with variable thickness of the sedimentary cover ranges for the Paleozoic to Miocene units. The depth of the top basement rocks ranges from 1500 to 7000 m. The calculated depths to the edges from magnetic analysis ranges from 292 to 3322 m. Some faults can be detected at 3900 m, and five possible sedimentary basins (depocenters) can be detected within the Qattara Ridge, trending NW–SE and N–S. Magnetic results also show that the central part of Qattara Ridge is affected by low magnetic anomaly, and many magnetization sources can be detected in the northern directions. The common trend in these sources is NW–SE. Most shallow depth to magnetic sources is concentrated at the northern part of the area, while the deeper sources are distributed in the west and south of the study area. The maximum depth recorded is about 3988 m. Inversion shows remarkable relations between the inverted magnetic susceptibilities and the different hydrocarbon productive and sealing zones in and close to the study area. The localized variations in the inverted anomalous magnetic susceptibilities in the Qattara Ridge were possibly produced by different intrasedimentary mineral magnetic phases developed near the surface due to hydrocarbon occurrences. Reducing gases, coming from the possible underlying hydrocarbon reservoir, play a critical role in the formation of these secondary magnetic minerals. The reservoir in the Qattara Ridge, based on the present study, is characterized by low magnetic susceptibility and low surface magnetic anomaly in the studied locations of productive wells. The interpretations show matching between the sedimentary thickness and position of the faults deduced from both the available drilled wells and seismic data with our magnetic results.

In Situ Continuous Monitoring of Borehole Displacements Induced by Stimulated Hydrofracture Growth

AbstractWe provide direct observations of the three‐dimensional displacements of a fluid‐driven fracture during water injections in a borehole at ∼1.5 km depth in the crystalline rock at the Sanford Underground Research Facility (USA). Micro‐shearing of the borehole initiates on a foliation plane at 61% of the minimum principal stress σ3. As the fluid pressure increases further up to 112% of σ3, borehole axial and radial displacements increase with injection time highlighting the opening and sliding of a new hydrofracture growing ∼10 m away from the borehole, in accordance with the ambient normal stress regime and in alignment with the microseismicity. Our study reveals how important it is to consider monitoring zonal deformation in conjunction with pressure and flow to better manage the complex hydromechanical evolution of the growing fracture.

Under Pressure: High-Pressure Metamorphism in the Alps

The mechanisms attending the burial of crustal material and its exhumation before and during the Alpine orogeny are controversial. New mechanical models propose local pressure perturbations deviating from lithostatic pressure as a possible mechanism for creating (ultra-)high-pressure rocks in the Alps. These models challenge the assumption that metamorphic pressure can be used as a measure of depth, in this case implying deep subduction of metamorphic rocks beneath the Alpine orogen. We summarize petro-logical, geochronological and structural data to assess two fundamentally distinct mechanisms of forming (ultra-)high-pressure rocks: deep subduction; or anomalous, non-lithostatic pressure variation. Furthermore, we explore mineral-inclusion barometry to assess the relationship between pressure and depth in metamorphic rocks.

Post-limit properties and correlation with spontaneous fracture dynamics in rocks

Spontaneous rock fracture can only occur beyond the ultimate stress limit. The currently known three classes of the post-limit rock behavior (class I, class II and class III) feature different dynamics of spontaneous fracture at the same initial conditions. This article discusses post-limit properties and fracture energy balances in these classes of the post-limit rock behavior. The author focuses on least-studied class III typical of seismic depths. It is shown that class III features the lowest destructive energy and the highest elastic energy release, which creates conditions for the uppermost dynamics of spontaneous fracture. Class III rocks are most instable at seismic depths and are most susceptible to initiation of both natural and induced earthquakes and deep-level rock bursts. Ideas on the spontaneous fracture conditions in strong and brittle rocks were developed concurrently with techniques of studying post-limit properties of rocks. The techniques were improved with sequential discovery of the three classes of the behavior of rocks having post-limit properties illustrated in this article. The bar chart of typical change in the frequency of earthquakes and aftershocks with depth is explained by the action of the fan mechanism. The depth of rocks having minimal fan strength conforms with the depth of the maximum seismic activity. At shallow depths outside the influence zone of the fan mechanism, the stick–slip mechanism is active. The study was supported by the Ministry of Science and Higher Education of the Russian Federation, Grant No. RFMEFI58418X0034.

ОСОБЕННОСТИ РОСТА И ФОРМИРОВАНИЯ ЛЕСНЫХ КУЛЬТУР НА ПЕРЕГНОЙНO-КАРБОНАТНЫХ ПОЧВАХ ВОРОНЕЖСКОЙ ОБЛАСТИ

The problem of afforestation of zonal humus-calcareous soils with close occurrence of chalk rocks has been considered. The research results of reclamation plantations on zonal humus-carbonate soils (Voronezh region, Ostrogozhsky district, Korotoyaksky district forestry) are presented. The main taxation indicators of silver birch (Betula pendula), English oak (Quercus robur), Scots pine (Pinus sylvestris), such as average height and diameter, bonitet, density, preservation, stock, increase in stock, have been found. The characteristics of the current state and productivity of protective plantations are given. The course of growth and the state of Scots pine plantations on humus-carbonate soils depends on the depth of the chalk rocks. Less demanding tree species for soil and soil conditions, such as Betula pendula, Pinus sylvestris, have higher growth rates than more demanding species. It is possible to grow Pinus sylvestris plantations on humus-carbonate soils with a thickness of 40-50 cm - I bonitet; 30-40 cm - II bonitet; 15-20 cm - II - III bonitet. The influence of slabby chalk depth on the coefficient of growth stress is at least 90% of the total amount of influencing factors. With an increase in the thickness of the humus-carbonate layer from 15 - 20 cm to 40 - 50 cm, the growth stress coefficient decreases 2.4-2.5 times. It is not recommended to create plantations with 1.0 × 0.5 m planting points (15-20 thousand units/ha). Such plantations have a very high growth stress coefficient and are biologically weakened

Gravity interpretation for delineating subsurface structures and depth of basement at El Moghra area, North Western Desert, Egypt

ABSTRACT El Moghra area represents a vital part of the national reclamation area at the northern part of Western Desert, Egypt. Delineating subsurface structures (faults & basins) and depth to the basement is the base of planning the area. Basins can be water aquifers or oil traps. Gravity data has been used to tackle such aims. The gravity (Bouguer) anomaly map is separated into regional components (deep sources), and residual component (shallower sources). The residual gravity map was used to delineate subsurface structural features dissecting the investigated area. Also, Euler deconvolution and Tilt Derivative methods have been used for delineating the structural elements. The gravity interpretation indicates that the most main tectonic have E–W, ENE–WSW, and N–S trends for the major structures, while the minor structures are aligned in NNE–SSW, NE–SW, NNW–SSE, and NW–SE. The results of depth estimation using 2D and 3D modelling show that the eastern and southwestern parts of the area under study exhibit a deep basement structure, reaches more than 7000 m (basin). However, the central and northwestern parts of the investigated area show shallower depth of basement rocks (4100 m).

Three-dimensional finite element analysis of urban rock tunnel under static loading condition: Effect of the rock weathering

Tunnel provide faster, safer and convenient way of transportation for different objects. The region where it is construction and surrounding medium has significant influence on the overall stability and performance of tunnel. The present simulation has been carried out in order to understand the behaviour of rock tunnel under static loading condition. The present numerical model has been validated with the laboratory scaled model and field data of underground tunnels. Both lined and unlined tunnels have been considered in this paper. Finite element technique has been considered for the simulation of static loading effect on tunnel through Abaqus/Standard. The Mohr-Coulomb material model has been considered to simulate elastoplastic nonlinear behaviour of different rock types, i.e., Basalt, Granite and Quartzite. The four different stages of rock weathering are classified as fresh, slightly, moderately, and highly weathered in case of each rock type. Moreover, extremely weathered stage has been considered in case of Quartzite rock. It has been concluded that weathering of rock and overburden depth has great influence on the tunnel stability. However, by considering a particular weathering stage of rock for each rock type shows varying patterns of deformations in tunnel.

Calculation of Damage Caused by Blasting Vibration on Surrounding Rocks of Water-conveyance Tunnel across the Yellow River

The commonly used method for tunnel excavation is the drilling and blasting method, but the surrounding rock will accumulate damage under the action of blasting, leading to engineering accident, and the consequences of the accident in the Yellow River-crossing tunnel will be more serious. The work proposed a quantitative evaluation calculation of the damage on surrounding rocks caused by tunnel blasting excavation to study the effect of tunnel blasting on the damage of surrounding rock. analyzes the damage plasticity model theoretically, and determines the rock constitutive curve used in the numerical calculation of vibration damage, based on which plane physical model is established to adopt several different stress control standards to calculate the vibration damage of surrounding rock. The results proved that in the damage settlement of planar model 1, the damage variable around the tunnel was 0.14 at the maximum and 0.10 at the minimum. In the curtain grouting area, the maximum damage variable was 0.05, and the minimum was 0.01. In the damage settlement of planar model 2, the damage variable around the tunnel was 0.45 at the maximum and 0.05 at the minimum. In the curtain grouting area, the maximum damage variable was 0.20, and the minimum was 0.05.the impact of blasting vibration on the surrounding rock is mainly concentrated near the cavern, Thus, with the rock depth increasing, the damage decreased. the damage in the grouting curtain area is relatively small. The results accurately reflected the damage caused by blasting vibration on surrounding rocks and provided references for engineering construction.