Overburden Thickness Research Articles

Rock mass classification in slope engineering with special emphasis on Slope mass rating: Current status and future projections

Rock mass classification (RMC) systems in the realm of rock slope engineering have gathered a lot of attention. The present review article delves into the major RMC systems, elucidating their fundamental principles, key parameters and practical applications. Among the various RMC systems for rock slope designing, Romana's Slope mass rating (SMR) was found to be the most comprehensive; therefore, the focus of the discussion centres around the SMR method. The article provides a crisp overview of the major advancements, evolution and potential challenges of SMR. The radical concept of wedge failure in SMR and the use of continuous functions are discussed in detail. A thorough discussion is provided on the efforts made by different researchers, encompassing the inclusion of novel factors such as slope height, heterogeneity in rock mass or lithology, weighted consideration of existing discontinuities, fuzzy sets and overburden thickness. Various automated calculation techniques and empirical correlations of SMR with other classification systems and rock engineering parameters are also outlined. Moreover, a critical examination of the variations among major extensions of SMR and their geotechnical relevance have also been discussed. Based on a meticulous assessment of the susceptibility to toppling failure in SMR, two sub‐factors to include block shape and interlayer slip between discontinuities have been suggested. These sub‐factors were validated by Goodman's tests for toppling failure. The scope of future projections or possible aspects for revisiting and refinement of the SMR method are suggested to enhance the applicability of the method under a diverse initial set of geotechnical conditions.

Slope Stability Analysis of Mounded Storage Tank under Different Compaction Coefficients

Mounded storage tank is to cover the storage tank with compacted soil on the ground to avoid steam cloud explosion, ensuring the stability and safety of the storage tank. In view of the influence of large diameter and surface radian of the tank, slope stability of mounded storage tank under different compaction coefficients has become the focus of research. In this paper, a series of laboratory tests were carried out to obtain the physical and mechanical parameters of the soil samples collected from the overburden of one specific engineering project. On this basis, Plaxis2D finite element software was used to establish a numerical model of the horizontal tank with a diameter of 7.6 m and a length of 76 m and the mounded slope with a height of 16.25 m as the research object. The effects of different compaction coefficients, slope angles, and overburden thicknesses on the slope stability of the mounded storage tank are investigated. Results indicate that the slope stability coefficients increase with the increase of compaction coefficient but decrease with the increase of slope angle and overburden thickness. Under the condition of the compaction coefficient 0.75–0.95, slope angle 30°–60°, and overburden thickness 0.5–1.3 m, the sensitivity ranking on the slope stability of mounded storage tank is: compaction coefficient, slope angle, and overburden thickness. The analysis results can provide an important theoretical basis and technical support for the safety and stability evaluation of mounded horizontal tank project.

Lithological and Structural Factors Affecting Groundwater Occurrence in Eruwa, South West Nigeria

The subsurface Lithological and Structural framework was investigated to understand its effects on groundwater aquiferous occurrence in this study, underlined by the Precambrian Basement Complex of Nigeria, with granite, gneiss, and schist occurring as the dominant rock types. To successfully map the subsurface, fifty-two (52) Vertical Electrical Sounding points were probed to a depth of current electrode spacing of 100m depth to obtain the variation in the resistivity measurement of the underlying weathered basement and basement rock in the subsurface. Apparent resistivity values and current electrode spacing are plotted on a bi-logarithm plot and correlated to standard curves to estimate subsurface layers' depth, thickness, and resistivity values. WinResist software uses a mathematical algorithm to estimate further the geoelectric parameters to find the best-fit model that matches the observed data. Golden Surfer software was used to represent the geoelectric parameters to aid in geospatial representation. Results show 3-5 lithological layers, which include Topsoil, Clay, Laterite, Sand, Sandy Clay, and Fresh Basement with resistivity value range 82.1Ωm - 2648.2Ωm, 21.8Ωm - 98.4Ωm, 102.3Ωm -167.5Ωm, 404.6Ωm - 2468.2Ωm and 606.8Ωm - 20,535.90Ωm indicating a weathered and fresh unweathered basement rocks layers with H, KH, HA, HKH, KHKH, QH and A geophysical curve which are also typical geometry of weathered material and limited or no fractures basement rock layer. Basement rock resistivity, Overburden thickness, Reflection coefficient, longitudinal conductance, Anisotropy coefficient range (606.8Ωm-20535.9Ωm, 2.6m - 35.6m, 0.3-1.0, 0.01-0.86 and 0.7-3.3) respectively which a typical value of shallow to deep overburden layer with limited or no-detected fracture basement rock). Incorporating the geoelectric parameters value obtained and calculated reveal limited structural deformation of the basement rocks to yield fracture capable of creating secondary porosity in the area while the lithology of the weathered layers becomes the exploitable source for groundwater recovery in the study area.

Experimental Study on Stability Analysis of Shallow-Buried Metro Station Hard Rock Excavation under Blasting Vibration Effect

Abstract By considering a certain metro station of Qingdao Metro Line 4 as the research object, a three-dimensional geotechnical testing model has been developed to analyze the stress and deformation characteristics of the surrounding rocks under blasting vibration effect. The simulation of the surrounding rock blasting process is achieved through an electric spark source. We conducted simulation tests on the excavation stability of shallow-buried hard rock metro stations with and without considering blasting damage effects, respectively. The stress, displacement, and primary support stress changing laws of the surrounding rock under different overburden thicknesses using the arch cover method and the primary support arch cover method have been revealed. Finally, we analyzed the applicability of the primary support arch cover method in terms of vault settlement, clearance convergence, and floor heave. Results show that the surrounding rock of the arch has roughly gone through three deformation stages, namely a slow deformation stage, rapid deformation stage, and stable deformation stage. Whether it is blasting excavation or non-blasting excavation, the settlement of the arch is within a safe and controllable range. Because of the refinement of the excavation process by the primary support arch cover method, the stress release is relatively stable throughout the entire excavation process, but the significant impact of blasting vibration on the surrounding rock cannot be ignored. The excavating of the left and right guide holes is the key process for the displacement and stress variation. The deformation and stress generated by the arch cover method have a small difference compared to the deformation and stress generated by the primary support arch cover method, indicating that the latter excavation method can be used under current engineering geological conditions. No large-area collapse and instability occurred in the experimental process, which provides a theoretical basis for similar projects.

Tunneling problems in weak rock conditions under shallow overburden and comparison between full-face excavation and sequence excavation methods

ABSTRACT The T8 tunnel was constructed within the scope of the Ankara – Sivas High-Speed Railway project. The tunnel route is formed completely by very weak and weak lithological units. The overburden decreases to 10 m, and the highest overburden thickness reaches up to 60 m. The tunnel is large with a 150 m2 excavation area and 14 m diameter. During the excavations in the section with an overburden thickness of 12 m, the supports failed, and the tunnel was completely collapsed. The purposes of the present study are to discuss the causes of the failure and engineering measures and to compare NATM and ADECO-RS methods with three-dimensional (3D) numerical analyses. Considering the mechanism of failure, extra engineering measures were proposed and the T8 tunnel was completed successfully. For the purpose of the study, a series of 3D numerical analyses were performed, and the results are discussed. The results obtained from the 3D numerical analyses showed that the ADECO-RS method yielded higher performance than the NATM method, for very weak and weak ground conditions (Category C).

Application of Geophysical Methods for Investigation of Groundwater Potential in Layunrun Village, Ogun State, Southwestern Nigeria

An investigation of the groundwater potential of the area for tube well construction has been conducted in Layunrun village in a typical basement complex of Ogun State using electromagnetic and electrical resistivity techniques in geophysical exploration. Six (6) electromagnetic profiles were used, and twenty-eight (28) Vertical Electrical Soundings (VES) were performed along some of the profiles' potential regions. The typical partial curve matching utilized to create the VES curves was examined, and the results were used to create themed maps of the region. Within the study area, between four and six geoelectric layers were found. These layers are Topsoil, weathered layer (clay), weathered layer, fractured basement, and fresh basement. According to the findings, a bigger percentage of the land has an overburden thickness ranging from 9 to 17 m, with a maximum overburden of about 23 m. It also showed how well fractured the research area is, with thicknesses of the fractures varying from about 12 m to more than 30 m. The study area has a good chance of accumulating groundwater and, consequently, developing groundwater through digging boreholes. The outcomes also suggested that a community with similar geological settings may use the electromagnetic method in addition to the electrical resistivity method to identify places with high groundwater potentials.

Diagenesis of carbonate density-flow deposits controlled by differential uplift of platform segments: examples from the Cretaceous of the Gargano Promontory, Italy

ABSTRACT Thin-section investigation (polarized-light, cathodoluminescence, and ultraviolet microscopy) combined with isotopic (δ18O, δ13C,87Sr/86Sr) analyses of bulk carbonate samples form the basis for evaluating the diagenetic alteration of Albian–Cenomanian and Maastrichtian density-flow deposits off two segments of the Apulia Carbonate Platform in the Gargano Promontory, Italy. We propose that differential platform uplift south and north of the Mattinata Fault controlled the diagenesis of density-flow deposits during Albian–Cenomanian times. In both cases, the: i) abundant blocky cement and vuggy pores in clasts, and ii) remnant blocky cement on allochems in the corresponding matrix samples with interparticle pores, indicate disintegration of at least partially cemented deposits before failure and reworking into density flows. The abundant rudist fragments suggest that they were sourced from the margin and upper slope. However, the δ13C compositions of the density-flow deposits south and north of the Mattinata Fault are different, and geochemical modeling based on presumed marine and terrestrial δ13C compositions indicates: A) The marine δ13C values of deposits south of the Mattinata Fault suggest that the margin- and upper-slope deposits were subjected to predominantly marine-burial diagenesis before failure. Albian–Cenomanian Sr-isotope ages support the marine-burial diagenetic scenario where strontium was redistributed locally during calcitization of aragonitic allochems and during precipitation of calcite cements. However, post-uplift precipitation of vadose cement in pores formed during marine-burial diagenesis has lowered the δ13C and increased the 87Sr/86Sr ratio in many of the samples. B) Twenty-five km north of the Mattinata Fault, the negative δ13C values suggest that oxidation of terrestrial plants supplied 12C-enriched CO2 to the pore-water carbon pool during subaerial exposures, thus lowering the δ13C compositions of the margin- and upper-slope deposits from values obtained during marine-burial diagenesis. This diagenetic model requires that residual aragonitic and high-Mg calcitic allochems were available in the deposits during penetration of meteoric water. However, the Albian–Cenomanian Sr-isotope ages and the geochemical modeling support a predominantly marine-burial scenario, with intraformational redistribution of strontium during meteoric diagenesis. A similar diagenetic model is envisaged for the Maastrichtian density-flow deposits south of the Mattinata Fault, but the less negative δ13C and geochemical modeling suggest less influence of meteoric diagenesis before reworking. The majority of separate- and touching-vug pores likely also formed during marine burial before failure and reworking of the margin- and upper-slope deposits. The large range in porosity (4–31%) of density-flow deposits with predominantly interparticle pores are inferred to reflect varying degrees of compaction caused by variable overburden thickness as well as sedimentary processes. The results of the present study indicate that the geochemical imprint of meteoric diagenesis can be expected to vary in density-flows deposited along coeval segments of carbonate platforms in tectonically active regions.

Analytical solution of the shallowest overburden thickness of special-shaped shield tunnel in layered soil

Analytical solution of the shallowest overburden thickness of special-shaped shield tunnel in layered soil

Multi-criteria groundwater potential zonation using GIS-based fuzzified AHP: Case study of Ondo metropolis Southwestern Nigeria

The study utilized the fuzzy analytical hierarchical process (F-AHP) in the multicriteria decision analysis of seven important hydrogeologic parameters associated with groundwater potentiality/yield. The purpose was to develop groundwater potential map using groundwater potential index values (GWPIV) for Ondo metropolis, Southwestern Nigeria. The hydrogeologic parameters were prioritize and assigned different weights hierarchically according to their level of importance using F-AHP, as aquifer layer thickness (0.05), aquifer layer resistivity (0.04), overburden thickness (0.12), transverse resistance (0.18), transmissivity (0.32), coefficient of anisotropy (0.25), and formation factor (0.03). From regional perspective, based on drainage basin, and river network, the region was categorized to be of low/moderate groundwater yield, with moderate to high flow connectivity. The higher and lower elevations are generally remarkable in the northern and southern areas respectively, hence possibility of movement of water towards the southern part with the northern forming the watershed. Furthermore, the longitudinal unit conductance recorded regional average value of 1.168, while 1.20, 1.16, and 1.10 were recorded for granite, gneiss and migmatite, which suggests moderate vulnerability to contamination. The average values recorded for overburden thickness, hydraulic conductivity, transmissivity, transverse resistance, formation factor, coefficient of anisotropy, fracture contrast, and reflection coefficient are 22.5 m, 0.33 m/d, 5.56 m2/d, 4966 ohm-m2, 2.42, 1.17, 15.3, and 0.66 respectively. The water table aquifer and the fractured basement are the major water bearing units in the area; while the geological units showed overlapping hydrogeologic properties. The obtained GWPIV ranged from 1.21 to 3.55 with regional average of 1.86, suggesting a moderate potential. Nevertheless, the southern part showed more propensity/yield than the northern area. The study showed the importance of geospatial mapping technique, involving fuzzy analytical hierarchical process, in groundwater evaluation, as it was able to solve and obtain different hydrogeological parameters, which were integrated to prioritize and define the area's groundwater prolificacy for the purpose of improving, expanding, and management of the existing water scheme in the study area.

Coupling analysis method of grouting construction with deformation response of adjacent existing tunnel

In the new tunnel under close distance through the existing tunnel risk source, the grouting scheme developed to compensate for stratum losses is still based on empirical methods, relying on the overburden thickness of existing tunnels. This can potentially lead to an excessively high or low probability of uplift of existing tunnels. Proposing a coupled deformation analysis method between the grouting construction and adjacent existing tunnels is of great theoretical significance for developing grouting schemes. In order to reasonably limit the design parameters of grouting construction, based on the theory of fluid–solid coupling elastic pore-column expansion and the theory of random media, the calculation method of stratum displacement which simultaneously considers the coexistence of grout compaction expansion and permeability diffusion mode is derived, and the accuracy of the calculation method is verified by engineering examples. The accuracy of this calculation method was verified through engineering examples. Combined with the deformation coordination condition, the existing tunnel is regarded as an elastic Euler-Bernoulli continuous beam, and the finite element coupling balance equation of the interaction between the existing tunnel and the surrounding soil is obtained. Based on this, a coupling calculation model of the grouting construction and the deformation response of the adjacent existing tunnel is established. Combined with three times of grouting construction examples in the shield tunneling project of Beijing Metro Line 12 under the existing airport line, the reliability of the coupling calculation model to determine the grouting construction parameters is verified. The calculation parameters in the coupling calculation model have clear physical meanings, which can provide a theoretical basis for the grouting design of similar risk source projects.

Geophysical Research on an Open Pit Mine for Geotechnical Planning and Future Land Reclamation: A Case Study from NW Macedonia, Greece

In open pit mining areas, knowledge of geotechnical conditions (e.g., overburden thickness, background slope, and fault locations) ensures geotechnical safety during exploitation as well as reclamation planning. The Greek Public Power Corporation initiated a research program after stability issues emerged on the southern side of the Mavropigi open pit mine in NW Macedonia. Geotechnical wells revealed steeply dipping bedrock and thin tectonic contact, indicating the need for the detailed imaging of the subsurface for future stability measures. For this purpose, a geophysical investigation aimed to extract information mostly for the dip of the interface between schist bedrock and overlaying Neogene sediments and/or limestones. Based on the high contrast of electrical properties between schists and limestones, as well as the differences in acoustic impedance and formation thickness, the seismic reflection and electrical resistivity tomography (ERT) methods were selected. The suitability of the seismic reflection for its application in this area was checked by generating synthetic seismic data, which resulted from the simulation of seismic wave propagation for geological models of the area. The acquisition parameters were determined after the noise test. Field seismic data processing produced a depth-migrated section, which revealed the existence of a fault. The use of dipole–dipole and gradient arrays, in 2D and 3D electrical resistivity measurements, ensured both the lateral and vertical mapping of schist bedrock and detected limestone bodies within the overburden. Also, the tectonic contact zone between limestone and schist formations was properly imaged. The comparison between geoelectrical and seismic sections indicated that the seismic reflection method provided a more accurate estimate of fault inclination. Finally, the geophysical survey enriched the geotechnical models necessary for sustainable mining (e.g., rational exploitation, the optimization of productivity, and zero accidents) including the planning of future reclamation.

Spatiotemporal variability of organic carbon in streams and rivers of the Northern Hemisphere cryosphere

The earth's cryosphere is the outpost of climatic warming, which leads to rapid changes of organic carbon (OC) transport from terrestrial to aquatic ecosystems. OC in the cryosphere rivers plays vital roles in the carbon cycle and river ecosystem health. Yet, we still lack a comprehensive assessment of the spatiotemporal patterns of riverine OC across the Northern Hemisphere cryosphere. Here, we compiled OC concentration, radiocarbon (14C), and the specific ultraviolet absorbance (SUVA) of dissolved OC (DOC) at 254 nm data from 1007 unique sites, extracted from 138 published literature between 1972 and 2022. Overall, the average DOC and particulate OC (POC) concentrations are 6.34 and 2.61 mg C L−1, respectively, with the average age of DOC and POC being ~1100 and ~4300 years BP, respectively, indicating the release of aged carbon pools. Seasonal variations in DOC and POC concentrations, Δ14C-DOC and SUVA254 were observed, with distinct spatial variations closely linked to specific watershed characteristics. We found permafrost-impacted watersheds displayed significantly higher DOC concentrations, younger OC ages but lower POC concentrations compared to glacier-impacted watersheds. Meanwhile, in boreal forest watersheds, DOC is the most concentrated and youngest in varied ecoregions. Additionally, in permafrost regions characterized by higher permafrost extent, ground ice content, or lowlands with thick overburden cover, riverine DOC is more concentrated and aromatic. We estimated that specific OC fluxes in glacier rivers are higher than that in permafrost rivers (4.77 and 1.86 g C m−2 yr−1, respectively). Our results highlight the complex and variable spatiotemporal patterns of riverine OC in the northern cryosphere, which are essential for assessing the impact of OC on the global carbon cycle and climate warming.

Prediction of the Water Inrush Risk from an Overlying Separation Layer in the Thick Overburden of a Thick Coal Seam

With the expansion of coal mining westward in China, water inrush from seam roofs has become a prominent safety problem during mining. The roof rock of the coal seam in the Shilawusu coal mine has the characteristics of a double-layer structure, and the overlying separation space formed in the mining process of the coal seam poses a risk of water inrush. To ensure the safety of coal mine production, considering the geological and hydrogeological data of the mining area, the core recovery rate, lithologic assemblage index, key aquifer thickness, hydrostatic head and lithologic structure index of the Zhidan Formation are selected as evaluation indexes. The index weights are calculated based on the attribute hierarchical model and coefficient of variation methods, and subjective and objective preference coefficients are introduced to determine the ranking of comprehensive indexes. The catastrophe progression method is improved, and a zoning prediction model for water inrush risk is established by the improved catastrophe progression method. The results show that only a tiny part of the mining area is in danger, and most areas are in the safe and transition zones. The model realizes the prediction of the risk of water inrush from the overlying separation layer in the study area and provides a theoretical basis for the prevention and control of water inrush from the overlying separation layer in coal mining.

Effect of Particle Size Distributions (PSDs) on ground responses induced by tunnelling in dense coarse-grained soils: A DEM investigation

Tunnelling-induced ground responses in coarse-grained soils often exhibit complex behaviours such as soil arching and progressive ground instability. However, the effect of particle size distributions (PSDs) on ground responses in tunnelling remains largely unexplored. This study provides new insights into PSD’s effect on tunnelling ground response and the underlying mechanism based on granular skeleton quantification. The coarse-grained soils with 9 typical PSDs were modelled by the discrete element method (DEM) with varied granular skeleton structures. A representative volume element (RVE) assembly method, with a novel iteration-based specimen generation method, is developed to build ground models incorporating millions of soil grains, where an eccentric displacement boundary was embedded for reproducing the tunnel volume losses. The results demonstrated that the change in skeleton structures from fine-grains to coarse-grains dominated leads to the acceleration of soil arch emergence and the deceleration of soil arch collapse-rebuilding. With an increase in ded, the strengthened soil arch leads to a more evident deformation localization in ground, and results in more significant hysteresis of ground instability from the tunnel to the surface. The effect of PSDs on ground responses becomes prominent as the overburden thickness decreases and the tunnel volume loss increases, and a decrease in ded would increase the risk of overall failure in tunnelling.

Numerical Computing Research on Tunnel Structure Cracking Risk under the Influence of Multiple Factors in Urban Deep Aquifer Zones

During the operation period of tunnels in urban deep aquifer zones, the geological environment around the tunnel is complex and the surrounding strata are rich in groundwater, which often poses a risk of structure cracking and groundwater leakage, seriously threatening the tunnel’s safety. To reduce the risk of tunnel cracking, a theoretical calculation model and a three-dimensional concrete–soil interaction thermo-mechanical coupling numerical computing model was established to analyze the tunnel structure cracking risk under the influence of multiple factors in urban deep aquifer zones. The response mechanism of structural stress and deformation under the influence of the grade of rock and soil mass, overburden thickness, temperature difference, structure’s length–height ratio, structure’s thickness, and structure’s elastic modulus was investigated, and the stress and deformation response characteristics of the structure with deformation joints were explored. The results show that the maximum longitudinal tensile stress of the structure increases with the increase in the grade of rock and soil mass, overburden thickness, temperature difference, structure’s length–height ratio, and elastic modulus. The temperature difference has the most significant impact on the longitudinal tensile stress of the structure, with the maximum tensile stress of the structure increasing by 2.8 times. The tunnel deformation joints can effectively reduce the longitudinal tensile stress of the structure, and the reduction magnitude of the tensile stress is the largest at the deformation joints, which is 64.7%.

Towards sustainable shale oil recovery in Jordan: An evaluation of renewable energy sources for in-situ extraction

Oil shale (OS) can significantly enhance energy security and diversify the energy mix in countries like Jordan. However, OS extraction and utilization are always associated with negative environmental impacts. This paper investigates a novel approach of using renewable energy to further retort the OS to produce oil. In this study, Al-Lajjun and Sultani OS resources in Jordan were analyzed using a mathematical model and simulation analysis using the system advisor model (SAM) software. The study aimed for in-situ shale oil extraction from a vast shale oil reserve in Jordan, with a focus on mitigating energy usage and environmental issues. The study suggested utilizing recovered heat from the production stream along with an external source, which may include natural gas, solar thermal energy, or a combination of both, to produce the substantial amount of heat energy necessary for in situ pyrolysis of OS. The study designed five different plants using the SAM program: gas steam boiler (GB), photovoltaic (PV) with batteries, parabolic trough with thermal energy storage (TES), PV integrated with GB, and parabolic trough coupled with GB. The economic analysis, project recovery, and environmental evaluation were conducted, and the results showed that drilling wells in the Sultani area was more expensive than in the Al-Lajjun area due to the thickness of overburden. The PV with GB was the most economically advantageous option, with a total cost of $79.4 M for Al-Lajjun and $89.89 M for Sultani. However, the levelized cost of energy (LCOE) for Al-Lajjun and Sultani are 10.41 and 9.18 ¢ per kWh, respectively. Conversely, PV systems with batteries and the parabolic trough with TES demonstrated a higher level of environmental friendliness compared to other shale oil recovery systems. Among these, the systems incorporating PV with GB and parabolic trough with GB, both featuring an SF of 30%, consistently demonstrate CO2 emissions of 0.016 kg CO2 per kg of shale oil produced. In contrast, the system solely reliant on GB without any solar contribution, holding a 0% SF, exhibited elevated CO2 emissions of 0.023 kg CO2 per kg of shale oil produced. The study recommends the use of PV with GB as the most economically viable option, while PV with batteries is the more eco-friendly choice for extracting shale oil from the Al-Lajjun and Sultani OS reserves located in Jordan. The study outcomes can be useful for policymakers and investors interested in developing the shale oil industry in Jordan. However, further research is needed to evaluate the long-term environmental impact and sustainability of the proposed method.

Multi-Criteria Analysis Method for Aquifer Vulnerability Investigation Using Godt Method at Idi-Ayunre, Ibadan, Southwestern Nigeria

Geophysical investigation involving Vertical Electrical Sounding (VES) Schlumberger array was carried out across Idi-Ayunre, Ibadan, a typical basement complex area having a rock composition of migmatite-gneiss, quartzite, and biotite-hornblende. A total of forty (40) vertical electrical sounding data were acquired with maximum current electrode separation of 100m using resistivity meter and its accessories. The aim of the study was to evaluate the aquifer vulnerability of the study area to contamination. The VES results were both qualitatively and quantitatively interpreted using partial curve matching and were further subjected to computer iteration using WINRESIST. The longitudinal conductance, thickness of layer overlying aquifer and hydraulic conductivity were generated and synthesized to produce the vulnerability map. A GODT multi-criteria model which is an acronym of Groundwater occurrence, Overburden thickness, Depth and Topography developed from the hydrogeologic parameters were evaluated alongside the longitudinal conductance values to determine the aquifer vulnerability of the area and to classify the study area accordingly. The curve type obtained are H and HA. The interpretation revealed three to four geoelectric layers: the topsoil (18.9-178.9Ωm), clayey (9.0-70.6Ωm), fractured basement (31.9-43.1Ωm) and fresh basement (1131-2916Ωm). The longitudinal unit conductance ranges from 0.032-0.93mhos. And from the GODT model derivations, the study area shows 92.5% of high vulnerability rating, 2.5% of low-moderate and 5% of moderate rating; areas with high rating are prone to contamination than areas with low-moderate and moderate rating. Hence, zones of high vulnerability may be not be encouraged for groundwater exploitation and, if need be, constant water quality assessment should be carried out before consumption.

A Framework of Probabilistic Seismic Risk Analysis of Urban Shallow-Buried Tunnels Subjected to Active Fault Dislocations

ABSTRACT This study develops a methodology for conducting a quantitative seismic risk assessment for shallow-buried tunnels that are induced by active fault dislocations. A case study for a tunnel crossing a strike-slip fault zone is performed using this method. The fault-tunnel crossing angle, the bedrock overburden thickness, the tunnel burial depth, the lining thickness, and the soil properties parameters are analysed in terms of their effects on the seismic responses, fragility curves, and seismic risks for the tunnels. This methodology could quantify the seismic risk of existing metro tunnels that pass through active fault zones, and could also assist in the establishment of a benchmark tunnel design for designing a tunnel that passes through an active fault zone.

Variability of Exploitation Coefficient of Knothe Theory in Relation to Rock Mass Strata Type

Geodesic measurements of mining area deformations indicate that their description fails to be regular, as opposed to what the predictions based on the relationships of the geometric-integral theory suggest. The Knothe theory, most commonly applied in that case, considers such parameters as the exploitation coefficient a and the angle of the main influences range tgβ, describing the geomechanical properties of the medium, as well as the mining conditions. The study shows that the values of the parameters a = 0.8 and tgβ = 2.0, most commonly adopted for the prediction of surface deformation, are not entirely adequate in describing each and every mining situation in the analysed rock mass. Therefore, the paper aims to propose methodology for determining the value of exploitation coefficient a, which allows to predict the values of surface subsidence caused by underground coal mining with roof caving, depending on geological and mining conditions. The characteristics of the analysed areas show that the following factors affect surface subsidence: thickness of overburden, type of overburden strata, type of Carboniferous strata, rock mass disturbance and depth of exploitation. These factors may allow to determine the exploitation coefficient a, used in the Knothe theory for surface deformation prediction.

Study on the Division of the Affected Zone under Construction Unloading and Its Construction Sequence of the Multiline Parallel River-Crossing Pipe Jacking

There are many advantages of reasonably determining the affected zone and its construction sequence for the multiline parallel pipe-jacking construction, such as convenient to reasonably arrange the pipeline section distribution mode, reducing the construction safety risk, and construction difficulty. Combined with the engineering construction practice of the multiline parallel pipe-jacking project for the north city drainage and flood control project through Chu River in Hefei, the strength reduction method has been utilized to study the surrounding stratum FOS for the pipe-jacking construction unloading under different overburden thickness Hs, different clear distance D, and different river water depth H w in this paper. The formula of the minimum critical overburden thickness Hsmin and the minimum critical clear distance Dmin of the surrounding stratum self-stability during pipe-jacking construction unloading have been derived. The division method of the affected zone for the multiline parallel river-crossing pipe-jacking construction which behaves as the mutual influence nonself-stability zone, the mutual influence self-stability zone, and the no mutual influence self-stability zone has been proposed. For further discussion, the construction sequence of the multiline parallel river-crossing pipe jacking has been studied.