Lower Bench Research Articles

Attenuation of blast-induced vibration on tunnel structures

The blast-induced vibration during excavation by drilling and blasting method has an important impact on the surrounding structures. In particular, with the development of tunnel engineering, the impact of blasting vibration on tunnel construction has attracted extensive attention. In this paper, the propagation attenuation characteristics of blast-induced vibration (PPV, peak particle velocity) on different tunnel structures were systematically studied based on the field monitoring data. Initially, the attenuation characteristics of blasting vibration PPV on the lower bench surface, the side wall of the excavated tunnel and the closely spaced adjacent tunnel were investigated. Subsequently, the capacity of several widely utilized empirical prediction equations to estimate the PPV on tunnel structures was examined, along with a comparative analysis of their prediction accuracy. The research findings indicate that it is feasible to predict the PPV on the tunnel structures using empirical equations. The attenuation characteristics of blasting vibration PPV are different in different structures and directions. The prediction accuracy of the empirical equations varies, while the discrepancies are minimal. The principal variation among these equations lies in the site-specific coefficients k, β, λ, highlighting the differential impact of structural and directional considerations on the predictive efficacy. Based on the empirical equation and safe PPV provided by the blasting vibration safe standards on tunnels of China (GB6722-2014), and considering the influence of all structures and directions, it is determined that the safe distance of blasting vibration in the tested tunnel project should be larger than 20.28–18.31 ​m, 18.31–16.16 ​m, and 16.16–13.75 ​m for blasting vibration frequency located in ≤10 ​Hz, 10–50 ​Hz, and >50 ​Hz.

Slope Design in Surface Mining with a Total Probability Methodology [Diseño de Taludes en Minería Superficial con una Metodología de Probabilidad Total

The main goal of this research is to propose a methodology for the design of optimal slopes in surface mining, by applying the probability of total failure in the process of determining the geometry of the berm-bench of rock slopes. The rock mass is characterized by being a discontinuous, anisotropic and random medium. Therefore, to design slopes, a deterministic value or Safety Factor that represents the reliability of the design is not sufficient, and the inherent uncertainty of the geotechnical properties must be considered. The stability of slopes at bench level is a function of the quality of the rock mass and is controlled by the strength of the intact rock, the structural rocks, or a combination of both. When the slope has a defined structural control, planar, wedge or toppling failure modes are formed; These, depending on the stability conditions and generates rockfall events. Therefore, it is necessary to apply an effective method to establish the optimal geometry of the bench. The purpose of the berm-bench is to retain and mitigate the risk of rockfall and contain spill from upper slopes due to inherent instabilities, to provide a safe environment for personnel and equipment working near the slopes. The proposed methodology considers the variability of the dip, dip direction, persistence, and friction of the discontinuities. The procedure begins with the collection and analysis of the geotechnical information of the rock mass, which defines geotechnical domains, design sectors and main families of discontinuities; then, statistical analysis and kinematic evaluation are carried out and the conceptual berm width is determined; finally, the kinetic and probability of total failure analysis is carried out, validating the design geometry. The research focused on a domain with 04 sectors of geotechnical design. The results show that the applicable design bench face angle is between 53° and 71°, which corresponds to a berm width of 9.3m to 8.6m and a geometric interramp angle between 36° and 48° respectively. Likewise, probabilities of total planar failure of up to 31% and total wedge of 41% were obtained according to the geotechnical peculiarities of each sector. It was proven that, in the sectors with a greater probability of failure, a lower bench face angle and a greater catch bench of the design berm are considered acceptable designs, due to a greater probability of crest loss. Finally, in the sectors with a lower probability of failure, a greater interramp angle is considered an acceptable design. In conclusion, through the applied methodology it has been demonstrated that the results of the berm-bench design process meet the acceptability criteria of the Probability of Failure. Therefore, the developed method, which considers the variability of the parameters of the rock mass discontinuities, allows designing safe and reliable slopes validated through an acceptable level of probability.

Crosswell Strain and Production-Interference Testing Integrated in the Permian Basin

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 212336, “How and Where Wells Talk: Integrating Crosswell Strain and Production-Profile-Interference Testing,” by Matthew Lawrence, SPE, Ziebel; Janel Andersen, SPE, PDC Energy; and Yuanshan Zhang, Ziebel. The paper has not been peer reviewed. _ In Permian Basin fracturing operations, azimuths and intensities recorded by single-use distributed fiber optics in two wells are integrated and compared with post-flowback production-allocation and interference testing acquired with intervention fiber optics to identify areas of hydraulically conductive fractures and communication between offset wells. The production-allocation/interference testing method appears to reveal hydraulically connected fractures even in the absence of strain data. Introduction Intervention-based fiber optics have proved a valuable and cost-effective tool in understanding during-fracturing and post-flowback well and section performance. During-fracturing diagnostics, such as crosswell strain measurements from an offset monitor well, describe where fractures intersect the monitor well and reveal details such as azimuth, fracture-propagation velocity, and activation and reactivation statistics. These critical data points help inform cluster, stage, and well-spacing decision-making. While the absence of observed strain activity does not indicate the absence of created fractures, the existence of a strain activity indicating a fracture does not guarantee hydraulic functionality. The hydraulically functional fracture network can be understood with post-flowback production profiling. Particularly when combined with interference testing, fiber-optic production profiling identifies and differentiates productive and unproductive sections of unconventional laterals. Combination of during-fracturing and post-flowback technologies reveals the clearest picture of the functional fracture network. On an eight-well pad in the Permian Basin, the operator acquired fiber-optic crosswell strain data on two wells using single-use fiber, revealing details about the created fracture network. Sixty days after the wells went on production, a combination production-allocation and interference sensing program was executed with intervention fiber optics on two of the wells. Designing a Diagnostic Project in the Delaware Basin The operator completed an eight-well pad in the Delaware Basin on the western slope of the Permian. The wells were landed in three rows across the upper and lower Wolfcamp, which had a formation thickness of approximately 600 ft true vertical depth. Four of the laterals were completed from south to north (Wells 11N, 14N, 21N, and 31N), and five of the laterals were completed north to south (Wells 12S, 13S, 22S, 23S, and 31S). Two of the north-to-south wells, one in the middle (23S) and one in the lower bench (31S), were designated as monitor wells for during-fracturing diagnostic data acquisition (Fig. 1). Zipper operations were conducted in three groups, with the laterals on the outside edges of the pad fractured first (11N, 14N, and 21N) in a south-to-north order, followed by the inner laterals in the second zipper group (12S, 13S, and 22S) in a north-to-south order.

Prevention of Large Deformation of Soft Surrounding Rock in Tunnel Construction

Large deformation of surrounding rock makes the internal space of a tunnel cannot meet the requirements of normal use after support, even leads to the instability of surrounding rock and destruction of the tunnel structure. In order to optimize the parameters of the primary support to control the deformation of surrounding rock, field tests and numerical simulations are carried out. Based on the engineering geological conditions and the deformation monitoring data of surrounding rock, four important creep parameters of the improved Burgers model are inversed by numerical simulation, considering the creep of surrounding rock in tunnel construction. The results show that it is feasible to use tunnel crown settlement as a control indicator to determine the thickness of shotcrete. Short rock bolts are preferentially used in the tunnel arches, and a combination of long and short rock bolts should be used on the sidewall to control the large deformation of surrounding rock. When the excavation method of upper-lower bench is used in the single-track railway with a relatively large high-span ratio, the horizontal convergence monitoring points of the upper bench are recommended to be set 0.8-0.9 times the height of the upper bench from the tunnel arch crown, and those of the lower bench are recommended to be set 0.6-0.7 times the total height of the upper-lower bench from the tunnel arch crown.

Deformation Characteristics Analysis of Temporary Support in Unsymmetrical Loading Tunnel Excavation under Composite Support

Based on practical engineering, considering the characteristics of unsymmetrical loading, shallow burying, and weak surrounding rock of the tunnel, MIDAS finite element software is adopted to analyze the influence effect and deformation characteristics of a temporary steel support when the tunnel is excavated by a two-step center diaphragm method (CDM). The simulation results are compared with the field monitoring results. It can be seen that: (1) Affected by the unsymmetrical loading, the settlement of the right spandrel of the tunnel is obvious. The existence of a temporary steel support reduces the settlement of the surrounding rock at the spandrel greatly, making the distribution of principal stress at the spandrel more reasonable. (2) The deformation of the temporary steel support at the upper bench undergoes four stages: convergence, expansion, convergence, and stabilization; and the deformation at the lower bench undergoes five stages: convergence, expansion, convergence, expansion, and stabilization. (3) There is an obvious “bench-type” phenomenon in the principal stress change of the temporary steel support. The analysis results provide a scientific basis and technical guidance for the construction optimization of unsymmetrical loading tunnels using the same support technology.

Propagation characteristics and prediction of blast-induced vibration on closely spaced rock tunnels

Excessive blast-induced vibration may cause damage and even the collapse of underground tunnels, and the monitoring and prediction of vibration have an important reference role for the control of these disasters. In this paper, the propagation characteristics and attenuation prediction equation of blast-induced vibration on closely spaced rock tunnels were discussed based on field monitoring and numerical simulation. First, the propagation and attenuation characteristics of blast-induced vibration (e.g. particle peak velocity, PPV) on rock tunnels were analyzed and the applicability of some commonly used empirical equations to predict the PPV on lower bench and sidewall of closely spaced adjacent tunnel was discussed and compared. Then, considering the diffraction characteristics of the wave around tunnels, the scaled distance (SD) of the empirical equations was improved to predict the PPV on the whole space of the rock tunnels. Finally, a new equation was proposed to predict the PPV on adjacent tunnel section in the blasting centre plane considering the diffraction and reflection amplification effects of blast-induced vibration around adjacent tunnel. The research results show that the vibration velocities of surrounding rock around the tunnels are different from those in the free field surrounding rock without the influence of tunnel cavities due to the reflection and diffraction of blasting vibration on the tunnel wall. The improved and proposed empirical equations (5) and (6) are more accurate in predicting the PPV on the closely spaced rock tunnels because the diffraction and reflection amplification effects of blast-induced vibration around tunnels are considered.

Squeezing deformation control during bench excavation for the Jinping deep soft-rock tunnel

Jinping II hydropower station in Sichuan Province, China, is one of the largest tunnel groups in the world. The tunnel was excavated using bench excavation with a top heading and a bench. Severe squeezing problems were reported immediately after the excavation of the top heading when crossing the chlorite schist stratum at Ch.1+537 m. Squeezing deformation could last for a long period during tunnelling, similar to the problem of rockburst reported in the marble stratum distributed in the middle and east of the headrace tunnels. One year after the top heading excavation, the profile of the top heading still violated the profile tolerance and had to be reshaped due to the large convergence. A new support scheme was proposed to ensure the stability of the surrounding rock mass and control the excessive squeezing deformation during the bench excavation. For this, laboratory triaxial tests were first conducted under saturated and dry conditions to acquire the mechanical properties of chlorite schist. Then, the mechanical parameters of intact and damaged surrounding rock mass were determined using Hoek empirical estimation and a displacement inversion method, respectively. Next, initial support design was re-reviewed and evaluated based on the field displacement measurements, and the potential for squeezing in the overstressed rock mass was estimated. Thereafter, 10 supplementary support schemes were proposed using the numerical method in combination with laboratory data and field observations. Finally, the optimised support scheme was selected based on the results of comparative analysis. Field application of the suggested scheme showed that the convergence was controlled to within an acceptable level throughout the entire period of excavation of the lower bench. The experiences of controlling excessive squeezing deformation and optimisation of the support scheme for rock strata in a high geo-stress environment provide a reference for similar projects in the presence of soft rocks.

Prevention and control of gas hazards in a tunnel under construction: a case study

This paper presents the results regarding the prevention and control of gas hazards in a high-gas tunnel under construction. First, some effective methods were introduced, and the results of the gas pressure and gas content measured with and without the prevention methods were compared. Next, the gas emission amounts were predicted according to the measurements, and the required air volume for preventing a potential gas explosion hazard was determined. Finally, a computational study was carried out to investigate the effects of the transverse and longitudinal outlet locations of the ventilation duct on the gas movement in the tunnel. The results showed that with an increase in the longitudinal distance between the outlet and the heading face, the percentage of dead zones at the heading face of the upper bench increased, while the percentage of dead zones at the heading face of the lower bench observably decreased at first and then increased gradually. Additionally, the maximum methane concentration decreases initially and then increases. The percentages of dead zones were at relatively low levels when the outlet was located at the tunnel vault, whereas some relatively higher percentages of dead zones existed when the outlet was located at the tunnel spandrel or hance. The maximum methane concentration increased gradually when the location of the ventilation outlet moved away from the tunnel axis. In this case, the optimal outlet location for the ventilation duct was suggested to be 20 m away from the heading face of the upper bench and located near the tunnel vault.

The change of rock mass pressure of Lianchengshan tunnel

Based on Lianchengshan tunnel, the changing of rock mass pressure with deformation, time and distance from the excavation face is analyzed by means of field monitoring and numerical simulation, and the main conclusions are as follows: (1) When the deformation increases rapidly, the rock mass pressure decreases first and then increases. After the settlement and clearance convergence are stable, the pressure of rock mass in each part is still increasing slowly. (2) The rock mass pressure is mostly between 0.1 and 0.3 MPa, and the variation lasts about 65 to 70 days. (3) During the period from mid-bench construction to inverted arch construction, the variation ratio of rock mass pressure is very high, which indicates that the stabilization time of this stage is too long. Therefore, it is suggested to shorten the length of mid-bench and lower-bench appropriately. (4) The space influence range of the excavation face propulsion is about 2.5 times the tunnel diameter of the hole (42 m). To decrease the rock mass pressure, ring closure should be reached as soon as possible. It is recommended to speed up the construction of middle bench and lower bench.

Numerical Modeling of the Strata Deformation During Tunnel Excavation Based on Discrete Element Method

The construction of transportation infrastructure is transferring from ground to underground, which could evacuate the urban traffic and is also the future trend of the expansion of our cities. The cobble stratum brings about many technical problems in the underground engineering. Based on the calibration test and macroscopic mechanical characteristic curve, the microscopic calculation parameters of particle flow code simulation used for cobble strata in Urumchi were determined. According to establishing the numerical model of pebble tunnels using double-side-drift method, both the ground deformation and force chain evolution were analyzed for the tunnels using subsurface excavation method. This manuscript presented the differentiation of influence on ground deformation in cobble stratum under different excavation stages, the influence extent was ranked as follows, upper bench > double-side-drift > lower bench; the result of numerical simulation test was compared with the field monitoring data, proving that it is reasonable to adopt the particle flow code to simulate the excavation of pebble tunnels, and the research result could be provided for reference for the similar engineering.

Propagation Laws of Blasting Seismic Waves in Weak Rock Mass: A Case Study of Muzhailing Tunnel

In order to study the propagation laws of blasting vibration waves in weak rock tunnels, the longitudinal and circumferential blasting vibration tests in Muzhailing Tunnel were carried out, and the measured data were analyzed and studied using the methods of Sadov’s nonlinear regression, Fourier transform, and Hilbert–Huang transform (HHT) to provide a reference for the optimization of blasting design of Muzhailing Tunnel or similar weak rock tunnels. The results showed that the tangential main frequency decreases rapidly and the radial main frequency decreases slowly with the increase of proportionate charge quantity. Under a certain charge quantity, as the distance from the explosion source increases, the spectrum width of the blasting vibration frequency becomes narrower, the overall energy is more concentrated, and the vibration frequency tends to be closer to the low frequency. At a certain distance from the explosive source, the frequency of blasting vibration decreases gradually, and the amplitude of low‐frequency region increases with the increase of charge quantity. The vibration velocity on the left side of the tunnel is larger than that on the right side, and the vibration velocity at the vault and the arch foot of lower bench decreases rapidly, while the vibration velocity at the arch feet of upper bench and middle bench decreases slowly. The vibration frequencies of the left arch foot of the middle bench and the right arch foot of the upper bench are higher than those of other positions, while the frequencies of the left arch foot of the upper bench are the lowest. During tunnel blasting, the energy input to the strata media is mainly concentrated in the stage of the blasting of the cut hole. The blasting has more energy input to the left arch foot of the upper bench and the tunnel vault, which is consistent with the conclusion of frequency analysis.

Coastal landscape evolution tracked from late Holocene wave-cut benches in the Sinan Archipelago, Southwest Korea

Glacio-isostatic adjustment (GIA) and tectonic activity are important factors in the formation of marine terraces. Late Holocene wave-cut benches in the eastern part of the West Sea of Korea, also called the Yellow Sea, can be divided into two steps: 531 cm above sea level (ASL) for the upper bench (T2) and 464–481 cm ASL for the lower bench (T1). Sediments on the benches are classified into four units, and are interpreted to be beach deposits according to gravel shape, texture, and seaward inclination. The overlying sediment indicates that T2 was formed at approximately 530 cm ASL before 2900 yr BP, and T1 at approximately 460–480 cm ASL before 1520 yr BP. Late Holocene (4000–2000 yr BP) relative sea level (RSL) curves based on GIA models are inconsistent with the wave-cut bench elevations. Comparing T1 and T2 benches to the RSL curves of the West Sea, the upper and the lower benches were uplifted by approximately 5–8 m and 4–7 m, respectively. Although the area is several hundred kilometers away from plate boundaries, the high frequency of earthquakes in the West Sea may have induced the uplift of wave-cut benches during the last 2000 years. These indicate that the west coast of the Korean Peninsula (KP) should no longer be considered an area of subsidence, but be assigned to a regime of uplift during the late Holocene.

Integrating Geomechanical Data Optimizes Completions Design

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 191768, “Integrating Rock Properties and Fracture-Treatment Data To Optimize Completions Design,” by Eric Bruesewitz, SPE, Hawkwood Energy; Jessica Iriarte, SPE, Well Data Labs; Joel Mazza, SPE, Carrie Glaser, and Eric Marshall, Fracture ID; and Scott Brooks, Hawkwood Energy, prepared for the 2018 SPE Liquids-Rich Basins Conference—North America, Midland, Texas, USA, 5–6 September. The paper has not been peer reviewed. In the process of analyzing treatment responses that occur during hydraulic fracturing, several variances in treating pressure exist that are not readily explained by examining the surface pressures and pipe friction in isolation. These variances are also apparent when looking at bottomhole injectivity. This paper demonstrates how engineers can take advantage of their most-detailed completions and geomechanical data by identifying trends arising from past detailed treatment analyses. Introduction The Eagle Ford Shale was deposited in the Late Cretaceous Period in a marginal to open marine setting. The Lower Cretaceous part can be divided into two second-order transgressive/regressive cycles that have been labeled lower and upper Eagle Ford. The deposition of these units varies across the formation as a result of topography at the time of deposition. Therefore, operators in the Eagle Ford and other shale plays must account for changing stratigraphy and facies to locate horizontal wells properly for optimal perforation intervals. This study is based on integrated geomechanical data, metered high-frequency treatment data, and post-job reports. The data set used for this study corresponds to six wells completed in the Lower Bench of the Eagle Ford formation in Brazos and Burleson counties in Texas. Integration of completions, drilling, and geomechanical data has been analyzed before in the literature. Those authors observed an increase in pressure in several stages with higher Young’s modulus and lower gamma ray values, in which they were forced to pump an extra wellbore volume of clean fluid (sweep) to place the designed proppant volume. These sweeps accounted for more than 20,000 bbl of additional fluid pumped. The wells analyzed in this study presented data showing multiple examples of difficult-to-treat stages, in which unplanned sweeps had to be pumped and screenouts occurred frequently. Because the treating-pressure anomalies were correlated with mechanical rock properties in other unconventional plays, it was suspected that similar investigation may yield savings, efficiency, and productivity improvements in the Eagle Ford. Methodology The six wells of this study similarly consist of an approximately 7,600-ft lateral completed with 5.5-in. casing and approximately 150-ft stage lengths for a total of 283 stages analyzed. The fracture-treatment design consisted of proppant ramps of 100-mesh and 40/70 white sand placed primarily with slickwater. However, the completion design of four wells included cross-linked gel to place the highest proppant concentrations ranging between 3.0 and 4.0 lbm/gal. All six wells were recorded and processed for geomechanical properties such as Young’s modulus and Poisson’s ratio; a subsequent petromechanical model; and high-frequency fracture-treatment data (treating pressures, rates, and fluid and proppant volumes) and perforation data. The geo mechanical data gathered along the wellbore were divided and assigned to each stage, matching the measured depths to compare variables across data sets. Then, these data sets were standardized to a common format, screened for quality control, normalized, and analyzed with a data-management application.

Characteristics analysis and control measures for the deformation development in a water-rich loess tunnel

Deformation is one of the most intuitive indicators for engineering safety in tunnel engineering, especially in weak surrounding rock tunnels. Field monitoring is an intuitive and efficient research method relying on typical engineering. The loess is affected easily by water to produce plastic deformation due to its collapsibility. In this study, the water-rich area is encountered during the excavation of the Guchengling loess tunnel in the northwest of China. According to the long-term deformation monitoring data of the waterless and water-rich area, firstly, the deformation characteristics of the loess tunnel in the water-rich area and the application effect of the actual deformation control measures are obtained after comparative analysis. The deformation developing rate became faster in early excavating stage, and the lower bench produced significantly larger deformation than before due to the water not being discharged in time. The cumulative deformation value is increasing continuously, even after 20 days. Deformation presents different development characteristics due to different spatial positions and different work conditions. Next, the regression analysis is made to indicate that deformation of the weak loess tunnel in this study accords with the exponential function that could predict the final cumulative deformation. In the end, after a series of control deformation measures taken, the performance of soil and support is improved and the deformation is significantly reduced and eventually converges to a stable value.

Distribution and Mobility Potential of Trace Elements in the Main Seam of the Most Coal Basin

The Most Basin represents a coal basin with a long mining history in the Czech Republic. The majority of palaeo-environmental and geochemical studies have been focused on the upper part of the coal-bearing Most Formation where the coal is generally enriched in As, Cr, Ni, Cu and Zn. This study evaluated the distribution of V, Cr, Ni, Cu, Zn, Pb, Se, As, and Mn from the lower part. Regarding to the transport of inorganic elements into environment, the evaluation of mobility potential was also conducted.The total of 51 samples were collected from the Lower Bench in the Holešice Member. The chemical analyses were performed together with optical microscopy. The X-ray spectroscopy and ICP-MS were used to detect trace element contents in the study set of samples. 4 samples were subjected to the Sequential Extraction Procedure. The prepared leachates were analysed using the ICP-MS method.In total, 13 elements were screened in samples within the study profile. The mode of occurrence is the key factor for identifying a potential source of the trace elements. All evaluated trace elements (V, Cr, Ni, Cu, Zn, Pb, Se, As and Mn) leached most in the oxidisable fraction. On the other hand, As, Mn, Ni, Zn and Cd leached in more mobile fractions, e.g. reducible and acid.

Longitudinal deformation profile of a tunnel in weak rock mass by using the back analysis method

Analysis of the rock mass deformation behavior is a very important aspect of the safety assessment for tunnel construction in weak rock mass. In this paper, the deformation characteristics of a soft rock mass tunnel using three beaches construction method were investigated, which include the crown settlement and horizontal displacement and have 9 sections with 3 different construction schemes. The optimized construction schemes by decreasing the beaches length and changing the geologist of primary support were proposed. Then, applying the displacement back analysis method to calculate the rock mass parameters, double parameters were analyzed by using the golden section method. Results show that the tunnel deformations were affected by the elastic modulus E and the lateral pressure coefficient λ of rock mass, and the change of E has greater influence than λ on the tunnel deformation. The change of λ has greater influence on the crown settlement than that on the horizontal displacement. Furthermore, the regularity and characteristics of longitudinal deformation profile (LDP) in a weak rock mass tunnel was studied by utilizing the Fast Lagrangian Analysis of Continua (FLAC), and the LDP of the three long-beach construction scheme and the three short-beach construction scheme were compared. The results show that the complete displacements of tunnel under the three short-beach construction scheme condition by decreasing the lengths of the middle and lower benches are smaller than that under the three short-beach construction scheme condition, however the pre-deformation of the tunnel deformation under this two construction scheme conditions is nearly the same. The extrusion deformation at the tunnel face of the three short-beach construction scheme is larger than that of the three long-beach construction scheme. Therefore, increasing the area of the core soil is a feasible measure to control the extrusion deformation on the tunnel face. Finally, the tunnel optimized construction scheme was verified benefit the tunnel stability. The measures of decreasing the length of middle and lower bench and closing the invert early and immediately will benefit the tunnel stability.

Determining standard of academic potential based on the Indonesian Scholastic Aptitude Test (TBS) benchmark

The aim of this article was to classify The Indonesian Scholastic Aptitude Test or Tes Bakat Skolastik (TBS) results for each subtest and describe scholastic aptitudes in each subtest. The subject of this study was 36,125 prospective students who took the selection test in some universities. Data analysis began by estimating testees’ ability using the Item Response Theory, and benchmarking process using the scale anchoring method applying ASP.net web server technology. The results of this research are four benchmarks (based on cutoff scores) on each subtest, characters which differentiate potential for each benchmark, and measurement error on each benchmark. The items netted give a description of the scholastic aptitude potential clearly and indicate uniqueness so that it could distinguish difference in potential between a lower bench and a higher bench. At a higher bench, a higher level of reasoning power is required in analyzing and processing needed information so that the individual concerned could do the problem solving with the right solution. The items netted at a lower bench in the three subtests tend to be few so that the error of measurement at such a bench still tends to be higher compared to that at a higher bench.

Analysis of spalling failure in marble rock slope: a case study of Neyriz marble mine, Iran

The expansion of the Neyriz marble mine into deeper levels caused an unexpected failure particularly in the toes of lower benches. This phenomenon can impact the overall stability of the quarry and results in undesirable environmental and technical consequences. To understand the failure mechanism, a comprehensive study including—laboratory testing, in situ field testing and theoretical analyses are carried out. The theory of the brittle failure which was mainly developed based on the experiences gained during excavation in granite rocks is adopted and augmented in this study to explain the governing mechanism of failure. Mechanical properties of the marble are determined using conventional rock mechanics tests, and the in situ stress field was evaluated using a modified under coring test. Analyzing the laboratory and field data with the available empirical criteria for brittle failure shows that the level of stress in the lower bench is high enough to initiate the brittle failure. Finally, constitutive models developed for this failure mode are adopted in conjunction with numerical modeling to investigate the observed failure in the quarry. Two modeling strategies, based on elastic and elastic–plastic analyses, are considered. Comparing the predicted failure surface with the observed failure profile, it can be concluded that the brittle failure criteria can very well capture the failure mechanism in this marble quarry. This shows that the criteria proposed to describe spalling failure around underground excavation in granite can be effectively employed for assessing the brittle failure in deep open cast and quarry mines in good quality rocks such as marble.

Deformation and mechanical model of temporary support sidewall in tunnel cutting partial section

A large cross-section shallow tunnel excavated by center cross diagram method (CRD) was constructed on a site with weak surrounding rock. Crown settlement and horizontal convergence were extensively monitored to investigate the performance of a temporary support wall. Based on field observations, effects of zone excavation on the temporary support sidewall were analysed extensively. Influenced by earth pressure applied by a subsequently zone excavated, the deformation of the temporary support sidewall at upper bench successively undergoes convergence, expansion, convergence, expansion and stabilisation five stages; and the deformation at lower bench undergoes convergence, expansion and stabilisation three stages. Based on the deformation and restriction condition of the temporary support sidewall during tunnel excavation, a small curvature beam was used to simulate the stress and deformation change of the temporary support sidewall. Then, mechanical model of the temporary support sidewall under the surrounding rock horizontal pressure and the upper structure loads were suggested, respectively. The total deformation of the temporary support sidewall induced by zoned excavation can be determined by superposition the deformation caused by different loads.

Incipient ferralization and weathering indices along a soil chronosequence in Taiwan

The low hilly topography of Green Island, a volcanic island off southeastern Taiwan, includes an altitudinal sequence of sub‐horizontal benches. We examined eight profiles along this sequence, ranging from pale brown loamy coral sand on the lowest bench that fringes the coast at an elevation of about 10 m to deep, intensely red and acid clay on the highest bench at about 240 m. Chemical analyses, differential Fe extractions, thin sections, X‐ray diffraction of the clay minerals and indices of pedochemical weathering and strain indicated that soil development progressed by weathering of primary and secondary phyllosilicates through argilluviation in the intermediate stages to the generation of increasing quantities of free Fe. The Fe accumulates as free sesquioxides, which crystallize with age. Taxonomically the soil types progress from sandy coral Arenosol, through Eutric Cambisol, Hypereutric Lixisol and Acrisol to incipient Ferralsol (Udipsamment → Eutrudept → Udalf → Udultisol → Udox in Soil Taxonomy). The profiles are interpreted as a chronosequence, although this is complicated by minor and upwardly diminishing contributions of reef coral to the mainly igneous parent materials. There are also variations in the andesitic‐basaltic bedrock, and minor aeolian inputs in the higher and older soil types. Regional eustatic sea‐level correlations, 14C dating of carbonates on the two lowest benches and estimates of local tectonic uplift indicate that the incipient Ferralsols on the upper bench might date from about 150 ka. The transition through argilluvial Acrisols to incipient sesquioxide‐dominated Ferralsols appears, therefore, to develop within 100–200 ka on Green Island, which is faster than usual.HighlightsGreen Island (Taiwan) has been volcanically dormant but tectonically active for 2 million years. The island has a toposequence of bevelled surfaces with relatively uniform andesitic regoliths. The soils of the surfaces form a chronosequence from Arenosols through Acrisols to incipient Ferralsols. The transition from argilluvial to ferralitic pedogenesis, at 100–200 ka, is relatively rapid.