•We concentrated on the stability prediction of underground entry-type excavations.•Three RF-based hybrid models are present to predict entry-type excavation stability.•MVO, GWO and MFO can assist ...the hyper-parameters tuning of RF.•The accuracy of the proposed models is better than the models in previous studies.•The models based on RF can update the critical span graph scientifically.
The stability evaluation of underground entry-type excavations is a prerequisite of the entry-type mining method, which directly affects whether workers can be provided with a safe and reliable working environment and whether subsequent mining operations can be carried out normally. The design and stability assessment of entry-type excavations in current mining engineering largely relies on an empirical design method called the critical span graph, which has been widely applied in the initial span design of various cut and fill stopes. In recent years, with the wide application of various intelligent algorithms in the field of mine engineering, models based on intelligent algorithms provide new research methods and ideas for the assessment of rock stability in entry-type excavations. This study aims to introduce several hybrid models based on the random forest (RF) algorithm into the stability evaluation work to find new data-driven methods with higher accuracy to update the critical span graph. To pursue better classification performance, this paper selects three optimization strategies, namely multi-verse optimizer (MVO), grey wolf optimizer (GWO) and moth-flame optimization (MFO) algorithm, to optimize two core parameters of RF, and establishes three corresponding hybrid models, abbreviated as MVO-RF, GWO-RF and MFO-RF, based on the database containing 399 samples from seven Canada mines. There are two input parameters in the database, i.e., opening span and rock mass condition (expressed as RMR), and the output parameter is rock mass stability, which is specifically divided into three categories: stable, potentially unstable and unstable. In addition, five commonly used measurement indexes applicable to multiclassification problems were adopted to verify the classification ability of the models, i.e., the accuracy (ACC), precision calculated using macro-average (PREM), recall calculated using macro-average (RECM), F1 score calculated using macro-average (F1M) and Kappa index (Kappa). The results indicate that the three hybrid models performed well based on the test set accounting for 25 % of the original database, in which the accuracy of the MFO-RF model was the highest: ACC = 0.9300; PREM = 0.9288; RECM = 0.8983; F1M = 0.9116; Kappa = 0.8666. To evaluate whether the three optimization strategies can effectively improve the performance of RF and judge the degree of improvement, the performance of an unoptimized RF model was discussed in this study. In addition, two support vector machine (SVM) models with different kernel functions were selected as references for performance evaluation. The results indicated that compared with the RF and two SVM models, the classification accuracy of the three hybrid models was obviously more satisfactory. The classification accuracy of the three hybrid models reached 0.91, which was sufficient to explain the excellent classification ability of these models. After tuning the RF hyperparameters of each hybrid model, the critical span graph was further updated according to the optimized classification models, which was the focus of this research. By comparing the critical span graphs obtained by the three hybrid models with the single RF model and two kinds of SVM models, it is certain that the three hybrid models proposed in this paper, MVO-RF, GWO-RF and MFO-RF, are promising in the study of evaluating the stability of entry-type excavations and may be deemed auxiliary decision tools to define the stability region of the critical span graph.
This book considers the Roman Empire's responses to the threats which were caused by the new geostrategic situation brought on by the crisis of the 3rd century AD, induced by the 'barbarians' who - ...often already part of Roman military structures as mercenaries and auxiliaries - became a veritable menace for the Empire.
Khirbat Faris McQuitty, Alison; Parton, Holly; Petersen, Andrew
2020
eBook
This volume is the first of three which chart the temporal and spatial occupational fluctuations at the site of Khirbat Faris in Southern Jordan and the stories of the communities that lived there. ...The excavation report follows the site and its environs throughout their many phases of use and occupation, from the 13th century BC to the present day.
Basement excavation may induce unsymmetrical and highly skewed loadings and (or) stress changes in an existing tunnel, not only in the transverse, but also in the longitudinal direction of the ...tunnel. Although basement–tunnel interaction has attracted intense academic interest recently, it is often simply treated as a plane strain problem. In this study, however, based on a dimensional analysis of the governing parameters, two three-dimensional centrifuge tests were designed and carried out in dry sand to investigate the effects of a basement excavation on an existing tunnel located in two horizontal offsets in relation to the basement. In addition, a preliminary three-dimensional numerical analysis was conducted to back-analyse the centrifuge test and to investigate the effects of the tunnel cover-to-diameter and unloading ratios on the existing tunnel. For the specific conditions simulated and soil type tested, a maximum heave of about 0.07% of the final depth of the basement excavation (H
e
) was induced in the tunnel that ran parallel to and beneath the basement. On the contrary, a maximum settlement of 0.014% H
e
was induced in the tunnel located at the side of the basement. For the former tunnel, the influence zone by the basement excavation on vertical tunnel displacement along the longitudinal direction was 1.2L (basement length). By inspecting the measured strains in the longitudinal direction of the existing tunnel, it was found that the inflection point, where the shear force is at a maximum, was located at 0.8L away from the basement centre. Due to stress relief from the basement excavation, the tunnel located directly beneath the basement was vertically elongated, but the one that lay at the side of the basement was distorted. A preliminary numerical parametric study found that tunnel heave decreased as the cover-to-diameter ratio increased, but at a reduced rate.
Bsed on the recent observations from two underground laboratories, the construction-induced excavation damage zone (EDZCI) caused by explosion or by mechanical excavation and stress-induced ...excavation damage zone (EDZSI) are distinguished. The key location for in situ testing of EDZ and method development has been the TBM tunnel in Äspö Hard Rock Laboratory in Sweden since the 1990s. The research and development has been continued between 2010 and 2012 with in situ stress measurement campaign and in 2013 with ground penetrating radar investigations with new GPR EDZ method. The new GPR EDZ method based on frequency analysis of the reflected signal indicates mean depth for EDZCI of 120mm. The same zone is indicated also by various other geophysical and laboratory methods, and is distinguished as construction-induced and continuous around the tunnel perimeter. Fracture mechanics modelling suggests a lowered hydraulic conductivity of 1.8×10−13m/s in EDZSI and 4.0×10−11m/s in EDZCI. Biaxial testing suggests a zone in which Young’s modulus values are lowered, and which is not continuous around the tunnel. This zone is distinguished as an observable part of stress-induced EDZSI.
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•The stress-induced excavation damage zone EDZSI and the construction-induced excavation damage zone EDZCI are distinguished and defined.•Several observations of the construction-induced damage zone are reported.•Observations of the stress-induced damage zone are reported.•Fracture mechanics modelling is used to study the properties of the EDZSI and EDZCI.
"Brings novel, synthetic insight to understanding a region that was a hub of waterborne trade and an important locus of production for some of the Maya's most valued crops."--Cynthia Robin, author ...ofEveryday Life Matters: Maya Farmers at Chan "This one of a kind volume shows us how important this region was to the ancient Maya with detailed and vivid descriptions of sociopolitical and economic organization and their relation to the unique landscape and geography of Chetumal Bay."--Laura J. Kosakowsky, author ofPreclassic Maya Pottery at Cuello, Belize
Chetumal Bay is central to discussions of ancient Maya politics, warfare, economy, exchange and communication because of its unique location. Although the ancient Maya invested prodigious amounts of labor in the construction of road systems calledsacbeob for communication and trade, recent archaeological discoveries around Chetumal Bay in both Belize and Mexico reveal an economic alternative to these roads: an extensive network of riverine and maritime waterways.
Focusing on sites ringing the bay such as Cerro Maya, Oxtankah, and Santa Rita Corozal, the contributors to this volume explore how the bay and its feeder rivers affected all aspects of Maya culture from settlement, food production, and the production and use of special goods to political relationships and social organization. Besides being a nexus for long distance exchange in valuable materials such as jade and obsidian, the region was recognized for its high quality agricultural produce, including cacao, achiote, vanilla, local fruits, honey, and salt, and for its rich marine environment. The Maya living on the fringes of the bay perceived the entire region as a single resource procurement zone. Waterborne trade brought the world to them, providing a wider horizon than would have been available to inland cities dependent only on Maya roads for news of the world. The research reveals that trade relations played a central role in the organization of human social life on Chetumal Bay. Contributors: James Aimers | Timothy Beach | Clifford Brown | Beverly A. Chiarulli | Lisa G. Duffy | Dori Farthing | David A. Freidel | Elizabeth Graham | Thomas Guderjan | Elizabeth Haussner | Linda Howie | Samantha Krause | Javier López Camacho | Sheryl Luzzadder-Beach | Marc D. Marino | Lucas R. Martindale Johnson | Heather McKillop | Nathan J. Meissner | Emiliano Ricardo Melgar Tísoc | Susan Milbrath | Satoru Murata | Maxine Oland | Terry Powis | Kathryn Reese-Taylor | Robin Robertson | Luis A. Torres Díaz | Araceli Vázquez Villegas | Debra S. Walker
To obtain a complete understanding of the stability of deep caverns after excavation disturbance, a laboratory simulation method for testing surrounding rock under excavation disturbance was ...systematically proposed. The rock creep mechanical behavior considering excavation disturbance was compared with that of rock without excavation disturbance, and the results show that the long-term rock strength considering excavation disturbance is significantly lower than that without excavation disturbance at a 2400 m depth. Based on this method, a step-loading triaxial creep and associated acoustic emission (AE) test was carried out with a single-stage loading time of 5 days and a total loading time of approximately 50 days. The results show that with an increase in stress level, the transient strain of the deep rock increases nearly linearly, while the axial creep strain rate increases exponentially. The AE monitoring results demonstrate that when the rock creep transforms from the initial creep stage to the steady-state creep stage, and from the steady-state creep stage to the accelerating stage, the AE amplitude will clearly exhibit a band-shaped distribution, and the AE count rate and AE energy rate will show a single peak or multiple peaks. Multistage AE data can be used to determine the long-term strength of rock. In addition, with an increase in the stress level, the microcracks of the deep rock under excavation disturbance transform from closed primary microcracks to initiating, propagating and coalescence secondary microcracks, which ultimately leads to macroscopic shear failure. The above research results can provide a reference for deep resource exploitation and deep cavern stability evaluation.
Soft computing techniques are becoming even more popular and particularly amenable to model the complex behaviors of most geotechnical engineering systems since they have demonstrated superior ...predictive capacity, compared to the traditional methods. This paper presents an overview of some soft computing techniques as well as their applications in underground excavations. A case study is adopted to compare the predictive performances of soft computing techniques including eXtreme Gradient Boosting (XGBoost), Multivariate Adaptive Regression Splines (MARS), Artificial Neural Networks (ANN), and Support Vector Machine (SVM) in estimating the maximum lateral wall deflection induced by braced excavation. This study also discusses the merits and the limitations of some soft computing techniques, compared with the conventional approaches available.
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•Systematic state-of-the-art review of soft computing applications in underground excavations.•Performance comparisons of chosen SCMs including MARS, ANN, XGBoost, and SVM.•Some discussions and further research recommendations provided.
Safely and high-efficiently breaking rock is of practical significance. In some engineering, explosive blasting may be restricted for its side effects. Traditional non-explosive methods like ...demolition agent and rock breaking machine are generally time-consuming. Therefore, this study proposes a novel liquid carbon dioxide rock-breaking technology and designs the relative device. The effectiveness, safety and high-efficiency of the proposed technology are investigated by shock pressure test, vibration site test and field rock breaking experiment. The experimental results show that the duration of the monitoring shock pressure is around 1500 μs. The shock pressure signal of liquid carbon dioxide tube breaking in free condition contains four stages, namely, increasing exponentially, decreasing oscillatory, stabilization, and negative pressure stage. As pressure sensor is set at 850 mm from the test tube radially, the shock pressure monitored increases to the maximum value of 115.7 kPa within 6 μs. During the liquid carbon dioxide rock breaking, the vertical component of the peak particle velocity of vibration is 173 mm/s, 85 mm/s and 35 mm/s along distance at 1.5 m, 2.5 m and 3.5 m from the tube, respectively. The Fourier power spectra results show that about 85% energy distributes at 6–60 Hz. The vibration caused by the novel technology can meet the requirement of mainstream blasting safety criteria better than that of explosive blasting. Finally, the technology is successfully applied in rock excavation at a metro station construction site. The proposed liquid carbon dioxide rock-breaking technology is preliminarily demonstrated to be safer than explosive blasting and more efficient than traditional non-explosive techniques.
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