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CONTENTS
Volume 28, Number 3, February10 2022
 

Abstract
In this study, the numerical analysis model of t-beam explosion is established to compare and analyze the failure modes of the t-beam under the action of explosive loads, thus verifying the accuracy of the numerical model. Then, based on the numerical analysis of different protection forms of t beams under explosive loads, the peak pressure of t beam under different protection conditions, the law of structural energy consumption, the damage pattern of the t beam after protection, and the protection efficiency of different protective layers was studied. The testing results indicate that the pressure peak of t beam is relatively small under the combined protection of steel plate and aluminum foam, and the peak value of pressure decays quickly along the beam longitudinal. Besides, as the longitudinal distance increases, the pressure peak attenuates most heavily on the roof's explosion-facing surface. Meanwhile, the combined protective layer has a strong energy consumption capacity, the energy consumed accounts for 90% of the three parts of the t beam (concrete, steel, and protective layer). The damaged area of t beam is relatively small under the combined protection of steel plate and aluminum foam. We also calculate the protection efficiency of t beams under different protection conditions using the maximum spalling area of concrete. The results show that the protective efficiency of the combined protective layer is 45%, demonstrating a relatively good protective ability.

Key Words
t-section concrete beam; explosion protection; failure mode; near-field explosion; pressure peak; protection efficiency

Address
Qixin Sun and Chao Liu: Department of Bridge Engineering, Tongji University, Shanghai, 200092, P.R. China

Abstract
Settlement evaluation is important for shallow tunnels in big cities to estimate the settlement that occurs due to the excavation of twin tunnels. The majority of earlier research on analytical solutions, on the other hand, concentrated on calculating the settlement for a single tunnel. This research introduces a procedure to evaluate the settlement induced by the excavation of twin tunnels (two parallel tunnels). In this study, a series of numerical analysis were performed to validate the analytical solution results. Two geological conditions were considered to derive the settlement depending on each case. The analytical and numerical methods were compared, which involved considering many sections and conducting a parametric study; the results have good agreement. Moreover, a comparison of the 3D flat model and 2D (FEM) with the analytical solution shows that in the fill soil, the maximum settlement values were obtained by the analytical solution. In contrast, the values obtained by the analytical solution in the rock is more conservative than those in the fill. Finally, this method was shown to be appropriate for twin tunnels dug side by side by utilizing finite element analysis 3D and 2D (PLAXIS 3D and PLAXIS 2D) to verify the analytical equations. Eventually, it will be possible to use this approach to predict settlement troughs over twin tunnels.

Key Words
analytical methods; FEM; ground movement; settlement; twin tunnel

Address
Xinrong Liu, Lojain Suliman and Xiaohan Zhou: College of Civil Engineering, Chongqing University, Chongqing 400045, China;
State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, China;
National Joint Engineering Research Center of Geohazards Prevention in the Reservoir Areas (Chongqing), Chongqing 400045, China
Ahmed Abd Elmageed: National Authority for tunnels, Cairo, Egypt

Abstract
Suitable techniques to stabilize organic soil and improve its engineering behaviour are in demand. Despite various alternatives, nano-additives proved to be an effective stabilizer owing to their strength enhancing properties. The study focuses on using nano-silica as a potential stabilizer to improve organic silt. Soil was treated with four dosages of nano-silica namely 0.2%, 0.4%, 0.6% and 0.8% of dry weight of the soil. Nano-silica treated soil showed a strength increase of nearly 25% at a dosage of 0.4% after curing for two hours. Strength of the treated soil improved with age. Strength improved by nearly 62.9% after 28 days of curing and 221.4% after 180 days of curing due to formation of Calcium – Silicate – Hydrate (CSH) gel in the soil matrix. Dosage of 0.6% nano-silica is observed to be the optimum dosage. Coefficient of permeability and compression index showed an increase by 13.32 and 5.5 times respectively owing to aggregation of particles and creation of void spaces as visualized from the scanning electron micrographs. Further model foundation study and numerical parametric studies using PLAXIS 2D indicate that optimized and economic results can be obtained by varying the additive dosage with depth.

Key Words
consolidation; model study; nano-silica; organic silt, permeability; strength, surface roughness

Address
Govindarajan Kannan and Evangelin Ramani Sujatha: Centre for Advanced Research in Environment, School of Civil Engineering, SASTRA Deemed to be University,
Thirumalaisamudram, Thanjavur - 613401, Tamil Nadu, India

Abstract
Lime stabilization has conventionally been listed amid the key techniques of chemical stabilization. Replacing lime with sustainable agro-based by-products have gained prominence in recent decades. Bagasse ash (BA) is one such potential alternatives, an industrial waste with abundance in production, and industries exploring sustainable solutions for its safe disposal. Supplementing BA with lime could be an ideal approach to reduce lime consumption. However, suitability of BA and lime for the stabilization of expansive clays, such as black cotton (BC) soil is yet to be explored. This paper therefore aims to investigate the suitability of BA-lime mixtures to stabilize BC soil with emphasis to compaction behaviors and unconfined compressive strength (UCS) using standard laboratory procedures. Suitability of BA-lime mixture is then assessed against addition of calcium sulphate which, from previous experience, is detrimental with lime stabilization. Experimental outcomes nominate 15% BA as the optimum value observed from both compaction and UCS data, while addition of 4% lime to 15% BA showed the best results. Mineralogical and microstructural analysis show the presence of cementitious compounds with addition of lime and calcium sulphate with curing periods. While, formation of Ettringite needles were noted with the addition of calcium sulphate in BA-lime mixtures (at optimum values) after 90-day curing, and UCS results showed a decrease at this point. To this end, addition of BA in lime stabilization showed encouraging results as assessed from the compaction and UCS results. Nonetheless usage of calcium salts, with utmost emphasis on calcium sulphate and equivalent should be avoided.

Key Words
calcium sulphate; compaction behavior; expansive clay; unconfined compressive strength

Address
H.N. Ramesh: Faculty of Engineering - Civil, University Visvesvaraya College of Engineering, Bengaluru 560056, Karnataka, India
Madhavi Gopal Rao Kulkarni: Department of Civil Engineering, Presidency University, Bengaluru, Karnataka, India
Mavinakere Eshwaraiah Raghunandan: Civil Engineering Discipline, School of Engineering, Monash University Malaysia, 47500 Bandar Sunway, Selangor, Malaysia
Nethravathi S.: Department of Civil Engineering, R.V. College of Engineering, Bengaluru 560059, Karnataka, India


Abstract
A set of slurry shield test system capable of cutter cutting and slurry automatic circulation is used to investigate the deformation characteristics, the evolution characteristics of support resistance and the distribution and evolution process of earth pressure during excavating and collapsing of slurry shield tunneling in circular-gravel layer. The influence of cover-span ratio on surface subsidence, support resistance and failure mode of excavation face is also discussed. Three-dimensional numerical calculations are performed to verify the reliability of the test results. The results show that, with the decrease of the supporting force of the excavation face, the surface subsidence goes through four stages: insensitivity, slow growth, rapid growth and stability. The influence of shield excavation on the axial earth pressure of the front soil is greater than that of the vertical earth pressure. When the support resistance of the excavation face decreases to the critical value, the soil in front of the excavation face collapses. The shape of the collapse is similar to that of a bucket. The ultimate support resistance increase with the increase of the cover-span ratio, however, the angle between the bottom of the collapsed body and the direction of the tunnel excavation axis when the excavation face is damaged increase first and then becomes stable. The surface settlement value and the range of settlement trough decrease with the increase of cover-span ratio. The numerical results are basically consistent with the model test results.

Key Words
circular-gravel layer; excavation face stability; model test; numerical simulation; slurry shield

Address
Xinrong Liu and Zuliang Zhong: School of Civil Engineering, Chongqing University, Chongqing 400045, China;
State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, China;
National Joint Engineering Research Center of Geohazards Prevention in the Reservoir Areas,
Chongqing University, Chongqing 400045, China
ongshuang Liu, Fei Xiong, Yafeng Han, Ronghan Liu, Qiang Chen and Wenwu Liu: School of Civil Engineering, Chongqing University, Chongqing 400045, China
Qingjun Meng: Nanning Rail Transit Co., Ltd, Nanning, Guangxi, 530029 China
Chengxian Weng: T.Y. Lin International Engineering Consulting (China) Co., Ltd, Chongqing 401121, China


Abstract
Landslides triggered by the combination of heavy precipitation and anthropological disturbance in hilly areas cause severe damage to human lives, properties, and infrastructure constructions. A comprehensive investigation of the influencing factors and failure mechanisms of landslides are significant for disaster mitigation and prevention. This paper utilized the combination of detailed geological investigation, physical experimental testing as well as numerical modelling to determine the failure mechanism, and proposed a countermeasures of the Lantian landslide occurred on 2, July 2017. The results reveal that the Lantian landslide is a catastrophic reactivated slide which occurred in an active tectonic region in Southwest China. Because of the unique geological settings, the fully to highly weathered basalts in the study area with well-developed fractures favored the rainwater infiltration, which is the beneficial to slide reactivation. Engineering excavation and heavy precipitation are the main triggering factors to activate the slide motion. Two failure stages have been identified in the landslide. The first phase involves a shallow mass collapse originated at the upper slopes, which extends from the road to platform at rear part, which is triggered by excavation in the landslide region. Subjected to the following prolonged rainfall from 19 June to 2 July, 2017, the pore water pressure of the slope continually increased, and the groundwater table successively rise, resulting in a significant decrease of soil strength which leads to successive large-scale deep slide. Thereinto, the shallow collapse played a significant role in the formation of the deep slide. Based on the formation mechanisms of the landslide, detailed engineering mitigation measures, involving slope cutting, anchor cable frame, shotcrete and anchorage, retaining wall and intercepting ditch were suggested to reduce the future failure risk of the landslide.

Key Words
excavation; landslide; mitigation measures; numerical simulation; rainfall

Address
Kun He and Bo Liu: Faculty of Geosciences and Environmental Engineering, Southwest Jiaotong University, Sichuan Chengdu, China
Guotao Ma: Faculty of Geosciences and Environmental Engineering, Southwest Jiaotong University, Sichuan Chengdu, China;
School of Engineering, University of Warwick, Coventry, United Kingdom
Xiewen Hu: Faculty of Geosciences and Environmental Engineering, Southwest Jiaotong University, Sichuan Chengdu, China; Engineering Laboratory combined with national and local of spatial information technology of high-speed railway operation safety,
Southwest Jiaotong University, Sichuan Chengdu, China
Mei Han: School of Mathematics, Southwest Jiaotong University, Sichuan Chengdu, China



Abstract
Water-resisting key stratum (WKS) between coal seams is an important barrier that prevents water inrush from goaf in roof under multi-seam mining. The occurrence of water inrush can be evaluated effectively by analyzing the fracture of WKS in multi-seam mining. A "long beam" water inrush mechanical model was established using the multi-seam mining of No. 2+3 and No. 8 coal seams in Xiqu Mine as the research basis. The model comprehensively considers the pressure from goaf, the gravity of overburden rock, the gravity of accumulated water, and the constraint conditions. The stress distribution expression of the WKS was obtained under different mining distances in No. 8 coal seam. The criterion of breakage at any point of the WKS was obtained by introducing linear Mohr strength theory. By using the mechanical model, the fracture of the WKS in Xiqu Mine was examined and its breaking position was calculated. And the risk of water inrush was also evaluated. Moreover, breaking process of the WKS was reproduced with Flac3D numerical software, and was analyzed with on-site microseismic monitoring data. The results showed that when the coal face of No. 8 coal seam in Xiqu Mine advances to about 80 m ~ 100 m, the WKS is stretched and broken at the position of 60 m ~ 70 m away from the open-off cut, increasing the risk of water inrush from goaf in roof. This finding matched the result of microseismic analysis, confirming the reliability of the water inrush mechanical model. This study therefore provides a theoretical basis for the prevention of water inrush from goaf in roof in Xiqu Mine. It also provides a method for evaluating and monitoring water inrush from goaf in roof.

Key Words
goaf; mechanical model; multi-seam mining; water inrush; water-resisting key stratum

Address
Kai Ma, Tianhong Yang, Yong Zhao, Xiangang Hou, Yilong Liu and Junxu Hou: Center for Rock Instability and Seismicity Research, School of Resources and Civil Engineering,
Northeastern University, Shenyang 110819, China;
Key Laboratory of Ministry of Education on Safe Mining of Deep Metal Mines,
Northeastern University, Shenyang 110819, China
Wenxian Zheng and Qiang Ye: Xiqv Mine, Shanxi Xishan Coal Power Co., Ltd, Taiyuan 030200, China



Abstract
Rock properties are important in the design of mines and civil engineering excavations to prevent the imminent failure of slopes and collapse of underground excavations. However, the time, cost, and expertise required to perform experiments to determine those properties are high. Therefore, empirical models have been developed for estimating the mechanical properties of rock that are difficult to determine experimentally from properties that are less difficult to measure. However, the inherent variability in rock properties makes the accurate performance of the empirical models unrealistic and therefore necessitate the use of soft computing models. In this study, Gaussian process regression (GPR), artificial neural network (ANN) and response surface method (RSM) have been proposed to predict the static and dynamic rock properties from the P-wave and rock density. The outcome of the study showed that GPR produced more accurate results than the ANN and RSM models. GPR gave the correlation coefficient of above 99% for all the three properties predicted and RMSE of less than 5. The detailed sensitivity analysis is also conducted using the RSM and the P-wave velocity is found to be the most influencing parameter in the rock mechanical properties predictions. The proposed models can give reasonable predictions of important mechanical properties of sedimentary rock.

Key Words
empirical models; Gaussian process regression; response surface method; rock properties

Address
Abiodun I. Lawal: Department of Energy Resources Engineering, Inha University Yong-Hyun Dong, Nam Ku, Incheon, Korea;
Department of Mining Engineering, Federal University of Technology, Akure, Nigeria
Sangki Kwon: Department of Energy Resources Engineering, Inha University Yong-Hyun Dong, Nam Ku, Incheon, Korea
Adeyemi E. Aladejare: Oulu Mining School, University of Oulu, Finland
Gafar O. Oniyide: Department of Mining Engineering, Federal University of Technology, Akure, Nigeria


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