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CONTENTS
Volume 30, Number 3, August10 2022
 


Abstract
Geotechnical materials such as silt, fine sand, or coarse granular soils may be unstable under undrained shearing or during rainfall infiltration starting an unsaturated state. Some researches are available describing the instability of coarse granular soils in drained or undrained conditions. However, there is a need to investigate the instability mechanism of unsaturated silty soil considering the effect of degree of compaction and net confining stress under partially and fully drained conditions. The specimens in the current study are compacted at 65%, 75%, & 85% degree of compaction, confined at pressures of 60, 80 & 120 kPa, and tested in partially and fully drained conditions. The tests have been performed in two steps. In Step-I, the specimens were sheared in constant water content conditions (a type of partially drained test) to the maximum shear stress. In Step-II, shearing was carried in constant suction conditions (a type of fully undrained test) by keeping shear stress constant. At the start of Step-II, PWP was increased in steps to decrease matric suction (which was then kept constant) and start water infiltration. The test results showed that soil instability is affected much by variation in the degree of compaction and confining stresses. It is also observed that loose and medium dense soils are vulnerable to pre-failure instability i.e., instability occurs before reaching the failure state, whereas, instability in dense soils instigates together with the failure i.e., failure line (FL) and instability line (IL) are found to be unique.

Key Words
constant shear stress; degree of compaction; failure line; instability; water infiltration

Address
Ali Murtaza Rasool: National Engineering Services Pakistan (NESPAK), Lahore, Pakistan; University of Central Punjab (UCP), Lahore, Pakistan; National College of Arts (NCA), Lahore, Pakistan 4Department of Civil & Environmental Engineering, Saitama University, Japan

Abstract
In this study, the city of Osijek is used as a case study area for low to medium seismicity regions with deep soil over deep geological deposits to determine horizontal PGA values. For this reason, we propose new regional attenuation equations for PGA that can simultaneously capture the effects of deep geology and local soil conditions. A micro-zoning map for the city of Osijek is constructed using the derived empirical scaling equations and compared to all prior seismic hazard estimates for the same area. The findings suggest that the deep soil atop deep geological sediments results in PGA values that are only 6 percent larger than those reported at rock soil sites atop geological rocks. Given the rarity of ground motion records for deep soils atop deep geological layers around the world, we believe this case study is a start toward defining more reliable PGA estimates for similar areas.

Key Words
deep geological sediments; deep soil; horizontal; microzoning; PGA

Address
Borko Đ. Bulajić: Faculty of Technical Sciences, University of Novi Sad, Trg Dositeja Obradovića 6, 21000 Novi Sad, Serbia
Marijana Hadzima-Nyarko and Gordana Pavić: Faculty of Civil Engineering and Architecture Osijek, Josip Juraj Strossmayer University of Osijek, Vladimira Preloga 3, 31000 Osijek, Croatia

Abstract
A field velocity resistivity probe (FVRP) can measure compressional waves, shear waves and electrical resistivity in boreholes. The objective of this study is to perform the soil classification through a machine learning technique through elastic wave velocity and electrical resistivity measured by FVRP. Field and laboratory tests are performed, and the measured values are used as input variables to classify silt sand, sand, silty clay, and clay-sand mixture layers. The accuracy of k-nearest neighbors (KNN), naive Bayes (NB), random forest (RF), and support vector machine (SVM), selected to perform classification and optimize the hyperparameters, is evaluated. The accuracies are calculated as 0.76, 0.91, 0.94, and 0.88 for KNN, NB, RF, and SVM algorithms, respectively. To increase the amount of data at each soil layer, the synthetic minority oversampling technique (SMOTE) and conditional tabular generative adversarial network (CTGAN) are applied to overcome imbalance in the dataset. The CTGAN provides improved accuracy in the KNN, NB, RF and SVM algorithms. The results demonstrate that the measured values by FVRP can classify soil layers through three kinds of data with machine learning algorithms.

Key Words
classification; conditional tabular generative adversarial network (CTGAN); field velocity resistivity probe (FVRP); machine learning; synthetic minority oversampling technique (SMOTE)

Address
Jong-Sub Lee, Junghee Park: School of Civil, Environmental and Architectural Engineering, Korea University, 145, Anam-ro, Seongbuk-gu, Seoul 02841, Republic of Korea
Jongchan Kim: Department of Civil and Environmental Engineering, University of California at Berkeley, Berkeley, CA 94720-1710, USA
Hyung-Koo Yoon: Department of Construction and Disaster Prevention Engineering, Daejeon University, Daejeon 34520, Republic of Korea

Abstract
Rockburst is a dynamic, multivariate, and non-linear phenomenon that occurs in underground mining and civil engineering structures. Predicting rockburst is challenging since conventional models are not standardized. Hence, machine learning techniques would improve the prediction accuracies. This study describes decision based uncertainty models to predict rockburst in underground engineering structures using gradient boosting algorithms (GBM). The model input variables were uniaxial compressive strength (UCS), uniaxial tensile strength (UTS), maximum tangential stress (MTS), excavation depth (D), stress ratio (SR), and brittleness coefficient (BC). Several models were trained using different combinations of the input variables and a 3-fold cross-validation resampling procedure. The hyperparameters comprising learning rate, number of boosting iterations, tree depth, and number of minimum observations were tuned to attain the optimum models. The performance of the models was tested using classification accuracy, Cohen's kappa coefficient (k), sensitivity and specificity. The best-performing model showed a classification accuracy, k, sensitivity and specificity values of 98%, 93%, 1.00 and 0.957 respectively by optimizing model ROC metrics. The most and least influential input variables were MTS and BC, respectively. The partial dependence plots revealed the relationship between the changes in the input variables and model predictions. The findings reveal that GBM can be used to anticipate rockburst and guide decisions about support requirements before mining development.

Key Words
accuracy; gradient boosting algorithm; modelling; rockburst; sensitivity; specificity

Address
Richard Kidega, Mary Nelima Ondiaka, Duncan Maina, Kiptanui Arap Too Jonah: Department of Mining and Mineral Processing Engineering, School of Mines and Engineering, Taita Taveta University, P.O. Box 635-80300 Voi, Kenya
Muhammad Kamran: Department of Mining Engineering, Institute Technology of Bandung, Indonesia

Abstract
A certain amount of random vibration excitation to subway track is caused by subway operation. This excitation is transmitted through track foundation, tunnel, soil medium, and ground building to the ground and ground structure, causing vibration. The vibration affects ground building. In this study, the results of ANSYS numerical simulation was used to establish back-propagation (BP) neural network model. Moreover, a back-propagation neural network model consisting of five input neurons, one hidden layer, 11 hidden-layer neurons, and three output neurons was used to analyze and calculate the vertical Zvibration level of New Capital's ground buildings of Qingdao Metro phase I Project (Line M3). The Z-vibration level under different working conditions was calculated from monolithic roadbed, steel-spring floating slab roadbed, and rubber-pad floating slab roadbed under the working condition of center point of 0-100 m. The steel-spring floating slab roadbed was used in the New Capital area to monitor the subway operation vibration in this area. Comparing the monitoring and prediction results, it was found that the prediction results have a good linear relationship with lower error. The research results have good reference and guiding significance for predicting vibration caused by subway operation.

Key Words
ground building; neural network; vibration induced by subway operation; Z-vibration

Address
Binghua Zhou, Yiguo Xue: Geotechnical and Structural Engineering Research Center, Shandong University, Ji'nan 250061, Shandong, China
Jun Zhang: Qingdao Metro Group Co. Ltd., Qingdao 266000, Shandong, China
Dunfu Zhang: Geotechnical and Structural Engineering Research Center, Shandong University, Ji'nan 250061, Shandong, China
Jian Huang: Qingdao Metro Group Co. Ltd., Qingdao 266000, Shandong, China
Daohong Qiu: Geotechnical and Structural Engineering Research Center, Shandong University, Ji'nan 250061, Shandong, China
Lin Yang: Qingdao Metro Group Co. Ltd., Qingdao 266000, Shandong, China
Kai Zhang: Geotechnical and Structural Engineering Research Center, Shandong University, Ji'nan 250061, Shandong, China
Jiuhua Cui: Geotechnical and Structural Engineering Research Center, Shandong University, Ji'nan 250061, Shandong, China

Abstract
Complex rock masses include various joint planes, bedding planes and other weak structural planes. The existence of these structural planes affects the mechanical properties, deformation rules and failure modes of jointed rock masses. To study the influence of the parameters of a nonpersistent joint network on the mechanical properties and failure modes of jointed rock masses, synthetic rock mass (SRM) technology based on discrete elements is introduced. The results show that as the size of the joints in the rock mass increases, the compressive strength and the discreteness of the rock mass first increase and then decrease. Among them, the joints that are characterized by "small but many" joints and "large and clustered" joints have the most significant impact on the strength of the rock mass. With the increase in joint density in the rock mass, the compressive strength of rock mass decreases monotonically, but the rate of decrease gradually decreases. With the increase in the joint dip angle in rock mass, the strength of the rock mass first decreases and then increases, forming a U-shaped change rule. In the analysis of the failure mode and deformation of a jointed rock mass, the type of plastic zone formed after rock mass failure is closely related to the macroscopic displacement deformation of the rock mass and the parameters of the joints, which generally shows that the location and density of the joints greatly affect the failure mode and displacement degree of the jointed rock mass. The instability mechanism of jointed surrounding rock is revealed.

Key Words
discrete fracture network; jointed rock mass; nonpersistent joint; synthetic rock mass technique

Address
Yongning Wu, Yang Zhao, Peng Tang, Wenhai Wang: State Key Laboratory of Mining Disaster Prevention and Control, Shandong University of Science and Technology, Qingdao 266590, China
Lishuai Jiang: State Key Laboratory of Mining Disaster Prevention and Control, Shandong University of Science and Technology, Qingdao 266590, China; Shandong Key Laboratory of Civil Engineering Disaster Prevention and Mitigation,
Shandong University of Science and Technology, Qingdao 266590, China

Abstract
Cantilever sheet pile walls having section thinner than masonry walls are generally adopted to retain moderate height of excavation. In practice, a surcharge in the form of strip load of finite width is generally present on the backfill. So, in the present study, influence of strip load on cantilever sheet pile walls is analyzed by varying the width of the strip load and distance from the cantilever sheet pile walls using finite difference based computer program in cohesionless soil modelled as Mohr-Coulomb model. The results of bending moment, earth pressure, deflection and settlement are presented in non-dimensional terms. A parametric study has been conducted for different friction angle of soil, embedded depth of sheet pile walls, different magnitudes and width of the strip load acting on the ground surface and at a depth below ground level. The result of present study is also validated with the available literature. From the results presented in this study, it can be inferred that optimum behavior of cantilever sheet pile walls is observed for strip load having width 2 m to 3 m on the ground surface. Further as the depth of strip load below the ground surface increases below the ground level to 0.75 times excavation height, the bending moment, settlement, net earth pressure and deflection decreases and then remains constant.

Key Words
cantilever sheet pile walls; cohesionless soil; embedded depth; FLAC2D; numerical analysis; strip load

Address
Akshay Pratap Singh and Kaustav Chatterjee: Department of Civil Engineering, Indian Institute of Technology Roorkee, Roorkee 247 667, India

Abstract
With the development of the economy, people's utilization of underground space are also improved, and a large number of cities have begun to build subways to relieve traffic pressure. The choice of subway station construction method is crucial. If an inappropriate construction method is selected, it will not only waste costs but also cause excessive deformation that may also threaten construction safety. In this paper, a subway station construction scheme selects model based on the AHP-fuzzy comprehensive evaluation. The rationality of the model is verified using numerical simulation and monitoring measurement data. Firstly, considering the economy and safety, a comprehensive evaluation system is established by selecting several indicators. Then, the analytic hierarchy process is used to determine the weight of the evaluation index, and the dimensionless membership in the fuzzy comprehensive evaluation method is used to evaluate the advantages and disadvantages of the construction method. Finally, the method is applied to Liaoyang east road station of Qingdao metro Line 2, and the results are verified by numerical simulation and monitoring measurement data. The results show that the model is scientific, practical and applicable.

Key Words
analytic hierarchy process; fuzzy comprehensive evaluation; monitoring measurement; numerical simulation; selection of construction method; subway station

Address
Daohong Qiu, Yuehao Yu, Yiguo Xue, Maoxin Su, Binghua Zhou, Huimin Gong, Chenghao Bai and Kang Fu: Geotechnical and Structural Engineering Research Center, Shandong University, Ji


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