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CONTENTS
Volume 34, Number 1, July10 2023
 

Abstract
This study conducts uniaxial compression tests on intact and single crack-contained rocks to investigate the time-frequency domain characteristics of acoustic emission (AE) signals monitored during the deformation failure process. A processing approach, short-time Fourier transform (STFT), is performed to obtain the evolution characteristics of time-frequency domain of AE signals. The AE signal modes at different deformation stages of rocks are different. Five modes of AE signal are observed during the cracking process of rocks. The evolution characteristics of time-frequency domain of AE signals processed by STFT can be utilized to evaluate the damage process of rocks. The difference of time-frequency domain characteristics between intact and cracked rocks is comparatively analyzed. The distribution characteristics of frequency changing from a single band-shaped cluster to multiple band-shaped clusters can be regarded as an early warning information of damage and failure of rocks. Meanwhile, the attenuation of frequency enables the exploration of rock failure trends.

Key Words
acoustic emission (AE); cracked rock; damage; early warning; time-frequency analysis

Address
Yong Niu: Key Laboratory of Rock Mechanics and Geohazards of Zhejiang Province, Shaoxing University, Shaoxing 312099, Zhejiang China;
School of Civil Engineering, Shaoxing University, Shaoxing 312099, Zhejiang China;
School of Earth Science and Engineering, Hohai University, Nanjing 211100, Jiangsu China
Jinguo Wang: School of Earth Science and Engineering, Hohai University, Nanjing 211100, Jiangsu China
Yunjin Hu, Gang Wang and Bolong Liu: Key Laboratory of Rock Mechanics and Geohazards of Zhejiang Province, Shaoxing University, Shaoxing 312099, Zhejiang China;
School of Civil Engineering, Shaoxing University, Shaoxing 312099, Zhejiang China


Abstract
Taking a subway shield tunnel in a certain section of Zhengzhou Metro Line 5 as an example, the field tests of shield cutting cement-soil monopile composite foundation were carried out. The load and internal force of the tunnel lining under the action of composite foundation were tested on-site and the distribution characteristics and variation laws of earth pressure around the tunnel under the load holding state of the composite foundation were analyzed. Five different load combinations (i.e., overburden load theory + g0, Terzaghi's theory + q0, Bierbaumer's theory +q0, Xie's theory + q0, and the proposed method (the combination of compound weight method and Terzaghi's theory) +q0) were used to calculate the internal force of the tunnel structure and the obtained results were compared with the measured internal force results. The action mode of earth pressure on the tunnel lining structure was evaluated. Research results show that the earth pressure obtained by the calculation method proposed in this paper was more consistent with the measured value and the deviation between the two was within 5%. The distribution of the calculated internal force of the tunnel structure was more in line with the distribution law of field test data and the deviation between the calculated and measured values was small. This effectively verified the rationality and applicability of the proposed calculation method. Research results provided references for the design and evaluation of shield tunnels under the action of composite foundations.

Key Words


Address
Chi Zhang, Yuan-cheng Guo and Ming-yu Li: School of civil engineering, zhengzhou university, 100 science avenue,
zhengzhou city, henan province, People's Republic of China
Shi-ju Ma: School of civil engineering, zhengzhou university of Technology, 6 Yingcai Street
zhengzhou city, henan province, People's Republic of China
Babak Safaei: Department of Mechanical Engineering, Eastern Mediterranean University, North Cyprus via Mersin 10, Turkey

Abstract
The 3D geospatial modeling of geotechnical information can aid in understanding the geotechnical characteristic values of the continuous subsurface at construction sites. In this study, a geostatistical optimization model for the three-dimensional (3D) mapping of subsurface stratification and the SPT-N value based on a trial-and-error rule was developed and applied to a dam emergency spillway site in South Korea. Geospatial database development for a geotechnical investigation, reconstitution of the target grid volume, and detection of outliers in the borehole dataset were implemented prior to the 3D modeling. For the site-specific subsurface stratification of the engineering geo-layer, we developed an integration method for the borehole and geophysical survey datasets based on the geostatistical optimization procedure of ordinary kriging and sequential Gaussian simulation (SGS) by comparing their cross-validation-based prediction residuals. We also developed an optimization technique based on SGS for estimating the 3D geometry of the SPT-N value. This method involves quantitatively testing the reliability of SGS and selecting the realizations with a high estimation accuracy. Boring tests were performed for validation, and the proposed method yielded more accurate prediction results and reproduced the spatial distribution of geotechnical information more effectively than the conventional geostatistical approach.

Key Words
3D geostatistical model; 3D integration; conditional simulation; dam site; SPT-N; subsurface stratification

Address
Mingi Kim: Division of Urban Infrastructure Research, Seoul Institute of Technology, 37, Maebongsan-ro, Mapo-gu, Seoul 03909, Republic of Korea
hoong-Ki Chung and Joung-Woo Han: Department of Civil Environmental Engineering, Seoul National University, 1, Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea
Han-Saem Kim: Earthquake Research Center, Korea Institute of Geoscience and Mineral Resources 124, Gwahak-ro, Yuseong-gu, Daejeon 34142, Republic of Korea

Abstract
Knowledge of minimum horizontal stress (Shmin) is a significant step in determining full stress tensor. It provides crucial information for the production of sand, hydraulic fracturing, determination of safe mud weight window, reservoir production behavior, and wellbore stability. Calculating the Shmin using indirect methods has been proved to be awkward because a lot of data are required in all of these models. Also, direct techniques such as hydraulic fracturing are costly and time-consuming. To figure these problems out, this work aims to apply the long-short-term memory (LSTM) algorithm to Shmin time-series prediction. 13956 datasets obtained from an oil well logging operation were applied in the models. 80% of the data were used for training, and 20% of the data were used for testing. In order to achieve the maximum accuracy of the LSTM model, its hyper-parameters were optimized significantly. Through different statistical indices, the LSTM model's performance was compared with with other machine learning methods. Finally, the optimized LSTM model was recommended for Shmin prediction in the well logging operation.

Key Words
long-short-term memory; machine learning; minimum horizontal stress; optimization; well logging

Address
Arsalan Mahmoodzadeh: Department of Civil Engineering, University of Halabja, Halabja, Kurdistan Region, Iraq
Seyed Mehdi Seyed Alizadeh: Petroleum Engineering Department, Australian University, West Mishref, Kuwait
Adil Hussein Mohammed: Department of Communication and Computer Engineering, Faculty of Engineering, Cihan University-Erbil, Kurdistan Region, Iraq
Ahmed Babeker Elhag: Department of Civil Engineering, College of Engineering, King Khalid University, Abha 61413, Saudi Arabia
Hawkar Hashim Ibrahim: Department of Civil Engineering, College of Engineering, Salahaddin University-Erbil, 44002 Erbil, Kurdistan Region, Iraq
Shima Rashidi: Department of Computer Science, College of Science and Technology, University of Human Development, Sulaymaniyah,
Kurdistan Region, Iraq


Abstract
In this research, the degradation rate of physical properties of the Angouran pit bedrock (calc-schist) is first investigated under the specific numbers of freeze-thaw (F-T) cycles. Then, the durability of calc-schist specimens against the FT cycle number (N) is examined considering the mechanical parameters, and using the decay function and half-time techniques. For this purpose, point load strength (IS(50)), second durability index (Id2), Brazilian tensile strength (BTS), and compressive (VP) and shear (VS) wave velocities of calc-schist specimens are measured after 0, 7, 15, 40, and 75 N. For comparing the degradation rate of mechanical properties of available rock types on the Angouran mine walls, these tests are also carried out on the limestone and amphibolite schist specimens beside the calc-schist. According to test results, the exponential regression models are developed between the mechanical parameters of rock specimen's and N variable. Also, the long-term durability of each rock type versus N is studied using the decay function and half-time techniques. Results indicated that the degradation rate differs for the above rock types in which amphibolite schist and calc-schist specimens have the highest and least resistance against the N, respectively. The obtained results from this study can play a key role in the optimal design of the mine's final walls.

Key Words
angouran mine; bedrock properties; decay function; freeze-thaw cycle; half-time; laboratory test

Address
Seyed Zanyar Seyed Mousavi and Mohammad Rezaei: Department of Mining Engineering, Faculty of Engineering, University of Kurdistan, Sanandaj, Iran

Abstract
To overcome the dilemma of the [BQ] method's inability to predict mountain tunnel support loads, this study is based on the Hoek-Brown criterion and previous results to obtain the connection equations from GSI scores to each parameter of the Hoek-Brown criterion and the link between the [BQ] scores and the GSI system. The equations were embedded in the Hoek-Brown criterion of FLAC6.0 software to obtain tunnel construction forecasts without destroying the in-situ stratigraphy. The feasibility of the secondary development of the Hoek-Brown criterion was verified through comparative analysis with field engineering measurements. If GSI > 45 with a confining pressure of less than 10 MPa, GSI has little effect on the critical softening factor while we should pay attention to the parameter of confining pressure when GSI < 45. The design values for each parameter are closer to the FLAC3D simulation results and the secondary development of the Hoek-Brown criterion meets the design objectives. If the Class V surrounding rock is thinned with shotcrete or the secondary lining is installed earlier, the secondary lining may act as the main load-bearing structure. The study may provide ideas for rapid prediction of mountainous tunnels in China.

Key Words
[BQ]; confining pressure; GSI; Hoek-Brown criterion; mountain tunnel

Address
Jian Zhou and Zhi Ding: Department of Civil Engineering, Hangzhou City University, Hangzhou 310015, China;
Zhejiang Engineering Research Center of Intelligent Urban Infrastructure, Hangzhou City University, Hangzhou 310015, China;
Key Laboratory of Safe Construction and Intelligent Maintenance for Urban Shield Tunnels of Zhejiang Province,
Hangzhou City University, Hangzhou 310015, China
Xinan Yang: The Key Laboratory of Road and Traffic Engineering, Ministry of Education, Tongji University, Shanghai 201804, China

Abstract
The cover plate and the building loads often make the semi-covered deep excavations with existing buildings bearing asymmetric load, presenting different deformation characteristics with normal excavations, which is not absolutely clear in current studies. Based on a typical engineering, the building storeys, the basement storeys, the pile length, the existence of the cover plate (CP) and the depth of the diaphragm walls (DW) were selected as variables, and 44 groups of simulation were designed to study the influence of existing buildings and the semi-covered supporting system on the deformation of the excavations. The results showed that the maximum lateral displacement of DW, shm, and the depth of shm, Hm, are affected seriously by the building storeys and the basement storeys. Asymmetric structures and loading lead to certain lateral displacement of DW at the beginning of excavation, resulting in different relationships between shm and excavation depth, H. The maximum surface settlement outside the pit, svm, increases significantly and the location, dm, moves away from the pit with the building storeys increases. svm has a quadratic correlation with H due to the existing buildings. CP and building load will affect the style of the lateral displacement curve of DW seriously in different aspects.

Key Words
deep excavation; deformation characteristics; existing buildings; numerical simulation; semi-covered method

Address
Linfeng Wang, Xiaohan Zhou, Xinrong Liu, Peng Liu and Bin Xu: 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 for Prevention and Control of Environmental Geological Hazards in the TGR Area,
Chongqing 400045, China
Tao Chen: China Railway Major Bridge Reconnaissance & Design Institute Co., Ltd., Wuhan Hubei 430050, China
Shaoming Wu and Feng Chen: Guangzhou Expressway Co.,Ltd., Guangzhou Guangdong 510000, China

Abstract
This study focused on understanding the relationship between the design of a tunnel boring machine disc cutter ring and its rock-breaking efficiency, as well as the applicable conditions of different cutter ring types. The discrete element method was used to establish a numerical model of the rock-breaking process using disc cutters with different ring types to reveal the development of rock damage cracks and variation in cutter penetration load. The calculation results indicate that a sharp-edged (V-shaped) disc cutter penetrates a rock mass to a given depth with the lowest load, resulting in more intermediate cracks and few lateral cracks, which leads to difficulty in crack combination. Furthermore, the poor wear resistance of a conventional V-shaped cutter can lead to an exponential increase in the penetration load after cutter ring wear. In contrast, constant-cross-section (CCS) disc cutters have the highest quantity of crack extensions after penetrating rock, but also require the highest penetration loads. An arch-edged (U-shaped) disc cutter is more moderate than the aforementioned types with sufficient intermediate and lateral crack propagation after cutting into rock under a suitable penetration load. Additionally, we found that the cutter ring wedge angle and edge width heavily influence cutter rock-breaking efficiency and that a disc cutter with a 16 to 22 mm edge width and 20 to 30 wedge angle exhibits high performance. Compared to V-shaped and U-shaped cutters, the CCS cutter is more suitable for soft or medium-strength rocks, where the penetration load is relatively small. Additionally, two typical case studies were selected to verify that replacing a CCS cutter with a U-shaped or optimized V-shaped disc cutter can increase cutting efficiency when encountering hard rocks.

Key Words
blade width; cutter ring type; damage crack; discrete element method; rock breaking; TBM construction; wedge angle

Address
Xiaokang Shao, Yusheng Jiang, Zongyuan Zhu, Zhiyong Yang, Zhenyong Wang and Jinguo Cheng: School of Mechanics and Civil Engineering, China University of Mining and Technology-Beijing, Ding, No. 11 Xueyuan Road,
Haidian District, Beijing 100083, P.R. China
Quanwei Liu: Qingdao Metro Line 6 Co Ltd, No.177 Binhai Road, Huangdao District, Qingdao 266000, P.R. China

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