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CONTENTS
Volume 27, Number 6, December25 2021
 


Abstract
There are various technical problems need to be solved in the construction process of pre-setting an isolation wall into a double lane in the outburst prone mine. This study presents a methodology that pre-setting an isolation wall into a double lane without a coal pillar. This requires the excavation of two small section roadways to dig a wide section roadway, followed by construction of the separation wall. During this process the connecting lane is reserved. In order to ensure the stability of the separation wall, the required bearing capacity of the isolation wall is 4.66 MN/m and the deformation of the isolation wall is approximately 25 cm. To reduce the difficulty of implementing support the roadway is driven by 5 m/d. After the construction of the separation wall, the left side coal wall is brushed 1.5 m to make the width of the gas roadway reach 2.5 m and the roadway support utilizes anchor rod, ladder beam, anchor cable beam and net configuration. During construction, the concrete pump and removable self-propelled hydraulic wall mold are used to pump and pour the concrete of the isolation wall. In the process of mining, the stress distribution of coal body and isolation wall is detected and measured on site. The results demonstrate that the deformation of the surrounding rock of roadway and separation of roof in the roadway is small. The stress of the bolt and anchor cable is within equipment tolerance validating their selection. The roadway is well supported and the intended goal is achieved. The methodology can be used for reference for similar mine gas control.

Key Words
double lane with pre-set isolation wall; high gas mine; mining monitor; roadway protection without coal pillar

Address
Hui Liu: Key Laboratory of Gas and Fire Control for Coal Mines, Ministry of Education, China University of Mining and Technology,Xuzhou 221116, Jiangsu, China;
Gucheng Coal Mine, Shandong Energy Lining Coal Mine Group, Jining, 272100, Shandong, China;
School of Safety Engineering, China University of Mining and Technology, Xuzhou 221116, Jiangsu, China
Xuelong Li: Mine Disaster Prevention and Control-Ministry of State Key Laboratory Breeding Base, Shandong University of Science and Technology, Qingdao, 266590, China;
College of Energy and Mining Engineering, Shandong University of Science and Technology, Qingdao 266590, China;
State Key Laboratory of Coal Mine Disaster Dynamics and Control, College of Resource and Safety Engineering, Chongqing University, Chongqing 400030, China
Xin Gao: College of Energy and Mining Engineering, Shandong University of Science and Technology, Qingdao 266590, China
Kun Long: State Key Laboratory of Coal Mine Disaster Dynamics and Control, College of Resource and Safety Engineering, Chongqing University, Chongqing 400030, China
Peng Chen: School of Safety Engineering, North China Institute of Science & Technology, Langfang 101601, China


Abstract
Due to the low strength and high compressibility characteristics, the loess deposits tunnels are prone to large deformations and collapse. An accurate stability evaluation for loess deposits is of considerable significance in deformation control and safety work during tunnel construction. 37 groups of representative data based on real loess deposits cases were adopted to establish the stability evaluation model for the tunnel project in Yan'an, China. Physical and mechanical indices, including water content, cohesion, internal friction angle, elastic modulus, and poisson ratio are selected as index system on the stability level of loess. The data set is randomly divided into 80% as the training set and 20% as the test set. Firstly, principal component analysis (PCA) is used to convert the five index system to three linearly independent principal components X1, X2 and X3. Then, the principal components were used as input vectors for probabilistic neural network (PNN) to map the nonlinear relationship between the index system and stability level of loess. Furthermore, Leave-One-Out cross validation was applied for the training set to find the suitable smoothing factor. At last, the established model with the target smoothing factor 0.04 was applied for the test set, and a 100% prediction accuracy rate was obtained. This intelligent classification method for loess deposits can be easily conducted, which has wide potential applications in evaluating loess deposits.

Key Words
intelligent classification; loess deposits; principal component analysis; probabilistic neural network; stability evaluation

Address
Guangkun Li, Maoxin Su, Yiguo Xue, Qian Song, Daohong Qiu, Kang Fu and Peng Wang: Geotechnical and Structural Engineering Research Center, Shandong University, Ji'nan 250061, Shandong, China

Abstract
Cofferdams made of teel sheet piles are commonly utilized as support structures for excavation of sea-crossing bridge foundations. As cofferdams are often subject to tide variation, it is imperative to consider potential effects of tide on stability and serviceability of sheet piles, particularly, ultralong steel sheet piles (USSPs). In this study, a real USSP cofferdam constructed using new construction technology in Nanxi River was reported. The design of key parts of USSP cofferdam in the presence of tidal action was first introduced followed by the description of entire construction technology and associated monitoring results. Subsequently, a three-dimensional finite-element model corresponding to all construction steps was established to back-analyze measured deflection of USSPs. Finally, a series of parametric studies was carried out to investigate effects of tide level, soil parameters, support stiffness and construction sequence on lateral deflection of USSPs. Monitoring results indicate that the maximum deflection during construction occurred near the riverbed. In addition, measured stress of USSPs showed that stability of USSP cofferdam strengthened as construction stages proceeded. Moreover, the numerical back-analysis demonstrated that the USSP cofferdam fulfilled the safety requirements for construction under tidal action. The maximum deflection of USSPs subject to high tide was only 13.57 mm at a depth of -4 m. Sensitivity analyses results showed that the design of USSP cofferdam system must be further improved for construction in cohesionless soils. Furthermore, the 5th strut level before concreting played an indispensable role in controlling lateral deflection of USSPs. It was also observed that pumping out water before concreting base slab could greatly simplify and benefit construction program. On the other hand, the simplification in construction procedures could induce seepage inside the cofferdam, which additionally increased the deflection of USSPs by 10 mm on average.

Key Words
construction design; deflection monitoring; three-dimensional finite-element analysis; tidal action; ultralong steel sheet pile cofferdam

Address
Ping Li, Xinfei Sun, Junjun Chen and Jiangwei Shi: Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering,
Hohai University, Nanjing, Jiangsu 210024, China

Abstract
From the effect of bound water, this study aims to seek the potential reasons for difference of mechanical experiment results of subgrades soils. To attain the comparatively test condition of bound water, dry forming (DF) and wet forming (WF) were used in the specimen forming process before testing, series of laboratory tests, i.e., CBR tests, direct shear tests and compaction tests. The measured optimal moisture contents, maximum dry densities, CBR, cohesion c, and internal friction angle o were given contrastive analysis. Then to detect the adsorptive bound water in the subgrade soils, the thermal gravimetric and differential scanning calorimetry (TG-DSC) test were employed under different heating rates. The free water, loosely bound water and tightly bound water in soils were qualitatively and quantitatively analyzed. It was found that due to the different dehydration mechanics, the lost bound water in DF and WF process show their own characteristics. This may lead to the different mechanical properties of tested soils. The clayey particles have a great influence on the bound water adsorbed ability of subgrade soils. The more the clay content, the greater the difference of mechanical properties tested between the two forming methods. Moreover, in highway construction of southern China, the wet forming method is recommended for its higher authenticity in simulating the subgrade filed humidity.

Key Words
bound water; clayey content; differential scanning calorimetry; specimen forming; subgrade soil

Address
Le Ding and Junhui Zhang: National Engineering Laboratory of Highway Maintenance Technology, Changsha University of Science & Technology,
Section 2, No.960, Wanjiali South Road, Changsha, China
Zonghuang Den: Jiangxi Tianchi Expressway High-Tech Development Co., Ltd., Jiangxi Provincial Expressway Investment Group, Co., Ltd, No.367, Chaoyangzhou Mid-road, Nanchang, China

Abstract
The gas permeability behavior of unsaturated bentonite-based materials is of major importance for ensuring effective sealing of high-level radwaste repositories. This study investigated this by taking a sample of Granular Bentonite Material (GBM) at the end of the Engineered Barrier Emplacement (EB) experiment in the Opalinus Clay, placing it under different humidity conditions until it achieved equilibration, and testing the change in the gas permeability under loading and unloading. Environmental humidity is shown to have a significant effect on the water content, saturation, porosity and dry density of GBM and to affect its gas permeability. Higher sensitivity to confining pressure is exhibited by samples equilibrated at higher relative humidity (RH). It should be noted that for the sample at RH=98%, when the confining pressure is raised from 1 MPa to 6 MPa, gas permeability can be reduced from 10-16 m2 to 10-19 m2, which is close to the requirements of gas tightness. Due to higher water content and easier compressibility, samples equilibrated under higher RH show greater irreversibility during the loading and unloading process. The effective gas permeability of highly saturated samples can be increased by 2–3 orders of magnitude after 105C drying. In addition, cracks possibly occurred during the dehydration and drying process will become the main channel for gas migration, which will greatly affect the sealing performance of GBM.

Key Words
effective gas permeability; granular bentonite material; irreversible change; microstructure

Address
Hongyang Ni: State Key Laboratory for GeoMechanics and Deep Underground Engineering, and School of Mechanics and Civil Engineering,
China University of Mining & Technology, Xuzhou 221116, China;
Laboratoire de Méchanique de Lille (LML), and École Centrale de Lille, BP 48, F-59651 Villeneuve d'Ascq Cedex, France
Jiangfeng Liu: State Key Laboratory for GeoMechanics and Deep Underground Engineering, and School of Mechanics and Civil Engineering,
China University of Mining & Technology, Xuzhou 221116, China;
CAEA Innovation Center on Geological Disposal of High Level Radioactive Waste,
Beijing Research Institute of Uranium Geology, China
Hai Pu, Guimin Zhang and Xu Chen: State Key Laboratory for GeoMechanics and Deep Underground Engineering, and School of Mechanics and Civil Engineering,
China University of Mining & Technology, Xuzhou 221116, China
Frédéric Skoczylas: Laboratoire de Méchanique de Lille (LML), and École Centrale de Lille, BP 48, F-59651 Villeneuve d'Ascq Cedex, France

Abstract
With the advantages of high permeability and strength, pervious concrete piles can be suitable for ground improvement with high water content and low bearing capacity. By comparing the strength and permeability of pervious concrete with different aggregate sizes (3-5 mm and 4-6 mm) and porosities (20%, 25%, 30% and 35%), the recommended aggregate size (3-5 mm) and porosity (30%) can be achieved. The model tests of the pervious concrete piles in soft soil (silt and clay) foundations were conducted to evaluate the bearing characteristics, results show that, for the higher consolidation efficiency of the silty foundation, the bearing capacity of the silty foundation is 16% higher, and the pile-soil stress ratio is smaller. But when it is the ultimate load for the piles, they will penetrate into the underlying layer, which reduces the pile-soil stress ratios. With higher skin friction of the pile in the silty foundation, the pile penetration is smaller, so the decrease of the pile axial force can be less. For the difference in consolidation efficiency, the skin friction of pile in silt is more affected by the effective stress of soil, while the skin friction of pile in clay is more affected by the lateral stress. When the load reaches 4400 N, the skin friction of the pile in the silty foundation is about 35% higher than that of the clay foundation.

Key Words
bearing characteristic; clay foundation; model test; pervious concrete pile; silt foundation

Address
Jun Cai and Han Xia: School of Transportation, Southeast University, Jiulong Lake Campus, P.R. China
Guangyin Du and Changshen Sun: Zhejiang Provincial Institute of Communications Planning, Design and Research, Westlake district, P.R. China

Abstract
Water inrush from fault is one of the most severe hazards during tunnel excavation. However, the traditional evaluation methods are deficient in both quantitative evaluation and uncertainty handling. In this paper, a comprehensive methodology method combined intuitionistic fuzzy AHP with a Bayesian network for the risk assessment of water inrush from fault in the subsea tunnel was proposed. Through the intuitionistic fuzzy analytic hierarchy process to replace the traditional expert scoring method to determine the prior probability of the node in the Bayesian network. After the field data is normalized, it is classified according to the data range. Then, using obtained results into the Bayesian network, conduct a risk assessment with field data which have processed of water inrush disaster on the tunnel. Simultaneously, a sensitivity analysis technique was utilized to investigate each factor's contribution rate to determine the most critical factor affecting tunnel water inrush risk. Taking Qingdao Kiaochow Bay Tunnel as an example, by predictive analysis of fifteen fault zones, thirteen of them are consistent with the actual situation which shows that the IFAHP-Bayesian Network method is feasible and applicable. Through sensitivity analysis, it is shown that the Fissure development and Apparent resistivity are more critical comparing than other factor especially the Permeability coefficient and Fault dip. The method can provide planners and engineers with adequate decision-making support, which is vital to prevent and control tunnel water inrush.

Key Words
Bayesian network; IFAHP; risk assessment; subsea tunnel; water inrush

Address
Qian Song, Yiguo Xue, Guangkun Li, Maoxin Su, Daohong Qiu, Fanmeng Kong and Binghua Zhou: Geotechnical and Structural Engineering Research Center, Shandong University, Ji

Abstract
The main objective of this study is to present a fast and reliable approach to predict the swelling potential of clay-bearing rocks. Investigations showed that there is a good correlation between the swelling potential of a rock and its desire to absorb water due to its clay content which could be measured using the "Contact Angle" test as one of the most common ways to determine the wettability. In this test, the angle between a water drop and the flat rock surface on which it rests is measured. The present method is very fast and returns repeatable results and requires minimal sample preparation. Only having a saw-cut surface of a sample with any shape is all one needs to perform this test. The logic behind this approach is that the swelling potential of a rock is a function of its mineral content and molecular structure, which are not only distributed in the bulk of the sample but also reflected on its surface. Therefore, to evaluate swelling behavior, it is not necessary to wait for a sample to get wet all the way to its "internal structure" (which, due to the low permeability of clay-bearing rocks, is very slow and time-consuming). Instead, one can have a good sense of swelling potential by studying its surface. Parametric studies on the effect of moisture content, porosity, and surface roughness on the contact angle measurements showed that using a saw-cut oven-dried sample is a convenient way to evaluate the swelling potential by this method.

Key Words
clay-bearing materials; contact angle test; swelling strain; swelling test; wettability

Address
Mahdi Moosavi and Saleh Ghadernejad:School of Mining Engineering, The University of Tehran, Tehran, Iran


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