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Volume 28, Number 6, March25 2022

Dune sands are poorly graded collapsible soils lacking fines. This experimental study explored the technical feasibility of sustainable invigoration of fine waste materials to improve the geotechnical properties of dune sand. The fine waste considered in this study is fine marble waste. The fine waste powder was mixed with dune sand at different contents (5, 10,15, 20, 25, 50%), where the gradation, void ratio, compaction, and shear strength characteristics were assessed for each fine marble waste -dune sand blend. The geotechnical properties of the dune sand-fine marble waste mix delineated in this study reveal the enhancement in compaction and gradation characteristics of dune sand. According to the results, the binary mixture of dune sand with 20% of fine marble waste gives the highest maximum dry density and results in shear strength improvement. In addition, a numerical study is conducted for the practical application of the binary mix in the field and tested for an isolated shallow foundation. The elemental analysis of the fine marble waste confirms that the material is non-contaminated and can be employed for engineering applications. Furthermore, the numerical study elucidated that the shallow surface replacement of the site with the dune sand mixed with 20% fine marble waste gives optimal performance in terms of stress generation and settlement behavior of an isolated footing. For a sustainable mechanical performance of the fine marble waste mixed sand, an optimum dose of 20% fine marble waste is recommended, and some correlations are proposed. Thus, for improving dune sand's geotechnical characteristics, the addition of fine marble waste to the dune sand is an environment-friendly solution.

Key Words
dune sand; fine marble waste; numerical modelling; shallow foundation; shear strength

Mohsin U. Qureshi and Hajar Al-Handasi: Faculty of Engineering, Sohar University, P.O. Box 44, P.C. 311, Sohar, Oman
Zafar Mahmood: Department of Civil and Architectural Engineering, University of Buraimi, P.O. Box 890, P.C. 512, Buraimi, Oman
Qazi U. Farooq: Department of Civil Engineering, Islamic University of Madinah, Madinah, Saudi Arabia
Qadir B.I.L. Qureshi: College of Engineering and Architecture, University of Nizwa, P.O. Box 33, P.C. 616, Nizwa, Oman
Ilhan Chang: Department of Civil Systems Engineering, Ajou University, Suwon 16499, Republic of Korea

Deep soil mixing, DSM technique has been widely used to improve the engineering properties of problematic soils. Due to growing urbanization and the industrial developments, disposal of brick dust poses a big problem and causes environmental problems. This study aims to use brick dust in DSM application in order to minimize the waste in brick industry and to evaluate its effect on the improvement of the geotechnical properties. Three different percentages of cement content: (10, 15 and 20%) were used in the formation of soil-cement mixture. Unlike the other studies in the literature, various percentages of waste brick dust: (10, 20 and 30%) were used as partial replacement of cement in soil-cement mixture. The results indicated that addition of waste brick dust into soil-cement mixture had positive effect on the inherent strength and stiffness of loose sand. Cement replaced by 20% of brick dust gave the best results and reduced the final setting time of cement and resulted in an increase in unconfined compressive strength, modulus of elasticity and resilient modulus of sand mixed with cement and brick dust. The findings were also supported by the microscopic images of the specimens with different percentages of waste brick dust and it was observed that waste brick dust caused an increase in the interlocking between the particles and resulted in an increase in soil strength. Using waste brick dust as a replacement material seems to be promising for improving the geotechnical properties of loose sand.

Key Words
cohesion-less soil; construction waste material; deep soil mixing; ground improvement; laboratory analysis; recycling & reuse of materials; reinforced soil

Mahdi Z. Alnunu and Zalihe Nalbantoglu: Department of Civil Engineering, Engineering Faculty, Eastern Mediterranean University,Famagusta, North Cyprus, via Mersin 10 Turkey

Water inrush may occur during seaside urban tunnel excavation. Various factors affect the water inrush, and the water inrush mechanism is complex. In this study, nine evaluation indices having potential effects on water inrush were analysed. Specifically, the geographic and geomorphic conditions, unfavourable geology, distance from the tunnel to sea, strength of the surrounding rock, groundwater level, tidal action, cyclical footage, grouting pressure, and grouting reinforced region were analysed. Furthermore, a two-step interval risk assessment method for water inrush management during seaside urban tunnel excavation was developed by a multi-index system and interval risk assessment comprised of an interval analytic hierarchy process, fuzzy comprehensive evaluation, and relative superiority analysis. The novel assessment method was applied to the Haicang Tunnel successfully. A preliminary interval risk assessment method for water inrush was performed based on engineering geological conditions. As a result, the risk level fell into a risk level IV, which represents a section with high risk. Subsequently, a secondary interval risk assessment method was performed based on engineering geological conditions and construction conditions. The risk level of water inrush is reduced to a risk level II. The results agreed with the current tunnel situation, which verified the reliability of this approach.

Key Words
construction management; seaside urban tunnel; two-step interval assessment; water inrush

Binghua Zhou, Yiguo Xue, Zhiqiang Li, Maoxin Su, Daohong Qiu and Fanmeng Kong: Geotechnical and Structural Engineering Research Center, Shandong University, Ji'nan 250061, Shandong, China
Haidong Gao: China Railway 18th Bureau Group Co. Ltd., 072750, Tianjin, China

The monopile-friction wheel hybrid foundation is an innovative solution for offshore structures which are mainly subjected to large lateral eccentric load induced by winds, waves, and currents during their service life. This paper presents an extensive numerical analysis to investigate the lateral load and moment bearing performances of hybrid foundation, considering various potential influencing factors in sand-overlaying-clay soil deposits, with the complex lateral loads being simplified into a resultant lateral load acting at a certain height above the mudline. Finite element models are generated and validated against experimental data where very good agreements are obtained. The failure mechanisms of hybrid foundations under lateral loading are illustrated to demonstrate the effect of the friction wheel in the hybrid system. Parametric study shows that the load bearing performances of the hybrid foundation is significantly dependent of wheel diameter, pile embedment depth, internal friction angle of sand, loading eccentricity (distance from the load application point to the ground level), and the thickness of upper sandy layer. Simplified empirical formulae is proposed based on the numerical results to predict the corresponding lateral load and moment bearing capacities of the hybrid foundation for design application.

Key Words
failure mechanism; FEM; lateral load and moment bearing capacities; monopile-friction wheel hybrid foundation; offshore wind turbine

Xinjun Zou and Yikang Wang: College of Civil Engineering, Key Laboratory of Building Safety and Energy
Efficiency of Ministry of Education, Hunan University, Changsha, Hunan 410082, China
Mi Zhou: School of Marine Science and Engineering, State key laboratory of subtropical building science,
South China University of Technology, 381 Wushan Rd, Guangzhou, Guangdong 510640, China
Xihong Zhang: School of Civil and Mechanical Engineering, Curtin University, Kent Street, Bentley 6102, Australia

Tendon reinforced cemented soil is applied extensively in foundation stabilisation and improvement, especially in areas with soft clay. To solve the deterioration problem led by steel corrosion, the glass fiber-reinforced polymer (GFRP) tendon is introduced to substitute the traditional steel tendon. The interface bond strength between the cemented soil matrix and GFRP tendon demonstrates the outstanding mechanical property of this composite. However, the lack of research between the influence factors and bond strength hinders the application. To evaluate these factors, back propagation neural network (BPNN) is applied to predict the relationship between them and bond strength. Since adjusting BPNN parameters is time-consuming and laborious, the particle swarm optimisation (PSO) algorithm is proposed. This study evaluated the influence of water content, cement content, curing time, and slip distance on the bond performance of GFRP tendon-reinforced cemented soils (GTRCS). The results showed that the ultimate and residual bond strengths were both in positive proportion to cement content and negative to water content. The sample cured for 28 days with 30% water content and 50% cement content had the largest ultimate strength (3879.40 kPa). The PSO-BPNN model was tuned with 3 neurons in the input layer, 10 in the hidden layer, and 1 in the output layer. It showed outstanding performance on a large database comprising 405 testing results. Its higher correlation coefficient (0.908) and lower root-mean-square error (239.11 kPa) were obtained compared to multiple linear regression (MLR) and logistic regression (LR). In addition, a sensitivity analysis was applied to acquire the ranking of the input variables. The results illustrated that the cement content performed the strongest influence on bond strength, followed by the water content and slip displacement.

Key Words
back propagation neural network; cemented soil; element pullout test; glass fibre reinforced polymer reinforcement; interface bond strength; machine learning; particle swarm optimisation

Genbao Zhang: College of Civil Engineering, Hunan City University, Yiyang, Hunan 413000, PRC;
Hunan Engineering Research Center of Structural Safety and Disaster Prevention for Urban Underground Infrastructure,
Yiyang, Hunan 413000, PRC
Changfu Chen: Key Laboratory of Building Safety and Energy Efficiency of the Ministry of Education, Hunan University,
Changsha, Hunan 410082, PRC;
College of Civil Engineering, Hunan University, Changsha, Hunan 410082, PRC
Yuhao Zhang: School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052, Australia
Hongchao Zhao: School of Geology and Mining Engineering, Xinjiang University, Urumchi 830000, China
Yufei Wang: Institute for Smart City of Chongqing University in Liyang, Chongqing University, Jiangsu, 213300, China
Xiangyu Wang: School of Design and Built Environment, Curtin University, Perth, WA 6102, Australia

A study of the evolution of overburden fractures under the solid-fluid coupling state was conducted based on the geological and mining characteristics of the coal seam depth, weak strata cementation, and high-intensity mining in the mining areas of West China. These mining characteristics are key to achieving water conservation during mining or establishing groundwater reservoirs in coal mines. Based on the engineering background of the Daliuta Coal Mine, a non-hydrophilic simulation material suitable for simulating the weakly cemented rock masses in this area was developed, and a physical simulation test was carried out using a water-sand gushing test system. The study explored the spatial distribution and dynamic evolution of the fractured zone in the mining overburden under the coupling of stress and seepage. The experimental results show that the mining overburden can be vertically divided into the overall migration zone, the fracture extension zone and the collapse zone; additionally, in the horizontal direction, the mining overburden can be divided into the primary fracture zone, periodic fracture zone, and stop-fracture zone. The scope of groundwater flow in the overburden gradually expands with the mining of coal seams. When a stable water inrush channel is formed, other areas no longer generate new channels, and the unstable water inrush channels gradually close. Finally, the primary fracture area becomes the main water inrush channel for coal mines. The numerical simulation results indicate that the overlying rock breaking above the middle of the mined-out area allows the formation of the water-conducting channel. The water body will flow into the fracture extension zone with the shortest path, resulting in the occurrence of water bursting accidents in the mining face. The experimental research results provide a theoretical basis for the implementation of water conservation mining or the establishment of groundwater reservoirs in western mining areas, and this theoretical basis has considerable application and promotion value.

Key Words
mining disturbance; solid-fluid coupling; spatial fracture of mining overlying strata; water bursting law; weakly cemented strata

Yangyang Li and Shichuan Zhang: State Key Laboratory of Water Resource Protection and Utilization in Coal Mining, Beijing, 102209, China;
State Key Laboratory of Mining Disaster Prevention and Control, Shandong University of Science and Technology, Qingdao,Shandong Province, 266590, China
Yingming Yang: State Key Laboratory of Water Resource Protection and Utilization in Coal Mining, Beijing, 102209, China
Hairui Chen: Shaanxi Zhengtong Coal Industry Co., Ltd, Xianyang, Shaanxi Province, 713600, China
Zongkai Li and Qiang Ma: Lin Yi. Shandong Energy Mining Group Co., Ltd, Linyi, Shandong Province, 276017, China

The standard penetration test (SPT) obtaining the N value of the number of blows has been widely used in various subsurface conditions, including in weathered soil and rock on fresh bedrock, in geotechnical studies pertaining to the design of foundations and earth structures. This study examined the applicability of SPTs terminated conventionally after 50 blows for a penetration of less than 30 cm, particularly in weathered strata, at four sites in Korea. The N values obtained during practical SPTs are typically extrapolated linearly at 30 cm penetration, despite the possibility of a nonlinear relationship between blow counts and penetration. Such nonlinearity in weathered strata has been verified by performing special SPTs ensuring 30 cm penetration. To quantify the nonlinearity in dense strata, we conducted statistical regression analyses comparing the differences (DN) between the N values measured by the special SPTs and those extrapolated using the practical approach with the differences (DP) between the 30 cm penetration and the penetration during 50 blows. Bi-linear relationship models between DN and DP were subsequently proposed for determining the N values at 30 cm penetration in weathered strata. The N values reflecting nonlinearity could be determined from the linearly extrapolated N values by adding a modeled DN value.

Key Words
blow counts; geotechnical design; N value; standard penetration test; weathered strata

Chang-Guk Sun, Hyung-Ik Cho, Han-Saem Kim and Moon-Gyo Lee: Earthquake Research Center, Korea Institute of Geoscience and Mineral Resources,
124 Gwahak-ro, Yuseong-gu, Daejeon 34132, Republic of Korea

Loess soils are unsaturated and widely distributed in the northwest zone in China. Many steep slope of unsaturated are observed are observed to be naturally stable. However, a low factor of safety (FoS) for these slopes would be computed from the slope stability analysis following local code practices. It seems that the analyzed results following the local code practices do not agree with the real condition as observed in the field. It is commonly known that soil suction plays an important role in slope stability due to a higher shear strength of the unsaturated soil as compared with that of the saturated soil. In this paper, it is observed that the computed FoS can also be affected by unsaturated unit weight of the soil. However, the effect of unsaturated unit weight of the soil on the slope stability is commonly ignored in engineering practice. Therefore, both the effects of shear strength and unit weight of the unsaturated soil on the computed FoS of unsaturated soil slope are investigated in this study. It is observed that the unsaturated unit weight of soil on the computed FoS increases with increase in slope angle. It is also observed that the effects of the unsaturated shear strength and unsaturated unit weight on the computed FoS are more significant than the effect of 3D analyses compared to the 2D analyses on the FoS.

Key Words
shear strength; slope stability; soil-water characteristic curve; unit weight; unsaturated soil

Qian Zhai, Gang Tian and Guoliang Dai: Key Laboratory of Concrete and Prestressed Concrete Structures of Ministry of Education, Bridge Engineering Research Center of Southeast University, Southeast University, 2 Sipailou, Nanjing 210096, Jiangsu, P.R. China
Weimin Ye: Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education, Tongji University,
Sipinglu 1239, Shanghai 200092, P.R. China
Harianto Rahardjo: School of Civil and Environmental Engineering, Nanyang Technological University,
Block N1, Nanyang Ave., Singapore 639798, Singapore
Shijun Wang: Economy & Technology Research Institute, Gansu Electric Power Corporation, State Grid, Lanzhou 730050, Gansu, P.R. China

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