Effect of Geometric Parameters and Construction Sequence on Ground Settlement of Offset Arrangement Twin Tunnels

A parametric study that examines the ground surface settlement due to the excavation of shallow offset arrangement twin tunnels is presented. Offset arrangement tunnels are those that run parallel to each other, but at different elevations. The study focuses on the influence of both the construction sequence and various geometric parameters on the induced soil settlement. A series of three-dimensional finite element analyses was carried out to investigate the settlement behavior and interactions between offset arrangement twin tunnels excavated in clay using a simplified mechanized excavation method. Analyses were carried out for three cover-to-diameter (C/D) ratios, three possible construction sequences, five angular relative positions, and five angular spacings. In addition, settlement data were also investigated by varying horizontal and vertical spacings while keeping the angular spacing constant. The total settlement of the excavated twin tunnels and the settlement induced solely by the new second tunnel are both presented, and special attention was paid to identifying the dominant geometric parameters. The observed data trends from this study are generally consistent with the limited data available in the literature. This study confirmed a few perceived behaviors. First, angular relative position better describes the settlement behavior in comparison to angular spacing. Second, the effect of the vertical distance is noticeably more significant than that of the horizontal distance between the two tunnels. Third, excavation of the lower tunnel at first induces higher total ground settlement than when the upper tunnel is excavated first or when both tunnels are excavated concurrently. Fourth, settlement due to the construction of the newer tunnel decreases with the increase in the cover depth. In addition, two design charts have been proposed to calculate the settlement induced from a new second tunnel excavation and the eccentricity of the maximum total settlement relative to the center of the new tunnel.

Settlement Behavior Evaluation of Soft-Clay Layer Reinforced with Sand Piles

In this study, the performances of the sand piles in Istanbul's Bağcılar and Zeytinburnu districts has been analyzed using Finite Element Method (FEM). Single and group (triple) piles with various length/diameter ratios (L/D) were placed in the water-saturated soft clay soil. Sand piles were modeled in various L/D ratios (10, 5.71, and 8.57). The distance between the piles was chosen as 2 meters and the group effect was also investigated. A uniformly distributed load of 162 kN/m2 is placed on the ground. In addition, the soil was modeled with the Soft-Soil soil model, the hardening soil model for the infill part, and the sand piles with the Mohr-Coulomb soil model. According to the results , the settlement of the soil decreases by 52.8% for a single pile with an L/D ratio of 8.57. However, the best L/D ratio for triple piles was found to be 5.71. In this case, the settlement decreases by 52.8% compared to the pileless situation. Finally it was concluded that the model with the L/D ratio of 8.57 reduced settlement in the best and the most efficient way.

Structures and Settlement Control of Yujingshan High-Speed Railway Tunnel Crossing Massive Rockfill in a Giant Karst Cave

The Yujingshan high-speed railway tunnel crosses a giant cavern system with a 108 × 104 m3 volume chamber and an 18 km long underground river. The massive project, which lasted three years, was eventually awarded the “Overcoming the Challenges” award by the International Tunneling and Underground Space Association (ITA) in 2020. However, since the cave chamber was filled with large-scale rockfill, structural settlement is a non-negligible problem. This paper presents the unique structures of a bridge supporting railway tracks wrapped by tunnel lining and the settlement control of the Yujingshan tunnel crossing massive rockfill in the giant cave. The geological characteristics and design considerations are systematically introduced. A three-dimensional coupling discrete element method (DEM) and finite difference method (FDM) numerical model and 13 months of long-term settlement monitoring were conducted to evaluate the settlement behavior. The results indicate that the morphology of cavern and internal deposits caused the whole rockfill to migrate to the lower left. The tunnel structure consequently developed a significant inclined settlement. The continuous construction load would increase the settlement value by 31.4%. The bottom reinforcement of steel-pipe pile with grouting could effectively inhibit settlement and differential settlement. Considering the simulation results, the tunnel bottom had greater settlement than the limit standard for high-speed railway embankment, which means this special structure form is reasonable for operation. Meanwhile, the monitoring results show that the tunnel bottom settlement in D3K279+891~D3K279+947 had not performed an apparent convergence trend after 13 months. Further structural monitoring and compensation grouting should be actively considered for operation maintenance.

Why People Settle in Shrinking Communities: A Unified Framework of Psychological, Environmental, and Cognitive Factors

The interpretation of settlement behavior in shrinking areas can provide insights into sustainability strategies in shrinking communities. However, the choice to settle in areas undergoing shrinkage is hard to interpret when considering residents as rational decisionmakers. To attain a deeper understanding of this decision-making process, a framework of residential decision making (RDM) considering a subjective environmental evaluation dimension, psychological dimension, and cognitive dimension is proposed. This process was further validated by conducting a questionnaire survey in Japanese communities. The results of the structural equation modeling reveal that the RDM framework proposed is applicable to RDM in shrinking communities. By considering geographical differences, we further found that residents in suburban communities tend to consider overall satisfaction with their location when deciding whether to stay, whereas residents in mountainous communities value emotional satisfaction factors such as place attachment when considering continuous residence. Different residential preferences contributing to the formation of RDM factors were also revealed between communities. The results of this study imply that sustainable development strategies to assist shrinking communities should be tailored to their geographical characteristics. Further, a regional design that can enrich residential experiences and neighborhood communication is important for promoting population settlement.

The Behavior of Strip Footing Resting on Soil Strengthened with Geogrid

The soil in Iraq has a low load carrying or bearing capacity and high deflections or settlement because of the applied loads. The use of strip footing as a foundation to support different kinds of heavy structures has become necessary nowadays through solving such problems by using geogrid. This soil improvement technique is widely used all over the world. In this paper, the bearing capacity and settlements were calculated using finite elements and analytical models for strip footing resting on different kinds of soil. The study parameters are footing rigidity, the number of layers in a geogrid, the dimension of geogrid, and spacing of geogrid layers. According to the findings, the geogrid improved the bearing ability of the footing and reduced settlement. The optimum geogrid dimension was three times the footing width, and three geogrid layers were optimum. The changing in footing rigidity also affects the stress and settlement behavior.

Studies with Rheological Behavior of Composite Lithium-Based Magnetorheological Grease

Magnetorheological (MR) grease has advantages of the anti-settlement behavior and excellent sealing property compared with conventional MR materials. However, the rheological behaviors of MR effect and shear yield stress are too small to limit the further applications with MR grease. This paper proposes a composite lithium-based MR grease with boric acid-hydroxyl stearic acid to improve the rheological behaviors. Eight different samples of composite lithium-based MR grease with different ratios of mass between lithium stearate and lithium borate are prepared by the saponification method. The rheological behaviors are tested and discussed with qualitative and quantitative analysis. The experimental results show that the off-state viscosity reduces with the decrement of the ratio of mass under low shear rate which changes from 68.7 Pa·s to 16.5 Pa·s. Lithium stearate content has more effects with off-state viscosity. Based on the Herschel-Bingham model, the shear stress of composite lithium-based MR grease can be improved dramatically by adjusting the ratio of mass which is increased by 170% under the magnetic flux density of 0.2 T. Compared with single lithium-based MR grease, the maximum yield shear stress is increased by 166.7% at off-state and the maximum MR effect is also increased by 19.1%. The MR effect can reach 23,600% with a specific mass ratio of the composite MR grease. The experimental results validate that the feasibility of the performance improvement by the composite lithium-based MR grease.

Coastal Settlement Behavior Setting in Kampung Blok Empang, North Jakarta

The purpose of the study was to find out behavior setting and its elements in Kampung Blok Empang. Kampung Blok Empang which is located on the coast of North Jakarta has a port setting and is bypassed by tourist access to the Kepulauan Seribu, so it is interesting to know how the behavior setting in this village is. Data collection is done by field observation and secondary data. The approach used in this research is deductive-qualitative with the research variables in the form of behavior setting. The Behavior Setting in Kampung Blok Empang is shown by how the setting of the urban village located in the port area affects most of the relationships between physical objects and the behavior of residents in the village. The best performance of behavior setting in Kampung Blok Empang is shown in the open space because its milieu-behavior interdependency. It is shown by the repetitive behavior in this specific milieu. The spatial Pattern type is formed by the collective activity of residents and the sea condition. They were characterized by the repetitive activities within their economic and social aspects.