Accurately capturing the seismic response of underground structures subjected to obliquely incident seismic waves, particularly when the angle of incidence surpasses the critical value, remains a challenging task in earthquake engineering. To address this gap, this paper presents a three-dimensional (3D) nonlinear seismic analysis of subway stations embedded in a layered site, specifically in response to obliquely incident shear (SV) waves at arbitrary angles. An innovative procedure, termed the coupled dynamic stiffness matrix-finite element method (DSM-FEM), is introduced to enable seismic input by transforming responses induced by arbitrarily incoming SV waves into equivalent nodal loads. To accurately simulate wave propagation within the site, a viscous-spring artificial boundary is utilized, while a nonlinear generalized Masing model that incorporates modified damping is employed. Using the Daikai subway station as a benchmark, the research examines the effects of varying oblique incident angles on the structural response, taking into account dynamic soil-structure interaction. The results reveal that the maximum response, including peak deformation, internal forces, Mises stress, occurs when the incident angle approaches the critical value. Beyond this critical angle, the seismic response notably diminishes. Additionally, the influence of horizontal incident angles is found to be noticeable, leading to variations in deformation patterns and internal forces across different structural components. Specifically, it has been observed that the drift ratio, displacement, shear force, acceleration, and Mises stress exhibit a decreasing trend as the horizontal incident angles increase. These findings highlight the significance of considering non-vertical input ground motion in seismic analysis, and offer valuable insights for the structural design and safety evaluation of underground structures.

Cement displays notable shortcomings in deep soil mixing column (DSM) applications,including columnforming failure in soft soil with a high water content and adverse effects on the environment. In this paper, a curing agent named FHC is introduced, specifically designed for soft soil with high moisture content and composed of GGBS, cement, fly ash, and sodium silicate. FHC was used for laboratory solidification treatment of soft clay with a water content of 80 %. The strength and deformation characteristics of FHCS were studied, and the solidification mechanism was analyzed. The findings show that the 7-day strength of FHCS reached 77 % of its 28-day strength, exhibiting notable early strength characteristics. The alkaline environment created by sodium silicate leads to a significant long-term increase in the strength of FHCS. Fitting a power function to strength, FHC content, and curing age allows for accurate prediction of FHCS strength. The failure strain (epsilon(f)) of FHCS slightly increases with the increase of FHC content, exhibiting pronounced brittleness. The deformation modulus (E-50) of FHCS increases with both the FHC content and age, satisfies with strength as: E-50 = (14 similar to 51)q(u). The quantity of gelling products in FHCS increases with increasing FHC content and age, during which soil particles are progressively enveloped, pores in the soil are filled, and the cross- becomes more flat, leading to a stable and dense structure and subsequent strength enhancement.

Deep soil mixing (DSM) is an established ground improvement technique employed in civil projects. Despite the superiority of field tests for understanding this technique, their high cost has directed researchers' focus on laboratory tests, resulting in limited attention given to operational factors. Consequently, in current research, a small-scale DSM setup was developed to investigate the influence of operational factors such as mixing time and execution procedure on strength and deformation characteristics of laboratory-scale DSM columns. For the installation of DSM columns, mixing times of 130, 190 and 250 seconds were used, together with normal and zigzag execution procedures, cement dosages (alpha) of 300, 400 and 500 kg/m(3), and total water-to-cement (W-total/C) ratios of 2.5, 3.0 and 3.5. Laboratory samples were also prepared using the same alpha values and (W-total/C) ratios for comparison with DSM columns. The sand bed was prepared with 5 % and 30 % moisture contents. Experimental observations showed that saturating the sand bed enhances the mixing quality by preventing slurry water infiltration into the soil surrounding the DSM columns. Results indicated that increasing mixing time and adopting zigzag execution procedure improved mixing quality, unconfined compressive strength (UCS), secant modulus (E-50), and strain at maximum stress (epsilon(Maximum Stress)), whilst reducing strength variability. Moreover, the outcomes showed that UCS and E-50 of samples have a direct and inverse relationship with alpha and (W-total/C), respectively, and that the nature of these relationships, not their magnitude, were not affected by mixing time and execution procedure. Additionally, findings indicated that the failure mode of DSM samples was influenced by operational factors, whereas (E-50/UCS) ratio was not.

This study focused on applying numerical simulations to assess damaged areas caused by debris flows, employing the LS-RAPID program while emphasizing the importance of terrain information. Terrain information used in the numerical simulation included a 1:5000 digital terrain map and a digital surface model using an unmanned aerial vehicle. Quantification of the amount of soil that collapsed from the road embankment slope, which is the source of the debris flow, facilitated the computation of the debris flow that closely resembled real-world conditions. In particular, incorporating the high-resolution digital surface model (DSM) with 3-cm topographic information resulted in an interpretation of the actual soil flow damage range that is similar to actual observations of the digital elevation model (DEM), which had 1-m grid topographic information. This difference arises from DSM as it reflects the information of low hills downstream. The range of damage changed as the direction of the debris flow changed because of the low hill. Many variables need adjustment for the accuracy of debris flow numerical simulation. However, the direction and range of flow vary greatly depending on topographic information, highlighting the necessity of applying high-resolution terrain information. The results of debris flow simulations with high-resolution terrain information are expected to improve accuracy and help prepare risk or damage maps.

The recent construction of an underground mass rapid transit (MRT) station in Singapore involved 21 m deep excavations within underconsolidated marine clay. The lateral earth support system comprised 1 m thick diaphragm walls socketed into the underlying Old Alluvium and 4 levels of preloaded cross-lot struts. Deep soil mixing (DSM) and jet grouting piles (JGP) were used to improve up to 15 m thickness of the marine clay formation. Field monitoring data showed that these ground improvement processes caused large outward deflections of the diaphragm wall panels at some locations prior to the excavation and may have caused yielding within the wall panels. In this paper, the impacts of these prior wall deformations on the subsequent performance of the excavation support system are investigated. The measured performance at two indicative cross sections is compared with results from simplified 2D finite element analyses. The analyses simulate the effects of ground improvement through prescribed boundary pressures and represent the yielding of the diaphragm wall panels through zones of reduced bending stiffness. We show that large outward wall deflections and curvature observed during jet grouting at one contribute to higher inward wall movements and strut loads measured during excavation, while smaller movements (and curvature) prior to excavation at a second similar cross cause negligible change in the performance of the temporary earth retaining system. The results highlight (1) the importance of controlling ground movements associated with ground modification processes such as jet grouting, (2) the uncertainties in estimating mechanical properties for the improved soil mass, and (3) the need to improve the representation of non-linear, flexural properties (M-kappa) of reinforced concrete diaphragm panels.