This study investigates the liquefaction characteristics of deep soil layers and their subsequent effects on the seismic response of subway station structures, utilizing shaking table tests and inputting seismic waves of varying principal frequencies. Macroscopically, the liquefaction of deep soil strata does not result in surface manifestations such as water spraying and sand bubbling. However, it still induces cracking and damage to the soil surrounding the structure. Analyzing from the perspective of the pore pressure ratio reveals that the ratio under free-field conditions is significantly lower than under structural conditions. Additionally, the pore pressure ratio caused by the Beijing Hotel wave is greater, followed by the Beijing artificial wave, while the Ming Shan wave results in the smallest ratio. In terms of the station structure, the structural acceleration and tensile strain increment induced by the Beijing Hotel wave are the most significant, followed by the Beijing artificial wave, with the least effect from the Ming Shan wave. This indicates that the liquefaction behavior of deep soil layers is primarily influenced by the overlying load and the frequency characteristics of seismic waves. The construction of subway stations reduces the overlying loads on soil layers, increasing the likelihood of soil layer liquefaction. Meanwhile, a lower main frequency of the seismic wave results in a higher degree of liquefaction in the deep soil layers. The seismic response of the station structure is contingent on the frequency characteristics of the seismic wave. The lower the primary frequency of the seismic wave, the higher the seismic response of the station structure. Furthermore, the liquefaction behavior of the deep soil layers also impacts the seismic response of the station structure, particularly the tensile strain response of the top and bottom slabs of the station structure.

Soil liquefaction is a significant cause of damage to buildings and structures during earthquakes, with several hazards, including ground failure, lateral spreading, soil oscillation, sand boiling, loss of bearing capacity, and settlement. Various soil improvement techniques aim to enhance the mechanical properties of soil, increasing bearing capacity, reducing volumetric deformations, and providing predictable soil behavior. This study examines the effectiveness of deep soil mixing (DSM) columns in reducing liquefaction hazards beneath raft foundations using a three-dimensional finite element method in the Midas GTS NX environment. The influence of DSM column (individual and wall) arrangements, diameter, height, and area improvement ratio on the foundation in reducing liquefaction potential and specifically excesss pore water pressure has been studied. The lambda\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\lambda$$\end{document} parameter, defined as the ratio of pore water pressure in the improved state to the unimproved state, is introduced to express the results better. The study finds that increasing the percentage of area improvement using DSM columns reduces the excess pore water ratio, and the individual column arrangement (ICA) is more effective than the wall column arrangement (WCA). The excess pore water pressure is primarily influenced by the area improvement ratio factor, as evidenced by the continued reduction of the excess pore water pressure ratio with increasing area improvement ratio in both column arrangements.

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.

Due to its inherent advantages, shield tunnelling has become the primary construction method for urban tunnels, such as high-speed railway and metro tunnels. However, there are numerous technical challenges to shield tunnelling in complex geological conditions. Under the disturbance induced by shield tunnelling, sandy pebble soil is highly susceptible to ground loss and disturbance, which may subsequently lead to the risk of surface collapse. In this paper, large-diameter slurry shield tunnelling in sandy pebble soil is the engineering background. A combination of field monitoring and numerical simulation is employed to analyze tunnelling parameters, surface settlement, and deep soil horizontal displacement. The patterns of ground disturbance induced by shield tunnelling in sandy pebble soil are explored. The findings reveal that slurry pressure, shield thrust, and cutterhead torque exhibit a strong correlation during shield tunnelling. In silty clay sections, surface settlement values fluctuate significantly, while in sandy pebble soil, the settlement remains relatively stable. The longitudinal horizontal displacement of deep soil is significantly greater than the transverse horizontal displacement. In order to improve the surface settlement troughs obtained by numerical simulation, a cross-anisotropic constitutive model is used to account for the anisotropy of the soil. A sensitivity analysis of the cross-anisotropy parameter alpha was performed, revealing that as alpha increases, the maximum vertical displacement of the ground surface gradually decreases, but the rate of decrease slows down and tends to level off. Conversely, as the cross-anisotropy parameter alpha decreases, the width of the settlement trough narrows, improving the settlement trough profile.

This study investigated the physical and mechanical properties of Malaysian kaolin clay treated with cement using unconfined compression strength and Oedometer tests. The objective was to simulate the actual conditions of soil-cement column installation employing the deep soil mixing method with cement slurry over a 180-day period. Cement content varied between 5%, 10%, 15%, and 20%. To ensure homogeneous mixing and workability, water content was maintained between the liquid limit and twice the liquid limit. Results indicated that increasing cement content enhanced the unconfined shear strength and elasticity modulus of the stabilized soil while decreasing water content after curing. Consolidation tests revealed a diminishing slope of the void ratio curve with increasing cement content and curing time. This study further introduced precise correlations between the void ratio and compression characteristics of cement-stabilized clay, achieving high accuracy. Additionally, the research conclusively demonstrated a robust linear correlation (R2 = 0.99) between unconfined compressive strength and consolidation yield pressure.

This study examines the impact of incorporating sodium alginate (SA) biopolymer into soft clay using the deep soil mixing method (DSM). SA-stabilised samples were tested under high-moisture (A) and low-moisture (B) conditions to assess their mechanical properties, chemical attributes, freeze-thaw resistance, and microstructure. Results indicate that samples cured under condition A outperformed those in condition B, primarily due to enhanced biopolymer gel formation. In both conditions, increasing the SA content and curing time led to higher peak strength, stiffness, and pH. The higher SA ratio improved ductility in condition A but increased brittleness in condition B. At the 28-day mark, a 1.0% SA ratio and a pH range of 8.2-8.4 were crucial for specimen strength increase. Freeze-thaw cycles had minimal impact, with a modest reduction in compressive strength observed. Scanning electron microscopy showed face-to-face bonding between clay particles and the gel -like materials due to electrostatic attraction. After 14 days, ramifications occurred around the core structure, and after 28 days, high agglomeration structures appeared, attributed to clay particle flocculation. Energy-dispersive X-ray (EDX) analysis indicated an increase in the Si/Al ratio boosted sample strength, while X-ray diffraction (XRD) results showed no crystalline phase in SA-stabilised samples due to encapsulating clay minerals with gel -like materials. In summary, this study suggests that SA biopolymer offers an eco-friendly, sustainable option for enhancing soft clay with DSM.

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.

This paper presents a 3D finite element analysis of deep soil mixing column-supported embankments (CSEs) with a geosynthetic platform. The numerical model simulated the CSE for the expansion (approximate to 1.0 km) of the existing runway at the Salgado Filho International Airport, in the city of Porto Alegre. The numerical model using Abaqus software was calibrated by comparing numerical calculations with good quality instrumentation data. Deep Soil Mixing (DSM) columns were used to improve the soil foundation. A novel approach to modeling the geosynthetic is also presented based on the mechanical properties of this material. The load transfer mechanisms and deformation of the column-supported embankments were analyzed by means of numerical and field results. Additional aspects such as the critical height and the pattern of vertical stress distribution in the columns and embankment as well as the stress distribution in the geosynthetic reinforcement were also investigated. The numerical model reproduces the vertical stress measured by the total stress cells installed above the columns and between the columns. The numerical model shows that the soil reaction of the thick compacted layer used as a work platform reduced the arching and membrane effect in the embankment.

1. Our knowledge on the responses of permafrost ecosystems to climate warming is critical for assessing the direction and magnitude of permafrost carbon-climate feedback. However, most of the previous experiments have only been able to warm the air and surface soil, with limited effects on the permafrost temperature. Consequently, it remains challenging to realistically simulate permafrost thawing in terms of increased active layer (a layer freezing and thawing seasonally above permafrost) thickness under climate warming scenarios. 2. Here, we presented the experimental design and warming performance of a novel experiment, Simulate Warming at Mountain Permafrost (SWAMP), the first one to successfully simulate permafrost warming and the subsequent active layer deepening in a swamp meadow situated on the Tibetan Plateau. Infrared heating was employed as above-ground warming to elevate the temperature of the air and surface soil, and heating rods were inserted vertically in the soil to provide below-ground warming for transmitting heat to the deep active layer and even to permafrost deposits. 3. In 3 m diameter warmed circular plots, the air and the entire soil profile (from surface soil to 120 cm) was effectively heated, with an increase of approximately 2 degrees C in the upper 60 cm, which progressively weakened with soil depth. Warming increased soil moisture across the growing season by inducing an earlier thawing of the soil. Values varied from 1.8 +/- 1.8 to 12.3 +/- 2.3% according to the soil depth. Moreover, during the growing season, the warmed plots had greater thaw depths and a deeper active layer thickness of 12.6 +/- 0.8 cm. In addition, soil thawing duration was prolonged by the warming, ranging from 22.8 +/- 3.3 to 49.3 +/- 4.5 days depending on the soil depth. 4. The establishment of SWAMP provides a more realistic simulation of warming-induced permafrost thaw, which can then be used to explore the effect of climate warming on permafrost ecosystems and the potential permafrost carbon-climate feedback. Notably, our experiment is more advantageous for investigating how deep soil processes respond to climate warming and active layer deepening, compare with experiments which use passive warming techniques such as open top chambers (OTCs).

Effects of permafrost degradation on carbon (C) and nitrogen (N) cycling on the Qinghai-Tibetan Plateau (QTP) have rarely been analyzed. This study used a revised process-based biogeochemical model to quantify the effects in the region during the 21st century. We found that permafrost degradation would expose 0.61 +/- 0.26 (mean +/- SD) and 1.50 +/- 0.15 Pg C of soil organic carbon under the representative concentration pathway (RCP) 4.5 and the RCP 8.5, respectively. Among them, more than 20% will be decomposed, enhancing heterotrophic respiration by 8.62 +/- 4.51 (RCP 4.5) and 33.66 +/- 14.03 (RCP 8.5) Tg C/yr in 2099. Deep soil N supply due to thawed permafrost is not accessible to plants, only stimulating net primary production by 7.15 +/- 4.83 (RCP 4.5) and 24.27 +/- 9.19 (RCP 8.5) Tg C/yr in 2099. As a result, the single effect of permafrost degradation would cumulatively weaken the regional C sink by 209.44 +/- 137.49 (RCP 4.5) and 371.06 +/- 151.70 (RCP 8.5) Tg C during 2020-2099. However, when factors of climate change, CO2 increasing and permafrost degradation are all considered, the permafrost region on the QTP would be a stronger C sink in the 21st century. Permafrost degradation has a greater influence on C balance of alpine meadows than alpine steppes on the QTP. The shallower active layer, higher soil C and N stocks, and wetter environment in alpine meadows are responsible for its stronger response to permafrost degradation. This study highlights that permafrost degradation could continue to release large amounts of C to the atmosphere irrespective of potentially more nitrogen available from deep soils.