Stone columns are, in general, constructed in an arrangement of regular polygons like triangles and squares. From the geometry, the stone column-improved ground with a regular polygon arrangement of stone columns cannot confirm the proportionate stress distribution from the foundation to the improved ground despite symmetric loading when the shape of the foundation is axisymmetric. In addition, the response of a large soft soil area that was improved with a group of stone columns was reported in very limited cases. In this study, a three-dimensional (3D) numerical model of the whole stone column-improved soft soil is developed in FLAC3D, which considers advanced constitutive models and the anisotropic flow of pore water to study the contact stress and vertical deformation in the improved soil under a symmetrically loaded axisymmetric large foundation for triangular and radial arrangements of the stone columns. In addition to the vertical settlement and contact stress, the rate of settlement, effect of embankment height, stress concentration ratio (SCR), and lateral displacement are studied numerically using the FLAC3D explicit finite-difference package. A 3D study is performed that considers the dissimilar positions of stone columns along different diametric sections, where only a quarter of the model is developed due to symmetry. The pattern of the stone column arrangement significantly affects the response of the stone column-improved soft soil. In addition, the effect of the arrangement is more prominent in the peripheral stone columns compared with stone columns near the center. Therefore, the radial pattern is the most suitable arrangement of stone columns in soft soil under uniformly loaded axisymmetric loading.
This paper presents a new type of large-diameter multi-disc soil anchor and its cavity-forming tool. The large-diameter multi-disc soil anchor is obtained by adopting a toothed chain, centrifuging holes to form cavities, forming multiple cavities, placing a steel strand with centering support, injecting cement mortar, and curing. In order to study the uplift bearing characteristics and creep property of the large-diameter multi-plate soil anchor, the equal-diameter soil anchor was taken as the control group. The ultimate pull-out bearing capacity, vertical displacement, axial force, anchor plate bearing load, and side friction resistance were simulated and analyzed by FLAC3D 5.0 64-bit software, and the creep property test of the anchor bolt was carried out. The results show that under the same conditions, the ultimate pulling capacity of the large-diameter multi-disc soil anchor is 125% higher than that of the same-diameter soil anchor. The vertical displacement of the large-diameter multi-disc soil anchor decreases by 51.74% compared with that of the equal-diameter soil anchor when the ultimate uplift capacity is reached. The side friction resistance of the large-diameter multi-disc soil anchor is small and its growth rate is slow. When the ultimate pulling capacity is reached, the load sharing of the anchor disc accounts for 76.54% of the total load applied. The creep rate of the large-diameter multi-plate soil anchor bolt is 0.91 mm, and the creep rate of the equal-diameter soil anchor bolt is 1.69 mm. By fitting the data, it is found that the large-diameter multi-disc soil anchor provides a method to increase the anchorage force of the soil anchor, and the research on its bearing characteristics and creep property provides a theoretical basis for the application of the soil anchor.
We have proposed a methodology to assess the robustness of underground tunnels against potential failure. This involves developing vulnerability functions for various qualities of rock mass and static loading intensities. To account for these variations, we utilized a Monte Carlo Simulation (MCS) technique coupled with the finite difference code FLAC3D, to conduct two thousand seven hundred numerical simulations of a horseshoe tunnel located within a rock mass with different geological strength index system (GSIs) and subjected to different states of static loading. To quantify the severity of damage within the rock mass, we selected one stress-based (brittle shear ratio (BSR)) and one strain-based failure criterion (plastic damage index (PDI)). Based on these criteria, we then developed fragility curves. Additionally, we used mathematical approximation techniques to produce vulnerability functions that relate the probabilities of various damage states to loading intensities for different quality classes of blocky rock mass. The results indicated that the fragility curves we obtained could accurately depict the evolution of the inner and outer shell damage around the tunnel. Therefore, we have provided engineers with a tool that can predict levels of damages associated with different failure mechanisms based on variations in rock mass quality and in situ stress state. Our method is a numerically developed, multi-variate approach that can aid engineers in making informed decisions about the robustness of underground tunnels. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).
The advancement of massive construction in urban subway projects contributes to the increased use of the artificial ground freezing (AGF) method in the construction of cross passages due to its reliability and environmental friendliness. However, the uplift or subsidence of the ground surface induced by the frost heave and thawing settlement of the soil can be a problem for existing buildings, and the current design method places way too much emphasis on the strength requirement of the freezing wall. In this study, FLAC3D was employed to develop a series of state-of-the-art numerical models of the construction of a typical subway cross passage by the AGF method, utilizing freezing walls with different thicknesses. The results of this study can be used to examine the ground deformation arising from the AGF method and the influence of the thickness of the freezing wall on the AGF method.
Owing to the high strength and abrasive characteristics of cobble-boulders, cutters are easily worn and damaged during shield tunneling, making construction inefficient. In the present work, the stress on the ripper and scraper on the cutterhead was analyzed by the PFC3D-FLAC3D coupling model of shield tunneling to get insight into the performance of the cutterhead for cutting underground cobble and boulders. The numerical calculation results revealed that the increase in trajectory radius leads to a rising stress on the cutters, and the stress on the front cutting surface is greater than that on the back of the cutters. Moreover, the correlation between cutter wear and stress is revealed based on field measurement data. The distribution of the cutter stress is consistent with the cutter wear and breakage characteristics in actual construction, in which more extensive cutter stress is exhibited, extreme cutter wear appears, and more cutter breakage occurs. Finally, the relationship between the cutterhead opening area's layout and cutter wear distribution was investigated, indicating that the cutter wear extent is the most severe in the region where the radial opening ratio dropped sharply.
随着地下空间的开发，必要情况下施工建设需要在相对寒冷的环境下进行，此时基坑建设可能会出现越冬情况，为研究越冬基坑的支护结构水平位移及桩侧冻胀力，运用三维快速拉格朗日数值分析软件（FLAC3D），在悬臂桩支护形式下，对不同桩体直径及插入比的越冬深基坑支护结构桩侧冻胀力及水平位移进行分析。分析得出，在冻结状态下，悬臂桩支护基坑水平位移峰值是常温时的4.5倍，桩侧冻胀力峰值增加了2倍，冻胀作用对基坑变形和受力影响非常显著；随着桩径增加，桩侧冻胀力随之迅速增加而水平位移峰值不断减小；桩体水平位移及桩侧冻胀力受插入比的变化影响很小。该成果可为以悬臂桩为主的排桩支护形式在越冬深基坑工程中的设计、施工提供理论参考。
随着地下空间的开发，必要情况下施工建设需要在相对寒冷的环境下进行，此时基坑建设可能会出现越冬情况，为研究越冬基坑的支护结构水平位移及桩侧冻胀力，运用三维快速拉格朗日数值分析软件（FLAC3D），在悬臂桩支护形式下，对不同桩体直径及插入比的越冬深基坑支护结构桩侧冻胀力及水平位移进行分析。分析得出，在冻结状态下，悬臂桩支护基坑水平位移峰值是常温时的4.5倍，桩侧冻胀力峰值增加了2倍，冻胀作用对基坑变形和受力影响非常显著；随着桩径增加，桩侧冻胀力随之迅速增加而水平位移峰值不断减小；桩体水平位移及桩侧冻胀力受插入比的变化影响很小。该成果可为以悬臂桩为主的排桩支护形式在越冬深基坑工程中的设计、施工提供理论参考。
随着地下空间的开发，必要情况下施工建设需要在相对寒冷的环境下进行，此时基坑建设可能会出现越冬情况，为研究越冬基坑的支护结构水平位移及桩侧冻胀力，运用三维快速拉格朗日数值分析软件（FLAC3D），在悬臂桩支护形式下，对不同桩体直径及插入比的越冬深基坑支护结构桩侧冻胀力及水平位移进行分析。分析得出，在冻结状态下，悬臂桩支护基坑水平位移峰值是常温时的4.5倍，桩侧冻胀力峰值增加了2倍，冻胀作用对基坑变形和受力影响非常显著；随着桩径增加，桩侧冻胀力随之迅速增加而水平位移峰值不断减小；桩体水平位移及桩侧冻胀力受插入比的变化影响很小。该成果可为以悬臂桩为主的排桩支护形式在越冬深基坑工程中的设计、施工提供理论参考。
为了研究季节性冻土地区隧道明洞边坡支护在应力场、温度场和水分场耦合作用下的冻融变形规律,文章利用FLAC3D有限差分软件对蛟西隧道明洞边坡喷锚支护破坏现象进行数值分析。研究结果表明:温度场变化、开挖坡度大小是影响边坡稳定性的重要因素;温度不同,边坡支护变形量不同,但变形规律相同;冻胀融沉引起边坡各点的变形量在坡肩处最大,在软弱岩土层附近变形量波动较大;满足边坡冻融时稳定性且符合经济合理性的最佳边坡开挖坡度为1∶1。研究结果与实测结果一致,表明了失稳评价模型能准确、科学地预测明洞边坡支护的安全状态,于工程施工具有较好的理论指导。
为了研究季节冻土路基温度场及变形场的动态变化规律,利用FLAC3D软件及内嵌的FISH语言,编写了路基计算参数随温度变化的程序,对兰新二线典型冻土路基的冻融变形问题进行了更准确的模拟分析。通过建立路基计算模型,对路基温度场与实测资料进行了对比分析,验证了模拟方法的有效性与可靠性;通过模拟不同高度的路基在冬、夏季时的冻融变形情况,得出路基高度H是影响冻土地区路基热稳定性的重要因素。研究表明:路基高度H不同,路基上各点的冻融变形随时间的变化规律相同,而变形量均不相同;冻融引起的路基表面和内部沿深度方向各点的变形差别很大;最后通过比较得到既符合路基稳定性又符合工程经济性的最佳路基高度,对冻土路基的设计和施工有一定指导意义。