Search Results (5)

The rapid advancement of modern megapolises has led to a dearth of surface space, and, in response, engineers have begun to trial substitutes below ground level. Shafts are generally used to provide temporary access and permanent work to the subsurface for tunnelling, as well as for lifts or ventilation purposes. In urban areas, one important design issue is the prediction of the excavation-induced displacements by open caisson shaft construction. Settlements and ground movements associated with open caisson shafts are influenced by the choice of construction method, soil composition, and excavation geometry. Compared with other geotechnical construction events, for instance, tunnelling, the literature relating to the ground deformations induced from open caisson shafts are comparatively limited. This review offers an evaluation of several case studies that utilize experimental and computational modeling techniques to provide clearer insights into earth pressure distribution and induced surface and subsurface soil displacements, as well as the associated ground deformations during open caisson shaft construction. The modeling test results are compared to the state of the practice ground deformation prediction theories and measured results from field monitoring data. Findings indicate that the lateral earth pressure distribution aligns closely with the theoretical predictions based on Terzaghi’s and Berezantzev’s models, and lateral earth pressure diminishes gradually until the onset of active wall displacement. Current modeling techniques generally fail to properly represent in situ stress states and large-scale complexities, emphasizing the need for hybrid approaches that combine physical and numerical methodologies. In future studies, modern approaches, including artificial intelligence (AI) monitoring (e.g., PINNs, ACPP), multi-field coupling models (e.g., THMC), and transparent soil testing, hold profound potential for real-time prediction, optimization, and visualization of soil deformation. Numerical–physical coupling tests will integrate theory and practice. Improving prediction reliability in complicated soil conditions such as composite and heterogenous strata using different modeling techniques is still unclear, and further investigation is therefore needed. Full article

Karst areas exhibit intricate geological attributes, and the geological and environmental issues caused by urban development cannot be ignored, especially the issue of karst surface collapses. In this study, we developed two analytical methods and analyzed the stability of the overburden stratum of 3D spherical karst caves with surface load, vacuum absorption erosion force, and groundwater table considerations. The first analytical method is based on the improved Terzaghi theory, while the second analytical method is based on the upper limit analysis. A case study was conducted in Wuhan, China. The results from both analytical methods indicated a potential susceptibility to collapse, suggesting the excellent accuracy of these two methods. The results were also compared with the numerical solutions from previous studies. Notably, the accuracy of the upper limit analysis was inversely proportional to the depth ratio, while the results obtained through the improved Terzaghi theory were consistent with those of the numerical solutions, particularly under conditions of relatively high depth ratios. This study examined various facets, including the development of karst caves, soil shear strength, groundwater table fluctuations, and boundary failure angles. Furthermore, we explored the effects of geometric and geotechnical parameters on the stability of karst caves. Full article

In order to solve the problem that the hole-forming rate of boreholes is low and it is difficult to reach the designed length when supporting a long pipe shed in loose stratum in a shallow buried section of a long-span tunnel, it is necessary to pre-reinforce the loose stratum in order to improve the strength and integrity of the surrounding rock. Relying on the grouting project of the shallow buried section at the exit of Botanggou tunnel, it is assumed that the grouting material is Newtonian fluid and the steel floral tube shows cylindrical infiltration and diffusion. Through the analysis of the structural characteristics of the injected stratum, the conceptual model of infiltration grouting is established. Twelve groups of test slurry were prepared with ordinary Portland cement and ultra-fine cement, and through the analysis of the slurry parameters of each group, ordinary Portland cement slurry was selected with a water–cement ratio of 1:1 plus 3% water glass to strengthen the gravel layer, and ultra-fine cement slurry with a water–cement ratio of 1:1 plus 3% water glass and 0.3% polycarboxylate superplasticizer to strengthen the fully and strongly weathered porphyritic granite layer. Through the on-site single-hole grouting test and combining with the empirical formula, the maximum diffusion radius of single-hole infiltration grouting is calculated, and the sliding width of the sidewall is deduced using Terzaghi theory. To ensure the grouting effect, the 5 m expansion of the excavation profile is taken as the grouting range. Grouting construction adopts the overall order of periphery and then interior, and three-sequence opening and grouting are adopted in the same row of grouting holes, which can effectively prevent grouting running and grouting. For the strata treated by surface grouting, the construction of the long pipe shed is smooth and reaches the designed length, and there is no large deformation of the surrounding rock when excavated using the CD method. The treatment effect is analyzed by the P-Q-t control method, excavation observation method, and deformation monitoring method. The results show that the injected stratum is fully infiltrated and gelled, forms an obvious grouting stone body, the integrity and strength of surrounding rock are obviously improved, and the convergence values of the tunnel surface, vault subsidence, and clearance do not exceed the alarm value of 60 mm. The research results provide some awareness and understanding of the grouting pre-reinforcement of loose stratum in a shallow buried section of a long-span tunnel in the future. Full article

A theoretical fluid mechanical model is proposed for the investigation of myocardial perfusion in healthy and stenotic conditions. The model hinges on Terzaghi’s consolidation theory and reformulates the related unsteady flow equation for the simulation of the swelling–drainage alternation characterizing the diastolic–systolic phases. When compared with the outcome of experimental in vivo observations in terms of left ventricle transmural perfusion ratio (T.P.R.), the analytical solution provided by the present study for the time-dependent blood pressure and flow rate across the ventricle wall proves to consistently reproduce the basic mechanisms of both healthy and ischemic perfusion. Therefore, it could constitute a useful interpretative support to improve the comprehension of the basic hemodynamic mechanisms leading to the most common cardiac diseases. Additionally, it could represent the mathematical basis for the application of inverse methods aimed at estimating the characteristic parameters of ischemic perfusion (i.e., location and severity of coronary stenoses) via downstream ventricular measurements, possibly inspiring their assessment via non-invasive myocardial imaging techniques. Full article

Marine soft soil foundation is a double-layer foundation structure with a crust layer and soft substratum. Moreover, it is common that there are various forms of drainage. Accordingly, based on Terzaghi’s consolidation theory and the continuous drainage boundary conditions theory of controllable drainage conditions, an improved double-layer soil consolidation theory considering continuous drainage boundary conditions was proposed. To improve the computational efficiency and accuracy, the Laplace transform and the Stehfest algorithm was used to deduce the numerical solution of the improved double-layer soil consolidation theory considering continuous drainage boundary conditions and to compile a computer program. Subsequently, the theory was validated and analyzed by the degenerated model of the perfectly permeable boundary conditions and the semi-permeable boundary conditions, respectively, which showed that this theory has higher accuracy. Simultaneously, the analysis of double-layer consolidation settlement under continuous drainage boundary conditions for marine soft soil foundation of Guangxi Binhai Highway was carried on. The result showed that the consolidation settlement calculated by the improved double-layer consolidation theory presented is basically consistent with the field measurement results, and that the correlation coefficient between them is higher. Accordingly, the research results can provide useful basic information for marine soft foundation engineering. Full article