This study presents the results of three-dimensional finite element modelling of Gediminas Hill in Vilnius, incorporating existing buildings and the remains of the Upper and Lower Castles. The main objective is to assess slope stability using the strength reduction method and to identify potential critical failure scenarios considering the interaction between soil and structural elements. Both static and dynamic loading conditions are analysed. Static loading includes the self-weight of soil layers, technogenic deposits, structural elements, and infrastructure, while dynamic effects are represented by fireworks-induced impact loads. The comparison of analyses reveals differences in displacement development and failure mechanisms. Strength reduction results highlight the zones of concentrated deformation within the technogenic layer, which are further evaluated in relation to the effects of dynamic loading.
The paper provides an overview of the Mizarai impact structure located in southern Lithuania, discovered in the course of geological mapping in 1969 and identified in 1975. Since then, the structure has been investigated by the mapping of gravity and magnetic fields, 2D and 3D seismic surveys, drilling and core studies. The structure is in the form of an oval depression situated within the Precambrian crystalline basement filled with presumably Ediacaran to Lower Cambrian detrital sediments derived from target rocks and ejecta and overlined with Mesozoic and Quaternary sediments. Gravity and seismic data have not indicated the presence of a central uplift within the Mizarai depression, suggesting a simple form. We estimate that the recent size of the crater is 3.8 x 4.2 km, after erosion in the course of similar to 300 Ma. Before erosion, the primary crater had a rim-to-rim diameter of up to 5 km and a depth of approximately 1 km. The impact metamorphism manifested in the transformation of target rocks into impact breccias and impact melt rocks, displaying shock features such as shatter cones, isotropization of quartz and plagioclase, planar deformation features (PDFs) in quartz, and kink-bands in biotite. While most impactites reflect the target rock composition, suevitic impact breccias and impact melt rocks (glass) are enriched by potassium.
To investigate the frost damage of Zoige Plateau Peat Permafrost and the stability of engineering foundations in seasonally frozen regions, this study builds upon previous research on the optimal mix ratio of composite stabilized peat soil using mineral powder-steel slag and basalt fibre as primary materials, supplemented with polycarboxylate superplasticizer and carbide slag. Indoor mechanical tests (unconsolidated undrained triaxial shear test, unconfined compressive strength test, and scanning electron microscopy test) were conducted on stabilized soils subjected to varying freezing temperatures and freeze-thaw cycles to explore the mechanical properties and microscopic mechanisms under freeze-thaw action. Based on the experimental dataset, the peak strength of stabilized peat soil was predicted using a particle swarm optimization backpropagation neural network (PSO-BP). The results indicate that the unconfined compressive strength and residual strength ratio of stabilized peat soil are positively correlated with freezing temperature and negatively correlated with the number of freeze-thaw cycles. The stress-strain curve characteristics of stabilized peat soil are generally consistent under different conditions. With increasing cycles, the peak strength and cohesion of the stabilized peat soil first decrease and then stabilize, while the internal friction angle remains relatively unchanged. In the peak strength model constructed using MATLAB, the PSO-BP neural network model exhibited a higher correlation coefficient (R2) and better overfitting performance compared to the BP neural network model, enabling a more accurate strength prediction of stabilized peat soil.
This study investigates the deformation and failure mechanisms of gently layered surrounding rock during underground excavation in a hydropower station in Shaanxi Province, China, through base friction physical simulation tests. Results indicate rock mass instability is governed by weak discontinuities (layer planes, joints, and faults). Four failure modes emerge: (1) tensile crack collapse at the tunnel arch induced by stress concentration, (2) shear slip at the sidewalls and shoulders due to exceeding shear strength, (3) bulging deformation of thin-layered rock under compressive stress, and (4) slight uplift at the invert of the main powerhouse due to upward pressure. The physical simulation tests replicate the deformation and failure evolution of the surrounding rock mass during excavation. Initially, the process is characterized by tunnel arch spall and slight slip, progressing to rock mass collapse due to structural plane coalescence. The study reveals the complex mechanical behaviour of failure in gently layered surrounding rock. The tunnel arch exhibits a "tension crack collapse - shear slip - bedding" failure mode, while the sidewall is primarily influenced by shear slip. Findings confirm discontinuities' control on the stability of layered surrounding rock, offering guidance for deformation support and long-term maintenance. These results provide significant theoretical and practical implications for engineering applications.
The construction of a deep geological repository (DGR) for the spent nuclear fuel and high-level long-lived radioactive wastes is prescribed in Lithuanian legislation. Therefore, geological investigations for DGR host formation and site selection are being carried out. This paper presents a comparative suitability evaluation of two potentially suitable Lithuanian clayey formations. The suitability evaluation of Lower Cambrian and Lower Triassic clays was performed using the data set of laboratory test results from two decades. The results of laboratory investigations performed on clay material obtained from the unpreserved cores of nine boreholes were analysed in order to quantify the parameters relevant to the formation suitability. The data set contains the results of hydraulic conductivity measurements of several samples, mineralogical analysis of clay minerals, determination of Atterberg limits, chemical analysis (EDS method), and particle specific surface area measurements (BET method). Analysis of laboratory test results allow to compare the suitability for DGR installation of two Lithuanian clayey formations according to several properties. The clay fraction of the Lower Triassic potentially suitable formation is dominated by smectite/montmorillonite group minerals (60-88%), and the dominance of illite (60-95%) is characteristic of Lower Cambrian clay. The determination of Atterberg limits indicates a similar (medium) plasticity of both formations. The specific surface area of particles ranges from 30.9 to 54.8 m(2)/g in Lower Triassic samples and from 28.0 to 32.7 m(2)/g in Lower Cambrian samples. A higher smectite content and a larger specific surface area show a greater swelling and sorption capacity of Lower Triassic clay. Clay swelling and sorption capacity are important features causing geological environment suitability for the DGR. Although the tests were conducted on unpreserved and degraded samples, their results support the conclusion that the suitability of the Lower Triassic potentially suitable formation is comparatively greater.
