KSCE Journal of Civil Engineering最新文献

To address the issue of stress concentrations afflicting non-circular tunnels caused by void defects, a method of analytical solution is introduced, which is grounded in the theory of complex variables. Firstly, the mapping function of the non-circular tunnel containing a void was obtained; then the power series method was implemented to determine the coefficients of the stress function and formulate the solution equations. Finally, the analytical solution was verified by simulation through Flac3D software. The effects of pore depth, width, stress inclination and stress ratio on the stress and deformation of the tunnel are considered analytically using the method of this paper. The findings indicate a strong agreement between the analytical solution and the numerical solution, and there is an obvious stress concentration at the defect location. The void depth, width, main stress field inclination and stress ratio contribute remarkably to the stress concentration at the location of tunnel void defects, thus affecting the mechanical behavior and safety condition after tunnel excavation. The results of the study propose a fast and accurate elasticity calculation method for non-circular tunnel excavation problems, offering a valuable reference to similar tunnel projects in design, construction and stability analysis.

In the current work, a DWT (Discrete Wavelet Transform) was linked to ANN, MLR, and RF to develop hybrid models WANN, WMLR, and WRF, respectively, for Brahmaputra River flow forecasting. We used ten-year daily flow data from Pandu Station, which was decomposed (up to five levels) into multiresolution time series using DWT and Daubechies wavelets db1, db2, db3, db8, and db10. The predicted discharge values for multiple lead times (2, 3, 4, 7, and 14 days) have been then obtained by feeding multiresolution time series data as the input to MLR, ANN, and RF. It was discovered that the WMLR-db10 model outperformed the WANN and WRF models for all lead times. Throughout the testing phase, the values of Nash-Sutcliffe efficiency (NS) along with RMSE (shown in bracket) for the WMLR-db10 model for lead times 2, 3, 4, 7 and 14 days have been observed to be, respectively, 0.998 (415.18 m³/s), 0.998 (514.21 m³/s), 0.996 (713.62 m³/s), 0.991 (1030.83 m³/s), and 0.977 (1638.64 m³/s). Additionally, it has been observed that WANN performed better for low-order wavelets (db1, db2, db3), WMLR performed better for high-order wavelets (db8, db10), and WRF performed worst of all the wavelets.

The undrained pullout capacity of granular pile anchors (GPA) can be sensitive to changes in soil shear strength. Researchers are intrigued by evaluating spatial variations in soil behavior in geostructures. However, there is a dearth of research on the effect of spatial soil variability on long GPA pullout capacity. The present study conducted probabilistic analyses of GPA pullout capacity using the local average subdivision method (LAS), considering the spatial variation of soil shear strength and its correlation with the soil elastic and shear modulus. The finite-difference method was used to predict GPA behavior in each random field realization to determine the probability of failure using the Monte Carlo method. The results demonstrated that consideration of GPA’s friction angle as a random parameter had negligible effects on pullout capacity. Moreover, the surface heave was limited by increasing the length/diameter ratio to more than 10. The pullout capacity of the GPA decreased by 30% due to a higher horizontal to vertical correlation length exceeding 5. In addition, the safety factor for the empirical equation obtained 1.5 and 2 for coefficient of variation higher and less than 0.2 in an isotropic random field, respectively. Finally, the concrete granular pile anchors were proposed to increase the pullout capacity and reduce corrosion effects on the anchor bar.

To evaluate the spatiotemporal evolution of pore water pressure in unsteady seepage flow ahead of a tunnel face, a partial differential equation for unsteady seepage is established. The ranges and boundary conditions of the unsteady seepage flow are specified, and the analytical solution of the unsteady seepage flow is obtained by the eigenfunction method. The obtained analytical solution additionally considers the time factor, which can be used to study the influence of seepage time on the seepage flow. And the pressure transmitting coefficient is introduced to analyze the influence of water and soil characteristics on the unsteady seepage. The analysis shows that the spatiotemporal evolution of the unsteady seepage flow pore water pressure ahead of a tunnel face is reflected in two aspects, the dissipation of the water pressure and the diffusion of the influence range of the unsteady seepage. The dissipation captures the gradual reduction of pore water pressure at a specific location as time progresses. Meanwhile, diffusion characterizes the alteration in the spatial distribution of water pressure. The pressure transmitting coefficient promotes the rate of unsteady seepage, while the height of water table has a greater influence on the magnitude of water pressure change in unsteady seepage flow.

In this study, temperature monitoring and freezing disaster investigation in winter were conducted in three high latitude cold regional tunnels of Northeast China. Observations indicate that the air temperature in the tunnel middle section and the deep buried central drainage pipe remains stable at 0–5°C, while at the entrance section and the side ditch, it fluctuates around −15°C for about 2 months. Consequently, warm water from the middle section supplies both ends of the tunnel, making the entrance section drainage system prone to ice jams and freezing damage. Field investigation reveals 5 types of freezing-induced catastrophic behavior in tunnel drainage systems. In addition, frost heave effects from drainage system failure are simulated, showing that the lining compressive stress due to frost heave of drainage system is about 450 kPa, which is 200% of the surrounding rock frost heave. Moreover, the tensile stress due to frost heave of the side wall crack seepage or cavity water is the most significant, followed by the arch springing, then the hance, and finally the vault. Finally, consideration of the frost heave effect induced by drainage system is crucial for ensuring tunnel operation safety in high latitude cold regions.

Applying isolation devices to nuclear power plant equipment can improve the equipment’s seismic safety. When the equipment is connected to piping, however, its seismic safety can rather be decreased due to the increase in the relative displacement of the connected pipes. An emergency diesel generator (EDG) supplies power when a generator and an external power source in a nuclear power plant do not operate. Isolation devices can be installed to improve EDG’s seismic safety. The seismic safety of EDG is generally evaluated considering only EDG and the isolation device. Since the piping connected to EDG is responsible for fuel supply and cooling, however, the seismic safety of EDG must be evaluated considering the piping as well. In this study, seismic fragility analyses were conducted according to the modeling of isolation devices for EDG equipped with the isolation device and the piping connected to EDG. Seismic response analyses were performed considering the fuel line in EDG to which the seismic isolation devices were applied, and seismic fragility curves were estimated based on the results of the seismic response analysis. The research results showed that the piping connected to EDG could be damaged earlier than EDG, indicating that proper piping system design and seismic safety assessment are required to apply isolation devices to EDG.

A study was conducted on the soil erosion process in the Baitarani River Basin in peninsular India, using two distinct methodologies based on drainage basin morphometry. The study covered 16 sub-basins, and evaluated the soil erosion dynamics using sixteen linear, areal, shape, and relief features. Weighted sum analysis (WSA) and a hybrid model named principal component based weighted sum analysis (PCWSA) were used to analyse the morphometry data and establish the likelihood of soil erosion occurrence. The results showed that based on the WSA approach six, four and six sub-basins had low, moderate and high flood priorities respectively, while based on the PCWSA technique five, six and five sub-basins had low, moderate and high flood priorities respectively. For quantitative validation MLR models were obtained using these two approaches based on USLE model based annual average soil erosion magnitude, and the derived values exhibit acceptable accuracy (48.2% and 55.2% respectively) in modelling soil erosion. The results showed that the PCWSA approach could produce better accuracy with only six principal components, compared to the WSA method with six uncorrelated factors. For qualitative validation, satellite data based Modified soil-adjusted vegetation index (MSAVI) map was applied which confirmed satisfactory agreement with the proposed approach.

In this study, a theoretical approach is presented for analyzing how rectangular barrettes respond laterally in layered transversely isotropic soil deposits. To do this analysis, a modified Vlasov model is used. In this study, the barrette and the soil around it are treated as a continuum system. The deformation of the barrette is analyzed using the Timoshenko beam theory. By multiplying the barrette’s displacement with a pair of decay functions, the horizontal soil displacement can be quantified. The equations that govern the barrette and soil are derived based on the principle of minimum energy, along with the appropriate boundary conditions. These equations are then solved using an iterative method. The accuracy of the results is confirmed by comparing the barrette response to two previously published results. Additionally, the impact of the shape of the rectangular cross section and the anisotropy of the soil on the static responses of a barrette are explored. The results show that the ratio E_sh/E_sv between the horizontal modulus and vertical modulus for the transversely isotropic soil has significant influences for the response of barrette. An increase of E_sh/E_sv from 0.5 to 3.0 can lead to a reduction of around 75%, 54%, 30%, 40% for the maximums of lateral displacement, rotation, moment, and soil reaction, respectively.

Squeezing-induced buckling or flexural deformation of rock layers always occurs on consequent rock slopes and laminated roof of tunnels or underground openings. To reveal the mechanical mechanism and inducing factors of this instability, tests on cuboid rock samples comprised of bedding sandstone under horizontal squeezing stress were conducted. In addition, numerical modeling based on cohesive-element-model was conducted to further reveal the influence of inter-layer bonding strength on the mechanical behavior of laminated rock. According to the results, remarkable size effects exist on the buckling-fracture characteristics of tested samples. Subjected to the same horizontal stress, tested samples with different dimensions have quite different failure patterns, including upper buckling-lower shearing, integral buckling and end squashing. It is recommended that the length-thickness ratio of tested samples for buckling failure research should be less than 150/8. Moreover, numerical simulations indicate that failure characteristics of the samples are greatly influenced by the bedding structure such as bedding thickness and inter-bedded bonding strength. Buckling deformation at one end becomes quite obvious when inter-bedded bonding strength decreases to a smaller value. The research results will not only contribute to understanding the buckling mechanism of stratified rock mass subjected to horizontal stress, but also provide a guidance for similar experimental design in terms of sample preparation, loading and monitoring.

The submerged floating tunnel (SFT) is a type that allows tunnel floating owing to the water buoyancy. SFTs are often subjected to high-water pressure and environmental loads, such as waves and currents, which differ from those experienced by typical underground tunnels. In these SFTs, a sudden, large water leak can occur owing to collisions with external objects (such as ships), mooring lines for anchoring, and structural fatigue failure. To address these unexpected situations, it is necessary to develop a disaster prevention system for leakages. However, tunnel leaks and their propagation characteristics within tunnels have not been studied in depth. In this study, numerical simulations were performed using the commercial software program FLOW-3D to evaluate the characteristics of the water flowing through the tunnel owing to local damages to tunnel segments. In the simulations, a representative cross-section of the SFT was modeled, and the water propagation characteristics with respect to the crack size and water depth were evaluated. The results confirmed that the crack size and water depth significantly affected the propagation characteristics of the leaks. The results of this study are expected to be used as useful data for the design of disaster prevention systems for leaks in SFT.