Analysis of Tunnel Water Inrush Considering the Influence of Surrounding Rock Permeability Coefficient by Excavation Disturbance and Ground Stress

Affected by the coupling of excavation disturbance and ground stress, the heterogeneity of surrounding rock is very common. Presently, treating the permeability coefficient as a fixed value will reduce the prediction accuracy of the water inflow and the external water pressure of the structure, leading to distortion of the prediction results. Aiming at this problem, this paper calculates and analyzes tunnel water inflow when considering the heterogeneity of permeability coefficient of surrounding rock using a theoretical analysis method, and compares with field data, and verifies the rationality of the formula. The research shows that, when the influence of excavation disturbance and ground stress on the permeability coefficient of surrounding rock is ignored, the calculated value of the external water force of the tunnel structure is too small, and the durability and stability of the tunnel are reduced, which is detrimental to the safety of the structure. Considering the heterogeneity of surrounding rock, the calculation error of water inflow can be reduced from 27.3% to 13.2%, which improves the accuracy of water inflow prediction to a certain extent.

The role of mural mechanics on cephalopod palaeoecology

Cephalopods transformed the molluscan shell into a buoyancy device that must be strong enough to resist external water pressure. Historically, unique features of the shell have been interpreted on the basis that the strength of the shell presents a hard limit on maximum habitat depth. One such feature is the mural flap, which is a semi-prismatic layer deposited on the inner surface of some coleoid septa that has been suggested to strengthen the shell and permit colonization of deeper waters. We test this hypothesis by constructing finite-element models that show how mural modifications affect the response of the shell to hydrostatic pressure. The mural flaps are found to have no notable structural function. Another mural modification discovered here is the adapical ridge flap that initially seemed to have a potential function in shifting peak stress away from the attachment site of the septum; however, the irregular distribution of this feature casts any functional interpretation in doubt. Ecological separation of belemnites and decabrachians is likely not mediated by the presence/absence of mural flaps. This work illustrates a potential caveat that not all unique septal features formed in response to increasing hydrostatic pressure and deeper habitats.

Analysis of External Water Pressure for a Tunnel in Fractured Rocks

External water pressure around tunnels is a main influential factor in relation to the seepage safety of underground chambers and powerhouses which make managing external water pressure crucial to water conservation and hydropower projects. The equivalent continuous medium model and the discrete fracture network (DFN) model were, respectively, applied to calculate the seepage field of the study domain. Calculations were based on the integrity and permeability of rocks, the extent of fracture development, and the combination of geological and hydrogeological conditions in the Huizhou pump-storage hydropower station. The station generates electricity from the upper reservoir and stores power by pumping water from the lower to the upper reservoir. In this paper, the external water pressure around the cavern and variations in pressure with only one operational and one venting powerhouse were analyzed to build a predictive model. The results showed that the external water pressure was small with the current anti-seepage and drainage system that normal operation of the reservoir can be guaranteed. The results of external water pressure around the tunnels provided sound scientific evidence for the future design of antiseepage systems.