Acceleration and displacement dynamic response laws of a shallow-buried bifurcated tunnel

In order to obtain the seismic dynamic laws of the acceleration and displacement of a shallow-buried bifurcated tunnel, the analysis of the numerical simulation was carried out by MIDAS-GTS/NX software. The results of the numerical simulation were verified by a shaking table model test. The results show that: (1) the numerical simulation and shaking table test coincide with each other in terms of variation law and peak value. The results of the numerical simulation are credible. (2) For different tunnel cross-section, the response of acceleration and displacement are significant difference. (3) The seismic response of the small distance tunnel (Section 6) is intense. The seismic response laws of the small distance tunnel are significant difference from other type tunnels. The seismic response of the measuring point at the middle rock column is intense. (4) Along the axis of the tunnel, the displacement of the tunnel firstly increases and then decreases. The displacement of the measuring point at the middle rock column is intense, which is in accordance with the law of the acceleration response. The seismic response laws of the tunnel are significantly affected by the middle rock column. The section structure size has a significant effect on the dynamic response of the tunnel

Experimental study on acceleration response laws of shallow-buried bias tunnels with a small distance

Based on the similarity theory, a physical testing model with scale of 1:10 was designed and fabricated. The Wenchuan wave (WC-XZ), Darui artificial wave (DR-XZ) and Kobe wave (K-XZ) were adopted as excitation waves which was XZ directions (horizontal and vertical loading at the same time). A series of shaking table tests were carried out to study the effect of the types, directions and peaks acceleration of the seismic waves on the acceleration response laws of the shallow-buried bias tunnels with small distance. The results show that: (1) in the horizontal direction, the types of the seismic waves have a little effect on the acceleration response, but the law is opposite with Kobe wave being the most serious, followed by Darui artificial wave and Wenchuan wave in the vertical direction. (2) The existing slope has a significant effect on the acceleration response of the right hole which is different from that of the left hole. (3) The acceleration response of the tunnel in the vertical direction is more severe than that of the horizontal direction and the acceleration amplification factors in vertical direction are is generally 1.02-3.94 times that of the horizontal direction. (4) in the seismic design of tunnel, different seismic measures should be adopted in different directions. The results have a significant reference for the anti-seismic design of the tunnel

Synchronous multimode ultrasound for assessing right-to-left shunt: a prospective clinical study

BackgroundRight-to-left shunt (RLS) is associated with several conditions and causes morbidity. In this study, we aimed to evaluate the effectiveness of synchronous multimode ultrasonography in detecting RLS.MethodsWe prospectively enrolled 423 patients with high clinical suspicion of RLS and divided them into the contrast transcranial Doppler (cTCD) group and synchronous multimode ultrasound group, in which both cTCD and contrast transthoracic echocardiography (cTTE) were performed during the same process of contrast-enhanced ultrasound imaging. The simultaneous test results were compared with those of cTCD alone.ResultsThe positive rates of grade II (22.0%:10.0%) and III (12.7%:10.8%) shunts and the total positive rate (82.1748%) in the synchronous multimode ultrasound group were higher than those in the cTCD alone group. Among patients with RLS grade I in the synchronous multimode ultrasound group, 23 had RLS grade I in cTCD but grade 0 in synchronous cTTE, whereas four had grade I in cTCD but grade 0 in synchronous cTTE. Among patients with RLS grade II in the synchronous multimode ultrasound group, 28 had RLS grade I in cTCD but grade II in synchronous cTTE. Among patients with RLS grade III in the synchronous multimode ultrasound group, four had RLS grade I in cTCD but grade III in synchronous cTTE. Synchronous multimode ultrasound had a sensitivity of 87.5% and specificity of 60.6% in the patent foramen ovale (PFO) diagnosis. Binary logistic regression analyses showed that age (odds ratio [OR] = 1.041) and risk of paradoxical embolism score ≥ 7 (OR = 7.798) were risk factors for stroke recurrence, whereas antiplatelets (OR = 0.590) and PFO closure with antiplatelets (OR = 0.109) were protective factors.ConclusionSynchronous multimodal ultrasound significantly improves the detection rate and test efficiency, quantifies RLS more accurately, and reduces testing risks and medical costs. We conclude that synchronous multimodal ultrasound has significant potential for clinical applications

Experimental study on the influence of curing methods on the compressive strength of improved sand

The properties of the improved soil are closely related to the properties of the improved materials added, and the curing process is the key process to make the performance of the improved materials play. In this paper, several groups of improvement tests on sandy soil were carried out, and the improved sand was placed under different curing conditions (standard curing, water curing, air drying curing, dry and wet cycle curing) to explore the improvement effects of each material under different curing conditions. Cement (6 %, 8 %, 12 %, 16 %), active magnesium oxide (4 %, 8 %, 12 %, 16 %), polyvinyl alcohol solution (PVA)(6 %, 8 %, 12 %, 16 %) and polypropylene fiber (PPF)(0.25 %, 0.5 %, 1 %, 2 %) were used as modified materials. The improvement effect was evaluated by unconfined compressive strength, stress-strain curve and scanning electron microscope observation of internal cementation state. The results show that the improved material has different effects under different curing conditions when the same material is added to the improved soil. The improvement effects of cement, active magnesium oxide, PVA and PPF on sand are all affected by curing conditions. Among them, cement improved sand is suitable for standard curing corresponding to cement. Activated MgO can obtain a higher strength of 2.7 MPa under dry and wet cycle curing. PVA modified sand has almost no strength under standard curing conditions, but can reach 0.9 MPa under dry curing conditions. The unconfined compressive strength of fiber-modified sand decreases with the increase of water content. The SEM results showed that the improved material strengthened by hydration reaction could form dense hydration products and fill the pores between the sand grains under appropriate curing conditions, while the reaction was incomplete or overreacted under other curing conditions, leading to the defects of the sample

Dynamic Response and Time-Frequency Characteristic of Dangerous Rocks under the Combined Action of Rock Cavity Weathering and Earthquake

In order to further reveal the failure mode and dynamic response law of dangerous rocks with different degree of weathering in the rock cavity under the action of earthquake and to provide early warning and forecast for steep slope of dangerous rocks in similar earthquake areas, a typical steep slope of dangerous rock in earthquake area of Sichuan, China, was taken as the research object, after detailed geological survey, and according to the chain development law of dangerous rock, the steep slope of dangerous rock before the earthquake was restored. Based on the 3D particle flow software PFC3D, the dangerous rock was divided into 3 modes according to the degree of weathering of the mudstone rock cavity, and the three-dimensional discrete element dangerous rock model under different modes was established. By introducing the horizontal and vertical two-way coupled seismic waves in Wenchuan, Sichuan, in 2008, the failure evolution process of steep slope of dangerous rock under the action of the horizontal and vertical coupled seismic waves was dynamically simulated, which proved the rationality of the simulation. The frequency spectrum of velocity-time history signal of each rock block in the dangerous rock model was analyzed by MATLAB programming, and the time-frequency characteristics of each dangerous rock model under the action of coupled seismic wave were studied. The research results have important scientific guiding significance and practical value for the dynamic stability evaluation and prediction of such steep slope of dangerous rocks under the combined action of rock cavity weathering and earthquake

Study on the Evolution Law of Internal Force and Deformation and Optimized Calculation Method for Internal Force of Cantilever Anti-Slide Pile under Trapezoidal Thrust Load

The evolution law of internal force and deformation of an anti-slide pile affects the slope stability and prevention design in a significant way. Based on the similarity theory, a test system for the bearing characteristics of a cantilever anti-slide pile was constructed, and the physical model test for the bearing characteristics of a cantilever anti-slide pile under trapezoidal thrust load was carried out. The distribution laws of internal force and deformation of a cantilever anti-slide pile were revealed, and the optimized calculation method for internal force of a cantilever anti-slide pile was proposed by taking the elastoplastic characteristics of steel bars and concrete into consideration. Furthermore, a numerical model was employed to conduct a parametric analysis of a cantilever anti-slide pile. The results show that the whole process of stress and deformation of a cantilever anti-slide pile can be classified as the uncracked stage, the cracks emerging and developing stage, and the steel bars yielding–failing stage. In the uncracked stage, the bending moment of the cantilever anti-slide pile calculated by the traditional method is smaller than that calculated by the optimized calculation method established in this paper. The traditional calculation method is no longer applicable in the stage of cracks emerging and developing. The lateral displacement and bending moment of the cantilever anti-slide pile are negatively and positively correlated with the strength of the pile material, respectively, and the influence of the deterioration of steel bars’ strength on the ultimate bearing performance of the anti-slide pile is more obvious than that of the deterioration of concrete strength. The bearing capacity of the anti-slide pile could not be significantly improved by increasing the length of the anchored section when the strength of the rock stratum embedded in anchored section was large enough. As the thrust load behind the pile increased, the difference of the bearing performances of the cantilever anti-slide pile under the uniform load and trapezoidal load increased gradually. The research results can provide guidance for the evaluation of the service performance of the cantilever anti-slide pile and the slope stability

Off-Policy Evaluation for Large Action Spaces via Conjunct Effect Modeling

We study off-policy evaluation (OPE) of contextual bandit policies for large discrete action spaces where conventional importance-weighting approaches suffer from excessive variance. To circumvent this variance issue, we propose a new estimator, called OffCEM, that is based on the conjunct effect model (CEM), a novel decomposition of the causal effect into a cluster effect and a residual effect. OffCEM applies importance weighting only to action clusters and addresses the residual causal effect through model-based reward estimation. We show that the proposed estimator is unbiased under a new condition, called local correctness, which only requires that the residual-effect model preserves the relative expected reward differences of the actions within each cluster. To best leverage the CEM and local correctness, we also propose a new two-step procedure for performing model-based estimation that minimizes bias in the first step and variance in the second step. We find that the resulting OffCEM estimator substantially improves bias and variance compared to a range of conventional estimators. Experiments demonstrate that OffCEM provides substantial improvements in OPE especially in the presence of many actions.Comment: accepted at ICML2023. arXiv admin note: text overlap with arXiv:2202.0631

The Influence of Lateral Restraining Stiffness on the Box-Girder Superstructure under Unbroken Solitary Waves

At present, box-girder superstructures are commonly used in coastal bridges, and their hydrodynamic performance under extreme waves such as tsunamis has attracted a lot of attention. There is a lack of research focusing on the effect of lateral restraining stiffness on box-girder superstructures under the extreme wave condition. In this paper, a two-dimensional numerical model based on the RANS equation and SST k-ω turbulence model is established. Combined with the dynamic mesh updating technique, the effect of lateral restraining stiffness on the superstructure of a box-girder and the dynamic characteristics of the movable box-girder under the solitary waves were investigated. To ensure the mesh quality, the numerical computational domain is divided into several regions that correspond to specific types of body motion. The numerical model is verified by comparing it with other numerical simulation results and experimental results. The dynamic characteristics and the wave forces of the box-girder superstructure under the effect of lateral restraining stiffness under the unbroken solitary waves are discussed. The results show that the horizontal and vertical forces on the box-girder superstructure under the action of unbroken solitary waves can be reduced by reducing the lateral restraining stiffness. However, with the decrease in lateral restraining stiffness, the lateral displacement of the box-girder superstructure would increase. Therefore, the lateral restraining stiffness and lateral displacement limit of the box-girder superstructure should be fully considered in practical engineering, and the appropriate lateral restraining stiffness should be selected to reduce the wave forces on the box-girder superstructure under extreme wave action, so as to improve the safety of the coastal box-girder superstructure. It is of great importance to study the interaction between the box-girder superstructure and unbroken solitary waves, which will help to have a deeper understanding to improve the disaster resistance of bridges