河道整治工程中的生态护坡防洪堤设计

防洪堤设计合理性与科学性直接关系到河道整治效果,提出河道整治工程中的生态护坡防洪堤设计。以某工程为工程背景,结合该工程实际情况对防洪堤断面型式设计为加筋土堤断面+土石复合堤断面,岸墙采用浆砌条石防浪墙+C20埋石混凝土重力式挡墙组合形式。通过对防洪堤性能验算,防洪堤渗透坡降、基地应力、抗滑及抗倾稳定系数等指标均符合规范要求,设计方案具有良好的可行性。

纯黏土条件下浅埋隧道掌子面稳定性分析

针对玉磨铁路的太达村隧道工程,并结合纯黏土特性,提出一种改进的破坏模型,用于分析纯黏土条件下浅埋隧道掌子面稳定性。所提出破坏模型可分为2部分:交叉层部分破坏模型为三维旋转破坏机制的一部分,覆盖层部分破坏模型是基于太沙基地应力理论。基于所提出破坏模型,采用非线性最小优化算法fminsearch获得掌子面极限支护压力值。研究结果表明:所提出的改进破坏机制能够大大提高极限支护压力的严格下限值,提升幅度约9%~19%;所提出模型获得的极限支护压力下限值略小于实际监测值;隧道掌子面极限支护压力值随黏聚力的增大而线性减小。

重力式挡土墙稳定性计算方法

挡土墙做为公路支档、防护工程设计的主要措施,其滑动稳定和倾覆稳定直接影响到工程的安全;本文作者结合多年工作经验,就挡土墙稳定性计算做一个简单清晰的演算,为设计工作者理清思路,提供设计依据。

溪古水电站进水塔稳定分析

进水塔为高耸建筑物,在各种工况特别是地震工况下的稳定性对整个枢纽的安全运行尤其重要,其稳定是指塔体抗浮、抗滑、抗倾和基地应力满足规范要求,本文结合有限元和常规方法稳定计算结果,分析了进水塔在各种工况下的稳定性。

Numerical analysis of crack generation within embankment built on expansive soil foundation

In order to analyze the initial cracking behavior of highway embankment in the regions of expansive soil, the changes in peaks of tensile stress and their location on top of the embankment for a typical highway embankment section were simulated by ABAQUS. The simulation results indicate that the matric suction was a concave distribution on top of the expansive soil foundation and that it induced differential deformation of foundation and embankment. The peaks of tensile stress on top of the embankment are not located at a fixed site, but gradually move towards the shoulder following the evaporation duration. When the evaporation intensity is larger, the peak of tensile stress on top of embankment increases at a faster rate following the evaporation duration,and its location is closer to the shoulder. The thicker expansive soil layer helps the peaks of tensile stress to reach the critical tensile stress quickly, but the embankment cannot crack when the expansive soil layer is no more than 1.5m after 30d soil surface evaporation; the higher the embankment, the smaller the peak of tensile stress occurring on top of the highway embankment, and its location will be further away from the shoulder. Therefore, a higher embankment constructed on a thinner expansive soil layer can reduce the crack generation within the highway embankment.

悬臂式挡土墙尺寸及稳定性验算

由于地基承载力的不足,悬臂式挡土墙越来越多的使用在公路、城市道路支档、防护工程设计中,其滑动稳定和倾覆稳定直接影响到工程的安全;本文作者结合多年工作经验,就挡土墙稳定性计算做一个简单清晰的演算,为设计工作者理清思路,提供设计依据。

Analytical solution for evaluating deformation response of existing metro tunnel due to excavation of adjacent foundation pit

The excavation of foundation pit generates soil deformation around existing metro tunnel with shield driving method,which may lead to the deformation of tunnel lining.It is a challenge to evaluate the deformation of shield tunnel accurately and take measures to reduce the tunnel upward displacement as much as possible for geotechnical engineers.A new simplified analytical method is proposed to predict the longitudinal deformation of existing metro tunnel due to excavation unloading of adjacent foundation pit in this paper.Firstly,the additional stress of soils under vertical axisymmetric load in layered soil is obtained by using elastic multi-layer theory.Secondly,the metro tunnel is regarded as a Timoshenko beam supported by Winkler foundation so that the shear effect of tunnels can be taken into account.The additional stress acting on the tunnel due to excavation unloading in layered soil are compared with that in homogeneous soil.Additionally,the effectiveness of the analytical solution is verified via two actual cases.Moreover,parametric analysis is conducted to investigate the responses of the metro tunnel by considering such factors as the variation of subgrade coefficient,offset distance from the excavation center to tunnel longitudinal axis as well as equivalent shear stiffness.The proposed method can be used to provide theoretical basis for similar engineering project.

Ultimate end bearing capacity of rock-socketed pile based on generalized nonlinear unified strength criterion

In order to study the mechanism of bearing behavior at the tip of a pile embedded in rock, the generalized nonlinear unified strength criterion and slip line principle for resolving the differential equation systems which govern the stress field were applied to derive the ultimate end beating capacity based on some reasonable hypothesis and failure plane model. Both numerical simulation and test results were compared with the theoretic solution. The results show good consistency with each other and verify the validity of the present approach. The depth effect with respective to embedment ratio and other influence factors like geological strength index, intermediate principal stress, overburden factor, and damage on end bearing capacity were discussed in the analytical solution. The results show that the proposed yield criterion can be much better for investigating the ultimate end bearing performance of rock-socketed pile. The end bearing capacity increases with embedment ratio and the increasing degree is influenced intensely by the above parameters. Furthermore, ignoring intermediate stress effect would underestimate the strength properties of the rock material and lead to a very conservative estimation value.

Predictive analysis of stress regime and possible squeezing deformation for super-long water conveyance tunnels in Pakistan

The prediction of the stress field of deep-buried tunnels is a fundamental problem for scientists and engineers. In this study, the authors put forward a systematic solution for this problem. Databases from the World Stress Map and the Crustal Stress of China, and previous research findings can offer prediction of stress orientations in an engineering area. At the same time, the Andersonian theory can be used to analyze the possible stress orientation of a region. With limited in-situ stress measurements, the Hock-Brown Criterion can be used to estimate the strength of rock mass in an area of interest by utilizing the geotechnical investigation data, and the modified Sheorey＇s model can subsequently be employed to predict the areas＇ stress profile, without stress data, by taking the existing in-situ stress measurements as input parameters. In this paper, a case study was used to demonstrate the application of this systematic solution. The planned Kohala hydropower plant is located on the western edge of Qinghai-Tibet Plateau. Three hydro-fracturing stress measurement campaigns indicated that the stress state of the area is SH - Sh 〉 Sv or SH 〉Sv 〉 Sh. The measured orientation of Sn is NEE （N70.3°-89°E）, and the regional orientation of SH from WSM is NE, which implies that the stress orientation of shallow crust may be affected by landforms. The modified Sheorey model was utilized to predict the stress profile along the water sewage tunnel for the plant. Prediction results show that the maximum and minimum horizontal principal stres- ses of the points with the greatest burial depth were up to 56.70 and 40.14 MPa, respectively, and the stresses of areas with a burial depth of greater than 500 m were higher. Based on the predicted stress data, large deformations of the rock mass surrounding water conveyance tunnels were analyzed. Results showed that the large deformations will occur when the burial depth exceeds 300 m. When the burial depth is beyond 800 m, serious squeezing deformations will occur in the surrounding rock masses, thus requiring more attention in the design and construction. Based on the application efficiency in this case study, this prediction method proposed in this paper functions accurately.

Numerical Analysis of the Interaction between Shallow （Square, Circular and Strip） Foundations and Subsoil

In this paper, the effects of the stiffness of circular, square and strip foundation structures and bonding effects were analyzed. Presented analysis was oriented on the influence of stiffness system ＂foundation--subsoil＂ and bonds （bi-directional bond and one-directional bond with and without friction）. The results of numerical calculations have proved that the relative stiffness of system ＂foundation--subsoil＂ affect considerably the value and the distribution of contact stresses （vertical normal and shear stresses） in the foundation gap and value of the displacements （settlement, deflection and relative deformations） of foundation. From the numerical point of view, this problem was solved by deformation variant of the FEM （finite element method）. The numerically obtained results were presented in the graphical and tabular forms. Obtained results were qualitative and quantitative compared with one another. From the calculation results it is obvious that relative stiffness of the system ＂foundation structure--subsoil＂ substantially affects distribution of contact stresses in the foundation subsoil and displacements （settlement, deflection and relative deformations, flexibility） of foundation. In the case of flexible foundations, the bond on the contact surfaces must be considered during the calculation. On the other hand, the effects of friction on the contact surface between the foundation and subsoil affect the distribution of contact stresses and deformations only to smaller extent.