Numerical simulation of crack propagation behavior of a semi-cylindrical specimen under dynamic loading

To design and evaluate the analytical crack propagation of a specimen under dynamic load, measurement of dynamic fracture parameters is necessary. However, analytical methods have significant complexity, and experimental methods are also time-consuming that require high precision and considerable funding. Therefore, numerical methods can be used to solve these problems. The Extended Finite Element Method (X-FEM) as a powerful and efficient tool can be used for this purpose. In this paper, X-FEM code in ABAQUS software was used in order to simulate crack growth in a semi-circular specimen with pre-existed crack and also intact specimen to determine dynamic stress intensity factor (DSIF) using displacement extrapolation method. To verify the numerical modeling output, the curve of crack surface opening displacement (CSOD) in X-FEM model has been compared with the experimental curve. Moreover, concrete damage plastic (CDP) model was used to validate X-FEM simulation results. The results show that the DSIF for a cracked sample under a maximum dynamic load 3000 N is equal to 0.5 Mpa . Comparison between the CDP and X-FEM results showed that in both approaches, the same area for crack propagation was also determined

A review on the buried pipeline responses to tunneling-induced ground settlements

The expansion of cities and urban areas has resulted in an increased demand for environmental and economic transport and services infrastructure. Tunneling, as one of mankind's engineering underground constructions, is taking place close to buried and surface structures such as gas, water, and wastewater pipelines. This paper reviews soil-pipe interaction behavior, tunneling-induced ground settlement, governing equations of soil-pipe settlement, the effects of tunnel depth, size, soil relative density, and volume loss on vertical and horizontal displacement, settlement, shear strain, dilation, pipe bending, and gap formation. A comprehensive literature review, analysis of published papers, and investigations were conducted to study the effect of various parameters on pipeline behavior. The results were obtained by studying the effect of tunneling on ground and pipeline settlement, soil-pipe interaction mechanism, and centrifuge physical modeling. The achieved results of investigations show that the settlement profile follows a Gaussian curve with a wider settlement trough in clay compared to sand. When the tunnel and pipeline are perpendicular to each other, maximum bending strain in the pipeline occurs and the pipeline settlement is symmetrical. The friction effect and formation of contraction and expansion zones lead to the difference between soil volume loss near the surface and tunnel volume loss. When the pipe-soil relative stiffness increases, the pipe bending is less than the maximum soil bending. Also, ground settlement, shear strain, pipeline displacement, and pipeline bending are greater in flexible pipes than in rigid pipelines. This is due to the low resistance of flexible pipelines against bending and settlement caused by tunnel excavation. Positive pipeline bending (downward) occurs near the tunnel axis, which is marked by sagging, but negative bending (upward) occurs at a distance from the tunnel axis, which is known as hogging.  In twin tunnels, by increasing the tunnel spacing the pipeline settlement profile changes from a V-shape to a U-shape and finally a W-shape. Understanding soil-pipe interaction behavior, tunneling-induced ground settlement, and the effects of different parameters on displacement, strain field, settlement, pipe bending, and gap formation beneath pipelines is crucial for engineers evaluating pipeline behavior. Additionally, comprehending these issues can help designers make informed decisions during tunnel construction