Buried water pipelines, as crucial urban infrastructure, play an essential role. However, the damage to the pipeline structure has emerged as a severe public safety hazard. Monitoring the state of the pipeline structure holds great significance for the normal operation of water pipelines. In this paper, a damage monitoring method for buried pipelines based on distributed acoustic sensing technology is proposed. Through a series of field experiments conducted on a pipeline, the feasibility of utilizing the attached fiber-optic cable to acquire vibration information has been demonstrated. The recorded vibration signals can indicate various damage statuses during the pipeline damage process, including rock/soil fall, pipeline seepage, and pipe wall failure. The results suggest that the fiber-optic cable accompanying the pipelines can be exploited as sensing resources to monitor damage risks to the pipelines, which presents advantages in the damage identification and location of buried pipelines. This research provides a valuable reference for the application of distributed acoustic sensing technology in the damage monitoring of urban buried water pipelines.

Screw piles are uniquely-shaped concrete piles with screw threads that have been widely used in various fields, including construction, structural design, and geotechnical engineering. Research on the dynamic characteristics of screw piles under vertical loads is limited compared with that investigating traditional circular piles. This report describes an analytical solution that has been developed to investigate the dynamic features of a screw pile under a longitudinal load while considering the cushion cap effect. The Laplace transform and Potential functions are applied to decouple the three-dimensional wave equations of the soil. The dynamic response of the screw pile is deduced using a modified impedance transfer function method. Finally, the cushion cap displacement and velocity in the frequency domain are determined by combining the initial conditions. The analytical solutions are compared with field-measured curves to validate the developed method. The results indicate that the soil around the pile can be regarded as a threedimensional continuous medium to simulate the radiation-damping effect as the wave propagates outward. The cushion cap reduces the screw pile damage caused by resonance, particularly in the low-frequency range. Considering the effects of vibrational loads, a screw pile should employ a large lightweight cushion cap, i.e., with the largest reasonable dimensions and with concrete materials that are as light as possible. The results of this study provide a theoretical basis for designing a dynamic foundation of a screw pile.

Lignin fiber is a type of green reinforcing material that can effectively enhance the physical and mechanical properties of sandy soil when mixed into it. In this study, the changes in the dynamic elastic modulus and damping ratio of lignin-fiber-reinforced sandy soil were investigated through vibratory triaxial tests at different lignin fiber content (FC), perimeter pressures and consolidation ratios. The research results showed that FC has a stronger effect on the dynamic elastic modulus and damping ratio at the same cyclic dynamic stress ratio (CSR); with the increase in FC, the dynamic elastic modulus and damping ratio increase and then decrease, showing a pattern of change of the law. Moreover, perimeter pressure has a positive effect on the dynamic elastic modulus, which can be increased by 81.22-130.60 %, while the effect on the damping ratio is slight. The increase in consolidation ratio increases the dynamic elastic modulus by 10.89-30.86 % and the damping ratio by 38.24-100.44 %. Based on the Shen Zhujiang dynamic model, a modified model considering the effect of lignin fiber content FC was established, and the modified model was experimentally verified to have a broader application scope with a maximum error of 5.36 %. This study provides a theoretical basis for the dynamic analysis and engineering applications of lignin-fiber-reinforced sandy soil.

Ground vibrations from operating railway in tunnels is a significant obstacle to sustainable development of subway. The backfill grouting layer, formed during shield tunneling, serves as a critical medium in propagation of tunnel vibrations, highlighting its potential in vibration mitigation. A semi-analytical model for the tunnelgrouting layer-soil system is proposed in this study, in order to clarify the influence of backfill grouting layer on the dynamic responses in a half-space, subjected to tunnel vibrations. In establishment of the closed-form solution, the tunnel and grouting layer are considered as two nested hollow cylinders embedded in a halfspace, with applying the Fourier transform and wave transformation. As a validation, the numerical results from the proposed semi-analytical model are compared with those reported in literature. Parametric studies, with respect to the geometric configuration (i.e., the thickness) and material parameters (i.e., the Young's modulus, material damping, and density) of the backfill grouting layer in the mitigation of tunnel vibrations, are carried out. It is found that incorporation of the backfill grouting layer significantly changes the dynamic responses of the soil and, by appropriately designing its material parameters, especially the Young's modulus, effective mitigation of tunnel vibrations can be achieved.

During pile installation, construction disturbances alter soil mechanical properties near the pile, significantly affecting the dynamic response of the pile. This paper develops a three-dimensional (3D) analytical model to investigate the vertical dynamic response (VDR) of a pile in radially inhomogeneous saturated soil. Firstly, by employing the separation variable method and incorporating the continuity and boundary conditions of the soilpile system, the exact solution of the whole system in the frequency domain was derived. Subsequently, the timedomain velocity response under semi-sinusoidal vertical excitation is obtained using Fourier inverse transform and the convolution theorem. The accuracy and superiority of the proposed solution were validated through comparison with previous analytical solutions. Finally, the developed solution is then used to examine the impact of parameters of saturated soil and pile on the VDR of a pile. The results demonstrate that the proposed saturated model better captures the VDR of a pile in radially inhomogeneous saturated soil compared to the single-phase model. The VDR of a pile is significantly influenced by the pore water, porosity, disturbed degree and range of the saturated soil, as well as the elastic modulus of the pile.

The dynamic response of historical masonry structures involves multiple sources of nonlinearity, arising from the materials used, the ageing, the complex geometries and boundary conditions involved. As a result, modelling the seismic response of these buildings requires detailed instrumentation beforehand. Crossed by active faults and frequently shaken by moderate earthquakes (Mw3-4), the Cusco region (Peru) has many stone and earth masonry buildings that turn out to be particularly vulnerable to the seismic hazard. We therefore conducted an ambient vibration-based survey in the 17th-century church of San Cristobal in Cusco, seriously damaged by the 1950 earthquake. By combining an Operational Modal Analysis, single-sensor monitoring for over a year and free-field microtremor measurements, our work highlights the existence of strong soil-structure interaction and topographic effects resulting in the excitation of a rigid-body-like mode. Continuous instrumentation also made it possible to study the structure's response to earthquakes, revealing an unexpected frequency drop during a Mw4.2 earthquake, followed by a slow recovery process that lasted more than two months. These results shed new light on the seismic vulnerability of the church, and call for further investigation into the processes behind the site effects and nonlinear dynamics that characterise the response of Andean built heritage.

With the Bulk Jupiter accident, the dynamic separation behavior of solid bulk cargoes in sea transportation, which is different from the usual liquefaction of cargoes, has gradually come to people's attention and is an almost empty field that urgently needs to be researched. In this work, we first conducted vibration table tests for bauxite, replaced bauxite with transparent soil with the same particle size distribution and moisture content, and combined image processing and analysis techniques to complete the detailed visualization of the dynamic separation process. Through the above research, this article reveals the essential characteristics of dynamic separation, including the changing rules of layer-wise water content, pore water pressure, particle motion, and pore water migration. It is concluded that the most apparent feature of the dynamic separation process is the generation of a free liquid surface containing fine particles in the upper layer. The article concludes with a systematic study of the dynamic separation of typical mineral soil. The novel experimental system developed in this study contributes to elucidating the mechanism of dynamic separation of minerals and soil from a precise perspective. [GRAPHICS] .

Soil-rock mixtures with large particle size variations are often used as fill materials for expressway construction in mountainous areas. Conventional testing methods do not enable fast and nondestructive monitoring of real-time changes in the compaction quality of soil-rock filled subgrades. Selecting an appropriate evaluation method is the key to controlling the compaction quality of a soil-rock filled subgrade. In this study, three-dimensional DEM models of subgrade materials were reconstructed by a spherical harmonic series whose harmonization degree was fixed at 15. The macroscopic and mesoscopic behaviours and characteristics of the subgrade under vibratory rolling were analysed. The results showed that the porosity, contact force and coordination number of the subgrades tended to be stable in the last two passes. The subgrades with 4 filler combinations presented the similar mechanical anisotropy and meso-mechanical states. On-site monitoring of subgrades under vibratory rolling and settlement after construction was performed, and the results were considered. An evaluation method and criterion to control the compaction quality of the SRM subgrade was proposed, i.e., whether the average value of the vibration compaction value from the second to last pass differed by more than 2% from the average value in the last pass.

The laying of the underground pipeline in the same ditch has caused great challenges to the attractive transportation mode of hydrogen mixed with natural gas pipeline in service. The tendency to damage of hydrogen to steel increases the possibility of flammable and explosive gas entering underground engineering significantly. A leakage monitoring method for buried hydrogen-doped natural gas pipeline based on vibration signals with machine learning is proposed. Firstly, the distributed vibration sensor captures the multisource vibration signals propagating in the soil. An optimal combination of wavelet basis functions, decomposition level, and threshold parameters is selected carefully for signal denoising and accurate extraction of leakage-generated signals. Then the characteristics extracted in different frequency bands are investigated with other influencing factors, including the hydrogen-doping ratio, which affects the propagation speed of the pressure wave. The unique characteristics of vibration signal generated by pipeline leakage are extracted. On this basis, combined with the high efficiency of machine learning recognition model, a leakage monitoring model for buried hydrogen-doped natural gas pipeline is established, which achieves a 2.01 % false alarm rate at a maximum positioning distance of 70 cm. It has been successfully applied to the leak detection and location of buried hydrogen-doped natural gas pipelines, which can significantly improve the safety and reliability of underground pipeline system engineering.

In recent years, some cities have adopted a new type of tunnel termed quasi-rectangular tunnel (QRT). Compared with the common double-line single-circle tunnel, the QRT has a smaller cross- and narrower spacing. Existing researches about QRTs mainly focus on their mechanical properties, with a lack of research on the influence of vibration and resulting noise on the surrounding environment. The vibration and structure-borne noise in the building along the subway line are adverse to human health when trains pass through the QRT. In this paper, the characteristics of vibration generated by train operation in the QRT and the propagation law in the soil are analyzed based on the finite element method-infinite element method (FEM-IEM) model. Combined with the monitoring data, vibration and indoor secondary structure-borne noise and their annoyance degrees in a 7-storey residential building 18m away from the line are also predicted and evaluated. Results show that during the ground vibration, indoor vibration and structure-borne noise of buildings along the line are mainly concentrated in the frequency band around 40Hz. The vibration and structure-borne noise of the first floor all exceed the night limit specified by an industry standard. The annoyance caused by vibration on the first floor is 0.96, which makes people feel very annoyed, while the annoyance caused by noise is 0.251, which makes people feel slightly annoyed. The research results highlight the effects of railway-induced vibrations in QRT on the building along the subway line, emphasizing their importance in the development of rail transit with QRT. The estimated vibration and noise levels, along with the degrees of annoyance, can be effectively utilized during the design and construction processes of both QRT and buildings to mitigate negative impacts on human comfort and health.