Earth embankment dams are one of the most commonly constructed hydraulic infrastructures worldwide. One mode of dam failure is piping through the embankment, which is initiated by internal erosion of soil particles inside dams. In this study, the applicability of microbially induced carbonate precipitation (MICP) for internal erosion control is examined in the laboratory using sand-kaolin mixtures of different particle sizes. A series of internal erosion tests are conducted using a newly designed rigid-wall column erosion test apparatus, which allows independent control of MICP treatment. Erosion rate/coefficient, volumetric change, and permeability are characterized during the internal erosion process. It is found that MICP treatment facilitates the reduction of erosion and volumetric contraction of sand-clay mixtures investigated in the current study. Carbonate precipitation increases the erosion resistance of sand-clay mixtures by absorbing/coating fine particles directly and bridging the conta...

Distributed Fiber Optic Sensing (DFOS) is one of the promising tools for structure health monitoring. It can measure physical quantities (such as temperature, strain, and vibration) of the fiber continuously (say 5 cm interval) along its length for long distance (say 10 km) due to its low-loss characteristic. By attaching an optical fiber cable to a structure or embedding it inside a structure, it is possible to monitor the changes of ambient parameters of the structure. In this paper, the measurement principles and their state-of-the-art status in terms of their capabilities are discussed. The main advantage is its high sensitivity over large distances and the ability to interface with a wide range of measurands in a distributed manner. The systems provide thousands of “strain gauges”, “thermo-couples”, or “accelerometers” along a single fiber optic cable connected to or embedded in structures, which can then serve as a civil infrastructure nerve system. It can be applied to flexible geometries, providing the ability to design a whole range of sensors with tremendous information carrying capacity. DFOS can provide a highly effective monitoring system for both short and long term to realize our concept of “smart infrastructure”.

目的 水合物沉积物开采过程是一个热-水-力-化多场耦合过程,该过程包含了不同土层间的热对流、压缩引起的局部变形以及胶结结构破坏引起的应力松弛。不适当的开采会引起出砂、塌孔等破坏问题。本文旨在建立天然气水合物沉积物多场耦 合计算模型,以量化由开采引起的地质灾害风 险。

Instrumented pile tests are vital to establish the performance of a pile and validate the assumptions made during initial design. Conventional instrumentation includes vibrating wire strain gauges and extensometers to measure the change in strain or displacements within a pile. Although these strain and displacement gauges are very accurate, they only provide strain/displacement readings at discrete locations at which they are installed. It is therefore common to interpolate between two consecutive points to obtain values corresponding to the data gaps between points; in practice, these discrete instrumented points could be tens of meters apart, at depths corresponding to different soil layers, and hence simple interpolation between the measurement points remains questionable. The Brillouin optical time-domain reflectometry fiber optic strain sensing system is able to provide distributed strain sensing along the entire length of the cable, enabling the full strain profile to be measured during a maintained pile load test. The strain data can also be integrated to obtain the displacement profile. This paper presents three case studies which investigate the performance of three concrete bored piles in London using both conventional vibrating wire strain gauges and distributed fiber optic strain sensing during maintained pile load tests, which enable comparisons made between the two instrumentation systems. In addition, finite-element analyses show that the ability to measure the full strain profiles for each pile is highly advantageous in understanding the performance of the pile and in detecting any abnormalities in the pile behavior.

The integrity of cast-in-place foundation piles is a major concern in geotechnical engineering. In this study, distributed fibre optic sensing (DFOS) cables, embedded in a pile during concreting, are used to measure the changes in concrete curing temperature profile to infer concrete cover thickness through modelling of heat transfer processes within the concrete and adjacent ground. A field trial was conducted at a high-rise building construction site in London during the construction of a 51 m long test pile. DFOS cables were attached to the reinforcement cage of the pile at four different axial directions to obtain distributed temperature change data along the pile. The monitoring data shows a clear development of concrete hydration temperature with time and the pattern of the change varies due to small changes in concrete cover. A one-dimensional axisymmetric heat transfer finite element (FE) model is used to estimate the pile geometry with depth by back analysing the DFOS data. The results show that the estimated pile diameter varies with depth in the range between 1.40 and 1.56 m for this instrumented pile. This average pile diameter profile compares well to that obtained with the standard Thermal Integrity Profiling (TIP) method. A parametric study is conducted to examine the sensitivity of concrete and soil thermal properties on estimating the pile geometry.