Gas-bearing sediments are widely distributed in marine and lacustrine areas. The engineering properties of gas bearing sediments, containing enclosed bubbles, are significantly different with that of saturated and unsaturated sediments. This paper investigates the consolidation behaviors of gas-bearing sediments with modulus varying along depth subjected to horizontal load using an extended precise integration method (XPIM). The compressibility of enclosed bubble is introduced to a new derived seepage equation and a varying modulus along depth is considered in governing equations. With the aid of integral transformation and Taylor expansion, such problems are solved by XPIM, which is proved to be markedly efficient and precise for boundary value problems of porous media than traditional numerical methods. Detailed comparisons against analytical solutions are performed to confirm the accurateness of XPIM. Extensive parametric investigations are conducted to examine the influence of saturation degree, varying modulus along depth and type of external load on the consolidation behaviors of gas bearing sediments. The present work is conveniently utilized to evaluate the behavior of gas-bearing sediments, and subsequently the response of foundations built in gas-bearing soil areas.

Modal parameters are of great significance in civil engineering because they can characterize the properties of structures and be used for vibration control and structural health monitoring. Subway tunnels are long linear truss structures combined with the mutual coupling of the surrounding soil. Therefore, the operational modal analysis of a mutual coupling tunnel is complicate, as is the modal identification of shield tunnels in a time–frequency domain, and these are hot civil engineering topics. Using the shield tunnel of Shanghai metro line No.12 project as a case study, we carried out the vibration response monitoring of a subway tunnel during operation and presented methods to identify structural modal parameters. The modal parameters of lower vibration modes were estimated using response measurements. Modal frequencies and shapes were identified with high precision and accuracy using the orthogonal polynomial clustering algorithm under hammer excitation conditions and the autoregressive-moving-average model under ambient excitation conditions. The dynamic behavior of a mutual coupling tunnel presented obvious low frequency characteristics, and the first 9th order mode frequencies were less than 100 Hz. The diagonal values of the modal assurance criteria were all greater than 0.85. The modal parameters can be used for the health monitoring of operational subway tunnels.

Disease in the liner back cavities of operational metro tunnels is alternately affected by groundwater environment, train cyclic load, and ambient environment conditions. Cavity disease is characterized by high levels of hiddenness and uncertainty; it also easily induces other tunnel diseases which can reduce the structure’s bearing capacity and degrade structural safety and stability throughout the tunnel. This paper proposes a novel cavity-locating method for operational shield tunnels, with special focus on single- and multiple-cavity diseases. Based on perturbation theory, dynamic behaviors (modal frequencies and shapes) of different cavity cases were obtained from an analytical model of the original tunnel structure. A modal strain energy cavity indicator (MSECI) was established to reveal the locations of both single cavity and multiple cavities. A typical shield tunnel was modeled as an Euler-Bernoulli beam on a Winkler foundation and evaluated to validate the proposed method. The perturbation theory appears to effectively characterize the dynamic characteristics of liner back cavities in metro tunnels. MSECI can be used to locate cavities accurately. This work may provide a valuable theoretical basis for the detection and analysis of tunnel cavity disease and other tunnel health-monitoring applications.

The structural health of operational metro tunnels is closely related to public safety. Prior research has focused on the locations of structural damage, but few researchers have examined both the location of damage and identifying the degree of damage, especially in metro shield tunnels. This paper proposes a new method for identifying structural damage that entails locating and detecting the degradation of tunnel performance, with a special focus on characterizing the degree of damage. First, the dynamic behaviors (modal frequencies and shapes) of different damage levels are obtained from an analytical model of the original tunnel structure. Second, a modal strain energy damage indicator (MSEDI) is introduced to locate the damage, regardless of size. Once the location of the damage is identified using MSEDI, a fuzzy logic-based damage identification (FLBDI) method is used to determine the actual extent of the damage. Finally, a simplified model of the tunnel is created using the Euler-Bernoulli beam theory and Winkler’s foundation, to further test the procedure under an incomplete modal information condition and with differing noise levels. The results reveal that the fuzzy logic- based system can identify the degree of damage and structural degradation with very high accuracy, in which the location of damage and the prediction of performance degradation is satisfactorily confirmed.

Saturated soils with overlying dry layers are frequently encountered in geotechnical engineering. In urban construction works, the underground water level is usually influenced by the extraction of water or complex fluid for industrial uses or oil exploitation tasks. The creep and consolidation behavior of saturated soils with overlying dry layers is drastically different from that of completely saturated soils. This paper presents an investigation on the creep and consolidation behavior of the layered saturated soils with overlying dry layers under the vertical load. With the aid of the Laplace-Hankel transform, typical viscoelastic models (e.g., the Kelvin, the Maxwell, or the standard linear solid model), and the correspondence principle, a semianalytical solution is presented for this investigation. Detailed comparisons between the present results with the published numerical and analytical results are given to confirm the solution, followed by an extensive parametric study examining the effect of types of viscoelastic models, thickness of the overlying layer, and viscosity. This paper aims to present a semianalytical solution to describe the time-dependent consolidation of layered saturated soils with the overlying layer accurately and to provide useful implications for foundation design on those soils.

Cavity defects in tunnel engineering have the characteristics of damage hidden and uncertainty.Aiming at cavity defect after tunnel wall,the dynamic characteristics of tunnel structure are put forward to illustrate the changing rules.Based on the perturbation theory analysis,coefficient ηrepresents the level of cavity defect was established,combined with the function δ,the modal behaviors of the analytical formula of shield tunnel structure were derived.The modal strain energy damage indicator was introduced to identify the cavity location.Finally,a metro tunnel in Shanghai city was taken as an example,the dynamic evolution analysis was carried out based on perturbation theory analysis and finite element analysis.The results show the modal strain energy damage indicator demonstrates that the introduced lining degradation can be successfully detected and located.The results can be used to provide theoretical basis for the dynamic monitoring of shield tunnel structure.

为了研究短时脉冲激振力下隧道结构振动响应及有效地提取隧道结构的模态特征。首先分析了锤击作用下的不同短时脉冲激振力精度及其频域特性，其次将短时脉冲激振力应用于上海地铁12号某盾构隧道进行了现场动力测试，最后分析了脉冲激振与隧道结构响应之间的传递函数，并结合随机减量、正交多项式法及自回归滑动平均模型法有效地提取隧道结构的模态参数。结果表明：短时脉冲激振力的中低频振动信号在隧道结构中传递特性较好，传递距离较远。隧道结构的模态频率呈现明显低频特征，前10阶模态频率在100 Hz以下。因此，短时脉冲激振力能够很好地应用于隧道动力测试及模态识别，可为基于模态特征的隧道结构损伤识别及健康监测多个研究领域提供有效的支撑和参考依据。