The Pulse-Pre-Pump Brillouin Optical Time Domain Analysis (PPP-BOTDA) based distributed fiber optic sensing (DFOS) technique has a unique advantage of achieving full-distributed structural strain with cm-order spatial resolution, which is ideal for fine stress monitoring of the pile foundation. The high spatial resolution helped to detect local changes and defects while inevitably led to noisy data meanwhile, especially a certain part of anomalous sensing data. Therefore, a robust algorithm of random sampling consistency (RANSAC) was employed to extract and process the DFOS data. In a field static load test, the variation of strain along a precast pile was measured with PPP-BOTDA interrogator. The axial force and frictional resistance were calculated based on the RANSAC processed strain data. The pile-soil interface properties were estimated as well. It shows the feasibility and good performance of PPP-BOTDA in the measurement of precast piles stress test. The RANSAC proves to be an effective method for processing DFOS data with a certain number of outliers. This work presents a valuable reference for DFOS based pile stress test and data analysis which will promote its application in other related structural health monitoring purpose.

The rapid progress of urbanization and industrialization has led to the accumulation of large amounts of metal ions in the environment. These metal ions are adsorbed onto the negatively charged surfaces of clay particles, altering the total surface charge, double-layer thickness, and chemical bonds between the particles, which in turn affects the interactions between them. This causes changes in the microstructure, such as particle rearrangement and pore morphology adjustments, ultimately altering the mechanical behavior of the soil and reducing its stability. This study explores the effects of four common metal ions, including monovalent alkali metal ions (Na⁺, K⁺) and divalent heavy metal ions (Pb²⁺, Zn²⁺), with a focus on how ion valence and concentration impact the soil’s microstructure and mechanical properties. Microstructural tests show that metal ion incorporation reduces particle size, increases clay content, and transforms the structure from layered to honeycomb-like. Small pores decrease while large pores dominate, reducing the specific surface area and pore volume, while the average pore size increases. Although cation exchange capacity decreases, cation adsorption density per unit surface area increases. Monovalent ions primarily disperse the soil structure, while divalent ions induce coagulation. Macro-mechanical tests reveal that metal ion contamination reduces porosity under loading, with compressibility rises as the ion concentration increases. Soils contaminated with alkali metal ions shows higher compression coefficients at all loads, while heavy metal ions cause higher compression under lower loads. Shear strength, the internal friction angle, and cohesion in metal-ion-contaminated clay decrease compared to uncontaminated field-state clay, with greater declines at higher ion concentrations. The Micropore Morphology Index and hydro-pore structural parameter effectively characterize both micro- and macrostructural properties, establishing a quantitative relationship between HPSP and the engineering properties of metal-ion-contaminated clay.

Earth pressure for saturated cohesive soils is closely related to the effective stress expression. For cohesionless soils, previous research indicated that the fraction of pore pressure (factor η) in the effective stress expression is below unity at high pressures. However, for cohesive soils, reliable η‐value has not been reported. In this study, experimental data from direct shear and triaxial tests were analyzed in order to derive the η‐values of two cohesive soils. It was shown that η‐value of cohesive soils decreases significantly with increasing effective stress, and the values of η derived from different experiments were consistent with each other. The obtained values of η were applied to the calculations of lateral earth pressure. The lateral earth pressure based on real η was compared with the results of traditional methods, i.e., effective stress analysis (ESA) and total stress analysis (TSA). The traditional ESA was conservative because of the overestimation of active earth pressure. Such conservatism was more significant for high plasticity clay. Contrastingly, TSA results were risky for both of the two cohesive soils.

During the shield tunneling, mud cake is one of the most common causes of cutterhead failure. Mud cake formation is a typical nonlinear process. Although the mud cake may block partial or all of the cutterhead opening, the relationship between mud cake and opening parameters has not been investigated. In this study, a prediction model of mud cake formation based on cutterhead opening is developed. The shapes of central and peripheral opening are quantified by central angle, central length, average peripheral width and standard deviation. The geological type is considered as another input parameter. A dataset of 151 real shield machines is normalized. The state of mud cake is labeled to train a model based on support vector machine (SVM). The proposed model is validated against the dataset and three other engineering cases in varied cities. Mutual relationship between mud cake and opening parameters is also investigated. It is shown that opening parameters play important roles in mud cake formation. Increasing central opening angle is an effective method to avoid mud caking. The risk of mud cake is rather small for the central angle larger than 80°. For higher length of central opening, the central angle can be even smaller. By checking the opening parameters, the risk of mud cake can be reduced before actual excavation.