Estimation of site amplification is important for a seismic hazard assessment. To develop site amplification predictionmodels, the models have utilized both measured and randomized profiles to ...compensate for the limited number of measurement database. One-dimensional site response analyses were performed to calculate linear and nonlinear responses, which were then separated into training and test data. While most amplification models are based on regression analysis using specific types of functions, this study utilized machine learning (ML) models with algorithms independent of prior functional forms. Random forest (RF) and deep neural network (DNN) models were used to train the model, and the test data were used to predict the amplifications. The DNN-based model shows more accurate results than the RF-based model, and the ML-based models were shown to outperform the existing regression-based model
The significance of predicting the dynamic response and damage of an existing concrete tunnel during underground blasting has increased owing to the close proximity between the newly built and ...existing tunnels. Peak particle velocity (PPV) is a commonly used criterion in the assessment of blast-induced structural damage. However, such structural damage is also associated with the frequency content of the blast wave. Nevertheless, the recommended threshold PPVs, which are based on empirical criteria, predict conservative estimations. Using stringent and regulated blasting methods often results in project delays and escalates the total project expenditure. In this paper, a three-dimensional finite element model of an underground tunnel has been developed in LS-DYNA to analyze damage to the concrete tunnels under blast loading. A suite of analyses was performed to examine the potential damage induced in the underground tunnel. A lower frequency load was found to have a greater potential for producing damage compared with a high frequency blast load. The results showed that the location of the cracking within the tunnel, such as the arch foot or tunnel wall, was also influenced by the frequency of the blast wave. The maximum allowable PPV for the concrete tunnel was determined for a range of frequencies based on predicted free field PPV and additional factors of safety of 1.2 and 1.5 were established, depending on the safety needs and importance of the tunnel construction. Thus, our findings provide useful information for improving the evaluation of tunnel damage and guaranteeing the safety of underground tunnels.
We assess the seismic response of homogeneous slopes composed of sand using the outputs of two-dimensional (2D) dynamic nonlinear finite element analyses. The slope models are configured to have a ...range of static factor of safety (FSstatic) by adjusting the slope geometry and soil shear strength. The Newmark displacements are numerically calculated from equivalent horizontal acceleration time histories, which are determined by integrating shear and normal stresses across the predefined failure surface. The Newmark displacements are correlated with a number of ground parameters, which include peak ground acceleration (PGA), peak ground velocity (PGV), arias intensity (Ia), and cumulative absolute velocity (CAV). It is demonstrated that PGV produces the strongest correlation with the Newmark displacement, whereas PGA yields a weak linkage with the numerically calculated displacement. Empirical functions that relate FSstatic and ground motion parameters with the Newmark displacements are proposed.
In this study, the seismic ground motion incoherency evaluation and numerical simulation based on spatial variability of rock site was performed using numerical analysis. To conduct this research, an ...inhomogeneous rock numerical models of 300 m x 150 m were generated using Finite Element Method (FEM) software, OpenSees. A case matrix based on the coefficient of variation and correlation length, a representative parameters indicating spatial variability, was generated. Through the dynamic numerical analysis, ground motions were obtained for each case, and the ground motion coherency functions were calculated. The empirical coherency function of the Pinyon-Flat site in the western United States was reproduced using numerical analysis, which showed the possibility of developing a coherency function of actual rock site using numerical simulation. And, as a result of the case study analysis, it was found that the spatial variability of the rock mass has a very large effect on the seismic ground motion coherency.
•We detect cavities formed around concrete sewage pipelines using impact echo method.•We develop a new impact device to apply a consistent impact energy.•A new quantitative index denoted sustained ...duration calculated from FFT and STFT is used to detect cavities.•Model and field tests demonstrate that presence of cavities can be reliably predicted using the proposed index.
Impact-echo method has been successfully used to detect flaws in concrete and to evaluate the state of grout bonding in tunnels. It has not yet been used to detect underground cavities formed by leakage of pipelines, which is becoming a major problem in many urban environments. We perform model and field tests to evaluate whether the impact-echo method can be used to detect cavities around concrete sewage pipelines. Fourier spectrum was used to determine the resonant frequency and the short time Fourier transform was used to determine the temporal variation of the resonant frequency component. Results show that the presence of cavity cannot be reliably predicted from the wave time history or Fourier spectrum. The spectrogram is demonstrated to be a better indicator for detecting the presence of a cavity. The cavity induces a longer tail in the spectrogram because of a higher impedance contrast and a lower attenuation. We propose a new quantitative index based on the resonant frequency and the spectrogram, denoted as the sustained duration. Both model and field tests demonstrate that the cavity in wet soils can be successfully detected using the proposed index.
Soil pollution caused by oil leakage from various industrial facilities such as gas stations, oil plants, military bases, and railway depots has become a serious global environmental and geotechnical ...issue. The indirect-heated microwave thermal desorption technology has been developed in this study for economical and efficient remediation of oil or organic pollutants. The conclusions were made based on laboratory tests and analyses of the environmental (TPH; total petroleum hydrocarbons) and geotechnical (physical and mechanical) properties of the soil before and after treatments. (1) As the newly-developed equipment was operated for 3 h with the electric power of 32 kW to reach target temperature of 600 °C, more than 99.8% of TPH was removed. (2) In the aspect of geotechnical properties, the internal friction angle, maximum dry density and permeability coefficient of the soil were reduced by oil contamination and were finally restored to the almost initial level of the soil after treatment. Therefore, treated soil is expected to be reusable for geotechnical construction purposes such as construction fill materials. (3) It was also found that the developed technology reduces 75% of energy cost and 25% of CO2 emissions for the remediation of lubricant oil-contaminated soil comparing with conventional one.
The behavior of laterally loaded pile groups is usually accessed by beam-on-nonlinear-Winkler-foundation (BNWF) approach employing various forms of empirically derived p-y curves and p-multipliers. ...Averaged p-multiplier for a particular pile group is termed as the group effect parameter. In practice, the p-y curve presented by the American Petroleum Institute (API) is most often utilized for piles in granular soils, although its shortcomings are recognized. In this study, we performed 3D finite element analysis to develop p-multipliers and group effect parameters for 3 × 3 to 5 × 5 vertically squared pile groups. The effect of the ratio of spacing to pile diameter (S/D), number of group piles, varying friction angle (φ), and pile fixity conditions on p-multipliers and group effect parameters are evaluated and quantified. Based on the simulation outcomes, a new functional form to calculate p-multipliers is proposed for pile groups. Extensive comparisons with the experimental measurements reveal that the calculated p-multipliers and group effect parameters are within the recorded range. Comparisons with two design guidelines which do not account for the pile fixity condition demonstrate that they overestimate the p-multipliers for fixed-head condition.
The feasibility of the electrical resistance heating method developed in this study was evaluated for the remediation of multi-contaminated silty sand in terms of environmental and geotechnical ...aspects. The multi-contaminated silty sand sampled in this study was polluted with 21,081 mg/kg of heavy oils, as well as heavy metals. Silty sand, treated using the electrical resistance _heating method was environmentally, as well as geotechnically, compared with the multi-contaminated silty sand in terms of residual concentration, leaching, shear modulus and modified California bearing ratio (CBR). The remediation test was conducted with a target temperature of 700 °C. The removal efficiency of total petroleum hydrocarbon (TPH) was estimated as 99.99% after remediation in 48 h; most of the heavy metals, as some of the contaminants, were isolated as a crystal in treated silty sand without any harmful leakage, and heavy oil was fully extracted with a form of mist and dust. Moreover, it was also geotechnically found that the decontamination process, including the removal of heavy metals and oils, had an effect on the increase in the internal friction angle, shear modulus and modified CBR of treated silty sand. In conclusion, it is shown that the electrical resistance heating method developed in this study is an environmentally and geotechnically effective technology for the recovery of clean construction fill material from hazardous-waste-contaminated silty sand.
This study aimed to develop a decision-making support system for managing the seismic performance of aged road facilities in a road network, based on their evaluated seismic performance. This study ...was divided into two parts. In Part 1, seismic fragility functions are developed for bridges, tunnels, retaining walls, and slopes, while considering aging. In Part 2, the degradation of the seismic performance of the road network, along with social and economic resilience are evaluated based on these seismic fragility functions. The developed decision-making support system was applied to domestic test beds in Korea, and the results are discussed in Part 2. To develop seismic fragility, various ground motions suitable for the ground conditions in South Korea were generated. In particular, reduced- and real-size bridge piers and bearings were tested to study the effect of aging on seismic behavior. Other types of facilities, such as tunnels, retaining walls, and slopes, were also analyzed to study the same. For simplicity, representative facilities that can properly represent the seismic behavior of similar facilities were selected from a large number of facilities. The limit states for these representative facilities were defined, and their seismic fragility curves were calculated using these limit states.
The time-averaged shear wave velocity of top 30 m (VS30) is the most commonly used parameter to classify a site and evaluate its amplification characteristics for the seismic design. The in-situ ...seismic tests must be performed up to a depth of 30 m for obtaining the shear wave velocity (VS) profiles to estimate VS30. It is intimated that, in most of the cases, the measured VS profile does not extend up to 30 m due to numerous reasons including limitation of testing techniques and unfavorable field conditions. Since, the measurements of VS30 are unavailable for the majority of Pakistan and the world, the local geology and topographic slope or its combination are used to estimate VS30. However, there is no field-based validation of the estimated VS30 is performed in Islamabad–Rawalpindi region, the proxy-based estimation may lead to unrealistic results. To accommodate this, region specific extrapolation methods are developed. This study develops an empirical data-driven function of VS30 from shallow VS profiles by correlating VS30 with the time-averaged VS to depths less than 30 m. In this regard, 85 VS profiles are used from Rawalpindi-Islamabad region. A comparative analysis of the proposed procedure is carried out with the published methods. It is revealed that VS30 predicted by the proposed function results in close matches with the data measured in the western United States. In addition, the results indicate that the local geology and topographic slope proxies may not be acceptable for usage in the region due to their greater uncertainty. Finally, a procedure for extrapolating the VS profile from available shallow depth measurements up to 30 m is proposed.
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