Sandy Soil Liquefaction Prediction Based on Clustering-Binary Tree Neural Network Algorithm Model

The neural network algorithm is a small sample machine learning method built on the statistical learning theory and the lowest structural risk principle. Classical neural network algorithms mainly aim at solving two-classification problems, making it infeasible for multiclassification problems encountered in engineering practice. According to the main factors affecting sand liquefaction, a sand liquefaction discriminant model based on a clustering-binary tree multiclass neural network algorithm is established using the class distance idea in cluster analysis. The model can establish the nonlinear relationship between sand liquefaction and various influencing factors by learning limited samples. The research results show that the hierarchical structure based on the clustering-binary tree neural network algorithm is reasonable, and the sand liquefaction level can be categorized accurately.

Pore water pressure responses of saturated sand and clay under undrained cyclic shearing

In this study, changes in the pore water pressure were observed for saturated specimens of a loose fined-grain sand (Nam O sand) and a soft silty clay (Hue clay) subjected to undrained cyclic shearing with different testing conditions. The cyclic shear tests were run for relatively wide range of shear strain amplitude (g = 0.05%-2%), different cycle numbers (n = 10, 50, 150 and 200) and various shear directions (uni-direction and two-direction with phase difference of q = 0o, 45o and 90o). It is indicated from the experimental results that under the same cyclic shearing condition, the pore water pressure accumulation in Hue clay is at a slower rate, suggesting a higher cyclic shear resistance of Hue clay than that of Nam O sand. Liquefaction is reached easily in nominally 50% relative density specimens of Nam O sand when g ³ 0.4%, meanwhile soft specimen of Hue clay is not liquefied regardless of the cyclic shearing conditions used in this study. The threshold number of cycles for the pore water pressure generation generally decreases with g meanwhile, the threshold cumulative shear strain for such a property mostly approaches 0.1%. In addition, by using this new strain path parameter, it becomes more advantageous when evaluating the pore water pressure accumulation in Nam O sand and Hue clay subjected to undrained uni-directional and two-directional cyclic shears.

Seismic Damage and Analysis of the Xiker Earth Dam During the 2020 Jiashi Earthquake, Northwestern China

The 2020 Jiashi Mw 6.0 earthquake occurred at the Kepingtage fold-and-thrust belt in the South Tianshan front, Northwestern China. The ground shaking caused extensive co-seismic deformation of the Xiker dam in the meizoseismal area. We obtained strata distribution characteristics of the dam foundation through drilling. Using laboratory and in situ tests, the particle size distribution, standard penetration, and shear wave velocity of each layer were obtained. Along with peak ground acceleration, we evaluated the potential of sand liquefaction in various layers and proposed a relationship between dam fissures and sand liquefaction. Our results suggest that sand liquefaction occurred in the silty sand layer 0–3 m beneath the dam foundation. Sand liquefaction occurs behind the dam, resulting in uneven settlement of the dam foundation, making the horizontal deformation of the backslope of the dam significantly larger than the foreslope of the dam. Using numerical simulations, we found that sand liquefaction behind the dam can cause different horizontal deformation vectors (maximum deformation is ∼7.45 cm) in the dam foreslope and backslope, which cause the dam to rotate in the downstream direction. Large fissures also formed on the dam crest.

Study on Sand Liquefaction Induced by Songyuan Earthquake with a Magnitude of M5.7 in China

A large-scale sand liquefaction producing typical and novel surface phenomena was found at the epicenter of Songyuan M5.7 earthquake occurring on May 28, 2018. Field survey and experimental test encompassing boring sampling, standard penetration test(SPT), cone penetration test(CPT), scanning electron microscopy(SEM), X-ray diffraction(XRD), and X-ray fluorescence(XRF) were performed to ascertain the liquefaction damage and site characteristic. Cone penetration test is an excellent assay for the identification of liquefied sand layer and acquisition of physio-mechanical parameter. Moreover, the assay is applicable for on-site post-earthquake investigation. Factors promoting the formation and controlling the distribution of the sand liquefaction were analyzed. The liquefaction impacted an 80 km2 area, and was primarily embodied as sand boil and water sprout on rice field, despite producing no significant structural damage. Due to the simple profile of local soil layer, ground motion, geomorphic condition, and groundwater level were the main factors governing the distribution of the liquefaction. Majority of the liquefied sand layer was discovered at the depth less than 10 m. However, deep layer liquefaction at the depth greater than 18 m was also discovered, which was demonstrated by the upward movement of liquefied sand towards the upper silty clay layer at the depth of 17 m. Most importantly, we have identified loess liquefaction, a phenomenon which had not been reported previously in Northeast China. Lastly, it is important to highlight the risk of significant liquefaction damage at Songyuan. Hence, investigating the liquefaction risk is potentially beneficial for augmenting planning on earthquake mitigation, engineering reconnaissance, and design project.

Geotechnical Engineering Properties of Soils Solidified by Microbially Induced CaCO3 Precipitation (MICP)

Microbially induced calcium carbonate precipitation (MICP) uses the metabolic function of microbes to carry out biochemical reactions with other substances in the environment. Through the controlled growth of inorganic minerals, soil particles are cemented and soil pores are filled to solidify the soil and reduce its permeability. Thus, the application of this technology was foreseen in geotechnical engineering and environment (building antiseepage, contaminated soil restoration, slope soil erosion, and sand liquefaction). In this review article, based on current research findings, the urea hydrolysis and the cementation mechanism of MICP are briefly described. The influences of factors such as enzyme activity, cementation solution concentration, pH, temperature, grouting method, and particle size on MICP-treated soil are discussed. The engineering properties of MICP-treated soils are evaluated, for instance, the strength, stiffness, liquefaction resistance, permeability, and durability. The applications of MICP technology in ground improvement, geotechnical seepage control, foundation erosion resistance, and fixation of heavy metals are summarized. Finally, future directions of the development of MICP technology are elucidated to provide a reference and guidance for the promotion of MICP technology in the geotechnical engineering field.