Most natural soils exhibit a certain degree of soil structure which, in general, leads to increased strength and stiffness properties. However, the mechanical characterization of these soils based on conventional laboratory testing proves difficult in many cases due to sample disturbance. The present work aims to characterize the microstructure of a postglacial, normally consolidated, fine-grained deposit in Seekirchen, Austria, adopting in situ testing, laboratory testing on high-quality samples, and numerical analysis. The latter involves recalculating in situ piezocone penetration tests (CPTu) using an advanced constitutive model for structured soil. In contrast to existing in situ interpretation methods, the results of the numerical study, the mineralogical and hydrochemical testing, as well as the oedometer and bender element testing on undisturbed and reconstituted samples suggest that the soil is characterized by a significant amount of structure. It is demonstrated that the difference in shear wave velocity measured in situ and through bender element testing on reconstituted samples can be used as an indicator for soil structure. Ignoring the effects of structure may lead to inaccurate parameter determination for advanced constitutive models, which are subsequently employed to solve complex boundary value problems in geotechnical practice. As a consequence, the prediction of expected displacement may not be reliable.

Vibroflotation has proven to be an effective method for treating loose and unevenly graded coral sand foundations formed through hydraulic filling. In this study, a series of model tests were conducted to investigate the effects of particle gradations on the response of coral sand foundation reinforced by vibroflotation. The main focus was on analyzing the changes in excess pore water pressure (EPWP) and horizontal earth pressure. Cone penetration tests (CPTs) were then used to evaluate the effectiveness of vibroflotation. The results indicate that the maximum settlement occurs after the first vibroflotation, with surface settlement significantly increasing as the distance to the vibro-point decreases. The reinforcement range expands radially, and the foundation can achieve a medium or dense state after vibroflotation. During the penetration stage, the EPWP rapidly peaks and increases with depth. Shallow foundations exhibit a higher excess pore pressure ratio compared to deep foundations. Foundations with lower coarse particle content show higher EPWPs compared to those with higher coarse particle content. Lower vibration frequency results in diminished reinforcement effects in foundations with high coarse particle content and increases the difficulty of penetration. Additionally, the residual soil pressure in foundations with high coarse particle content significantly rises after three vibroflotation reinforcements. The increase in strength after reinforcement is more pronounced because the foundation has a greater coarse particle content. The reinforcement effect diminishes with increasing distance from the vibrator.

The overconsolidation ratio considerably affects the physical and mechanical properties of soil as well as the interaction between structures and soil. Scale and consolidation time limitations render the preparation of overconsolidated soil for small-scale model tests difficult. Therefore, studying structure-soil interactions, especially the vertical bearing capacity of pile foundations in overconsolidated soil becomes challenging. Given the importance of reliable overconsolidated soil in physical model tests for studying soil-structure interactions, this study, based on the fundamental of the overconsolidation ratio, established a reliable method for preparing overconsolidated soil by altering centrifuge acceleration. Piezocone penetration tests were conducted to validate the accuracy of this method. Furthermore, vertical bearing capacity of pile foundations was evaluated in various overconsolidated soils. The vertical ultimate bearing capacity of pile foundations, cone penetration resistance, pore water pressure, and sleeve friction resistance were obtained in soils with various overconsolidation ratios. Based on the results of both tests, a formula was developed to calculate the vertical ultimate bearing capacity of pile foundations, taking into account the overconsolidation ratio of soil. This proposed method for evaluating vertical bearing capacity of pile foundations in overconsolidated soil can also be applied to study interactions between other marine structures and soil. The results of the study can provide technical support for designing the foundations of offshore oil and gas facilities, wind power, and other structures.

The cone penetration tests have been employed extensively in both onshore and offshore site investigations to obtain the strength properties of soils. Interpretation of effective internal friction angle gyp' becomes complicated for cones in silty clays or clayey silts, since the soil around the advancing cone may be under partially drained conditions. Although there exist several robust methods to estimate gyp ' , the pore pressure at the cone shoulder has to be measured to represent the drainage conditions. Many cone penetrometers in practice are not equipped with a pore pressure transducer. Even for a piezocone, the pore pressure recorded in-situ may be unreliable due to the poorly saturated or clogged filter. These limitations prohibit the application of existing methods. Large deformation finite element analyses were carried out within the formula of effective stress to reproduce the cone penetrations under various drainage conditions. The numerical approach was validated against the existing model tests in centrifuge and chamber, with wide ranges of penetration rates and soil types. A backbone curve is proposed to estimate the normalized cone resistance varying with the normalized penetration rate. Based on the backbone curve, a procedure is developed to predict gyp' of cohesive soils under undrained or partially drained conditions, replacing the pore pressure with the normalized penetration rate. The procedure can be used for soils with an overconsolidation ratio no larger than 5.

The generation of negative excess pore water pressure (u2) during cone penetration test (CPT) in a given environment represents a deviation from the actual situation, thereby affecting the accuracy of the parameter inversion. Dissipation tests have been conducted to ascertain the dissipation of the u2 over time, which in turn allows for the parameters to be corrected. However, the tip resistance (qc) and sleeve friction resistance (fs) in dissipation process also vary with time, despite its potential impact on the inversion process. In this paper, the evolution of qc and negative u2 with time is successfully obtained through the utilization of indoor CPTs on silt soils. In conjunction with a viscoelastic model, the existence of stress relaxation of qc is demonstrated and the causes of qc decay are analyzed. The detailed conclusions are as follows: (1) The CPT parameters obtained from the dissipation test can be employed to rectify the discrepancy in negative u2 that arises during soil classification. (2) The qc undergoes a gradual decrease, reaching a final equilibrium state during the dissipation process. The stress-time relationship is consistent with the Three-element viscoelasticity model, which represents a stress relaxation phenomenon. The relaxation process can be divided into three distinct phases: fast relaxation, decelerating relaxation, and residual relaxation. The residual stress is found to be correlated with the depth of the soil layer. (3) During residual phase, the loss rate of qc is observed to decrease in a linear fashion with the rate of u2, prior to which the relationship is exponential. As the penetration rate increases, the rate of u2 also increases.

The 2017 Pohang earthquake [the second largest local magnitude (M-L) of 5.4 since 1978] caused significant damage: numerous sand boils and a few building settlements were observed in rice paddies and residential areas, respectively, representing unprecedented case histories of earthquake-triggered liquefaction and cyclic softening. This study evaluated liquefaction triggering and cyclic softening potentials using three in situ tests [standard penetration test (SPT), cone penetration test (CPT), and downhole (DH) test for shear wave velocity (V-S)] and laboratory tests (grain size and soil indices) for the observed sand boils and building settlements. We selected six sites, four of which had sand boils (Sites 1, 2, 3, and 4), and two of which had experienced building settlements that may have resulted from cyclic softening (Sites 5 and 6). The SPT, CPT, and V-S adequately assessed liquefaction triggering [i.e., factor of safety (FS)2 at all depths. The site-specific cyclic stress ratio through the maximum shear stress ratio computed from site response analysis appropriately evaluated the liquefaction triggering and cyclic softening at the considered sites. The results of the soil index test are consistent with the liquefaction and cyclic softening susceptibility criteria for fine-grained soils. We publicly provide the field and laboratory measurements in this study to enrich case history data on liquefaction and cyclic softening induced by intermediate-size earthquakes (e.g., a moment magnitude, M<6), which might significantly contribute to geotechnical earthquake engineering and engineering geoscience communities

In the reconstruction and expansion of expressways in soft soil areas, controlling the differential settlement between the new and existing subgrades is of vital importance. To investigate the settlement and deformation characteristics of both the new and existing subgrades, piezocone penetration test (CPTU) and dissipation tests were conducted on these subgrades. The CPTU dissipation data was utilized to determine the soil's degree of consolidation, and settlement calculations for the new and existing road subgrades were based on the CPTU test results. Subsequently, a finite element model was developed using the CPTU test findings to analyze the horizontal displacements, vertical settlements, and differential settlements of the new and existing subgrades before and after the reconstruction and expansion. Based on the measured settlement results, the new and old subgrade settlement calculation results are verified. The outcomes revealed that the degree of consolidation for the existing road subgrade of the Lianhuai Expressway ranged between 42 % and 96 %. The maximum horizontal displacement of the subgrade pre- and post-expansion occurred at the slope toe. Before expansion, the maximum vertical settlement was observed along the road's centerline, while after expansion, it was located in the centerline of the widened section. The maximum additional settlement amounted to 274.77 mm. During the new road construction phase, the differential settlement between the new and existing road subgrades increased rapidly over time, peaking at its maximum value. However, during the operational phase of the new road, this differential settlement tapered off as time progressed.

The utilization of cone penetration test (CPT & CPTu) results to assess the bearing capacity of deep foundations stands as a crucial application in geotechnical engineering. This study focuses on leveraging the outputs of the CPT test, considering the distinctive features of piles and the abundance of reliable information, coupled with the rapidity of the test. The CPT test outcomes can be employed both directly and indirectly to ascertain the capacity of the toe and shaft resistance of piles. In seismic conditions, applying earthquake acceleration to sensitive and liquefiable soils induces an increase in pore water pressure Delta u, leading to a subsequent reduction in soil strength. Thus, investigating changes in excessive pore water pressure serves as a key dynamic load indicator in seismic scenarios. This research initially determines the bearing capacity of deep foundations through common methods using CPT data. Subsequently, key parameters influencing the development and dissipation of Delta u, such as soil sensitivity (St), undrained shear strength (Su), and dimensionless parameters of pore water pressure 1-Bq\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\left( {1 - B_{q} } \right)$$\end{document} and 1-u2qt\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\left( {1 - \frac{{u_{2} }}{{q_{t} }}} \right)$$\end{document}, are meticulously evaluated. This study proceeds to investigate the impact of these parameters on the bearing capacity of deep foundations, drawing insights from a comprehensive database encompassing CPT & CPTu data from 18 diverse sites worldwide. Comparative analysis between the proposed method and conventional approaches reveals a significant reduction in the aforementioned parameters' influence on the bearing capacity of deep foundations. Consequently, this finding underscores the necessity of incorporating such considerations in geotechnical bearing capacity calculations for projects situated on soils prone to liquefaction.

Ensuring safe extraction is a prerequisite for the development of deep-sea resources. As an in-situ exploration technique, cone penetration test (CPT) can accurately analyze the physical, strength, and deformation characteristics of deep-sea sediments and hydrate reservoirs after data interpretation, thereby ensuring the safe extraction of deep-sea resources. CPT calibration chamber (CCC) testing is considered one of the most effective means to determine the correlation between lab measurement values of soil and its undisturbed mechanical properties. Currently, the stress conditions of the CCCs that have been established are limited in scope and insufficient to simulate the high-stress field conditions of deep-sea sediments as well as the high-pressure and low-temperature conditions where deep-sea hydrates occur. Therefore, based on the traditional CCC, this article independently developed a high-pressure and temperature-controlled CCC with a type of boundary condition one (BC1), which can be used to simulate the process of CPT penetrating marine sediments (including the in-situ environment of hydrate reservoirs). This CCC features a maximum loading force of 200 KN at the top and 150 KN at the bottom. With a maximum confining and pore pressure of 25 MPa, and a temperature range from -15 degrees C to room temperature, it can effectively replicate in-situ effective stress, pore pressure, and temperature conditions necessary for hydrate formation. The maximum sample size is 300 mm in diameter and 600 mm in height, and two sizes of CPT probes (2 cm2 and 5 cm2) can be replaced to test the boundary effect. To verify the feasibility of the CCC, a series of CPT penetration experiments were conducted on silty sediments under highpressure and temperature-controlled conditions in the established CCC. It was found that cone tip and friction resistance increase with the increase of effective stress. This CCC contributes to establish the relationship between CPT data and various mechanical properties of marine sediments, and providing theoretical support for evaluating the stability of marine hydrate reservoirs during exploitation.

CPTu (piezocone penetration test) is widely used in engineering practice to determine various parameters of clays under partially drained conditions. However, most existing research is based on undrained or fully drained conditions for clays, leading to underestimation or overestimation of soil strength. By applying the Eulerian-Lagrangian large deformation finite element method to analyse the water-soil interaction, the CPTu driving mechanism in offshore saturated soft clays under different drainage conditions is revealed. An advanced hypoplastic constitutive model for clays is used to simulate the nonlinear behaviour of kaolin under different drainage conditions. The generation, accumulation, and dissipation of excess pore water pressure under different drainage conditions are analysed, as well as the influence of excess pore water pressure on cone tip resistance and the effective stress of the soil during the CPTu penetration process.