The foundation soil is often over-consolidated due to the change of soil consolidation history in practical engineering. The effect of over-consolidation ratio (OCR) on the mechanical properties and microstructure of silt has not been sufficiently studied especially on the Yellow River alluvial silt. A series of triaxial undrained shear tests and corresponding SEM tests of the Yellow River alluvial silt were then carried out under different confining pressures and OCRs. The stress and strain curves of the silt show strain-hardening characteristics. The hardening characteristics become more significant, and the peak stress increases significantly as the confining pressure and OCR increase. The silt specimens show phase transformation behavior under a normal consolidation state, which is characterized by stages of initial contraction, temporary phase transformation, and later dilation. The silt tends to be more dilative for over-consolidated specimens and the dilation behavior was more obvious with higher OCRs. The deviatoric stress of the silt can be normalized by the consolidation pressure. The normalized undrained shear strength of the silt generally increased with OCR. The cohesion and internal friction angle of the silt increase with OCR increasing which behaved more like the typical clays as it has more silt content and clay content. The apparent porosity decreases and the average shape coefficient increases with the increase of confining pressure and OCR which shows the silt is denser and the grain shape is closer to circular under higher confining pressure and OCR. The relationship between macroscopic strength characteristics and the microscopic apparent porosity is also discussed. It shows that the macroscopic peak strength gradually decreases with the increase of the microscopic apparent porosity. Such behavior is mainly caused by the internal pore volume reduction and the rise in the contact area between soil particles.

This study investigates the geotechnical properties of soft Pak Phanang marine clay, prevalent in Nakhon Si Thammarat province, Thailand, where rapid economic development demands a comprehensive understanding for sustainable construction. Triaxial tests on undisturbed marine clay specimens with various stress histories and strain rates were conducted, focusing on over-consolidation ratios (OCRs) of 1, 2, 4, and 8. Shearing was performed at rates of 0.020%, 0.075%, 1.000%, and 8.500% per minute after K0 consolidation. The strain rates selected for this study represent specific values that have been chosen for a comprehensive exploration of Pak Phanang clay behavior under different loading conditions. The effects of stress histories on the marine clay behavior at various strain rates under K0 conditions were investigated. It is indicated that the greater strain rates under K0 conditions potentially lead to the larger undrained shear strengths and reduce pore water pressure for varied over-consolidation ratios. On the other hand, the greater over-consolidation ratios commonly result in lower shear strengths at all strain rates. Examination of pore pressure parameter at failure (Af\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${A}_{f}$$\end{document}) and secant Young's modulus reveals significant strain-rate-dependent behavior and OCR influence on the marine clay's response. Undrained shear strength increases with higher OCRs, emphasizing OCR's pivotal role. Rate effect analysis confirms undrained behavior, with a consistent 28% strength increase, regardless of OCR variations. Pore pressure responses exhibit a transition at OCR 4. Secant Young's modulus decreases with rising OCR, establishing a linear correlation with undrained shear strength.

The mechanical behaviour of soils subjected to any stress path in which deviatoric stresses are present is heavily characterised by non-linearity, irreversibility and is strongly dependent on the initial state of stress. The latter, for the majority of geotechnical applications, is normally determined by the at-rest earth pressure coefficient K0, even though this state is valid, strictly speaking, for axisymmetric conditions and for zero-lateral deformations only. Many expressions are available in the literature for the determination of this coefficient for cohesive and granular materials both for normal consolidated and over-consolidated conditions. These relations are available for low to medium stress levels. Results of an extensive experimental investigation on two sands of different mineralogy up to very high stress (120 MPa) are reported in the paper. For reach very high vertical stresses, a special oedometer has been realised. In the loading phase (normal consolidated sands), the coefficient K0n depends on the stress level. It passes from values of about 0.8 to values of about 0.45 in the range of effective vertical stress sigma ' v = 0.5-4 MPa. Subsequently, K0n is about constant and varies between 0.45 to 0.55 up to very high vertical effective stresses (120 MPa). For the sands employed in the tests, Jaki's relation did not lead to reliable results at relatively low pressures, while at high pressures, the same relationship seems to lead to reliable predictions if it refers to the constant volume angle of shear strength. For the over-consolidated sands, K0C strongly depends on the OCR, and for very high values of OCR, K0C could be greater than Rankine's passive coefficient of earth pressure, Kp. This result is due to the very locked structure of the sands caused by the grain crushing, with intergranular contact of sutured and sigmoidal, concavo-convex and inter-penetrating type, that confer to the sand a sort of apparent cohesion and make it similar to weak sandstone.

Ground settlement resulting from consolidation may lead to tilted buildings, cracks in the pavement, damage to underground utilities, etc. Therefore, it is crucial to understand the consolidation behaviors (including primary consolidation and secondary compression) of the soil of the subgrade. There is a large amount of soft clay deposited in Nanjing, located in the Yangtze River Basin. The consolidation behavior of Nanjing soft clay can significantly affect foundation design and the cost of construction. In this study, experimental measurements of the consolidation behavior of Nanjing soft clay were conducted, and parameters (such as pre-consolidation pressure, secondary consolidation index and secondary consolidation ratio) related to consolidation were assessed. The concept of simulated over-consolidation ratio (OCRs) was proposed, and the close relationship between primary consolidation and secondary compression settlement and the OCRs of Nanjing clay was investigated.