scholarly journals Strain-Softening Characteristics of Hydrate-Bearing Sediments and Modified Duncan–Chang Model

2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Mengqiu Yan ◽  
Rongtao Yan ◽  
Haihao Yu
Keyword(s):  
Strain Softening ◽  
Triaxial Compression ◽  
Compression Tests ◽  
Empirical Formulas ◽  
Softening Behavior ◽  
Initial Modulus ◽  
Hydrate Saturation ◽  
Hydrate Bearing Sediments ◽  
Triaxial Compression Tests ◽  
Chang Model

Marine hydrate exploitation may trigger the seabed geological disaster, such as seafloor collapse and landslide. It is critically important to understand the mechanical properties of hydrate-bearing sediment. Strain-softening observation is a typical behavior of hydrate-bearing sediment (HBS) and exhibits more significant at higher hydrate saturation. This paper performed a series of triaxial compression tests on methane hydrate-bearing sand to analyze the influence rule and mechanism of hydrate saturation on the strain-softening characteristic, stiffness, and strength and introduced the strain-softening index to quantificationally characterize the strain-softening behaviors of HBS with different hydrate saturations. Based on the analyses on the mechanical behavior of HBS, the Duncan–Chang model is extended to address the stress-strain curves of HBS. Two empirical formulas with hydrate saturation embedded are used to characterize the enhanced initial modulus and strength for HBS, respectively. To address the strain-softening behavior of HBS, the modified Duncan–Chang model introduced a damage factor into the strength of HBS. To validate the modified Duncan–Chang model, four different triaxial compression tests are simulated. The good consistence between simulated result and experimental data demonstrates that the modified Duncan–Chang model is capable of reflecting the influence of hydrate saturation not only on the stiffness and strength but also on the strain-softening characteristics of HBS.

scholarly journals Mechanical Modeling of Frozen Coarse-Grained Materials Incorporating Microscale Investigation

2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Shan-Zhen Li ◽  
Liang Tang ◽  
Shuang Tian ◽  
Xian-Zhang Ling ◽  
Yang-Sheng Ye ◽  
...  
Keyword(s):  
Strain Softening ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Coarse Grained ◽  
Peak Strain ◽  
Compression Tests ◽  
Engineering Structures ◽  
Softening Behavior ◽  
Coarse Grained Material ◽  
Predicted Values

In the cold regions of China, coarse-grained materials are frequently encountered or used as backfilling materials in infrastructure construction, such as dams, highways, railways, and mineral engineering structures. Effects of confining pressure (0.2, 0.5, and 1 MPa) and frozen temperature (−2, −5, −10, and −15°C) on the stress-strain response and elastic modulus were investigated using triaxial compression tests. Moreover, the microscale structures of a coarse-grained material were obtained by X-ray computed tomography. The coarse-grained material specimens exhibited strain-softening and significant dilatancy behaviors during shearing. A modified model considering microstructures of the material was proposed to describe these phenomena. The predicted values coincided well with the experimental results obtained in this study and other literatures. The sensitivity analysis of parameters indicated that the model can simulate the initial hardening and post-peak strain-softening behavior of soils. And the transition of volume strain from contraction to dilatancy can also be described using this model. The results obtained in this study can provide a helpful reference for the analysis of frozen coarse-grained materials in geotechnical engineering.

scholarly journals An Analysis of the Mechanical Characteristics and Constitutive Relation of Cemented Mercury Slag

2017 ◽  
Vol 2017 ◽  
pp. 1-14
Author(s):  
Xinwei Li ◽  
Sui Zhang ◽  
E-chuan Yan ◽  
Duoyou Shu ◽  
Yangbing Cao ◽  
...  
Keyword(s):  
Triaxial Compression ◽  
Failure Process ◽  
Guizhou Province ◽  
Coarse Grained ◽  
Uniaxial Compression Test ◽  
Compression Tests ◽  
Slag Structure ◽  
Triaxial Compression Tests ◽  
Chang Model ◽  
Coarse Grained Soil

This study focuses on mercury slag in the Tongren area of Guizhou Province, China. Computed tomography (CT) is used with uniaxial and triaxial compression tests to examine the mechanical changes in cemented mercury slag and its formation. The CT results for the uniaxial compression test reveal the overall failure process of the mercury slag structure. Based on the coarse-grained soil triaxial test, a modified Duncan-Chang model is compared with the actual monitoring results and is found to be suitable for the analysis of the slag constitutive model.

A Simple Unconsolidated Undrained Triaxial Compression Test Emulator

2015 ◽  
Vol 771 ◽  
pp. 104-107
Author(s):  
Riska Ekawita ◽  
Hasbullah Nawir ◽  
Suprijadi ◽  
Khairurrijal
Keyword(s):  
Triaxial Compression ◽  
Measurement Data ◽  
Radial Strain ◽  
Compression Tests ◽  
Viscous Effects ◽  
Axial Pressure ◽  
Strain Stress ◽  
The University ◽  
And Storage ◽  
Triaxial Compression Tests

An unconsolidated undrained (UU) test is one type of triaxial compression tests based on the nature of loading and drainage conditions. In order to imitate the UU triaxial compression tests, a UU triaxial emulator with a graphical user interface (GUI) was developed. It has 5 deformation sensors (4 radial deformations and one vertical deformation) and one axial pressure sensor. In addition, other inputs of the emulator are the cell pressure, the height of sample, and the diameter of sample, which are provided by the user. The emulator also facilitates the analysis and storage of measurement data. Deformation data fed to the emulator were obtained from real measurements [H. Nawir, Viscous effects on yielding characteristics of sand in triaxial compression, Dissertation, Civil Eng. Dept., The University of Tokyo, 2002]. Using the measurement data, the stress vs radial strain, stress vs vertical strain, and Mohr-Coulomb circle curves were obtained and displayed by the emulator.

Strength envelope of granular soil stabilized by multi-axial geogrid in large triaxial tests

2020 ◽  
Vol 57 (3) ◽  
pp. 448-452 ◽  
Author(s):  
A.S. Lees ◽  
J. Clausen
Keyword(s):  
Triaxial Compression ◽  
Triaxial Tests ◽  
Compression Tests ◽  
Failure Envelope ◽  
Element Analysis ◽  
Linear Elastic ◽  
Perfectly Plastic ◽  
Elastic Perfectly Plastic ◽  
Triaxial Compression Tests ◽  
Properties Of Soil

Conventional methods of characterizing the mechanical properties of soil and geogrid separately are not suited to multi-axial stabilizing geogrid that depends critically on the interaction between soil particles and geogrid. This has been overcome by testing the soil and geogrid product together as one composite material in large specimen triaxial compression tests and fitting a nonlinear failure envelope to the peak failure states. As such, the performance of stabilizing, multi-axial geogrid can be characterized in a measurable way. The failure envelope was adopted in a linear elastic – perfectly plastic constitutive model and implemented into finite element analysis, incorporating a linear variation of enhanced strength with distance from the geogrid plane. This was shown to produce reasonably accurate simulations of triaxial compression tests of both stabilized and nonstabilized specimens at all the confining stresses tested with one set of input parameters for the failure envelope and its variation with distance from the geogrid plane.

scholarly journals Semi-empirical elastic–thermoviscoplastic model for clay

2016 ◽  
Vol 53 (10) ◽  
pp. 1583-1599 ◽  
Author(s):  
David Kurz ◽  
Jitendra Sharma ◽  
Marolo Alfaro ◽  
Jim Graham
Keyword(s):  
Stress Level ◽  
Axial Strain ◽  
Triaxial Compression ◽  
Compression Tests ◽  
One Dimensional ◽  
Load Duration ◽  
Compression Creep ◽  
Overconsolidated Clays ◽  
Semi Empirical ◽  
Triaxial Compression Tests

Clays exhibit creep in compression and shear. In one-dimensional compression, creep is commonly known as “secondary compression” even though it is also a significant component of deformations resulting from shear straining. It reflects viscous behaviour in clays and therefore depends on load duration, stress level, the ratio of shear stress to compression stress, strain rate, and temperature. Research described in the paper partitions strains into elastic (recoverable) and plastic (nonrecoverable) components. The plastic component includes viscous strains defined by a creep rate coefficient ψ that varies with plasticity index and temperature (T), but not with stress level or overconsolidation ratio (OCR). Earlier elastic–viscoplastic (EVP) models have been modified so that ψ = ψ(T) in a new elastic–thermoviscoplastic (ETVP) model. The paper provides a sensitivity analysis of simulated results from undrained (CIŪ) triaxial compression tests for normally consolidated and lightly overconsolidated clays. Axial strain rates range from 0.15%/day to 15%/day, and temperatures from 28 to 100 °C.

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