Honghua Zhao

Low Viscosity Pore Fluid to Manufacture Transparent Soil

Transparent soil has been investigated for its potential as a substitute research media for natural soil. The mechanism for manufacturing the transparent soil is through adding an appropriate pore fluid to silica gel particles with the same refractive index. Two types of high viscosity pore fluids were identified by Iskander in 1994. However, because of the high viscosity of these two pore fluids, air was easily entrapped, which made the manufacture of a large mass of transparent soil difficult. In addition, the identified pore fluids caused serious membrane deterioration during triaxial laboratory testing. This research presented herein is an experimental investigation on low viscosity pore fluids to manufacture transparent soil, including the fluid/particle interaction in the stimulant matrix. Two low viscosity pore fluids were identified with minimum interaction with latex membranes.

A long-term investigation on microstructure of cement-stabilized handan clay

In order to better understand the mechanisms of cement treatment on the expansive clay, this study presents a long-term study on the micro-structure evolution of the cement-treated highly expansive clay (Handan clay) over a curing period of one and an half years through scanning electronic microscope (SEM) tests and X-ray diffraction analyses. A series of unconfined compression tests were also conducted on cement-modified clay. SEM testing results revealed the microstructure change and cement hydration process during cement treatment of the highly expansive clay. Cement added to the expansive clay generally experiences a hydration, initial setting to form a gel membrane, final setting to form a semi-solid gel and eventual solidification process. The microstructure of the highly expansive clay goes through a series of changes, from a dispersive structure before adding cement, to a flocculated and agglomerated structure after adding cement, further becoming a semi-solid and chained net structure due to the hydration and hardening of cement, and finally forming a stacked dense solid structure. Testing results indicated that the pozzolanic reaction happens very early after adding cement. However, well-crystallised pozzolanic products form at about 28 days in this study. The pozzolanic reaction continues more than one year in this study. The unconfined compressive strength increases with curing time and is closely related with the microstructure change of cement-treated clay. Void ratio estimated from SEM images also indicates that the cement-treated clay has a dense structure.

A Study of Injection of Chemical Agents in an Expansive Clay

Expansive clays exhibit high potential for volume change because of changes in soil moisture. It is estimated that the annual cost of damage to facilities built on expansive clay in the United States exceeds

Numerical Simulation of Triaxial Test on the Dense Sand by DEM

9 billion. Because of the physico-chemical nature of expansive clay behavior, the use of chemical agents to improve their behavior is common. The research reported involved development of a viable method to simulate injection of chemical agents into soils and evaluation of the results. The agents included in this study were lime, a potassium based agent and a group of what are called ionic agents. The clay utilized was weathered from the Eagle Ford Shale formation in north central Texas. An injection treated layer of the clay, using one of the differing chemical agents, was placed between a relatively wet layer and relatively dry layer of untreated clay, to test each chemicals affects on moisture movements. The sealed cylinders were allowed to have what moisture movements during a fifteen week period. The cylinders were opened and the soil layers tested for water content, dry unit weight, soil suction, and swell potential. Cylinders of untreated clay, constructed in the same way, but not injected were also analyzed. The injection process developed is believed to have simulated field injections well. The results of moisture movement, soil suction, and swelling potential provided insight into how these chemical agents can affect moisture movements and soil behavior when injected in this clay.

Influences of Stiffness Ratio, Friction Coefficient and Strength Ratio on the Macro Behavior of Cemented Sand Based on DEM

In this study, a numerical triaxial test simulation on the dense sand was carried out using the three dimensional particle flow code (PFC3D) with a linear contact model. The influences of the friction coefficients on the stress-strain behavior of the sand were analyzed. Numerical test results show that the higher friction coefficients lead to the higher peak strength for the dense sand. Further, the formation and development of the shear band was also investigated. Numerical simulation test proved that PFC3D can simulate triaxial test very well. It also showed that the microscopic parameters of the model can greatly influence the macroscopic behavior of the granular materials. The PFC3D numerical simulation method is able to capture the very small-strain behavior of the dense sand.

Stamping coal cake simulation with Duncan- Kelvin-Maxwell constitutive relations

A study was conducted on cemented sand modeled with a contact bond model to investigate the influences of micro parameters on its macro properties based on a three dimensional discrete element simulation. The influences of the micro parameters of the stiffness ratio, the strength ratio and the friction coefficient on the unconfined compression behavior of the cemented sand are revealed and a qualitative relationship is established between each individual micro parameter and the macro properties of Young’s modulus and compressive strength based on 3D numerical discrete element simulation data. The results are important for the multi-scale study and will offer guidance to use the discrete element method, to model cemented sands or cemented aggregates.

Implementation of Numerical Optimization Techniques in Constitutive Model Calibration

Abstract In stamp charging coke making, the lack of stamping process analysis and design information such as coal box pressure causes debasement of the design quality of related devices. To achieve a radical solution, a simulation is thus recommended, in which the essence is the appropriate description of the behaviour and reaction of stamped coal blend. To accomplish the mission, finite element method was applied in the current study to conduct a simulation on the stamping coal cake process, and a constitutive model was developed to meet the specific requirements of stamping coal. The constitutive model was established by combining Duncan–Chang from soil mechanics and Kelvin–Maxwell model from viscoelastic mechanics, and then extended to three-dimensional, and its numerical solution was also given. The simulation result are consisted with the field test data, which shows that the method is a feasible tool for studying stamping coking coal, and the proposed constitutive model is able to describe to some extent the inherent behaviour of the coal cake.

Physicochemical Characterization of Cement Stabilized Highly Expansive Soil

When a conventional method such as linear regression is insufficient to identify the constants and parameters of an advanced constitutive model, numerical optimization techniques are often used. In employing numerical optimization to constitutive model calibration, an objective function essentially needs to be formulated in the form of nonlinear least squares where the sum of the differences between the measured and computed data points are quantified. When a minimum value of the objection function is obtained, the corresponding variables are the optimized model constants and parameters. Due to the complexity in the format of objective functions in constitutive model calibration, gradient-based methods are seldom used. In this paper, non-gradient based methods namely Direct algorithm was implemented to calibrate a modified Cam-Clay model against laboratory data.

A New Image-Based Soil Deformation Measurement System

South-to-North Water Diversion project in China is the largest water diversion project of the world. This is a huge hydraulic engineering project, crossing Yangtze River, Huai River, Yellow River, and Hai River, total water volume of 44.8 billion m 3 transferred per year. The middle line of the project is starting from Danjiangkou and ending at Beijing and Tianjin, total length of the main canal about 1432 km, 279.7 km of the main canal located in the expansive soil zone. In order to control the damage caused by the swelling of the expansive soil, cement was adopted as the major stabilizing agent to reduce the swelling potential and increase the strength of the soil. This research examined the physicochemical characterization of cement treated highly expansive soil (Handan clay) from the project. SEM analysis was conducted on Handan clay at different curing time (1h, 4h, 12h, 24h, and 7d) during cement treatment. The cations’ concentration in the pore water before and after cement treatment was also examined at different time during a 7-day curing period. The cations of the exchange complex of treated Handan clay was also examined at different time (1h, 4h, 12h, 24h, and 7d) during a 7-day curing period. The strength development of the cement treated soil was investigated at different curing time (1h, 4h, 12h, 24h, and 7d).The testing results revealed the strength increasing mechanism of the cement treated expansive soil from chemical and miscrostructural point of view.

Investigation on the shear moduli and damping ratios of silica gel

A Soil Deformation Measurement System using OPENCV library and FFTW library in C++ was developed in this paper. The system applied camera calibration based on neural network and Fasst Fourier Transform (FFT) cross-correlation algorithm for Particle Image Velocimetry (PIV). It is used to obtain soil deformation data, such as displacements, velocity and strain, and visualize the deformation. Experiments show that this system could acquire deformation data from soil images accurately, efficiently and continuously, which provides a strong proof that image processing technology has practical significance and application value in the research field of geotechnical engineering.