Sandy Soil Improvement Using MICP-Based Urease Enzymatic Acceleration Method Monitored by Real-Time System

This paper aims at monitoring the improvement of sandy soil properties with biocementation through the microbially induced calcite precipitation (MICP) method with reaction accelerations by self-developed soybean urease enzymes. In this study, the concentration of calcium ions (Ca2+ ions as CaCl2) is varied at 50, 100, 250, and 500 mM to determine an optimum shear strength. The self-developed soybean urease enzymes of 20% by volume (v/v) are used to accelerate the MICP reaction to finish within 7 days. Based on real-time monitoring bender element system and direct shear tests, the optimum Ca2+ concentration is found as 250 mM. However, a detrimental effect occurs in case of high concentration of Ca2+ as CaCl2 (500 mM) because of solution acidification from high Cl− concentration. This condition lowers CaCO3 precipitation causing the reduction of biocementation process. At equivalent shear modulus, the biocementation time of MICP-based sand with acceleration by urease enzymes is about 10 times faster than that without. Using spectrophotometer and pH meter, the ammonification rate and the solution pH of biocemented sand with acceleration by urease enzymes for 3 days are found relatively higher than those without urease enzymes for 40 days. The analyses by scanning electron microscopy (SEM) and X-ray diffraction (XRD) confirm not only the occurrence of CaCO3 binding sand particles together but also the improvement of physical strengths of sandy soil samples with the MICP-based urease enzymatic acceleration method. These results introduce an option to accelerate biocemented sandy soil improvement.

Spectral attenuation of gravity wave and model calibration in pack ice

We investigate an instance of wave propagation in the fall of 2015 in thin pack ice (<0.3 m) and use the resulting attenuation data to calibrate two viscoelastic wave-in-ice models that describe wave evolution. The study domain is 400 km by 300 km adjacent to a marginal ice zone (MIZ) in the Beaufort Sea. From Sentinel-1A synthetic aperture radar (SAR) imagery, the ice cover is divided into two regions delineated by the first appearance of leads. According to the quality of SAR retrievals, we focus on a range of wavenumbers corresponding to 9∼15 s waves from the open water dispersion relation. By pairing directional wave spectra from different locations, we obtain wavenumber-dependent attenuation rates, which slightly increase with increasing wavenumber before the first appearance of leads and become lower and more uniform against wavenumber in thicker ice after that. The results are used to calibrate two viscoelastic wave-in-ice models through optimization. For the Wang and Shen (2010) model, the calibrated equivalent shear modulus and viscosity of the pack ice are roughly one order of magnitude greater than that in grease/pancake ice reported in Cheng et al. (2017). These parameters obtained for the extended Fox and Squire model are much larger than laboratory values, as found in Mosig et al. (2015) using data from the Antarctic MIZ. This study shows a promising way of using remote sensing data with large areal coverage to conduct model calibration for various types of ice cover.

Investigation on Torsion Stiffness of Thick-Walled Composite Hollow Shaft

A non-classical mechanical analysis method was used to derive the equivalent torsional stiffness <GIp> of thick-walled CFRP drive shaft. The equivalent shear modulus calculated by classical lamination theory, finite element analysis method and non-classical mechanical analysis method were compared. Experimental work was carried out on six composite tubes made of same dimensions but different lay-ups. All the results show that the layers with ±45° fiber orientation angle located on the outside of the wall thickness can increase the torsion stiffness of the composite tube. The non-classical mechanical analysis method predicts the torsion stiffness of thick-walled composite tube more precisely than the theory classical lamination, and agree well with experimental results. This method provides a convenient, accurate and fast method for the torsion stiffness.

Buckling of a spinning elastic cylinder: linear, weakly nonlinear and post-buckling analyses

An elastic cylinder spinning about a rigid axis buckles beyond a critical angular velocity, by an instability driven by the centrifugal force. This instability and the competition between the different buckling modes are investigated using analytical calculations in the linear and weakly nonlinear regimes, complemented by numerical simulations in the fully post-buckled regime. The weakly nonlinear analysis is carried out for a generic incompressible hyperelastic material. The key role played by the quadratic term in the expansion of the strain energy density is pointed out: this term has a strong effect on both the nature of the bifurcation, which can switch from supercritical to subcritical, and the buckling amplitude. Given an arbitrary hyperelastic material, an equivalent shear modulus is proposed, allowing the main features of the instability to be captured by an equivalent neo-Hookean model.

Longitudinal Shear Modulus of Honeycomb Cores Based on Shear-Compressive Model

The deformation mechanism of unit cell wall is investigated by use of FEM, and the numerical simulation results show that the predominant deformations consist of shear deformation and compressive deformation. One new model based the shear deformation and the compressive deformation is put forward to investigate the longitudinal shear modulus of honeycomb cores. Owing to taking skin effect into consideration in our model, it is found that the equivalent shear modulus depends on not only the material properties and configuration parameters of cores, but also the material properties and configuration parameters of facesheets.

Creep Force Characteristics of Wheel/Rail Contact Under Friction Control

In this investigation, a creep force model for contact with friction modifiers is developed and validated by comparing with the experimental results. To this end, a creep force model is developed by introducing a concept of equivalent shear modulus of rigidity, and a two-roller test rig is developed and used for validating the proposed model. Furthermore, relationships between the model parameters and the amount of friction modifiers applied to the contact patch are discussed. It is demonstrated that good agreements are obtained for the creep force characteristics obtained using the proposed model and the two-roller test rig developed in this investigation. Furthermore, it is shown that the proposed model can be used as a semi-empirical model, in which one can define the model parameter as a curve-fitting parameter and, at the same time, physical interpretations regarding the lubrication state between the wheel and rail interface can be obtained using the identified parameters.

Simple shear testing of sensitive, very soft offshore clay for wide strain range

Stiffness and damping properties of sensitive, very soft clay sediments of the Italian Adriatic continental shelf are determined by means of two series of cyclic simple shear tests (one with 12 stages and one with two stages). The apparatus used in this research is capable of investigating the stress–strain behaviour of the soil in a wide range of shear strains from about 0.0004% to 1%. Test results were expressed in terms of small-strain shear modulus (G0), normalized equivalent shear modulus (Geq/G0), and damping ratio (D) versus cyclic shear-strain amplitude (γc). These parameters were analyzed in the framework of existing literature by comparison with empirical correlations developed for onshore materials of different plasticity and, limited to G0, also for soft soils. The dependence of G0, Geq/G0–γc, and D–γc on factors such as void ratio, stress history, and loading cycles is analyzed and discussed.

Shear modulus and damping of soft Bangkok clays

The shear modulus and damping ratio of undisturbed Bangkok clay samples were measured using a cyclic triaxial apparatus. Although abundant literature on this topic exists, selection of the most suitable empirical correlation for a seismic analysis cannot be done unless site specific data are obtained. The apparatus used in this research can measure the stress–strain relationships from strain levels of about 0.01%. The equivalent shear modulus measured at these strains was about 80% of the value obtained from the shear wave velocity measurements. The degradation curves of the equivalent shear modulus fell into the ranges reported in the literature, for clay having similar plasticity. The damping ratios varied from about 4–5% at small strains (0.01%) to about 25–30% at large strains (10%). The effects of load frequency and cyclic stress history on the shear modulus and damping ratio were also investigated. An increase in load frequency from 0.1 to 1.0 Hz had no influence on the shear modulus characteristic, but it did result in a slight decrease in the damping ratio. The effects of the small amplitude cyclic stress history on the subsequently measured shear modulus and damping ratio were almost negligible when the changes in void ratio were taken into account.Key words: soft clay, shear modulus, damping ratio, cyclic triaxial test, cyclic stress history.