Impact of mica on geotechnical behavior of weathered granitic soil using macro and micro investigations

The micaceous weathered granitic soil(WGS)is frequently encountered in civil engineering worldwide,unfortunately little information is available regarding how mica affects the physico-mechanical behaviors of WGS.This study prepares reconstituted WGS with different mica contents by removing natural mica in theWGS,and then mixes it with commercial mica powders.The geotechnical behavior as well as the microstructures of the mixtures are characterized.The addition of mica enables the physical indices of WGS to be specific combinations of coarser gradation and high permeability but high Atterberg limits.However,high mica content in WGS was found to be associated with undesirable mechanical properties,including increased compressibility,disintegration,and swelling potential,as well as poor compactability and low effective frictional angle.Microstructural analysis indicates that the influence of mica on the responses of mixtures originates from the intrinsic nature of mica as well as the particle packing being formed withinWGS.Mica exists in the mixture as stacks of plates that form a spongy structure with high compressibility and swelling potential.Pores among the plates give the soil high water retention and high Atterberg limits.Large pores are also generated by soil particles with bridging packing,which enhances the permeability and water-soil interactions upon immersion.This study provides a microlevel understanding of how mica dominates the behavior of WGS and provides new insights into the effective stabilization and improvement of micaceous soils.

Simulation of Cement Hydration and Porous Structures by the Hydration-Pixel Probability Model

This research proposes a new pixel-based model called the hydration-pixel probability model which aims to simplify cement hydration as a probability problem.The hydration capacity of cement,the solution within pores,and the difiusion of solid particles are represented by three probability functions derived from experimental data obtained through electrical resistivity and hydration heat measurements.The principle of the model is relatively simple,and the parameters have clear physical meanings.In this research,the porous structures of difierent cement pastes with w/c ratios of 0.3,0.4,and 0.5 are investigated.The results indicate that the porosity of the cement paste decreases during the first few hours,followed by a rapid decline,and eventually reaches a steady state.The porosity of the paste decreases as w/c ratio decreases,and the rate of decrease is more rapid in the early stages.Referring to the porosity curves,the average degree of hydration and depth of hydration can be derived.The simulation results show that the hydration degree of paste composed of irregular particles is higher than that of the paste composed of round particles.The trend in the development of the average hydration depth is similar to that of the average hydration degree.Upon analyzing the average growth rate of the hydration depth,it is observed that there are two peaks in the curves,which correspond to the three characteristic points in the electrical resistivity test.

Biomineralization of soil with crude soybean urease using different calcium salts

Calcium salt is an important contributing factor for calcium-based biomineralization.To study the effect of calcium salt on soil biomineralization using crude soybean urease,the calcium salts,including the calcium chloride (CaCl_(2)),calcium acetate ((CH_(3)COO)_(2)Ca) and calcium nitrate (Ca(NO_(3))_(2)),were used to prepare the biotreatment solution to carry out the biomineralization tests in this paper.Two series of biomineralization tests in solution and sand column,respectively,were conducted.Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were performed to determine the microscopic characteristics of the precipitated calcium carbonate (CaCO_(3)) crystals.The experimental results indicate that the biomineralization effect is the best for the CaCl2 case,followed by (CH_(3)COO)_(2)Ca,and worst for Ca(NO_(3))_(2) under the test conditions of this study (i.e.1 mol/L of calcium salt-urea).The mechanism for the effect of the calcium salt on the biomineralization of crude soybean urease mainly involves: (1) inhibition of urease activity,and (2) influence on the crystal size and morphology of CaCO_(3).Besides Ca^(2+) ,the anions in solution can inhibit the activity of crude soybean urease,and NO_(3)− has a stronger inhibitory effect on the urease activity compared with both CH_(3)COO^(−) and Cl^(−) .The co-inhibition of Ca^(2+) and NO_(3)− on the activity of urease is the key reason for the worst biomineralization of the Ca(NO_(3))_(2) case in this study.The difference in biomineralization between the CaCl_(2) and (CH_(3)COO)_(2) Ca cases is strongly correlated with the crystal morphology of the precipitated CaCO_(3).

Earthquake safety assessment of concrete arch and gravity dams

Based on research studies currently being carried out at Dalian University of Technology, some important aspects for the earthquake safety assessmcnt of concrete dams are reviewed and discussed. First, the rate-dependent behavior of concrcte subjected to earthquake loading is examined, emphasizing the properties of concrete under cyclic and biaxial loading conditions. Second, a modified four-parameter Hsieh-Ting-Chen viscoplastic consistency model is developed to simulate the rate-dependent behavior of concrete. The earthquake response of a 278m high arch dam is analyzed, and the results show that the strain-rate effects become noticeable in the inelastic range, Third, a more accurate non-smooth Newton algorithm for the solution of three-dimensional frictional contact problems is developed to study the joint opening effects of arch dams during strong earthquakes. Such effects on two nearly 300m high arch dams have been studied. It was found that the canyon shape has great influence on the magnitude and distribution of the joint opening along the dam axis. Fourth, the scaled boundary finite element method presented by Song and Wolf is employed to study the dam-reservoir-foundation interaction effects of concrete dams. Particular emphases were placed on the variation of foundation stiffness and the anisotropic behavior of the foundation material on the dynamic response of concrete dams. Finally, nonlinear modeling of concrete to study the damage evolution of concrete dams during strong earthquakes is discussed. An elastic-damage mechanics approach for damage prediction of concrete gravity dams is described as an example. These findings are helpful in understanding the dynamic behavior of concrete dams and promoting the improvement of seismic safety assessment methods.

Effect of Freeze-Thaw Cycles on Mechanical Properties and Permeability of Red Sandstone under Triaxial Compression

Geological disasters will happen in cold regions because of the effects of freeze-thaw cycles on rocks or soils, so studying the effects of these cycles on the mechanical characteristics and permeability properties of rocks is very important. In this study,red sandstone samples were frozen and thawed with 0,4, 8 and 12 cycles, each cycle including 12 h of freezing and 12 h of thawing. The P-wave velocities of these samples were measured, and the mechanical properties and evolution of the steady-state permeabilities were investigated in a series of uniaxial and triaxial compression tests. Experimental results show that, with the increasing of cyclic freeze-thaw times, the P-wave velocity of the red sandstone decreases. The number of freeze-thaw cycles has a significant influence on the uniaxial compressive strength, elastic modulus, cohesion, and angle of internal friction. The evolution of permeability of the rock samples after cycles of freeze-thaw in a complete stress-strain process under triaxial compression is closely related to the variation of the microstructure in the rock. There is a highly corresponding relationship between volumetric strain and permeability with axial strain in all stages of the stress-strain behaviour.

Nonlinear dynamic analysis of cantilevered piezoelectric energy harvesters under simultaneous parametric and external excitations

The nonlinear dynamics of cantilevered piezoelectric beams is investigated under simultaneous parametric and external excitations. The beam is composed of a substrate and two piezoelectric layers and assumed as an Euler-Bernoulli model with inextensible deformation. A nonlinear distributed parameter model of cantilevered piezoelectric energy harvesters is proposed using the generalized Hamilton＇s principle. The proposed model includes geometric and inertia nonlinearity, but neglects the material nonlinearity. Using the Galerkin decomposition method and harmonic balance method, analytical expressions of the frequency-response curves are presented when the first bending mode of the beam plays a dominant role. Using these expressions, we investigate the effects of the damping, load resistance, electromechanical coupling, and excitation amplitude on the frequency-response curves. We also study the difference between the nonlinear lumped-parameter and distributed- parameter model for predicting the performance of the energy harvesting system. Only in the case of parametric excitation, we demonstrate that the energy harvesting system has an initiation excitation threshold below which no energy can be harvested. We also illustrate that the damping and load resistance affect the initiation excitation threshold.

Experimental investigation on the relevance of mechanical properties and porosity of sandstone after hydrochemical erosion

Under the effect of chemical etching,the macroscopic mechanical properties,mesoscopic structure,mineral content,and porosity of rocks undergo significant changes,which can lead to the geological disasters; thus,an understanding of changes in the microscopic and macroscopic structure of rocks after chemical etching is crucial.In this study,uniaxial mechanical tests and nuclear magnetic resonance(NMR) spectroscopy were carried out on sandstone samples that had been previously subjected to chemical erosion under different p H values.The aim was to study changes in properties and mechanical characteristics,including deformation and strength characteristics,of the rock,and microscopic pore variation characteristics,and to perform preliminary studies of the chemical corrosion mechanism.Results show that different chemical solutions have a significant influence on the uniaxial compressive strength,the axial strain corresponding to the peak axial stress,elastic modulus,etc.With the passage of time,porosity increases gradually with exposure to different chemical solutions,and exposure to chemical solutions results in large changes in the NMR T2 curve and T2 spectrum area.Sandstone exposed to different chemical solutions exhibits different corrosion mechanisms; the root cause is the change of mineral.

A Crashworthy Device Against Ship-OWT Collision and Its Protection Effects on the Tower of Offshore Wind Farms

At present, more and more offshore wind farms have been built anti ntnnerous projects are on the drawing tables. Therefore, the study on the safety of collision between ships and offshore wind turbines （OWT） is of great practical signifieance. The present study takes the advantage of the famous LS-DYNA explicit code to simulate the dynamic proeess of the collision between a typical 3MW offshore wind turbine model with monopile fi）undation and a simplified 2000t-class ship model. In the simulation, the added mass effect of the ship, contact nonlinearity of collision, material nonlinearity of steel and aluminum foam and adaptive mesh tectmique for large structure deformation have been taken into considera- tion. Proposed is a crashworthy device for OWF of new conceptual steel sphere shell-cireular ring aluminum foam pad, and the good pe.rfurmanee of the device under the conditions of ship-OWT front impact and side impact has been verified from the views of theoretical analysis and numerical results. The new crashworthy device can effectively smooth the contact force and reduce the top structure dynamic response, using its own structure plastic deformation to absorb most of the ship collision enerty. As a result, the main structure of the OWF and the inside key electric control equipments can be saved by scarifying the structural plastic deformation of new sphere crashworthy device. What is more, the sphere configuratiun design of the crashworthy device can effectively guide the ship to run away from the main OWT structure and reduce the damage of the ship and OWT to some degree during side impact.

Synthesis and Characteristics of Mesoporous Silica Aerogels with One-step Solvent Exchange/Surface Modification

The synthesis procedures and physical properties of the ambient dried hydrophobic silica aerogels by using different contents of ethanol （EtOH）/trimethylchlorosilane （TMCS）/n-Hexane as surface modification agent were investigated. One-step solvent exchange and surface modification were simultaneously progressed by immersing silica hydrogels in EtOH/TMCS/n-Hexane solution. It is found that microstructures as well as properties of silica aerogels like porosity, specific density and specific surface area are affected by the contents of surface modification agent in the sol from the results of SEM, TEM morphology, FT-IR chemical structure, BET surface area and BJH pore size analyses. The volume of TMCS is of 10% and 20% of hydrogels, and the final product is hydrophilic xerogels. When TMCS＇s percent （v/v） is elevated to 75 %-100%, hydrophobic silica aerogels with good performance are synthesized, the porosities of aerogels are in the range of 93.5%-95.8% and the average pore size diameter is less than 20 nm.

Hydrodynamic Comparison of a Semi-submersible,TLP,and Spar:Numerical Study in the South China Sea Environment

The South China Sea contains tremendous oil and gas resources in deepwater areas. However, one of the keys for deepwater exploration, the investigation of deepwater floating platforms, is very inadequate. In this paper, the authors studied and compared the hydrodynamics and global motion behaviors of typical deepwater platforms in the South China Sea environment. The hydrodynamic models of three main types of floating platforms, e.g. the Semi-submersible, tension leg platform (TLP), and Truss Spar, which could potentially be utilized in the South China Sea, were established by using the 3-D potential theory. Additionally, some important considerations which significantly influence the hydrodynamics were given. The RAOs in frequency domains as well as global motions in time domains under time-varying wind, random waves, and current in 100-y, 10-y, and 1-y return period environment conditions were predicted, compared, and analyzed. The results indicate that the heave and especially the pitch motion of the TLP are favorable. The heave response of the Truss Spar is perfect and comparable with that of the TLP when the peak period of random waves is low. However, the pitch motion of Truss Spar is extraordinarily larger than that of Semi-submersible and TLP.

Influence of arrangement field on magnetostrictive and mechanical properties of magnetostrictive composites

Non-aligned and aligned polymer-bonded Tb0.3Dy0.7Fe2 composites with 20%particle volume fraction were prepared under different arrangement fields(i.e.0,10 kA/m,20 kA/m,30 kA/m,60 kA/m and 100 kA/m)during their gel process.Static magnetostriction,dynamic magnetostriction,elastic modulus and compressive strength of all specimens were tested and compared. Experimental results indicate that all the parameters are positively dependent on the arrangement field.The dependence is significant at low field levels,the critical value of which is 30 kA/m for the composites fabricated.No obvious improvement of the properties can be observed for a larger field.Such critical values are defined as the optimal arrangement field to manufacture magnetostrictive composites.

Control strategies and experimental verifications of the electromagnetic mass damper system for structural vibration control

The electromagnetic mass damper （EMD） control system, as an innovative active control system to reduce structural vibration, offers many advantages over traditional active mass driver/damper （AMD） control systems. In this paper, studies of several EMD control strategies and bench-scale shaking table tests of a two-story model structure are described. First, two structural models corresponding to uncontrolled and Zeroed cases are developed, and parameters of these models are validated through sinusoidal sweep tests to provide a basis for establishing an accurate mathematical model for further studies. Then, a simplified control strategy for the EMD system based on the pole assignment control algorithm is proposed. Moreover, ideal pole locations are derived and validated through a series of shaking table tests. Finally, three benchmark earthquake ground motions and sinusoidal sweep waves are imposed onto the structure to investigate the effectiveness and feasibility of using this type of innovative active control system for structural vibration control. In addition, the robustness of the EMD system is examined. The test results show that the EMD system is an effective and robust system for the control of structural vibrations.

Impact of an artificial chute cutoff on the river morphology and flow structure in Sipaikou area of the Upper Yellow River

Artificial chute cutoff can fundamentally eliminate the threat of flood caused by the meandering river,but it significantly changes its morphodynamic characteristics.Channel adjustments after cutoff are rapid,which makes it difficult to study the interaction between river morphology and flow structure only through field measurement.However,numerical simulations can provide insights into the hydrodynamic characteristics after artificial chute cutoffs.In this study,both field measurement and numerical simulation are employed to investigate the flow structure and bed morphology caused by an artificial chute cutoff in Sipaikou area of the Upper Yellow River in 2018.The measured hydrological data provide boundary conditions and initial values for the numerical model.The field measurement results reveal that the concave bank of the study area is severely scoured up to 270 m after the artificial cutoff,and a 20 m deep scour hole and a 2.26 km long pool are formed at the entrance and near the left bank of the chute channel.The numerical simulation results of velocity at typical cross-sections are in good agreement with the measurement results.Flow separation and stagnation zones are observed near the right bank during the low flow conditions(discharge of at least 902 m^(3)/s),but this phenomenon is not seen during larger flow conditions(discharge exceeds 2000 m^(3)/s).Interestingly,flow recirculation zones are also found near the left and right banks of the scour hole.Further,a long flux belt is formed at the scour hole and the pool.Consequently,the impact of the bed topography on the hydrodynamic characteristics is relatively prominent when the discharge is small,while the impact on the river banks and river bed is more noticeable when the water discharge is large.In addition,high shear stress is observed near the left bank at the downstream of the studied area,which indicates that the left bank at the downstream is still being scoured.These results suggest that bank protection measures along the left bank are required to maintain the effectiveness of the artificial chute cutoff.

Dynamic Performance of a Semi-Submersible Platform Subject to Wind and Waves

By applying experimental and numerical simulations, the motion performance of a semi-submersible platform with mooring positoning system under combined actions of wind and waves is studied. The numerical simulation is conducted by the method of nonlinear time domain coupled analysis, and the mooring forces are calculated by the piecewise extrapolating method. The scale in the model experiment is 1:100, and the mooring system of the model is designed with the method of equivalent water-depth truncation by comparing the numerical and the experimental results, the platform motion and mooring forces subject to wind and waves are investigated. The results indicate that the numerically simulated mooring forces agree well with the experimental results in static equivalent field, but show some difference in dynamic equivalent field; the numerically simulated platform motions coincide well with the experimental results. The maximum motion of the platform under operating conditions is 20.5 m. It means that the horizontal displacement is 2% less than the water depth, which satisfies the operating requirements.

Study on the adsorption of Cr( Ⅵ) onto landfill liners containing granular activated carbon or bentonite activated by acid

The adsorption capacity of landfill liners containing granular activated carbon (GAC), or bentonite activated by acid, for Cr(VI) was investigated by batch testing. The results show that both GAC and activated bentonite could be used as sorptive amendments for trapping Cr(VI) in landfill liners. The Cr(VI) sorption to GAC and activated bentonite is much greater than Cr(VI) sorption to natural clay. The adsorption capacity of Cr(VI) onto all the soils increases with increasing temperature; adsorption capacity is also significantly influenced by soil-solid concentration. As the soil-solid concentration increases the adsorption capacity first decreases logarithmically, but then stabilizes when the soil-solid concentration exceeds a critical value (e.g. 400 g/L). Permeability tests were conducted in the laboratory. The results indicate that the hydraulic conductivity of landfill liners containing GAC or activated bentonite can meet the engineering requirement of 1 nm/s. One-dimensional transport simulations for Cr(VI) were performed to evaluate the effect of GAC and activated bentonite on landfill liners. The results of the simulations indicate that landfill liners containing GAC, or activated bentonite, significantly retard the transport of Cr(VI) relative to a conventional clay liner.

Influence of Water Content on Conductivity and Piezoresistivity of Cement-based Material with both Carbon Fiber and Carbon Black

The influence of water content on the conductivity and piezoresistivity of cement-based material with carbon fiber （CF） and carbon black （CB） was investigated. The piezoresistivity of cement-based material with both CF and CB was compared with that of cement-based material with CF only, and the changes in electrical resistivity of cement-based material with both CF and CB under static and loading conditions in different drying and soaking time were studied. It is found that the piezoresistivity of cement-based material with both CF and CB has better repeatability and linearity than that of cement-based material with CF only. The conductivity and the sensitivity of piezoresistive cement-based material with both CF and CB are enhanced as the water content in piezoresistive cement-based material increases.

FRACTURAL PROCESS AND TOUGHENING MECHANISM OF LAMINATED CERAMIC COMPOSITES

Based on the model of multi-layer beam and the assumption of micro-inhomogeneity of material, the 3D fractural characteristics of laminated ceramic composites have been studied with numerical simulation. Under three-point bending load, crack initiation, coalescence, propagation, tuning off in the weak interface and final rupture have been simulated. The spatial distribution and evolution process of acoustic emission are also presented in the paper. The simulation verifies the primary mechanism of the weak interface inducing the crack to expand along there and absorbing the fractural energy. The disciplinary significance of the effect of strength and properties of material on the toughness and strength of laminated ceramic composites is, therefore, discussed in this paper.

Shaking table test and numerical simulation on the effect of reinforcement on the seismic safety of dam slopes

The seismic safety of the reinforcement dam slope is studied through shaking table test and numerical simulation.The dynamic characteristics of dam slopes,failure mechanism,seismic stability,as well as the effect of reinforcement during earthquakes are discussed.An elasto-plastic analysis method (FLAC) is used to simulate the dynamic failure process of the reinforcement dam slope.The change law of permanent displacement of dam slope is studied.The effect of the length and the space of reinforcement on the depth of slip surface and the slope stability are investigated.Good agreement is obtained between the numerical results and those from shaking table tests.The results show that the dynamic failure is a gradual process not at a particular time.With the increase of the reinforcement length or the decreasing reinforcement spacing,the slip surface becomes deeper and thus the slope stability is improved.The reinforcement can obviously enhance the overall stability of slope dam.It can also effectively control the shallow sliding of slope.These researches provide basic data for reinforcement measures design of earth-rockfill dam.

Dynamic response of a beam on a Pasternak foundation and under a moving load

The dynamic response of an infinite beam placed on a Pasternak foundation when the system was subjected to a moving load was investigated.We used the double Fourier transform and its inversion to solve the formulations of the problem.A closed form analytic solution of the beam was obtained by the theorem of residues.We selected a numerical example to illustrate the dynamic response of the beam on Pasternak and Winkler foundations,respectively.We discuss the effect of the moving load velocity on the dynamic displacement response of the beam.The maximum deflection of the beam increases slightly with increased load velocity but increases significantly with reduced shear modulus of subgrade at a given velocity.The maximum deflection of a beam resting on a Pasternak foundation is much smaller than that of a beam on a Winkler foundation.

Design of low-energy building and energy consumption analyses

In China,a new "Design standard for energy efficiency of residential buildings (for cold region)" was introduced in 2006. In this new standard,more high level insulation of the building envelope is required,yearly energy requirement for heating must be less than 55 kWh/(m2·a)(regarded as a low-energy house). The new attempt was carried out in the process of architecture design with an evaluation on energy consumption of the building. The design plan was brought forward and compared. PHPP software from German was applied to calculate energy consumption of the passive residential building. The optimum design planning was discussed and model of passive house suited to China's national conditions were attempted. The compactness,solar air collector and the window-wall ratio have essential influence on the energy consumption of buildings. The annual heat demands for the buildings with the window-wall ratio 0.35 and 0.50 are 48 kWh/(m2·a) and 46 kWh/(m2·a),respectively. The yearly auxiliary heat of building with the wall-mounted solar air collectors and the window-wall ratio 0.35 is just 4.8 kWh/(m2·a).