Numerical simulation for rheological characteristics of alternating distribution of soft and hard rock layers

The difficulty of selecting appropriate rheological model and parameters for the alternating distribution of soft and hard rock layers was often encountered due to the unhomogeneity, discontinuity and anisotropy of rock mass. The Burgers and generalized Kelvin models were applied to the soft and hard rock respectively and the rheological parameters were obtained based on the method of optimum separation. By using the simulated code FLAC^(3D), the stability of surrounding rocks of a certain underground plant was analyzed. The effect of surface load and weakening the parameters intensity of argillaceous and bioclastic interlayers between soft and hard rock on rheological behavior of layer composite rock mass was investigated. The results indicate that the rheological characteristics of soft and hard rock layer in composite rock mass can be described well with above two rheological models.

Response of Surface Soft Soil and Fine-Grained Sand Layers to Seismic Waves

Shanghai is located in eastern China and is built on overburden soil layers. It can be seen from the Mexico M S=8.1 earthquake on September 19, 1985 and the Hanshin M S=7.4 earthquake on January 17,1995 that heavy casualties and property losses have a direct relationship with overburden soil layers. Ground motions caused by earthquakes are significantly amplified when passing through the soil layers. Under the influence of these amplified motions, building structures, whose nature frequency is within the frequency band of soil amplification response, will experience more severe damage than those built on bedrock. Therefore, engineering seismologists have paid considerable attention the amplification responses in the Shanghai overburden soil layers. The amplification responses of soil and sand layers in this paper are given by the M L=4.1 earthquake in Nantong, Jiangsu Province on December 25, 2001 at 31.8° N, 120.9° E. It can be seen that the responses of soil and sand layers are very different. That is important.

Physical model test and numerical simulation on the failure mechanism of the roadway in layered soft rocks

To explore the failure mechanism of roadway in layered soft rocks,a physical model with the physically finite elemental slab assemblage(PFESA)method was established.Infrared thermography and a video camera were employed to capture thermal responses and deformation.The model results showed that layered soft roadway suffered from large deformation.A three-dimensional distinct element code(3 DEC)model with tetrahedral blocks was built to capture the characteristics of roadway deformation,stress,and cracks.The results showed two failure patterns,layer bending fracture and layer slipping after excavation.The layer bending fracture occurred at positions where the normal direction of layers pointed to the inside of the roadway and the layer slipping occurred in the ribs.Six schemes were proposed to investigate the effects of layered soft rocks.The results showed that the deformation of ribs was obviously larger than that of the roof and floor when the roadway passed through three types of strata.When the roadway was completely in a coal seam,the change of deformation in ribs was not obvious,while the deformation in the roof and floor increased obviously.These results can provide guidance for excavation and support design of roadways in layered soft rocks.

Time-dependent squeezing deformation mechanism of tunnels in layered soft-rock stratum under high geo-stress

Large squeezing deformation of layered soft rock tunnel under high geo-stress has a significant time-dependent deformation behavior.In this paper,we studied the deformation mechanism during the construction period of deep-buried softrock tunnel by means of a combination of field observations and a numerical method.First,a new classification criterion for large deformations based on the power exponent variation law between the deformation and the strength-stress ratio is proposed.Then,the initial damage tensor reflecting the bedding plane(joint)distribution and an equivalent damage evolution equation derived from the viscoplastic strain are introduced based on the geometric research method,i.e.,a new rheological damage model(RDL model)of layered soft rock is established consisting of elastic,viscous,viscoelastic,viscoplastic and plastic elements.A field test was conducted on the Maoxian tunnel in Sichuan province,southwestern China,which is in broken phyllite(layered soft rock)under high geo-stress.The tunnel has experienced large deformation due to serious squeezing pressure,thus we adopted double primary support method to overcome the supporting structure failure problems.The rheological parameters of phyllite in the Maoxian tunnel were recognized by using SA-PSO optimization,and the RDL model does a good job in describing the time-dependent deformation behavior of a layered soft-rock tunnel under high geo-stress.Thus,the RDL model was used to investigate the supporting effect and bearing mechanism of the double primary support method.Compared with the single primary support method,the surrounding rock pressure,secondary lining force,surrounding rock deformation,and the depth of the damage to the rock mass was reduced by 40%-60%after the double primary support method was used.

A three-layer structure model for the effect of a soft middle layer on Love waves propagating in layered piezoelectric systems

A three-layer structure model is proposed for investigating the effect of a soft elastic middle layer on the propagation behavior of Love waves in piezoelectric layered systems, with ＂soft＂ implying that the bulk-shear-wave velocity of the middle layer is smaller than that of the upper sensitive layer. Dispersion equations are obtained for unelectroded and traction-free upper surfaces which, in the limit, can be reduced to those for classical Love waves. Systematic parametric studies are subsequently carried out to quantify the effects of the soft middle layer upon Love wave propagation, including its thickness, mass density, dielectric constant and elastic coefficient. It is demonstrated that whilst the thickness and elastic coefficient of the middle layer affect significantly Love wave propagation, its mass density and dielectric constant have negligible influence. On condition that both the thickness and elastic coefficient of the middle layer are vanishingly small so that it degenerates into an imperfectly bonded interface, the three-layer model is also employed to investigate the influence of imperfect interfaces on Love waves propagating in piezoelectric layer/elastic sub- strate systems. Upon comparing with the predictions ob- tained by employing the traditional shear-lag model, the present three-layer structure model is found to be more ac- curate as it avoids the unrealistic displacement discontinuity across imperfectly bonded interfaces assumed by the shearlag model, especially for long waves when the piezoelectric layer is relatively thin.

Numerical Analyses of Caisson Breakwaters on Soft Foundations Under Wave Cyclic Loading

A caisson breakwater is built on soft foundations after replacing the upper soft layer with sand. This paper presents a dynamic finite element method to investigate the strength degradation and associated pore pressure development of the intercalated soft layer under wave cyclic loading. By combining the undrained shear strength with the empirical formula of overconsolidation clay produced by unloading and the development model of pore pressure, the dynamic degradation law that describes the undrained shear strength as a function of cycle number and stress level is derived. Based on the proposed dynamic degradation law and M-C yield criterion, a dynamic finite element method is numerically implemented to predict changes in undrained shear strength of the intercalated soft layer by using the general-purpose FEM software ABAQUS, and the accuracy of the method is verified. The effects of cycle number and amplitude of the wave force on the degradation of the undrained shear strength of the intercalated soft layer and the associated excess pore pressure response are investigated by analyzing an overall distribution and three typical sections underneath the breakwater. By comparing the undrained shear strength distributions obtained by the static method and the quasi-static method with the undrained shear strength distributions obtained by the dynamic finite element method in the three typical sections, the superiority of the dynamic finite element method in predicting changes in undrained shear strength is demonstrated.

A study on mixed coal simulation soft layer of gas adsorption

Based on the single coal adsorption gas, hard coal and soft coal of intake airway in Shanxi Heshun Tianchi Coal Mine were chosen to simulate the soft coal seams in coalbed as those in different qualities are mixed with delamination. Experiments on characteristics of adsorption gas of hard coal and soft coal in different quality ratios were done according to the Langmuir single molecule layer absorption theory. Gas constant mensuration instrument WY-98B was used during the experiments. Isothermal adsorption curves, adsorption constants a and b of the mixed coal samples in different quality ratios were established for qualitative and quantitative analysis. The relationship curves of adsorption quantity with changing pressure and variation equation of adsorption constants a, b with changing thickness ratio shows that the thickness of soft layer and hard coal approximately equal, thus resulting in outburst at greatest risk, then a theoretical base for the mechanism of coal and gas outburst has been put forward and a technical support scheme for engineering control of gas outburst is laid out.

Enhancing Mar and Abrasion Resistance of Acrylic Hard Coatings with Soft Base Layer

Mar and abrasion resistance were investigated by a progressive load scratch test and steel wool abrasion test, respectively. Two acrylic coating systems including trimethylolpropane triacrylate (TMPTA) and pentaerythritol triacrylate (PETA) were prepared. A soft base layer was introduced as an intermediate layer between two different types of top layer and poly (methyl methacrylate) (PMMA) substrate to demonstrate the effect of soft base layer on mar and abrasion resistance. Abrasion damage on the coating surface was found to be less severe, when the soft base layer was incorporated into the coating systems. The reduction in scratch coefficient of friction (SCOF) and surface roughness was also observed. The results suggested that mar and abrasion resistance was greatly influenced by the presence of soft base layer, although different top layers were used. Moreover, it was found that abrasion resistance was further improved as the thicker soft base layer was applied.

Synergistically enabling the interface stability of lithium metal batteries with soft ionic gel and garnet-type Li_(6.4)La_(3)Zr_(1.4)Ta_(0.6)O_(12)ceramic filler

Lithium metal batteries based on solid electrolytes are considered as promising candidates with high energy density and safety.However,the weak solid-solid contact between electrolyte and electrode can easily lead to interface instability and lithium ions discontinuous migration,which seriously reduces the electrochemical performance of the battery.Herein,we construct a soft gel interfacial layer to improve the stability of the solid-solid interface between electrolyte and electrode by means of polyester-based monomers and imidazole-based ionic liquids.Based on this,garnet-type Li_(6.4)La_(3)Zr_(1.4)Ta_(0.6)O_(12)(LLZTO)particles as inorganic ceramic filler were introduced in the layer to obtain composite electrolytes with high ionic conductivity(up to 1.1×10^(-3)S/cm at 25℃).As a result,the assembled lithium symmetric battery of Li|THCE-15%LLZTO|Li suggests excellent cycling stability with 700 h at 0.1 mA/cm^(2)at 50℃,and the lithium metal batteries of LFP|THCE-15%LLZTO|Li delivers high initial discharge capacity of 128.2 mA·h/g with capacity retain of 75.48%after 150 cycles at 2 C.This work paves a new route to build safe and stable lithium metal batteries with synergistic introduction of composite electrolytes between electrolyte and electrode using soft gel interfacial layer and inorganic filler.

Effect of Nano-sized CeO_2 Abrasives on Chemical Mechanical Polishing of Silicon Wafer

The conception of the soft layer during chemical mechanical polishing(CMP) was proposed for the first time. The soft layer was a reaction layer formed on the silicon surface; it was softer than the silicon substrate and its thickness was about several nanometers. The existence of the soft layer could increase the material volume removed by one particle and increase the material removal rate during CMP. At the same time, the soft layer could decrease the cutting depth of the abrasive particle so as to realize ductile grinding, and it is useful to decrease the roughness of the polished surface and to improve the polishing quality.

Bearing Capacity of Defective Reinforced Concrete Pile in Sand-model Study

Concrete piles that were poorly constructed or analyzed in their soil analyses may have structural or geotechnical defects.To examine such defects,an experimental study was conducted to investigate how a defective reinforced concrete pile behaved.These piles were installed and subjected to a compression axial load in the sand that had relative densities of 30%,60%,and 80%.The tests were performed using four concrete model piles:one intact pile and the other three piles had a structural defect(necking)at three different positions of the pile at(0.25 L from the top,center,and 0.25 L bottom).Geotechnical defect(soft layer or debris)was studied using Styrofoam layer at various vertical distances under the pile toe with Y/D=(0,0.5,1 and 1.5)D.The test results showed that the bearing capacity of the structural defect was the most in the case of a neck at 0.25 L from the bottom,followed by a neck at the center,and finally a neck at 0.25 L from the top.In the case of a geotechnical defect,the bearing capacity of the pile decreased with the decrease of the vertical distance between the soft layer and the pile toe.

Crack evolution of soft–hard composite layered rock-like specimens with two fissures under uniaxial compression

Acoustic emission and digital image correlation were used to study the spatiotemporal evolution characteristics of crack extension of soft and hard composite laminated rock masses(SHCLRM)containing double fissures under uniaxial compression.The effects of different rock combination methods and prefabricated fissures with different orientations on mechanical properties and crack coalescence patterns were analyzed.The characteristics of the acoustic emission source location distribution,and frequency changes of the crack evolution process were also investigated.The test results show that the damage mode of SHCLRM is related to the combination mode of rock layers and the orientation of fractures.Hard layers predominantly produce tensile cracks;soft layers produce shear cracks.The first crack always sprouts at the tip or middle of prefabricated fractures in hard layers.The acoustic emission signal of SHCLRM with double fractures has clear stage characteristics,and the state of crack development can be inferred from this signal to provide early warning for rock fracture instability.This study can provide a reference for the assessment of the fracture development status between adjacent roadways in SHCLRM in underground mines,as well as in roadway layout and support.