Probabilistic assessment of slope failure considering anisotropic spatial variability of soil properties

Anisotropic spatial variability of soil properties is frequently encountered in geotechnical engineering practice due to the complex depositional process.To quantitatively evaluate the response of slope failure related to anisotropic spatial variability of soil properties and reveal the underlying influence of anisotropic spatial variability of soil properties on the slope reliability,this study integrates the random finite difference method(RFDM)into a probabilistic assessment framework and adopts general spatial variability and a cohesive-frictional soil slope example for illustration.A parametric analysis is carried out to investigate the influence of general anisotropic spatial variability of soil properties on slope failure probability and failure characteristics.The results show that the directional angles of scales of fluctuation of general anisotropic spatial variability significantly affect the slope failure probability.The dominant failure mode is the intermediate type in most cases of general anisotropic spatial variability,which is distinguished from the shallow failure mode occurring in the homogenous state.Overestimation of cross-correlation between c and u(qc;u),scales of fluctuation(dmax and dmin)in general anisotropic spatially variable soils significantly influences the average slip mass volumes of deep and multi-slip failure mode.Compared with transverse anisotropic spatial variability,general anisotropic spatial variability significantly ampli-fies the effects of qc;u,dmax and dmin on slope reliability.

Reliability Analysis of Slope Stability Considering Temporal Variations of Rock Mass Properties

Temporal variation of rock mass properties,especially the strength degradation due to drying-wetting cycles as well as the acidic wetting fluid(rainfall or reservoir water)is crucial to stability of reservoir rock slopes.Based on a series of drying-wetting cycling and experiments considering the influences of pH values,the degradation degree models of the reduced cohesion𝑐𝑐′,friction angle𝜑𝜑′are developed.2D stability analysis of the slope is subsequently carried out to calculate the factor of safety(Fs)via limit equilibrium method(LEM)and a predictive model of Fs is built using multivariate adaptive regression splines(MARS),revealing the effect of the drying-wetting cycles and pH value.The reliability analysis by Monte Carlo simulation is performed to rationally consider the uncertainty and the temporal variation of the shear strength parameters of rock mass.Results indicate that the MARS-based model can estimate the Fs accurately.The Fs and the reliability indexβdecrease with increase of drying-wetting cycles,and the temporal variation of rock mass properties has significant influence on the slope reliability.Overlooking the temporal variation of rock properties may overestimate the Fs and reliability indexβin the longer term.

Regional gray matter atrophy and neuropsychologcal problems in relapsing-remitting multiple sclerosis

In multiple sclerosis, gray matter atrophy is extensive, and cognitive deficits and mood disorders are frequently encountered. It has been conjectured that focal atrophy is associated with emotional decline. However, conventional MRI has revealed that the pathological characteristics cannot fully account for the mood disorders. Moreover, there is no correlation between cognitive disorders and MRI results in clinically isolated syndromes or in cases of definite multiple sclerosis. In this casecontrol study, voxel-based morphometric analysis was performed on 11 subjects with relapsing-remitting multiple sclerosis, and the results show that these patients exhibit gray matter atrophy. Moreover, the gray matter atrophy in the superior and middle gyri of the right frontal lobe in patients with multiple sclerosis was correlated with scores from the Hamilton Anxiety Rating Scale. The scores obtained with the Repeatable Battery for the Assessment of Neuropsychological Status were associated with gray matter atrophy in the middle gyrus of the left frontal lobe, the superior and middle gyrus of the right frontal lobe, the middle gyrus of the left cingulate, the superior and middle gyri of the left frontal lobe, and the triangular area of the left frontal lobe. However, there was no statistical significance. These findings suggest that the cingulate and frontal cortices of the dominant hemisphere are the most severely atrophic regions of the brain, and this atrophy is correlated with cognitive decline and emotional abnormalities.

Tunneling and deep excavations in spatially variable soil and rock masses:A short review

In an urbanization process,infrastructure elements such as tunnels and deep excavations are widely used to service the development of cities.Owing to the lengthy geological processes of geomaterials and the limited availability of site-specific test data,soil and rock properties exhibiting spatial variability are frequently encountered in geological and geotechnical engineering.This paper presents a comprehensive review of the application of spatial variability in tunneling and deep excavation over the past 20 years.It is found that the spatial variability is generally modeled as a random field(RF)in finite element software,based on random field theory(RFT).This model has been widely used in the design,stability evaluation,and probabilistic analysis of tunnels and excavations.Previous works have proven that the performance of tunnels and deep excavations can be better captured by considering the spatial variability,as compared with conventional deterministic analysis methods.Nonetheless,current research still faces many factual scientific problems.Therefore,this paper also identifies some research gaps,as well as recommendations for further investigations.

Brain gray matter volume changes associated with motor symptoms in patients with Parkinson's disease

Background:Parkinson's disease (PD) is a common neurodegenerative disease.Most studies have found that the histopathological lesion is not only localized at the extrapyramidal area (basal ganglia) but also at the cortex in PD patients.Voxel-based morphometry (VBM) based on the voxel as a unit is described for quantitative detection of density and volume of brain tissue.In this study,VBM was used to investigate the brain gray matter changes associated with motor symptoms in PD patients.Methods:Twelve outpatients with PD and 12 healthy controls were recruited in our hospital from September 2013 to March 2014.VBM was performed on the whole brain of all subjects.Image processing and statistical analysis were performed using SPM8.A two-sample t test and multiple regression analysis were performed.Results were displayed with a threshold of P ＜ 0.01,corrected by false discovery rate (FDR) correction and cluster size ＞30 voxels.Results:Comparing control healthy subjects with the patients,the data showed that PD patients had reduced gray matter volume in the postcentral gyrus,the right supramarginal center,superior temporal gyrus,precentral gyrus,Brodmann area 41,transverse temporal gyrus,Brodmann area 3,and inferior parietal Iobule.The data also found that between gray matter volume and UPDRSIII in PD patients,there were negative correlations in the right middle frontal gyrus,BA06,right precentral gyrus,right superior frontal gyrus,and medial frontal gyrus,and between gray matter volume and Hoehn-Yahr (HY) in PD patients,there were negative correlations in the right middle frontal gyrus,right superior frontal gyrus,BA6,and right precentral gyrus.Conclusions:These data supported that extensive changes associated with motor symptoms in the gray matter volume was mainly located in the related area of movement,which had obvious relevance with the progression of PD.

Numerical investigation of pile responses induced by adjacent tunnel excavation in spatially variable clays

The pile responses induced by adjacent tunnel excavation have been a hot research topic in geotechnical engineering.Tunnel excavation may exert disturbance to the surrounding soil mass and then influence the adjacent pile foundations.In this paper,the random finite difference analysis considering the spatial variations of soil properties is conducted to explore the effect of tunnel excavation on the adjacent pile response by varying the distance of pile away from the tunnel centerline(D),the pile length(L),the pile diameter(d_(p)),the tunnel depth(h),and the anisotropic ratio between the horizontal and the vertical scales of fluctuation(δ_(x)/δ_(y)).A set of pile response curves are developed to assess the influence of tunnel excavation on the adjacent passive pile foundations in spatially variable clays and provide guidelines for the tunnel excavation in the complex constructed environment.

Altered regional homogeneity of prefrontal cortex in Parkinson's disease with mild cognitive impairment

Background:Mild cognitive impairment (MCI) is a common non-motor symptom of early Parkinson's disease (PD),but the neural mechanisms underlying it remain poorly understood.The aim of the present study was to investigate the characteristics of cognition-related brain activities in the PD patients with MCI.Methods:The brain fMRIs and cognition tests were acquired in 39 PD patients and 22 healthy controls (HC) from September 2013 to January 2015.The patients were divided into two groups:PD-MCI (n--18) and PD with normal cognition (PDNC,n =19).we used resting state fMRI and a regional homogeneity (ReHo) method to explore patterns of intrinsic brain activity in patients with PD-MCI as compared with PDNC subjects and HC.Results:Compared with the PDNC group,the PD-MCI group exhibited significantly increased ReHo in parts of the prefrontal cortex regions (e.g.right superior frontal gyrus,right middle frontal gyrus and orbitofrontal cortex).Compared to the HC group,a decrease of ReHo value in left thalamus was found in PD-MCI.However,this reduction was not found in the left thalamus of PDNC group,but in the above prefrontal regions (p ＜ 0.05,with Bonferroni correction).Conclusions:These results demonstrate that the ReHo of prefrontal cortex in resting state is changed in PD patients with MCI.The presence of MCI in PD may be attributed to abnormal regional activity in prefrontal cortex regions.