Effective Cohesion Research Articles

Influence of spatial variability of soil strength parameters on probabilistic seismic slope displacement hazard analysis

Permanent sliding displacement analysis is commonly used to evaluate the seismic performance of slopes. Specifically, the fully probabilistic seismic slope displacement hazard analysis (PSSDHA) has attracted increasing attention recently, since it appropriately accounts for various sources of uncertainties associated with the estimation of sliding displacement. Within this analysis, the uncertainty of soil strength parameters (e.g., effective cohesion c′ and effective internal friction angle ϕ′) is commonly quantified by a logic-tree method, in which the spatial variability of c′ and ϕ′ is simply ignored. This study aims at proposing an extended PSSDHA framework by rigorously accounting for the spatial variability of c′ and ϕ′, and then investigating its influence on the resultant slope displacement hazard curves based on the Newmark rigid-block model. Two different approaches, namely an analytical-based and a simulation-based method, are proposed separately. The results of the analytical-based method are found to be consistent with those obtained by the simulation-based one. It is also shown that the displacement hazard would be underestimated if the spatial variability of c′ and ϕ′ is ignored; such underestimation is more significant for slopes with soil parameters exhibiting weak c′-ϕ′ correlation and strong spatial variability. Besides, it suggests that the proper configuration of logic-tree framework plays an important role in developing displacement hazard curves, and a relatively large range of discrete strength values is recommended to better account for the effect of the spatial variability of soil strength parameters.

The Effect of Acidic and Alkaline Chemical Solutions on the Behavior of Collapsible Soils

In this research, the effect of acidic and alkaline chemical solutions on the behavior of loessial soil was investigated. To evaluate the severity of acidity and alkalinity of chemicals, two factors sulfuric acid and sodium hydroxide were used in the pH of 3, 5, 9, 11. In this research, the effect of acidic and alkaline solutions on the collapse potential, shear strength parameters and unconfined compression of collapsible soils were investigated. Experimental tests results showed that acidic solutions with a low pH increase the collapse potential and effective cohesion of soil and decrease effective internal friction angle; on the other hand, alkaline solutions with a high pH decrease the collapse potential and effective cohesion of the soil and increase effective internal friction angle. The results of unconfined compression tests showed that with increasing the acidity and alkalinity in soil, the undrained strength of the soil decreased. SEM test results showed an increase in soil cavities in acidic solution while the soil cavities were fixed in alkaline solution.

Study on shear strength characteristics of loess dam materials under saturated conditions

A loess accumulation dam in Ansai Area, Yan’an, Shaanxi province is selected as the research object, and the remolded soil of the dam body is taken as the test material to conduct the saturated loess indoor triaxial test. The test shows that the peak stress of saturated remolded loess increases with the enhancement of confining pressure and dry density, and the pore water pressure rises rapidly in the shear of the samples with a dry density of 1.4–1.6 g/cm3and gradually flattens out. When the samples with a dry density of 1.7 g/cm3 in the process of shearing, the pore pressure rises rapidly and then decreases as the volume increases. The total internal friction angle and effective internal friction angle increase with the augment of dry density, and the total cohesion and effective cohesion show a changing trend of first rising, then falling and then rising due to the different development of original cohesion, sliding friction and rolling friction. Meanwhile, combined with field monitoring, it can be determined that the dam a total of three times more obvious damage. According to the comparison of field test and laboratory test, the concept and calculation method of “inspection threshold” are put forward.

Trust in Institutions Between Objective and Subjective Determinants: A Multilevel Analysis in European Countries

Trust is an essential element for effective social cohesion and a correct expression of the principles of representative democracy. In many countries of the Western world, we are witnessing the advance of anti-establishment political movements and a steady decline of trust in institutions. Crisis, perception of crisis, climate of opinion around it have an impact on political attitudes and diversified feelings (interest, trust, resentment), on political participation and on voting. Social analysts are called to deepen the reasons for the variability of these phenomena according to socio-cultural contexts and individual characteristics. The main aim of this paper is to analyse: (1) if and how much the spread of trust in institutions is different among the EU citizens and (2) what are the determinants of trust, deepening the intensity and the direction of the relationships with subjective and objective indicators. Our purpose is to outline the differences among the EU countries regarding trust in national and international institutions, simultaneously considering macro (country) and micro (individual) level of analysis by using a multilevel approach. The empirical analysis is based on the data collected by European Social Survey (ESS-Round 8) in 2016 (microdata) and on some variables (macrodata) taken from other statistical sources (Eurostat, Transparency International). The sample of individuals counts about 37 thousand subjects. Data analysis includes the construction of synthetic indices, using appropriate synthesis methods, and the identification of the determinants of Trust in Institutions, considering both micro and macro level explanatory variables, resorting to Multilevel Regression.

Shear Strength Parameters of Cement Stabilized Amorphous Peat of Various Water Additive Ratios at Different Natural Moisture Contents under Consolidated Undrained Triaxial Test

Peat is a problematic soil which has a low shear strength characteristic. Addition of cement can improve the properties and strength of peat soil. This paper presents the findings of the shear characteristic of cement stabilized amorphous peat under consolidated undrained (CU) triaxial test. Three different natural moisture contents of peat which are 1210%, 803% and 380%, were stabilized using cement with water to additive (W/A) ratio of 2.0 and 3.0. CU triaxial test was conducted to the specimens after cured for 90 days. The shear parameters and characteristics were investigated towards the change of W/A ratio of the samples with different moisture contents. The result shows that the stabilized peat specimens exhibited ductile behavior and were sensitive to the over consolidation. The total and effective cohesion (ccu, c′) of the stabilized peat were found to be greater at W/A ratio of 2.0 compared to W/A ratio of 3.0, and greater at lower initial moisture content specimens. The total and effective friction angles (φcu, φ′) are ranged from 14o to 27o and 36o to 47o consecutively and found to be increased upon the increase of W/A ratio except for the specimens with moisture content 1210% and 803% in term of total friction angle.

An analytical method for a pile-stabilised slope considering soil anisotropy

The use of stabilising piles is an effective method of reinforcing a slope against landslides. Soil arching between the piles promotes more load transfer into the piles, thus improving slope safety. However, few analytical solutions have been proposed for assessing the safety of an anisotropic slope with soil arching between stabilising piles, especially in most current design procedures. Based on BS 8006-1:2010, an analytical method was developed to evaluate the stability of a slope reinforced with stabilising piles, taking the anisotropy of soil strength and the horizontal soil-arching effect into account. A field case was used to assess the results of the proposed analytical method; differences of approximately 0·6–8·9% were found. To validate the proposed analytical method, a three-dimensional numerical simulation considering soil anisotropy was conducted; variation of the soil cohesion with depth and the direction of principal stress was introduced into the numerical analysis. The safety factors predicted by the numerical simulation agreed well with those derived by the proposed analytical method, with differences of 0·7–17%. The safety factor was found to decrease with increasing anisotropy coefficient and increase with higher effective cohesion and effective friction angle.

Monotonic triaxial shear strength and cyclic triaxial properties of undisturbed soft soil

The static and dynamic characteristics of Tianjin coastal soft soil are researched by cyclic triaxial test. For triaxial shear test, the specimens are isotopically consolidated under initial pressures of 100 kPa, 200 kPa, 300 kPa and 400 kPa, respectively; for the dynamic triaxial test, the specimens are consolidated under initial isotropic consolidation pressures of 100, 200, 300 kPa, respectively. The applied dynamic displacements are graded for each specimen, and the pore-water pressure is completely dissipated before application of next displacement amplitude. These tests show that the effective cohesion is 6 kPa and the effective internal friction angle is 26.5 degrees under consolidated undrained condition. The maximum shear modulus of soil is related to effective confining pressure, and its relationship with effective confining pressure can be expressed by Janbu’s formula. The shear modulus of soil is related to shear strain and decreases with the increase of shear strain. Hardin-Drnevich can be used to normalize the shear modulus.

Predicting sandy-clayey soil properties using electrical resistivity testing

Non-destructive tests are economical and easy-to-use techniques to determine different soil properties, which speed up the determination of sub-surface characteristics. They include ground-penetrating radar, seismographs, shear wave velocity and electrical resistivity testing. The latter is gaining worldwide popularity for determining sub-surface geology in geotechnical engineering as it does not require extensive testing. The aim of the study reported in this paper was to develop empirical correlations of electrical resistivity testing with different soil parameters by performing extensive conventional laboratory tests. These correlations would help in computing the required soil parameters by performing solely electrical resistivity testing, saving the time and effort required by conventional tests. The correlations developed included the relationship of resistivity values of soil with the drained angle of internal friction, effective cohesion, Atterberg's limits, maximum dry density, optimum moisture content and bearing capacity of a variety of shallow foundations. The regression coefficients obtained ensured the development of quite a good correlation, such that the result of electrical resistivity testing can be used for reasonably accurate determination of sandy-clayey soil properties

The unsaturated shear strength of calcareous soil in comparison with silicate soil

Marine calcareous sediments are quite prevalent in coasts of tropical regions. Significant differences have been observed between marine calcareous and silicate soils in terms of mechanical behaviors, shear strength, liquefaction resistance, etc., mainly due to considerable intra-particle voids in calcareous sediments. In the present study, constant water content (CW) triaxial tests were performed on two similar grain size distributions of both calcareous and silicate specimens to evaluate unsaturated shear behavior of calcareous soil for the first time, and compare it with a reference silicate soil. Saturated triaxial tests were also conducted to obtain saturated shear strength parameters of both soils. Porous structure of calcareous soil was studied using scanning electron microscopy and mercury intrusion porosimetry tests. Soil–water retention curves resulting from pressure plate tests were also obtained for both soils. Calcareous soil showed higher water retention capacity, attributing to its porous microstructure, and it experienced higher suction changes during CW tests. Effective stress parameter (χ) and capillary cohesion of calcareous soil were indirectly influenced by its microstructure, and were higher compared to silicate soil. Like the silicate soil, for the calcareous soil, critical state line was unique and close to saturated state.

Indirect estimation of poverty indicators at poviat level

The availability of detailed and precise data on poverty at a low level of spatial aggregation is important when pursuing an effective cohesion policy. In Poland, this type of information is gathered during household surveys conducted by Statistics Poland and is made available at country, region, and selected socio-economic group level. Direct estimates relating to domains not included in a survey are burdened with a serious estimation error. In a situation of a limited (or in extreme cases zero) sample size, an estimation becomes possible through the application of small area estimation methods – indirect estimation. These techniques use variables which are strongly correlated with the researched phenomenon and which come from a census or from an administrative register. The aim of the study discussed in the article is to estimate two indicators: the rate of poverty and the depth of poverty at a poviat level, with the application of the Empirical Bayes (EB) method. The first indicator provides information on the scale of the phenomenon and the other one on its intensity, and so they constitute complementary measures of poverty. The study used data from the European Union Statistics on Income and Living Conditions of 2011 and the National Census of Population and Housing 2011. Information about the scale and intensity of poverty at the poviat level was obtained through the adaptation of the EB method based on the linear mixed model and Monte Carlo simulations. The indicators estimated this way allow for an assessment of the diversity of poverty at a local level. In addition, they are more precise and consistent with administrative registers in comparison to direct estimation results.

Забезпечення справедливої винагороди персоналу на рівні інституційного регулювання та нr-менеджменту

Обґрунтовано, що забезпечення справедливої винагороди персоналу вимагає консолідації інституційної сфери механізму державного регулювання (профспілкових організацій як юридично встановлених структур захисту прав працівників; органів державної влади, які через створення умов бізнес-середовища та регламентацію концептуальних засад управління персоналом мотивують роботодавців до відповідних кроків) та HR-менеджменту (роботодавців як суб’єктів господарювання). Деталізовано процес забезпечення справедливої винагороди персоналу за інституційним, функціональним, ресурсним забезпечення, управлінським інструментарієм та поточними управлінськими діями. Охарактеризовано механізм нової системи мотивації та оплати праці персоналу, що включає: диференціацію персоналу; проведення оцінювання посад працівників; вибір системи оплати праці, її форм, видів; вибір системи додаткових пільг і нематеріальної мотивації; формування структури компенсаційних пакетів.

Geotechnical properties of lateritic soil from Nimo and Nteje areas of Anambra State, Southeastern Nigeria

The strength and durability of materials used as subbase and subgrade for pavement design and construction are the main factors determining the performance and service life of highway pavements and airfields. This study investigates the geotechnical properties of lateritic soils from Nimo and Nteje areas of Anambra State, Southeastern Nigeria. The soil samples obtained from the two study areas are hereinafter referred to as LAT-1 and LAT-2 for Nimo and Nteje areas, respectively. The samples were collected at depths ranging from 1 to 1.5 m, and were analyzed at the Anambra State Materials Testing Laboratory, Awka. Geotechnical tests such as Atterberg limits, Standard Proctor Compaction, California Bearing Ratio (CBR), Tri-axial tests and Particle size Distribution analysis were conducted on the soils. All the geotechnical tests were done in accordance with the ASTM and British standards. The soil samples were classified as A-2-7, while the unsoaked CBR values of the soils were 0.89 and 1.43 % for LAT-1 and LAT-2, respectively. The Plasticity Index and Maximum Dry Density of the soils were 21 and 17 %, and 1.93 and 2.19 Mg/m3 for LAT-1 and LAT-2, respectively. Similarly, the effective friction angle and effective cohesion of LAT-1 and LAT-2 were determined as 13.54 and 22.09°, and 38.72 and 10.43kPa, respectively. It was found that the lateritic soil from Nteje (LAT-2) showed higher strength and compaction properties than the soil from Nimo (LAT-1). However, the general trend of the results indicates that the lateritic soils are not suitable for use as subbase and subgrade in pavement construction.

Analysis of deformation and failure characteristics of undisturbed loess under three axis test

The water content has a very obvious influence on the deformation and strength characteristics of loess, which is related to the safety of geological environment. In this paper, the triaxial test of loess is carried out, and the deformation characteristics of the loess are studied. The strength characteristics of different loci are studied. The study shows that as the water content increases, the effective cohesion of loess decreases and the effective internal friction angle changes. The amplitude is not large, indicating that the water content only affects the effective cohesion of the loess and does not affect the effective internal friction angle. When the water content reaches a certain value, the effective cohesion is no longer reduced and remains stable. The corresponding moisture content corresponds to the plastic limit. The Mohr-Coulomb strength theory is suitable for fitting shear failure and bulging deformation. While Griffith The strength theory is more suitable for fitting the splitting failure, indicating that the strength theory suitable for different failure modes is different.

Study on tropical organic soil stabilization based on biogrouting

Biogrouting is a new environmental friendly stabilization method to stabilize soft soils by applying microorganisms. The microorganisms produce CaCO3, which fill voids of soil particles and bond the particles. This work studied biogrouting of high plasticity tropical organic soil applying Bacillus subtilis bacteria. In order to study the effectiveness of biogrouting using Bacillus subtilis, unconsolidated undrained triaxial and direct shear tests were conducted on the untreated and stabilized soils. The curing time for the stabilized soil specimens were 7, 14 and 28 days before the tests were conducted. In order to study the influence of the amount of Bacillus subtilis, 6 ml and 12 ml of Bacillus subtilis liquid culture was injected into the soil specimens. The soil became stronger as the amount of Bacillus subtilis used increased. The results indicated that the longer curing time and the higher amount of Bacillus subtilis reflected better soil improvement in term of cohesion, friction angle and shear stress. After 28 days of curing time, injection of 6 ml and 12 ml Bacillus subtilis liquid culture increased the effective stress cohesion values by 180% and 270%, respectively.

Seismic landslides hazard zoning based on the modified Newmark model: a case study from the Lushan earthquake, China

Seismically triggered landslides can cause great damage to the road construction in mountainous areas. The permanent displacement analysis based on Newmark sliding-block model can evaluate risk of these landslides from the perspective of deformation damage and overall failure probability of slopes. However, the sliding-block model does not consider the attenuation effect of the shear strength on the sliding surface during earthquake, causing the calculated value of Jibson method to be less than the actual value. Therefore, the Newmark model was modified by adding attenuation coefficients to the effective internal friction angle and the effective cohesion of geologic units. The landslide areal density was proposed for hazard zoning with the Wenchuan earthquake data. The results showed that the predicted values agreed well with the real distribution of the landslides triggered by the Lushan earthquake. The proposed hazard zoning method in this paper can predict the severity of seismic landslides in consideration of the environmental changes in mountainous regions after the earthquake and provide support for the site selection in highly seismic areas.

Mechanical behavior of intact completely decomposed granite soils along multi-stage loading–unloading path

Completely decomposed granite (CDG) soils in Shenzhen, China are usually subjected to loading-unloading due to the demolition/reconstruction of buildings and excavation/backfilling of foundation pits during the rapid development of the city. To investigate the mechanical behavior including the failure mode of the CDG soils under loading-unloading, consolidated drained triaxial tests along multi-stage loading-unloading paths were carried out in this study. Four types of loading sequences with one, two, three, and four loading-unloading cycles, respectively, were applied to investigate the mechanical properties of the CDG soil. Test results show that, as the number of the loading-unloading cycles increased from one to four, the effective cohesion (c') increased from 45.4 to 63.6 kPa; however, the effective friction angle (φ') first increased from 22.0° to 27.1° and then decreased to 19.0°. These results are mainly related to the strain-hardening property of the CDG soil after compressed by a relatively low deviator stress in the first two cycles and the structural damage of the specimens caused by a higher deviator stress in the last two cycles. In addition, the secant modulus also increased in the first two cycles, but decreased in the last two cycles due to the aggravation of soil structural damage. However, the unloading modulus (Eur) decreased all the way from 162.9 to 22.7 MPa is attributed to the number of loading-unloading cycles and the different confining stresses applied in the tests. The unloading modulus was not only affected by the confining pressure and, more importantly, also affected by the accumulated structural damage of soils.

Shear strength of an unsaturated loam soil as affected by vetiver and polyacrylamide

Shear strength is an important soil mechanical property that its improvement is one of the rehabilitation program for the reduction of soil erosion and degradation. The objective of this study was to investigate the effect of polyacrylamide (PAM) and the vetiver system as a cheap and long-term bioengineering method and their combination on unsaturated shear strength parameters (effective cohesion, c' (kPa), angle of effective internal friction, φ' (°) and angle of internal friction related to matric suction, φb (°)) of a loam soil. The experimental treatments included vetiver plant (VP0), two concentrations of PAM dissolved in water [0.2% (V0P2) and 0.4% (V0P4)], and simultaneous presence of vetiver and two concentrations of PAM (VP2 and VP4). Direct shear tests were performed at combinations of three normal stresses of 25, 50 and 100 kPa and four matric suctions of 0, 10, 30 and 50 kPa (12 tests per each treatment) to determine the shear strength parameters. It was found that vetiver and PAM decreased apparent angle of internal friction (φ) and φ', and increased c', total cohesion (c), φb, and as a result increased unsaturated shear strength. However, the positive effect of vetiver on shear strength was greater than that of PAM. It seems that PAM and vetiver enhanced the contact area, inter-particles bonds, aggregation, and inter-aggregate porosity, and as a consequence, increased the soil effective saturation, effective stress, cohesion and shear strength. Also, when matric suction increased the c and shear strength increased although the φ increased slightly. Simultaneous application of vetiver and 0.4% of PAM resulted in maximum shear strength, indicated although vetiver can increase the cohesive strength, it would be more pronounced when PAM was simultaneously applied. Simultaneous application of vetiver and PAM through increasing soil shear strength can be suggested as the rehabilitation program to reduce soil erosion and degradation.

PSYCHOLOGICAL AND PEDAGOGICAL CONDITIONS FOR COGNITIVE DEVELOPMENT OF CHILDREN WITH AUTISM

The article analyses the psychological and pedagogical conditions necessary for development of autistic children’s cognitive processes. The influence of pedagogical conditions on the pedagogical system is analyzed, and it reflects the totality of educational and material-spatial possibilities during the educational process. The performed theoretical analysis of the above-mentioned studies allowed us to determine the pedagogical conditions as pedagogical circumstances, when the components of the educational process (content, teaching and learning), vocational training, psychological and pedagogical support are interconnected in the best way and create an atmosphere of fruitful cooperation between a teacher and his/her pupils. The performed correlative analysis have shown that the correlations between cognitive activity, memory, verbal communications, imitation, space structuring, and autism deepness are the most important fir the group of children with autism. Adequate psychological and pedagogical conditions - the space structuring and the improvement of correctional teachers’ skills - facilitate the successful adaptation of such children at the inclusive environment. There is a line of pedagogical conditions ensuring pedagogical system functioning and effective development. The most important of them are organizational, psychological, pedagogical, didactic conditions. The organizational and pedagogical conditions are a combination of purposefully designed contents, forms, methods of the holistic pedagogical process that underlie functioning and development of the procedural aspect of the pedagogical system (as a holistic process). The specificity of the developing educational environment for children with autism is manifested in the organization of environmental resources into various complexes. For this purpose, the following principles are applied: safety, culturally significant objects, supported poly-sensor perception and semantic orderliness. Safety means a certain objective and spatial organization of the environment that minimizes the feelings of uncertainty and fear of a child with autism. The environment saturated with culturally significant objects helps children to contact with various information carriers (gives them certain information about the world), which greatly stimulates their cognitive activities, involuntary and voluntary attention. The supporting poly-sensor perception correctional-developing environment stimulates and ensures obtainment of information from various sense organs, at perception of both separate objects and relations existing between them. The environment organization in the semantic order provides children with effective cohesion, stimulates their active interactions and cooperation with other people, and puts children into situation when they work in the zone of their actual and near development.

Horizontal capacity of single piles: an extension of Broms’ theory for c-ϕ soils

Several methods are available for the evaluation of the horizontal capacity of piles in cohesionless (c′ = 0) or in purely cohesive (su > 0 and ϕu = 0) soils. In this paper, the well-known theory by Broms (1964a, 1964b) is extended to soils possessing both cohesion and friction (c-ϕ soils). A simple profile of the ultimate soil pressure (plim) with depth is assumed, accounting for soil cohesion and pile embedment and encompassing Broms’ profile for drained loading. By considering translational and rotational equilibrium, equations for the different mechanisms of failure – short, intermediate and long piles - are given. The results are also presented in the form of non-dimensional graphs, allowing for an expeditious evaluation of the horizontal capacity of piles and the maximum bending moment. For most cases, it is found that giving consideration to the soil’s effective cohesion (c′) can lead to significant advantages in terms of increased pile capacity and the consequent reduction in pile dimensions and costs. A comparison of the proposed solution with some documented field cases allows for the first validation of the study.

Probabilistic stability analysis of an embankment dam considering soil spatial variability

A probabilistic stability analysis of an embankment dam taking into account soil spatial variabilities is presented in this paper. The effective cohesion and friction angle of the backfill are modelled as two anisotropic cross-correlated lognormal random fields by using the Karhunen–Loève Expansion. The probabilistic analyses are performed by a meta-modelling technique SPCE/GSA which combines the Sparse Polynomial Chaos Expansion (SPCE) and the Global Sensitivity Analysis (GSA). This technique is targeted to deal with high dimensional stochastic problems and can provide a variety of interesting results in terms of probability density function (PDF) and statistical moments of the model response, failure probability and sensitivity index of each input variable. Concerning the deterministic calculations, two models (limit equilibrium and finite difference) are created and compared in a probabilistic framework. The influences of the soil spatial variability and the cross-correlation between the shear strength parameters on the reliability analysis results are investigated.