Shear Strength Of Clayey Soils Research Articles

Evaluating the Effect of Nano-SiO2 on Different Types of Soils: A Multi-Scale Study

A rapid growth in the population leads to a large increase in engineering construction. This means there is an inevitability in regard to building on problematic soils. Soil reinforcement becomes an important subject due to the fact that it is a concern for engineers and scientists. With the development of nanotechnology, more and more nanomaterials are being introduced within the practice of soil reinforcement engineering. In this study, the reinforcing effect of novel nanomaterial nano-silica (SiO2) applied to different kinds of soils was systematically studied. The nano-SiO2-reinforced soil possessed lower final water evaporation loss, and evaporation rates. The nano-SiO2 increased the shear strength of clayey soil and sandy soil under both cured and uncured conditions, but the reinforcing effect on clayey soil was more obvious. The addition of nano-SiO2 promotes the friction angle and cohesion of clayey soil; further, it also increases the cohesion of sandy soil. The unconfined compressive strength of clayey soil was enhanced by nano-SiO2, meanwhile, the nano-SiO2-reinforced soil possessed greater brittleness. The microstructure of nano-SiO2-reinforced soil is shown via SEM analysis, and the results of X-ray diffraction (XRD) tests show that there are no new mineral components generated during the reinforcing process. It was also found that nano-SiO2 possessed little influence on the soil pH value. Adding nano-SiO2 will not damage the original chemical environment of the soil. The microstructure of nano-SiO2-reinforced soil was observed to prove the results above. In general, nano-SiO2 is an excellent soil additive that can improve the mechanical properties of both clayey soil and sandy soil effectively. This research provides more ideas and directions for the purposes of selecting soil reinforcement materials.

Experimental Investigation on the Variation in Shear Strength of Clayey Soil Reinforced with Randomly Distributed Alkali-Resistant Glass Fiber

Geotechnical investigations are one of the most crucial parts of the construction to save the time and effort spent on the projects. Particularly, in the case of the clays with high plasticity are encountered, the analysis of bearing capacity and settlement of structures such as buildings, roads, and dams governs the design. The possible solutions can be leaving the land, reaching a strong soil bypassing the weak one, removing the weak soil by replacing it with a higher strength of the material, and applying soil improvement methods. Glass fibers are one of the synthetic additives which may be used to address improving the weak soil properties. In this study, the effect of alkaline-resistant glass fiber additive on the undrained shear strength of the clayey soils was investigated. Fibers with distinct lengths were added to the natural soil at increasing rates, and the mixtures were prepared in the optimum water content. The prepared mixtures were compacted in a compaction mold with a diameter of 50 mm and a height of 100 mm with standard energy. Unconfined compression test (UC) were conducted on a total of 210 cylindrical samples, 10 of natural clay and 200 of fiber-reinforced. The maximum increase was at 0.5% of a fiber blend of 40 mm length. As a result of 210 UC tests, it was observed that the alkaline-resistant glass fiber additive increased the shear strength of the clay soil.

Developing multivariate adaptive regression splines model for predicting the undrained shear strength of clayey soil from cone penetration test data

Developing multivariate adaptive regression splines model for predicting the undrained shear strength of clayey soil from cone penetration test data

Impacts of Nano-silica on Physical Properties and Shear Strength of Clayey Soil

Impacts of Nano-silica on Physical Properties and Shear Strength of Clayey Soil

The short-term and creep mechanical behaviour of clayey soil-geocomposite drainage layer interfaces subjected to environmental loadings

In this paper, to investigate the impact of environmental loadings on the short-term and creep mechanical characteristics of different types of clayey soil-Geocomposite Drainage Layers (GDL) interfaces, a series of rapid loading and creep shear tests were conducted on Mercia Mudstone Clay-GDL interfaces and Kaolin Clay-GDL interfaces subjected to drying-wetting cycles, thermal cycles and elevated temperature, etc, using a bespoke temperature and stress-controlled large direct shear apparatus. The experimental results indicate that, compared with the original specimens, the interfaces subjected to drying-wetting cycles, thermal cycles and elevated temperature, have lower peak shear strength and creep shear resistance. For example, under 25 kPa normal stress, the peak shear strength of original Mercia Mudstone Clay-GDL interfaces and Kaolin Clay-GDL interfaces falls by 11.91% and 10.11%, respectively, when subjected to 1 drying-wetting cycle. This can be ascribed to the weakening of interlocking effects and skin friction between soil and GDL caused by the softening of drainage core and geotextile fibres of GDL. The peak shear strength of clayey soil-GDL interfaces subjected to one drying-wetting cycle is lower than that subjected to one thermal cycle because of the reduction in the peak shear strength of clayey soil above GDL during drying-wetting cycles. The impact of drying alone on the decrease in the peak shear strength of clayey soil-GDL interfaces during drying cycles with heating is small, and the main influence factor is the elevated temperature.

Investigation of drying−wetting durability of cement-stabilised clayey soil

Few studies have reported the effect of cement content and surcharge pressure on the drying−wetting durability of cement-stabilised clayey soil. The aim of this research was thus to understand the effect of these two factors on the drying−wetting durability of cement-stabilised clayey soil. Clayey soil, dredged from Taihu Lake in Wuxi, China, was stabilised with three different cement contents. Drying−wetting tests were performed on the cement-stabilised clayey soil under five different surcharge pressures and direct shear tests were conducted using a modified conventional direct shear device. The cement content was found to have a significant effect on the drying−wetting durability of the cement-stabilised clayey soil. Drying−wetting appears to decrease the shear strength of clayey soil with a low cement content, whereas drying−wetting appears to increase the shear strength of clayey soil with a high cement content. The variation in shear strength of the cement-stabilised clayey soil is attributed to drying-induced bond damage and drying-temperature-induced hydration and pozzolanic reactions. The surcharge pressure had a significant impact on the drying−wetting durability in a certain range. The findings are interesting from a practical perspective for earthworks involving cement-stabilised clayey soils.

Ageing effect on compressibility, permeability and shear strength of clayey soils exposed to salt solutions

The present study investigated the ageing effect on compressibility, permeability and shear strength behavior of kaolin and bentonite samples in the presence of NaCl and CaCl2 solutions. The compressibility, permeability and shear strength parameters were determined on the 60, 190, and 250 days cured samples. The results have shown that, the kaolin sample becomes more compressible in the presence Ca2+ ions with ageing. Generally, the normalized compression index values of bentonite samples increased at the end of 60 days and 250 days curing time periods. The normalized permeability value of kaolin decreased by ageing in the presence of Na+ ions almost twofold. The permeability values of bentonite increased both in NaCl and CaCl2 solutions during ageing. In the presence of Na+ ions kaolin had higher max. shear stress value than Ca2+ ions. When the max. shear stress values of 0, 60 and 190 days samples were compared, it was seen that NaCl solution had no significant effect on the shear strength of kaolin sample. However, the shear strength of kaolin increased in the CaCl2 solution during ageing. In the presence of Ca2+ ions the max. shear stress value of bentonite was higher. The results of this study have shown that ageing has significant effects on the compressibility, permeability and shear strength of kaolinitic and bentonitic clayey soils.

A comparison between undrained shear strength of clayey soils acquired by “PMT” and laboratory tests

A pressuremeter test (PMT) is one of the in situ tests, which is used to evaluate deformation and strength parameters of soils for various projects, including subway projects. The limit pressure (PL) and undrained shear strength (Su) are the key parameters that are obtained directly and indirectly from the pressuremeter testing results. This research was carried out using geotechnical information obtained from a subway project in Qom city, Iran. Based on 44 PMT and uniaxial tests on very stiff to hard saturated clayey soils, a linear empirical equation between Su − PL and Su − PL* = (PL − σH) with R2 = 0.68 was proposed and it was found that σH had an insignificant effect on the proposed relationship. The effect of physical properties of soil, including plastic index (PI), liquid limit (LL), and water content (ω), was evaluated, and a multivariate equation was proposed between them. A comparison between the equations obtained in this research and those proposed by other researchers reveals that the empirical relationships between Su and PL are associated with the consistency of soils; the stiffer the soil is, the slope of relationship between Su and PL is less.

Mechanical Properties of Mega-Thick Alluvium and Their Influence on the Surface Subsidence

Surface subsidence caused by mining is closely related to the nature and structure of overburden and soil layer. Characteristics of mining subsidence under the condition of mega-thick alluvium are special. Through analyzing the mechanism of mining subsidence with mega-thick alluvium, surface subsidence was divided into three parts, i.e., bedrock surface subsidence with non-alluvium, bedrock surface subsidence with mega-thick alluvium and consolidation subsidence. Mechanical Properties of Mega-thick Alluvium and their Influence on the Surface Subsidence were studied by means of geotechnical test and numerical simulation. The shear strength of clayey soil in Jiaozuo mining area were researched through unconsolidated undrained triaxial test. The ranges of internal friction angle and cohesion force of clayey soil in this area were presented. Taking a panel covered by mega-thick alluvium as an example, based on the test results, the influences of thickness, friction angle and cohesive force of alluvium on surface subsidence were analyzed. Results of numerical simulation were compared with field data. Results show that the maximum surface subsidence value increases with the increase of the thickness of alluvium, decreases with the increase of the friction angle and cohesive force. This paper combines geotechnical tests of alluvium mechanical properties with surface subsidence, which has a certain guiding significance for the study of mining subsidence.

The performance of six neural-evolutionary classification techniques combined with multi-layer perception in two-layered cohesive slope stability analysis and failure recognition

Six population-based hybrid algorithms are applied to train the multilayer perceptron (MLP) to improve the classification accuracy, in the stability assessment. A complex problem of slope stability against failure is designed in Optum G2 software. Considering four key factors of shear strength of clayey soil, slope angle, the ratio of foundation distance from the slope to the foundation length, and the applied surcharge, the stability or failure of the proposed slope are anticipated. The provided data are used to develop the MLP combined with biogeography-based optimization (BBO), ant colony optimization (ACO), genetic algorithm (GA), evolutionary strategy (ES), particle swarm optimization (PSO) and probability-based incremental learning (PBIL). The results revealed that the BBO-MLP with the obtained area under the receiving operating characteristic curve (AUROC) of 0.995 and the classification ratio (CR) of 92.4% is the most accurate model followed by GA-MLP (AUROC = 0.960 and CR = 84.3%), PBIL-MLP (AUROC = 0.948 and CR = 79.3%), ES-MLP (AUROC = 0.879 and CR = 65.7%), PSO-MLP (AUROC = 0.878 and CR = 71.3%), and ACO-MLP (AUROC = 0.798 and CR = 60.7%).

Numerical simulation of water content dependent undrained shear strength of clays

A nonlinear mathematical model for estimating the water content dependent undrained shear strength of clayey soils was developed. Three types of clay mixtures (kaolinite, bentonite, and kaolinite-bentonite) were considered. The shear strength of the given soil samples was determined via torvane tests. Experimental results were compared with three numerical results: (i) the analytical function fit, (ii) modeling without the water content effect, and (iii) modeling with the water content effect using the Mohr-Coulomb (M-C) model. There was good agreement among the experimental, analytical, and numerical results with and without the water content effect in the fully softening zone. However, there was a large difference between the numerical results obtained from the developed model with and without the water content effect in the flow zone with a high liquidity index, because the shear strength may decrease significantly to low value in the case of an abrupt increase of the water content. The greatest advantage of the developed model is that it can simulate the reduction of the shear strength and shear band development under the high water content condition, which may trigger a large mobile mass movement.

Comparative Study of Consistency Behavior and Shear Strength of Clayey Soils of Rajshahi District, Bangladesh

This paper aims at introducing the Fall Cone Test (FCT) to obtain the shear strength of clayey soils and reveals its applicability by comparing the results obtained from that of Unconfined Compression Test (UCT). Furthermore, the liquid and plastic limit obtained from Casagrande method also compared with that obtained from FCT. For these, soils were collected from Godagari, Tanore, and Nauhata from Rajshahi District (RD). At first, Hydrometer analysis was performed in each soil to know the physical properties. Then Atterberg Limit test was carried out by considering Casagrande Method. After that UCT was shown in each land to find the shear strength of the clay soils. Lastly, FCT was conducted to find out the shear strength, LL and PL. FCT shows a lower amount of liquid and plastic limit than the values measured in the Casagrande Method except plastic limit for Tanore for FCT whereas Godagari shows the higher value of shear strength considering FCT. This research can be concluded with further research should be conducted to ensure its accuracy. On the other hand, it can be drawn which soil have more consistency and shear strength considering others.

Swell and Consolidation Characteristics of Fiber Reinforced Cohesive Soil

Naturally occurring expansive clays show detrimental changes in volume when subjected to variation in water content. It leads to significant damages in foundations that are seated on these materials used for the construction in pavement, bridges especially in light weight buildings. The improvement could be in terms of reducing the swelling and differential settlement or increasing the shear strength of clayey soil. Reinforcing soil using fiber is one of the ground improvement techniques in which fibers are mixed randomly with the soil, in similar fashion to mixing with lime, cement or other additives. It eliminates the potential weak planes and maintains the strength isotropy by random reinforcement. The main objective of this study is to investigate the effect of synthetic polypropylene fibers on the swelling and consolidation characteristics of clay soil. The parameters considered for the study include the swelling pressure, swell potential and consolidation characteristics. Polypropylene fiber with aspect ratio (l/d) 12 is varied at 0%, 0.1%, 0.25%, 0.50% and 0.75% by dry weight of the soil is used as reinforcement. The swell potential(S%) and the swelling pressure(P) decreased with the addition of fiber. From the experimental results, 0.5% of polypropylene fiber is considered to be optimum. The results also revealed that the rate of heave formation is very less compared to that of unreinforced soil. From the consolidation test, it was observed that compression index, co efficient of compressibility and co efficient of volume change are 0.22, 0.8 mm2/N and 0.48mm2/N at the optimum fiber percentage.

Probabilistic analysis of monopile-supported offshore wind turbine in clay

The dynamic behaviour of monopile supported offshore wind turbines (OWTs) is considerably influenced by inherent variabilities of soil properties and loading. This study investigates the effect of uncertainties in soil shear strength properties, and wind and wave loads on the reliability of OWT structures founded in clay. The OWT system is modeled as an Euler-Bernoulli beam and soil-structure interaction is incorporated using the American Petroleum Institute based cyclic p-y relationships. The uncertainties in soil undrained shear strength, in the parameters and equations of the p-y method, and in wind velocity are considered. Random wave loads are estimated from the code specified power spectral density function of the vertical sea surface elevation. Uncertainties in OWT responses are quantified using Monte Carlo simulations. The effects of length and diameter of the monopile, vertical sea surface displacement spectrum, and the probability distribution of wind speed on the dynamic responses of OWT are investigated. The study shows that the various power spectral density functions of wave surface displacement and various probability density functions of wind speed have a marginal effect on the response and fatigue life of OWTs. The mean fundamental frequency of the OWT system is significantly affected by the variability of the undrained shear strength of clayey soil.

Effect of sodium sulphate on the shear strength of clayey soils stabilised with additives

The effect of sulphates on the soil stabilisation using mineral additives such as lime, cement and fly ash has been reported by several researchers. The effect of sodium sulphate (Na2SO4) (0–6% by dry weight of soil) on the behaviour of the grey clayey soil (GS) and red clayey soil (RS) stabilised with lime (L) (0–8%), natural pozzolana (NP) (0–20%) and with a combination of lime-natural pozzolana (L–NP) was investigated. The soil specimens were subjected to testing of direct shear strength after 7, 30, 60 and 120 days of curing period. In the absence of Na2SO4, the results show that both clayey soils can be successfully stabilised with L or with a combination of L–NP, which substantially increases their shear strength and produces high values of shear parameters. However, at short curing period and for any content of Na2SO4, a further increase in shear strength and shear parameters is observed. Moreover, after 30 days of curing, the RS specimens stabilised with L or with NP alone are altered when the Na2SO4 is greater than 2%, whereas the GS specimens are not altered. However, the alteration of RS specimens is little when the L and NP are combined on curing with a high content of Na2SO4. Generally, the effect of Na2SO4 on both stabilised clayey soils depends on the curing time, percentage of additives used and their type, mineralogical composition of stabilised soils and Na2SO4 content.

Effect of porewater salinity on residual shear strength of clays and their mixtures

Abstract It has been long recognized that the residual shear strength of clayey soil is influenced by porewater chemistry due to physico-chemical interactions between clay and porewater. However, although the correlation between the residual shear strength of clayey soils and salinity of porewater has been discussed by many researchers, it has not been quantitatively specified either in theory or experiment. In this study, the residual shear strength of pure and mixed clays made of smectite, interlayered illite/smectite and kaolinite were investigated after being saturated with NaCl solutions of various concentrations. It was found that the residual shear strength of smectite significantly increased when the concentration of the NaCl was in the range of 0–1 mol L −1 and showed little change when the NaCl concentration was higher. The residual shear strength of kaolinite displayed insignificant change when NaCl concentration varied. Variation of the residual shear strength of interlayered illite/smectite with porewater salinity was quite similar to that of smectite, but with much less magnitude. Moreover, the residual shear strength of the clay mixtures also displayed great variation with the porewater salinity, and the variation may be mainly attributed to aggregation when porewater salinity varied as a result of change in double-layer thickness among clay particles.

Shear strength of clayey soils from the vicinity of Gorlice and Ciężkowice

Abstract The work presents results of maximum and residual strength tests of six clayey soils from the landslide areas near Gorlice and Ciężkowice. The tests were carried out in a direct shear apparatus on samples of dimensions 60 × 60 mm that were sheared at least three times. A shearing strain rate was equal 0.1 mm·min–1, and the range of horizontal deformation of the samples was equal 20%. The results of the tests revealed that multiple shearing of the soil caused a significant decrease of its shear strength, resulting in significant changes in cohesion, and the smaller changes in the angle of internal friction. It was shown that the three-time shearing reduced the initial shear strength of about 50%, and further three series of shearing decreased it approximately 15% more. The study also showed that by using a Coulomb-Mohr shear strength linear equation, the analyzed soils had a little residual cohesion. Therefore, to describe the characteristics of the residual strength, there were used two non-linear equations proposed by Mesri and Shanien (2003) and Lade (2010), which led to the same results. It was also shown that the use of non-linear characteristics of the residual strength at low values of the normal stresses gave more unfavourable results of stability calculations in relation to the method based on the linear strength characteristic taking into consideration the presence of the residual cohesion.

Effect of soil moisture in the analysis of undrained shear strength of compacted clayey soil

An experimental study was undertaken to study the principles of soil compaction and establish a relation between the undrained shear strength of compacted clay and its moisture content. Compaction of soil is an important prerequisite for the construction of man-made structures like bridges, roads, dams, embankments etc. In the present study fine grained saturated clay finer than 2 × 10-6 m were used for all purposes. An important property of cohesive soils is that compaction increases their shear strength and compressibility. The shear strength of clay is the maximum shear stress it can sustain. It is helpful as the common soil failures are due to shear failures (Iannacchione et al., 1994). Undrained condition of clayey soil occurs when pore water pressure of soil changes due to external loading. If the soil is sheared without changing the water content its strength remains the same. During the study the optimum moisture content was analyzed from the compaction curve. Finally, the shear strength curve was drawn for different compaction efforts which clearly showed an exponential decrease in the shear strength of clayey soil with gradual increase in the water content. Factors other than the change in water content and compaction energy were not considered. Key words: Undrained shear strength, optimum moisture content, dry density, compaction curve.

Experimental Study on Temperature Effect on Engineering Properties of Clayey Soils

Temperature significantly influences the engineering properties of clayey soil and this temperature effect usually depends on soil type. In this investigation, laboratorial experiments were conducted on three soils to evaluate the adsorbed water content, Atterberg limits, swelling, shear strength and permeability under different temperatures (5-50°C). The results indicate that liquid limit decreases, swelling increases, permeability increases with increasing temperature. It is fundamentally due to the change of adsorbed water content. Hydrophilic minerals, which contain large amounts of adsorbed water, play an important role in the temperature effect. With the increase of hydrophilic minerals, the temperature effect on liquid limit increases and the effect on swelling ratio decreases. The hydrophilic minerals content also has significant impact on the temperature effect of permeability. With increasing temperature, the adsorbed water is transformed to free water, and then the permeability may increase significantly. The shear strength of clayey soils with higher content of hydrophilic mineral is more sensitive to temperature variation. The cohesive force mainly changes linearly with the temperature. Different phenomena, i.e. thermal-hardening or thermal-softening, was observed on strength behaviour due to different hydrophilic mineral content, moisture content and dry density of sample.

Formulation of uplift capacity of suction caissons using multi expression programming

Suction caissons have increasingly been used as foundations and anchors for deepwater offshore structures in the last decade. The increased use of suction caissons defines a serious need to develop more authentic methods for simulating their behavior. Reliable assessment of uplift capacity of caissons in cohesive soils is a critical issue facing design engineers. This paper proposes a new approach for the formulation of the uplift capacity of suction caissons using a promising variant of Genetic Programming (GP), namely Multi Expression Programming (MEP). The proposed model is developed based on experimental results obtained from the literature. The derived MEP-based formula takes into account the effect of aspect ratio of caisson, shear strength of clayey soil, point of application and angle of inclination of loading, soil permeability and loading rate. A subsequent parametric analysis is carried out and the trends of the results are confirmed via previous studies. The results indicate that the MEP formulation can predict the uplift capacity of suction caissons with an acceptable level of accuracy. The proposed formula provides a prediction performance better than or comparable with the models found in the literature. The MEP-based simplified formulation is particularly valuable for providing an analysis tool accessible to practicing engineers.