Shear Strength Of Fine-grained Soils Research Articles

Stabilizing fine-grained soil by electrically injecting Ca2+, CO32-, and HPO42- ions

This paper presents a new technique that can electrically inject stabilizing ions, which can be used to stabilize soil. Other processes also occur simultaneously during treatment such as electrolysis, dissociation, sorption, and exchange mechanisms, etc. The aim of the research is to evaluate the effectiveness of the injection of stabilizing ions (Ca2+, CO32-, and HPO42-) in enhancing the shear strength of fine-grained soils. The shear strength of the soil increased up to 127% after treatment when measured near the anode and up to 495% when measured near the cathode. The results show that the proposed method can significantly increase soil strength; hence, it overcomes bearing capacity problems in soft fine-grained soils with low hydraulic conductivity.

A two-dimensional effective stress framework for modelling whole-life soil strength changes due to pore pressure generation and dissipation, Part 1: Formulation

The undrained shear strength of contractive fine-grained soils changes with time, reducing due to pore pressure generation and increasing during consolidation. There is an increasing appetite to recognise these temporal soil strength changes in offshore geotechnical design, as it provides a basis for potentially less conservative designs. Contributions to this endeavour are reported across two companion papers. This first paper extends an existing effective stress framework that relates the generation of pore pressure to accumulated plastic shear strain, allowing undrained shear strength to be calculated within the context of critical-state soil mechanics. The main development is the extension of the computational domain to two dimensions, allowing calculations to be made for boundary value problems that cannot be satisfactorily simplified to one-dimensional conditions. The magnitude and distribution of accumulated shear strain surrounding objects buried in soil are quantified through a series of large deformation finite element analyses. These spatial distributions are described using a strain influence function in the new 2D framework to calculate the extent and magnitude of excess pore pressure, and in turn the mobilised soil strength around the buried object. The performance of the 2D framework is examined in the companion paper through retrospective simulations of experimental and numerical data.

CPT-Based estimation of undrained shear strength of fine-grained soils in the Huanghe River Delta

CPT-Based estimation of undrained shear strength of fine-grained soils in the Huanghe River Delta

A new methodology to assess the potential of conjectural trigger mechanisms of submarine landslides exemplified by marine gas occurrence on the Balearic Promontory

The destructive potential of submarine landslides for populated coastal areas and maritime infrastructure has been described many times. However, the geological processes that can trigger such landslide events have not yet been fully established. In order to be able to conclusively assess the trigger potential of these processes, a quantification of the slope stability is indispensable. This requires a precise knowledge of the geotechnical and geological boundary conditions before and after the investigated landslide event, as well as the change in these boundary conditions caused by the alleged trigger mechanism. In order to make these described preconditions and the work process generally applicable, a universally adaptable methodology for the identification of trigger mechanisms was developed. Here, it is successfully applied to marine gas occurrence, which has recently been considered as a trigger mechanism due to the negative influence of enclosed gas bubbles on the shear strength of fine-grained soils. The constitutive model by Sultan and Garziglia (2014) is applied to simulate the gas-influenced undrained shear strength of a marine soil from a sediment starved margin on the Balearic Promontory and a range of Finite Element Limit Analyses (FELA) are conducted to determine the resulting loss of stability of different slope geometries. Within the scope of these calculations, the first set of Modified Cam Clay model parameters for a soil from the western Mediterranean is introduced. Based on the simulations, it can be concluded that marine gas occurrence decreases the overall stability of a slope compared to the saturated state. However, it also becomes obvious that the prevailing slope geometries with low inclinations are stable with a substantial capacity reserve for all simulated scenarios. Conclusively, gassy soil can be designated as a preconditioning factor decreasing the slope stability, as the state of failure can only be reached if the slope was in a precarious state before, or in combination with other impacts.

Correlation of Undrained Shear Strength and Liquidity Index of Fine-Grained Soils in West Java, Indonesia

The undrained shear strength of fine-grained soils is an important property in geotechnical engineering. However, the process of determining undrained shear strength can be challenging. Hence, the correlation of undrained shear strength with other soil properties needs to be established. Several studies have estimated undrained shear strength using the liquidity index. In the current study, we aim to find the best correlation of undrained shear strength and liquidity index of fine-grained soils in West Java, Indonesia at various water contents using the form of correlation of undrained shear strength and liquidity index and also factors influencing the undrained shear strength. The values of undrained shear strength and liquidity index are obtained by laboratory test and data collection from previous studies of soils in West Java. Results show a good linear relationship between the logarithmic value of undrained shear strength and liquidity index for 173 variations of soil samples. We also can conclude that the undrained shear strength of fine-grained soils is controlled by the proportion of finer grains presence and also the plasticity of the soils.

Undrained Interface Shear Strength of Fine-Grained Soils for Near-Shore Marine Pipelines

The peak and residual interface shear strengths for a variety of normally consolidated soils were measured using a torsional ring shear apparatus modified to suit soil and interface testing under the undrained condition, which is usually prevalent at soil–marine pipeline interfaces. Five solid surfaces with different roughnesses were utilized in this single-stage shear testing program. Tests were conducted at normal stresses in the intermediate range that are mobilized on soil–pipeline interfaces under near-shore conditions. For comparison, drained peak and residual shear strengths of a representative interface were also measured using a different version of the torsional ring shear apparatus. Based on the analyses and interpretations of the test results, a simple equation is introduced to estimate the undrained peak and residual interface efficiencies as a function of the solid surface roughness. The analyses also revealed that the normalized undrained peak and residual shear strengths of the soils and interfaces are insensitive to the change in soil plasticity. The ratios between these undrained strengths and the corresponding drained strengths decrease with decreasing soil plasticity and increasing interface roughness. Recommendations for the initial assessment of the pipe-soil shearing resistance and the preliminary stability analyses of near-shore marine pipelines are suggested based on the findings of this study.

Relation water content ratio-to-liquidity index versus the Atterberg limits ratio evaluated with the Kaniadakis exponential law

ABSTRACTWater content ratio (WCR) is defined as the ratio water content to liquid limit (LL) and it is proved to be a good replacer of the well-known parameter liquidity index (LI) to predict shear strength of fine-grained soils. An interesting correlation between the slope of LI and WCR and LL/PL ratio was observed. However, this trend is poorly described by conventional regression functions. By employing the Kaniadakis exponential law based on the relativistic mechanics, 22 data set, considering the LL/PL vs the slope of LI and WCR, were very-well matched.

Influence of coarse particles on the physical properties and quick undrained shear strength of fine-grained soils

Soils are generally classified as fine-grained or coarse-grained depending on the percentage content of the primary constituents. In reality, soils are actually made up of mixed and composite constituents. Soils primarily classified as fine-grained, still consists of a range of coarse particles as secondary constituents in between 0% to 50%. A laboratory scale model test was conducted to investigate the influence of coarse particles on the physical (e.g., density, water content, and void ratio) and mechanical (e.g., quick undrained shear strength) properties of primarily classified fine-grained cohesive soils. Pure kaolinite clay and sand-mixed kaolinite soil (e.g., sand content: 10%, 20%, and 30%) having various water contents (60%, 65%, and 70%) were preconsolidated at different stress levels (0, 13, 17.5, 22 kPa). The quick undrained shear strength properties were determined using the conventional Static Cone Penetration Test (SCPT) method and the new Fall Cone Test (FCT) method. The corresponding void ratios and densities with respect to the quick undrained shear strength were also observed. Correlations of the physical properties and quick undrained shear strengths derived from the SCPT and FCT were also established. Comparison of results showed a significant relationship between the two methods. From the results of FCT and SCPT, there is a decreasing trend of quick undrained shear strength, strength increase ratio (Su/Po), and void ratio (e) as the sand content is increased. The quick undrained shear strength generally decreases with increased water content. For the same water content, increasing the sand content resulted to a decrease in quick undrained shear strength due to reduced adhesion, and also, resulted to an increase in density. Similarly, it is observed that the change in density is distinctively noticeable at sand content greater than 20%. However, for sand content lower than 10%, there is minimal change in density with respect to water content. In general, the results showed a decrease in quick undrained shear strength for soils with higher amounts of sand content. Therefore, as the soil adhesion is reduced, the cone penetration resistances of the FCT and SCPT reflects internal friction and density of sand in the total shear strength.

Assessing the Potential Improvement of Fine-grained Clayey Soils by Plastic Wastes

Because of progressively dumping of plastic wastes (PWs) obtained from beverage industry it is of interest to use them as reinforcement material in civil engineering projects. For assessing potential use of plastic wastes in improvement of shear strength of fine-grained soils, two clayey soils were mixed with different amount of plastic wastes (i.e. 0.5%, 1.0%, 1.5% and 3.0% by weight) and consolidated undrained triaxial tests were performed on the compacted samples. Test results indicate that variations of shear strength and pore water pressure depend on the amount and type of plastic waste. It is observed that, irrespective of clay plasticity, adding plastic waste to the fine-grained soils improves their shear strength and plastic waste content (PWC) of 3.0%, within the range of used amounts, has the best effect on the shear strength. Moreover, adding plastic waste causes to decrease shear-induced pore water pressure slowly. Furthermore, deformability of samples changes in term of plastic waste content, type of plastic and clay type. It can be concluded that there is a possible usage of clay-plastic waste mixtures as construction materials and, thereby, plastic wastes can be managed by recycling them in the field of geotechnical engineering, thus contributing to clean up the environment.

Evaluation of Undrained Shear Strength of Fine-Grained Soils in Consideration of Soil Plasticity

Undrained shear strength (su) is one of the key geotechnical parameters for both natural and remolded soils. While it is basically a function of water content, it is also related to soil plasticity. There has been a long-lasting debate as to whether the su at the plastic and liquid limits are constant and whether the ratio of the su at the plastic limit to the su at the liquid limit is mostly fixed to 100. While this view is embraced by a great majority of researchers, some proclaim that the range of both the su at the plastic limit (PL) and the su at the liquid limit (LL) is rather wide; therefore, constant values of the su cannot be assigned for either the PL or the LL. Accordingly, the view that there is a constant ratio between the two shear strengths is invalid. The scope of this investigation is to reassess this problem using the laboratory vane shear test (VST) along with a new supplementary tool, the mud-press machine (MPM). Sixty remolded soil samples were employed as the study material. The variation of soil strength at both the plastic and liquid limit is investigated using the VST and MPM methods. While the VST method does not portray a distinctive relationship between the su and the two Atterberg limits, the newly introduced MPM method clearly shows that there is a meaningful relationship between the extrusion force, which is considered akin to the undrained shear strength, at the Atterberg limits and the two consistency limits, particularly the liquid limit. Concerning the constant ratio between the two shear strengths, namely the one at the plastic limit to the one at the liquid limit, it was found that this ratio is a constant, but it increases with the increase in soil plasticity. Keywords: Undrained shear strength, soil plasticity, vane shear test, mud press method, remolded soils.

Revisiting the Bjerrum's correction factor: Use of the liquidity index for assessing the effect of soil plasticity on undrained shear strength

The undrained shear strength (su) of fine-grained soils that can be measured in situ and in laboratory is one of the key geotechnical parameters. The unconfined compression test (UCT) is widely used in laboratory to measure this parameter due to its simplicity; however, it is severely affected by sample disturbance. The vane shear test (VST) technique that is less sensitive to sample disturbance involves a correction factor against the soil plasticity, commonly known as the Bjerrum's correction factor, μ. This study aims to reevaluate the Bjerrum's correction factor in consideration of a different approach and a relatively new method of testing. Atterberg limits test, miniature VST, and reverse extrusion test (RET) were conducted on 120 remolded samples. The effect of soil plasticity on undrained shear strength was examined using the liquidity index instead of Bjerrum's correction factor. In comparison with the result obatined using the Bjerrum's correction factor, the undrained shear strength was better represented when su values were correlated with the liquidity index. The results were validated by the RET, which was proven to take into account soil plasticity with a reliable degree of accuracy. This study also shows that the RET has strong promise as a new tool for testing undrained shear strength of fine-grained soils.

Residual shear strength of fine-grained soils and soil–solid interfaces at low effective normal stresses

A laboratory research program was undertaken to study the large-strain shear strength characteristics of fine-grained soils under low effective normal stresses (∼3–7 kPa). Soils that cover a wide range of plasticity and composition were utilized in the program. The interface shear strength of these soils against a number of solid surfaces having different roughness was also investigated at similar low effective normal stress levels. The findings contribute to advancing the knowledge of the parameters needed for the design of pipelines placed on sea beds and the stability analysis of shallow soil slopes. A Bromhead-type torsional ring-shear apparatus was modified to suit measuring soil–soil and soil–solid interface residual shear strengths at the low effective normal stresses. In consideration of increasing the accuracy of assessment and depicting the full-scale field behavior, the interface residual shear strengths were also measured using a macroscale interface direct shear device with a plan interface shear area of ∼3.0 m2. Correlations are developed to estimate the soil–soil and soil–solid interface residual shear strengths at low effective normal stresses. The correlations are compared with soil–soil and soil–solid interface drained residual shear strengths and correlations presented in the literature.

Use of Reverse Extrusion Method to Determine Undrained Shear Strength

The unconfined compression test (UCT) is one of the most common tools to measure the undrained shear strength of fine-grained soils. Soft to very soft soils often pose problems such that the determination of failure load is unclear using this test. Similarly, fissured clays would endeavor failure along pre-existing planes of weakness. The reverse extrusion test (RET), a mechanical metallurgy tool, has been used recently in some soil mechanics applications. The scope of this investigation is to evaluate the potential of the RET as a substitute for the UCT. Sixty remolded soils and 75 natural soils were subjected to the RET and UCT. Remolded soils were tested on mixtures prepared at the plastic limit. It was found that the ratio of extrusion pressure at failure to the undrained shear strength is relatively consistent and concentrates around 14. The same ratio was found to be 15 for natural soils. The conclusion reached, upon a series of tests on both the remolded and natural soil samples, is that the RET better represents the undrained shear strength of soil than does the UCT, that the practical difficulties with UCT is eliminated by the RET, and the results may be improved by taking into account soil plasticity.

Discussion of “Mechanics of the Casagrande liquid limit test” 1 Appears in the Canadian Geotechnical Journal, 49(9): 1015–1023 [doi:10.1139/t2012-066

The discusser wishes to express his appreciation to the author for shining a more useful light on the theoretical issues related to the conventional Casagrande percussion method, which is used for determining the liquid limit of fine-grained soils worldwide with the exception of a few countries where the fall cone method is preferred. Particularly, the author deserves a compliment for demonstrating theoretically that the results obtained from the Casagrande percussion and fall cone methods represent two different mechanical properties of the soil. This finding is in concurrence with the outcome of research by the discusser and his colleague presented in many of their publications (e.g., Sridharan and Prakash 1998, 1999, 2000; Prakash and Sridharan 2006). However, the basis and approach adopted by the two groups (i.e., the author on one side and the discusser with his research colleague on the other) to achieve the same goal are different. The author has shown theoretically through the Newmarkian analysis of the Casagrande percussion test that the Casagrande percussion liquid limit is a measure of soil specific strength, while the fall cone liquid limit is a direct measure of the undrained strength of the soil. The clay minerals composing the fine-grained soils are no longer inert, but are physicochemically active by virtue of their surface charge deficiency. The extent to which the fine-grained soils are active depends upon their clay mineralogical composition, which controls their behavior. It is unfortunate that the clay mineralogy of soils is ignored in most of the present-day research dealing with fine-grained soils even though most of the field problems associated with these soils can be attributed to their clay mineralogical composition. The liquid limit behavior has been proven to be a dominant function of the soil clay mineralogy. While the liquid limit of montmorillonitic soils is due primarily to the diffuse doublelayer-held water (Sridharan et al. 1986), that of kaolinitic soils is mainly due to the soil fabric as governed by the interparticle attractive forces (Sridharan et al. 1988). The undrained shear strength of fine-grained soils has been shown to have two components: viscous shear resistance and frictional shear resistance (Sridharan and Prakash 1999, 2000). An exhaustive experimental study of the mechanisms that come into play during the Casagrande percussion and fall cone methods of determining the liquid limit of soils has shown that the value of the liquid limit obtained by the Casagrande percussion method is controlled primarily by the viscous shear resistance while that obtained by the fall cone method is controlled essentially by undrained frictional shear resistance (Sridharan and Prakash 2000; Prakash and Sridharan 2006). The above illustrations reveal very clearly that the liquid limit values obtained by the Casagrande percussion and fall cone methods cannot be the same and hence, the liquid limits obtained by the two methods represent two different soil properties controlled by two different mechanisms. This conclusion is very much in line with that of the author, proven by a different approach altogether. The discusser also agrees with the author in that there is a growing tendency towards using the fall cone method to determine the liquid limit without understanding its limitations. In that direction, the author’s effort in proposing a methodology using the fall cone method itself to arrive at the liquid limit equivalent to that by the Casagrande percussion method is welcome. However, while doing so, the author is trying to equate the undrained shear strengths of the soils at the Casagrande percussion and fall cone methods’ liquid limits, which is not fully justifiable. This is because the undrained shear strengths mobilized during testing by the two methods are not of the same nature, as indicated by the discusser in the previous paragraphs. The discusser is aware that the author’s approach is theoretical, which does not take into account the physicochemical nature of liquid limit of fine-grained soils and the controlling mechanisms that are operative during the two testing procedures. Bringing these complex parameters into the theoretical formulation is not that simple. Apart from this issue, the discusser wishes to bring the following major discrepancies in the paper under discussion to the attention of the author for his comments: • Equation [6] appears to be incorrect. For a saturated soil mass, the correct relation should have been the following equation (where w is the mass density of water):

A New Pressurized Vane Shear Apparatus

Abstract The new vane shear test apparatus enables shear strength investigations of fine-grained soils at different pressures and shear velocities, such as those acting in a working chamber of an Earth pressure balance tunnel boring machine. The main conceptual innovation is the application of a confining pressure onto the test specimen while the vane shear test is performed. This allows for the exploration of pressure dependency on the shear strength of fine-grained soils, e.g., conditioned with foams and polymers. The technical innovation is that the torque sensor is located inside the pressure chamber. This permits for accurate torque measurement by excluding friction at contact areas and sealed insertions. The new vane shear test apparatus is a fast and reliable device to measure the shear strength of any fine-grained soils with soft consistency. In this paper pressure and rate-dependent shear strength data of kaolinite and illite clays and of “conditioned soils” made of kaolinite and illite clays mixed with foam and polymer additives are presented and the applicability of the apparatus is validated.

Predicting the normalized, undrained shear strength of saturated fine-grained soils using plasticity-value correlations

In soil mechanics, the plasticity of fine-grained soils is expressed using the plasticity index. This represents the difference between the water content at the liquid and plastic limits, which are often collectively referred to as the Atterberg (or consistency) limits. They are of key importance in soil mechanics because they determine, in a simple way, the interaction between the solid and liquid phases in soils, and thus provide the possibility to classify soils into groups with similar mechanical properties. As the Atterberg limits are the most distinctive and the easiest property of fine-grained soils to measure, several researchers have tried to use them to predict various mechanical properties, such as the normalized, undrained shear strength of fine-grained soils. The most widely used expression for predicting this value from the plasticity index was suggested by Skempton. Since then, there have been several studies to examine the validity of his relation. A lot of the data agree with this relation; however, there is an equally large volume of data that contradicts it. The present study shows that the correlation between the normalized undrained shear strength of cohesive soils and the plasticity index really exists, but it is not as simple as was suggested by previous studies. By considering the mineralogical properties of clay minerals and their impact on the quantity and state of water in soils, it was found that there is no uniform criterion to determine the normalized undrained shear strength from the plasticity index for all fine-grained soils.

Effect of cyclic loading on monotonic shear strength of fine-grained soils

In this study the effect of cyclic loads on monotonic shear strength has been studied on torsional apparatus. Tests have been conducted on both reconstituted and undisturbed fine-grained hollow soil specimens. The plasticity index of soils is in the range from 2 to 33 for reconstituted specimens, prepared by dry pluviation, and from 5 to 13 for undisturbed soil specimens. The existence of a critical shear strain level, called yield shear strain, where softening starts, is determined from cyclic tests. The level of cyclic yield strain is ± 0.75% for the reconstituted soil specimens and ± 0.5% for the undisturbed soils. If soil undergoes a cyclic shear strain level below the cyclic yield strain, reduction of monotonic strength of reconstituted and undisturbed specimens is limited, but when cyclic shear strain level is larger than yield strain monotonic strength decreases down to 40% of its initial strength.

Relationship between the Undrained Shear Strength, Water Content, and Mineralogical Properties of Fine-Grained Soils

The relationship between the undrained shear strength of fine-grained soils and the water content can be described with a nonlinear function in which the type of soil is determined by two parameters. It is well known that these parameters depend mainly on the mineral compositions of soils; these relationships, however, have not yet been investigated. The findings described in this paper define those mineralogical properties of soils which determine the values of both parameters. Experimentally obtained results suggest that the parameters primarily depend on the size of the clay minerals, their quantity in soil composition, and the interlayer water quantity in the expanding clay minerals. As this dependence is well defined, the parameters, and thus the undrained shear strength at different water content, can be defined from knowledge of these mineralogical soil properties.

Strength behaviour of lime-treated soils in the presence of sulphate

Lime has been used extensively to improve the shear strength of fine-grained soils. It has been recently reported that the presence of sulphate causes abnormal volume changes in lime-stabilized soil. The paper presents the strength behaviour of lime-treated montmorillonitic natural black cotton soil in the presence of varying sulphate contents after curing for periods of up to 365 days. Alteration of soil–lime reactions in the presence of sulphate affects the strength development by cementation. Consequently, the stress–strain behaviour effective stress paths of soil cured with sulphate are similar to those of normally consolidated soil rather than cemented soils. The reduction in shear strength due to a reduction in effective cohesion intercept occurs for lime-treated soil cured with sulphate for long periods.Key words: clays, cohesion, fabric, friction, shear strength.