Fall Cone Test Research Articles

The Influence of Soil Saturation on the Geotechnical Test Results

The consistency limits are important properties of soil. The fall cone test method has a good repeatability, and the operator’s judgement has little effect on the results. This paper presents a new sample preparation method, in which the sedimentation method and consolidation test are combined, to prepare the saturated specimens for fall cone test for determining the consistency limits, and the sample prepared by this new method can be considered completely saturated. For the specimens prepared by the previous sample preparation method, the decrease in the water content leads to a decrease in the degree of saturation of soil. The test results show that the specimens prepared by this new method can reach a low water content, and the minimum penetration depths are as low as 2 mm, and the plastic limit could be obtained directly. In addition, the van shear test results show that the unsaturated specimens have larger values of undrained shear strength than the saturated specimens at the same water content, which could explain the difference of consistency limits obtained from different specimen preparation methods.

Reappraisal of Fall-Cone Flow Curve for Soil Plasticity Determinations

Abstract Several attempts have been made to devise alternate plastic limit (PL) determination methods, targeting higher degrees of repeatability and reproducibility. Among these, empirical-type correlations linking the plasticity index (PI) to the flow index (FI)—the slope magnitude of the flow curve—seem to be gaining increased attention, particularly for the fall-cone (FC) approach, and hence demand further examination. To better understand the true potentials and limitations of this emerging practice for soil plasticity determination, this study presents a critical statistical appraisal of FI-based correlations—using a large and diverse database of 230 FC tests (for the 80 g–30° cone)—in estimating the PI (and hence the PL). It is demonstrated that the so-called “strong” correlation between the PI and FI reported in some literature, favoring the use of FI as a PI estimator, is an overlooked “statistical pitfall” originating from an over-reliance on the coefficient of determination (R2) statistic. Employing appropriate error-related statistics, it is shown that the PI predictions made by FI-based correlations are associated with high average errors of 22–33 %. Hence, such correlations, at best, can only provide a rough approximation of the actual PI (and hence PL). An attempt is also made to assess the validity of FI-based correlations in the context of soil classification using the Casagrande-style plasticity chart. The agreement level between the conventional classification approach and that performed using PI deduced from FI-based correlations was 75–80 %. This analysis, however, did not account for errors in the rolling-thread plastic limit data, maintaining a strong possibility that FI-based correlations may be suitable for routine soil classification purposes.

Field measurements, laboratory tests and empirical relations for investigating the solid-to-fluid transition of a rapid earthflow

Earthflows are widespread phenomena in the Mediterranean area. These landslides involve fine-grained soils and clay-bearing rocks, and despite their low speed are responsible for significant economic losses in vast areas. The dynamics of these landslides is still relatively obscure thus reducing our ability to forecast and mitigate their effects. In this study, we present a methodological approach for the characterization of active earthflows based on the combination of geophysical surveys, laboratory tests, and empirical formulas. Geophysical surveys consist of periodic measurements of Rayleigh wave velocities repeated over time to evaluate the change of stiffness with time of the landslide material. Laboratory tests combine Atterberg limits, fall cone and oedometric tests and allow to constrain the empirical correlations between geophysical and geotechnical properties. The method is designed to obtain relevant data when direct methods like boreholes or geotechnical soundings are not possible for safety reasons, with the aim of investigating the solid-to-fluid transition that can occur in rapid earthflows. We applied this approach to study the Montevecchio landslide (Northern Apennines of Italy), an active earthflow in young marine clays which was affected by multiple reactivations in the recent years. Results show that after a surge the earthflow material is very soft (shear wave velocity in the order of 50–60 m/s) and characterized by a high water content. However, the exact value of the Liquidity Index remains unknown due to the lack of direct measurements and to the uncertainty dictated by the empirical relationships.

Undrained Shear Strength cu and Undrained Elastic Modulus Eu of Anthropogenic Soils from Laboratory Tests

Undrained shear strength cu and undrained elasticity modulus Eu are one of the basic mechanical parameters describing soil properties in engineering practice. In a simple way cu can be established by fall cone test or, similar as the Eu modulus, can be determined from the stress-strain curve obtained from the uniaxial or triaxial compression tests. The paper presents the results of laboratory tests od cu and Eu parameters carried out on anthropogenic soil in uniaxial compression tests and fall cone tests. The soil used in the study represented different types of materials used in earthworks - containing different share of clay fraction. Tests were provided on the soil in different bulk density and water contents. The paper proposes a method of estimating Eu50 on the basis of cone penetrometer tests. Such test does not require any additional preparation and can be performed directly on the soil compacted in the cylinder of the Proctor’s apparatus, which allows for a quick assessment of the soil elasticity parameters.

Machine learning techniques for relating liquid limit obtained by Casagrande cup and fall cone test in low-medium plasticity fine grained soils

The liquid limit is a key property of fine soils closely related to the stress-strain behaviour and other relevant characteristics of soils such as the expansive potential. There are two standardized methods for its determination, the Casagrande cup and the fall cone test, among which there are many correlations that offer heterogeneous results. In the present study, a compilation of 113 data from fine soil samples with low-medium plasticity has been carried out. Then, a comparative study of different machine learning algorithms was carried out to relate the liquid limit obtained from both methods, having in consideration other parameters such as the plastic limit and the percentages of passing through the 0.40 and 0.075 mm sieves. The result of this study has shown that extremely randomized trees algorithm provides the best performance. Consequently, the algorithm has been tuned to enhance the precision, obtaining a coefficient of determination (R2) value of 0.99. The results demonstrate the potential of machine learning techniques for relating liquid limit obtained by Casagrande's method and fall cone test in fine-grained soils with low-medium plasticity, mainly for values of the liquid limit higher than 30 for which classical linear regression approaches provide lower performance metrics.

Effect of organic matter content on Atterberg limits and undrained shear strength of river sediment

The Atterberg limits and the undrained shear strength are crucial soil properties in the preloading design of reclamation foundation projects using dredged river sediment. These properties can be significantly affected by the presence of organic matter in the sediment. This study investigates the physical properties and undrained shear strength of river sediment, based on data from a series of fall cone tests performed on river sediment with different organic matter contents, and undrained shear strength data for reconstituted clay collected from the literature. It was found that the liquid limit, plastic limit, and plasticity index increase with an increase in organic matter content. The effect of organic matter on the undrained shear strength of remolded soil at a given water content can be attributed to the effect of organic matter on the liquid and plastic limits. The undrained shear strength is a function of the liquid and plastic limits; it can be normalized by the liquidity index, irrespective of the organic matter content. Highlights Investigating role of organic matter in the Atterberg limits Investigating role of organic matter in shear strength Understanding key factors of controlling shear strength Establishing organic matter–liquidity index–shear strength interrelations

Effect of calcium bentonite clay and fly ash on the stabilization of organic soil from Alberta, Canada

This paper presents findings of the effect of calcium bentonite (Ca-bentonite) and pulp mill fly ash (PFA) on the compressibility behavior, and microstructural evolution of organic soil. A natural soil consisting of 26% organic matter was collected from the wetlands in the Wabasca region, Northern Alberta, Canada. A various mix design was prepared for the laboratory tests with the addition of 5%, 8%, 10%, 12%, 15%, and 20% Ca-bentonite with constant 30% PFA. One-dimensional consolidation tests were carried out to evaluate compressibility behavior of the stabilized organic soil. In addition, fall cone tests were conducted to evaluate change in undrained shear streth of soil after stabilization. A series of scanning electron microscope (SEM) tests with energy dispersive X-ray (EDS) and X-ray diffraction (XRD) experiments were conducted to investigate the microstructural and chemical aspects of the organic soil treated with Ca-bentonite and PFA. The results showed that a mixture of 10% Ca-bentonite with 30% PFA was the optimum dosage for improving compressibility of organic soil regardless of the curing method. Microstructural and chemical analysis revealed that the mineralogical and morphological contents of the stabilized organic soil were affected due to the pozzolanic reaction. The results showed that Ca-bentonite and PFA were able to considerably improve the strength and compressibility of the selected organic soil.

Physio-Chemical Properties, Consolidation, and Stabilization of Tropical Peat Soil Using Traditional Soil Additives — A State of the Art Literature Review

Peat is formed by the degradation of plants and animals in the lack of oxygen and is widely known for its very weak geotechnical characteristics. This is the reason to be considered as an unsuitable foundation soil for construction activities. Several attempts have been made to characterize and stabilize peat soil to make construction viable. This study encapsulates an extensive literature review of the available published data for Atterberg limits, consolidation, and stabilization of peat soil using traditional additives, especially cement and lime. Moreover, peat formation and distribution around the world are also discussed. The analysis of the gathered data shows that peat soils having a high amount of fibers may suffer a large amount of secondary consolidation when the load is applied. Besides, the compressibility factors vary for Malaysian peat due to different water and organic contents. The improvement of peat soil is challenging and expensive, requiring an extra amount of stabilizer for the initiation of the stabilization process. However, the optimum and threshold stabilizer’s dosage for peat is also a challenging task to predict due to several factors affecting the stabilization process. Lastly, the study concludes with recommendations on the implication of the fall cone and thread rolling tests for the determination of Atterberg limits of fibrous peat, effective consolidometer for peat, and utilization of traditional additives for peat soil stabilization.

Hydraulic conductivity and undrained shear strength of clay-construction and demolition solid waste materials mixtures

The study aims to investigate the effects of three different construction and demolition materials (CDMs), including crushed waste asphalt (CWA), crushed waste bricks (CWB), and crushed waste concrete (CWC), on some geotechnical properties of low plastic clayey soil, particularly, the undrained shear strength (Su) and the hydraulic conductivity (k). A set of experimental tests were performed on clayey soil and on clayey soil-CDM mixtures at mixing ratios of 5%, 10%, 15%, and 20% by dry weight. The results show that the soil plasticity decreases as the CDMs increase. Quantitatively, it is found a maximum of 12%, 6%, and 6% decrease in the liquid limits (LL) and a maximum of 9%, 4%, and 6% decrease in the plasticity limit (PI) of the mixtures with 20% of CWA, CWB, and CWC, respectively. The results of the Su estimated empirically from the fall cone tests show that the Su decreases as the CDMs increase. The Su reduces by approximately 10% and 2% of the mixtures with 20% CWA and CWB, respectively. But the Su is not affected by the CWC additive for water content lower than approximately 35%. The k value increases as the CDMs increase. The results show that the reported k value increases by 75%, 79%, and 247% of the mixtures with 20% of CWA, CWB, and CWC, respectively. Additionally, the k values obtained from the consolidation test confirm the findings of the effect of the CDMs on the coefficient of hydraulic conductivity.

Advancement in Estimation of Undrained Shear Strength through Fall Cone Tests

AbstractFall cone tests provide simple and rapid estimate of undrained shear strength (su) of fine-grained soils at various water contents. The accuracy of such su estimation depends greatly on the...

On Empirical Correlations for Normalised Shear Strengths from Fall Cone and Direct Simple Shear Tests in Soft Swedish Clays

Empirical correlations provide valuable information in early design stages, and they help to validate or discard single values from site investigations. This paper presents a multivariate database from commercial projects consisting of evaluated shear strengths obtained from direct simple shear tests and fall cone tests (which are calibrated to the field vane test), including index tests. The multivariate database is used to investigate the performance of common transformation models and to test the recommended correction for fall cone tests. It is found that the measured normalised shear strength evaluated from direct simple shear tests and fall cone tests is correlated to the liquid limit and that the results conform to Swedish and Norwegian recommendations. However, the scatter is large, more for fall cone tests than for direct simple shear tests, which is thought to depend mainly on sample disturbance. It can however be concluded that the trend of normalised shear strengths increases with increasing plasticity.

Measurement uncertainty of the fall cone (FC) test

The most common method to determine liquid limit, sensitivity and undrained shear strength of clay in Nordic countries is to use fall cone test (FC). However, all these properties include some uncertainty arising from different sources e.g. the geological conditions, test procedure and sample disturbance. In this study, the measurement uncertainty of the fall cone test was analysed. The parameters of interest were the penetration depth of the cone and the interpreted intact undrained shear strength. The test set consisted of high-quality block samples (d=132mm) collected from six different depths at soft clay site in Finland. The diameter of the samples made it possible to perform four parallel fall cone tests per depth, so total of 24 fall cone tests were done. The calculated COV-values for each parameter at each depth were between 0.02 and 0.08, thus indicating very low measurement uncertainty. These values also included the inherent variability of the soil. Overall, the results showed that the fall cone test is reliable method for determining the intact undrained shear strength, if the test is done with care.

EVALUATING MECHANICAL STRENGTH OF PEAT SOIL TREATED BY FIBER INCORPORATED BIO-CEMENTATION

Peat soil is an accumulation of partially decayed vegetation, formed under the condition of nearly permanent water saturation, which makes the high moisture and compressibility as two main features of peat. In recent years, the lack of construction lands diverts researchers' attention to make use of marginal grounds, like peatland, after some improvements. The past decade has witnessed a growing interest in microbial induced carbonate precipitation (MICP) due to its reliability, broad application, and potential contribution to sustainable and green development. This study has two primary aims: (i) investigating the feasibility and effectiveness of MICP in peat soil combined with bamboo fiber reinforcement, and (ii) ascertaining the mechanism of bamboo fiber incorporated MICP. Bamboo fiber possesses some unparalleled advantages owing to its fast growth and ability to survive in diverse climates. This study differs from previous researches in the use of native bacteria isolated from the peat soil, while most of them were conducted using exogenous bacteria, which might pose a threat regarding adaption and microbial pollution. Different concentrations of cementation resources (1-3 mol/L) and proportion of fibers (0-50%) were studied, and each case was well designed. Treated samples were subjected to the fall cone test to estimate the undrained shear strength at certain time intervals. The results revealed that samples with higher fiber content gained higher strength than others did, whereas high initial cementation resources in soil could reduce strength. Microscale observations were also performed on treated samples to clarify the mechanism of MICP incorporated with fiber.

Influence of the mix composition on the thixotropy of 3D printable mortars

Digital fabrication of concrete elements requires a better understanding of the rheological behaviour of the cementitious material used. Fresh concrete is known to be a thixotropic material having time-dependent characteristics. Moreover, fresh mortars used in three-dimensional (3D) printing should maintain a sufficient shear stress to avoid any deformation or failure during printing. This paper concentrates on the experimental investigation of the buildability properties of different printable materials, on the basis of shear stress, measured using the Fall cone test. The effect of different constituents such as high-range water reducer, viscosity-modifying agent, limestone filler and water content on the evolution of the yield stress in mortars, derived from the shear stress, are studied experimentally and discussed in detail. Accordingly, the change of variables induces a quasi-linear relationship with the growth of the structuration rate and structural build-up (Athix) of mortars, which corresponds to the variation of the yield stress with time. These findings enable the use of the Athix concept and the proposed curves for designing new printable mixes that better suit the buildability properties of large-scale 3D printed structures.

Soil consistency and interparticle characteristics of various biopolymer types stabilization of clay

An environmentally friendly improvement method with using biopolymer stabilization of soil has been currently paid more attention for geotechnical engineering practices. And the existing concerns focused on the performance of biopolymers treated clay due to the occurrence of electrical interaction. Therefore, the effect of biopolymer types and water content on the behaviors of biopolymer-clay mixture should be firstly explored in terms of biopolymer applications. In this study, fall cone tests were conducted to evaluate the consistency variations of eight types of biopolymers treated clay, e.g., carrageenan kappa gum (KG), locust bean gum (LBG), xanthan gum (XG), agar gum (AG), guar gum (GG), sodium alginate (SA), gellan gum (GE) and chitosan (CH) at various biopolymer concentrations (e.g., between 0.1% to 5% biopolymer to soil mass ratio). The results indicated that neutral biopolymers (e.g., LBG and GG) significantly caused the increase of liquid limit and undrained shear strength regardless of biopolymer concentration. And the liquid limit and undrained shear strength of negative charged biopolymers (e.g., KG, SA, GE and XG) treated clay decreased firstly following increased, while AG and CH had limit effect on soil consistency. In addition, the trend of plasticity index was similar to liquid limit altering the USCS classification of biopolymer treated clay as silt or clay. Moreover, empirical equations determining undrained shear strength and shear viscosity of biopolymer-treated clay were also established.

Effect of clay fraction and mineralogy on fall cone results of clay–sand mixtures

In this study, the relationships among plasticity ratio, clay fraction and liquidity index of clay-sand mixtures were investigated. Two types of clays, namely, kaolin (K) and calcium-montmorillonite (CM) were used to prepare clay-sand mixtures of different grain size distributions. Clays were mixed with clean sands of two different grain size distributions (well graded sand-SW and poorly graded sand-SP) at clay contents ranging between 0% to 100% by increments of 10%, in terms of dry weight. Fall cone, Casagrande, plastic limit and laboratory vane shear tests were performed on various clay- sand mixtures with different clay contents. Experimental results revealed that, above 100% water content, undrained shear strength values of CMSW and CMSP mixtures were determined to be around 50 kPa. On the other hand, undrained shear strengths of KSW and KSP mixtures are around 30 kPa, for a water content of 30%. Average undrained shear strengths of CMS and KS mixtures at their plastic limits are obtained as 210.68 kPa and 119.62 kPa, respectively. Average undrained shear strengths of these mixtures at their liquid limits are determined to be 2.40 kPa and 1.88 kPa, respectively. It is concluded that various mechanisms control liquid and plastic limits of clay-sand mixtures which are influenced by gradation of sand, clay content as well as origin of clay. As a result, several relationships among parameters including water content, liquidity index, undrained shear strength, cone penetration depth, fall cone liquid limit and Casagrande liquid limit were presented.

The fall cone test in unsaturated soil and tailings pastes

The fall cone test (FCT) is usually performed in saturated paste-like geomaterials to determine their undrained shear strength or liquid limit. Here the test is used to determine strength when a geomaterial is unsaturated and paste-like in its consistency. A mechanics-based interpretation is used, where the pore air pressure, pore water pressure and suction which prevail around the cone tip post-test are incorporated in strength and bearing capacity equations. The pore air and water pressures combine to form an apparent cohesion that dominates cone penetration resistance and can be determined from a FCT result. When the volumetric air content (va/v) is less than 0·15, samples become unvented and effectively sealed, and the FCT induces volumetric compression in the sample. This causes the apparent cohesion post-test to be smaller than the initial value. The ratio between the two is proportional to va/v for three tailings in a unique way. The initial apparent cohesion ranged from 0·6 kPa to 28 kPa. The post-test value was smaller by an amount depending on va/v. When va/v > 0·15, the pore air becomes connected to the atmosphere and very different pressure changes and volume changes occur around a penetrating cone, for which an alternative interpretation method is needed.

Mohajerani method: Tool for determining the liquid limit of soils using fall cone test results with strong correlation with the Casagrande test

The European Standard EN ISO 17892-12:2018 describes the means of determining the liquid limit (LL) of soils using two independent test methods: the Casagrande percussion cup and fall cone test. The first method is characterized mainly by its universality and the second by its simplicity. However, these two methods are known to provide different results. The higher the LL, the greater is the difference between the results. In 2019, Shimobe and Spagnoli established a correlation between the Casagrande and fall cone tests for soils with LL < 150%, based on an analysis of over 100 experimental datasets. However, further studies are required for soils with LL > 150%. Mohajerani method, which combines the universality of the former method and the simplicity of the latter, is applicable for such soils. The main objective of the study was to apply the Mohajerani method to determine the LLs based on fall cone test results and to compare them with those of the Casagrande test (soft base), with focus on soils with LL > 150%. The experimental results showed that for high plasticity soil (containing bentonite, etc.), the differences in the LL between the Casagrande and fall cone tests are significant (ab to relative ratio 30%), and some modification of the fall cone test evaluation is required. This study confirmed excellent agreement between the LL evaluated using the Mohajerani method (i.e., modification of the fall cone test evaluation) and that obtained from the Casagrande test, even for soils with higher LLs. Furthermore, the fall cone test results were used to determine the plastic limit (PL) for those soils with LLs within 20–50% for which the Casagrande LL and standard fall cone LL were correlated (where the latter was not modified by the Mohajerani method). Determination of the PL for these types of soils via the fall cone test results offers credible results comparable to those of the standard thread rolling test.

Fall cone tests considering water content, cone penetration index, and plasticity angle of fine-grained soils

Abstract This paper analyzed the consistency of some parameters of soils in the literature and experimental results from fall cone test and its application to soil plasticity classification. Over 500 data from both literatures and experiments using fall cone and Casagrande methods were compiled to assess the relationships among specified water content, cone penetration index ( β ) , and plasticity angle ( α ) of fine-grained soils. The results indicate that no unique correlation exists among β , liquid limit of the fall cone test (LLc) and α . The water content at 1 mm cone penetration ( C 0 ) correlates well with β , plasticity ratio ( R p ) (i.e. the ratio of plastic limit to liquid limit), and α . Finally, the potential of using the β − tan α diagram to classify soil plasticity was also discussed.

Observations and findings on mechanical and plasticity behavior of sand-clay mixtures

This paper presents effects of particle size distribution and plasticity on geotechnical properties of sand-clay mixtures. Two different clay types (kaolinite and bentonite) were mixed with different-sized clean sand at mixture ratios of 0 to 100% with increasing 10% by dry weight. An intensive series of standard compaction, Casagrande, fall cone, and plastic limit (wP) tests were performed on specimens. Experimental results showed that the maximum dry density (ρdmax) values of the mixtures increased up to 10% clay content (threshold clay content) then decreased with increasing clay content. Besides, optimum water content (ωopt) values of the mixtures decreased up to around 10–20% of clay content and then increased continuously. It was found that fall cone liquid limits were 2–4% higher than obtained from the Casagrande device. The undrained shear strength at liquid limit is approximately 2.19 kPa, but, though the undrained shear strength at plastic limit has a wide range in comparison with liquid limit (17–636 kPa), as its recommended value, 143.95 kPa was proposed by the researchers. Moreover, results also reveal that consistency limits of specimens are governed by the content and type of clay and grain size distribution of the sand-clay mixtures. Finally, some equations were proposed between various findings (i.e., optimum water content-maximum dry density, plasticity index (PI)-optimum water content, undrained shear strength (Su)-liquid limit (wL)) that were derived from the test results.