Shear Strength Of Cohesive Soils Research Articles

Determination of the overconsolidation ratio and undrained shear strength of cohesive soils by CPTu measurement

Estimations of the undrained shear strength (Su) and overconsolition ratio (OCR) of cohesive soil are essential for the evaluation of geology investigation. In comparison to time-consuming laboratory tests, the field piezocone penetration test (CPTu) can rapidly evaluate these parameters. However, existing studies have mainly relied on empirical correlations to estimate the undrained shear strength Su and OCR from CPTu measurements. These correlations are mainly empirical, involving fixed coefficients multiplied by CPTu measurement. Based on the coupled Eulerian-Lagrangian method, this study employed large deformation finite element modeling to summarize and extend the relationships between CPTu measurement and the estimation of undrained shear strength Su and OCR in cohesive soils. These relationships allow for predictions based on CPTu measurements without the requirement for laboratory calibration or referencing to field benchmarks. The accuracy and applicability of the proposed prediction formulas are validated through field case studies for comparative analysis.

Salinity effects on the consistency limits and shear strength of cohesive soils of the Red River, Fargo, North Dakota

Salinity effects on the consistency limits and shear strength of cohesive soils of the Red River, Fargo, North Dakota

Sediment penetration performance of a portable underwater robot for core sampling

AbstractAs described in this paper, we investigate the sediment penetration performance of a portable underwater robot with a helical screw pipe using marine thrusters with limited force. First, we derive a mathematical model based on an empirical and simple method using the undrained shear strength of cohesive soil to provide a rough estimate of maximum penetration depths. Then, we perform numerical analysis for estimating the maximum depth of sediment penetration and for designing a sampling pipe. Additionally, we use experimentation to investigate the relation between the penetration depth of the helical screw pipe and the force of marine thrusters mounted on the portable underwater robot. After testing the penetration performance in a water tank, we conduct a field experiment at Lake Biwa and obtain results of the penetration depths. The maximum penetration into the lake sediment is at least 0.30 m. The results demonstrated the possibility of using the derived mathematical model to make a rough estimation of the maximum penetration depth for clay sediments. Additionally, we can use non‐powerful thrusters equipped with small autonomous underwater vehicles (AUVs) and remotely operated vehicles (ROVs) for sediment sampling. The proposed method is also applicable for the installation of underwater sensors using small AUVs and ROVs.

Effect of Specimens’ Height to Diameter Ratio on Unconfined Compressive Strength of Cohesive Soil

Abstract The undrained shear strength (Su) and cohesion (Cu) of cohesive soils are frequently determined using an unconfined compression test. However, the test results are heavily dependent on specimen size. This causes uncertainty in geotechnical analyses, constitutive models, and designs by overestimating or underestimating the shear strength of cohesive soils. Therefore, the study aims to assess the effect of the height-to-diameter ratio on the unconfined compressive strength (UCS) of cohesive soil. The soil specimen was tested on a compacted cylindrical specimen at the maximum dry density and optimum moisture content with a height to diameter (H/D) ratio of 1–3 for 38, 50, and 100 mm specimen diameters. Disturbed sample specimens were considered for the laboratory program. Accordingly, the standard Proctor compaction test determines soil classification and compaction characteristics. The unconfined compression test was performed for undisturbed and compacted remolded states of various diameters of cohesive soil specimens to investigate the strength variation with the specimen variation in H/D ratio. The laboratory test results revealed that cohesive soil's unconfined compression strength value drops rapidly with height-to-diameter ratios and the soil specimens’ diameter increases. However, the UCS value was stable at H/D ratio from 1.75 to 2.25. As the specimens’ diameter and H/D ratio increased, the peak UCS value axial strain decreased. Similarly, the gap between the axial strains of peak UCS value for the smallest and the most significant H/D ratio decreased with increase in the specimens’ diameter.

A new method for estimation of undrained shear strength of cohesive soil for design use from CPTU

電気式コーン貫入試験（CPTU）結果のみからなる，新たな粘性土の設計用非排水せん断強さ（本論文ではsu(mob)と称す）の評価手法を提案する。この手法は，CPTU から得られるコーン貫入時の過剰間隙水圧から粘性土の正規圧密状態における強度増加率を推定し，得られた値と実効コーン貫入抵抗の一次的関係から算定されるコーン係数を介して su(mob)を評価するものであり，国内外 25 地域 31 地点で得られたデータに基づいている。本手法で求めた su(mob)は，別途室内試験および原位置試験から求めた su(mob)と比較され，その信頼性と適用性を実証している。提案する手法によれば，人的誤差を伴う，ボーリング～乱れの少ない試料採取～室内せん断試験という過程なしに，当地の粘性土の su(mob)を評価できる。

Ultrahigh static pore pressure effects on the undrained shear behavior of deep-sea cohesive soil

Due to the unique ultrahigh water stress environment, the physical and mechanical behavior of deep-sea sediments is significantly different from those of offshore and terrestrial soils. However, the effect of water depth-induced ultrahigh static pore pressure on the mechanical properties of deep-sea soils has rarely been considered. Here, a series of consolidated undrained (CU) shear tests on cohesive soil from the deep South China Sea were conducted to investigate the ultrahigh static pore pressure effect on undrained shear behavior. The test results confirmed that there is a slight deviation in Terzaghi's expression of effective stress under ultrahigh static pore pressure stress conditions. The soil strength will be underestimated without considering the real static pore pressure condition in the deep-sea environment. A distinction is made between the external pressure-induced and pore pressure-induced contact stress between soil particles, providing a good understanding of the skeleton stress that determines soil strength. Then, the mechanism of ultrahigh static pore pressure on the shear strength of cohesive soil is discussed. Additionally, to estimate the effect of the water depth-induced pore pressure, a strength-related parameter η is introduced to the modified strength expression. Based on the Mohr–Coulomb criterion and test results, a novel method to determine the value of η is proposed. The research results herein could help provide deeper insight into the mechanical properties of deep-sea cohesive soil.

Influence of calcareous nodules content on scaling effect in shear strength of cohesive soil containing calcareous nodules

The difference in the shear strength and other characteristics of the cohesive soil containing calcareous nodules (CSCN) between samples with large size and corresponding scaling size, which is called scaling effect, is significantly affected by its calcareous nodule content (CNC) of the gradation composition. However, current researches rarely reveal the influence of the CNC on the scaling effect in shear strength of samples. In this study, how and why the CNC affects the scaling effect in shear strength were explored. Then a method to reduce the scaling effect based on the reason for influence was proposed. Results show that the correlation between the scaling effect in shear strength and the CNC presents a step curve. This is attributed to that it is easier to form a skeleton effect in samples with scaling size for the same CNC. Considering the skeleton effect, a calculation model for the shear strength parameters of CSCN samples with large size is proposed to reduce the scaling effect. This paper demonstrates that the proposed calculation model provides an access to obtain calculated shear strength parameters of CSCN samples with large size by using measured results of samples with corresponding scaling size.

Depth factors for ring foundations in cohesive soil using numerical analysis

ABSTRACT Shallow foundations are seldom rested on the ground surface and are often embedded below the surface. The undrained bearing capacity of embedded footings and the depth factors associated with it for circular and strip foundations were extensively studied in the past. However, the effect of embedment on the undrained bearing capacity of ring foundations has not received much attention. In this paper, the results of numerical analysis to study the effect of embedment of ring foundations resting on cohesive soil are presented. The influence of variation in the geometry of the ring foundation, the footing side roughness coefficients, and the increasing shear strength of cohesive soil has also been studied. The results show a variation in the depth factors by varying the inner and outer diameter of the ring foundation, footing side roughness coefficient, embedment depth, and increasing shear strength of the soil. Based on the results of the analysis, the authors have proposed an equation to evaluate the depth factors for embedded ring foundations in cohesive soil. The failure pattern of subsoil has also been presented and discussed. The depth factors obtained from this study can be used by practicing engineers to evaluate the bearing capacity of onshore and offshore ring foundations in cohesive soils.

Study on the Mechanical Effect and Constitutive Model of Montmorillonite under the Action of Acid Rain: A Case Study on Montmorillonite-Quartz Remolded Soil

Clay minerals are the common insoluble cementing substances in soil. To study the mechanical effect of montmorillonite under the action of acid rain, the variation law and mechanism of the cohesive force and internal friction angle were discussed by immersing montmorillonite-quartz remolded soil in HNO3 solution with pH = 3. It was found that, under acidic conditions, the cohesive force increased after the first drop and subsequently decreased again, while the internal friction angle remained basically unchanged. Considering the vertical pressure of soil landslide, the change in the shear strength of cohesive soil under acid rain is consistent with the change in the cohesive force. The X-ray diffraction (XRD) results showed that the acid could erode the cement-montmorillonite, and no new substance was generated, which caused a decrease in cohesion. In addition, based on the microcementation nature of montmorillonite and the change mechanism of cohesion under acid rain, the cohesive force model of saturated montmorillonite-quartz remolded soil under acid rain was established. The change trend of calculated cohesion values was consistent with the one of measured values, and the error was small.

Detailed Geophysical Mapping and Hydrogeological Characterisation of the Subsurface for Optimal Placement of Infiltration-Based Sustainable Urban Drainage Systems

The continuous growth of cities in combination with future climate changes present urban planners with significant challenges, as traditional urban sewer systems are typically designed for the present climate. An easy and economically feasible way to mitigate this is to introduce a Sustainable Urban Drainage System (SUDS) in the urban area. However, the lack of knowledge about the geological and hydrogeological setting hampers the use of SUDS. In this study, 1315 ha of high-density electromagnetic (DUALEM-421S) data, detailed lithological soil descriptions of 614 boreholes, 153 infiltration tests and 250 in situ vane tests from 32 different sites in the Central Denmark Region were utilised to find quantitative and qualitative regional relationships between the resistivity and the lithology, the percolation rates and the undrained shear strength of cohesive soils at a depth of 1 meter below ground surface (m bgs). The qualitative tests enable a translation from resistivity to lithology as well as a translation from lithology to percolation rates with moderate to high certainty. The regional cut-off value separating sand-dominated deposits from clay-dominated deposits is found to be between 80 to 100 Ωm. The regional median percolation rates for sand and clay till is found to be 9.9 × 10−5 m/s and 2.6 × 10−5 m/s, respectively. The quantitative results derived from a simple linear regression analysis of resistivity and percolation rates and resistivity and undrained shear strength of cohesive soils are found to have a very weak relationship on a regional scale implying that in reality no meaningful relationships can be established. The regional qualitative results have been tested on a case study area. The case study illustrates that site-specific investigations are necessary when using geophysical mapping to directly estimate lithology, percolation rates and undrained shear strength of cohesive soils due to the differences in soil properties and the surrounding environment from site to site. This study further illustrates that geophysical mapping in combination with lithological descriptions, infiltration tests and groundwater levels yield the basis for the construction of detailed planning maps showing the most suitable locations for infiltration. These maps provide valuable information for city planners about which areas may preclude the establishment of infiltration-based SUDS.

A Laboratory Study on the Influence of Anisotropy on the Soil Behavior

Anisotropy refers to any directional-dependence on material property. In recent years, the anisotropy of intermediate-strain behavior and shear strength, small-strain stiffness anisotropy has attracted attention. The main aim of this paper is to clarify the influence of inherent anisotropy on the compressibility characteristics and shear strength behavior of fine-grained soils. A special manufactured device has been made in order to prepare and collect the samples in different directions. Then, a series of conventional tests have been carried out on the soil samples consists of unconfined compressive and Oedometer tests. Low plasticity clay has been used with three liquidity indices (0.22, 0.32, and 0.44) in order to achieve the goal of the study. The results have showed that the anisotropy had an impact on the undrained shear strength of cohesive soil and the soil strength can be considered as strength anisotropy. The higher anisotropy angle causes the more reduction in the shear strength. The settlement is affected by anisotropy, increasing of the anisotropy leads to the increase of the settlement, the compression and the swelling indices. The coefficient of consolidation in the vertical direction is lower than the coefficient in inclined direction and the ratio of (ch/cv) tends to increase with anisotropy angle the highest ratio is 1.4.

Optimizing the Impact of Detergents Contamination on the Geotechnical Properties of Soils

The main purpose of this research is to investigate the impact of disposing commonly used detergents, namely Sodium Hypo-Chlorite, with a commercial name (Clorox), and Quaternary Ammonium Chloride commercially, known as (Flash), to soil on some of the geotechnical properties of different soils selected from three different locations in the northern part of Jordan. To achieve the goal of this research, two cohesive soils (Soil I and II) were selected.The initial physical properties of the selected soils including optimum moisture content, maximum dry density, grain size distribution, and cohesive soils unconfined compression tests were determined. Several samples were prepared by mixing the soil with different percentages of detergents (Clorox and Flash) and their effects were studied by conducting different experiments such as the modified proctor compaction test, the unconfined test and Atterberg limits test. The results indicated that as the percentage of detergents increased, the plasticity index is slightly increased but the maximum dry density, water content and shear strength of cohesive soils (Soil-I and Soil-II) were decreased.

Experimental Study on Shear Strength of Cohesive Soils Reinforced with Stone Columns

Stone columns are mostly designed to carry compressive loads. However, in some cases, the movement of soil mass can result in lateral deformations, and consequently shear stresses in soil and stone column. The study presented herein is an experimental program, aimed to investigate the shear strength of soft clay bed reinforced with stone column. Modeling of undrained, short-term behavior of clay bed reinforced with stone column was performed using a large direct shear testing device with in-plane dimensions of 305 × 305 mm. In this study, the effect of key parameters including area replacement ratio, stone column arrangement, normal pressures value, and stone column material was experimentally evaluated. For this purpose, three different replacement ratios, stone column arrangements (single, square and triangular) and normal pressures (35, 55 and 75 kPa) and two different materials including crushed gravel and fine-grained sand were used in experiments. Results showed that in the presence of stone column, the shear strength and the overall stiffness of soft clay bed increased. The stone column arrangement, area replacement ratio and stone column material were also shown to have an impact on improving the shear strength. The most and the least increase in shear strength and stiffness values were related to square arrangement of columns and single column, respectively. In this study, the variation of stress concentration ratio of stone columns under shear loads were measured using suitable instruments. Also, the equivalent shear strength and equivalent shear parameters measured from experiments were compared with those predicted by analytical relationships at stress concentration value of 1 and stress concentration value obtained from experiments.

Experimental study on shear strength of clay under load

In order to truly reflect the shear strength index of soil in the project, the engineering soil sample was loaded and unloaded on a compression instrument, and then the shear strength τ of the excavated sample was measured by direct shear test, the shear strength of the soil sample without loading and unloading was compared with that of the soil sample without loading and unloading, and the influence of loading and unloading on the shear strength was analyzed. The results show that the shear strength of cohesive soil decreases within 2 % after loading and unloading, but the shear strength decreases with the increase of compressive stress.

Discussion of “Correlations for Fully Softened Shear Strength Parameters” by B. A. Castellanos, T. L. Brandon, and D. R. VandenBerge, This Article Was Published in Geotechnical Testing Journal, Vol. 39, No. 4, 2016. [DOI: 10.1520/GTJ20150184

Abstract In this paper, the authors criticize the use of a torsional ring shear device for measuring the fully softened strength (FSS) of fine-grained soils based on problematic ring shear data from Castellanos (2014). This is unfortunate and necessitated taking important time and energy to write this discussion. I have over 26 years of commercial soil testing experience while managing the Woodward-Clyde Consultants and AECOM Technical Services Laboratory in Santa Ana, California. I started performing Bromhead torsional ring shear tests to measure the residual strength (RS) of shear surfaces for landslides in 1991. As Professor Stark expanded his shear strength correlations and the geotechnical engineering practice embraced the use of FSS in stability analyses, I started using the Bromhead torsional ring shear device for FSS testing in 2009. The RS and FSS tests are performed in accordance with ASTM D6467, Standard Test Method for Torsional Ring Shear Test to Determine Drained Residual Shear Strength of Cohesive Soils, and ASTM D7608, Standard Test Method for Torsional Ring Shear Test to Determine Drained Fully Softened Shear Strength and Nonlinear Strength Envelope of Cohesive Soils (Using Normally Consolidated Specimen) for Slopes with No Preexisting Shear Surfaces, test methods, respectively.

Use of Fall Cone Test for the determination of undrained shear strength of cohesive soils

CT156, Geotechnics and civil engineering, has been developing efforts to create standards with the generic designation EN ISO 17892, Geotechnical investigation and testing - Laboratory testing of soil. The recent publication of EN ISO 17892-part 6, Fall Cone Test which describes in detail the use of this test method to estimate the undrained shear strength of cohesive soils leads to the necessity for the laboratories to get familiar with this test method and to acquire the required sensibility to analyse the results obtained. Originally designed to determine the liquid limit of fine soils, for which purpose it is considered as an accurate substitute of the Casagrande method, the method may constitute an alternative to the direct shear test, which takes certainly longer time to be carried out and is more complex. The present work aims to compare the values for liquid limit obtained with the Casagrande's method and the cone method and as well as the use of this test to estimate undrained shear strength, correlating with results from other laboratory tests such as the Direct Shear Test and the Laboratory Vane Test on remoulded samples. The results obtained show that there is a good correlation between the applied test methods for determination of the liquid limit and that, for some water contents, the results obtained by the three test methods are comparable.

Utilization of soil nailing technique to increase shear strength of cohesive soil and reduce settlement

This article deals with the assessment of the soil nailing technique with a vertical inclusion to improve the geotechnical parameters of cohesive soil. A series of unconfined compression tests and direct shear tests were carried out to establish the stress–strain relationship and strength characteristics of the reinforced clay sample by vertical steel nails. The shear strength performance of the new composite material was tested by varying the number of vertical inclusions, the embedment depth and the alignment radius. The results confirmed that the vertical bars/inclusions shared the vertical applied load with clay. Increase in the number of vertical inclusions significantly increases the shear strength and the stiffness with a remarkable reduction in settlement. When the clay samples were reinforced with six inclusions along the perimeter, the shear strength was increased to 231% for the embedment depth ratio equal to 0.85. To obtain the optimum effect in eliminating shear failure, the vertical inclusions should be extended to a deeper zone with sufficient numbers. It has been found that the vertical inclusions significantly influence the shear strength, and the brittle or general shear failure of the unreinforced sample can be diverted to partial/plastic shear failure.

Experimental Study on Thermal Effect of Shear Strength of Cohesive Soil

The paper mainly studies the influence rules of temperature (10°C~60°C) and curing time on shear strength indexes of cohesive soil, such as cohesion and internal friction angle, which are very significant in civil engineering works as the temperature of the earth’s surface increases. Such influence plays an even more important role in the design of the ground source heat pump and the geological disposal of high-level radioactive wastes. In this paper, the triaxial unconsolidated-undrained tests on unsaturated cohesive soil samples have recently been performed. And the testing results show that the shear strength increase as temperature and curing time increase, which is a phenomenon that needs further researches. The cementation get reinforced and the change of the content of closed air caused by the temperature curing may be the key factors.

Capacidad de carga tridimensional de celdas estructuradas apoyadas en suelo cohesivo: método de análisis simplificado

In this paper a simplified analysis method to compute the bearing capacity of structured cell foundations subjected to vertical loading and supported in soft cohesive soil is proposed. A structured cell is comprised by a top concrete slab structurally connected to concrete external walls that enclose the natural soil. Contrary to a box foundation it does not include a bottom slab and hence, the soil within the walls becomes an important component of the structured cell. This simplified method considers the three-dimensional geometry of the cell, the undrained shear strength of cohesive soils and the existence of structural continuity between the top concrete slab and the surrounding walls, along the walls themselves and the walls structural joints. The method was developed from results of numerical-parametric analyses, from which it was found that structured cells fail according to a punching-type mechanism.

スウェーデン式サウンディング試験機のスクリューポイントによる粘性土の非排水せん断強さの推定

戸建住宅の地盤調査法としては，スウェーデン式サウンディング試験が，一般的に用いられている．しかし，この試験機の欠点は，自沈荷重のコントロールの難しさにあり，これによって推定された粘性土の非排水せん断強さは信頼性の面において問題がある．ただし，スクリューポイントの回転による抵抗は，粘性土の非排水せん断強さと深く関係を有している可能性が高い．そこで，本研究では，室内実験として，ベーンの形状をスクリューポイントの高さ・幅（径）に相似させた特殊翼を作製し，そのトルク値やスクリューポイントのトルク値から粘性土の非排水せん断強さとの関連性を検討した．その結果，いずれも粘性土の非排水せん断強さと密接な関係があることが明確にされ，トルク値による粘性土の非排水せん断強さの推定式を提案することが出来た．そして，現場実験により，推定式の妥当性を検証し，推定式が十分に適用できる見通しをつけることができた．