Plasticity Index Ip Research Articles

Cyclic threshold shear strain for pore water pressure generation and stiffness degradation in marine clays at Yangtze estuary

Cyclic threshold shear strain is a fundamental property of saturated soils under cyclic loading. To investigate the cyclic threshold shear strain for pore water pressure generation (γtp) and stiffness degradation (γtd), a series of strain-controlled multistage undrained cyclic triaxial tests were carried out on in-situ saturated marine clay in the Yangtze estuary with different plasticity index Ip. The test results show that both γtp and γtd increase with increasing Ip, and γtp is larger than γtd for the same marine clay tested under the same conditions, with γtp = 0.017 ~ 0.019%, γtd = 0.008 ~ 0.012% for Ip of 17, γtp = 0.033 ~ 0.039%, γtd = 0.020 ~ 0.025% for Ip of 32, and γtp = 0.040 ~ 0.048%, γtd = 0.031 ~ 0.036% for Ip of 40. Moreover, the development of stiffness degradation may not necessarily require the generation of pore water pressure but can be aggravated by it. Furthermore, the γtp and γtd of marine clay are compared with terrestrial soils and marine clays cited from the published literature, the results indicate that the special marine sedimentary environment and the combined action of flow and tidal wave system cause the γtp and γtd of marine clay in the Yangtze estuary to be smaller than that of the terrestrial clays and marine clays in other sea areas.

The critical states of saturated loess soils

This paper presents an experimental investigation on eleven loess soils retrieved from NW China to explore the influence of grading and age on soil mechanics. There are overall consistent characteristics in stress-strain relationship and stress paths for the loess tested though detailed property depends on the combination of vi and p0'. The critical state parameters are quantitatively analyzed against the soil properties. The critic state line (CSL) in p' − q plane is less variable. The M value of specimens tested varies from 1.15 to 1.41 and the corresponding φcs' is between 28.8° and 34.8°, which is not clearly related to the loess grading and plasticity index. In the volumetric plane, the intercept Γ of CSLs varies from 1.63 to 2.17 and the gradient λ of loess fall within a narrow range of λ = 0.08 ± 0.03. The λ linearly increases with the increasing plasticity index Ip. The intercept Γ and gradient λ against grading indices has an overall liner trend, i.e., decrease with the increase of D50 and increase with the increasing Cu and Cc values. The intact loess usually has a higher IB value, roughly between 0.5 and 0.9, indicating a relatively high liquefaction potential.

Prediction of Undisturbed Clay Rebound Index Based on Soil Microstructure Parameters and PSO-SVM Model

The rebound index Cr is an important design parameter in engineering construction, and its determination is cumbersome and susceptible to errors. Explaining the macroscopic rebound characteristic parameter Cr from the perspective of microscopic mechanism is an important research area that is addressed in this study. In this paper, the different soil parameters, including the Cr parameter and the physical parameters (void ratio er liquid limit water content WL, and plasticity index Ip), have been determined through experiments for the undisturbed clay of Chongming East Shoal (CES), Shanghai. Further, scanning electron microscopy (SEM) imaging was used to analyze the microstructural features. Through SEM, the grey correlation degree, the average abundance of structural units ACp and the average equivalent diameter of pores ADv were determined as the soil microstructure parameters with the most significant correlation with Cr. The predictive analysis model of Cr was then carried out combined with the PSO-SVM algorithm. In order to evaluate the influence of microscopic parameters of soil on the prediction accuracy, four sets of input parameter combinations were used. The results indicate the high prediction accuracy of the developed model. Sensitivity analysis was also carried out, which showed that the sensitivity of Cr to ACp and ADv was significantly lower than e; however, the difference from wL and Ip was small, indicating that it is imperative to consider microscopic parameters while predicting Cr. This study, thus, provides a basis and method for predicting the rebound index of soil from the microstructure perspective.

Application of Gene Expression Programming to Evaluate Strength Characteristics of Hydrated-Lime-Activated Rice Husk Ash-Treated Expansive Soil

Gene expression programming has been applied in this work to predict the California bearing ratio (CBR), unconfined compressive strength (UCS), and resistance value (R value or Rvalue) of expansive soil treated with an improved composites of rice husk ash. Pavement foundations suffer failures due to poor design and construction, poor materials handling and utilization, and management lapses. The evolution of sustainable green materials and optimization and soft computing techniques have been deployed to improve on the deficiencies being suffered in the abovementioned areas of design and construction engineering. In this work, expansive soil classified as A-7-6 group soil was treated with hydrated-lime activated rice husk ash (HARHA) in an incremental proportion to produce 121 datasets, which were used to predict the behavior of the soil’s strength parameters utilizing the mutative and evolutionary algorithms of GEP. The input parameters were HARHA, liquid limit ( w L ), (plastic limit w P , plasticity index I P , optimum moisture content ( w OMC ), clay activity (AC), and (maximum dry density (δmax) while CBR, UCS, and R value were the output parameters. A multiple linear regression (MLR) was also conducted on the datasets in addition to GEP to serve as a check mechanism. At the end of the computing and iterations, MLR and GEP optimization methods proposed three equations corresponding to the output parameters of the work. The responses validation on the predicted models shows a good correlation above 0.9 and a great performance index. The predicted models’ performance has shown that GEP soft computing has predicted models that can be used in the design of CBR, UCS, and R value for soils being used as foundation materials and being treated with admixtures as a binding component.

Perbaikan Subgrade pada Jalan Kampung Keramat di Kota Pangkalpinang dengan Menggunakan Kapur Padam Sebagai Bahan Stabilisasi Tanah

Soil is the main support in a construction. Unstable soil conditions, especially in the subgrade can cause damage to the road. Based on the results of a direct survey in the field, it was found that the condition of the Jalan Kampung Keramat in Pangkalpinang City was damaged. This might be caused by the condition of the subgrade on the road which is unstable and the subgrade is categorised as clay soil type. This study aims to improve the subgrade on Jalan Kampung Keramat in Pangkalpinang City by using limestone as a soil stabilization material. This study used an experimental method in the laboratory by making mixture between clay soil and limestone with four different variations in the percentage of limestone, namely 0%, 3%, 5%, 7%. There are four parameters of the mixed characteristics that are tested and analysed, namely: the Atterberg limit, specific gravity, soil gradation and CBR value. The results show that the Atterberg limit values ​​(liquid limit-LL and plasticity index-IP) and specific gravity tend to decrease with increasing percentage of limestone extinguished. However, the plastic limit value (PL) shows the opposite tendency, i.e. it increases with the decreasing percentage of limestone. The specific gravity values ​​obtained based on the percentage of lime outages (0%, 3%, 5%, 7%) are 2.63, 2.61, 2.60, and 2.58, respectively. In addition, the addition of limestone causes changes in soil gradation, namely the addition of retained fraction # No.200 and the reduction of passed fraction # No.200. The Addition of limestone can increase the CBR value of the soil, where the addition of 7% of limestone produces the highest CBR value (21.3%) compared to 5% limestone (15.7%), 3% limestone (13.4%) and 0% limestone (11.2%). Therefore, using limestone can improve quality of subgrade, which can be seen from the value of CBR obtained.

Intelligent modelling of clay compressibility using hybrid meta-heuristic and machine learning algorithms

Compression index Cc is an essential parameter in geotechnical design for which the effectiveness of correlation is still a challenge. This paper suggests a novel modelling approach using machine learning (ML) technique. The performance of five commonly used machine learning (ML) algorithms, i.e. back-propagation neural network (BPNN), extreme learning machine (ELM), support vector machine (SVM), random forest (RF) and evolutionary polynomial regression (EPR) in predicting Cc is comprehensively investigated. A database with a total number of 311 datasets including three input variables, i.e. initial void ratio e0, liquid limit water content wL, plasticity index Ip, and one output variable Cc is first established. Genetic algorithm (GA) is used to optimize the hyper-parameters in five ML algorithms, and the average prediction error for the 10-fold cross-validation (CV) sets is set as the fitness function in the GA for enhancing the robustness of ML models. The results indicate that ML models outperform empirical prediction formulations with lower prediction error. RF yields the lowest error followed by BPNN, ELM, EPR and SVM. If the ranges of input variables in the database are large enough, BPNN and RF models are recommended to predict Cc. Furthermore, if the distribution of input variables is continuous, RF model is the best one. Otherwise, EPR model is recommended if the ranges of input variables are small. The predicted correlations between input and output variables using five ML models show great agreement with the physical explanation.

Permeability Coefficient of Low Permeable Soils as a Single-Variable Function of Soil Parameter

Based on the results of experimental studies concerning the filtration coefficient, the Darcianity of the observed flows for eight cohesive soils at four hydraulic gradients was analyzed. It is observed that linear dependence of flow velocity on hydraulic gradient is an approximation only, and it is the worse the more cohesive a given soil is. Despite this, Darcy’s law can be a correct approximation of the empirical relationship between hydraulic gradient and the flow velocity, also in very cohesive soils. A statistical analysis was carried out to identify correlation between soil properties and permeability coefficient. For each soil, 109 parameters were analyzed, among others applying mercury intrusion porosimetry, scanning electron microscopy, dynamic image analysis, and laser diffraction. Ultimately, three single-variable models best fitted to the experimental data were found, using the plasticity index IP as the independent variable, the average pore diameter DP, and the convexity of silt fraction particles. All model parameters are statistically significant at p < 0.05. Comparison with reference multi-variable models showed that the best fit for experimental data is observed by the model with the plasticity index, while the results suggest low usability of single-variable models with structural parameters.

A novel hybrid surrogate intelligent model for creep index prediction based on particle swarm optimization and random forest

Long-term settlement issues in engineering practice are controlled by the creep index, Cα, but current empirical models of Cα are not sufficiently reliable. In a departure from previous correlations, this study proposes a hybrid surrogate intelligent model for predicting Cα. The new combined model integrates a meta-heuristic particle optimization swarm (PSO) in the random forest (RF) to overcome the user experience dependence and local optimum problems. A total of 151 datasets having four parameters (liquid limit wL, plasticity index Ip, void ratio e, clay content CI) and one output variable Cα are collected from the literature. Eleven combinations of these four parameters (one with four parameters, four with three parameters and six with two parameters) are used as input variables in the RF algorithm to determine the optimal combination of variables. In this novel model, PSO is employed to determine the optimal hyper-parameters in the RF algorithm, and the fitness function in the PSO is defined as the mean prediction error for 10 cross-validation sets to enhance the robustness of the RF model. The performance of the RF model is compared specifically with the existing empirical formulae. The results indicate that the combinations IP–e, CI–IP–e and CI–wL–Ip–e are optimal RF models in their respective groups, recommended for predicting Cα in engineering practice. What’s more, these three proposed models demonstrably outperform empirical methods, featuring as they do lower levels of prediction error. Parametric investigation indicates that the relationships between Cα and the four input variables in the proposed RF models harmonize with the physical explanation. A Gini index generated during the RF process indicates that Cα is much more sensitive to e than to CI, Ip and wL, in that order – although the difference among the latter three variables can be negligible.

Application of Artificial Neural Networks for the prediction of undrained shear modulus in cohesive soils

AbstractThe paper presents a study carried out in a Hollow Cylinder Apparatus (HCA) to determine the shear modulus Gu in undrained conditions. Selected results of tests performed for undisturbed cohesive soils are presented. Values of undrained shear modulus Gu have been determined at shear strain of 0.1% and 0.5%. Laboratory tests were performed on slightly overconsolidated clay (Cl) and sandy silty clay (sasiCl) with an overconsolidation ratio OCR of about 3.5 and 2.7, and a plasticity index Ip of 77.6% and 34.7%, respectively. HCA tests were performed with anisotropic consolidation and shearing in undrained conditions. Results of laboratory tests have allowed to assess the influence of the principal stress rotation on the values of undrained shear modulus Gu using Artificial Neural Networks (ANNs).

Automatic classification of fine-grained soils using CPT measurements and Artificial Neural Networks

Soil classification is a means of grouping soils into categories according to a shared set of properties or characteristics that will exhibit similar engineering behaviour under loading. Correctly classifying site conditions is an important, costly, and time-consuming process which needs to be carried out at every building site prior to the commencement of construction or the design of foundation systems. This paper presents a means of automating classification for fine-grained soils, using a feed-forward ANN (Artificial Neural Networks) and CPT (Cone Penetration Test) measurements. Thus representing a significant saving of both time and money streamlining the construction process. 216 pairs of laboratory results and CPT tests were gathered from five locations across Northern Croatia and were used to train, test, and validate the ANN models. The resultant Neural Networks were saved and were subjected to a further external verification using CPT data from the Veliki vrh landslide. A test site, which the model had not previously been exposed to. The neural network approach proved extremely adept at predicting both ESCS (European Soil Classification System) and USCS (Unified Soil Classification System) soil classifications, correctly classifying almost 90% of soils. While the soils that were incorrectly classified were only partially misclassified. The model was compared to a previously published model, which was compiled using accepted industry standard soil parameter correlations and was shown to be a substantial improvement, in terms of correlation coefficient, absolute average error, and the accuracy of soil classification according to both USCS and ESCS guidelines. The study confirms the functional link between CPT results, the percentage of fine particles FC, the liquid limit wL and the plasticity index IP. As the training database grows in size, the approach should make soil classification cheaper, faster and less labour intensive.

Laboratory Examination of Frost-heaving Properties of Road Unbound Mixtures Based on Fines Content and Plasticity Index

In order to ensure the bearing capacity and durability of road pavement in cold climate areas, it is necessary use materials which are resistant to harmful frost impact, known as frost-heaving. Frost heave cause adverse volume changes, the upwards swelling of the pavement after freezing and deterioration of the bearing capacity of the structure after thawing. In winter, road carriageway temperatures may reach tmin = -30̊C under Polish conditions, which results in the freezing of the structural pavement and subgrade layers. Due to frost penetration into the pavement and the subgrade, heaves may form in soils and in structural layers (unbound mixtures), and during the thaw period a high level of moisture is maintained in the frozen layers, and therefore the structure has a low bearing capacity. The aim of this research was to evaluate frost susceptibility of aggregates mixtures based on content of fine-grain fractions and plasticity index IP. Potential frost susceptibility of road materials and soils is determined by laboratory testing. Frost susceptibility is connected directly with the content and quality of fines, which is why the basic test is that material grading. The criterion based on fines content is the most frequently used indicator in determining frost susceptibility for soils. The article shows whether the limit values adopted for this criterion are also applicable to aggregates. The results of frost-heaving properties are presented of 14 typical natural aggregate road mixtures, continuously graded 0/31.5 mm. Frost susceptibility was determined based on laboratory testing of the following features: content of fine-grain fractions, smaller than 0.002 mm, 0.02 mm, 0.075 mm, 0.125 mm, plasticity index IP and the value of the actual frost-heave of a compacted aggregate mixture frozen in a cylinder. The article shows the test results and their analyses according to the frost susceptibility evaluation criteria for unbound mixtures in road construction. The tests presented in the article were carried out at the Road and Bridge Research Institute in Warsaw.

Prediction of the modulus of elasticity of compacted unsaturated expansive soils

A semi-empirical model was proposed by for predicting the variation of the modulus of elasticity with respect to matric suction for soils with plasticity index Ip values lower than 16%. This model has been extended in this paper to predict the modulus of elasticity of unsaturated expansive soils. The information required for using the model include the soil–water characteristic curve (SWCC) and the modulus of elasticity of soil under saturated condition along with two fitting parameters. Experimental data of triaxial tests for three different expansive soils from the literature were used to examine the validity of the model. The results of the study suggest that the model can reasonably predict the modulus of elasticity of unsaturated expansive soils. The study results are encouraging in reliably using the modulus of elasticity based method proposed by for estimation of the volume change behavior of expansive soils.

Influence of the rotation of principal stress directions on undrained shear strength

Abstract Influence of the rotation of principal stress directions on undrained shear strength. The paper presents the results of research on natural cohesive soil carried out in the Hollow Cylinder Apparatus (HCA). The main goal of this study was to determine the values of undrained shear strength at different angle of the rotation of principal stress directions. The research were carried out with anisotropic consolidation and shearing in undrained conditions (CAU) on cohesive soil with overconsolidation ratio (OCR) equals 4 and plasticity index (Ip) about 77%. The results of laboratory tests allow to assess the influence of the rotation of principal stress directions on undrained shear strength

Thermo-hydro-mechanical behaviour of a sandy clay on isotropic paths

An experimental study of the thermo-mechanical behaviour on isotropic paths of a sandy clay prepared in the laboratory has been carried out. The material is characterised by its liquid limit wL = 38% and plasticity index Ip = 19%. Thermal consolidation tests under constant stress followed by mechanical consolidation tests at imposed temperatures were carried out on samples preconsolidated under a vertical stress of 100 kPa. The results of heating tests with measurement of volume changes highlighted the equivalence between thermal consolidation and mechanical consolidation. Thermal compressibility modulus of a normally consolidated material derived from these tests increases with temperature. Mechanical consolidation at different given temperatures shows a decrease of the thermal compressibility modulus at high temperature (80 °C). In addition, permeability increases with temperature.

Strength mobilization in clays and silts

A large database of 115 triaxial, direct simple shear, and cyclic tests on 19 clays and silts is presented and ana- lysed to develop an empirical framework for the prediction of the mobilization of the undrained shear strength, cu, of natural clays tested from an initially isotropic state of stress. The strain at half the peak undrained strength (gM=2) is used to normal- ize the shear strain data between mobilized strengths of 0.2cu and 0.8cu. A power law with an exponent of 0.6 is found to describe all the normalized data within a strain factor of 1.75 when a representative sample provides a value for gM=2. Multi-linear regression analysis shows that gM=2 is a function of cu, plasticity index Ip, and initial mean effective stress p 0 0. Of the 97 stress-strain curves for which cu, Ip, and p 0 were available, the observed values of gM=2 fell within a factor of three of the regression; this additional uncertainty should be acknowledged if a designer wished to limit immediate founda- tion settlements on the basis of an undrained strength profile and the plasticity index of the clay. The influence of stress his- tory is also discussed. The application of these stress-strain relations to serviceability design calculations is portrayed through a worked example. The implications for geotechnical decision-making and codes of practice are considered.

Strain-rate effect on consolidation behaviour of Ariake clay

A total of 114 constant rate of strain (CRS) consolidation tests and 15 incremental loading (IL) consolidation tests were conducted for undisturbed Ariake clay samples from three boreholes in the Saga Plain, Kyushu, Japan, to systematically investigate the strain-rate effect on the consolidation behaviour of Ariake clay. The test results show that the consolidation yield stress (pc) of Ariake clays increased by about 15–16% with a tenfold increase in strain rate, and no clear correlation exists between the strain-rate effect and the clay content or plasticity index Ip of the samples. For a given strain level, the strain rate does not influence the compression index Cc, which implies that an isotach model is applicable to Ariake clay. It has been newly found that, under a given effective vertical stress, the coefficient of consolidation cv increases with increase of the strain rate, resulting mainly from the increase of hydraulic conductivity k with strain rate. Linear regression gives about a 33% increase in cv with a tenfold increase in the strain rate. For the Ariake clay tested, the pc and cv values of CRS tests with a strain rate of 0·02%/min are comparable with those of IL tests.

Comportement thermo-hydro-mécanique d'une argile sableuse non saturée sur chemin de cisaillement triaxial

ABSTRACT A new experimental device has been designed to study the THM behavior of a soil on triaxial paths. The material is a laboratory sandy clay with a liquid limit wL = 38 and a plasticity index Ip = 19. Three initial states of samples have been studied: (1) normally consolidated NC (2) overconsolidated OC (3) compacted to Proctor optimum water content and maximum density. Saturated triaxial tests under controlled temperature conditions and unsaturated triaxial tests under controlled temperature and suction conditions were performed on the material in the different initial states. In the saturated domain, the results show the influence of temperature and initial state on the secant modulus, maximum strength and pore pressure changes during the undrained deviatoric loading. In the unsaturated domain, the coupled effect of suction and temperature on the evolution of the secant modulus and maximum strength is highlighted.

Laboratory Behaviour of Rio de Janeiro Soft Clays. Part 2: Strength and Yield

This paper summarizes the yield and strength behaviour of clays studied in the State of Rio de Janeiro in the last forty years, with emphasis on the role of the clay structure on strength and yield. The undrained strength normalised by the overconsolidation stress is analyzed against the plasticity index IP. Values of the clay friction angle φ’ are also analyzed against the plasticity index IP. Both data are compared with the available literature data, but the Rio de Janeiro clays have higher IP and also show more data scatter. As far as yield is concerned, it is shown that the use of the SHANSEP method results in the destruction of the clay structure with the loss of its anisotropic characteristics. An evaluation of the level of structure destruction is presented.

Settlements in Fine-Grained Soils Under Cyclic Loading

Based on the methods previously presented by the authors (Yasuhara et al., 1992, 1994, 1996) for predicting the degradation in strength and stiffness of soft clays in the course of cyclic loading, a methodology has been developed to estimate the cyclic loading-induced settlements. The method also includes not only immediate settlements but also post-cyclic long-term settlements due to dissipation of cyclically induced excess pore pressures in soft soils. The simplified formulae included in the proposed methodology are given as functions of the amplitude of cyclic-induced excess pore pressure normalized by the confining pressure, u/p'c, plasticity index Ip and factor of safety against bearing capacity failure, Fs. The calculations of cyclic-induced settlements were conducted for soft soil deposits with different index and geotechnical properties. The results calculated using the proposed methodology are presented in the form of a design chart to give the settlement versus normalized excess pore pressure ratio relations including the effects of the plasticity index and safety factor for bearing capacity. An example of the calculated results using the proposed procedure for the earthquake-induced settlements of embankments founded on soft clay, is presented to demonstrate the practicality of the method for design at fields.

Cyclic Shear Strength of Undisturbed and Remoulded Marine Clays

Undisturbed clay samples were taken from alluvial deposits at seven different urban coastal locations in Japan. At several of the locations samples were taken from different depths in order to sample different sedimentary environments. The samples were then triaxially tested in both undisturbed and remoulded states. A testing programme was devised to separately examine the influence of plasticity index, aging factors and overconsolidation ratio on the undrained cyclic strength of clays. The cyclic data for normally consolidated samples was used to define the cyclic strength of the clays as an intrinsic function of the plasticity index Ip. This was modified to take into account the initial vertical yield stress ratio and degree of aging, and then further modified for the effect of geological OCR. A further series of tests was carried out on samples which were anisotropically consolidated by being subjected to an initial drained shear stress for 24 hours. The cyclic strength of the anisotropically consolidated clays at low initial drained shear stress ratios increased with increasing plasticity. This reversed as the drained shear stress ratio increased. It was possible to define a simple function for the cyclic strength normalised by the isotropic cyclic strength against the initial drained shear stress ratio. This function was shown to be dependent on plasticity index Ip but independent of stress history.