Undrained Triaxial Research Articles

Prediction of yield shear strength of saturated sandy soils using artificial neural networks

ABSTRACT The undrained shear strength of sandy soils during flow failures and liquefaction is a critical metric in the analysis of undrained stability. In our study, the numerical technique known as Artificial Neural Network (ANN) is used for simulating the triaxial stress–strain relationship of sandy soils. This paper aims to predict the undrained shear strength of saturated sandy soil. The proposed program requires simple laboratory soil data to proceed. They are median grain diameter (D50), fines content percentage (FC%), void ratios and relative density. In addition, the stress data of undrained loading such as effective vertical stress (σ’1) and effective horizontal stress (σ’3) are needed. Then, using the program, the deviator stress at yield (qu yield) and, consequently, the yield shear strength of sandy soil (Su (yield)) can be determined. A database of experimental undrained triaxial of saturated sandy soils was collected from the literature and prepared to be the inputs of the network. Two artificial neural networks have been built. By comparing the effectiveness of the two networks, the Back Propagation Neural Network (PBNN) approved higher results and more accuracy than the General Regression Neural Network (GRNN). The computer program, yield shear strength prediction application, written in visual basic, has been developed by the author. For model validation, seven case studies (seven patterns of the production set), which were not seen by the network previously, were presented to the application and the results are compared to the actual output. The produced yield shear strength is very close to the actual strength.

Effect of Microbial Biopolymers on Mechanical Properties of Bauxite Residue

Natural polymer (biopolymer) treatment of engineered soil/waste is recognized as an environmentally-friendly sustainable method. This paper presents the findings in the improvement of strength characteristics of bauxite residue (red mud tailing) using two microbial biopolymers, xanthan (XG) and guar gum (GG), used individually and also together as a composite. A set of laboratory tests namely compaction test, sieve and hydrometer analysis, Atterberg limits, unconsolidated undrained triaxial (UU) test, unconfined compression (qu) test, chemical analysis, X-ray diffraction (XRD) and scanning electron microscopy (SEM) have been performed on biopolymer stabilized specimens at varying biopolymer concentration and curing period. The results showed that qu increases polynomially with the increase in biopolymer content (P) and curing period (t). Also, when compared with the conventional method, qu at 0.5% XG was similar to 10% cement stabilized bauxite residue at 28 days curing period. The influence of a composite biopolymer on the strengthening behaviour of bauxite residue is also observed due to the additional ability to create a cross-linking network. XRD and SEM micrographs have also confirmed that bauxite residue particles are linked through the biopolymer, resulting in improved shear resistance. Finally, considering environmental perspectives, the economic feasibility of biopolymer treatment is also examined in comparison to cement and found that the biopolymer usage is an excellent substitute to the conventional engineered materials (cement) for soil/waste treatment.

Laboratory and field investigation of cement-stabilized organic soil near flood-prone area

Cement stabilization of very high plasticity organic soils (gyttja) near flood-prone areas, is a key to constructing water-retaining structures with optimized foundation works. The company Geo has documented the strength of cement stabilized gyttja samples from the area Jyllinge Nordmark in Denmark, for Keller Funderingsteknik Danmark ApS, who have carried out the stabilization. The strength was determined by Unconfined Compressive Strength (UCS) tests, with support of Consolidated Undrained Triaxial (CU) tests and field vane tests to determine undrained shear strength of the stabilized soil. In the laboratory, specimens were prepared with five different cement contents (60, 80, 100, 125, 150 kg/m3) and the strength determined after curing times of 7, 28 and 91 days. To document the in-situ strength and correlate laboratory and in-situ measurements, two UCS tests and three undrained triaxial tests were carried out on intact specimens taken from the cement stabilized soil. The investigation showed a good correlation between cement content, water content, curing time and compressive strength. Further, comparison with similar tests from Sweden, where cement stabilization is a far more common method, shows good correlation to the Jyllinge Nordmark results.

Effects of crude oil contamination on geotechnical properties of sand-kaolinite mixtures

Abstract In this study, a series of laboratory tests were performed to investigate the interaction between crude oil, clay minerals, and sand particles in contaminated soils and the effect of crude oil on the engineering properties of sand-kaolinite mixtures with different weight ratios of clay to sand was evaluated. Mixtures with a weight ratio of 10%, 30% and 50% kaolinite to sand contaminated with different contents of crude oil (including 0%, 4%, 6% and 8% by dry weight of soil) have been considered. Standard compaction, unconsolidated undrained triaxial, permeability, pH, and water holding capacity (WHC) tests have been conducted on the clean and contaminated specimens at the same dry density. In addition, Scanning Electron Microscope (SEM) has been used to identify the microscopic interactions between crude oil, kaolinite and sand particles. The results show that due to an increase in contamination, the maximum dry density, optimum water content, permeability and pH values were decreased. Different ratios of clay/sand had a significant effect on WHC value and soil shear strength parameters in the presence of the crude oil. While in the sandy specimens with low clay quantity, the addition of crude oil decreased the internal friction angle, in the specimens with high clay quantity, the angle of friction increased. SEM images showed that crude oil contamination caused aggregation of clay particles and a flocculated structure with more macropores. The findings of this paper can clarify the hydro-chemo-mechanical properties of a wide range of soils and help in geotechnical designs of contaminated soils.

A laboratory study of shear strength of partially saturated sandy soil

ABSTRACT This experimental research aims to evaluate the effect of the degree of saturation and relative density of the liquefaction resistance of Chlef sand. A series of undrained triaxial was carried out at an initial relative density of 12% and 75% corresponding to a loose and dense state, respectively, and under a confining pressure of 100 kPa for Skempton coefficients of 22%, 45% and 92%. The test results show that an increase of degree of saturation leads to a decrease of the shear strength of the sand. However, the maximum shear strength decreases linearly and the residual shear strength decreases logarithmically with the increase of the degree of saturation, while the excess pore pressure increases logarithmically with the increase of the degree of saturation (B). The internal friction angle decreases logarithmically with the increase of the degree of saturation.

Influence of Banana Fiber on Shear Strength of Clay Soil

Recently, the agricultural waste have been enticed increasing attention in geotechnical engineering as a natural soil reinforcement in improving strength and stability of soils. Agricultural waste fiber was chosen as it is cheap, locally available, bio-degradable and eco-friendly. In this study, the implementation of banana fibers has been used as a natural soil reinforcement in influencing the strength of clay soil. In order to investigate the influence of banana fiber in strengthen the clay soil, three different percentage mixing of banana fiber in clay soil has been tested using Unconsolidated Undrained Triaxial and California Ratio Bearing (CBR) tests. The results of X-Ray Fluorescense (X-RF) indicated that average 45% of chemical compositions inside the banana fibers are calcium hydroxide which resulting the pozzolanic reactions and lead to the modification of soil properties and improve the strength of soil. This research is important in order to find the suitability of banana fiber as admixture in soil stabilization. Banana fiber as admixture in soil stabilization will contribute to conservation of the environment. The results from the tests conducted have shown that the soil treated with 1% fibre content improved termendously in term of shear strength compared to untreated sample. However, based on the regression analysis, 0.5% mixing of banana content indicate the optimum percentage mixing of banana fiber in clay soil.

Shear Strength Parameters of Cement Stabilized Amorphous Peat of Various Water Additive Ratios at Different Natural Moisture Contents under Consolidated Undrained Triaxial Test

Peat is a problematic soil which has a low shear strength characteristic. Addition of cement can improve the properties and strength of peat soil. This paper presents the findings of the shear characteristic of cement stabilized amorphous peat under consolidated undrained (CU) triaxial test. Three different natural moisture contents of peat which are 1210%, 803% and 380%, were stabilized using cement with water to additive (W/A) ratio of 2.0 and 3.0. CU triaxial test was conducted to the specimens after cured for 90 days. The shear parameters and characteristics were investigated towards the change of W/A ratio of the samples with different moisture contents. The result shows that the stabilized peat specimens exhibited ductile behavior and were sensitive to the over consolidation. The total and effective cohesion (ccu, c′) of the stabilized peat were found to be greater at W/A ratio of 2.0 compared to W/A ratio of 3.0, and greater at lower initial moisture content specimens. The total and effective friction angles (φcu, φ′) are ranged from 14o to 27o and 36o to 47o consecutively and found to be increased upon the increase of W/A ratio except for the specimens with moisture content 1210% and 803% in term of total friction angle.

AVISA: anisotropic visco-ISA model and its performance at cyclic loading

In this work, a constitutive model able to capture the strain rate dependency, small strain effects and the inherent anisotropy is proposed considering the influence of the overconsolidation ratio (OCR). Small strain effects are captured by using an extended ISA plasticity formulation (Fuentes and Triantafyllidis in Int J Numer Anal Methods Geomech 39(11):1235–1254, 2015). The strain rate dependency is reproduced by incorporating a third strain rate mechanism (in addition to the elastic and hypoplastic strain rate). A loading surface has been incorporated to define a three-dimensional (3D) overconsolidation ratio and to account for its effects on the simulations. Experimental investigations using Kaolin Clay and Lower Rhine Clay with horizontal bedding plane have shown that under undrained cycles of small strain amplitudes (<10^{-4}), the effective stress path in the p–q space is significantly inclined towards the left upper corner of the p - q plane. Consequently, a transversely (hypo)elastic stiffness has been successfully formulated to capture this behaviour. The performance of the model has been inspected by simulating the database of approximately 50 cyclic undrained triaxial (CUT) tests on low-plasticity Kaolin Clay (Wichtmann and Triantafyllidis) considering different deviatoric stress amplitudes, initial stress ratios, displacement rate, overconsolidation ratio and cutting direction. Furthermore, 4 CUT tests conducted on high-plasticity Lower Rhine Clay were simulated, whereby the influence of the displacement rate, as well as the deviatoric stress amplitude, has been analysed. The simulations showed a good congruence with the experimental observations.

Effect of silica fume on engineering properties of expansive soil

Rapid growth of urbanization and industrialization has led to drastic industrial waste which has become a giant threat to our nature. Minimizing industrial waste now days posing a serious problem in the present scenario. To tackle the problem now a days many innovative and non-traditional researches on waste utilization is gaining importance. The primary purpose of this experimentation is to evaluate the suitability of using the low-cost material i.e. Silica fume as a soil stabilization material. This project work presents the study of expansive soil stabilized with silica fumes which was assembled from an idyllic area named Kalatunga located in Kendrapada district of Odisha state. Soil stabilization was done with various percentages of silica fumes (10 to 100%). The differential free swell (DFS), Atterberg’s limits, standard proctor compaction, california bearing ratio (CBR), unconfined compressive strength (UCS) test and unconsolidated un-drained triaxial (UU) test were carried out on natural and silica fume stabilized soils. Results display that addition of SF scales down the DFS. The compaction curves point out that addition of silica fume results in an increase in optimum moisture content (OMC) and decrease in maximum dry density (MDD). The addition of stabilizers (i.e. silica fumes) escalates the cohesion (C) values in UCS along with an in increase in cohesion and angle of shearing resistance (Ø) in UU triaxial test demonstrating progress in the strength properties of soil.

Determination of relationship between standard penetration test and geotechnical parameters in Ahwaz soil

ABSTRACT The present study is the result of more than 150 geotechnical investigations that were conducted over 2 years (from 2015 to 2016) on the Ahwaz soil (which is mainly composed of clay with low plasticity in different regions). The standard penetration test was performed at all the boring locations, and after preparing the undisturbed Shelby tube samples from different depths, the unconsolidated undrained triaxial (UU), Atterberg limits, in situ moisture content and grading tests were performed on all samples. All of the abovementioned parameters are presented for the Ahvaz soil, and the range of values of each of the parameters were investigated, and finally, the relationship between the modulus of elasticity and the standard penetration test was studied. The effect of different soil parameters and their contribution to the determination of soil elasticity modulus is another important result of this study. The most important result of this study could be the different classifications of soil elasticity moduli by using the sample Nspt values to estimate the elasticity moduli because the standard penetration test value has the highest correlation and the most significant relationship with elasticity moduli.

Estimation of the undrained shear strength of Adapazari fine grained soils by cone penetration test

A comprehensive study to determine the undrained shearing resistance of fine grained soils by the use of cone penetration test (CPTu) was carried out on the thick fluvial sediments of the plain of Adapazari, Turkey. The soundings were performed adjacent to geotechnical boreholes for comparison. Eighty-three undisturbed samples of low, intermediate and high plasticity were procured in the process, which were classified and tested in unconsolidated undrained triaxial (UU) conditions in the laboratory. The cone resistance, sleeve friction and pore water pressure values recorded along the length of undisturbed sampling were averaged to obtain characteristic values. It is known that the empirical formulae to interpret CPT readings use cone factors Nk, Nkt and Nke which can be highly variable. This can lead to unacceptable error levels in the assessment of undrained shear strength (su). Nevertheless, it was noticed in this study that the undrained strengths estimated by employing the traditional relationships for CPT came out quite close to the values measured in the laboratory if soil classes are taken into account. Since soil sampling is not done in the cone penetration test by default, classification of the soil is attempted by the use of the soil type behavior index (Ic). This study showed that the error margins for su values measured in the laboratory and inferred from CPT are considerably reduced by using the soil type behavior index (Ic) to determine soil behavior type specific cone factors.

Particle-Scale Mechanisms in Undrained Triaxial Compression of Biocemented Sands: Insights from 3D DEM Simulations with Flexible Boundary

Particle-Scale Mechanisms in Undrained Triaxial Compression of Biocemented Sands: Insights from 3D DEM Simulations with Flexible Boundary

Consolidated Undrained Triaxial Compression Tests and Strength Criterion of Solidified Dredged Materials

Consolidated undrained triaxial compression tests were performed to investigate the shear strength behavior of the solidified dredged materials (SDM). The variation law of deviator stress and excess pore water pressure with the increase of the applied confining pressure was investigated. It is found that the shear strength envelope is consisted of two lines, and there exists a transitional stress on the intersection point. The undrained shear strength develops slightly with the increase of applied normal stress in the preyield state. However, the undrained shear strength increases significantly in the postyield state, and the strength envelope is nearly a straight line with the extension through the origin. Based on the triaxial test data and the binary medium model, a strength criterion considering strength evolution mechanism is proposed and the relevant parameters of the strength criterion were discussed. Comparisons of the predicted results and experimental data demonstrate that the proposed strength criterion can properly describe the strength evolution rules of the SDM.

Development of Data Acquisition System for Consolidated Undrained Triaxial Test

Consolidated Undrained (CU) triaxial test is a common laboratory test used in practice for determining effective and total shear strength parameters of soil. This paper reported works carried out to develop a data acquisition system for a self-assembled triaxial machine. The developed system was capable of acquiring signals from the installed sensors (i.e. pressure transducer, load cell, LVDT), interpreting and presenting the data in real-time graphs. In addition, the study highlighted the advantages of performing double vacuuming method to saturate the soil specimen. The saturation can be obtained quicker and at a significantly lower cell pressure compared to the conventional stepwise increment of back pressure and cell pressure method.

Effect of Particle Shape on Dilative Behavior and Stress Path Characteristics of Chamkhaleh Sand in Undrained Triaxial Tests

The behavior of Chamkhaleh sand and three other recognized sands namely, Babolsar, Firouzkuh, and Standard (Ottawa) sands are compared using triaxial apparatus under undrained monotonic loading conditions. Chamkhaleh and Babolsar sands are supplied naturally from southern Caspian Sea shorelines, whereas artificial Firouzkuh and Standard sands were supplied commercially. Samples were prepared using wet tamping with regard to the reduced compaction effect at relative density of 15 % under isotropic consolidation pressures of 100, 300, and 500 kPa. The results of triaxial tests have indicated that Chamkhaleh sand has much more dilation tendency than the other sands. To evaluate the reasons behind this behavior, the sphericity and roundness of all the four sand particles were measured using an image processing method. It was revealed that the sphericity of the four sands is not much different, but Chamkhaleh sand is more angular than the other sands. For comparison of the dilative response of the sands in undrained triaxial tests, a “dilation tendency index” is introduced. This index may be used as a criterion for measuring the dilation of sands in undrained tests. Results have shown that the internal friction angle under the steady-state condition is more dependent on the shape of particles than the maximum strength condition. For sphericities greater than 0.5, the dependency rate of sand behavior on the roundness is decreased.

Finite Element Modelling of a Deep Excavation in Boston Blue Clay

The work investigates the behaviour of a deep excavation that forms part of a wide basement located in Boston, Massachusetts, USA. The glacial marine clay deposit is modelled with a kinematic hardening model for structured soils, its reduced bubble model version and the well-known Modified Cam Clay model. The aim of the work is to assess the effects of the added features of the advanced model, such as small-strain stiffness, structure degradation and anisotropy, on the numerical prediction of the overall behaviour of the excavation. The first part of the paper provides a brief description of the site conditions, ground profile and construction sequences for the case study under consideration. Then, the soil model calibration process using experimental undrained triaxial, self-boring pressuremeter and constant rate of strain consolidation tests is discussed. Finally, the comparison of the predicted wall deflection and ground settlements profiles with observed movements is presented.

Initiation processes for run-off generated debris flows in the Wenchuan earthquake area of China

The frequency of huge debris flows greatly increased in the epicenter area of the Wenchuan earthquake. Field investigation revealed that runoff during rainstorm played a major role in generating debris flows on the loose deposits, left by coseismic debris avalanches. However, the mechanisms of these runoff-generated debris flows are not well understood due to the complexity of the initiation processes. To better understand the initiation mechanisms, we simulated and monitored the initiation process in laboratory flume test, with the help of a 3D laser scanner. We found that run-off incision caused an accumulation of material down slope. This failed as shallow slides when saturated, transforming the process into debris in a second stage. After this initial phase, the debris flow volume increased rapidly by a chain of subsequent cascading processes starting with collapses of the side walls, damming and breaching, leading to a rapid widening of the erosion channel. In terms of erosion amount, the subsequent mechanisms were much more important than the initial one. The damming and breaching were found to be the main reasons for the huge magnitude of the debris flows in the post-earthquake area. It was also found that the tested material was susceptible to excess pore pressure and liquefaction in undrained triaxial, which may be a reason for the fluidization in the flume tests.

Static Liquefaction of Sands under Isotropically and K0-Consolidated Undrained Triaxial Conditions

By using the state-dependent strength criterion and dilatancy function, a state-dependent nonassociated elastoplasticity hardening model was proposed to unify modeling the constitutive relationships of sands with different initial void ratios. According to the second-order work theory, the criteria for predicting the potential instability and static liquefaction of sands were obtained. The proposed model and criteria were used to predict a series of isotropically consolidated and K0-consolidated undrained triaxial tests. The results showed that the potentially unstable point and the onset of static liquefaction under undrained conditions coincided with the attainment of a deviatoric stress peak in very loose sand, whereas, with the decrease of the initial void ratio, the onset of static liquefaction fell behind the potential instability. When the sand specimen was dense enough, static liquefaction did not occur, although the stress state was located inside of the potentially unstable region. The potential instability and static liquefaction occurred before the effective stress reached the failure surface, and they were the precursors though not the results of the sand failures.

Soil characterisation of South Pars field, Persian Gulf

South Pars, located in the Persian Gulf, southwest of Iran, is one of the largest offshore gas fields in the world. During the past decade, numerous geotechnical investigations have been carried out in this area for designing deep foundations of offshore oil- and gas-extraction facilities. Generally, such geotechnical site investigations consist of various in situ and laboratory tests. Downhole piezocone penetration tests are widely performed in this area up to a depth of about 130 m below the seabed. Shear strengths of different soil layers are evaluated using various in situ and laboratory methods including unconsolidated undrained triaxial, pocket penetrometer, torvane, and miniature vane tests. In this paper, local geotechnical site characterisation of the South Pars field is presented based on a large amount of data collected from developed phases of the field. This research is particularly focused on the cone factor, which relates the undrained shear strength of soil to the cone tip resistance of the cone penetration test (CPT). The variation of the cone factor within the South Pars field is presented based on CPT results. The deformation characteristics and the stress history parameters have also been evaluated for marine clays of the field. The influence of stress state on cone factors has been studied as well.

Basic parameters governing the behaviour of cement-treated clays

Although extensive research has been conducted on the mechanical behaviour of Portland cement-treated soft clays, there has been less emphasis on the correlation of the observed behaviour with clay mineralogy. In this study, experimental results from the authors have been combined with the data found in the literature to investigate the effect of parameters such as curing time, cement content, moisture content, liquidity index, and mineralogy on the mechanical properties of cement-treated clays. The findings show that undrained shear strength and sensitivity of cemented clays still continue to increase after relatively long curing times; expressions are proposed to predict the strength and sensitivity with time. This parametric study also indicates the relative importance of the activity of the soil, as well as the water–cement ratio, to the mechanical properties of cementitious admixtures. Two new empirical parameters are introduced herein. Based on the results of unconfined compression, undrained triaxial, and oedometer tests on cement-enhanced clays, expressions that use these parameters to predict undrained shear strength, yield stress, and the slope of the compression line are proposed. The observed variations in the mechanical behaviour with respect to mineralogy and the important effect of curing time are explained in terms of the pozzolanic reactions. The possible limitations of applying Abrams׳ law to cement–admixed clays are also discussed.