Unconsolidated Undrained Tests Research Articles

SHEAR STRENGTH OF SOFT CLAY REINFORCED WITH ACRYLONITRILE BUTADIENE STYRENE (ABS) COLUMN

The troublesome soil that many geotechnical engineers encounter in the sector is clay soil. It presents a major danger to the foundations of light structures. Granular columns have proved beneficial in resolving foundation stabilisation and settling issues, making soft clay more appropriate for foundation building. This study aims to determine whether adding acrylonitrile butadiene styrene (ABS) to kaolin clay increases its shear strength. The physical, mechanical, and morphological properties of the materials used in this research (i.e., kaolin and ABS) must first be identified. The soft clay kaolin was strengthened with ABS columns and tested using the unconfined compression test (UCT) and the unconsolidated undrained test (UUT). The diameter of the columns used in this study was 8, 12, and 16 mm, while the penetration depth ratio used was 0.5, 0.75, and 1.0. The highest improvement in shear strength occurred at a height penetration ratio of 0.5 with values of 102.94%, 48.56%, and 50.02%. The UCT results demonstrated a decrease in the volume of the replacement ratio, followed by an increase in the height of the column. The UUT was conducted to evaluate the soft clay's shear strength when reinforced with an ABS column. The cell pressure used was 50, 100, and 200 kPa with the same column diameter specification as the UCT. The friction angle, υ, increased significantly from 8.92% to 18.21%. Furthermore, there was an improvement in cohesiveness, c, which increased from 4.54% to 45.45%. The results show that installing ABS columns improves the strength and compressibility of clay samples.

The Potential Usage of Bitumen Cold Mix and Tire Chips as Stabilization Material on Clay Soil Strength Characteristics

Clay is a soil with fine particle size less than 0.002 mm, low permeability, cohession, high swelling, and slow consolidation process. Due to that problem it needs some improvement to stabilize the condition of soil before the process of construction conducted. The purpose of this study is to determine the effect of adding shredded tire and cold mix bitumen as the value of shear strength changing are cohession, friction angle, and shear strength with triaxial unconsolidated undrained test. To see the effect of those mixture, this study uses 48 soil samples with 4 variation of shredded tired (0%, 1%, 1,5%, and 2%) and 4 variation of cold mix bitumen (0%, 1%, 2%, dan 3%). The result of this study showed that the adding of shredded tired and cold mix bitumen in soil compositition can increase parameters of soil. The optimum cohession is on variation 1% SB+2% B (T99B2SB1) with the value 0.61 kg/cm2. Meanwhile the optimum value of friction angle is on variation 1.5% SB+ 1% B (T98.5B1SB1.5) with the value 7.43o. The shear strength as the sum of cohession and friction angle tends to increase with the optimum value about 0.995 kg/cm2 in variation 2% bitumen and 1% shredded tire (T99B1SB1). From the study, the adding of shredded tired and cold mix bitumen improve the shear strength. The optimum value of shear strength is on variation 2% B+1% SB (T99B1SB1) with the value 0.995 kg/cm2. This study shows that stabilization material used in this research can be an alternative material for soil stabilization.

Mechanical Properties and Microscopic Mechanism of Cement-Stabilized Calcareous Sand Improved with a Nano-MgO Additive

Calcareous sand fractures easily, has poor mechanical properties, and usually needs to be stabilized for engineering applications using additives. In this study, nano-MgO was used to enhance the mechanical properties of cement-stabilized calcareous sand (CCS). Unconfined compressive strength (UCS) and unconsolidated undrained (UU) triaxial shear tests were conducted on nano-MgO-modified CCS (MCCS) specimens, and the microscopic mechanism was investigated using scanning electron microscopy and X-ray diffraction. Finally, models to predict the UCS and shear strength of MCCS were formulated. The results showed that the addition of nano-MgO can enhance the strength and stiffness of CCS, with MCCS reaching its maximum strength of 2.1 MPa at 28 days when the nano-MgO content was 1%. Furthermore, the deviatoric stress first increased and then decreased as the nano-MgO content increased, reaching its maximum value when the nano-MgO content was 1.5%. The optimal nano-MgO content obtained from the UCS tests was different from that obtained from the UU tests. This improvement in CCS strength was due to the nano-MgO filling and cementation of hydrates such as Mg7Si8O22(OH)2, Mg(OH)2, and CaAl2Si3O10(H2O)2. However, too much nano-MgO reduces the strength of CCS because the nano-MgO expands during hydration.

Study of Dynamic Evolution of the Shear Band in Triaxial Soil Samples Using Photogrammetry Technology

In order to avoid the influence of end restraint on triaxial stress and strain measurements, this study combines photogrammetry and computer technology to apply to the unconsolidated undrained test of triaxial soil samples. The novel method can establish an intuitive shear band evolution model of soil samples and help attain a clear and intuitive shear band evolution law. On the basis of the conventional triaxial test, this new method needs to paste the RAD (Ringed Automatically Detected) code points on the rubber film, plexiglass cover and brackets and then take pictures of the RAD code points in the loading process in a surrounding manner, with which the 3D shape of the restored soil samples can be determined. After eliminating the influence of refraction, the coded point cloud coordinates measured in the experiment can be used to calculate the axial deformation and radial deformation of the soil sample in the deformation process and determine the local stress–strain curve and three-dimensional displacement field diagram of the soil sample. The test shows that the new method can clearly determine the peak value and inflection point of the stress–strain curve in the middle region of soil samples, enabling it to reflect the shear change process of the soil sample more accurately. In addition, the displacement field can be used to directly observe the formation, development and penetration process of the shear band in soil samples.

Experimental Study on the Mechanical Properties of Diatomite-Modified Coastal Cement Soil.

Diatomite is a non-metallic mineral resource rich in SiO2, which can be used to modify coastal cement soil. In order to explore the mechanical modification effect of diatomite on coastal cement soil at the age of 7 days, based on coastal cement soil with cement content of 5% (mass fraction), diatomite of 0%, 5%, 10%, 15% and 20% (mass fraction) was mixed for modification. Through the unconfined compressive strength test, the triaxial unconsolidated undrained test, backscattered electron imaging (BSE), and energy-dispersive spectroscopy (EDS) technology, the influence of diatomite content and confining pressure on the peak strength of modified coastal cement soil was explored. The empirical formula between the peak strength of the DE specimen and the content of diatomite and confining pressure was established by curve fitting, and the fitting effect was ideal. When diatomite was mixed with coastal cement soil, the optimal dosage of diatomite was 5% from the perspective of mechanical properties and economic benefits of the maximum growth rate of compression and shear. The unconfined compressive strength test showed that the peak strength and elastic modulus of the modified coastal cement soil with 5% diatomite content were 37% and 57% higher than those of cement soil, respectively. The triaxial unconsolidated undrained test showed that the internal friction angle of the modified coastal cement soil was stable at about 30°, and cohesion of DE-5, DE-10, DE-15, and DE-20 increased by 28%, 48%, 78%, and 97%, respectively, compared to cement soil. The microscopic test found that the pore distribution of modified coastal cement soil is closely related to the strength change. The results show that the addition of diatomite can effectively improve the mechanical properties of soil-cement.

Mapping shear strength and compressibility of soft soils with artificial neural networks

Soft soils are widely distributed in the Guangdong-Hong Kong-Macao Greater Bay Area of China. The soft soils are featured with large water content, high compressibility and low permeability, posing great challenges in dealing with bearing capacity and foundation settlements. Extensive laboratory tests have to be conducted to determine parameters for shear strength and compressibility properties of soft soils. This is really time consuming and costly. In addition, sample disturbance and lab testing error are also unavoidable. The aim of this study is to develop a simple, efficient while satisfactorily accurate tool for prompt assessments of parameters for shear strength and compressibility of soft soils. The artificial neural network (ANN) technique is employed to reach this goal. A large database is first presented for measured physical and mechanical parameters of soft soils sampled from a core city in the Greater Bay Area. The data are obtained from six types of geotechnical laboratory tests, including direct shear test, consolidation test, unconsolidated undrained test, total stress consolidated undrained test, effective stress consolidated undrained test and compression test. Then, the ANN is applied to map the shear strength and compressibility properties of the soft soil from its physical parameters. The analytical forms of the ANN models are derived and presented to enhance their practical value. Next, the accuracies of the six ANN models are evaluated using model bias statistics where model bias is the ratio of measured to predicted value. The evaluation results showed that the ANN models are practically unbiased on average and the dispersions in prediction accuracy are low. Furthermore, the probability distributions of the model biases are characterized. This study helps saving time and cost of geotechnical investigation for soft soils in the area.

Study on Triaxial Mechanical Properties and Micro Mechanism of Fly Ash Reinforced Cement Calcareous Sand

In order to study the mechanical properties and micro-mechanism of industrial waste fly ash-reinforced cement calcareous sand (FCS), the triaxial unconsolidated undrained (UU) test and scanning electron microscope tests (SEM) were carried out on it. The results of UU test show that the peak stress and energy dissipation of the FCS sample first increase and then decrease with the increase in fly ash content. Fly ash enhances the cement calcareous sand by increasing both the cohesion and internal friction angle, and adding 10% content of fly ash gives the largest values. The SEM test results shows that the hydration products of cement and fly ash filled the pores and cracks on the surface of the calcareous sand, which increased the compactness and structure of the FCS samples. The porosity of cement calcareous sand can be reduced from 27.6% to 12.8% by adding 10% fly ash. A brittleness evaluation index based on energy dissipation is proposed to quantitatively characterize the brittleness of FCS samples. The results show that when the content of fly ash is 5%, the brittleness of FCS samples is the lowest. This study shows that the mechanical properties of cement calcareous sand can be effectively enhanced by adding the appropriate amount of fly ash.

Artificial Neural Network (ANN) Model for Shear Strength of Soil Prediction

Geotechnical structures, design of embankment, earth and rock fill dam, tunnels, and slope stability require further attention in determining the shear strength of soil and other parameters that govern the result. The shear strength of soil commonly obtained by conducting laboratory testing such as Unconfined Compression Strength (UCS) Test and Unconsolidated Undrained (UU) Test. However, random errors and systematic errors can occur during experimental works and caused the findings imprecise. Besides, the laboratory test also consuming a lot of time and some of them are quite costly. Therefore, soft computational tools are developed to improve the accuracy of the results and time effectively when compared to conventional method. In this study, Artificial Neural Network (ANN) was employed to develop a predictive model to correlate the moisture content (MC), liquid limit (LL), plastic limit (PL), and liquidity index (LI) of cohesive soil with the undrained shear strength of soil. A total of 10 databases was developed by using MATLAB 7.0 - matrix laboratory with 318 of UCS tests and 451 of UU tests which are collected from the verified site investigation (SI) report, respectively. All the SI reports collected were conducted in Sarawak, Malaysia. The datasets were split into ratio of 3:1:1 which is 60:20:20 (training: validation: testing) with one hidden layer and eight hidden neurons. The input parameter of Liquidity index (LI) has shown the highest R-value (regression coefficient) which are 0.926 and 0.904 for UCS and UU model, respectively. In addition, the predictive models were tested and compare with the predicted and observed cohesion obtained from the collected experimental results. In summary, the ANN has the feasibility to be used as a predictive tool in estimating the shear strength of the soil.

Evaluation of Site Variability Effect on the Geotechnical Data and Its Application

Abstract This study focused on evaluating the laboratory measurement errors and site variability due to soil deposition and operator using the following tests: unconsolidated-undrained (UU), Atterberg limits, small direct shear, and California bearing ratio (CBR) tests. Four clay soils with different plasticity indexes (PIs) were tested in the laboratory (PI = 11, 21, 38, 53), in addition to sandy soil and 3 aggregate base materials. Five different operators tested three specimens for each soil type to investigate the effect of operator on testing results. The maximum coefficient of variation (COV) data due to operator were 10.9 %, 7.8 %, 18.2 %, 16.9 %, 19.5 %, and 15.6 % for UU, liquid limit, plastic limit, plasticity index, direct shear, and CBR tests, respectively. The effect of operator and equipment on field testing results was evaluated using 28 cone penetration tests (CPTs) points performed in the same site at different times by two contractors. The spatial variability of CPT data was evaluated for each contactor and both combined. The values of COV for CPT data were different for the two contractors. The average COVs of pile design method and site variability were used to calibrate the Load Resistance Factor Design (LRFD) resistance factor, Φ, which showed high value for lower variability data, and vice versa for high variability data. The operator and equipment variabilities caused Φ to reach 0.24 for CPT data. In addition, the standard penetration test (SPT) and unconfined compressive strength test (qu) were collected from 21 borings and used to evaluate site variability. The value of Φ increased from 0.41, when COV of pile design method was only included, to 0.55, when site variability was included for SPT data. The same scenario was done for qu, in which Φ was increased from 0.34 when including COV of pile design method only to 0.39 when using the average COV of both method and site.

Microscopic and mechanical properties of undisturbed and remoulded red clay from Guiyang, China

Unconsolidated-undrained (UU) tests were conducted to investigate the mechanical and morphological properties of undisturbed and remoulded red clay, with the microscopic characteristics determined by scanning electron microscopy (SEM). The microanalysis showed that the red clay aggregate was granular, curved-slice and thin layered and flower-shaped ellipsoid, with X and Y-type cracks and pores in the undisturbed red clay. Moreover, the contact modes of red clay aggregates were point contact, line contact, surface contact and mosaic contact. In addition, the main microstructure red clay was flocculation, honeycomb and pseudosphere structures. The pores in undisturbed soil were arranged in one direction, with no obvious directionality in remoulded red clay. The pore area, perimeter and maximum length of undisturbed red clay were smaller than those of remoulded red clay, with a larger probability entropy, probability distribution index and fractal dimension of pore distribution of undisturbed red clay than remoulded red clay. UU tests showed that the shear strength of undisturbed red clay was higher than that of remoulded red clay.

The Influence of Freeze-Thaw Cycles on the Mechanical Properties and Parameters of the Duncan-Chang Constitutive Model of Remolded Saline Soil in Nong’an County, Jilin Province, Northeastern China

In seasonally frozen areas, physical and mechanical soil properties change dynamically under the effect of the freeze-thaw cycles (FTCs), which is a problem that cannot be ignored in geotechnical engineering. In order to study the effect of the FTC on the strength and the mechanism of deformation and failure of saline soil, this paper took Nong’an saline soil as the research object. In total, 105 groups of remolded samples with different salt contents (S) after FTCs were examined in unconsolidated-undrained tests. On the basis of the experiment results, the influence of FTCs on the mechanical properties of Nong’an saline soil was analyzed. The failure principal stress difference (σ1 − σ3)f and cohesion (c) were both decreased with FTC. This occurred especially rapidly after the first cycle and became stable between 30 and 60 cycles. The internal friction angle φ increased at first and then decreased. According to experimental data, a modified Duncan-Chang model was established. Compared with the experiment results, this model was reasonable to simulate the stress-strain relationship of Nong’an saline soil. Furthermore, the empirical formulas of Duncan-Chang model parameters were obtained by regression analysis. This provides a theoretical basis for saline–soil foundation and subgrade engineering in seasonal frozen areas.

Analysis of Factors Affecting Performance of Cement-Bentonite Mud Impervious Wall

The triaxial unconsolidated undrained test, unconfined compressive strength test and variable head penetration test were used to study the water-cement ratio (Rwc between 3.85 and 5.88) and water-bentonite ratio (Rwb between 3.85 and 7.14) in different indoor mix ratios. Effect on mechanical properties and permeability of cement-bentonite mud impervious wall. The test results showed that: (1) The unconfined compressive strength of cement-bentonite anti-seepage wall has a double exponential function relationship with water-cement ratio and water-bentonite ratio. (2) When the water-bentonite ratio is constant, the deformation modulus increases with the decrease of water-cement ratio. When the water-cement ratio is constant, the influence of water-bentonite ratio on deformation modulus is not obvious, but too much bentonite will reduce deformation modulus. (3) As the strength of the cut-off wall increases, the modulus of deformation also increases, and there is a good linear relationship between the two. (4) The permeability coefficient of cement-bentonite anti-seepage wall has a double exponential function relationship with water-cement ratio and water-bentonite ratio.

Influence of vertical cylindrical tetrahydrofuran hydrate veins on fine-grained soil behaviour

Over the last 10 years, marine gas hydrate drilling expeditions utilizing advances in pressure coring techniques and imaging have routinely encountered gas hydrates residing in fine-grained sediments. The hydrate typically occurs as fracture-filling, near vertical, veins that displace the sediment, potentially leading to increased sediment strength that may prevent normal consolidation of the sediment thus leading to underconsolidation. Destabilization of this hydrate, through climate change or human activity on the seafloor, may cause dramatic loss of strength of the sediment and pose a significant geohazard. To assess the impact of hydrate veins on sediment behaviour, this paper reports on a series of consolidated (CU) and unconsolidated undrained (UU) triaxial tests carried out on fine-grained soil specimens hosting simplified, vertical, cylindrical tetrahydrofuran (THF) hydrate veins of varying diameters. The results show that increasing hydrate vein diameter significantly increases strength and stiffness, including the development of post-peak strain-softening. The mode of failure of the hydrate veins influenced the specimen strength, but did not affect the specimen stiffness. Hydrate dissolution during CU tests prevented quantitative comparison with UU tests. However, CU test results on the soil specimens containing the largest hydrate vein suggest that increasing lateral confining stresses increase the sediment strength.

Large-scale shallow foundation load tests on soft clay – At the National Field Testing Facility (NFTF), Ballina, NSW, Australia

This paper presents field test data from four instrumented rigid square pad foundations on soft clay that were brought to failure under concentric vertical loading. The test programme comprised two unconsolidated undrained (UU) foundation tests as well as two consolidated undrained (CU) tests. In the latter case the two foundations were preloaded to a proportion of the UU capacity and the soil was allowed to consolidate before being brought to undrained failure. In this paper, the site works and testing procedures are presented along with the load- and time-settlement responses of all four foundations. Horizontal stress and pore pressure data are presented for the two CU tests. The undrained and consolidated undrained load-settlement responses are shown to agree well with theoretical and numerical predictions. Results from the UU tests were the subject of a prediction exercise, summarised in a companion paper presented in this special issue.

Influence of Synthetic and Natural Fibers on Dewatering Rate and Shear Strength of Slurries in Geotextile Tube Applications

This study investigates the effect of fibers on the dewatering time, filter cake properties, and shear strength of filter cakes with fine-grained silty clay. Synthetic nylon fibers with lengths of 6, 12, and 18 mm and one natural jute fiber with an average length of 8 mm were added to slurries with 33 % fines in concentrations of 0.5 % by soil mass. Optimum dose tests for particle flocculation showed that slurries reached a turbidity of 20 NTU with up to 19 % less flocculatant material compared to slurries with no fibers. Pressure filtration tests showed that the dewatering time decreased significantly with both synthetic and jute fibers, but were not dependent on fiber length. However, fall cone tests and unconsolidated undrained tests showed that the increase in shear strength was dependent on fiber length. Increases in shear strength were over 100 % with 12 mm nylon fibers, while filter cakes with 6 and 18 mm nylon fibers increased the shear strength by 43 %. Jute fibers did not show as high of a strength gain as the nylon fibers, but did increase dewatering times by an average of 14–22 % compared to filter cakes with nylon fibers.

On the Utilization of Fly Ash and Cement Mixtures as a Landfill Liner Material

Cement was added to class F type of fly ash in the proportion of 0, 2, 5 and 10 % to study for its suitability as a landfill liner material. Mixtures were compacted to their optimum moisture content (OMC) and maximum dry density (MDD). The results from the consolidation tests showed a relatively lower value of compression index for all the mixtures indicating the settlement due to application of overburden pressure would be small. Hydraulic conductivity of the samples were found to be decreased with the increasing the load. However, none of the mixtures exhibited a hydraulic conductivity value less than 10−9 m/s, a limiting criterion set by various environmental agencies for the material to be used as a landfill liner. However, mixtures of 90 % fly ash + 10 % cement compacted at 5 % wet of OMC-MDD exhibited a hydraulic conductivity value less than 10−9 m/s. On drying, all the mixtures shrunk marginally. The unconsolidated undrained test results indicated that the shear strength parameters increase with increase in the cement content in the mixtures.

Energy Absorption Capacity and Shear Strength Characteristics of Waste Tire Crumbs and Sand Mixtures

The primary objective of the study is to estimate the energy absorption (EA) capacity, brittleness index (ductility) and stiffness characteristics of Sand-Tire Crumb Mixtures (STCM) using direct shear test and Unconsolidated Undrained (UU) triaxial test for the effective reuse of waste tire crumbs as isolation materials. The properties considered include, strength and deformation characteristics of a STCM. A relatively uniform sand and readily available tire crumb grouped into four size has been selected to generate STCM. Experimental studies have been carried out on STCM with constant density of 1.54 g/cc. Stress-strain curve obtained from UU test has been used to estimate EA. The experimental results show that peak strength, EA and stiffness increases with increasing percentage of tire crumbs up to 25% and starts decreasing thereafter. Among the tested tire crumb sizes, crumb size IV provide the maximum EA without compromising on strength compared to other tire crumb sizes.

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.

Properties and Applications of Cement-Treated Sand-Expanded Polystyrene Bead Lightweight Fill

AbstractTo mitigate settlement problems associated with bridge approach embankments over soft soil, a newly-developed lightweight material was proposed in this study. This lightweight material consisted of expanded polystyrene beads, the hydraulic sand from the Yangtze River, and cement. The mechanical properties of the mixed lightweight material were determined through a series of laboratory tests, including standard Proctor tests, unconfined compression tests, California Bearing Ratio (CBR) tests, unconsolidated-undrained tests, and consolidated-undrained tests. The laboratory results showed the favorable properties of the lightweight material and that it can be used as a backfill material in highway embankment projects. A field study was also conducted to verify the performance of the embankment backfilled with this lightweight material, which resulted in a smaller settlement than the embankment backfilled with lime-stabilized soil (with and without any other ground improvement). Sand cone and CBR test...

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.