Unconsolidated Undrained Triaxial Compression Tests Research Articles

Rubber bark dust-zeolite composite improved mechanic strength of soft paddy soil through improved microstructure

<p>Soft paddy soils are not a stable soil structure that leads to the decline of rice production in Kedah, Malaysia. The soil had high compressibility and water content, and low soil strength thus the agricultural machines could not be operated above this soil. Therefore, this study was conducted to improve the mechanical strength of soft soils in paddy fields using an organic amendment. The organic amendment used in this study was made from amended materials comprising clinoptilolite, kieserite, humic acid, and rubber bark dust. The study was carried out in the paddy field area of Alor Pudak district, Kedah, Malaysia, and it was divided into five treatments of amendment dose, i.e: 0 kg (control or P0), 125 kg (P1), 250 kg (P2), 375 kg (P3) and 500 kg (P4) with each plot size about 0.20 ha. The soil samples were then analyzed using X-ray diffraction (XRD), scanning electron microscope (SEM), and the unconsolidated undrained triaxial compression test (UU-test) to characterize their amended properties. The XRD results clearly exhibited changes in the mineralogical composition of all treated plots with an increasing smectite content (1200 to 1300 intensity). Furthermore, the SEM results showed that clay particles in the treated plots have been flocculated to form close-knit, more stable soil structures. After the organic amendment application, the mechanical strength of the treated plots increased to an optimum level (50 kPa in P2) for resisting mechanical pressure from agricultural machinery. Overall, this study of the efficacy of organic amendment offers new insight into a soft paddy soil remediation method that is more effective and economical than the conventional method.</p>

Effect of phytoremediation on the shear strength characteristics of silty clayey sand

Pollution of the environment by crude oil is a global problem that changes the geotechnical properties of soil, including its shear strength. In this study, the effects of phytoremediation of soil contaminated with crude oil have been investigated using Ophiopogon japonicus and Platycladus orientalis. The results of phytoremediation were tested at 30 and 60 days of treatment. The results were compared with samples that had not undergone phytoremediation. The soil shear strength parameters were determined using unconsolidated undrained triaxial compression tests at confining pressures of 50, 100, and 150 kPa. The results showed that an increase in the crude oil content led to a decrease in deviatoric stress at failure associated to an axial strain level of 20%. The deviatoric stress in the treated samples was about 15% higher than the samples without phytoremediation. The internal friction angle and cohesion decreased as the crude oil content increased. This decrease was less in the remediated samples, especially those exposed to P. orientalis. The results of the triaxial compression tests revealed the positive effect of phytoremediation in reducing the negative effects of crude oil on the soil shear strength characteristics. SEM images of the contaminated soil samples showed that soil flocculation initially increased with an increase in the crude oil content and time and then decreased subsequent to the application of phytoremediation.

Performance of Microfine Cement Grouted Sands Under Quick Loading Conditions

An experimental investigation was conducted to evaluate the influence of factors pertinent to the suspension and the sand on the effectiveness of microfine cement grouts under quick loading conditions, that is, conditions, where the grouted soil mass is loaded at a rate which is much faster than the rate of pore water pressure dissipation and total stress behavior may be of interest. Unconfined compression and unconsolidated-undrained triaxial compression tests were conducted on grouted sand specimens obtained by injecting suspensions of 12 cements with three water to cement (W/C) ratios into four sands with different grain sizes. A Mohr–Coulomb type linear failure criterion describes satisfactorily the shear strength behavior of cement grouted sands in total stress terms. The values of the activated shear strength parameters generally increase with increasing axial deformation during loading. Grouting with suspensions having W/C = 1 yields unconfined compression strength of grouted sands up to 9 MPa, adds cohesion to the sands reaching 1.7 MPa, increases by 6–14 times the initial modulus of elasticity, reduces by 5–10 times the failure deformation and may increase up to 20% the angle of internal friction of the sands. The stress–strain–strength behavior of sands grouted with suspensions having W/C = 1 is similar to that of cement suspension sediments with the same W/C ratio, whereas the behavior of sands grouted with suspensions having W/C = 3 is similar to that of the clean sands.

Fundamental mechanical behavior of CMMOSC-S-C composite stabilized marine soft clay

This study aims to address the fundamental mechanical behavior of soft clay stabilized by the composite of citric-acid-modified magnesium oxysulfate cement, silica fume, and clinker (CMMOSC-S-C composite) at different initial soil-water contents (w), amounts of stabilizing agent (Wg), and curing time (T). X-ray diffraction analysis and Scanning electron microscopy indicate that the main products of the curing reaction can be summarized as 5·1·7 phase, gel, dolomite, pyrophyllite, and minor amounts of CaO and MgO, which could be attributed to the hydration, carbonation, ion exchange, and filling. The unconfined compressive strength tests, one-dimensional consolidation tests and unconsolidated undrained triaxial compression tests show that the unconfined compressive strengths (qu), secant Young's modulus (E50), and shear strength parameters (c and φ) are positively dependent on Wg and T. However, these parameters demonstrate a negative relationship with w. The compression efficient (a2–4) is positively and negatively related to w, Wg, and T. In view of these test results, empirical relationships between the fundamental mechanical parameters of CMMOSC-S-C composite stabilized soft clay and key effect factors (w, Wg, T) are developed to predict the qu, E50, a2–4, c, and φ values at any w, Wg, and T.

Performance of silty sand reinforced with aqueous solution of polyvinyl alcohol subjected to freeze-thaw cycles

This study aimed to examine the change in the mechanical properties of the silty sand reinforced with an aqueous solution of polyvinyl alcohol (PVA) subjected to freeze-thaw cycles. A series of unconsolidated undrained triaxial compression tests were conducted to determine the compressive strength, resilient modulus, cohesion, and internal friction angle. Experimental samples were prepared by adding aqueous solutions of different PVA concentrations (5%, 7.5%, and 10% of the weight of the water) into silty sand. The numbers of freeze-thaw cycle (0, 5, 10, 15, 20) were realized in a closed system. A comparison of reinforced and unreinforced samples of silty sand showed that the addition of an aqueous solution of PVA can significantly affect the mechanical properties of silty sand. It was experimentally proven that the positive impact on the mechanical properties of soil increases with increasing concentration of PVA in the solution and with increasing number of freeze-thaw cycle. When a 10% aqueous solution of PVA was added into the soil, the strength of the samples after 20 freeze-thaw cycles increased by 8.5% compared with the strength before freezing. The resilient modulus of unreinforced samples after 20 cycles decreased by 16.1%, while that of reinforced samples after 20 cycles increased by 30.2%. According to the results, the reinforcing additive has a significant effect on the cohesions of soil both before and after the freezing process.

Appraisal of Geotechnical Characteristics of Ormara Soil, Baluchistan, Pakistan

Ormara is located 240 km west of Karachi which is a coastal and port city (25° 16' 29N, 64° 35' 10E) ofPakistan. Present study evaluates engineering properties of soils of Ormara for future construction plans and possibleexpansions in the area. Fifty bore holes were done in study area at depths of 20m, 40m and some (10 bore holes) were60m deep. The study area was divided into three major zones i.e. Foot hills, on-shore and off-shore. Groundwater wasencountered at depths of 2.75m on onshore and offshore zones and at 3.65m depth in foothill zone. Laboratory testingi.e. moisture content (12 to 38 %), liquid limit (from 26 to 34), plasticity index (10 to 18) of soil samples indicate thatsoils are low plastic to moderate plastic in nature. Soil samples of granular soils indicate angles of internal friction (ø)varying from 260- 36ºin upper sand layers while 260 to 30º in lower silt layers (encountered after the clay layer) andCohesion ranges 0 to 0.04kg/cm2 in all three zones. Further, unconsolidated undrained triaxial compression tests on aclayey soil sample indicated an undrained cohesion value of 28 kPa. Density values ranges from 1.6 to 2.05gm/cm3.Consolidation (Cv = 0.20 to 0.40 cm2/minute, Cc = 0.149 to 0.17) has been calculated for clay layer. Chemical testscarried out on soil samples indicated that soil and water both are reactive aggressively and may cause corrosion to steeland concrete disintegration.

Appraisal of Geotechnical Characteristics of Ormara Soil, Baluchistan, Pakistan

Ormara is located 240 km west of Karachi which is a coastal and port city (25° 16' 29N, 64° 35' 10E) ofPakistan. Present study evaluates engineering properties of soils of Ormara for future construction plans and possibleexpansions in the area. Fifty bore holes were done in study area at depths of 20m, 40m and some (10 bore holes) were60m deep. The study area was divided into three major zones i.e. Foot hills, on-shore and off-shore. Groundwater wasencountered at depths of 2.75m on onshore and offshore zones and at 3.65m depth in foothill zone. Laboratory testingi.e. moisture content (12 to 38 %), liquid limit (from 26 to 34), plasticity index (10 to 18) of soil samples indicate thatsoils are low plastic to moderate plastic in nature. Soil samples of granular soils indicate angles of internal friction (ø)varying from 260- 36ºin upper sand layers while 260 to 30º in lower silt layers (encountered after the clay layer) andCohesion ranges 0 to 0.04kg/cm2 in all three zones. Further, unconsolidated undrained triaxial compression tests on aclayey soil sample indicated an undrained cohesion value of 28 kPa. Density values ranges from 1.6 to 2.05gm/cm3.Consolidation (Cv = 0.20 to 0.40 cm2/minute, Cc = 0.149 to 0.17) has been calculated for clay layer. Chemical testscarried out on soil samples indicated that soil and water both are reactive aggressively and may cause corrosion to steeland concrete disintegration.

Influence of Rice Husk Ash on the Swelling and Strength Characteristics of Expansive Soil

Black cotton soils are expansive soils which exhibit high swelling and shrinking when exposed to changes in moisture content. Durability of structure resting on expansive clays is always in question due to swelling/shrinkage of such clays. The performance of paved and unpaved road pavements constructed over such expansive soil subgrades is often poor and in most cases show cracking, potholes, wheel path rutting, serious differential settlements and heaving in various locations. In addition to problems related to expansive soils another problem arising in all developing and developed countries is due to the wastes generated from various activities which not only cause severe environmental problems, but also occupy a huge area of land for its disposal. Rice husk ash (RHA) is one such wastes produced from the burning of rice husk and if used as an additive to expansive soil shall not only significantly reduce the swelling/shrinkage characteristics of such soils but also solve the environmental and disposal problems being created by the ash. The paper presents the results of an experimental investigation conducted to study the effect of RHA on swelling, shrinkage and compaction characteristics of the expansive soil. The RHA was mixed with expansive soil in varying proportions. Free swell index, Atterberg limits, light compaction tests, unconsolidated undrained triaxial compression tests, California bearing ratio tests were carried out with specimens containing varying percentages of RHA. It is concluded that addition of RHA in appropriate proportions not only reduces the swelling and shrinkage behavior of expansive soil significantly but also makes it more stable.

A Statement on the Stress Field of Pipe-Soil Structure

Abstract In this study, stress analyses of buried flexible pipes were carried out using a newly designed experimental setup for the method of photoelasticity. Several universal tests using a Dynamical Mechanical Analyzer and the parallel plate test in a polariscope were performed to obtain the mechanical and optical properties of a ring that is made from a thin plate of optically sensitive Araldite, which modeled the pipe cross section. Additionally, the mechanical properties of soil used in the experiment have been determined by unconsolidated-undrained triaxial compression tests and specifically developed photoelastic tests. This test method, which provided satisfactory results for estimating the coefficient of lateral earth pressure, can be used as a fast method to obtain this coefficient for general cases. From the buried ring experiment, the distributions of the circumferential stresses along the inner surface and the absolute value of the Tresca stresses along the outer surface of the ring were calculated by some precise photoelastic measurements. Comparing the results with those from the parallel plate test, the lack of design criteria were clarified. The buried ring experiment clarified that the pipe-soil structure keeps the field of elastic stress-strain that is due to a loading until a higher load is applied. The distributions of stresses were compared to those obtained from the finite element analysis of a half ring under the loads determined by Michell’s formulation.

Self-boring in situ shear pressuremeter testing of clay from Dalian Bay, China

A new geotechnical in situ test technique using a self-boring in situ shear pressuremeter (SBISP) is developed to evaluate the initial state (horizontal at rest pressure Ph), deformation (yield pressure Pf and pressuremeter modulus EP) and strength characteristics (cohesion C and internal friction angle φ) of soil. The SBISP possesses a self-boring drilling functionality that can greatly reduce the disturbance of the tested soil. The multistage compound loading method, which applies normal stress incrementally to the soil in the test hole while repeatedly applying shear stress, was adopted.Relying on the investigation of the cross-sea traffic engineering of Dalian Bay, three sites in the sea area of Dalian Bay were selected for SBISP testing of clay. The field vane shear test (FVT), pressuremeter test (PMT) and unconsolidated-undrained triaxial compression test (UU) were also evaluated at each testing site to compare with the SBISP test. The results measured by the SBISP and comparative tests (FVT, PMT and UU) showed the same trends with an increase in depth and change in strata. The differences in the test results were discussed in terms of the disturbance effect, anisotropy of undrained shear strength, differences in loading methods and instrumentation used in the different tests. A comparison between the results measured by the SBISP and in comparative tests shows that the engineering characteristics of Dalian Bay clay evaluated by SBISP are fairly accurate and can provide reference for the investigation and design of the cross-sea traffic engineering of Dalian Bay.

Performance of clay soil reinforced with fibers subjected to freeze-thaw cycles

In order to study the strength properties of the weak soil reinforced by fibers, a series of unconsolidated undrained triaxial compression tests of fine-grained soil subjected to freeze-thaw cycles were conducted. Experimental samples were made by adding various contents of basalt and polypropylene fibers (0, 0.25, 0.5, 0.75% of the dry weight of the soil) into clay soil; freeze-thaw cycles were performed in a closed system (0, 2, 5, 8, 10, 15 cycles). Reinforcing fibers of circular cross-section were employed. A decrease in the strength of the test samples was observed with an increase in the freeze-thaw cycle, by carrying out triaxial compression experiments. A comparison of the strength properties of clay soil between unreinforced samples and reinforced ones with different fibers was made. The greatest decrease in the strength of clay was observed in samples after 15 freeze-thaw cycles, but it was noted that the using of fibers helps to prevent a decrease in the strength of clay subjected to the freeze-thaw cycle. After 15 freeze-thaw cycles, the strength of all unreinforced and fiber-reinforced samples decreases approximately by 30–35%. When reinforcing 0.75% with polypropylene fibers, the strength increases by 70%. Inclusion of 0.75% basalt fiber increases the strength by 41.2% before freezing and by 27.1% after the 15th cycle. Cohesion of unreinforced soil after the 15th cycle is reduced from 56.9% of unreinforced soil to 50.4% with reinforcement 0.25%, up to 54.4% at 0.5% and up to 54.0% with reinforcement 0.75% basalt fiber. The resilient modulus of all samples decreases with increasing freeze-thaw cycles, however, samples which were reinforced with fiber showed an increase in the resilient modulus as compared with not reinforced samples both before and after freezing-thawing.

Shear strength of purple soil bunds under different soil water contents and dry densities: A case study in the Three Gorges Reservoir Area, China

Purple soil bunds are embankments constructed along the contour on purple soil sloping farmlands, and play a key role in controlling soil erosion. The soil shear strength makes a significant influence to the bund stability; however, few reports have documented how purple soil shear strength responds to the soil physical properties. The main goal of the present study was to determine how indicators of soil shear strength vary with the soil water content and dry density. In this study, we collected soil samples from 3 purple soil bunds in Zhong County, in the Three Gorges Reservoir Area in China, and performed an unconsolidated undrained triaxial compression test to study the soil shear strength in terms of the cohesion (c), internal friction angle (φ), and the principal stress difference (σ1–σ3). The test results show that when the dry density was constant and the soil water content increased, the soil cohesion increased and then decreased, and the results fitted to a quadratic curve. As the soil water content increased, the internal friction angle of the soil bunds decreased and displayed a first-order exponential decay. As the soil water content increased and the confining pressure remained constant, the principal stress difference decreased rapidly. When the soil water content was constant and the dry density increased, the soil cohesion, internal friction angle, and the total principal stress difference increased, although at different rates. In general, the water content had a greater effect on the cohesion, internal friction angle, and the principal stress difference than the dry density, but there were little or no interaction between water content and dry density. Furthermore, except when the water content was 6%, the stress–strain characteristics were similar across the range of water contents. For a low water content, fixed confining pressure, and an increasing dry density, the curves gradually changed from the hardening type to the weak hardening type and then to the softening type. In most cases the curves corresponded with the hardening type as the confining pressure increased.

Efficient solution algorithms for multiaxial probabilistic elasto‐plastic constitutive simulations of soils

SummaryA Fokker‐Planck‐Kolmogorov (FPK) equation approach has recently been developed to probabilistically solve any elastic‐plastic constitutive equation with uncertain material parameters by transforming the nonlinear, stochastic constitutive rate equation into a linear, deterministic partial differential equation (PDE) and thereby simplifying the numerical solution process. For an uniaxial problem, conventional numerical techniques, such as the finite difference or finite element methods, may be used to solve the resulting univariate FPK PDE. However, for a multiaxial problem, an efficient algorithm is necessary for tractability of the numerical solution of the multivariate FPK PDE. In this paper, computationally efficient algorithms, based on a Fourier spectral approach, are presented for solving FPK PDEs in (stress) space and (pseudo) time, having space‐independent but time‐dependent coefficients and both space‐ and time‐dependent coefficients, that commonly arise in probabilistic elasto‐plasticity. The algorithms are illustrated by probabilistically simulating 2 common laboratory constitutive experiments in geotechnical engineering, namely, the unconfined compression test and the unconsolidated undrained triaxial compression test.

A Simple Unconsolidated Undrained Triaxial Compression Test Emulator

An unconsolidated undrained (UU) test is one type of triaxial compression tests based on the nature of loading and drainage conditions. In order to imitate the UU triaxial compression tests, a UU triaxial emulator with a graphical user interface (GUI) was developed. It has 5 deformation sensors (4 radial deformations and one vertical deformation) and one axial pressure sensor. In addition, other inputs of the emulator are the cell pressure, the height of sample, and the diameter of sample, which are provided by the user. The emulator also facilitates the analysis and storage of measurement data. Deformation data fed to the emulator were obtained from real measurements [H. Nawir, Viscous effects on yielding characteristics of sand in triaxial compression, Dissertation, Civil Eng. Dept., The University of Tokyo, 2002]. Using the measurement data, the stress vs radial strain, stress vs vertical strain, and Mohr-Coulomb circle curves were obtained and displayed by the emulator.

Laboratory Simulation of Field Sampling: Comparison With Ideal Sampling and Field Data

Tube sampling disturbance effects are investigated in this paper based on the results of constant rate of strain consolidation tests and unconsolidated undrained triaxial compression tests conducted on resedimented Boston blue clay sampled in the laboratory using a specifically designed device and employing various tubes differing in size, diameter to thickness ratio, and tip geometry. The effects of tube geometry were assessed based on comparison of the residual effective stresses, the reconsolidation strains, the undrained strength, and the one-dimensional drained compression behavior. Increasing degradation in the engineering properties was observed with decreasing diameter to thickness ratio (B∕t) , and the negative impact of a blunt tip geometry could not be compensated for even by a substantial increase in B∕t . Comparison of these results to those obtained from triaxial element tests in which disturbance was simulated according to the ideal sampling approach (ISA), indicated that tube sampling is a...

A study on the subsoil of the Tower of Pisa based on results from standard and high-quality samples

In this paper, an updated geotechnical characterization of the soils underlying the leaning Tower of Pisa is presented, based on results from a recent experimental investigation as well as on results from previous investigations. Careful analysis of the cone penetration tests carried out in the past have permitted a detailed distinction between the cohesive and the cohesionless portions of the upper deposits. The mechanical behaviour of the soils has been investigated through a large number of laboratory tests performed on samples retrieved with standard tube samplers and with a large diameter thin-walled sampler. The mechanical behaviour of the soft upper clayey deposit is shown to be rather sensitive to sampling disturbance; the large diameter sampler allowed for the observation of a high compressibility that had not been evidenced in the previous investigations. A comprehensive set of soil parameters is derived for the clay strata. Normalized triaxial stress paths describe a state boundary surface similar to that predicted by the simple Modified Cam Clay model fitted on the experimental data. Also, the undrained shear strength predicted by the model is shown to be in good agreement with the experimental results obtained from standard unconsolidated undrained triaxial compression tests. Values of the small-strain shear modulus determined experimentally compare satisfactorily with those given by an empirical relationship. A profile for the small-strain shear modulus is proposed accordingly.Key words: case history, clays, compressibility, in situ testing, laboratory testing, sampling.

A study on the subsoil of the Tower of Pisa based on results from standard and high-quality samples

In this paper, an updated geotechnical characterization of the soils underlying the leaning Tower of Pisa is presented, based on results from a recent experimental investigation as well as on results from previous investigations. Careful analysis of the cone penetration tests carried out in the past have permitted a detailed distinction between the cohesive and the cohesionless portions of the upper deposits. The mechanical behaviour of the soils has been investigated through a large number of laboratory tests performed on samples retrieved with standard tube samplers and with a large diameter thin-walled sampler. The mechanical behaviour of the soft upper clayey deposit is shown to be rather sensitive to sampling disturbance; the large diameter sampler allowed for the observation of a high compressibility that had not been evidenced in the previous investigations. A comprehensive set of soil parameters is derived for the clay strata. Normalized triaxial stress paths describe a state boundary surface similar to that predicted by the simple Modified Cam Clay model fitted on the experimental data. Also, the undrained shear strength predicted by the model is shown to be in good agreement with the experimental results obtained from standard unconsolidated undrained triaxial compression tests. Values of the small-strain shear modulus determined experimentally compare satisfactorily with those given by an empirical relationship. A profile for the small-strain shear modulus is proposed accordingly.Key words: case history, clays, compressibility, in situ testing, laboratory testing, sampling.

Prevention of Sample Deterioration

Abstract A series of unconsolidated undrained triaxial compression tests was carried out on specimens of reconstituted kaolin to determine the effects on modulus and strength of two different methods of sample storage after unloading. These results are compared with the values obtained when no unloading occurs, and when unloading is followed immediately by testing. It is seen that use of a simple sample compressor to restore the in-situ vertical effective stress in the specimen is very successful in reducing the deterioration of samples between unloading and testing.

A Method for Correcting Undrained Shear Strength for Sample Disturbance

In order to find out an appropriate method for correcting the undrained shear strength for sample disturbance, a series of triaxial compression tests is performed on mixed soil samples having wide range of plasticity index. Conditions of the ideal and perfect samples are brought to by the K 0 consolidation and the shear stress release after the consolidation, then further disturbance is given to specimens by cyclic loadings. Model sampling is made for obtaining the “undisturbed” samples, and unconsolidated undrained triaxial compression tests are performed on these “undisturbed” samples. In these compression tests, the pore pressure is measured for assessing the residual effective stress in the ideal, perfect and “undisturbed” samples respectively. Results of the compression tests show that the pore pressure can increase on shear stress release for soils of low plasticity index, and that the effect of sample disturbance is similar to the effect caused by cyclic loadings. By combining the concepts of strength reduction due to rebound and reduction in effective stress due to sample disturbance, a comprehensive way for correcting the measured value of the undrained shear strength for sample disturbance is proposed.

Analyses of Waco Dam Slide

The investigation was performed to study the factors influencing the undrained shear strength of Pepper shale, a stiff-fissured clay, and to apply the results of the study to the analysis of a slide which occurred during construction of Waco Dam, founded on the Pepper shale. Unconsolidated-undrained triaxial compression tests were performed on undisturbed samples of Pepper shale to investigate the influence of anisotropy, sustained loading and specimen size. The study showed that the Pepper shale is highly anisotropic, possessing a much lower strength along a horizontal plane than along other planes. The influence of sustained loading and of specimen size was found to be negligible. Analyses showed that the assumption of isotropic shear strengths, measured on vertical specimens, indicated stable conditions, while the use of anisotropic shear strengths produced results in agreement with the observed failure and pronounced noncircular failure surface.