Laboratory Oedometer Tests Research Articles

A case study on the variability of the coefficient of consolidation and its design reliability

The consolidation characteristics of cohesive soils are estimated using established relationships between the coefficient of consolidation (cv) and index tests, as well as laboratory oedometer tests. While the design cv is preferred from the field dissipation tests, the conversion from a horizontal to vertical value needs to be considered. A trial load was used to verify the consolidation parameters during a Queensland Road upgrade, which involved both road widening and raising of the existing embankments over compressible soils. Construction was done in 4 stages, and with preloading and surcharging in selected areas. Settlement monitoring and Asaoka plots were used to validate the design, and “moderately conservative” design values were adopted. This case study is used to show the large variability of the cv by the various test methods. While 99% of the site settlement was within the magnitude and time predicted during design, a 25 m length was not consistent with the data and performance of the rest of this site within the flood plain. The back-calculated cv was below the lowest test value and even data from nearby settlement plate monitoring from adjacent stages. In situ tests were located within 25m of this unconforming area and given that stratigraphy was consistent then the cv value adopted may not be representative. The lessons learnt show the various verification and validation process required to envelope risks, but all conditions with a “moderately conservative” design may not be covered.

Assessment of the coefficient of consolidation with Queensland data

Established relationships between the coefficient of consolidation (cv) and index tests are used during both preliminary design and as a cross check during detailed design. The laboratory oedometer test provides compressibility parameters and a lower bound of cv, while the coefficients of consolidation are preferred from the field dissipation tests. However, cv is dependent on the method used to determine its value, stress level, and over-consolidation ratio. In practice, the coefficient of consolidation values obtained from dissipation tests are used to predict settlement time, while oedometer tests are useful in obtaining the parameter required to predict the magnitude of settlement. However, dissipation tests measure the horizontal coefficient of consolidation (ch) which needs to be related back to the vertical value. These standard approaches are discussed using test data from Queensland sites. Inconsistencies in correlations are used to show that design should consider the wide variability in interpretations that can occur, and correlations of cv with index tests should not be used in detailed design. Additionally, the cv values obtained from oedometer testing is a poor predictor of time for consolidation. This could also be due to the size of samples being not large enough for the soil structure. Monitoring data from construction sites are used to assess a “moderately” conservative design value from dissipation and lab tests.

Relevance of finite element analysis to simulate oedometer test for estimating the compressibility of soil

One-dimensional consolidation behavior of soil is usually evaluated by the conventional laboratory oedometer test, which is a time-consuming test process. Several researchers have focused on to correlate compressibility with various index properties in terms of single and multiple regressions. However, those correlations are not generalized and have some limitations. The main objective of this paper has been to simulate the compressibility behavior of soil with laboratory experimental data using three-dimensional (3D) finite-element (FE) model in PLAXIS-3D. This analysis is performed assuming the material behavior as linear elastic perfectly-plastic Mohr-Coulomb (MC) model. Furthermore, FE simulations were compared with the laboratory test results as well as existing empirical equations to verify the outputs of the numerical analyses. It has been noticed that, the empirical equations suggested in previous studies are found to have uncertainties (−80 to +374% deviation) in estimating compression index and simulation results by the proposed model are reliable (+1.92 to +12.03% deviation) to the laboratory test values.

Method to Determine the Constitutive Permeability Parameters of Non-Linear Consolidation Models by Means of the Oedometer Test

This paper presents an easy-to-apply methodology that allows obtaining the permeability index and the initial hydraulic conductivity of clayey soils, basic constitutive parameters in non-linear models of consolidation, based on the laboratory oedometer test. For this, the data of the void ratio, compressibility index and characteristic consolidation time are taken from the test and, as an inverse problem, the constitutive permeability parameters sought are determined by applying the universal solutions of the characteristic time for a general non-linear consolidation model with constitutive relations void ratio-effective soil stress and hydraulic conductivity-void ratio of logarithmic type. The application protocol of the inverse problem is described in detail and illustrated by a series of applications carried out on real laboratory data belonging to two different soils. The influence that errors in laboratory parameter measurements can have on the final values of the permeability index and initial hydraulic conductivity is studied, showing the maximum deviations that may appear and, by last, the precision of the results obtained.

A FEM analysis of the settlement of a tall building situated on loess subsoil

Abstract In order to correctly model the behaviour of a building under load, it is necessary to take into account the displacement of the subsoil under the foundations. The subsoil is a material with typically non-linear behaviour. This paper presents an example of the modelling of a tall, 14-storey, building located in Lublin. The building was constructed on loess subsoil, with the use of a base slab. The subsoil lying directly beneath the foundations was described using the Modified Cam-Clay model, while the linear elastic perfectly plastic model with the Coulomb-Mohr failure criterion was used for the deeper subsoil. The parameters of the subsoil model were derived on the basis of the results of CPT soundings and laboratory oedometer tests. In numerical FEM analyses, the floors of the building were added in subsequent calculation steps, simulating the actual process of building construction. The results of the calculations involved the displacements taken in the subsequent calculation steps, which were compared with the displacements of 14 geodetic benchmarks placed in the slab.

Multiple Regression and ANN ( MLP) Model for Predicting Swelling index of Ramadi Cohesive Soil

The response of expansive soils in the form of swelling and shrinkage due to changes in water content is frequently expressed as heaving and settling of lightly loaded structures such as roads, buildings, and canal linings. Compression and/or swelling indices are used for the calculation of the consolidation settlement of fine grained soils. They are conventionally determined by laboratory oedometer tests. Because of the time and expense involved in performing consolidation tests, it is often desirable to obtain approximate values of swelling index, Cs by using other soil properties which are more easily determined. A database consisting of 102 consolidation tests from different parts of Ramadi city were compiled, identified, and used to conduct and utilized a statistical study to estimate suitable relations to determine the swelling index. this study develops the artificial neural networks based multi-layer perceptron, ANN-MLP and multiple regression, MR models. Neural model offers significant improvements in prediction accuracy of the statistical models.

Improving the Stability of the Inflatable Soil of Diamniadio by Using Typha Australis in Order to Value It in Partitioning Wall

The construction industry in Senegal is experiencing an upsurge in the development of residential housing units and administrative buildings within the new Diamniadio municipality, an area located just about 35 km from the capital city of Dakar. Laboratory oedometer or expansive-index tests, however, show poor density and compromised shear strength in the soil samples within the area -posing serious construction problems due to significant volume changes (swellings) that occur when subjected to moisture, thus, bringing into question the structural performance integrity of the soil, and the financial implications of substitute soil types used to compensate for its poor tensile strength. By way, the companies collect the soil of this location (Diamniadio) and throw it to make pile or micro-pile (pious) for their structures. This article demonstrates how we can value the soil of Diamniadio and the Typha Australis in residential building with a reasonable cost. Typha Australis is a plant generally luxuriant within the northern and central belts of Senegal but also known for its negative ecological impacts on the agricultural production of rice. The valorisation of the soil of Diamniadio will pass by the ability to increase its stability or to decrease its shrinkage/swelling rate. When we achieve it, the soil associate with Typha Australis will be used for small bricks which can be useful for partition wall and so the soil will not be ever thrown as a non-useful material. Tests results of soil specimens extracted from the site show a shrinkage rate of 29.19% with estimated cracking depths of 3.5 cm. But by adding gradually Typha Australis, the shrinkage rate will pass from 29.19% to 5.13% with the material treats with 10% by mass of Typha Australis. Moreover, the crackings in the cylindrical specimen disappear. That shows the increase of the stability; thus the composition will be used for building bricks. However, the densities will also be affected by the presence of Typha Australis. The density is decreased from 2032.28 Kg/m3 for the soil without Typha Australis to 937 Kg/m3 for the one with 10% of Typha Australis.

Estimation of preconsolidation stress of clays from piezocone by means of high-quality calibration data

An extensive database of high-quality piezocone (CPTU) and laboratory oedometer test data on onshore and offshore clays worldwide has been established. The database covers a wide range of index parameters and overconsolidation ratios (OCR) in the range 1 to 5. The purpose is to derive general correlations to model preconsolidation stress in clays from CPTU data based on high-quality laboratory data. Several studies have already discussed such correlations for different clay types, where the preconsolidation stress is defined as a function of the cone resistance and/or the pore pressure measured in CPTU tests. Often, these correlations are characterized by high uncertainty, mainly because of the sample quality of the laboratory data. New correlations are proposed based on the new database. These correlations are meant to be used for preliminary assessment of preconsolidation stress in the absence of laboratory data or as a comparison tool when limited test data is available.

Settlement prediction of gypsum sludge based on different test methods

AbstractPaper compares the laboratory and filed tests results, obtained at the red gypsum sludge impoundment Za Travnik, permanently covered with water. Tests were carried out in order to predict the long term sludge settlements below the dry filter cake fill above it. A good prediction of settlements is important to prevent water pounding on final vegetation cover. Settlements were calculated based on field tests results and from laboratory oedometer tests with and without creep. Comparison of calculated and measured settlements show that secondary consolidation (creep) plays an important role in settlement forecast.

Expansive soil stabilised by calcium carbide residue–fly ash columns

The volumetric changes in expansive soils due to variations of seasonal moisture are the cause of many problems in structures. This paper reports laboratory oedometer test results performed on expansive soil stabilised by calcium carbide residue–fly ash (CCR–FA) columns with different percentages of CCR and FA, on seven columns of different orientations and diameters. A significant reduction in the swell potential and swell pressure was observed, 62% (CCR:FA = 20:80) and 68% (CCR:FA = 20:80), respectively. The influence of the binder content on the properties of the treated soil was interpreted by means of particle size distribution, mercury intrusion porosimetry, scanning electron microscopy and x-ray diffraction analyses. Soil parameters such as particle size, pore size, soil texture and amount of montmorillonite underwent a considerable change that can be attributed to the migration of the binder along with water to the surrounding soil columns. Soil strength development will be fundamental for further study.

Accuracy of determining pre-consolidation pressure from laboratory tests

Shear strength and compressibility of fine-grained soils is strongly influenced by their stress history and the maximum (pre-consolidation) pressure ([Formula: see text]). Accurate determination of [Formula: see text] is thus critical for settlement and stability analysis involving fine-grained soils. Many graphical techniques are available for estimating [Formula: see text] from the interpretation of soil compression in laboratory consolidation (oedometer) tests. However, the accuracy of these methods has not been extensively proven or compared with each other. A series of 30 laboratory oedometer tests is carried out in this study based on controlled rate of strain and incrementally loaded testing techniques. Several Canadian clay specimens are subject to cycles of one-dimensional compression loading and unloading to produce a known stress history and [Formula: see text]. The imposed [Formula: see text] values are compared with the predictions of 11 methods for determining [Formula: see text]. The accuracies of these methods are subsequently evaluated by comparing their predictions with [Formula: see text] imposed during the consolidation experiments. While these methods mostly overestimate [Formula: see text], it is determined that a bilogarithmic graphical approach based on the slopes of the virgin compression and recompression segments of a soil compression curve provides the most accurate predictions of [Formula: see text]. The potential ranges of errors associated with the application of each method are also presented.

Effect of Daily Fluctuation of Groundwater Level on Land-Subsidence

Laboratory oedometer tests were conducted to investigate the effect of small intermediate reloading–unloading (r-u) cycles (in over-consolidated range) on a general unloading path and that of small unloading–reloading (u-r) cycles on a general reloading path on the permanent deformation of Ariake clay samples. The test results indicate that the permanent deformation increased with r-u cycles, and decreased with u-r cycles. The test results were simulated well using an existing static u-r model. Then two case histories of land-subsidence were analyzed. The engineering significance of considering daily variations of ground-water levels on the simulated results has been confirmed by comparing with the field measurements.

Prediction of compressibility parameters of the soils using artificial neural network.

The compression index and recompression index are one of the important compressibility parameters to determine the settlement calculation for fine-grained soil layers. These parameters can be determined by carrying out laboratory oedometer test on undisturbed samples; however, the test is quite time-consuming and expensive. Therefore, many empirical formulas based on regression analysis have been presented to estimate the compressibility parameters using soil index properties. In this paper, an artificial neural network (ANN) model is suggested for prediction of compressibility parameters from basic soil properties. For this purpose, the input parameters are selected as the natural water content, initial void ratio, liquid limit and plasticity index. In this model, two output parameters, including compression index and recompression index, are predicted in a combined network structure. As the result of the study, proposed ANN model is successful for the prediction of the compression index, however the predicted recompression index values are not satisfying compared to the compression index.

Comparison of geotechnical uncertainties linked to different soil characterization methods

ABSTRACTOne of the essential inputs in settlement prediction models is the soil modulus, which may be obtained from laboratory tests or estimated from in situ measurements. The total uncertainty in predicting the confined modulus of a sandy soil is quantified with data from side-by-side in situ testing using the standard penetration test, the static cone penetration test, the light dynamic probing and the laboratory oedometer test. To estimate transformation errors, correlations are proposed between in situ and laboratory data. The results indicate that similar magnitudes of total uncertainties are associated with the in situ methods, which are approximately twice as high as those from the direct oedometer method. The quantified uncertainties are an important input for reliability-based designs of foundations under similar soil conditions.

Deformation behaviors of peat with influence of organic matter.

Peat is a kind of special material rich in organic matter. Because of the high content of organic matter, it shows different deformation behaviors from conventional geotechnical materials. Peat grain has a non-negligible compressibility due to the presence of organic matter. Biogas can generate from peat and can be trapped in form of gas bubbles. Considering the natural properties of peat, a special three-phase composition of peat is described which indicates the existence of organic matter and gas bubbles in peat. A stress–strain–time model is proposed for the compression of organic matter, and the surface tension effect is considered in the compression model of gas bubbles. Finally, a mathematical model has been developed to simulate the deformation behavior of peat considering the compressibility of organic matter and entrapped gas bubbles. The deformation process is the coupling of volume variation of organic matter, gas bubbles and water drainage. The proposed model is used to simulate a series of peat laboratory oedometer tests, and the model can well capture the test results with reasonable model parameters. Effects of model parameters on deformation of peat are also analyzed.

Effect of stress ratio on the volume change behavior of compacted highly expansive clay

This paper aims at emphasizing the influence of stress conditions on the volume change behavior of expansive soils. A series of triaxial tests were conducted on remolded highly expansive clay specimens inundated under different combinations of stress ratios, K (ranging between 0.5 and 1.45) and axial inundation stress, σ ai (ranging between 50 and 800 kPa). Volume change characteristics obtained from these tests included axial inundation strain (e ai), volumetric inundation strain (e vi), and axial swelling pressure (σ s). Results of the experimental program showed that the stress ratio had a significant effect on magnitude of axial inundation strain. Test results revealed that axial inundation strain decreased with increase in axial inundation stress. However, stress ratio had a negligible effect on the volumetric inundation strain–mean inundation stress relationship. Furthermore, the axial inundation strain and axial swelling pressure obtained from triaxial tests were compared with that obtained from one-dimensional oedometer tests conducted on identical specimens and applied axial stress. The differences between axial inundation strain and axial swelling pressure evaluated from triaxial and oedometer testing were quantified by using corrections factors. Using these correction factors, a systematic procedure was proposed for the realistic estimation of axial inundation strain in the field based on results of laboratory oedometer tests and knowledge of in situ axial stress and stress ratio.

Assessment of Stress History of Jiangsu Clay Deposits from Seismic Piezocone Penetration Testing (SCPTU) Data

The stress history as indicated by the profile of overconsolidation ratio (OCR) or preconsolidation pressure of a soil deposit is one of the dominant factors that influence the engineering behavior of soils. A commonly used method to obtain the parameter is a laboratory oedometer test, which is of low accuracy and time consuming because of inevitable sample disturbance. The purpose of this article is to assess the capability of existing interpretation methods and develop new methods to reasonably predict the OCR of clayey soils utilizing the seismic piezocone penetration test (SCPTU) data. Seven sites in Jiangsu province of China were used for this study. At each site, in situ SCPTU tests were performed and soundings of cone tip resistance (q c ), sleeve friction (fs), pore pressures (u 2), and shear wave velocity (Vs) were recorded. High-quality Shelby tube samples were collected close to the SCPTU tests and used to conduct laboratory oedometer consolidation tests to evaluate the reference OCR values. The predicted OCR values from different methods were compared with the laboratory OCR values. The results showed that all the investigated SCPTU methods overpredict the laboratory-calculated OCR. The collected data were further used to develop two new SCPTU methods that can estimate the OCR reasonably.

Stress History Estimation Method of Underconsolidated Soil by Partial Piezocone Dissipation Tests

The paper discusses a new method to put forward to determine the initial pore pressure by extrapolating the last segment of measured pore pressure versus the inverse square root of time scale through incomplete pore pressure dissipation test. For underconsolidated soil, the estimated initial pore pressure is greater than the hydrostatic pore pressure. With the calculation of the initial pore pressure, the status of the consolidation of underconsolidated soil can be evaluated by calculating the apparent degree of consolidation which is defined as excess pore pressure generated by piezocone penetration divided by the difference between the total pore pressure measured by piezocone and in situ hydrostatic pore pressure. The apparent degree of consolidation is less than one as the soil is underconsolidated. The Northern Expressway Connection project of Chongqi Bridge is introduced as an example of practical application. In this case, the studied area is slightly underconsolidated, which is consistent with the results of the laboratory oedometer tests. Finally, compared with overconsolidation ratio (OCR) values from the oedometer tests, a new formula to estimate the OCR of underconsolidated soil using the apparent degree of consolidation was presented. It indicates that the OCR of underconsolidated soil can be proposed directly from partial piezocone dissipation tests.

Effects of salt solutions on the hydro-mechanical behavior of compacted GMZ01 Bentonite

In this study, the effects of salinity of infiltrating solutions on the swelling strain, compressibility, and hydraulic conductivity of compacted GMZ01 Bentonite were investigated. After swelling under vertical load using either distilled water or NaCl solutions with concentrations of 0.1, 0.5 M, and 1 M, laboratory oedometer tests were conducted on the compacted GMZ01 Bentonite. Based on the oedometer test results, hydraulic conductivity was determined using the Casagrande’s method. Results show that the swelling strain of highly compacted GMZ01 Bentonite decreases as the concentration of NaCl solution increases. The compression index C c * increases and then turns to decrease with an increase in the vertical stress or a decrease in the void ratio for different solutions, and the C c * decreases as the concentration of NaCl solution increases. The secondary consolidation coefficient C α increases linearly with the increase of the compression index C c * . Furthermore, a bi-linear relationship between the swelling index C s * and the secondary consolidation coefficient C α can be characterized clearly. The hydraulic conductivity increases as the concentration of NaCl solution increases, however, this increase can be prevented if a high confining stress is applied.

Consolidation settlement due to ramp loading

In one-dimensional consolidation analysis, it is generally assumed that the load is applied instantaneously. In reality, the load is applied over certain duration which has an effect on computations. This paper presents some ramp loading tests using a standard oedometer to support some simple theoretical developments. It is shown that during ramp loading, the plot of settlement v. time, normalized with respect to the end of ramp loading values, is relatively independent of the clay type and loading duration. This normalized plot can be used to predict the settlement pattern during the construction period and the coefficient of consolidation, using a single measurement at any time during construction. Post-construction settlements are predicted separately by assuming a sinusoidal initial pore water pressure distribution at the end of the construction period that is applied instantaneously. Laboratory oedometer test data show very good agreement with the theory.