Oedometer Test Data Research Articles

Assessment of soil parameters during post-liquefaction reconsolidation of loose sand

Saturated deposits of loose sand may suffer liquefaction under earthquake shaking. Liquefaction-induced damage occurs during the earthquake loading and may continue during the post-liquefaction reconsolidation stage in which excess pore pressures gradually dissipate. An accurate evaluation of soil parameters is of great significance for the full depiction of this process. Consolidation-related problems are typically investigated using Terzaghi's one-dimensional consolidation theory, assuming a constant permeability, one-dimensional stiffness, and consolidation coefficient throughout this process. Some studies based on physical model tests suggest that an assumption of a single and constant value of soil parameter is not appropriate to study the reconsolidation of liquefied sand. This paper presents the results of three geotechnical centrifuge experiments to contribute to the current understanding of this phenomenon. The centrifuge data is combined with oedometer and fluidization test data, producing several empirical relationships to estimate the soil parameters related to the reconsolidation of liquefied sand. A simplified method is adopted to reproduce the time histories of excess pore pressure dissipation and ground surface settlement using the estimated soil parameters as the input. It is shown that the coefficient of consolidation and one-dimensional stiffness vary as a function of effective stress or excess pore pressure ratio, markedly increasing during the reconsolidation of liquefied sand. The predictions of the proposed methodology appear to match the experimental measurements reasonably well as long as appropriate soil parameters are used.

CPTU-based settlement modelling for Kujala test embankments on overconsolidated silty clay: A probabilistic approach

Sounding resistance, such as CPTU cone tip resistance, is often used to estimate the settlement of the subsoil when designing ground-supported structures. This paper utilizes CPTU-based probabilistic modelling to estimate the settlement of two test embankments located in Finland. The model is based on an empirical correlation between CPTU net cone resistance and constrained modulus (M0 ), described by factor α. Besides the existing correlation (prior distribution of α), this paper also considers the site-specific observations via Bayes’ theorem. By means of Monte Carlo simulation, the settlement histograms were produced and the results compared to the observed settlements. Lastly, the effect of dry crust on the embankment load transmission was considered in order to decrease the model bias. The results indicate that for the other embankment the effect of dry crust has to be considered in order to acquire satisfactory results. It is concluded that this CPTU-based settlement model might be suitable for stiff, overconsolidated silty clay soils in Finland. However, model calibration using site-specific oedometer test data is recommended. On the other hand, such simplified model with a singular modulus should not be used for normally consolidated clay subsoils.

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.

Model updating and uncertainty analysis for creep behavior of soft soil

Of late, various constitutive models have been proposed in the literature for the purpose of capturing the various complex physical mechanisms governing the creep behavior of soft soil. However, the more complex the model, the greater the number of associated uncertain parameters it has, and the less robustness it is. In this study, the Bayesian model class selection approach is applied to select the most plausible/suitable model describing the creep behavior of soft soil using laboratory measurements. In total, one elastic plastic (EP) model and eight elastic viscoplastic (EVP) models are investigated. To assess the performance of the different models in the prediction of creep behavior of soft soils, Bayesian model class selection is respectively performed using the oedometer test data from the intact samples of Vanttila clay and reconstituted samples of Hong Kong Marine Clay collected from the literature. All unknown model parameters are identified simultaneously by adopting the transitional Markov Chain Monte Carlo (TMCMC) method, and their uncertainty is quantified through the obtained posterior probability density functions (PDFs). The result shows that the proposed method is an excellent candidate for identifying the most plausible model and its associated parameters for different kinds of soft soils. The approach also provides uncertainty evaluation of the model prediction based on the given data.

Predicted and measured behaviour of a test embankment on Ballina clay

A test embankment was established on the soft Ballina clay and practising engineers and academics were invited to make predictions of the behaviour of the embankment. Comprehensive geotechnical investigations were performed and the testing data were provided to the predictors. This paper presents Class A and Class C predictions made by the authors for the embankment. In Class A prediction, the soft clay was modelled as a single homogeneous layer. The Class A prediction showed good agreement with measurements for settlement, but not for pore pressure and lateral ground movement. Class C prediction divided the soft clay into two layers based on the information of ground investigation, and achieved better predictions for settlement, pore pressure and lateral movement. Finite element analysis using Plaxis 2D was carried out for the prediction, and Soft Soil Creep model was used for the soft clay. Consolidation parameters were assessed by statistical analysis of the oedometer test data. Sensitivity studies were performed to investigate the influence of parameters on the analysis results. Results of the predictions and sensitivity studies are discussed in the paper.

New observational method for prediction of one-dimensional consolidation settlement

The Chapman–Richards model is adopted in this paper to best fit the Terzaghi's one-dimensional consolidation curve. The obtained formula fits the theoretical solution well, with a regression coefficient R2 of 0·9995 and an error of less than 2%. By adopting this model, a new method to predict the ultimate settlement and the coefficient of consolidation using monitoring settlement data is proposed. The accuracy of the proposed method is verified against oedometer test and field monitoring data. For the cases verified, the ultimate settlement predictions from the proposed method are more reliable than those from the Asaoka's method for the different range of settlement data.

EFFECT OF PILE CONNECTIONS ON THE PERFORMANCE OF THE NAILED SLAB SYSTEM ON THE EXPANSIVE SOIL

Expansive soils are clay that swells and shrinks with changing moisture content. The pavement that constructed on these soils is subjected to large uplifting forces caused by swelling. Hence, there is an imperative need to counteract the problem posed by these soils by devising innovative pavement technique. An attempt to develop a simple, easy to install and cost-effective alternative pavement system, nailed slab system was developed, wherein slab pavement will be connected to a reinforced concrete mini piles.This research examines the emerging role of mini piles in the context of reducing soil uplift movement and the nailed slab system (pile supporting slab pavement) a system for minimizing slab movement due to swelling in expansive soil by conducting small-scale experimental modeling in laboratories. The heave prediction also doing by using the correlation between change in moisture content and vertical strain from oedometer test data. The results of this study indicate that reinforcing the soil by using the mini piles can reduce heave of soil, and the nailed slab system experiencing smaller upward movement than an unsupportedslab. The connection between the pile and the slab has a significant effect on the system’s ability to withstand the upward movement of expansive soil. When pile and the slab were monolithically connected, the system shows the better performance than those the slabs with the free head pile. Thereafter a heave prediction analysis provided the amount of heave that slightly overestimates, but still good enough for a rough estimation.

Compressibility and stress history of very soft organic clays

The compression index, swelling index and preconsolidation stress values are essential for reliable settlement calculations. However, it is a challenge to obtain representative parameters for very soft, organic, high-plasticity clays, which are often found in the Jacarepaguá Lowlands, Rio de Janeiro, Brazil. In recent decades, several geotechnical correlations have been proposed for estimating the parameters to check oedometer test data. The compression index can be estimated based on simple laboratory index tests and the preconsolidation stress can be found by means of piezocone and vane tests. In this paper, data from 24 different investigation clusters located in the region are analysed. Undisturbed samples were collected from 20 different locations; 67 piezocone tests and 48 vane tests were carried out, which resulted in a comprehensive data bank. Then correlations were developed and compared with a number of equations to assess their reliability. Special emphasis was given to correlations between the compression index and soil water content, and also between the preconsolidation stress and the corrected cone resistance and shoulder pore pressure measured in the piezocone tests.

Numerical Simulation of Long-term Peat Settlement Under the Sand Embankment

Long-term surface settlement in the cities, which were founded in swamp lands, is a reason of road pavement, underground pipelines, building damage. One of such cities is Arkhangelsk, which was founded on the swamp with peat thickness of 4-6 meters and even 8 meters. In such difficult geological conditions, the prediction of long-term settlements of a peat layer under an embankment is the significant task. One of the contemporary and effective ways of its solution is numerical simulation. The numerical simulation was performed using the software PLAXIS. The model of Soft Soil Creep was used.The objective of this project was comparing the long-term peat settlement values by way of numerical simulation, using the results of peat compression tests as initial data, with the data of monitoring. Thus, we can say about the model verification.On the first step of the research input parameters λ*, μ* were received from the laboratory tests data according to the basic methods. After that numerical simulation of oedometer tests was done. The small disarrangement between calculated settlement-in-time plots and the oedometer test data showed that that the SSC model gives an adequate representation of the physical processes in the peat specimen.On the second step, we simulated the experimental field, which settlement data has being collected more than 23 years. During this period, peat settlement was 1.4-4 m, depending on the thickness of the sand embankment. Input parameters λ*, μ* from the oedometer test were used. The comparison showed the low level of convergence of the settlement-in-time plots with the field data, so the model parameters calibration was required. The correction factors were to be added to the parameters λ* and μ* calculated by the results of oedometer tests.

Stress-dependent hydraulic properties of clayey-silt aquitards in eastern Australia

Clayey-silt aquitards account for 60 % of the ~100-m-thick alluvial sediment sequence in the Gunnedah area of eastern Australia. To better understand the stress-dependent hydraulic properties of these low-permeability units, oedometer test data presented for the first time in this study have been integrated with geotechnical centrifuge permeameter tests. Estimates of vertical pre-consolidation effective stress (\(\sigma_{\text{p}}^{'}\)), vertical in situ effective stress (\(\sigma_{\text{i}}^{'}\)), and over-consolidation ratio (OCR) were used to determine whether centrifugation stresses caused compression of core samples, and the degree to which vertical hydraulic conductivity (Kv) assessments were representative of the core samples tested. Results suggest that minimally disturbed drill core from semi-consolidated sediments (e.g., alluvial, colluvial, and eolian deposits) evaluated in this study should have target centrifugation stress less than \(\sigma_{\text{p}}^{'}, \) where OCR 1 to avoid significant changes in hydraulic properties during plastic straining. The results also imply that the stress-dependent response of aquitards is critical to understand the sensitivity of groundwater resources in areas with multiple stakeholders such as mining, coal seam gas, and agriculture developments. Groundwater in alluvial sediments that is essential for irrigation, water supply, and base flows to rivers must be sufficiently disconnected from groundwater in coal seams that are depressurized for extraction of energy resources.

Preconsolidation of Søvind Marl—A Highly Fissured Eocene Clay

Abstract Determination of the preconsolidation stresses is a key tool in geotechnical engineering used to evaluate and estimate the behavior of soils. However, it has proven difficult to accurately estimate these stresses in highly fissured, overconsolidated clays, due to the influence of the fissured structure. In the current study, oedometer tests were performed on Søvind Marl, a plastic Eocene clay containing a large number of fissures and slickensides. Four incremental loading oedometer tests and four continuous loading oedometer tests were performed in order to determine the preconsolidation stresses. Multiple assessment methods were used to assess preconsolidation stresses based on the oedometer test data, results of which are presented and discussed on this paper. All of the test and interpretation methods yielded very similar results, with two possible values calculated as the preconsolidation stresses. However, only the upper stress bound is actually identified as being associated with preconsolidation; the lower bound is generated as a result of the collapse of the fissured structure in response to increasing stresses that were applied during testing. The upper bounds of the preconsolidation stresses of Søvind Marl were between 6300 and 8900 kPa, whereas the lower were between of 600 and 800 kPa.

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.

Aftershocks and the whole-life seismic performance of granular slopes

Shallow embankment slopes are commonly used to support elements of transport infrastructure in seismic regions. In this paper, the seismic performance of such slopes in non-liquefiable granular soils is considered, focusing on permanent movement and dynamic motion at the crest, which would form key inputs into the aseismic design of supported infrastructure. In contrast to previous studies, the evolution of this behaviour under multiple sequential strong ground motions is studied through dynamic centrifuge, numerical (finite-element, FE) and analytical (sliding-block) modelling, the centrifuge tests being used to validate the two non-physical approaches. The FE models focus on the specification of model parameters for existing non-linear constitutive models using routine site investigation data, allowing them to be used routinely in design and analysis. Soil-specific constitutive parameters are derived from shearbox and oedometer test data, and are found to significantly outperform existing empirical correlations based on relative density, highlighting the importance of specifying a suitably detailed site investigation. An improved sliding-block (‘Newmark') approach is also developed for estimating permanent deformations during preliminary design, in which the formulation of the yield acceleration is fully strain-dependent, incorporating both material hardening/softening and geometric hardening (re-grading). The site-specific (improved) FE models and the new sliding-block approach are shown to outperform considerably existing FE parameters and sliding-block models in capturing the permanent deformations of the slope under virgin conditions, and further, only the improved FE and sliding-block models are found to capture correctly the behaviour of the ‘damaged' slope under subsequent earthquakes (e.g. strong aftershocks). The FE models can additionally accurately replicate the settlement profile at the crest and quantify the dynamic motions that would be input to supported structures, although these were generally overpredicted. The FE procedures and sliding-block models are therefore complementary, the latter being useful for preliminary design and the former for later detailed design and analysis.

Intrinsic Compression Behavior of Remolded and Reconstituted Clays-Reappraisal

Evaluating the impacts of soil structure on mechanical behavior for natural sedimentary clays is an important issue in geotechnical engineering. Burland introduced void index for normalizing the compression curves of various remolded and reconstituted clays to obtain the intrinsic compression line, which provides a reference framework to assess the in-situ compression behavior. However, it does not quantitatively account for the effects of initial water content on compressive behavior of remolded and reconstituted clays and the initial water contents of clays are not always limited to 1.0 - 1.5 times the liquid limits defined by Burland. A modification based on collected tests data was presented on the expressions of and defined by Burland. Extensive oedometer test data were also collected on various remolded and reconstituted soils with distinct liquid limits and initial water contents to verify the validity of modified expressions. A normalized compression line deduced by intrinsic compression line is proposed in the e-log p plot, which can be used to evaluate the effects of soil structure quantitatively on the intact compressive behavior for natural sedimentary clays.

Discussion of “Time-dependent behaviour of the Bearpaw Shale in oedometric loading and unloading” 1Appears in the Canadian Geotechnical Journal, 49(4): 427–441 [doi:10.1139/t2012-004

This is an application of theoretical equations of compressibility given by the principle of natural proportionality to the interpretation of experimental oedometer test data on the Bearpaw Shale.

Discussion of “One-dimensional consolidation behavior of cement-treated organic soil” 1Appears in the Canadian Geotechnical Journal, 48(7): 1100–1115 [doi: 10.1139/t11-020

This discussion is an application of theoretical equations of compressibility given by the principle of natural proportionality to the interpretation of experimental oedometer test data of cement-treated organic soil.

Predicting the long-term performance of a geogrid-reinforced embankment on soft soil using two-dimensional finite element analysis

The consolidation of the soft foundation soil of a geogrid-reinforced embankment, improved with prefabricated vertical drains (PVDs), is modelled in this paper using two-dimensional (2D) plane strain coupled finite element (FE) analysis to predict long-term multiple behaviour characteristics (e.g., settlement, lateral displacement, excess pore-water pressure response, geosynthetic strain) of the embankment. Two sets of analyses were carried out with the foundation soil being modelled using relatively simple elastic–viscoplastic (EVP) models. A nonlinear creep function was used in association with them. The input material parameters were determined from extensive laboratory testing or were taken from reliable sources except for the horizontal permeability, which was systematically back-estimated using oedometer test data and the first year of field settlement data. The results from both analyses were compared with the long-term (up to 6 years) field-monitoring data and were found to be in good agreement with the field measurements.

Change of hydraulic conductivity during compression of undisturbed and remolded clays

Eight series of falling head hydraulic conductivity tests were performed on both undisturbed and remolded specimens of four clays from China using a modified oedometer to investigate the change of hydraulic conductivity during compression. Similar to their compression behavior, the undisturbed specimens showed the curves of hydraulic conductivity versus effective vertical stress lying above those of the remolded specimens. Past studies showed that the compression curves of remolded clays could be unified into a unique line using the void index. However, such unification between the void index and the hydraulic conductivity for remolded clays was not found in this study. The relationship between the void index (or void ratio) and the hydraulic conductivity for undisturbed specimen was almost identical to that of the remolded specimen. The relationship between the void ratio and the hydraulic conductivity on a logarithm scale was nearly linear with a slope of 0.5 times the initial void ratio at strains <20%, and became concave upwards within the full range of strains during compression. Similar to the oedometer test data, the relationship between the specific volume and the hydraulic conductivity could be expressed by a straight line in a bilogarithmic plot within the full range of strains during compression.

Assessment of standard research sand for laboratory testing

tandard soils are used worldwide as reference materials with which new model or single element experiments may be performed, assessed and calibrated. The testing databases associated with these are valuable resources that are particularly important when developing new procedures. However, the finite extent and variability of all natural deposits creates the possibility that standard soils may vary, or become unavailable, over time. The Ham River Sand (HRS), from the Thames Valley in the UK has been researched continuously and comprehensively in a series of studies since the 1940s, leading to a large database that includes recent advanced hollow cylinder, stress path triaxial and dynamic testing. Fresh samples are now unavailable and the paper describes a study of alternative sampling sources within the Thames Valley. Microscopic visual inspections, index measurements, direct shear, high pressure oedometer, bender element and stress path triaxial test data are presented in the paper, focusing on the natural variability and the ranges seen in material test response. A replacement for the original HRS is identified, so allowing those developing new tests the possibility of conducting experiments on material that is compatible with the existing HRS database. Reference is also made to advances in bender element testing achieved as part of the study.

Wetting-Induced Compression of Compacted Oklahoma Soils

The wetting-induced compression of compacted Oklahoma soils was investigated. One-dimensional oedometer tests were conducted on 22 Oklahoma soils that encompassed relative compaction and moisture contents within typical embankment specifications. Results show that factors directly related to the fines composition can be used for preliminary estimation of collapse potential. Statistical analysis of the oedometer test data indicates that variables having the most impact on collapse index were compaction moisture content, dry unit weight, plasticity index, and clay-size fraction. Charts were developed to facilitate the estimation of collapse settlement of fills for different conditions, including fill height, moisture content, and soil type. Three case histories involving embankments that experienced significant settlement are presented for comparison. The comparison shows a reasonable agreement between predictions and field estimates of collapse settlement at the embankment centerlines; the limited evidence suggests that predictions based on one-dimensional assumptions may underestimate actual settlements possibly due to the two-dimensional nature of embankments.