Effect Of Partial Drainage Research Articles

The Effect of Partial Drainage on the Short-Term Bearing Capacity of Saturated Clay Foundations

The Effect of Partial Drainage on the Short-Term Bearing Capacity of Saturated Clay Foundations

Centrifuge model tests on spudcan penetration and extraction in sand-clay mixed soil

Jack-up vessels have been used for the construction of offshore wind turbines, and various studies have been conducted on the ground behavior during the penetration and extraction of their spudcans. In this study, the ground behavior of sand-clay mixed soil was investigated. Specifically, a series of actual operations, such as penetration, repeated loading, extraction, and repenetration, were reproduced by centrifuge model tests using sand and clay, as well as their mixtures with different fine-grain contents. Several elemental tests were also conducted prior to the model tests. In addition, the bearing capacity of the spudcan was discussed using estimation equations. The results of the elemental tests showed that in the soils used, the effect of partial drainage became more pronounced when the fine-grain content exceeded 20%, and the permeability, consolidation coefficient, and shear properties changed. These results were close to those of clay when the fine-grain content exceeded 50%. In the centrifuge model tests, the deformation characteristics of the ground changed, and the penetration resistance decreased as the fine-grain content increased. The influence of consolidation and drainage conditions was suggested. The estimation equations of the bearing capacity showed that, in the case of mixed soil, the bearing capacity obtained by the estimation equation under drained or undrained conditions differed significantly from the test results, and the estimation equation that considered the effect of partial drainage could be used to calculate the bearing capacity.

Characterization of Partial Drainage during Medusa Flat Dilatometer Testing

Abstract The flat dilatometer (DMT) is a widely recognized in situ test for site characterization and parameter identification. The penetration procedure is stopped periodically for total stress measurements (A, B, and C pressures) along a circular, expandable membrane, situated at one side of the blade. Changes in pore water pressure are not measured during test execution and are assumed to remain constant for data interpretation. The enhanced Medusa DMT equipment used in this study enables a fully automated test execution and requires no manual membrane expansion by the operator. Changes in pore water pressure can be studied by measuring the A pressure automatically over time at a defined membrane expansion. In the present study, Medusa DMT were executed at three test sites (Rhesi and Lokalbahn Salzburg in Austria; Fucino in Italy) to investigate, on the one hand, partial drainage effects in different soil types using variable membrane expansion rates and repeated A readings and on the other hand, to study the influence of partial drainage on existing correlations (used for parameter identification). The present results indicate that partial dissipation of generated excess pore water pressures occurs in a wide range of soils during test execution. The degree of dissipation can additionally be influenced by the soil heterogeneity, especially in silty soils. Soil parameters and intermediate parameters determined based on A readings are less influenced by partial drainage effects compared with parameters, derived from the difference of corrected B and A readings. The influence of partial drainage on the latter correlations increases in fine-grained soils, characterized by small differences in B and A pressure. Therefore, pressure readings should be corrected about partial drainage effects based on an enhanced testing procedure, considering repeated A readings (DMT-RA).

A numerical approach for simulation of stress-controlled cyclic shear loading in a soil column considering partial drainage

Liquefaction strength curves (LSCs) are commonly generated based on undrained stress-controlled cyclic testing to define the liquefaction potential of sands. However, these LSCs do not consider the effect of partial drainage on liquefaction potential. This is mainly because there are very limited experimental techniques to run stress-controlled tests for partially drained sands. This manuscript proposes a procedure to numerically simulate a saturated sand column with a free drainage boundary at the top (or top and bottom), accelerated horizontally at the bottom with constant acceleration cycles of duration designed to generate constant cyclic shear stress histories in the column. This is done for columns subjected to low and high overburden pressures. The paper starts with numerical simulations of a typical undrained cyclic direct simple shear, CDSS tests by applying a stepped velocity wave to a single soil element, an already established approach. This approach only works for a single element in undrained condition which is fixed at the base. Then, the proposed procedure is implemented by applying stepped acceleration time histories at the base of soil columns having one or two drainage boundaries. In these stepped acceleration runs, the durations of the acceleration cycles are controlled to achieve a partially drained stress-controlled CDSS kind-of-loading at specific elevations within the soil columns. The technique is used to show the effect of partial drainage on sand liquefaction behavior at both low and high overburden pressures. The results show that the effect of drainage is much more significant at higher overburden. The existence of both top and bottom drainage boundaries resulted in less liquefaction vulnerability, as compared to having only one drainage boundary at the top of the sand column. The results show that liquefiable sand layers in the field may be less prone to liquefaction under high overburden pressure than predicted by the current state-of-practice, which relies mainly on undrained small-scale cyclic tests.

A Unified Approach for the Analysis of CPT Partial Drainage Effects within a Critical State Soil Mechanics Framework in Mine Tailings

Results from both laboratory and in-situ cone penetration tests (CPTs) on predominantly sandy silt platinum tailings from an operational mine in South Africa are reported. The CPTs were conducted with four different cone diameters at varied penetration rates. With the results interpreted in terms of the normalized tip resistance and the initial state parameter, in addition to dissipation tests, it was possible to identify the CPTs affected by significant partial drainage effects. A review of the partial drainage concept enabled the formulation of a novel characteristic surface approach, which uses a unified continuous equation to estimate the state parameter from the CPT data from drained to partially drained and undrained regimes and from contractive to dilative states. A review of different methods for the estimation of the coefficient of consolidation, and hence the normalized penetration velocity, enables a comparison of the estimated state parameter with independent values calculated from recovered saturated samples, showing the ability of this technique to infer the state parameter from CPT tests where partial drainage occurs.

Numerical study of piezoball dissipation test with penetration under partially drained conditions

The piezoball, a full-flow penetrometer equipped with a pore pressure transducer, is increasingly being used in in-situ investigations due to its advantages of characterizing soft soils relative to the piezocone. The operative coefficient of consolidation, ch, can be estimated by monitoring the dissipation of excess pore pressures after piezoball penetration. However, the determination of ch from the dissipation test becomes complicated if the piezoball is penetrated under partially drained conditions. The performances of piezoball penetration and subsequent dissipation are investigated using a coupled large deformation finite-element approach. The numerical results are verified by comparing with existing centrifuge tests, against both undrained and partially drained conditions. A comprehensive interpretation method is then presented for inferring ch from piezoball tests against various drainage conditions. It is found that the variation of ch with drainage conditions is essentially dependent on the distribution of pore pressures before dissipation. Two backbone curves determining the nominal initial excess pore pressure at the equator of the probe and the coefficient of consolidation are obtained to assess the effect of partial drainage, which capture the influences of the piezoball geometry, stress level and over-consolidation ratio.

Studying the effect of partial drainage on the response of soft clays reinforced with sand column groups

Studying the effect of partial drainage on the response of soft clays reinforced with sand column groups

Numerical investigation of spudcan penetration under partially drained conditions

Estimation of spudcan penetration resistance during jack-up rig installation is critical to determine its final resting depth under full pre-load. The penetration resistance profile is conventionally calculated by assuming undrained conditions for clay and fully drained conditions for sand in current practice, but partial drainage in intermediate soils, such as in silts and sandy silts, leads to the resistance in between. This paper reports the results from a series of numerical investigations conducted to explore spudcan penetration response, which spans from fully undrained to fully drained conditions. The investigation is carried out using a large deformation finite-element approach within the framework of effective stress analysis. The numerical approach is validated by simulating existing centrifuge tests. Parametric studies are then performed using a wide range of normalized penetration velocity. The transition point where partially drainage occurs is identified, and is compared with those obtained from centrifuge tests. The variation of normalized penetration resistance with normalized velocity is compared with the published experimental data on UWA kaolin and silt. The backbone and consolidation index curves for Malaysian kaolin are subsequently provided to quantify the influence of different drainage conditions. Finally, the partial drainage effects for spudcan and penetrometers is compared and discussed.

Observations and challenges in simulating post-liquefaction settlements from centrifuge and shake table tests

Liquefaction-induced reconsolidation settlements occur as excess pore pressures generated during shaking dissipate and can lead to significant damage to overlying infrastructure. Designing resilient infrastructure in areas affected by liquefaction requires methods to predict these settlements for different soil types and boundary conditions. Simplified empirical models are commonly utilized to evaluate settlements but they exhibit several limitations that might hinder the accuracy of settlement predictions, including effects of partial drainage, thin layers, non-liquefiable crusts, or soil fabric. Numerical models can capture these effects but require proper calibration and validation. This study uses a numerical approach to simulate centrifuge and shake table experiments with free-field level, ground conditions and five different sands for evaluating reconsolidation settlements. The numerical platform FLAC and constitutive relationship PM4Sand are utilized. The necessity of soil-specific calibration of post-liquefaction stiffness and an excess pore pressure ratio dependent hydraulic conductivity to accurately model the observed pore pressures and settlements is analyzed. A new relationship between the increase in hydraulic conductivity due to liquefaction and grain size diameter is proposed. The numerical simulations are able to capture the general trends, but the bias in the results appears to be correlated with the grain size distribution of the tested soil.

Effect of partial drainage on the pullout behaviour of a suction bucket foundation

Suction-bucket-supported jacket foundations are being used increasingly for offshore wind turbines, the advantages being large bearing capacity and efficient installation. For a large-capacity wind turbine, the pullout capacity and displacement of the bucket in the tripod or tetrapod jacket can be critical to the safety of the structure. The loading rate, which is commonly dominated by the offshore environmental conditions, has a significant effect on the ultimate capacity and stiffness of the bucket foundation. In this paper, a numerical model is developed to investigate the response of a bucket foundation under vertical pullout loading at different rates. A bounding-surface model based on critical state soil mechanics is introduced to account for the soil behaviour under different stress states and drainage conditions. The model is modified and calibrated against a comprehensive set of laboratory tests, including both triaxial compression, triaxial extension and direct simple shear tests in drained and undrained conditions. How partial drainage affects the load–displacement response and pore pressure field are thus presented. A parametric study on the selection of soil parameters is also conducted to shed light on practical foundation design.

Study of mining tailings geotechnical parameters obtained from SCPTu tests carried on dry and saturated layers

The correct interpretation of in situ and laboratory test results is an important step in the design of mining tailing containment structures. This study aims to analyze the Seismic Cone Penetration Test (SCPTu) results obtained into a mining tailing reservoir composed of two material layers: a thick-dry and a tick-saturated. It is possible to observe that in a same tailing reservoir, the CPTu test interpretation can lead to a classification of each layer as a different soil with specific behavior and properties. This condition demonstrates that tailings with intermediate permeability (10-5 m/s < k < 10-8 m/s) may present partial drainage conditions during a standard cone penetration test (CPTu) (v=20 mm/s), if saturated conditions are verified. The effects of partial drainage can affect test results, and can induce to errors in the prediction of soil behavior and geotechnical parameters. To evaluate the possible effects of partial drainage, in situ test results were compared to laboratory tests results. It was possible to verify that estimated behavior of dry layers, obtained from in situ tests results, present more similarity to the results from laboratory tests. Probably, the partial drainage effects verified through the interpretation of dissipation tests, distorted the estimated behavior of the saturated layer material.

Experimental Study of Modeling Partially Drained Dense Sand Behavior in Monotonic Triaxial Compression Loading Tests

Abstract Sand behavior is significantly affected by the drainage conditions being either fully drained, partially drained, or undrained. Partially drained conditions are often encountered in reality; however, partial drainage effects are not commonly considered at a soil element level. As a common soil element test, triaxial testing is carried out with either fully drained or undrained conditions for the shearing phase, as specified according to the soil type and design application. In this study, a series of monotonic triaxial compression tests were performed under various drainage conditions with a special filter device to investigate partially drained behavior of dense sand. Partially drained behavior resulted in simultaneous excess pore water pressure generation and volumetric strain and behaved more similar to the undrained condition at the beginning of shearing and more similar to the fully drained condition at the large strains. Using three different degrees of drainage induced by three filter devices with different steady-state flow capacity and different shearing strain rates suggest that a ratio of the axial strain rate to the filter flow capacity can be used as a unique parameter to represent degree of drainage in a partially drained test.

Simplified Model for Interpretation of Undrained Shear-Strength from Field-Vane Tests in Transient Soils

AbstractInterpretation of field vane tests in transient soils requires assessing partial drainage effects within the soil surrounding the vane. This subject is investigated in this paper using a no...

Effect of Partial Drainage on Cyclic Strengths of Saturated Sands in Dynamic Centrifuge Tests

AbstractThe effects of partial drainage on the cyclic strength of saturated sand in a set of dynamic centrifuge model tests were evaluated. Three models of level profiles of saturated Ottawa F-65 s...

Comparison of Shear Wave Velocity Prediction Models to Yangtze River Deltaic Sediments Based on Piezocone Test Data

Seismic piezocone (SCPTu) data compiled from 37 sites in the southern Yangtze delta, China, are used to evaluate several existing empirical correlations in predicting the shear wave velocity of deltaic sediments. Four indices were employed in the assessment: the ratio of the estimated values to the measured Vs values, the root-mean-square error, the ranking index, and the ranking distance. It is shown that all the considered prediction models are biased, generally over-estimating the observed shear wave velocity of the predominant intermediate soils in the Yangtze delta. The results also reveal that the overall best correlation for the mixed deltaic soils is given by Robertson [Can Geotech J 46(11):1337–1355, 2009]. It is hypothesized that the unique depositional environment of the considered soils is the primary source of the observed prediction bias. Further statistical analysis indicates that partial drainage effects during cone penetration in deltaic intermediate sediments should be taken into careful consideration to derive reliable Vs values from CPTu data when applying correlations from the literature. More suitable site-specific shear wave velocity prediction correlations should be introduced, according to the recent findings on the Yangtze delta SCPTu database.

Numerical study of partially drained penetration and pore pressure dissipation in piezocone test

The piezocone penetration test (CPTU) is commonly used as a fast and economical tool to identify soil profile and to estimate relevant material properties in soils ranging from fine to coarse-grained. Moreover, in the case of fine-grained soils (clays and silts), the consolidation coefficient and the permeability can be estimated through the dissipation test. Undrained conditions are commonly assumed for the interpretation of CPTU in fine-grained soils, but in soils such as silts, penetration may occur in partially drained conditions. This aspect is often neglected in data interpretation thus leading to an inaccurate estimate of soil properties. This paper investigates numerically the effect of partial drainage during penetration on the measured tip resistance and the subsequent pore pressure dissipation response contributing to a more accurate interpretation of field data. A realistic simulation of the cone penetration is achieved with the two-phase Material Point Method, modelling the soil response with the modified Cam-Clay model. The approach takes into account large soil deformations induced by the advancing cone, soil–water, and soil–structure interactions, as well as nonlinear soil behavior.

The Interaction Between Reinforcement and Vertical Drains and Effect on the Performance of Embankments on Soft Ground

This paper reviews the behaviour of reinforced embankments on soft ground. Case of the Almere test embankment is used as an example to demonstrate the key function of reinforcement in improving the performance of embankments on soft foundation. The effects of partial drainage are summarized for reinforced embankments and contrasted the results from undrained analyses to highlight the effect of partial consolidation during construction. Effects of the interaction between reinforcement and prefabricated vertical drains (PVDs) are presented. It is concluded that the combined effects of partial consolidation provided by PVDs and the tension mobilized in reinforcement can substantially increase the stability of an embankment on a given soft soil. This paper also provides brief explanation of a recent design approach for embankments on soft soil, considering the combined effect of reinforcement and PVDs. Effects of the creep/relaxation characteristics of geosynthetic reinforcement and rate-sensitive nature of soft cohesive foundation soil are discussed. It is shown that time-dependent nature of geosynthetics and foundation can decrease the failure height of a reinforced embankment. Also, the long-term performances of a reinforced embankment can vary significantly depending on the soil and reinforcement characteristics. The results suggest the need for care when the foundation soil is rate-sensitive.

Single-element simulations of partial-drainage effects under monotonic and cyclic loading

Liquefaction-induced seepage and pore-water pressure redistribution can locally change a sands' void ratio, such that in-situ strength and deformation behavior following an earthquake depend on the coupled diffusion process and not only on pre-earthquake soil properties. The effects of partial drainage on the monotonic, cyclic, and post-cyclic behavior of liquefied sand are explored at the element scale in this study, using the constitutive model PM4Sand [1] and the finite-difference code FLAC [2]. The ability of a critical state-based constitutive model to approximate partially drained loading responses is evaluated by comparing single-element simulations to available lab data and trends. The calibrated model is then used to examine the potential effects of partial drainage on the cyclic stress–strain behavior and accumulation of shear strains for dense-of-critical sand. The importance of liquefaction-induced seepage and void redistribution to the in-situ strength and deformation behavior of liquefied sands is discussed in view of the results of these partially drained laboratory element tests and simulations.

In situ strength characterisation of peat and organic soil using full-flow penetrometers

Full-flow penetrometers have been shown to overcome problems experienced with the cone penetrometer when measuring resistance in very soft peat and organic soil, and give a much more uniform measure of resistance than the cone in fibrous peat. However, at present there is no guidance on the interpretation of strength parameters in these soils using the T-bar and ball. This paper examines the results of tests using these devices at two research sites in the Netherlands in conjunction with high-quality Sherbrooke sampling for laboratory testing. In fibrous peat, the T-bar and ball provided a more uniform measure of resistance with a lower degree of scatter than the cone. The in situ testing results have been compared with the laboratory tests to assess the range of resistance factors relating penetration resistance to the undrained shear strength (su) and have been shown to occupy a lower range of values than the cone penetrometer. However, penetration tests in these soils are likely to be influenced by partial drainage effects and this should be considered during testing and the subsequent interpretation of results. Recommendations are made for the use of full-flow penetrometers to obtain strength parameters in these soils.

Analysis and interpretation of piezocone data on the silty soils of the Venetian lagoon (Treporti test site)

This paper reports the main results of an extensive piezocone testing campaign performed over the last years at the Treporti test site (Venice, Italy) within a long-lasting and comprehensive research project aimed at developing a reliable geotechnical model of the heterogeneous and highly stratified Venetian lagoon basin. The project included the construction of a full-scale vertical-walled cylindrical test bank, together with a detailed monitoring system of surface settlements, pore-water pressures, subsoil strains, and stresses beneath the loaded area. The analysis of the large amount of data thus available, referring to different phases of the loading history, confirms the great potential of piezocone as an in situ testing technique, especially for stratigraphic profiling of the predominantly silty subsoil of the Venetian lagoon, but at the same time reveals some limitations of widely used empirical correlations for the relevant soil characterization, with special reference to compressibility and consolidation properties of such intermediate sediments. Indeed, partial drainage effects during cone penetration, as well as potentially dilative behaviour of these soils, should be taken into careful consideration to derive reliable soil parameters from in situ measurements. More suitable site-specific correlations have been introduced, according to the recent findings on piezocone data interpretation.