Laboratory Consolidation Tests Research Articles

Development of Innovative Plate Load Testing Equipment for In-Situ Saturated Clays Soils

This study proposes a method of gradually loading plate load on-site using lever arms to squeeze out pore water from clayey soils, allowing the soil to settle. Several types of tests were conducted, including a conventional field plate load test (CFPLT), a numerical field plate load test (NFPLT) and an innovative field plate load test (IFPLT) proposed in this study. Three trial pits with soils of varied engineering properties were studied using CFPLT, which employed the use of a heavy jack for load application, the NFPLT test using PLAXIS and an IFPLT, which employed a lever arm to magnify the applied static load. Disturbed soil samples collected from these trial pits were tested for index properties while the undisturbed soil samples were tested using the undrained triaxial compression test (UTCT) and laboratory consolidation tests. The results of the index properties classified these three clay soils as silt of low plasticity (ML) for clay from site 1, and clay of low plasticity (CL) for clay from site 2 and 3. The cohesion and angle of internal friction from the UTCT recorded cohesion values were 28, 29 and 37 kN/m2 for sites 1, 2 and 3, respectively, while the angle of internal friction values were 13, 8 and 6° for sites 1, 2 and 3, respectively. The plate load testing using the three methods showed similar graph pattern except that the allowable load occurred at approximately 350 kN/m2 for the CFPLT and 150 kN/m2 for the IFPLT. The high value of bearing capacity in CFPLT is due to the short period of time taken to load from a jack, which allowed the test to be completed within a short period of time. The ultimate bearing capacities computed from the laboratory test have values of 315.0, 231.0 and 270.0 kN/m2 for sites 1, 2 and 3, respectively. These values agree closely with the bearing capacities obtained for CFPLT but higher than the values recorded for the IFPLT. This is probably due to the long period of sustained loading during testing, which allowed for dissipation of pore water during each loading. Settlements obtained using the IFPLT were close to 25 mm, which is recommended as minimum settlements for building structures BS 8004, 1986.

Investigating the Consolidation Behaviour of Cement-Bentonite Barrier Materials Containing PFA and GGBS

Cement-Bentonite (CB) barriers are expected to become a sustainable and reliable engineering solution. The deformation of CB is of interest to engineers to comprehend, particularly how CB responds to changes in loading during its construction and service life. The purpose of this study was to examine how samples of CB mixtures behaved during consolidation. This study investigated: (1) the influence of curing time and constituent materials on the consolidation properties of CB samples, (2) the volumetric change and the rate of volumetric change in response to a specific loading condition via consolidation tests. For this purpose, a laboratory consolidation test with a load range of 50 to 3200 kPa was carried out in accordance with BS 1377-7:1990 using the oedometer apparatus. This study discovered that the consolidation characteristics of CB samples are similar to those of overconsolidated soil. The CB sample became more resistant to consolidation under varying loads as curing progressed. The presence of more bentonite resulted in an increase in the recompression index. The inclusion of GGBS contributed to the consolidation characteristics of CB through the following mechanisms: (1) the significant decrease of the degree of consolidation with a curing period longer than 28 days, despite the slow strength development of the early-age curing; (2) the increase of the preconsolidation pressure; and the addition of GGBS was found to be more effective than the addition of more bentonite in increasing the preconsolidation pressure. Doi: 10.28991/CEJ-2023-09-03-02 Full Text: PDF

Improved radial consolidation in soft clay using pervious concrete piles

The efficacy of a pervious concrete pile (PCP) in accelerating the rate of consolidation in unconsolidated soft clay deposits was explored. A series of laboratory consolidation tests was performed on PCPs, sand drains and stone columns in two different soft soils (clay with high compressibility (CH) and clay with intermediate compressibility (CI)) and their consolidation characteristics were compared. A novel annular setup was used to determine the consolidation characteristics of all three techniques employed. Compared with the sand drain and stone column, the PCP provided an extensive enhancement in consolidation characteristics such as the coefficient of compressibility and the coefficient of consolidation. The enhanced compression index obtained using the PCP implied a compelling scope for accelerating the radial consolidation of the surrounding soil, which was less in the case of the stone columns and sand drains. An improvement in the rate of consolidation in the radial direction was observed in both the CI and CH soils when a PCP was employed. The acceleration in consolidation was greater in the CH soil than in the CI soil.

Consolidation testing of tailings in a slurry consolidometer using constant rate and accelerated loading

A high rate of rise of fine-grained mine tailings slurry on disposal in a tailings storage facility (TSF) may maintain their condition as underconsolidated. The proper simulation of such field deposition of tailings in conventional laboratory consolidation testing is challenging. A slurry consolidation test using a high constant rate of loading (CRL) simulates a faster rate of tailings disposal in a TSF. A better simulation is achieved, however, by applying accelerated loading in a slurry consolidometer to allow for the increased drainage path length as tailings are built up in the TSF. CRL and accelerated loading were used in a purpose-built, large, instrumented, stress-controlled slurry consolidometer to examine and compare the consolidation behaviour of coal tailings, red mud and gold tailings. At the end of the CRL and accelerated loading tests, the excess pore water pressures had not fully dissipated and the maximum applied stress was maintained to achieve full primary consolidation. The findings of this study showed that the consolidation behaviour of the tailings studied varied with the nature of the tailings and with the loading applied.

Calibration and validation of a new elastoviscoplastic soil model

AbstractThis paper presents the calibration and validation for a new 3D elastoviscoplastic soil model, MIT‐SR, for Resedimented Boston Blue Clay (RBBC). The calibration procedure requires selection of material constants from standard types of laboratory consolidation and undrained shear tests, and a procedure for initialization of state variables. The formulation includes two key input parameters that describe sensitivity of rate dependence, β, and creep behavior, ρα, for which the calibration requires data including CRS consolidation tests at a range of strain rates and drained creep tests. The calibrated MIT‐SR model is benchmarked through a series of simulations of K0‐consolidated triaxial shear tests and direct simple shear tests on RBBC performed at different rates of shear strain. The calibrated model provides very good predictions of the effects of shear strain rate on key engineering properties such as undrained shear strength, strain to peak shear resistance and critical state conditions as functions of the consolidation stress history. The predictions of multistage, undrained relaxation tests are also in good agreement with unique measured behavior reported for RBBC. The comparisons provide clear evidence of the advances in predictive capabilities achieved using the proposed MIT‐SR formulation compared to preexisting isotache‐type models.

Analytical solution for one-dimensional nonlinear consolidation of double-layered soil with improved continuous drainage boundary

Following the assumptions proposed by Davis and Raymond, an analytical solution for one-dimensional nonlinear consolidation of double-layered soil under constant loading is derived by introducing an improved continuous drainage boundary condition. The effectiveness of the present solution is assessed by comparing against other existing analytical solutions and laboratory consolidation test results. A parametric study is then conducted to investigate the consolidation behaviour of double-layered soil for different interface parameters or stress ratios (i.e. final effective pressure over initial effective pressure, Nσ ). The results show that, the average consolidation degree defined by soil settlement U s increases with the increase of N σ, and the average consolidation degree defined by excess pore water pressure U p decreases with the increase of Nσ . The magnitude of U s is always larger than U p, and the difference between U s and U p increases with the increase of Nσ . Compared with the Xie's solution, the stress ratio Nσ has little effect on U p in the solution with continuous drainage boundary condition.

Analysis of oedometer and rowe cell consolidation compared to experimental testing

Consolidation settlement in clay soils can be predicted by analyzing the consolidation parameters. Consolidation parameters were obtained from the results of a laboratory consolidation test using an oedometer and rowe cell. The rowe cell can measure pore water pressure, soil saturation, and back pressure as a simulation of field condition while the Oedometer cannot. However, there are significant differences between the results of the analysis with the consolidation settlement occurred in the field caused by drainage conditions, the micro characteristics of the soil structure, and the thickness of the soil layer. Therefore, it is necessary to validate the results of settlement in oedometer and rowe cell consolidation analysis with the value of settlement of experimental results. The method used is a laboratory consolidation test using an oedometer and rowe cell as well as a laboratory-scale experimental consolidation test. The results obtained 79% of differences between experimental and oedometer, while rowe cell had a difference of 37% from experimental. Based on this, analysis using rowe cell consolidation parameters can predict a settlement in consolidation in the field more accurately than oedometer, because it has a smaller difference in value.

Consolidation behaviour of double-porosity clay using flexible wall permeameter

Restoration of a site that has previously been prepared using dredged clay is a serious geotechnical challenge. Much of these clays exists as lumps suspended in slurry. These double-porosity soils consolidate due to the expulsion of water from the voids within each lump and the voids between the lumps. Due to this complex nature, the conventional theory of consolidation is not applicable to them. This study discusses the laboratory consolidation test results of double porosity samples. The tests were conducted on 10–30 mm clay lumps. The size, initial packing and the stiffness of the lumps were the variables. At low confining pressure the 30 mm lumpy samples experienced a significantly higher deformation than the 10 mm lumpy samples. In all the tests, the lumps and slurry merged to close the inter-lump voids as confining pressure neared or reached the pre-consolidation lump pressure. This paper also discusses the use of a simple constitutive relationship to model the behaviour of double-porosity fill. It uses the structured clay framework to describe the volumetric strain in the double-porosity samples by using two parameters, in addition to those required in the critical state soil mechanics. A parametric study demonstrated the capabilities of this model.

Coefficient of Consolidation and Volume Change for 3-D Consolidation

The settlement is the most serious problem of fine soil. This settlement is caused by a phenomenon called soil consolidation. Most previous studies were concerned with studying one (1-D) and two-dimensional (2-D) consolidation. That in some cases does not give a simulation of reality representation. It was necessary to study the three-dimensional (3-D) consolidation to simulate what happens to the fine soil in nature. Therefore, the consolidation behavior of four fine soils was studied in this paper. The studied soil samples were collected at the foundation levels of four different sites in El-Qalubia governorate, Egypt. A series of laboratory consolidation tests were carried out as one, two and three dimensional consolidation by using manufactured Oedometer apparatus. So, the effect of consolidation conditions (1-D, 2-D and 3-D) on consolidation coefficient (Cv) and volume change coefficient (mv) was investigated. Also, an empirical equation was correlated the relationship between Cv and mv.

Coefficient of Consolidation and Volume Change for 3-D Consolidation

The settlement is the most serious problem of fine soil. This settlement is caused by a phenomenon called soil consolidation. Most previous studies were concerned with studying one (1-D) and two-dimensional (2-D) consolidation. That in some cases does not give a simulation of reality representation. It was necessary to study the three-dimensional (3-D) consolidation to simulate what happens to the fine soil in nature. Therefore, the consolidation behavior of four fine soils was studied in this paper. The studied soil samples were collected at the foundation levels of four different sites in El-Qalubia governorate, Egypt. A series of laboratory consolidation tests were carried out as one, two and three dimensional consolidation by using manufactured Oedometer apparatus. So, the effect of consolidation conditions (1-D, 2-D and 3-D) on consolidation coefficient (Cv) and volume change coefficient (mv) was investigated. Also, an empirical equation was correlated the relationship between Cv and mv.

Geotechnical investigations at the caminada headlands beach and dune in coastal Louisiana

The Caminada Headlands is a beach and dune system near Port Fourchon in coastal Louisiana that provides natural protection for back barrier marshes against storm surges and wave overtopping. Due to significant shoreline erosion and regional subsidence, a beach and dune restoration project was initiated in 2012 to replenish the shoreline front. Because of the underlying soft deltaic sediments, this restoration effort was expected to cause significant increase in the applied vertical stress and thus sediment settlement. To quantify the degree of settlement occurring within the compressive sediment layers and the fill, extensive geotechnical investigations were conducted for design and installation of settlement plates and subsurface settlement anchors to monitor the field performance. This paper presents the geological and geotechnical investigations, measured material properties, and corresponding empirical correlations developed from fifty-one (51) laboratory consolidation tests. The pre- and post-survey elevations of the site are also used to determine the change in vertical stress with depth at the instrumented sites. The measured material properties and vertical stress profiles can be used to calibrate the numerical modeling of the sediment and fill settlements.

Appropriate Method of Determination of Coefficient of Consolidation for Municipal Solid Waste

Abstract To predict the rate of settlement of municipal solid waste specimens (MSW), it is essential to estimate the value of the coefficient of consolidation (Cv) using laboratory consolidation test results. Literature suggests that the various empirical curve-fitting methods used for assessing Cv are Casagrande’s logarithm of time fitting method and Taylor’s square root of time fitting method for the same test data. Both methods are derived from the time factor and degree of consolidation (T–U) relationship and corresponding laboratory time–compression (T–δ) relationship. For different types of wastes and loading conditions, the shapes of curves vary considerably, and the validity of these approaches is not established. In all these cases, the estimation of the Cv poses a serious problem. To overcome the above difficulties, the rectangular hyperbola method is used, in this article, to determine the Cv by U–T or t versus δ relationship. Earlier, this method was used for different coefficient of consolidation values of time for completion of different percentages of consolidation. It is found that the calculated values of Cv are found to be more reliable when the time for 60 % of consolidation is taken. The estimated Cv values from the rectangular hyperbola method lie between the existing standard methods of Casagrande’s and Taylor’s. The rectangular hyperbola method is simple and can be used for all shapes of time–compression curves, and the specific advantage of this method is that the initial compression need not be known and is devised to separate the initial, primary, and secondary compression for any load increment.

Radial consolidation characteristics of soft undisturbed clay based on large specimens

In recent years, reconstituted small samples have often been used to assess the performance of radial consolidation due to prefabricated vertical drains (PVDs), but the permeability and compressibility of samples of undisturbed soil often differ from those of the remoulded ones. The problem seems more complex in marine environment due to the presence of random coarse particles including gravels, shells and natural partings. Performing small-scale laboratory experiment with reconstituted samples, especially in marine environment, cannot predict the exact soil behaviour in the field. This paper describes an experimental programme that measures radial consolidation using a conventional Rowe cell and a large-scale consolidometer, where the samples of undisturbed soil obtained from a site along the Pacific Highway (north of Sydney) were compared using measured settlements and excess pore pressures. Moreover, this paper highlights the implications of the smear effect and sample size influence, which are imperative in translating the laboratory testing practices to actual real-life behaviour. The effect of vacuum pressure on the coefficient of radial consolidation of a large-scale undisturbed test specimen is also discussed. The paper demonstrates that the extent of smear zone in the field can be very similar to the large-scale laboratory consolidation test using a scaled-down drain and mandrel, but considerably different from the data obtained for small laboratory specimens.

Profiling the in situ compressibility of cretaceous shale using grouted-in piezometers and laboratory testing

Grouted-in vibrating wire pressure transducers (VWPs) can be used to measure the in situ laterally constrained compressibility (mv) of deep claystone aquitards through measurement of barometric loading efficiency. Here, we present the results from 27 VWPs installed in overconsolidated argillaceous glacial till and claystone formations in southern Saskatchewan, Canada at two sites over depths ranging from 10–325 m below the ground (m BGS). The measured mv profiles at both sites produced similar trends of decreasing mv with depth. The trends in compressibility with depth were compared to the results from laboratory consolidation testing of core samples taken from the same Cretaceous shale profile. An apparent pre-consolidation pressure σc′ compression index (Cc), and the swelling index (Cs) were determined using 1-D consolidation testing. These tests yielded Cc values ranging from 0.12–0.41 x¯=0.27±0.11 andCs from 0.015–0.09 x¯=0.05±0.03. The theoretical depth profile for mv (during unloading) was calculated for a range of compression indices (Cc, Cs) and the in situ void ratio (e)estimated from the consolidation testing, the vertical effective stress σv′ calculated based on the effective unit weight of overburden and laboratory determined preconsolidation values σc′. Varying the values of σc′, Cc, or e in the hypothetical depth profile demonstrated minor influences on these profiles when compared to that of. The resulting theoretical profiles of mv with depth orσv′ exhibited a similar pattern to the laboratory and field observations; however, for the laboratory test data to replicate the in situ profiles, the laboratory measured values of Cs had to be reduced by an order of magnitude in order to compensate for both the applied strain increment differences, as well as sample destruction during recovery and testing. The good agreement between the theoretical and the in situ measured mv profiles with depth highlight the potential to combine in situ measurements of mv with laboratory consolidation test results to characterize the mechanical properties of deep claystone aquitards.

Direct-push Based Seismic Crosshole Testing for Geotechnical Engineering Applications

ABSTRACT In areas with an unknown geology, boreholes are usually placed either at the planned location of buildings and infrastructure or following a semiregular pattern. The number of boreholes is typically limited by installation cost, especially the number of boreholes to be used for geophysical testing, such as those used for downhole, crosshole, or tomographic analyses. An alternative approach to conventional drilling is the use of mobile pushing devices, i.e., direct-push procedures. By placing geophysical tools into the pushing rods, geophysical methods become more flexible and adaptive during drilling, and investigation techniques can be implemented more expeditiously. From a geoengineering perspective, the in-situ tests are relatively efficient because they generate near continuous data and are considerably more accurate in comparison to laboratory consolidation tests. In this paper we present a combination of a direct-push system with seismic crosshole measurements as a cost effective alternativ...

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.

Field scale hydraulic conductivity and compressibility of organic clays

This paper uses the results of an extensive subsurface investigation performed along the Inner Harbor Navigational Canal in New Orleans, Louisiana to identify the scale effect of soil hydraulic conductivity (K) and compressibility (mv) for geotechnical and geoenvironmental analyses. The magnitude and variability of soil hydraulic conductivity and compressibility parameters were obtained from laboratory 1-D consolidation and permeameter tests, CPTu dissipation tests, field piezometer slug tests, and multiple well pump tests. The geometric means of horizontal hydraulic conductivity (Kh) measured by the laboratory permeameter, slug, and field pump tests are 2.5×10−7, 1.6×10−6, and 1.3×10−5cm/s, respectively. This represents a scale effect of about 50 times when increasing the sample volume tested from the laboratory to field scale. The uncertainty in vertical hydraulic conductivity (Kv), Kh, and mv values was determined using a coefficient of variation, which ranges from 0.34 to 0.73. While Kh is scale dependent, a comparison of mv evaluated from field pump and 1-D consolidation tests indicates that sample volume does not significantly impact measured values of mv, which signifies that laboratory consolidation tests can be used to predict field scale compressibility.

ESTIMATING LOAD-DISPLACEMENT BEHAVIOR OF SOFT CLAYS

Prediction of long term settlement of soft soils below civil engineering structures is an important issue in geotechnical engineering. The data from laboratory consolidation tests are used to estimate the ultimate settlement and problems arise in predicting settlement-time behavior in the field. In order to overcome this difficulty some empirical models or adjustments have been proposed based on field settlement measurements, even if they are available at least for the early stages of loading. In this study, laboratory test results and field settlement measurements obtained for the long term settlement of clayey layers underlying the Alibey Dam in Istanbul, Turkey are used in conjunction with a model proposed by Edil and Mochtar (1984) for peat-like soils. The soil parameters of the proposed model have independently been obtained using both laboratory test data and field measurements, and model predictions are compared with actual recorded settlements. It is observed that the field measurements could be predicted more closely if the model parameters are obtained from field measurements, but predictions based on laboratory consolidation and creep test results also provide satisfactory results following the initial stages of loading.

Consolidation Coefficient by Combined Probabilistic and Least Residuals Methods

Abstract Accurate prediction of the rate of consolidation settlement is dependent upon a reliable method of determining the coefficient of consolidation (cv) and the time to end of primary consolidation of the natural soil. For this purpose, and to circumvent errors associated with graphical procedures in evaluating cv, a FORTRAN program was developed to determine the best fit of laboratory consolidation test data using a combination of a probabilistic method and a minimization of the sum of squared residual (SSR) method. The proposed computer procedure does not use any particular point on the time-settlement curve. The program uses ranges of probable values of d0, d100, and cv. For each set of values d0, d100, and cv selected in a random manner, the SSR is computed. The set of values with the smallest SSR is considered as the best fit. This procedure leads to suitable reference values of the coefficient of consolidation and the end of primary consolidation, and permits an assessment of the accuracy of classical graphical log(t) and t1/2 procedures.

Stress-strain behaviour analysis of Middle Polish glacial tills from Warsaw (Poland) based on the interpretation of advanced field and laboratory tests

Abstract The selected parameters of the Wartanian and Odranian tills, with relation to their spatial occurrence, grain size distribution, mineralogical composition, matric suction and other physical characteristics, are presented. The assessment of the lithogenesis and stress history on the microstructure is attempted. The comparison of the compression and permeability characteristics from field and laboratory tests has been performed. Laboratory consolidation tests carried out with up to 20MPa vertical stress, revealed two yield stress values, one in the range of a couple hundreds kPa, the other in the range of a couple thousands kPa. Based on those results, the reliability of the soil preconsolidation assessment, with the use of the two different methods is discussed. The aspect of the triaxial strength reduction under the dynamic loading of diverse frequency and amplitude is raised. The research results depict a variety of possible geological-engineering characteristics, under the divergent constraints scenarios, of compression or strength weakening origin. The effects of the specialized research program will widen the possibilities of physio-mechanical and structural characterization of soils for geological-engineering purposes.