Consolidation Test Results Research Articles

Influence of Pore Fluid Viscosity on the Dynamic Properties of an Artificial Clay

This paper presents the results of vane shear, laboratory compaction, isotropic consolidation, cyclic triaxial, bender element, and resonant-column tests that were performed to characterize the dynamic properties of an artificial soil called modified glyben. Modified glyben comprises a mixture of glycerin, water, and bentonite that can be used in scaled model tests performed at 1 G or n G in a centrifuge to study seismic soil–structure interaction. The results described in this paper show that the vane shear strength, coefficient of consolidation, dynamic modulus, and damping ratio are strongly influenced by the viscosity of the pore fluid which can be varied by altering the ratio of glycerin-to-water. In addition, the properties of modified glyben are stable during prolonged exposure to air and multiple largestrain load cycles making it a suitable model soil for scaled model tests involving seismic soil–structure interaction.

Electrokinetic treatment on a tropical residual soil

The results of shear box and consolidation tests on electrokinetically-treated tropical residual soil are presented. Injections of selected chemicals (calcium chloride, aluminium chloride and phosphoric acid) into the soil samples at the anodes or cathodes were carried out in cylindrical electrokinetic cells via applications of 30 V DC electrical potential for 168 h. Four different open-anode and open-cathode electrokinetic systems utilising different anolytes and catholytes were employed to treat the soil samples. The shear resistances of the treated soil utilising distilled water as the anolyte and 1·0 mol/l phosphoric acid as the catholyte was enhanced, whereas the treated soil near the cathode showed significant reduction in compressibility. Soil treated utilising the other chemicals showed no significant changes.

Experimental Investigation on Dynamic Constitutive Model of Saturated Sandy Pebble Soil

The dynamic constitutive model could show the dynamic characteristics of soil, so it was essential in ground motion in earthquake safety evaluation and seismic response analysis of soil, and it had great influence on research and analysis of seismic performance of soil and the stability of the foundation. Sandy pebble soil distributed abroad in Sichuan, so it was widely used in engineering construction. Based on the test results of dynamic triaxial non-drain consolidation test，this paper studied the dynamic constitutive model of saturated sandy pebble soil to provide reference for the future use.

On the Use of Skempton’s Compression Index Equation

In this study, an alternate approach to establish the e-log p relationships for clayey soils within a vertical pressure range of 10–1,000 kPa is discussed. Skempton’s compression index equation correlating the liquid limit, w L, and the compression index, C c, and the reported equation correlating the void ratio at liquid limit, e L, and the void ratio at a vertical pressure of 100 kPa, e 100, by Burland (1990), were used to establish the e-log p relationships for several reconstituted normally consolidated clayey soils. Consolidation test results of 13 clayey soils covering a sufficiently wide range of liquid limit were selected from the literature. Also, consolidation tests were carried out on two highly expansive soils in this study. A comparison of the experimental consolidation test results with the calculated e-log p relationships in the current study indicated that in general, the agreements between the calculated relationships and the experimental results are good. The agreements were found to be slightly better for soils with liquid limits less than about 70%. A comparison of the calculated e-log p relationships in the current study with that determined following methods suggested by Nagaraj and Srinivasa Murthy (1983) and Burland (1990) showed that all the three methods yielded very similar results for soils with liquid limit less than 70%. For soils with liquid limits greater than 70%, the difference between the e-log p relationships calculated in this study and that following Burland (1990)’s method was insignificant, whereas Nagaraj and Srinivasa Murthy (1983)’s method slightly over-predicted the void ratios at larger vertical stresses.

Proposal of a Simple Method for Assessing the Susceptibility of Naturally Deposited Clay Grounds to Large Long-Term Settlement due to Embankment Loading

A simple method that utilizes the results of laboratory tests has been proposed for determining the susceptibility of soft clay grounds to large residual consolidation settlement due to embankment loading. It was found that there is a possibility of large long-term settlement if the sensitivity and compression index ratios of the clay material that constitutes the ground are equal to or more than 8.0 and 1.5, respectively. The compression index ratio is defined in this paper as the ratio (Cc/Ccr) of the steepest gradient of the compression curve of an undisturbed sample to that of the remolded sample. Through the SYS Cam-clay model, an elasto-plastic constitutive model that describes the actions of the soil skeleton structure, it was found that clays with large sensitivity and compression index ratios are characterized by initially highly structured soils and that decay/upgradation of the structure can easily occur due to plastic deformation. In addition, by following Schmertmann's graphic method for in-situ compression curve (1953), this paper proposes a method of deducing the in-situ initial conditions from the results of laboratory consolidation tests on undisturbed samples. These investigations revealed not only that large delayed settlement is facilitated in clays, which have higher degrees of structure and faster rates of structural decay, but also that the Δe method and other simple methods of predicting settlement may underestimate the amount of settlement.

Variability of Physical and Consolidation Test Results for Relatively Uniform Clay Samples Retrieved from Osaka Bay

ABSTRACT Samples collected from both Holocene and Pleistocene layers in Osaka Bay were examined in this study. The objective of this study is to evaluate variations of soil parameters in a sample length of about one meter. The retrieved samples from EL. (elevation) -37.5 to -38.5 m and from EL.-125.5 to -126.5 m with a length of about one meter were divided into every 25 mm long to trim consolidation specimens. Variations of soil parameters obtained from laboratory tests were evaluated. Clay microfabric was also evaluated by scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). The clay layers are relatively homogeneous with variation coefficient CV in a range of 0.025 to 0.12 for the consolidation parameters (e, p′c, Cc and cv). CV of void ratio e is only 0.025 to 0.056. In contrast, CV values of the other consolidation parameters are significantly greater than this, but the average is less than 0.1. It can be concluded that CV of soil consolidation parameters for the homogeneous natural clay deposits dealt in this study is less than about 0.1. These variations are mainly influenced by sedimentary environment. Even the soil is said to be homogeneous, because the specimen size for the laboratory tests is sufficiently large in consideration of microscopic heterogeneity obtained from SEM and MIP.

Soil-water characteristic curve and consolidation behavior for a compacted silt

Measurement of the soil-water characteristic curve (SWCC) in the laboratory is commonly conducted under zero confining pressure. However, in the field, the soil is under a confining stress. Therefore, it is important to study the effects of the confining stress on SWCC. In addition, the consolidation curve is normally generated under saturated conditions. However, the soil above the water table is usually unsaturated. Hence, it is also necessary to investigate the effects of matric suction on the characteristics of the consolidation curves. This paper presents the SWCCs under different net confining stresses and the isotropic consolidation curves under different matric suctions that describe the volume change characteristics of unsaturated soils with respect to stress state variables, net normal stress, and matric suction. A series of SWCCs was determined for statically compacted silt specimens in a triaxial cell apparatus under different net confining stresses. Isotropic consolidation tests under different matric suctions were also carried out. The results of the SWCC tests show that the air-entry value increased with increasing net confining stress. The yield points (i.e., yield suction, s0) obtained from the SWCC tests also increased with increasing net confining stress. The results of isotropic consolidation tests indicate the strong influence of matric suction on compressibility and stiffness of the compacted silt specimens.Key words: soil-water characteristic curve, isotropic consolidation, pore-water pressure, volume change, NTU mini suction probe, matric suction.

Elastoplastic model for unsaturated soil with incorporation of the soil-water characteristic curve

An elastoplastic model is proposed in this paper that incorporates the soil-water characteristic curve (SWCC) for obtaining soil parameters of unsaturated soil. The SWCC is shown to govern the rate of change in the soil parameters for the elastoplastic model with respect to matric suction. A series of isotropic consolidation tests under different matric suctions and tests for obtaining SWCC were carried out on statically compacted kaolin specimens. Nanyang Technological University (NTU) mini suction probes were installed along the height of the specimen to measure pore-water pressures during isotropic consolidation and SWCC tests. The results of isotropic consolidation tests demonstrate the strong influence of matric suction on compressibility and stiffness of the soil specimens. The experiments were also simulated using the proposed elastoplastic model and SWCC of the compacted kaolin. The simulated results agree closely with the experimental results. In addition, the proposed elastoplastic model was also verified against published data from the literature.Key words: matric suction, yield surface, soil-water characteristic curve, mini suction probe, elastoplastic model, unsaturated soil.

Long term compression behavior of fibrous peat

This paper discusses a long term compression behavior of fibrous peat, analyzed based on data obtained from consolidation test performed in Rowe cell with excess pore water pressure measurement. The preliminary test results show that the peat used in this study is classified as fibrous peat with low to medium degree of decomposition and of very high organic and fiber contents which are typical of peat found in Peninsular Malaysia. The results of consolidation test show that the fibrous peat has a high compressibility with primary compression index of 3.15 and significant secondary compression stage which is not constant with the logarithmic of time. The secondary compression started as early as 65% degree of primary consolidation. The study showed that the consolidation test with pore water pressure measurement using Rowe cell is advantageous because it enables the observation of the large deformation and better assessment of the long term compression behavior of fibrous peat. The separation of primary and secondary consolidation is very important for the evaluation of long term compressibility behavior of fibrous peat.

Study The Effect of Industrial Waste (Industrial Water) on The Engineering Properties of Expansive Clayey Soil

This Research deals with the effect of industrial waste on the engineering properties of clayey soil .The investigated soil was obtained from (1.0) meter depth Al- Yarmook district in Mosul City. The soil can be described as light brown stiff clay, in organic clay with high plasticity (CH), and it contains (38%) clay size particles (≤ 0.002 mm). The soil was treated with four types of industrial waters, taken from several factories located in Mosul city and from fertilizers factory in Baiji region. The Results, show that the industrial waters caused a little reduction in the liquid limit and Increased the plasticity index, except the fertilizers factors Industrial waters where plasticity index of the soil decrease with increasing the addition of this type of industrial waters. As far as the effect of industrial waters on the compaction characteristics, the result showed that the maximum dry density of the soil increased with the addition of industrial waters and the optimum moisture content decreased. The industrial waters increased the unconfined compressive strength and the shear strength parameters (angle of internal friction (φ’ ) and cohesion (c’)) , except the industrial waters from sugar and yeast factories decreased the angle of internal friction . The study, showed that the swelling percentage and swelling pressure increased with increasing the concentration of industrial waters, except the industrial waters of the fertilizers factory, where the swelling characteristics decreased.The results of consolidation test showed that the compression Index (cc) and coefficient of consolidation (cv) increased when the soil was treated with industrial waters. The results of chemical tests showed that the values of cat ion exchange capacity and organic matter content increased while the (pH- value) decreased for treated soil, except the Industrial waters of fertilizers factory, which caused an increase in the (pH- value) .

Nonlinear compressional waves in marine sediments

A theory for nonlinear waves in marine sediments must account for the presence of a granular frame filled with water and possibly gas bubbles. When grains are in full contact, the stress–strain relation for the sediment contains a contribution varying as strain to the power 3/2, referred to as the Hertz force. The quadratic nonlinearity parameter derived from the second pressure derivative with respect to density thus diverges in the limit of small strain. We present a simple nonlinear wave equation model (a variant of the NPE) for compressional waves in marine sediments that avoids Taylor expansion and the problem of diverging nonlinearity parameter. An equation of state for partially consolidated sediments is derived from consolidation test results. Pressure is found to increase with overdensity to the power 5/2, indicating an increase in the number of contacts per grain as density increases. Numerical results for nonlinear compressional waves show agreement with analytic self-similar profiles derived from the nonlinear wave equation. [Work supported by the ONR.]

Analysis of Results of Consolidation Tests of Saturated Clayey Soils

It is shown that the dependence of soil deformation on the distance to the drainage boundary, which is noted by a number of experimenters for the stage of secondary consolidation, is explained by incorrect interpretation of test data. Laboratory results demonstrating an apparent lack of creep in the stage of primary consolidation are explained by characteristic features of the generalized consolidation equations and relationships between their parameters.

Fundamental Parameters of Cement-Admixed Clay—New Approach

The fundamental parameters such as after-curing void ratio (eot) and cement content (Aw) have been found sufficient to characterize the strength and compressibility of cement-admixed clay at high water contents. From analyses performed on the results of unconfined compression tests, the ratio eot/Aw has been proven to combine together the influences of clay water content, cement content, and curing time on the strength of cement-admixed clay. Moreover, the results of oedometer consolidation tests revealed that while Aw governs the position of the postyield compression line, the magnitude of eot determines the magnitude of the one-dimensional vertical yield stress σvy′ at particular Aw. The value of eot reflects, primarily, the clay water content and, secondarily, the cement content and the curing time. Normalizing the after-curing unit weight, after-curing water content, and after-curing specific gravity were incorporated in an empirical relationship of eot.

Investigation of mass wasting on the continental slope and rise

A methodology is presented for the investigation of submarine slope instability. This approach integrates the results of a variety of tools and methods, including multibeam, side scan and subbottom acoustic data, geotechnical sampling and testing, and advanced dating techniques. For slides/slumps that have the potential for causing tsunamis, the use of long, large-diameter piston corers is a cost-effective way of obtaining good quality sediment samples. Using a Multi-Sensor Core Logger and geotechnical analyses, a baseline of sediment properties is developed from nearby stable, unfailed regions, which is then compared to more active areas where faulting and instability is suspected. Clear evidence of past and recent slope failures can often be obtained from the stress history of the sediment derived from consolidation test results and from careful identification of naturally deposited sediments overlying relic failures. This methodology was applied for the investigation of slope failures along a study corridor in deepwater Gulf of Mexico. Large failures were identified from multibeam data, and coring locations were chosen based on subbottom and side scan data obtained with a deep-tow system. Buried failures were identified from detailed bulk density measurements, geotechnical test results, and paleomagnetic and 14C dating techniques. Dating of these failures can provide information regarding the triggering mechanisms of these events, which can be used to assess the current risk of new instabilities.

Pore pressure development and progressive dewatering in underthrust sediments at the Costa Rican subduction margin: Comparison with northern Barbados and Nankai

At subduction zones, pore pressure affects fault strength, deformation style, structural development, and potentially the updip limit of seismogenic faulting behavior through its control on effective stress and consolidation state. Despite its importance for a wide range of subduction zone processes, few detailed measurements or estimates of pore pressure at subduction zones exist. In this paper, I combine logging‐while‐drilling (LWD) data, downhole physical properties data, and laboratory consolidation tests from the Costa Rican, Nankai, and Barbados subduction zones, to document the development and downsection variability of effective stress and pore pressure within underthrust sediments as they are progressively loaded by subduction. At Costa Rica, my results suggest that the lower portion of the underthrust section remains nearly undrained, whereas the upper portion is partially drained. An inferred minimum in effective stress developed within the section ∼1.5 km landward of the trench is consistent with core and seismic observations of faulting, and illustrates the important effects of heterogeneous drainage on structural development. Inferred pore pressures at the Nankai and northern Barbados subduction zones indicate nearly undrained conditions throughout the studied intervals, and are consistent with existing direct measurements and consolidation test results. Slower dewatering at Nankai and Barbados than at Costa Rica can be attributed to higher permeability and larger compressibility of near‐surface sediments underthrust at Costa Rica. Results for the three margins indicate that the pore pressure ratio (λ) in poorly drained underthrust sediments should increase systematically with distance landward of the trench, and may vary with depth.

Consolidation Inverse Analysis Considering Spatial Variability and Non-Linearity of Soil Parameters

One-dimensional consolidation inverse analysis based on the stochastic nonlinear consolidation model (SNCM) is discussed in this study. The model is determined from the standard consolidation test results, and represents the non-linearity and spatial variability of the coefficient of volume compressibility and the coefficient of permeability simultaneously. Furthermore, the inverse analysis method is proposed on the basis of the SNCM and the finite element method mixed with the Monte Carlo simulation. Measured settlement and pore water pressure are used as observation data in the inverse analysis. The method is applied to the consolidation test results of kaolin clay, and its applicability is confirmed firstly. Then the inverse analysis of an actual soft ground is performed. Future consolidation behavior of the ground is predicted, and the spatial variability and the non-linearity of the consolidation parameters are identified. It is clarified in this study that complicated spatial variability and non-linearity of the consolidation parameters could be considered appropriately in the proposed inverse analysis method, and the method gives accurate prediction of consolidation behavior.

Geotechnical characterization of calcareous sediments from the Dry Tortugas Keys and Marquesas Keys CBBL SRP study sites, Lower Florida Keys

Geotechnical characteristics of carbonate sediments from two test sites (Dry Tortugas Keys and Marquesas Keys) in the Lower Florida Keys were investigated as part of the Coastal Benthic Boundary Layer Special Research Program, through an extensive field coring and laboratory testing program conducted by the Marine Geomechanics Laboratory of the University of Rhode Island. Based on results from physical measurements, water content and wet bulk density values for both sites generally showed large variations in the upper 25 cm and little variation below this depth. Sediment samples exhibited low plasticity or nonplastic characteristics. Constant-rate-of-deformation consolidation test results showed strong apparent overconsolidation (stress state ratio >7.5) in the surface sediments (upper 50 cm) at the Dry Tortugas Keys, and light overconsolidation (stress state ratio <1.5) below 50-cm depth at the Marquesas Keys site. In-situ permeability values were between 10–4 and 10–7 cm/s at both sites and showed no strong depth dependence in the upper 2 m. Undrained shear strength profiles for Dry Tortugas Keys sediments indicated a marked stiffening with depth, whereas the Marquesas Keys sediments showed a gradual increase with depth. Consolidated isotropically undrained triaxial shear strength test results indicate that the undisturbed sediments had an average effective angle of internal friction of 38°, which is not fully realized until large axial strains on the order of 11% have accumulated. Evidence of cementation was not found in triaxial compression or consolidation test results. The general behavior and characteristics of these sediments are similar to those of granular materials, which is primarily due to their high calcium carbonate contents and lack of cementation.

Settlement and slaking problems in the world's fourth largest rock-fill dam, the Ataturk Dam in Turkey

The Ataturk Dam is the fourth largest clay cored rock-fill dam in the world. Located in southeastern Turkey, it is the centrepiece of a project called the Southeastern Anatolian Project (GAP). The construction of the dam was finished in the short time of 3 years and 8 months in August 1990. As the reservoir level started to rise, settlement problems started to occur along the crest reaching considerable levels by May 1992 and the weathered vesicular basalt used in the rock-fill section of the dam started to slake seriously. The elevation of the crest has fallen down to such an extent that now the upper part of the dam is being reconstructed to the original height of 549 m in order to maintain the 7 m freeboard and keep the dam operational. The settlement and slaking problems of the dam were investigated both in the field and the laboratory using soil and rock mechanical techniques. Standard proctor tests were run to determine the optimum moisture content at which the highest dry density (best compaction) is obtained during compaction of the impervious clay core. Consolidation tests were performed on undisturbed compacted clay core samples to determine if the field compaction of the clay core was done to the standards determined in the laboratory. Unconfined compression tests were run on the two different (sound aphanitic and weathered vesicular) basalts used in the rock-fill section of the dam to determine their unconfined compressive strengths. Slake durability tests were run on the same basalts to determine their durability under wetting and drying cycles. Petrographic and X-ray analysis were done so as to study the mineralogical contents of the two basalts and in turn, to determine the cause of rapid slaking of the vesicular textured weathered basalt. The consolidation test results show that, the field compaction of the impervious clay core of the dam was not done to the standards determined through the proctor tests in the laboratory. The unconfined compressive strength of the sound aphanitic basalt is more than ten times greater than the weathered vesicular basalt, and while the former has extremely high durability the latter only has medium durability. Because of nontronite (iron montmorillonite) and secondary calcite amygdules filling the vesicles, the weathered vesicular basalt used in the rock-fill section is slaking badly causing additional settlement and landslides both in the clay core which is already settling and the rock-fill section of the dam. With the continuing slaking, the present reconstruction of the crest up to the theoretically intended height of 549 m to maintain the 7 m freeboard and keep the dam operational seems only to be a temporary solution.

Prediction of Field Compressibility from Laboratory Consolidation Tests of Peats and Organic Soils

Abstract Gibson and Lo (1961) compressibility parameters a and b for an organic soil can be determined from the organic content and the current pressure using the model presented by Gunaratne et al. (1998). These parameters, however, were developed based on results of laboratory one-dimensional consolidation tests and are valid for the K0 state. Researchers such as Edil et al. (1984) have found that the experimentally determined values of b in particular are larger for field situations. Therefore, the compressibility parameters have to be modified to predict field settlement under surcharges. This paper describes an extended model that addresses this issue and demonstrates how the laboratory-based b value can be corrected for field loading conditions. Finally, results of a full-scale, instrumented field settlement study of organic soil are shown to correlate well with the predictions of the extended model.

Modelling the rate-sensitive characteristics of the Gloucester foundation soil

Stages 1 (1967) and 2 (1982) of the Gloucester test embankment are studied using a fully coupled finite-element model. The rate-sensitive characteristics of the foundation soil are modelled using an elastoviscoplastic constitutive equation based on the elliptical cap yield surface and Perzyna's overstress theory of viscoplasticity. The aspect ratio of the yield surface for the Gloucester foundation soil is estimated using conventional laboratory shear and consolidation test results. Calculated and measured behaviour during consolidated isotropically undrained triaxial tests and long-term Rowe cell consolidation tests are compared and the ability of the model to describe the measured behaviour of stages 1 and 2 of the Gloucester test embankment is studied. This paper explores the implications of modelling the residual or restructured properties of the Gloucester foundation soil and demonstrates the ability of a single elastoviscoplastic yield-surface model to describe the undrained and drained response of the Gloucester foundation soil during laboratory and field loading conditions.Key words: elliptical cap, rate sensitive, elastoviscoplasticity, embankment settlements, pore pressures, field performance.