Intrinsic Compression Line Research Articles

A new framework for evaluating the virgin compression curves of reconstituted clays at different initial water contents

The influence of initial water content on the virgin compression of reconstituted clays is a topic of great importance. This study introduces a novel perspective based on the concept of intrinsic compression. It is demonstrated that the virgin compression curves of the reconstituted clays are similar in shape to the intrinsic compression line and can be obtained through vertical shifting and stretching. Building upon this concept, the intrinsic compression line is further extended to the compression curve cluster, enabling a direct evaluation of the influence of initial water content. The validity of the compression curve cluster is verified using independent data from the literature as well as data collected by our research team. In addition, a comparison with other relevant theories further underscores the superiority of the proposed framework.

Compressive Behavior of Reconstituted Soils at High Initial Water Content: Case Study on South-Western Region Of Bangladesh

This study illustrates the experimental investigation of the effect of high initial water content on the compression behavior of reconstituted soil. For this attempt, disturbed soil samples were collected from two selected locations of the KUET campus, Khulna, Bangladesh. The reconstituted soils were prepared in the laboratory at different initial water content, ranging from 0.7 to 1.2 times their corresponding liquid limit. The main focus of this study was to investigate the compression behavior of reconstituted clays using oedometer tests. This work was complementary to the intrinsic compression line concept proposed by Burland (1990). In the laboratory, ASTM methods were followed to measure the initial properties of soils. Here, it can be observed that e - logσv compression curves show an inverse "S" shape as a result of resisting deformation due to pressure. Moreover, some important correlations were developed based on the initial void ratio and the void ratio at the liquid Limit e0/eL . It has been observed that the void index is a dominating parameter to normalize the squeezability characteristics at different initial water contents in the plastic post-yield regime. A non-unique relationship is obtained for different soils to express the intrinsic compression line concept. However, there is a proportional relationship between intrinsic compressibility and initial water contents or liquid limits. Journal of Engineering Science 14(1), 2023, 1-9

Effects of organic content on sewage sludge compression behaviour

Five sewage sludge specimens with different organic contents were prepared by mixing mass ratios of 0, 5, 10, 20 and 40% dry soil powder into raw sewage sludge. The addition of dry soil powder can reduce the organic content of sewage sludge without significantly changing its particle composition. Oedometer tests were conducted, starting from a small effective vertical stress [Formula: see text]. It is observed that the [Formula: see text] compression curves show an inverse ‘S’ shape due to suction pressure resisting deformation. The suction pressure decreases exponentially with the organic content, a regression equation for which is provided. Burland’s concept of the intrinsic compression line (ICL) is adopted for correlating the compression curves of sludge with various organic contents. It is found that the ICL with a high organic content lies above the low one – that is, the higher the organic content, the greater the void index. In addition, the shape of the ICL for organic sludges is an inverse S rather than slightly concave upwards for inorganic reconstituted clays. An average ICL is provided to normalise the compression curves of sludges with different organic contents. The intrinsic compression parameters [Formula: see text] and [Formula: see text] can be correlated with the organic content, which increase linearly with the organic content, and the regression equations for them are provided.

Geotechnical characterization of deep Shanghai clays

To date, investigations of soils in Shanghai have mainly focused on upper clays, namely, Layer 2–6, generally within 30–40 m depth. Knowledge of the deep clays of Layer 8 and 10, at depths of approximately 50 m and 100 m, respectively, is very limited. In this study, the detailed geotechnical properties of the deep Shanghai clays of these two layers were investigated through a series of field and laboratory tests. Physical property tests showed that both clays can be classified as low-plasticity silty clay. For the first time in Shanghai, high-quality intact clay samples were retrieved from the deep soil using a double-tube rotary sampler. High-pressure oedometer tests and consolidated undrained (CU) triaxial tests were conducted to evaluate the compressibility and shear strength of intact samples. The oedometer tests indicate that Layer 8 is an overconsolidated clay with an overconsolidation ratio (OCR) of 2–3, and Layer 10 is a normally consolidated clay with a light degree of structure. CU triaxial tests further confirmed the above findings. The compressibility of the Layer 8 clay is lower, and its undrained shear strength and effective friction angle are larger than those of Layer 10, with the latter being deeper. The sensitivity framework, based on Burland's intrinsic compression line (ICL) and sedimentary compression line (SCL), can be used to characterize the overconsolidation/structure nature of the deep Shanghai clays. The strain energy method was found to be more suitable than the Casagrande method for determining the preconsolidation pressure of the deep Shanghai clays.

Experiment study on normalized compression behaviour of marine diatomaceous soil considering microstructure of biogenic silica

There are many sites in the world where diatom microfossils have been detected, but very little is known about their effect on sediment geotechnical properties. Diatomaceous soils (herein called “biogenic silica soils”) are usually composed by a mix of sand, fine-grained clay and diatom (and, or radiolarian). This paper presents an experimental investigation on the compression behaviour of biogenic silica-kaolin (BSi-K) clay mixtures and natural marine diatomaceous soils. The results show that the BSi composition dominates the compression when the BSi content is higher than 50%. The microstructure of biogenic silica frustules is first characterized and a skeletal void volume model (BSi-SVV model) is proposed. By using this model, the addition water in biogenic silica frustules can be quantitatively evaluated, which is up to 92.6% as the BSi content is 78%. It can be explained as the cause of high natural water content and low plasticity of diatomaceous soils. By introducing the effective void ratio, the compression curves can be normalized; furthermore, a new intrinsic compression line (BSi-ICL) suitable for BSi-K clay mixtures is developed based on the intrinsic compressibility concept of Burland (1990). It is considered as an extension of Burland's ICL. Finally, the effect of initial water content on the normalized compression behaviour is investigated. The findings in this study can provide a deeper insight into the geotechnical properties of marine diatomaceous soils.

Effects of initial water content on compression behaviour of municipal sewage sludge

To investigate effects of initial water content on compression behaviour of municipal sewage sludge and clarify its intrinsic compression characteristics. Oedometer tests were conducted on sludge with various initial water content of 0·13–1·48 times the liquid limit. It is observed that the sludge is organic high liquid limit silt, whose e–log σ′vcompression curves are inverse ‘S’ shape due to organic floc structure of sludge potentially. When the effective vertical stress σ′v > 100 kPa, a clear gap of compression curves of various initial water content still exists, different from Burland's viewpoint that compression curves tend to be consistent. Burland's concept of intrinsic compression line (ICL) is adopted for correlating compression curves of sludge well, and an ICL of the sludge is derived. The ICL of sludge is below ones reported by Hong and Burland when σ′v < 100 kPa, due to the difference in initial water content. A generalised void index is tentatively proposed by introducing generalised intrinsic parameters e*y1and e*y2, which may be related to the loading history of the soil and the maximum load that the soil may bear in future engineering, respectively.

Microscopic Evolution of Pore Characteristics and Particle Orientation of Granite Residual Soil in One-Dimensional Compression

This study investigates the microstructural changes of granite residual soil (GRS) upon compression, the aim being to understand further the deformation mechanism from a microscopic perspective and establish the relationship between the mechanical behavior and microstructural characteristics of GRS. By means of (i) experimental compression tests with different loadings and (ii) scanning electron microscopy (SEM), the structural evolution of GRS during compression tests is investigated systematically from both macroscopic and microscopic perspectives. Microstructural characteristics including particle morphology, pore size distribution, and particle preferred orientation are investigated specifically through SEM quantification methods. With an obvious turning point, thee–log σv′curve for natural GRS approaches the intrinsic compression line gradually when the vertical pressure exceeds the preconsolidation pressure, which indicates the significant influence of cementation bonding on the mechanical behavior of intact GRS. At the microscopic scale, the deformation of natural GRS is attributed to the compression and transformation of large pores, while the deformation of remolded GRS is also related to the transformation from mesopores to small pores. Upon compression loading, particles show higher preferred direction angle perpendicular to vertical loading, thereby facilitating the preferred orientation. With increasing vertical loading, the microfabric can no longer sustain the initial alignment pattern and tends to be rearranged and reoriented into a more stable and stronger structure. This study offers guidance for the deformation analysis of subgrade related to GRS.

A Constitutive Model for Overconsolidated Structured Soils Using Structural Variable

Due to the influence of soil structure, structured soils exhibit significantly different mechanical behavior compared to the reconstituted soils having the same material. In this work, a theoretical analysis focusing on the mechanical behavior of structured soils is presented. Based on the mechanical behavior of the structured soil, a newly defined variable structural index was used as a measurement of the integrity of soil structure based on the concept of intrinsic compression line of intact structured soils. Furthermore, a novel correlation for the variation in volume of structured soils is established using effective stress and newly defined structural index as the constitutive variables. The novel correlation provided interpretation about the mechanism of compression behavior of the structured soils. Afterwards, the proposed correlation for the variation in volume was extended to triaxial stress state in the framework of subloading surface to include the effect of overconsolidation. Comparisons between the predictions and experimental results validated the proposed constitutive model for structured soils.

Volume change behavior of reconstituted marine clay: effect of initial and leaching pore fluid salinity

Because the salinity of marine clay changes continuously in response to the migration of seawater toward land or freshwater from river to sea, the intrinsic pore fluid salinity of the clay-water system may change periodically. Recent studies indicate that pore-water salinity changes the intrinsic properties of reconstituted homoionic artificial clay. However, the effect of seawater on the intrinsic properties of marine clay is unknown. The aim of this study was to investigate changes in the compression parameters of marine clay for the leaching salinity of seawater with respect to tap water. The results show that ratio $${e}_{0}/{e}_{\mathrm{L}}$$ is more sensitive to salinity than $${e}_{100}^{*}$$ . Although the Iv − log p for all samples at different intrinsic/leaching salinities were located on the intrinsic compression line (ICL); some deviation from the ICL was observed at low-stress levels. In high-salinity reconstituted samples, the osmotic gradient caused the low-salinity water to penetrate the clusters and separate individual particles, increasing the size of intra-cluster pores and settlement during consolidation. The distance between the particles at any stress level was larger than in diffuse double layer theory because of a deviation from the assumed parallel fabric in the theory.

Influence of Structure and Liquid Limit on the Secondary Compressibility of Soft Soils

The macroscopic mechanical properties of natural sedimentary soft soils, which are usually linked to their microstructure, are different from those of remolded soils. The interaction between soil structure and mechanical behavior is a manifestation of structural mechanics effects. It is essential to understand the effects of secondary compressibility to predict long-term foundation deformations. The effects of soil composition on secondary compression deformation are little studied, and the soil structure is rarely involved in the compression process. The sedimentary environment creates the initial composition and structure of soft soil, and it also basically determines its grain size and mineral composition, while different depths give soft soil different overburden pressures, and the soil composition and depth directly affect its yield stress during compression. So, natural sedimentary soft soils sampled at different depths and from different sedimentary environments (such as marine-neritic facies, sea shore facies and limnetic facies) were selected to study the influence of structure on the secondary compression coefficient Cα during pressure change and the relationship between soil composition and Cα. One-dimensional compression and consolidation creep tests were carried out on undisturbed and remolded samples. The undisturbed samples were obtained by the thin-wall samplers in rotary wash borings, and the quality of the samples met the test standard. Based on the concept of the void index Iv and the intrinsic compression line (ICL) proposed by Burland, the role of structure in the compression process was studied, and the influence of soil composition and structure on secondary compression characteristics was summarized. The Cα/Cc values are 0.031, 0.034, 0.030, and 0.036 for Shanghai, Tianjin, Suzhou, and Ningbo soft soils, respectively, within the range of inorganic clays and silts (0.04 ± 0.01) given by Mesri. According to the compression index Cc obtained by compression test, Cα/Cc can be used to estimate Cα. The yield stress of normal consolidated soil is near pre-consolidation pressure, while that of structural soft soil is greater than its pre-consolidation pressure. Natural sedimentary soft soils show over-consolidation characteristics due to the action of the structure; the soil structure resists the external load and hinders secondary compression. When the soil structure is almost destroyed, the pressure reaches the structure full yield stress P′. The tests of structural soft soils show that Cα changes with pressure before the structure completely yields, first increasing and reaching peak Cαmax near P′; the value of P′ is approximately 1.6–3.0 σ’k, where σ’k refers to the structure yield stress of soil obtained by the Casagrande method. After the structure disappeared, Cα gradually decreased and then stabilized, which is considered to be independent of the load. The Cαmax is positively correlated with the liquid limit, indicating that the peak value that can be reached by the Cα is related to the maximum content of bound water in soft soil, thus the soil composition has a significant influence on secondary compressibility, which contributes to the prediction of long-term foundation deformation.

Influence of grading on the compressibility of saturated loess soils

A series of oedometer tests was carried out on natural loess and artificial soils. The loess soils were retrieved from sandy loess, silty loess and clayey loess zones within the Chinese Loess Plateau, as well as Yili area, Xinjiang Province outside the Chinese Loess Plateau. The results show clear influences of grading on soil compressibility. With the finer particle content increasing in loess, the compression paths turn from slightly upwards concave to upwards convex. The collapse index Ic defined in this study increases with the increasing Cu and decreases with the increasing D60. Locations of the soil normal consolidation lines in v–log σ′v plane are also influenced by soil grading characterised by the D60 and Cu. The intact clayey loess has more significant structure effect than the intact silty loess. Compared with the silty and clayey loess, the intact sandy loess has negligible structure effect on soil compressibility. For a given sampling site, deep loess has a higher yielding stress point and is more difficult to compress to the intrinsic compression line than shallow loess, revealing the effect of stress history on the soil compressibility.

Assessment of the effects of the structure on the compression behaviour of a young alluvial silty soil

A comprehensive series of tests was performed to investigate the effects of the in-situ structure and sample preparation technique on the compression behaviour of a shallow young alluvial silty soil. Two different particle size distributions were investigated by testing intact, compacted, and slurry samples in an oedometer. The compression of the slurry samples, created at different initial water contents, gave a unique intrinsic compression line for one of the two distributions. This was used as a reference for analysing the effects of the structure of the compacted and intact specimens. The compacted samples were prepared by means of static and dynamic compaction in one or more layers with vertical holes simulating those created by plant roots in natural samples. The results showed that a unique normal compression line is defined regardless of the number of layers or the number of holes, with a clear effect of the structure when compared to the slurry samples. The significant effects of the in-situ structure of the intact samples were observed even at high stress levels. An important finding was the non-uniqueness of the compression line for the second distribution. For the case of the slurry samples, the compression lines remained parallel to each other even at high stress levels, whereas a unique line was found for the compacted samples. These results are contrary to those often given in the literature, namely, that the sample preparation technique can create very robust initial structures resulting in a mode of behaviour that has been called “transitional”. The research also emphasises how the quantification of the natural structure is critically dependent on the way in which the intrinsic samples are prepared.

Engineering behaviour and mechanical–empirical relationships for a problematic New Zealand tropical residual soil

Unlike sedimentary clays, many tropical residual soils do not exhibit clear mechanical–empirical relationships to assist in their engineering characterization. In contrast, this paper discusses one residual clay in which such relationships may be determined, and further examines whether the effects of structure in this clay may be assessed using a framework previously developed for sedimentary clays. The Northland Allochthon tropical residual clay of New Zealand is a problematic soil of the fersiallitic type, prone to slope instability. Atterberg limit tests on soils from five field sites in the same geological unit show considerable variation, but that they are mechanically related. Laboratory element tests were performed on reconstituted and intact soil specimens from one field site. Normalization of the strength envelope using the equivalent stress on the intrinsic compression line suggests that soil structure, which is destroyed in reconstituted specimens, plays a role in the shear strength of this soil in its intact state. Overconsolidated behaviour, in the absence of geological preloading, points to the existence of a pseudo-preconsolidation pressure associated with weathering processes. The results further show that the saturated mechanical behaviour of this residual soil is in line with that of sedimentary clays and that mechanical–empirical relationships developed for such clays may be applied in this case.

Influence of structure on the compression behaviour of two very stiff fissured high plasticity Eocene clays

A series of one-dimensional compression tests have been performed on reconstituted specimens of Søvind Marl. A clear correlation is obtained between the location and the gradient of the intrinsic compression lines and the void ratio at the liquid limit. The found correlation has subsequently been used to normalise the compression curves of 12 one-dimensional compression tests on intact specimens of Søvind Marl and Little Belt Clay obtained from various depths at two sites at Aarhus Harbour. Søvind Marl and Little Belt Clay are both marine sedimentary clays of Eocene age, which can be characterised as very stiff fissured clays with a very high plasticity. From a comparison of the reconstituted and intact compression paths the influence of structure is analysed and discussed in the paper. The majority of intact specimens of Søvind Marl and Little Belt Clay from Aarhus Harbour show similar behaviour; a very stiff recompression path and yielding at high stress level after crossing the intrinsic compression line. The displayed behaviour indicates an insignificant influence of fissuring on the pre-yield behaviour. Post-yield the compression paths indicate a stable structure dominated by fabric rather than metastable interparticle bonds. The paper furthermore highlights the importance of considering the effect of pore water salinity when assessing the influence of structure on the compression behaviour of smectite rich natural marine clays.

Pore water salinity effect on the intrinsic compression behaviour of artificial soft soils

The framework of the intrinsic compression behaviour of normally consolidated soft clay proposed by Burland (1990) is widely adopted in engineering practices. However, further investigations should be conducted on its validity in the coastal and offshore environments to verify the effect of pore water salinity. In the present work, oedometer tests were performed on remoulded artificial soft clays (mixtures of kaolin and bentonite with 0%, 5%, 10%, and 20% of bentonite by mass). The artificial clays were salinized with sodium chloride solutions at concentrations 0 mol/L (distilled water), 0.17 mol/L, 0.51 mol/L, 0.86 mol/L, and 1.70 mol/L at water contents equal to 1.0–1.5 times of the liquid limits. The results showed that the ‘intrinsic’ properties of clays, including the compression index Cc⁎(100–1000 kPa), void ratio e100*, and compression line based on the void index Iv, changed with the pore water salinity. Following the empirical correlation proposed by previous researchers, the decrease in Cc⁎ caused by pore water salinity could be generally characterised by the liquid limit and void ratio at the liquid limit (eL). The dispersed correlation between the predicted e100⁎ and the experimental results in this study were caused by the significant changes in e0/eL controlled by pore water salinity. The relationships between void index Iv and vertical stress σv’ deviated from the intrinsic compression line (ICL) under the saline environment. For the artificial clay rich in smectite, the slopes of Iv–log σv’ before yielding increased with pore water salinity at the initial water content. Pore water salinity affected the intrinsic compression behaviour of soft clays primarily composed of kaolinite to a lesser extent.

Effect of initial water content and pore water chemistry on intrinsic compression behavior

ABSTRACTThe effect of initial water content (w0) and pore water chemistry on the intrinsic compression curve of clays was investigated experimentally. The test results indicate that w0 had a considerable effect on the intrinsic compression curve of a clay, and the degree of the effect is a function of pore water chemistry. The fundamental mechanism of the effect of w0 and pore water chemistry on the intrinsic compression curve is through its influence on the microstructure of clays. For relatively stable flocculated microstructures, the effect of w0 will disappear under a small value of effective vertical consolidation stress, σ′v, for example, σ′v < 20 kPa; under one-dimensional deformation condition, but for a dispersive microstructure, the effect of w0 can remain up to σ′v > 1,000 kPa. Furthermore, it has been shown that when σ′v is larger than the remolded yield stress, almost all the test data follow the intrinsic compression line (ICL) proposed by Burland. Finally, based on the test data, a new equation for estimating void ratio () under σ′v = 100 kPa on ICL from the void ratio (el) corresponding to the liquid limit water content has been proposed.

Behavior of diatomaceous soil in lacustrine deposits of Bogotá, Colombia

This work presents a study on the behaviors of diatomaceous soils. Although studies are rarely reported on these soils, they have been identified in Mexico City, the Sea of Japan, the northeast coast of Australia, the equatorial Pacific, and the lacustrine deposit of Bogotá (Colombia), among other locations. Features of this kind of soil include high friction angle, high initial void ratio, high compressibility index, high liquid limit, and low density. Some of these features are counterintuitive from a classical soil mechanics viewpoint. To understand the geotechnical properties of the diatomaceous soil, a comprehensive experimental plan consisting of more than 2400 tests was performed, including physical tests such as grain size distribution, Atterberg limits, density of solid particles, and organic matter content; and mechanical tests such as oedometric compression tests, unconfined compression tests, and triaxial tests. Laboratory tests were complemented with scanning electron microscope (SEM) observations to evaluate the microstructure of the soil. The test results show that there is an increase in liquid limit with increasing diatomaceous content, and the friction angle also increases with increasing diatomaceous content. In addition, several practical correlations were proposed for this soil type for shear strength mobilization and intrinsic compression line. Finally, useful correlations were presented, such as the relationship between the state consistency and the undrained shear strength, the friction angle and the liquid limit, the void ratio at 100 kPa and the liquid limit, the plasticity index and the diatomaceous content, among others.

Geotechnical characteristics and consolidation properties of Tianjin marine clay

Tianjin, which is located on the west shore of the Bohai Sea, is part of China\'s Circum-Bohai-Sea Region, where very weak clay is deposited. From the 1970s to the early 21st century, Tianjin marine clay deposits have been the subject of numerous geotechnical investigations. Because of these deposits\' geological complexity, great depositional thickness, high water content, large void ratio, excessive settlement, and low shear strength, the geotechnical properties of Tianjin marine clay need to be summarized and evaluated based on various in situ and laboratory tests so that Tianjin can safely and economically sustain more infrastructure in the coming decades. In this study, the properties of Tianjin marine clay, especially its consolidation properties, are summarized, evaluated and discussed. The focus is on establishing correlations between the geotechnical property indexes and mechanical parameters of Tianjin marine clay. These correlations include the correlations between the water content and the void ratio, the depth and the undrained shear strength, the liquid limit and the compression index, the tip resistance and the constrained modulus, the plasticity index and the ratio of undrained shear strength and the preconsolidation pressure. In addition, the primary consolidation properties of Tianjin marine clay, such as the intrinsic compression line (ICL), sedimentation compression line (SCL), compression index, Cc, coefficient of consolidation, Cv, and hydraulic conductivity change index, Ckv, are evaluated and discussed. A secondary consolidation property, i.e., the secondary compression index, Ca, is also investigated, and the results show that the ratio of Ca/Cc for Tianjin marine clay can be used to calculate Ca in secondary consolidation settlement predictions.

On the evaluation of the structure in sedimentary soils

Oedometer intrinsic compressibility of common inorganic soils can be explained with a few fundamental parameters obtained from simple laboratory tests. Specifically, on the basis of the liquid limit and clay percentage of a soil (fine or semi-fine), the coordinates of its intrinsic compression line can be calculated. Hence, by plotting both the oedometer compression curve of an undisturbed soil sample and the relative (measured or calculated) intrinsic compression line, the natural soil structure derived from its geological history can be estimated. Since the natural soils generally differ in mineralogical composition, the data normalisation appears to be of fundamental importance to evaluate the soil element structure in sedimentary soil profiles. The aim of this paper is to build a unique ‘straight intrinsic compression line’ SICL correlating the compression behaviour of soils with different mineralogical compositions based on the Burland’s concept of evaluating soils structure. Specifically, it is possible to obtain the ‘sedimentation compression curve’ SCC of the intact soil elements down a sedimentary soil profile, which can be compared directly with the SICL and SCC of others soil profiles.

On the compression behavior of remolded cement-admixed soft clay

ABSTRACTAlthough extensive research has been performed on the mechanical properties of cement-stabilized clays, quite a few attempts have been made on the compression behavior of remolded cement-admixed clays. The results from oedometer tests have been discussed to investigate the compressibility of remolded cement-admixed clays, taking into consideration cement amount and curing time. The findings show that the difference in shape and position of compression curves is attributed to cement amount and curing time. Most compression index (Cc) values of remolded cement-admixed clays are greater than those of untreated clay due to the presence of remolded yield stress σ′yr that is closely related to initial water content and clay fabric. Based on the obtained test data, the relationships of Cc vs. e0, Cc vs. w0, Cc vs. e1, Cc vs. eyr, and σ′yr vs. eyr are preliminarily discussed and quantitatively established. Especially, an important divergence of void index Iv at effective stress σ′v less than remolded yield stress σ′yr can be observed at different cement amounts and curing durations. Being independent on cement amount, curing time, and initial state of soil, an excellent convergence occurs at stress σ′v greater than yield stress σ′yr. The normalized compression curves of Iv vs. σ′v at σ′v > σ′y can be expressed by a unique line that agrees well with intrinsic compression line (ICL) and extended ICL.