Oedometer Apparatus Research Articles

Mechanical properties of two expansive clay soils from Sudan

The mechanical responses of two highly expansive plastic alluvial soils from Sudan are reported. When wetted from their in-situ state, such soils frequently lead to damage of civil engineering structures. Disturbed samples of a black cotton clay and a more plastic red clay were collected from two locations in the vicinity of Khartoum. Intrinsic properties were established from reconstituted samples using oedometer and triaxial apparatus. Natural undisturbed block samples of the black cotton clay were obtained and tested in an unsaturated state, as found in situ. Basic characteristics of both soils are presented. Detailed information on the intrinsic properties of both clay soils was established and found to conform with Burland's earlier published framework. Shear planes formed during shearing in almost all triaxial samples and strengths reduced to post-rupture values. K0-consolidated reconstituted samples exhibited a more brittle response to undrained shearing compared with isotropically consolidated samples. Peak failure conditions can be represented by linear failure envelopes for both soils, regardless of consolidation path, although those from shearing in extension do not pass through the origin: reasons for this are discussed. Oedometer tests on the intact black clay soil indicate a high potential for swelling on wetting (volumetric strains of almost 50%), decreasing with increasing stress level (swelling pressure of about 1 MPa). Unconsolidated undrained triaxial tests on the intact unsaturated samples show increasing strength and decreasing brittleness with increasing confining pressure.

Performance evaluation of the soft soil reinforced ground palm oil fuel ash layer composite

This study seeks to validate the possible reuse of the ground palm oil fuel ash (POFA) in soft soil improvement. POFA used in the present study was derived from the abundantly available palm oil waste residues from the nearby palm oil mill. Once the POFA is dried, it is further grounded to two different particle sizes i.e. 30 μm (large particle) and 12 μm sieve (small particle) in order to determine the effect of the POFA fineness in soft soil improvement. Furthermore, a one dimensional deformation analysis was carried out using the oedometer apparatus to investigate the effect of water saturation in soft soil samples incorporating both the original unground POFA. The result showed that the improvement factor portrayed by the smaller particle size of the ground POFA was much more pronounced as compared to the larger particle size. Similar trend was found in the consolidation results especially when the soft soil sample was fully saturated. Also, the shear strength parameters of the reinforced soft soil with ground POFA increased significantly at about 50%–60% for both the internal friction angle and the cohesion values.

TREATMENT OF EXPANSIVE SOILS WITH QUALITY SALINE PORE WATER BY CYCLIC DRYING AND WETTING

Expansive soils can be found in many parts of the world particularly in arid and semi-arid regions. These soilspose a significant hazard to civil engineering structures due to its high swelling and shrinkage potential. This paperpresents the results of an experimental program developed to investigate the effect of cyclic drying and wetting on theswelling potential of expansive soils with various pore water qualities. Soil samples were prepared by staticcompaction with distilled and saline pore water solutions consisting of sodium chloride (NaCl) with 50 and 250 g/Lconcentrations. Soil samples were subjected to drying and wetting cycles using a modified oedometer apparatus,under a surcharge pressure of 10 kPa. Axial deformations caused by drying and wetting during various cycles weremeasured until shrink-swell equilibrium condition was attained. The results indicated that conducting consecutivedrying and wetting causes a considerable reduction in the swelling potential of soil samples prepared with differentqualities of pore water. Shrink-swell equilibrium in soil samples prepared with distilled water and 50 g/L NaClsolution was achieved after 5 consecutive cycles while soil samples with 250 g/L NaCl solution as pore water,reached equilibrium condition after approximately 3 or 4 cycles. Furthermore, the overall swelling potential for soilsamples prepared with 250 g/L NaCl solution was seen to be greater compared to distilled water and 50 g/L NaClsolution respectively.

An Oedometer-Based Method for Preparing Reconstituted Clay Samples

It is well known that the mechanical behavior of the natural intact soft clay is usually quite different from that of the reconstituted counterpart. Hence, how to predict the influences of soil structure on the mechanical behavior of natural clays is an important issue in geotechnical engineering.The mechanical behavior of structured soils can usually be quantitatively assessed based on the mechanical behavior obtained from corresponding reconstituted clays. The preparing method for reconstituted soils will affect the quality of reconstituted samples greatly, and therefore, affect their mechanical parameter. To guarantee the quality of reconstituted soil samples, a large diameter oedometer apparatus is developed. Also, an oedomer-based method for preparing reconstituted clay samples is proposed. Typical soft Lianyungang city clay from China is chosen to testify the methods and corresponding procedures. The feasibility of the improved method is confirmed by comparing its results with those of the normal oedometer test.

Effects of sugarcane bagasse ash (SCBA) on the strength and compressibility of cement stabilized peat

This research objective is to evaluate effectiveness of sugarcane bagasse ash (SCBA) inclusion in peat stabilization. To develop the optimal mix design, stabilized peat specimens were tested in unconfined compression. Energy Dispersive Xray (EDX) and Scanning Electron Microscope (SEM) apparatus was used to examine elemental composition and microstructure. Consolidation tests were carried out in a standard Oedometer apparatus on the obtained optimum peat-cement-bagasse (PCB) mixture. It was found that stabilized peat comprising 20% partial replacement of OPC with SCBA has the maximum UCS and discovered to be about 1.2 times greater than UCS of peatcement (PC) specimen. The UCS of optimum PCB mixture specimens increased with curing duration in water. Compared to untreated soil, SEM results for stabilized peat gave the significant pore improvement. EDX results prove that lower carbon (C) and higher calcium (Ca) fractions shows the better results of strength. There was a significant reduction of void ratio (e) for optimum PCB mixtures as compared to untreated peat. It was observed that preconsolidation pressure, σ’c were increase with curing period. Results finding shows that the stabilized peat Cα/Cc ratios were decline dramatically from untreated peat which is indicating the stabilized mixture can effectively reduce the secondary compression.

Experimental and analytical framework for modelling soil compaction

Compacted materials are fundamentally unsaturated soils whose behaviour can be expansive or collapsible depending upon changes in water content or stresses. Their behaviour is strongly dependent upon matric suction, water content, and stress history.This paper presents a methodology for investigating the stress/strain, and suction/water content paths during one dimensional compaction of unsaturated soils. It focuses on anisotropic behaviour. The testing programme was carried out in a new automated oedometer apparatus that allows measurement of axial strain, radial and axial stresses, suction, and water content during tests.The laboratory component used in this study involves kaolin compacted with different water contents. After compaction, the soil was subjected to wetting while the volumetric changes and stress paths were being examined. The results were interpreted within an anisotropic elasto-plastic framework. The proposed methodology provides new insights into the behaviour of unsaturated soils during compaction and wetting.

Assessment of the Swelling Pressure of the Green Clay of Tangier (Morocco) Compared with the Soil-Moisture Conditions

The swelling phenomenon appears seriously when changing the soil-moisture conditions. The swelling pressure induced by the expansive soil can causes unfavourable problems or instability for the civil structures. So, understanding the soil behavior is considered a valuable work for engineers and consultants in the geotechnical and civil engineering sectors. In reality, the assessment of the swelling pressure of expansive soil depends, first of all, of test conditions related to the change of soil-moisture, as it happens, the influence of the combination “loading-start wetting” and also the unloading process after saturation. To this end, we establish an experimental study on the green clay of Tangier to evaluate the swelling pressure by using oedometer apparatus. Secondly, attention is bore to the combination “initial water content-dry density”, another factor related to the change of the soil-moisture, to show the influence of initial state condition on the swelling pressure.

Effect of lime treatment on geotechnical properties of Dunkirk sediments in France

The increasing cost associated with high-quality materials has lead to the need for sediments to be treated and then used in road construction in the context of durable development. Therefore, the modification and stabilisation of Dunkirk marine sediments by using lime is necessary to study for their potential use in road construction. Based on the physical characteristics of untreated sediments, a series of laboratory tests to investigate the geotechnical properties of untreated sediments and lime-treated sediments, such as unconfined compressive strength tests, standard oedometer tests, direct shear tests and triaxial tests, were performed. Lime was added in percentages of 3% and 6%, by weight of dry sediments. The test results show a significant improvement in unconfined compressive strength and shear strength due to the addition of lime. From the strain–stress relationship of compressive strength tests, it can be found that the failure mode of solidified sediments develops gradually from plastic failure to brittle failure, while the failure strength increases and the failure strain decreases with lime content. Compared with untreated sediments, the shear strength parameters of solidified sediments determined by direct shear tests, such as internal friction angle and cohesion, are increased owing to the pozzolanic reaction between lime and clay minerals. Using the oedometer apparatus, it is observed that after lime treatment, the preconsolidation pressure, the coefficient of consolidation and the compression index are increased, while the swelling index is decreased. The characteristics of the deviator stress–axial strain relation and the pore water pressure distribution under different confining stresses are compared with untreated and treated sediments, and the effect of lime content on cohesion and internal friction angle determined by triaxial tests is discussed.

Drainage controlled uniaxial swelling cell

A modified oedometer apparatus, the drainage controlled uniaxial swelling cell, is described. While inward vertical and radial flow paths are effectively adjustable, a drainage controlled uniaxial swelling cell can be applied to measure the vertical swelling pressure value at a predetermined drain path, when integrated with a closed-loop mechanical testing load frame. Aiming for calibration of the cell, a set of validation standard constant volume swell tests (ASTM D4546) is conducted on remoulded unsaturated expansive clay specimens. The results revealed an upper bound for the ultimate vertical swelling pressure under multilateral drainage condition.

Temperature Effects on Geotechnical Properties of Kaolin Clay: Simultaneous Measurements of Consolidation Characteristics, Shear Stiffness and Permeability Using a Modified Oedometer

The increased worldwide use of shallow geothermal energy systems including ground source heat pumps (GSHPs) have given concerns of possible temperature effects on soil geotechnical properties. In this study, the effects of temperature on mechanical characteristics such as consolidation settlement, shear stiffness, and permeability of kaolin clay were investigated. A modified oedometer apparatus which allows the simultaneous measurements of consolidation settlement, shear wave velocity, and hydraulic conductivity was developed and used. Consolidation tests on preconsolidated kaolin samples (two sample sizes: ϕ 6 cm x H 10 cm and ϕ 6 cm x H 2 cm) were performed under sequentially increasing consolidation pressures at three different temperatures (5 °C, 15 °C, and 40 °C). Larger apparent preconsolidation pressure, Pac, was seen at higher temperature (40 °C) for both sample sizes, but only for samples having relatively high initial void ratios between 1.53 and 1.62. Relatively higher shear modulus as a function of void ratio was observed for samples at higher temperature, suggesting that changes in fabric structure (likely caused by enhanced inter-particle forces between clay particles at higher temperature) resulted in the increased shear stiffness and, thus, higher Pac at 40 °C. Oppositely, temperature effects on the Manuscript received February 5, 2013. This work was partly funded by a grant from the Research Management Bureau, Saitama University, the grant-in-Aid for Scientific Research of Japan Society for the Promotion of Science (JSPS) (No.22860012), and a JSPS bilateral research project. This work was also partially supported by a CREST project, a research grant from the Japan Science and Technology Agency (JST). E. E. Mon is with Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura ku, Saitama, 338-8570, Japan. (phone/fax: (+81) 48-858-3116; e-mail: nyima.eimon@gmail.com). S. Hamamoto, is with Graduate School of Science and Engineering, and Institute for Environmental Science and Technology, Saitama University, 255 Shimo-okubo, Sakura ku, Saitama, 338-8570, Japan. (e-mail: hamasyo@mail.saitama-u.ac.jp) K. Kawamoto is with Graduate School of Science and Engineering, and Institute for Environmental Science and Technology, Saitama University, 255 Shimo-okubo, Sakura ku, Saitama, 338-8570, Japan. (e-mail: kawamoto@mail.saitama-u.ac.jp). T. Komatsu is with Graduate School of Science and Engineering, and Institute for Environmental Science and Technology, Saitama University, 255 Shimo-okubo, Sakura ku, Saitama, 338-8570, Japan. (e-mail: komatsu@mail.saitama-u.ac.jp). P. Modrup is with Department of Biotechnology, Chemistry, and Environmental Engineering, Aalborg University, 9000 Aalborg, Denmark. (e-mail: pm@bio.aau.dk). permeability of kaolin clay were not significant within the studied temperature range between 5 °C and 40 °C.

The role of particle breakage in the mechanics of a non-plastic silty sand

A detailed investigation was carried out on a silty sand from Boštanj, Slovenia, in order to identify the role that particle breakage plays in test interpretations and mechanics. The soil was tested up to a high pressure in the triaxial and oedometer apparatus. Unexpected for a silty sand, the basic patterns of behaviour, in terms of strength and stiffness, were found to be similar to those of many previously investigated clean sands, with unique and parallel Normal Compression and Critical State Lines at higher stress levels and a horizontal asymptote to the Critical State Line at lower stress levels. The stiffness was controlled primarily by the state of the soil relative to the location of these lines. Despite the better grading, there was still very significant particle breakage. However, the breakage was largely confined to the coarse fraction. The grading curves after various tests all showed convergence with the initial grading towards 1μm, which may therefore represent the comminution limit. It is believed that it is the particle breakage that caused the behaviour to follow a simple Critical State type of framework and why transitional or non-convergent compression behaviour was not found.

A New Concept on the Compressibility of Mixed Soils: Experimental and Numerical Approach

In this article, a new concept on the compressibility of mixed soils is proposed. Six characteristic structures of mixed soils are recognized, defined and described based on the percentage of the ground material in the mixture. The compressibility mechanism and the deformational behavior of each structure are extensively studied by both laboratory and numerical experiments. Two series of compressibility tests are initially conducted in the laboratory, using artificial mixtures of sand and clay at different ratios and subjected to typical compressibility tests using the oedometer apparatus. Then, a numerical approach is employed, based on the finite element method and Monte-Carlo simulations, in order to reproduce the conditions of the laboratory tests and to further study the compressibility of each characteristic structure. From the results obtained, it is concluded that the deformational behavior of mixed soils depends strongly on the percentage of the ground in the mixture and on the mechanical properties of the components of this mixture. Furthermore, it is shown that the estimated deformations and stress states can be highly unrealistic when the mixed soil is not properly modelled and is assumed to be governed by the properties of its weaker component.

Wet Compaction and Lime Stabilization to Mitigate Volume Change Potential of Swelling Clayey Soils

In this study, the possibility of wet compaction method to reduce swelling potential of high plasticity (active) clayey soils has been investigated and compared with lime stabilization method. Swell (and shrink) potential tests were performed using an oedometer apparatus on sand-bentonite mixtures which were compacted immediately after mixing with water. Tests were then repeated on different samples of the same composition after allowing 3-day free swelling prior to compaction. This method of sample preparation is herein referred to as “wet compaction”. Additional tests conducted on lime stabilized samples with and without wet compaction enabled comparison of the wet compaction and lime stabilization methods. Test results showed that wet compaction reduces the swelling potential of sand-bentonite mixtures and can thus work as a mitigation technique to reduce swelling potential of high plasticity (active) soils. However, as expected, lime treatment was found to be superior, especially if the dose corresponded to or was higher than lime fixation point. In addition, the volumetric change of both untreated and treated samples after drying at 40°C in an oven (during drying, shrinkage deformations were measured) as well as the effect of cyclic wetting and drying on the unconfined compression strength (UCS) of lime-stabilized samples were investigated.

Analysis of the behaviour of a natural expansive soil under cyclic drying and wetting

Analysis of the behaviour of a natural expansive soil under cyclic drying and wetting

LEACHING BEHAVIOR OF GYPSEOUS SOILS

A series of laboratory tests were carried out on disturbed soil samples containing different gypsum contents. The soil samples were obtained from al-Jazeera south-west of Iraq. Tests were performed to obtain the physical and mechanical properties of the soil. In addition; permeability-leaching tests were conducted by using oedometer and large-scale Rowe cell apparatus to obtain the variation of the coefficient of permeability, dissolved gypsum and leaching strain with time. All samples were tested under similar conditions, e.g. the hydraulic gradient, vertical stress and leaching period. The soil samples designated N1, N2, and N3 are obtained from depths (0.5-0.75), (1.0-1.25), and (3.25-3.5) m and having gypsum content (31.43), (51.37), and (4.86) percentage respectively. Results of experimental work show that the coefficient of permeability, the percentages of dissolved gypsum and leaching strain measured from the oedometer test are higher than that measured from large-scale Rowe cell test for the same soil sample. The gypseous soil with higher gypsum content exhibited significant amount of leaching strain.

Geotechnical properties of a municipal water treatment sludge incorporating a coagulant

The geotechnical properties of a municipal water treatment sludge from an upland catchment are presented. The gelatinous sludge comprised flocs of mainly quartz, manganoan calcite, and clay-sized organic solids, and incorporated an alum coagulant and an anionic polyelectrolyte. Standard Proctor compaction yielded low bulk density values of 0.95–1.10 t/m3and dry density values of 0.12–0.36 t/m3(water content is 160%–780%) in line with the low specific gravity of solids value of 1.86. The undrained shear strength and the water content were inversely related on a semi-log plot. The effective stress shear strength parameter values were c' = 0 and ϕ' = 39°. The consolidation properties were studied using the oedometer, consolidometer, and triaxial apparatus. The material was highly compressible with primary compression index (Cc) values of 2.5–3.7, and primary compression ratio (C*c) values of 0.20–0.28. The majority of the strain response occurred due to primary consolidation although the material had a very low permeability (coefficient of permeability values decreasing from 2 × 10−9to 5 × 10−11m/s for an effective vertical stress of σ'v= 3–800 kPa). Secondary compression was minor, with a mean secondary compression index (Cαe) value of 0.15, and Cαe/Cc= 0.04–0.06.

Um instrumento para medida de potencial matricial nos solos sem ocorrência de cavitação

A tensão nos solos tem sido vista pelos cientistas do solo como um aspecto de importância crescente sendo bastante usada como informação relevante na agricultura desde o início do século passado. Seu conhecimento permite melhores intervenções antrópicas não só em aspectos relativos à vegetação e a agricultura, mas também no que concerne à estabilidade de um talude. Para medir a tensão no solo tensiometros cada vez mais sofisticados tem sido desenvolvidos. É apresentado neste trabalho o estado da arte da evolução dos tensiômetros, além do desenvolvimento de um deles, o qual mede valores de tensão de até pelo menos 1.500 kPa. Diversos protótipos foram preparados. Observou-se que se comportam diferentemente de acordo com as características de seus componentes, sem grande influência nos resultados nos domínios de leitura possíveis em cada caso. Assim, os efeitos de tipo de transdutor, tamanho do reservatório de água, dimensões e permeabilidade ao ar da pedra porosa foram analisados, monitorando-os quando instalados em lisímetros, junto com outros equipamentos, como equitensiômetros e TDRs. Os resultados mostraram que o protótipo pode ser usado in situ e em laboratório, sendo facilmente adaptável para uso em oedômetro ou aparelho de ensaio triaxial. Comentários sobre o papel das forças atrativas de Van der Waals na cavitação do sistema são também apresentados, esclarecendo-se os procedimentos para deslocamento do ponto de cavitação para limites superiores com a diminuição dos possíveis núcleos de gás no sistema.

Volume change behaviour of saturated clays under drained heating conditions: experimental results and constitutive modeling

One of the essential features of thermomechanical behaviour of saturated fine-grained soils is the thermally induced volume change occurring under a drained heating condition. In this study, a modified oedometer apparatus, able to handle temperatures up to 100 °C, was used to investigate the thermally induced volume change behaviour of soft Bangkok clay. The results of this experimental study provide additional experimental evidence and insights that may enhance the understanding of volume change behaviour of saturated clays at elevated temperatures. This paper also introduces an isotropic thermoelastoplastic constitutive model that closely predicts the thermally induced volume change behaviour of saturated clay specimens under normally consolidated conditions as well as overconsolidated conditions obtained by unloading process in the temperature range of 20–95 °C. Two yield limits, namely: loading yield limit and thermal yield limit, each of which can be measured from simple experimental results, are proposed to capture the volumetric plastic strain behaviour induced either by mechanical or thermal loading (or any combination thereof). The capability of the proposed model has been verified against experimental results obtained on soft Bangkok clay as well as on two other clays (Boom clay and MC clay) as reported in the literature.

Collapse Behavior of Compacted Silty Clay in Suction-Monitored Oedometer Apparatus

This paper presents a methodology to investigate the collapse behavior of unsaturated soils using suction-monitored oedometer tests. By incorporating independent suction measurement, the oedometer apparatus is capable of following the same stress paths as in double oedometer tests, while continuously monitoring the suction. The proposed method has been used to investigate the collapse behavior of a compacted silty clay and to confirm the uniqueness of the loading-collapse surface as identified from loading and wetting paths. A new mathematical form of the yield surface within an elastoplastic framework is proposed on the basis of test results over a wide range of suctions (0 to 30,000 kPa) and net stresses (up to 7,000 kPa). The fundamental assumptions of the newer type of elastoplastic framework, which incorporate the degree of saturation within their stress variables, are evaluated, and the limitations of such models are identified. The collapse behavior of samples with different fabrics induced by differing compaction characteristics is also investigated within an elastoplastic framework. The difference in fabric, which is observed through a petrological microscope, can be presented in a quantitative way with different model parameters.

Prediction of collapse behaviour in soil

ABSTRACT The drastic decrease in volume of a natural, unsaturated soil deposit or compacted fill that occurs upon wetting at virtually constant total stresses is termed “collapse”. Several methods can be found in the literature that predict collapse behavior based on easily obtained soil parameters. Nevertheless, discrepancies were reported among the results of these methods. This paper presents the results of an experimental investigation on carefully conducted laboratory prepared collapsible soils in the oedometer apparatus. These results were used to develop an empirical model for predicting soil collapse in terms of the initial dry unit weight, initial water content and the soil gradation. The values predicted by the proposed model agreed well with the experimental results of the present investigation and those available in the literature.