Compacted Marls Research Articles

An Improved Unsaturated Triaxial Device to Characterize the Pore-Water Pressure and Local Volume Change Behavior of a Compacted Marl

Abstract Compacted fills in earthworks are in an unsaturated state, with suctions (negative pore-water pressures) usually ranging from several kPa to several MPa. Characterizing the variation of pore-water pressure is a major concern in the estimation of embankment stability and, at the same time, a big challenge when its value falls below –80 kPa. This technical note presents an improved triaxial system based on the standard triaxial cell, equipped with a tensiometer, a thermocouple psychrometer, and local strain gauges. The main objective of these improvements is to measure the pore-water pressure and local volume changes during isotropic loading. In this study, three compacted specimens were tested under undrained conditions. Pore-water pressure was continuously measured by means of the psychrometric probe in the range of –3,000 to –100 kPa and by the tensiometer in the range of –80 to 1,100 kPa. Volume change was measured by the local strain gauges. Analysis and development of the results from both this study and the literature lead to the conclusions that i) specimens with occluded air bubbles (e.g., at the standard Proctor optimum) behave like a saturated soil, as Bw is close to unity when pore-water pressure becomes positive, and ii) a pore-water pressure coefficient Bw close to 1 is not necessarily a sign of saturation, as soil in an unsaturated state may also have a pore-pressure coefficient close to unity, especially at the beginning of the mechanical loading.

Changes on diametral compression behaviour of compacted marls due to drying

Cracking due to desiccation can compromise the behaviour of earth structures built with compacted clayey soils by promoting water access and consequent volume changes on further wetting. Tensile strength therefore is important to be considered when studying the behaviour of such structures, and in particular its dependence on the degree of saturation or water content. The influence of water content in tensile behaviour of compacted marls was investigated by performing diametral compression tests (Brazilian splitting tests), where axial deformations were measured besides strength. The samples were prepared by compaction at optimum point using standard compaction energy (optimum water content 16%) and then dried by vapour equilibrium to reach water contents between 5% and 16%. The correspondence between water content and suction was done by using the drying branch of the water retention curve, measured using WP4 equipment (Water Dewpoint Potentiometer). Good relationships were found between tensile strength and the water content (and suction). In addition, the study was completed with the analysis of other parameters such as the semi-contact angle created in the loaded area and the stiffness of the material, which also showed changes with water content.

Influence of crushed granulated blast furnace slag and calcined eggshell waste on mechanical properties of a compacted marl

Abstract Marls are considered difficult soils in the construction of road infrastructure. They are generally associated with high compressibility, high plasticity, and evolutionary behavior, resulting in many structural failures in the road embankment. The objective of this research is to study the mechanical behavior of a compacted marl treated with a new hydraulic binder composed of Crushed Granulated Blast Furnace Slag (CGBS) active by Calcined Eggshell Waste (CES). To conduct this research, unconfined compressive strength tests (UCS), soaked California Bearing Ratio (CBR) tests, and triaxial shear tests are performed for different cure periods. The specimens were prepared with a binder content, which varies between 0 and 15% by dry weight. The results indicate that the mechanical properties of the treated marl improved significantly. The addition of 15% of this new binder is capable of increasing the CBR index 22 times its initial value. Furthermore, an appreciable improvement in cohesion and internal friction angle is observed due to treatment, especially at later ages. The new hydrates produced by the pozzolanic reaction (C-S-H) were identified after treatment by Scanning Electron Microscopy (SEM). Overall, it appears that calcined eggshell activated blast furnace slag can be used as an effective binder for the stabilization of clay soils.

Modelação do comportamento evolutivo de margas compactadas considerando a presença dos fragmentos

Alguns aterros da Autoestrada A10 foram construídos com margas compactadas, que consistem num conjunto de fragmentos cujas dimensões e arranjo dependem do processo de compactação. Porque as margas são materiais com comportamento evolutivo, os fragmentos de marga sofrem forte degradação física quando sujeitos às acções atmosféricas (essencialmente molhagem e secagem), de onde resultam assentamentos que poderão ter consequências no comportamento dos aterros. Foram efectuados ensaios edométricos de material compactado de modo a caracterizar o seu comportamento quando sujeito a ciclos de molhagem-secagem. Observou-se uma evolução de um comportamento típico de materiais tipo enrocamento, quando ainda não há degradação dos fragmentos, para um comportamento típico de materiais argilosos, após haver degradação. Neste artigo apresenta-se o estudo efectuado para compreender este fenómeno e para definir um modelo constitutivo para as margas compactadas. Na primeira parte é efectuado o estudo do mecanismo de degradação de um fragmento rochoso devido a saturação, com base num modelo de elementos finitos, recorrendo a com um modelo constitutivo aplicável a solos não saturados. Na segunda parte apresenta-se o modelo constitutivo definido para o fragmento considerando a sua degradação física através de um parâmetro de dano. Este modelo é depois incorporado no modelo definido para as margas compactadas, que se apresenta na terceira parte. Trata se de um modelo elastoplástico com endurecimento e amolecimento, definido em termos de tensões totais e que inclui a sucção como variável de estado. Considera a existência de dois níveis estruturais (o do arranjo dos fragmentos e o dos próprios fragmentos) e a sua interacção através de funções de interacção. Este modelo foi usado para reproduzir vários ensaios edométricos.

A constitutive model for compacted expansive and bonded marls

This paper focuses on understanding the mechanical response of non-saturated compacted marls used to build some motorway embankments in Portugal. The compacted material consists of crushed marls, which can be assumed to be a set of fragments with relatively large dimensions. Experimental studies on the hydromechanical behaviour of this compacted, evolving material show that it behaves as a material in the transition between rockfill (when the fragments can be considered approximately intact) and a clayey soil (when a large number of fragments show strong physical disaggregation). Existing models for compacted rockfill and compacted clayey materials are not adequate to reproduce this complex behaviour. Constitutive models able to reproduce this behaviour are required for predicting the behaviour of earth structures such as these embankments. A model is proposed for the prediction of volumetric deformations for stress and strain boundary conditions corresponding to the oedometric test. It consists of an elasto-plastic unsaturated, double-structure, constitutive model in which the compacted material is assumed to be the macrostructure, and the microstructure is the fragment itself. Owing to the fundamental role of the loss of structure of the marl fragments in global behaviour, a constitutive equation for soft rocks is given, which includes a rule for bond loss depending on suction. Good results are obtained when the model is used to reproduce experimental tests performed on samples of compacted marls to which stress and suction cycles are applied. Other than the model proposed in this paper, attempts to reproduce the behaviour of compacted soft rocks are unknown.

Experimental behaviour of compacted marls

Jurassic marls from Abadia, Portugal, were used in the construction of some motorway embankments. Large fragments of this evolving material remained after the construction process, and their degradation was of concern because of the expected change of the engineering properties of the compacted material. The material exhibits a very complex behaviour, which is difficult to reproduce with existing constitutive models for unsaturated structured materials. This paper focuses on understanding and providing data on the interaction between the pure marls (rock) and the aggregate behaviour. It presents the main results of tests performed to characterise the hydro-mechanical behaviour of compacted marls in specimens prepared with different grading size distributions and subjected to oedometer tests where both stress and suction changes were applied. The experimental data obtained were analysed, considering the presence of fragments and their degradation. The marl matrix was characterised to complete the existing data previously published for this material, but now with the purpose of providing a better explanation for the volumetric behaviour of the aggregate. The discussion is assisted by the explanation provided by a simple elasto-plastic model for unsaturated soils. Discrepancies with model predictions help to highlight the singularity of the marl aggregate. Compacted marls behave as materials in the transition between rockfill (when the fragments remain brittle) and a clayey soil (when the degradation accumulates). Therefore the compacted marl exhibits a dual behaviour. If it is dry, deformations are explained by the breakage of particles and rearrangement of the structure. If it is wet, the compacted marl is dominated by bond degradation of the material, the release of swelling potential and simultaneous changes in the stiffness and strength of the fragments. It appears that the transition from dry to wet can be identified by the current suction; moreover, it is rather abrupt.

Hydro-mechanical characterization of lime-treated and untreated marls used in a motorway embankment

Some embankments on the A10 motorway, in Portugal, were built with marls. A lime treatment was prescribed for the material placed on the shoulders to protect it from the actions of the weather. This zoned profile design solution was a cheaper alternative to giving the embankment a full treatment.Two major concerns emerged during the construction, which motivated the research presented in this paper. The first was the possibility of cracking induced by the different stiffness of the core and treated shoulders, thus providing access of rain water to the core material, which was exactly what the treatment intended to avoid. The second was the difficulty in estimating the amplitude of long-term deformations, which can be expected due to the evolving nature of the marls used.The research program included the instrumentation of a selected embankment and laboratory tests on samples of treated and untreated compacted marls. The instrumentation allowed the measurement of vertical displacements and water content distribution to investigate if long-term displacements would be a concern during operation. The laboratory tests characterized the hydro-mechanical behavior of the material and its changes with the lime treatment. This research also stimulated discussion of some ideas about the expected performance of the embankment during its life cycle.

Degradation of Compacted Marls: A Microstructural Investigation

Embankments made with marl and other soft clayey rocks result in an agglomerated structure of finite size particles. These particles evolve however, resulting in major changes of the overall behaviour of the aggregate. The development of settlements and the loss of strength in time are the main concerns in practice. The mechanisms leading to the breakage and eventually the destructuration of one single rock particle are investigated using the concepts of unsaturated soil mechanics since wetting and drying cycles, controlled by atmospheric changes, result in strong suction changes and are one of the main reasons for rock degradation. Numerical simulations of the behaviour of individual rock fragments when wetted until full saturation were performed. Several contributing factors, namely suction change rate, initial suction and confinement were investigated. The knowledge learned with the simulation of the degradation of single rock fragments was extended to simulate the behaviour of particle arrangements under some representative stress and suction paths. Some results of suction controlled tests used for the calibration of the models are presented. The calculated behaviour of single particles and aggregates under wetting is discussed and qualitatively compared with experimental observations of the individual rock fragments and the compacted material. The results obtained provide a new insight into the nature of degradation induced by wetting and drying. They provide also a mechanical explanation, at the level of rock fragments, for the overall behaviour of aggregates.

Clegg Hammer—California-Bearing Ratio Correlations

This investigation was conducted to assess the efficacy of the Clegg impact hammer (CIH) for estimating the strength of compacted soils by conducting a comparative study between the California-bearing ratio (CBR) and CIH tests. The study was carried out in two phases. In phase 1, compacted marl samples were prepared in the laboratory under three different compactive efforts and different molding moisture contents and then subjected to CBR and CIH tests. Phase 2 focused on conducting in situ CBR and CIH tests on existing soils at some preselected locations as part of ongoing projects in Saudi Arabia. The test results of both phases were statistically analyzed and indicated that the Clegg impact value correlates relatively well with the CBR value for both the laboratory and field tests. These correlations were compared with those reported in the literature. A general, reliable, best-fit model has been proposed for the laboratory, field, and literature data.

Mechanical behaviour of compacted marl (in French) : Carvalo, J C; Crispel, J J; Mieussens, C Proc 12th International Conference on Soil Mechanics and Foundation Engineering, Rio de Janeiro, 13–18 August 1989V1, P25–27. Publ Rotterdam: A A Balkema, 1989

Mechanical behaviour of compacted marl (in French) : Carvalo, J C; Crispel, J J; Mieussens, C Proc 12th International Conference on Soil Mechanics and Foundation Engineering, Rio de Janeiro, 13–18 August 1989V1, P25–27. Publ Rotterdam: A A Balkema, 1989

Architecture of the pre‐pottery neolithic settlement in Nemrik, Iraq

Abstract The excavations at the site of Nemrik in northern Iraq have revealed a unique series of pre‐pottery neolithic settlements dating from the ninth to the first half of the seventh millennium be. Especially notable is the evidence for house architecture, including interior fittings and the unusual pillar structures which seem to have been supports for the roof. The architecture displays a clear course of development in technique of construction, form, roof support system and the conception of interior fixtures, from the earliest simple hut‐like structures to large, relatively richly furnished mud‐brick houses with wooden and later, unique to Nemrik, compacted marl roof‐supporting pillars. Technological progress is seen as the major factor in the architectural transformations of the eighth and seventh millennia bc.