Rafaela Cardoso

A Comparative Study of Soil Suction Measurement Using Two Different High-Range Psychrometers

An extensive experimental study was performed to compare the measurement capabilities within different ranges of two total suction measurement equipment: SMI transistor psychrometers and a chilled-mirror dew-point psychrometer (WP4 Dewpoint PotentiaMeter). The equipment were used in a systematic way to determine the relative humidity of the environment surrounding different compacted clayey soils along drying paths and covering a wide total suction range (0.1 to 70 MPa). The equipment description and the calibration protocols followed are presented, as well as suggestions regarding the improvement of their performance. The water retention curves of two different compacted clayey soils are presented and commented by taking into account the corrections proposed for the readings. A possible explanation for differences in the measurements observed between both instruments in the high suction range is presented in terms of the hydraulic paths undergone by the soils during the measurement period.

Use of recycled aggregates from construction and demolition waste in geotechnical applications: A literature review

The use of recycled aggregates (RA) in construction constitutes a significant step towards a more sustainable society and also creates a new market opportunity to be exploited. In recent years, several case-studies have emerged in which RA were used in Geotechnical applications, such as filling materials and in unbound pavement layers. This paper presents a review of the most important physical properties of different types of RA and their comparison with natural aggregates (NA), and how these properties affect their hydraulic and mechanical behaviour when compacted. Specifically, the effects of compaction on grading size distribution curves and density are analysed, as well as the consequences of particle crushing on the resilient modulus, CBR and permeability. The paper also contains an analysis of the influence of incorporating different RA types on the performance of unbound road pavement layers as compared with those built with NA by means of the International Roughness Index and deflection values. The results collected from the literature indicate that the performance of most RA is comparable to that of NA and can be used in unbound pavement layers or in other applications requiring compaction.

Impact of Bituminous Subballast on Railroad Track Deformation Considering Atmospheric Actions

High-speed ballasted track design standards usually require the use of sand and gravel layers as subballast to fulfill an accurate protection of the formation layers, not only against traffic loads, but also against the effects of weather. Seasonal changes in soil water content, or suction changes, are responsible for cyclic volumetric strains on railroad trackbed layers, thus on the infrastructure. Being almost completely water-resistant when compared with granular-only layers, bituminous subballast offers a higher protection of the subgrade, consequently improving its behavior along the infrastructure life cycle. This question is investigated through the comparison of the performance of the track formation against atmospheric actions, taking into consideration the unsaturated state of the geomaterials. The method adopted consists of modeling the vertical displacements of both bituminous and granular subballast designs through a finite-element coupled thermo-hydro-mechanical (THM) analysis. The comparison of the two design solutions confirms that the adoption of a bituminous subballast layer might allow important reductions in seasonal vertical displacements.

Degradation of marls; two case studies from the Iberian Peninsula

Abstract The strength degradation of two marl formations (Pamplona marls in Spain and Abadia marls in Portugal) is analysed in the paper. In the case of Pamplona marls, a number of large-scale direct shear tests on natural and saturated specimens of the undisturbed material were performed. Tests on marl–concrete interfaces were performed and are also presented. Both cases analysed show that the saturation of the marl leads to a strong reduction of friction and effective cohesion. Negative effects of suction changes on the mechanical behaviour of the marls were investigated in more detail in suction controlled tests on Abadia marls, a more plastic material. A numerical simulation of wetting effects on a marl fragment of finite size helps to identify the nature of degradation mechanisms, which are associated with the development of tensile surfaces inside the marl matrix. They, in turn, are due to the expansive behaviour of the clay fraction of the marl relative to suction changes.

A review on models for the prediction of the diameter of jet grouting columns

Jet grouting is a known ground improvement technique largely used worldwide for different applications. One of the major limitations of this technique is mainly related to obtaining good predictions of the geometry of the final grouted body, as it is a function of the injection parameters and soil properties. Over the years, many studies have been conducted and few models and design methodologies have been developed to obtain more accurate predictions. A short review on some models found in the literature with a theoretical background is provided in this paper, highlighting the advantages and the limitations of each approach presented. A brief overview on emerging approaches is presented as well.

Soil Structure Influence on Electrokinetic Dewatering Process

The control of water content or water movement in soils is fundamental not only to ensure some desired characteristics but also for different applications, such as consolidation, dewatering, conditioning, and decontamination. In clayey soils, due to the small size of clay particles their behavior is ruled by the interactive electrochemical forces rather than gravity forces. Their natural negative electrical charge at the particles surface forming a double layer explains water sensitivity and osmotic effects, and therefore their suitability for applying electrokinetic techniques (EKT). In this chapter, the equations used to describe EK processes in the soil from a geotechnical point of view are reviewed emphasizing the electro-hydraulic coupled behavior and how it is affected by soil structure. The results from tests performed on samples of commercial white kaolin compacted to known structures are presented as example of the chemo-electro-hydraulic coupled behavior of clays. The main purpose of the experimental study was to study the effect of soil structure on its hydraulic, electrical, and electroosmotic conductivities. The results are interpreted considering the existence of two types of voids, the microvoids of the clay aggregates and the macrovoids between these aggregates and identifying the dominant pore size for each phenomenon. It can be concluded that the hydraulic and electrical conductivities depend mainly on the size of the macropores, while the electroosmotic conductivity depends on global porosity due to electro-chemical interaction between the water and the clay minerals. It is believed that the main applications of EKT in the future are in the domain of Environmental Engineering, where contaminants are present in pore fluid affecting its electrical conductivity as well as the size of micropores. For this reason, a better knowledge of the coupled chemo-electro-hydraulic behavior of impervious materials like clayey soils linked to their mechanical behavior (volume changes and consequently stiffness and strength changes) caused by the interaction between the two structural levels may help defining better models to be used at design of efficient solutions using EKT.

Direct Estimate of the Breach Hydrograph of an Overtopped Earth Dam

AbstractThe quantification of the breach hydrograph of an overtopped earth dam remains a challenge, even in controlled laboratory conditions. In this work, the breach hydrograph is calculated as th...

Influence of Water–Cement Ratio on the Hydraulic Behavior of an Artificially Cemented Sand

In general, the prescription of the amount of water used in soil–cement mixtures is done to define the optimal compaction conditions for bases and sub-bases, or to ensure the fluidity necessary for a good mixture by injection. A better knowledge about the hydraulic behaviour of the resulting mixtures may be useful in service conditions, when permeability is important or when the layers are exposed to wetting and drying cycles. The relationship between saturated hydraulic permeability, coefficient of water absorption by capillarity and water retention properties were investigated for an artificially cemented sand prepared with different and realistic cement dosages, and with different water–cement ratios for each dosage. The water–cement ratio was considered in the analysis because it affects porosity and pore size distribution of the cement paste, and consequently tortuosity. Low values of this ratio mimic compacted sand–cement mixtures and large values simulate grouted sands. The dosages adopted simulate those used in pavement layers and obtained in grouted bodies. The results of an extensive set of experimental tests, performed to determine the hydraulic properties mentioned, are interpreted in the paper considering the presence and structure of the hardened cement paste. The materials prepared with low water–cement ratio have higher permeability and different water retention properties from those prepared with high ratios. Nevertheless, the water used in the hydration of the cement also affects the porosity and tortuosity of the hardened paste and may increase porosity if grout is very fluid. This study contributes to increase the knowledge about the effects of design parameters cement dosage and water–cement ratio on the hydraulic behaviour of the mixtures, which may be relevant when evaluating water retention and percolation.

Settlement Prediction of High Speed Railway Embankments Considering the Accumulation of Wetting and Drying Cycles

The hydro-mechanical behaviour of a compacted silt clayey soil from an experimental railway embankment was investigated. Laboratorial tests were performed, in which compacted samples were subjected to some wetting and drying cycles to simulate the effect of atmospheric actions. Data from the tests allowed studying the effect, on volumetric behaviour, of cumulative deformations caused by the cycles. Also, experimental data allowed finding the constants of the constitutive model for unsaturated soils BBM. The volumetric behaviour of the experimental embankment was simulated using program Code Bright. Atmospheric actions were considered and seasonal deformations were calculated. The results can be useful to estimate maintenance needs of railway infrastructures.

Biocementation as Rehabilitation Technique of Porous Materials

The main findings when using microbially induced calcite precipitation, MICP, in two case-studies, a sandy soil and a mortar surface, are presented. The first case is focused on studying biocementation in sands to improve their mechanical properties. Tests were carried out with the aim to check the biological activity and understand MICP effects on a porous medium. By visual inspection it was possible to see the presence of calcite in the top of the specimens confirming that this type of treatment is mainly superficial and must be improved to be more uniform in depth. In the second case, biodeposition was tested in order to understand how it would affect the main properties of porous cement mortar such as elastic stiffness, capillarity coefficient, water vapour permeability, roughness and open porosity. These properties are relevant mainly for walls. Treatment was applied in mortar specimens by submersion in the treatment solutions during the first 28 days of curing. The results were compared with those found in similar tests performed in samples which were not subjected to treatment, which were submerged in tap water or cured in wet environment. These different porous media are used as example of the improvement that can be achieved using this technique to treat volume or area. Considerations are done concerning the extrapolation of the results for other porous materials used for Civil engineering applications in the context of rehabilitation and how this technique could be implemented in the construction sites.