Paulo J. Venda Oliveira

Behavior of an Atypical Embankment on Soft Soil: Field Observations and Numerical Simulation

This paper compares the behavior of an embankment with nonsymmetric geometry built on soft soil with that predicted numerically using four elastoplastic soil models. Two of these models are based on isotropic conditions (Modified Cam-Clay on its own or in association with Von Mises) and two other are derived from anisotropic conditions (Melanie on its own or conjugated with Mohr Coulomb). The performance of the models, whose parameters are derived from experimental data, is checked against triaxial tests results. For the embankment, the measured and computed displacements and excess pore pressure are compared, with the isotropic models performing best. The maximum horizontal displacements versus settlements, the change in excess pore pressure versus vertical stress, the extent of the yield domain and the contours of the effective vertical and horizontal stress increments are also examined. The numerical results are explained based on the characteristics of the numerical models, namely the size and shape of the yield surface. The embankment, despite its nonsymmetric geometry, exhibits some similarities with typical behavior.

Effect of Organic Matter Content and Curing Conditions on the Creep Behavior of an Artificially Stabilized Soil

This paper examines the effect of organic matter content and the curing conditions on the one-dimensional compressibility of Portuguese soft soil stabilized with binders, with a special emphasis on creep behavior. Consolidation and creep oedometer tests were carried out on remolded and stabilized soil samples to study the effects of these factors. The increase of the organic matter content induces the increment of compressibility characteristics, including creep. Curing conditions also affect the one-dimensional compression behavior of the stabilized soil because the underwater curing, the increase of the vertical stress applied on the sample, and the increase of the curing time improve the compressibility characteristics, inducing the reduction of creep deformations.

Effect of Stress Level and Binder Composition on Secondary Compression of an Artificially Stabilized Soil

This paper examines the effect on the compressibility of a Portuguese soft soil stabilized with binders, with a special emphasis on creep characteristics. The effects of vertical stress during curing time and binder composition (type and content) on the creep behavior of a sta- bilized material are analyzed with oedometer tests. The results show the decrease of the secondary compression index with the decrease of the vertical stress applied during creep phase and with the increment of the binder content. The best binder type for this soil, in terms of creep be- havior, iscomposedof portland cement and flyash witha dryweight proportionof 75/25, becausethis promotes thedevelopment of secondary pozzolanicreactions.Theresultsalsorevealthatthebindercompositionshouldhaveaminimumquantityofcementtoimprovethecompression characteristicsofthestabilizedsoiladequately.DOI:10.1061/(ASCE)GT.1943-5606.0000762.

Municipal solid waste shear strength parameters defined through laboratorial and in situ tests

This paper presents the parameters of municipal solid waste shear strength determined in the laboratory (triaxial tests) and by in situ tests: standard penetration tests (SPT) and cone penetration tests (CPT). The results analyzed here are part of a study carried out on the Santo Tirso landfill (north of Portugal) between 2001 and 2007. The influence of the strain levels, waste composition, and waste age on the shear strength parameters is presented, as well as an attempt to establish some correlations between the SPT and CPT tests and to estimate municipal solid waste (MSW) friction angles from the SPT tests. The results indicate that the aging of the waste, which is characterized by a decrease in fibrous and organic materials and an increase in inert materials and fine fraction, leads to an increase in frictional resistance and to a decrease in cohesion. The results of the SPT and CPT tests indicate higher penetration resistance in older and deeper waste. Estimating the frictional resistance from the SPT test seems to obey an empirical relationship expressed by a power function, which depends on the strain level. Implications: Comparison of shear strength parameters of municipal solid waste (MSW) determined through laboratory (triaxial tests) and in situ tests (SPT and CPT) showed that the greater amount of fibrous and granular elements leads to an increase in “cohesion” and in friction angle values, respectively. Waste aging results in an increase in frictional resistance and in a decrease in “cohesive” resistance. This is consistent with the composition changes with aging: increase of the relative quantity of inert materials and fine fraction, and decrease in particle size, in organic matter content, and in fabrics and plastics.

Comparison of the Ability of Two Bacteria to Improve the Behavior of Sandy Soil

AbstractThis paper presents a laboratory study of the ability of two bacteria to improve the geomechanical properties of a sandy soil by calcium carbonate precipitation. The performance of two bacteria (Sporosarcina pasteurii and Idiomarina insulisalsae) is compared, based on unconfined compressive strength and splitting tensile strength tests. The effects of curing time and the concentration of I. insulisalsae on the strengthening process are also analyzed. Although the optimum environmental conditions for the bacterial growth were not adopted, the potential to improve the geomechanical properties of natural sandy soils is shown by the results. The bacteria I. insuliasalsae is shown to be more efficient than S. pasteurii in strengthening the soil, and increases in the concentration of I. isuliasalsae induce an increase in the geomechanical properties. However, this effect is not proportional to the amount of bacteria, probably due to a lack of nutrient.

Effect of Organic Matter Content and Binder Quantity on the Uniaxial Creep Behavior of an Artificially Stabilized Soil

AbstractThe objective of this work is to analyze, based on the results of uniaxial creep tests, the effect of organic matter content and binder quantity on the creep behavior of a Portuguese soft soil chemically stabilized with binders. In general, the results show that the application of a creep load induces a slight degradation of the mechanical properties of the composite material of the same age, as a consequence of the breakage of some cementation bonds owing to the creep deformation. This degradation grows with the increases in binder quantity and the decreases in organic matter content. The uniaxial creep tests indicate an increase in the creep strain rate with log time, allowing the definition of two creep compression indices, Cα1∗ and Cα2∗. Whereas the initial creep compression index (Cα1∗) is independent of the strength and shows a low scatter of values (0.00013–0.0003), the final creep compression index (Cα2∗) decreases with the increment of the strength, i.e., for higher binder quantities and ...

Experimental Study of Isotropic and Anisotropic Constitutive Models

AbstractThis paper analyzes the validity of the yield surface and flow rule of several isotropic and anisotropic constitutive models. These aspects are studied based on drained triaxial tests, with a number of different stress paths in a computer-controlled stress path cell. The Cam clay, modified Cam clay, and p-q-θ models are used to study the isotropic behavior, whereas the anisotropic conditions are analyzed using the Melanie, MIT-E3, and S-CLAY1 models. Both under the isotropic and anisotropic conditions, the results indicate that the surface described by the undrained effective stress path is suitable for simulating the yield and plastic potential surfaces. In terms of isotropic behavior, the p-q-θ model is the most suitable for predicting the yield, whereas the plastic potential function is closely simulated by the yield function of the modified Cam clay model. For the anisotropic models studied, the MIT-E3 model provides a better approximation of the anisotropic behavior of the Santa Clara clay.

Effect of Soil Type on the Enzymatic Calcium Carbonate Precipitation Process Used for Soil Improvement

AbstractThis work analyzes the effect of soil type on the process of enzymatic calcium carbonate (CaCO3) precipitation. This methodology is tested for the stabilization of five soil types (poorly g...