Enhancement of local soils with fibers and cement for the construction of stabilized pavement bases, canal lining, and support layers for shallow foundations shows great economical and environmental advantages, avoiding the use of borrow materials from elsewhere, in addition to the need of a spoil area. In previous studies, a unique dosage methodology for cemented soils has been established based on rational criteria in which the porosity-to-cement ratio plays a fundamental role in the assessment of the target unconfined compressive strength (qu). The present paper extends previous work by quantifying the influence of the amount of cement, the porosity, and the porosity-to-cement ratio in an assessment on tensile strength (qt) and compressive strength of a fiber-reinforced artificially cemented sand, in addition to the evaluation of the qt/qu relationship. A program of splitting tensile tests and unconfined compression tests considering four distinct dry densities and five cement contents, varying...

Based on a large database of unconfined compressive strength ($q_u$ ) and splitting tensile strength ($q_t$ ) results of cement-bonded clean granular soils with varying characteristics, distinct porosities, cement types and contents, and curing time periods, this paper advances the understanding of key strength controlling parameters. The $q_u$ and $q_t$ values were normalized, and a broad-spectrum empirical relationship (a general model) for cement-bonded clean granular soils controlling both tensile and compressive strength for an entire range of porosities and cement contents was proposed and successfully checked against literature data, contributing to the establishment of the blends’ strength behavior. From a practical perspective, it means that, at limit, carrying out one unconfined compression/splitting tensile test for one specimen (molded with a specific cement amount, at a specific porosity, and cured for a given time period) allows the determination of the curve that controls the strength for an entire range of porosities and cement contents. This also contributes to minimizing the number of specimens that need to be molded and tested, thus also reducing project development cost and time.

The improvement of soils that are not suitable for a particular purpose through techniques that combine densification and the incorporation of portland cement have been extensively done for decades in spite of the poor environmental performance related to such material. In this context, the development of alternative binders through the use of industrial byproducts may be an alternative to mitigate environment-related issues. Therefore, the current study aims to evaluate the performance of a gap-graded soil via incorporation of a binder composed of coal fly ash and hydrated lime. For this, strength, stiffness, and durability tests were carried out on compacted soil–coal fly ash–hydrated lime specimens molded at different porosities and with distinct coal fly ash and hydrated lime contents. Moreover, the stiffness of the specimens was also assessed during wetting-drying cycles. Results of all mechanical tests have shown the significant influence exerted by porosity, followed by the relatively minor impact of the amounts of binder (here composed of lime plus fly ash). Hence, good correlations between the response variables and the adjusted porosity/binder index ($\eta /B_{iv}^{0.28}$ ) were obtained. Furthermore, an innovative approach to replacing the laborious durability test is proposed.

In order to investigate techniques to improve the mechanical behaviour of mine tailings, an investigation of the cyclic shear response of fibre-reinforced mine tailings was carried out in the present study. Cyclic simple shear tests were conducted on fibre-reinforced and non-reinforced mine tailings. The tailings, produced from gold mining, were classified as sandy silt with traces of clay. Polypropylene fibres (zero and 0.5%) were added to the material. Under monotonic shear conditions, the addition of fibres unstiffens the material. Under shear stress-controlled cyclic conditions, fibres improved the material shear response and produced a stiffer material. Under shear strain-controlled cyclic conditions, no improvement was observed as a result of addition of fibres and there was no effect on material stiffness. The agreement of the strength envelopes of both monotonic and cyclic stress paths, under different cyclic loading conditions, allows the use of the same strength parameters for mixtures analysed under different loading conditions.

Fibre addition and Portland cement treatment are used to amend the adverse characteristics of some fine-grained soils and to enhance their mechanical properties. The present study proposes a single power function that quantifies the effects of the amount of cement and porosity on the unconfined compressive (q_u) and split tensile (q_t) strength of fibre-reinforced fine-grained soil-cement mixtures. The practical value of the equation is that only one unconfined compression (or split tensile) test of a specimen moulded with a specific fibre type, fibre amount, specific cement amount, porosity, and cured for a given time period is required to estimate the strength of the fibre-cement soil mixture. The equation can be used for a wide range of porosities and cement contents, and for other fibre-reinforced fine-grained soils treated with cement.

Sulfate-rich dispersive soils are worldwide responsible for damaging earthworks, such as roadway roadbeds and embankments. One of the causes for such behavior is the high amount of exchangeable sodium ions adsorbed on their clay particles vastly increasing erosion susceptibility, being responsible for problems as piping, ravines, and water turbidity. In order to reduce the erodibility, it is usual to treat such soils with calcium-based stabilizers. However, in the presence of sulfates, when combined with calcium-based stabilizers in the soil, reactions take place between stabilizers and sulfates to form expansive minerals. Namely, these minerals are known as ettringite and thaumasite and are responsible for excessive volumetric swell. In this context, the present research aims to develop alternative soil stabilizers (industrial byproducts plus artificial pozzolans) and reinforcements (fiberglass) to solve problems associated with sulfate-rich dispersive soils. Thus, a binder composed of carbide lime and ground glass was used. In addition, fiberglass was applied to look for enhanced mechanical properties of the materials. To assess the efficiency of the proposed stabilization and reinforcement, unconfined compressive and splitting tensile strength, ultrasonic pulse velocity, wet and dry durability, and fatigue life tests were carried out. Soil–ground glass–carbide lime-fiberglass blends were molded at different porosities, carbide lime, ground glass, and fiberglass contents. Results show that unconfined compressive and split tensile strength and initial shear modulus are highly dependent on changes in porosity and lime content. Durability, expressed as the accumulated loss of mass, could be assessed through the adjusted porosity/lime index ($\eta /L_{iv}$ ). Fiberglass inclusion resulted in higher tensile strength. The fatigue life was correlated to the $\eta /L_{iv}$ index through a negative exponent. The greater the carbide lime level, the smaller was the fatigue life for all treated specimens. An increase in porosity results in fewer contacts between particles, whereas an increase in carbide lime content enhanced the specimen’s rigidity.