Sobhan, Khaled

The Florida Everglades is considered as a vulnerable wetland composed primary of organic rich peat soils, experiencing saltwater intrusion. Impact of increasing salinity on the strength and deformation properties of peat is unknown. A laboratory study was undertaken to evaluate how the growing salinity level due to sea level rise may alter the compressibility behavior of the Everglades soils. Sixteen 1-dimensional oedometer tests were conducted on undisturbed Everglades peat soils in two phases. Phase I included samples from Site 1 (saltwater) and Site 3 (freshwater) without any salinity addition. Phase II consisted of soil from Site 3 (freshwater) saturated in six different levels of salinity artificially added to the samples. Compressibility properties investigated in this study include compression index (Cc), coefficient of consolidation (Cv), hydraulic conductivity (K), and the Ca/Cc ratio. In general, it was observed that the increase in salinity beyond a threshold value tends to increase the soil compressibility properties, indicating a possible reduction in soil stability with saltwater intrusion.

This study tests the long-term durability that can be developed in concrete batches made with recycled aggregate concrete. Durability is a broad term used to define the resistance of a material to weathering effects, but in this scenario, durability will be defined as a drop in the compressive strength of the concrete. To test this, thermal sensing was used to determine the maturity of the concrete, or in other words how far along the curing process the concrete is. This was then plotted against the corresponding concrete compressive strength to create a relationship that can be exploited to project the later age strength of the concrete. This data is paramount in determining the viability of recycled concrete aggregate because it is a sustainable alternative to other coarse aggregate material, an essential part to making concrete, but its’ properties are largely unknown since they can be highly variable.

The coupled effect of using geosynthetic reinforcement and randomly distributed fibers on the stability of slopes was evaluated using finite element modeling and limit equilibrium methods by analyzing a case study in Oslo, Norway. The main objective was to simulate the failure condition of the original slope and quantify the improved stability of a hypothetical reinforced slope constructed with geosynthetic layers and distributed discrete fibers. The stability of the slope was evaluated in both the short-term condition with its' undrained shear strength parameters, and the long-term drained condition. Results indicate that the combination of the techniques was found to have a possible increase of about 40% in the short-term condition and about 60% in the long-term condition of the factor safety associated with the slope.

The reuse of crushed aggregates for producing structural concrete is a major
concern especially when it comes to its strength and durability. This study evaluated
recycled aggregate concrete (RAC) for its strength and durability under simulated
environmental degradation in the form of wetting-drying (W-D) cycles. The study
consisted of two phases, each involving the determination of the compressive strength and
modulus of elasticity using the conventional method and also a nondestructive ultrasonic
pulse velocity method (Pundit Lab). Phase 1 involved 7-day curing followed by 30 W-D
cycles, while Phase 2 included 28-day cured samples subjected to 15 W-D cycles. It was
found that RAC specimens subjected to W-D cycles had minimal degradation in strength,
making the use of RAC in construction very promising. Results from Pundit Lab compared
reasonably well with conventional test results, showing promise as a nondestructive tool
for the evaluation of RAC properties.

Geopolymer concrete (GC) is a sustainable construction material and a great
alternative to regular concrete. GC is a zero-cement material made from a combination of
aluminate, silicate and an activator to produce a binder-like substance.
This investigation focused on the effects of wet and dry cycles on the strength and
durability of fly ash-based recycled aggregate geopolymer concrete (RAGC). The wet-dry
cycles were performed approximately according to ASTM D559 standards.
RAGC specimens with nearly 70% recycled materials (recycled aggregate and fly
ash) achieved a compressive strength of approximately 3600 psi, after 7 days of heat curing
at 60ºC. Although the recycled aggregate is prone to high water absorption, the
compressive strength decreased by only 4% after exposure to 21 wet-dry cycles, compared
to control specimens that were not exposed to the same conditions. Accordingly, the RAGC
material developed in this study can be considered as a promising environmentally friendly
alternative to cement-based regular concrete.

An analytical investigation was conducted to evaluate the geotechnical safety and
stability of MSW landfills constructed with significantly steepened slopes achieved
through geosynthetic reinforcement. The primary motivation for this endeavor was to
propose a new design/construction methodology for innovative expansion of landfill
capacity. A 2-D plane strain linear elastic analysis was performed with ANSYS finite
element software on full-scale MSW landfill structures (with and without geogrids),
having slopes of 1:1, 1:2, and 1:3. Both local and global factors of safety were
determined employing the Mohr-Coulomb failure criteria, and compared with traditional
solutions using the Bishop's Modified Method. It was found that the landfill slopes could
be steepened up to 1:1 using geogrid reinforcement, resulting in higher storage capacity
and consequential environmental and economic benefits.

Three vital factors, namely environmental protection, savings in costs, and
strength/durability benefits, make it advantageous to incorporate fly ash of controlled
quality and composition in all concrete made from construction demolition (C&D)
recycled aggregate. The specific objective of this research was to compare the
performance characteristics of High-Volume-Fly-Ash (HVFA) structural concrete
containing C&D aggregate with that of normal recycled aggregate concrete containing no
fly ash.
A coordinated experimental program was undertaken which comprised of ( 1)
Compressive and Split Tensile strength tests; (2) ASTM durability tests by measuring
resistance to chloride-ion penetration; and (3) Flexural strength tests on reinforced
concrete beam specimens. Three mix designs were used, all of which had the same
water/cement ratio of 0.45 and the same amount of recycled aggregate/yd^3. Mix 1
contained cement and no fly ash, Mix 2 contained 16% replacement of cement by weight, and Mix 3 contained 40% replacement of cement, called a HVF A mix. Results
indicate that fly ash increases compressive strength, improves both moment carrying
capacity and tension resistance, and increases resistance to chloride-ion attack.

Flexible or asphalt pavements constitute nearly 94% of the 2.7 million miles of existing roadways in the United States. In a typical rehabilitation project, the existing asphalt pavement is milled up to a prescribed depth for removing the near surface distresses such as excessive cracking and rutting, and a new overlay is placed. The average time between resurfacing projects varies depending on the level of pavement deterioration which is significantly accelerated when poor subgrade conditions are encountered. The use of geosynthetic reinforcement within the new asphalt overlay is often perceived as a mitigation strategy that can delay the onset and propagation of reflection cracking, and also control the rutting and differential settlement. However, some mixed reviews about the performance of the geosynthetic reinforced overlays have been reported in the literature.
In Phase I of this study, a laboratory investigation was conducted for evaluating the flexural fatigue behavior, permanent deformation response, and fracture characteristics of geogrid reinforced asphalt beam specimens made from a typical overlay material. The laboratory specimens included geogrid as a single-layer inclusion either at the bottom third depth or at the mid height, and as double-layer inclusion, with geogrid placed both at the bottom third and at the middle of the beam. In Phase II, a case study involving geogrid reinforced overlay constructed over a deteriorated pavement underlain by soft subgrade in southeastern Florida was numerically simulated. It was found that the geogrid reinforcement significantly improved the fatigue and fracture properties of the asphalt beams compared to unreinforced specimens. Results from numerical simulation demonstrated that the double reinforced overlay resulted in the minimum tensile stress at the bottom of the asphalt layer (reducing the cracking potential) and minimum vertical strain on the top of the subgrade (reducing the rutting potential), compared to unreinforced or bottom-third reinforced overlays. Accordingly, it is concluded that the double layer reinforcement of asphalt overlays with an appropriate geosynthetic product can be beneficial for the performance and long term preservation of the pavement system when soft soils are encountered.

A transparent soil model of granular fused quartz is developed to study the mechanics of shallow foundations. Soil models, unreinforced and reinforced, prepared at relative densities 0.34 (loose) and 0.64 to 0.69 (medium dense) are tested using a rectangular footing (25 mm wide x 40 mm long) under strain-controlled loading. Digital Image Correlation is used to identify displacements of a seeded central plane parallel to footing width (B) and construct vector fields and contour plots. Fiber-reinforced soil model data analysis is inconclusive. For the unreinforced medium-dense soil, minimum and peak magnitude horizontal displacements occurred directly under the footing at the footing edges; whereas in the loose soil, peak magnitude horizontal displacement occurred directly under the footing. Vector and contour plots revealed that a medium dense soil gradually distributes smaller magnitude displacements over a broad area, in contradistinction to acute, highly localized displacements of larger magnitude in a loose soil.

Geotechnical engineers are commonly faced with the need to perform ground
improvement techniques to achieve the necessary bearing capacity for a project. Some of
the most common techniques involve the excavation and replenishment of problematic
geomaterial with one of better quality. Common projects, such as road embankments and
retaining walls, also require the selection of backfill material. The guidelines for selecting
backfill material are typically limited to complying with certain gradation bands, relative
densities and allowable fines content.
Round-grained silica sand, and beach sand from Boca Raton, FL, were used to generate
a total of 16 binary granular mixtures containing different amounts of finer material, for
which a series of direct shear tests were conducted. Based on the experimental results, it
may be possible to provide an alternative criteria for selecting backfill material based on
granulometric parameters and the amount of finer material.