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Mohammed Gabr

Distinguished Professor of Civil Engineering and Construction


Fitts-Woolard Hall 3224


Mo Gabr holds the position of Distinguished Professor at the Department of Civil, Construction, and Environmental Engineering at North Carolina State University. After obtaining his Ph.D. in 1987, he have worked in various sectors of industry and academia, including performing work related to offshore geotechnics and geoenvironmental engineering at two international institutions, international consulting firm, two universities, and as a Research Faculty at the Army Corps of Engineers Waterways Experiment Station in Vicksburg (now renamed as Engineer Research and Development Center.) Dr. Gabr served as the acting Director of the North Carolina Renewable Ocean Energy program for four years. He has held leadership positions chairing national technical committees at the Transportation Research Board of the National Research Council and at the Geo-Institute of the American Society of Civil Engineers. He is elected Fellow of the American Society of Civil Engineers and was inducted as a Diplomate of the Geo-Institute Academy of Geotechnical Professionals. He is a registered professional engineer in five States, with actively practicing Engineering in the State of North Carolina.

Offshore foundation systems supporting renewable energy structures; Innovative soil improvement techniques including the use of geosynthetics with zero carbon balance; sustainability of hydro power and flood defense earth structures under extreme storms, embankment and pier scour assessment and mitigation measures.


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Date: 08/01/23 - 7/31/25
Amount: $394,572.00
Funding Agencies: NC Department of Transportation

Traditional practice of bridge local scour estimation relies upon the use of analytical models such as the one specified in Hydraulic Engineering Circulars, HEC-18 and HEC 20 (Arneson et al., 2012). Models such as HEC-18 were however developed based on data collected mainly from flume testing on sand. The data used for HEC-18 model development were mainly for narrow pier erosion in sand (scour depth/pier width>1.4) per Benedict and Knight (2017). Yet the model is applied in practice to intermediate and wide pier cases as well. In addition, the materials classified as “soils” include sand, and/or silt, and/or clay with a grain size distribution that can yield a bed soil behavior that may not be captured by a single parameter, such as D50. Approaches such as the HEC-18 model also lump the flow channel and bridge hydraulic and geometrical parameters with the bed erosion resistance parameters in one equation. While such an approach is simple to use, there is consensus in literature that it yields overly conservative scour estimates. On a fundamental level, the magnitude of erosion and scour can be assessed through knowledge of the flow-induced shear stress, the soil’s erodibility parameters, which include the critical shear stress (τc), co- efficient of erodibility (α'), and m, which is “an exponent defining the functional variation of the soil erosion rate with the flow-induced shear stress.” This approach is fundamentally implemented in the FHWA Hy- draulic Toolbox and adopted by the NextScour Program. In parallel, geotechnical site investigation by the North Carolina DOT commonly involves the performance of SPT, and the retrieval of soil samples for characterization of physical and engineering properties. As such, there is an opportunity to obtain the site- specific erodibility (τc, α', and m) through linking such parameters with the geotechnical data for a rational assessment of site-specific scour magnitude, accounting for variability of channel-bed soil layers with depth.

Date: 08/01/21 - 7/31/23
Amount: $301,146.00
Funding Agencies: NC Department of Transportation

In a recent research project a pipe material selection software was developed. This software enables estimation of the service life of pipes made from different materials based on their anticipated exposure conditions. The linked GIS database is used to automatically compute the anticipated exposure condition corresponding with GPS coordinates input by the user for a given project. The culvert pipe materials commonly used by NCDOT have been included in the software: reinforced concrete, galvanized steel, aluminized steel, cast iron, mild steel, aluminum alloy, and polymeric pipes. Based on conversations with NCDOT, additional scope for the software is desired and identified as follows: i. The developed software selection guide only considers material type and exposure condition in the selection process. It is desirable to integrate NCDOT’s structural requirements into the selection process such that NCDOT engineers can use a single software to select pipe materials based on both durability and structural requirements. ii. The current software does not provide an estimate of how service life can be extended by repair and rehabilitation. It is desirable to upgrade the software to account for the additional service life expected from various rehabilitation measures, and to develop a comparative analysis of possible repair methods in terms of expected impact on service life. iii. The current software does not account for the effects of approaches to mitigate adverse subsurface exposure on the service life of installed pipes. Addressing the effects of mitigation is desirable since in many projects, backfill soil is different from native soil. The work proposed herein aims to update the current software to include: (i) An upgraded pipe selection guide software that integrates structural requirements, repair and rehabilitation methods, and mitigation strategies into a unified pipe selection guide, and (ii) provisions accounting for the effects of various repair and rehabilitation methods on the service life of the pipe materials.

Date: 01/01/16 - 6/30/23
Amount: $929,007.00
Funding Agencies: US Dept. of Homeland Security (DHS)

The integrity and reliability of flood-control earthen dams and levees are essential components to homeland safety. The failure of such systems due to natural or man-made hazards may have monumental repercussions, sometimes with dramatic and unanticipated consequences on human life and the country’s economy. The levees network in the Sacramento-San Joaquin Delta support exceptionally rich agricultural area (over a $500 million annual crop value). Currently, the risk of levee failure in this area from potential flooding or draught threatens the lives of individuals living behind the levees, but also, the water quality in this water-transfer system. Preliminary risk assessment demonstrated a 40% chance that at least 30 islands within the Delta area would be flooded by simultaneous levee failures in a major earthquake in the next 25 years. The teamwork proposed herein will extend the remote sensing monitoring by InSAR and Joint Scatterer interferometry (JSInSAR) to monitor levees deformation with a resolution on the order of a few millimeters. The research team ay NCSU will participate by integrating the use of measurement data and modeling techniques, using the concept of performance limit states, to effectively achieve a performance based health assessment of the delta levees network.

Date: 08/01/19 - 5/15/22
Amount: $335,480.00
Funding Agencies: NC Department of Transportation

The North Carolina Department of Transportation (NCDOT) routinely performs assessment of scour potential at bridge foundations. The availability of representative approaches for estimating first order scour magnitude is needed as such information is used for the design of new bridges, designating bridges as “scour- critical,” and for deciding on the need for implementing scour countermeasures. As stated by Mr. Jerry Snead, the applicability and potential modification of USGS Scour Envelope Curves, developed for the state of South Carolina, to North Carolina soils is the focus of the research proposed herein. Such investigation is needed to assess the robustness of the first order scour estimates and to provide reliable quality control measure to ensure the reasonableness of bridge scour magnitudes estimated by other means.

Date: 08/01/19 - 12/31/21
Amount: $336,834.00
Funding Agencies: NC Department of Transportation

The North Carolina Department of Transportation (NCDOT) routinely performs road improvement projects where a portion of the right-of-way might be contaminated. Based on the field evaluations carried out by NCDOT, at times subsurface utilities including water and/or drainage pipes are present, or need to be installed, in environments where soil and groundwater contamination exists. The currently funded project (RP 2017-08 with end date on July 31, 2019), is focused on the laboratory evaluation of contaminant migration through concrete pipes, as well as evaluation of the effect of contaminants on the mechanical performance of PVC pipe and three gasket materials (Neoprene, Buna-N, and Viton) when exposed to contaminated water. In addition, modeling of hardening methods and evaluating their efficacy is conducted as a part of the ongoing project.

Date: 08/01/19 - 12/31/21
Amount: $299,710.00
Funding Agencies: NC Department of Transportation

A large number culvert pipes are installed every year in North Carolina. While the loading and structural requirements for these pipes are considered during the selection process, the exposure condition of these culverts receives less attention. Many pipe choices exist including reinforced concrete, galvanized steel, aluminum, aluminized, and various types of plastic. Choosing the right pipe for the right installation is a non-trivial task that carries significant financial impact. Factors such as structural capacity, environmental durability, anticipated life-span, required pipe size, site conditions, and available construction expertise are all important when selecting a pipe. Existing NCDOT selection tables provide some limited guidance, but often result in highly-conservative selections being made, particularly from the perspective of matching pipe materials to site environmental conditions. Selection of the wrong pipe material (or an overly-conservative pipe material) can result in significant excess cost. If materials degrade too quickly, costly re-work is required, and additional costs and risks may be incurred due to reduced performance of the degraded pipe. If high-cost and high-performance materials are selected in areas where they are not needed, then initial construction costs can increase dramatically. For example, in many situations, aluminized corrugated steel pipe can likely provide the same useful service life as corrugated aluminum pipe at a dramatically reduced cost. Aluminum pipe may be justified in regions with salt-water exposure, however, it is likely an over-conservative choice for regions where contact with salt will be incidental. Accounts from NCDOT personnel have indicated widespread use of aluminum pipe in regions where it is likely not needed (i.e., regions with limited salt exposure).

Date: 08/01/16 - 7/31/19
Amount: $387,441.00
Funding Agencies: NC Department of Transportation

The North Carolina Department of Transportation (NCDOT) routinely performs road improvement projects where a portion of the right-of-way might be contaminated. Potential sources of contamination include underground storage tanks in the vicinity of the road improvement site, old unlined landfills, or abandoned industrial and agricultural operations with practices leading to soil and/or groundwater contamination. It has been reported by NCDOT in RNS#7406 that in several situations, subsurface utilities including drainage pipes are present in environments where soil and groundwater contamination exists. The effect of the contamination on the integrity and durability of the subsurface drainage pipes and gaskets is largely unknown but such integrity is a function of the type of contamination and the physicochemical properties of pipe, gasket, and other materials forming a given subsurface utility. In addition to the variety of contaminants and concentrations that prevail at these sites, a wide variation in soil geological formation and hydrogeological conditions exist across the state. While in general the groundwater table is expected to be high in the North Carolina (NC) Coastal Plain Physicographic region, it is expected to be deep in the Mountains. On the other hand, it is more likely that groundwater will feed surface water springs and streams in the NC Mountains. Therefore, a "typical" contaminated site is difficult to define. Accordingly, the adverse effect of subsurface contamination on drainage pipes and the efficacy of hardening measures are usually developed on a site-specific basis. Objectives of this project are to (i) catalog the prevalent types of contaminants and their concentrations at sites where subsurface utilities are installed, (ii) document the typical materials used in subsurface utilities and drainage systems in NC, (iii) quantify the effect of contaminants on the long-term durability of commonly used hardened and unhardened materials that are used in construction of subsurface utilities, (iv) quantify the rate and extent of migration of common contaminants through concrete utilities, (v) recommend effective hardening methods for different materials, and (vi) provide documentation and better understanding of the effect of subsurface utility installation on the contamination of groundwater and surface water through simulation of several typical scenarios. These objectives will be achieved through a multidisciplinary effort of the research team as outlined in the project plan. Objective (i) will be achieved through examination of available data from the NC Department of Environmental Quality (DEQ). If necessary, limited sampling of groundwater and surface water will be conducted in consultation with NCDOT in areas where subsurface utilities have been installed and contamination is known to exist or expected to occur. Objectives (ii), (iii), and (iv) will be accomplished through literature review and accelerated coupon testing in our laboratory. Objective (v) will be achieved by analyzing test results and literature data. Objective (vi) will be accomplished through numerical simulations.

Date: 08/15/13 - 12/31/16
Amount: $247,840.00
Funding Agencies: State of Alaska, Department of Transportation

A research project on reinforced concrete filled pipe piles concluding in May of 2013 had the following objectives: (1) Develop recommendations for strain limits for use in seismic design at key design limit states as a function of diameter/thickness (D/t) ratio and material properties, (2) Develop an equation (via computation) for the plastic hinge length of ?below ground hinges?, (3) Quantify the impact of reinforcing steel on performance and confirm that strain compatibility can be used for prediction of the force-displacement response. These three objectives have been studied through the use of large scale experimental testing, and the analysis of pile members. In addition, work in the project provided recommendations for equations to estimate equivalent viscous damping, which are required for implementation in a direct displacement-based design approach. This proposal builds upon the work previously conducted through the following tasks: (1) Large scale testing of reinforced concrete filled pipe piles in soil; and (2) FEA and fiber-based SSI analysis. The specific goals of this proposed research project are to examine the impact that soil stiffness has on: (1) Pipe pile strain limit states; (2) Plastic hinge length and integration of curvature for deformations; (3) Proposed analysis methods, and (4) Damping

Date: 09/01/13 - 8/31/16
Amount: $134,182.00
Funding Agencies: NC Department of Transportation

The North Carolina Department of Transportation (NCDOT) has funded a research project (will be referred to as Phase I study) to develop criteria for situations where soft soils need to be undercut and replaced and/or stabilized with mechanical or chemical measures (undercut refers to the removal of soft subgrade during the construction or reconstruction of new pavement sections). In this funded study, a large scale laboratory testing program was conducted to evaluate the performance of undercut subgrade stabilization measures under construction traffic loading, prior to final paving. Twenty-two simulated undercut sections, with four different stabilization configurations, were built in a large-scale test pit. Undercut areas backfilled with aggregate base course (ABC) and reinforced with geosynthetics showed improvement over unreinforced sections, but only when reinforcement was placed at depth approximately equal to the loaded area diameter and after initial displacements mobilized the strength of the geosynthetic. The soft nature of the subgrade and its consequences on the ability to compact the ABC layer showed the importance of carefully analyzing the results when viewed on a comparative basis, and the need for documented field performance. In this case, a trend of an accelerated deformation rate was observed during the first two hundred load cycles, with a steady state deformation rate emerging after approximately 1000-2000 loading cycles. It is not clear, however, whether this is a situation specific to the results from the laboratory testing, due to the limitation of the laboratory-sized equipment, or it is a behavior representative of field performance, and is occurring due to the limited ability to compact backfill over the soft subgrade layer. The main objective of the proposed project is to validate the findings from the Phase I laboratory study at a construction site in the Piedmont geologic area of North Carolina. The proposed work will seek to investigate the applicability of the proposed undercut criteria in the Piedmont Physiographic region and validate approaches to improving soil bearing properties investigated in the laboratory. The proposed plan includes the field implementation of four instrumented test pads for performance monitoring. In addition to a control pad, one pad will implement undercutting and replacement with select fill, a second will include undercutting in conjunction with ABC and the use of geosynthetics, and a third will include chemical stabilization. The research work will address the following objectives: i. Identify test sites in the Piedmont Physiographic region for implementation of alternative or supplemental approaches to undercut, including the use of geosynthetics and/or chemical stabilization. ii. Instrument test pads at the identified site and monitor performance in terms of induced rut depth, maximum curvature, tension cracks development, and stress attenuation with depth under repeated truck loading. iii. Perform Dynamic Cone Penetrometer (DCP) testing to validate proposed undercut criteria for site conditions. In addition, perform FWD testing to supplement the DCP data for comprehensive subgrade characterization. iv. Use field data to verify performance of alternative or supplemental approaches to undercut to limit volume change and improve soil properties and workability. Accordingly, update and verify the undercut criteria and comparative cost analyses developed during Phase I. Provide a recommendation of the relative cost of each measure and the most suitable stabilization measure(s).

Date: 08/16/12 - 6/30/16
Amount: $328,080.00
Funding Agencies: NC Department of Transportation

The main objective of the proposed project is the more economical design of temporary slopes and retaining structures in North Carolina (NC) residual soils. In general, the current design methods and procedures for temporary slopes and temporary excavation support systems do not consider the short-term characteristics of NC residual soils, and therefore may result in overly conservative designs and unnecessary construction costs. Even though the geotechnical engineers are aware of the over conservatism of the current design methods and procedures, they do not have rational means by which to improve the design cost effectiveness. It is the development of these rational design procedures that is the heart of the proposed research.

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