Ahmed Mohamed Nasr’s research while affiliated with Tanta University and other places

Collapsible soil is considered one of the most dangerous issues facing geotechnical engineers nowadays, as it exhibits considerable strength when dry, but after inundation, it experiences significant volume reduction and loses its strength. Geotechnical engineers have sought to treat this kind of soil by several methods, of which the most common is the chemical one, but they are considered environmentally unfriendly materials. Thus, it is necessary to find alternatives to traditional stabilizers. One such alternative is the use of biopolymers, which are produced from agricultural plants or animal products. Three biopolymers were investigated: xanthan gum, sodium alginate, and gelatin. The current study was conducted to assess an approach to enhance surface soil layers that are subjected to collapse after saturation. In this study, a numerical model was used to investigate the effect of biopolymer type, biopolymer content, improved soil depth, and improved soil width on the subgrade reaction, bearing capacity, and collapse settlement of the soil. The unsoaked and soaked soil properties were estimated after being mixed with the biopolymers at different contents of 0, 0.5, 1, 2, 3, and 4%. The used model depends on the soil–water characteristics curve and the unsaturated soil theories to evaluate the soil suction effect due to progressive inundation. The results showed that with increasing biopolymer content, improved soil width, and improved soil depth, the collapse settlement significantly decreased, but the bearing capacity and subgrade reaction of the soil increased. The results revealed the efficiency of this technique in reducing wetting-induced collapse settlements.

Many offshore structures with pile foundations have failed due to the inadequate design for torsional loads caused by earthquakes, winds, and storms. To address this, the PLAXIS 3D V20 software was used to conduct a comparative analysis between the innovative XCC pile and the conventional circular CCC pile, both sharing the same cross-sectional area. This analysis assessed the performance of the XCC section pile under pure torsion loads, inclined loads, and a combination of both, along with studying the effect of load direction on the XCC pile. The findings indicated that the XCC shape significantly enhances performance under torsional and inclined loads. Specifically, for an XCC pile with a radius (r xcc) of 0.45 m, open arc spacing (ap) of 0.14 m, open arc degrees (θ) of 90 degrees, and a pile length (L p) of 10 m, and a CCC pile with an equivalent radius (r ccc) of 0.342 m, constructed in clay soil with a cohesion (Cu) of 70 KN/m 2 , the XCC section pile showed an enhancement ratio of 490% under pure torsion, and up to 39% under inclined loads. Furthermore, torsional loads reduced the inclined load capacity by approximately 6-21% in circular piles and 11-15% in XCC piles, corresponding to a total displacement of 0.05D m. The increased bearing capacity of the XCC pile can be attributed to an increase in total skin resistance, arching effect, and passive resistance, enhanced by the pile's effective shape. ARTICLE HISTORY

This study is concerned with stabilizing collapsible soil with eco-friendly materials. The additives used in this study are classified as types of biopolymers. Biopolymers have been utilized nowadays in many fields as alternatives to unfriendly materials. This study investigates the potential of using biopolymers to stabilize the collapsible soil which was collected from New Borg-Alarab City, Egypt. Gelatin, sodium alginate, and xanthan gum were added to the soil in contents of 0.5, 1, 2, 3, and 4% to investigate to what extent the biopolymer content affected the soil’s characteristics. The soil was mixed with biopolymers using the wet mixing technique. The compaction characteristics, shear strength parameters, and collapse index have been evaluated for the soil before and after treatment. Moreover, the microstructure of the untreated and treated soils was examined by carrying out scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. The effect of biopolymers on the soil characteristics was obvious, as the biopolymers improved the shear strength and decreased the collapse index. When 4% gelatin, sodium alginate, and xanthan gum were mixed with the soil, its unsoaked shear strength increased by 79%, 275%, and 313%, respectively. While, the soaked shear strength increased by 232%, 285%, and 327%, respectively. The results showed that a 4% concentration of gelatin, sodium alginate, and xanthan gum greatly decreased the collapse index by 85%, 93%, and 98%, respectively. Additionally, the interaction between the biopolymers and the fine-grained particles is obvious in the SEM and XRD results.

Contaminated soil can reduce the stability of structures and infrastructure, endangering their structural integrity. Hence, this study tries to determine how oil pollution influences the torsion behavior of model steel piles at varied soil densities. This study is critical for determining piles' structural integrity and stability in oil-contaminated situations. A mixture of heavy motor oil and clean sand samples was prepared in proportions ranging from 0 to 8% of the dry weight of the soil. In this study, the relative densities (Dr), pile slenderness ratio (Lp/Dp), oil concentration (O.C%), and contaminated sand layer thickness (LC) all varied. The study also includes an examination of piles of combined load (vertical and torsional). Results revealed that the pre-applied torsion force reduced the pile's vertical bearing capabilities. Furthermore, at Dr = 30%, we determined that the maximum vertical load under amalgamated load at constant torsional load T = (1/3Tu, 2/3Tu, and Tu) in cases of (Lc/Lp) = 1 and (Lp/Dp) = 13.3 is 1.67, 3.4, and 5% less than piles under pure vertical load, respectively. This highlights the importance of considering torsional forces in pile design to guarantee precise load-bearing capabilities. Engineers should carefully assess both vertical and torsional loads to optimize the performance and stability of piles in various conditions.

Liquefaction is one of the most dramatic defects of gran-ular soil. This phenomenon is mostly observed when loose sand is subjected to a dynamic load or earthquake. In this study, the liq-uefaction that affected the loose soil is evaluated, and some recommendations are introduced. (2-D) Numerical analysis using Plaxis (8.2) was conducted to simulate the behavior of the loose soil under dynamic loads. The studied model was carried out on multi-layer soil supported by stone columns subjected to dynamic loads. It was found that stone columns enhanced the soil behavior and reduced the damage that occurred. Liquefaction of the loose soil could be constrained by increasing the shearing parameters of the soil. The damages of a dynamic load are time-dependent, so the corresponding damage increases as the time of the applied dynamic load increases. Moreover, the many straining actions are evaluated, and a comparative study is introduced, such as access pore water pressure, total vertical displacement, deformation of soil, and velocity.

Ground improvement techniques are crucial in construction, particularly in weak soil conditions. This study examines ordinary stone columns (OSC) and encased stone columns (ESC) to enhance endurance, shear strength, and soil hardness. The research investigates their behavior under strip footing in contaminated sand subgrades. Utilizing a Finite Element Model (FEM) in PLAXIS 3D, 74 cases were analyzed, focusing on OSC and ESC with diameters of 0.5m and 0.6m and a constant length of 12m. The contaminated sand content varied (2%, 5%, and 10%), and internal friction angles were 35°, 40°, and 45°. Results showed a significant increase in endurance for both OSC and ESC on untreated soil, with ESC demonstrating higher performance. For a 5% contaminated sand content, OSC's endurance increased by 100%-180% and ESC's by 275%-375%, depending on diameter and friction angle. The study aims to offer insights into OSC and ESC efficacy as geotechnical solutions for soil improvement in construction. This research provides valuable data for understanding and optimizing ground improvement techniques for weak soil conditions.

A series of three–dimensional finite – element models (PLAXIS 3D V20) were developed to investigate the non-linear behavior of XCC section piles under torsional load in clay soil with various soil cohesion states. Piles were assumed to behave in a linear elastic model, while the soil was modeled using the non-linear (HSM) hardening soil model. The influence of pile length to pile diameter ratio (Lp/Dp), 0pen arc spacing to pile diameter ratio (ap/Dp), and open arc degrees(θ˚) were explored. the numerical results showed that the torsional capacity of the pile increases with the increase of clay cohesion. At the ratio of pile length to pile diameter (Lp/Dp) = 15, and the ratio of the open arc spacing to pile diameter (ap/Dp) = 0.14, open arc degrees(θ˚) = 90 the efficiency of improvement in the torsional capacity reached to 3.96, 5.06, and 5.71 times of torsional capacity of conventional pile with the same cross-sectional area at clay cohesions of 70 KN/m², 40 KN/m², and 30 KN/m², respectively. furthermore, the torsional capacity of the XCC section pile increases with the increase in soil cohesion (Cu), pile diameter (Dp), pile length (Lp), and open arc spacing. but it decreases with the increase of open arc degrees(θ˚). The change of shape to XCC shape can significantly increase the earth pressure and skin friction around the pile by creating a passive zone, and increasing the perimeter.

Pile foundations may be exposed to torsional loads caused by horizontal eccentric loads brought on waves, wind and earthquakes, as well as axial load brought on by supporting superstructures. This paper highlights a recent strategy to modify piles known as the finned pile. A series of experimental tests were conducted to increase the torsional capacity of a single pile with/without fins in sand under the influence of vertical loads (V), torsional loads (T) and combined loads (T → V), these experiments involved altering fins' length, width, shape, and number and knowing the effect of these variables on the piles' maximum torsional capacity. The vertical load-displacement response and the torsion-rotation response have been observed. The results showed that fins improve piles' torsional capacity. It also showed that on piles' maximum vertical capacity for independent vertical or torsional loads is different from that of piles under combined loading. It was found that fins' optimum geometry is that their length equal to 0.6 of the embedded pile's length and their width equal to the pile's diameter, where piles' maximum torsional capacity was (4.12 and 7.36) N.m for regular and finned piles, respectively. Fins increased piles' maximum torsional capacity by about 79%. ARTICLE HISTORY

In varieties of coastal soil, deep foundations, particularly pile foundations, are used because the soil in these areas may be subjected to numerous factors that change the engineering properties of the soil, such as oil pollution. The pile foundations might be vulnerable to torsional stresses from eccentric, horizontal loads brought on by winds, earthquakes, shipwrecks, and waves, in addition to the loads carried by supported superstructures. In this laboratory investigation, tests have been carried out to investigate the behavior of piles under torsional load (T) and combined torsional-vertical load (T → V) in contaminated sandy soils. Additionally, investigations examined how the Lp/Dp ratio, relative density (Dr), and depth of the contaminated layer (Lc) affect their maximum torsional bearing capacity, which was discussed in detail. According to the findings, oil contamination significantly decreased pile response, and it also demonstrated that independent load differs significantly from combined load, in which the ultimate vertical bearing capacity of the piles in Dr = 30% installed in contaminated sand under pre-applied torque T → V loading at Lc/Lp = 1 decreases by 3.3, 3.9, and 5.1% for Lp/Dp 20, 16.67, and 13.3, respectively. These results show that the pile design must take into account the amalgamated loading of contaminated sand.