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Article
Experimental Study on Compressibility, Volume Changes, Strength and Permeability Characteristics of Unsaturated Bentonite-Sand Mixtures

Authors: Mohammed Y. Fattah --- Nahla M. Salim --- Entesar J. Irshayyid
Journal: Engineering and Technology Journal مجلة الهندسة والتكنولوجيا ISSN: 16816900 24120758 Year: 2016 Volume: 34 Issue: 7 Part (A) Engineering Pages: 1308-1323
Publisher: University of Technology الجامعة التكنولوجية

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Abstract

Expansive soils are generally found in arid and semiarid regions. These soils undergo volumetric changes upon wetting and drying, thereby causing ground heave and settlement problems. This characteristic causes considerable construction defects if not adequately taken care of. Solving the unsaturated soil problems needs the assessment of suction variation in time and space as a response to the variation of environmental factors such as rainfall and evaporation.To investigate the effect of the changes of the soil suction on the volume changes, expansion index, swelling pressure, shear strength and the coefficient of permeability, small scale experiments were conducted using pure bentonite and the bentonite mixed with sand in proportion of: 30%, 40% and 50% at different initial water contents and dry unit weights was chosen from the compaction curves. The study shows that the swelling-potential, swelling-pressure, the soil-suction, the soil-strength and the coefficient of permeability are affected by the initial-conditions (water-content and dry-unit weight), where all these parameters except the permeability-coefficient marginally decrease with the increase in soil-water content, while the coefficient-of permeability increases with increasing the water-content.


Article
Influence of Geogrid Reinforced Loose Sand In Transfer of Dynamic Loading To Underground Structure

Authors: Mohammed Y. Fattah --- Nahla M. Salim --- Mohammad S. Ismaiel
Journal: Engineering and Technology Journal مجلة الهندسة والتكنولوجيا ISSN: 16816900 24120758 Year: 2016 Volume: 34 Issue: 11 Part (A) Engineering Pages: 1915-1927
Publisher: University of Technology الجامعة التكنولوجية

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Abstract

Underground facilities are an integral part of the infrastructure of modern society and are used for a wide range of applications, including subways and railways, highways, material storage, and sewage and water transport. Underground facilities built in areas subject to dynamic activity must withstand both dynamic and static loading. This study focuses on the effect of the geogrid reinforcement in transfer of the dynamic load to the underground structure. The underground structure was simulated as a PVC pipe 110 mm in diameter inside the sandy soil. In order to investigate the response of soil, footing and underground tunnel to dynamic loading, a physical model was manufactured. The manufactured physical model could be used to simulate the application of dynamic loading. The total number of the tests carried out is 4 models. All the 4 model tests with relative density equal to 40% corresponding to loose sand. The applied harmonic load has an amplitude of 0.5 ton and a frequency of 2 Hz. For each amplitude and frequency of the load, the sand models were tested without geogrid and with geogrid of three series of geogrid depths from the model surface (0.5B, 1B and 1.5B) and width equal to (1B), where B is the strip footing width. The dynamic load was applied in the tests by a hydraulic jack system. The response of the tunnel to dynamic loading includes measuring the pressure above the crown of the tunnel by using a pressure cell (manufactured by Geokon company) as well as measuring the amplitude of displacement by using a vibration meter. The response of footing was elaborated by measuring the total settlement using sensors in the dynamic load apparatus. It was found the pressure above the crown of the tunnel decreased by about (14-33) % when using geogrid reinforcement. Also, it was found the settlement decreased by about (13-20) % when using geogrid reinforcement.

Keywords

Tunnel --- dynamic load --- geogrid --- load transfer

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