Applications of Geotextiles and Geomembranes - Ground Improvement - Lecture Notes, Study notes of Geology

Download Applications of Geotextiles and Geomembranes - Ground Improvement - Lecture Notes and more Study notes Geology in PDF only on Docsity! Objectives_template Module 7:Geotextiles and Geomembranes Lecture 20:GeneralApplications of Geotextiles and Geomembranes The Lecture Contains: Geotextile And Geomembrane file:///D|/Dr.patra/ground_improvement_techniques/lecture20/20_1.htm [10/12/2011 10:41:52 AM] Objectives_template Module7:Geotextiles and Geomembranes Lecture 20:GeneralApplications of Geotextiles and Geomembranes Geotextiles and Geomembranes Applications Major applications 1. Embankments over very soft soils 2. Unpaved road supports 3. Retaining walls 4. Slope stabilization 1. Embankments Embankment can fail in a multitude of ways involving excessive settlement and lateral spreading, with or without single or multiple failure surfaces and surface bulging becoming apparent. Geotextiles provides restraint against lateral deformation and assist in load distribution on the soft subsoil. Stability analysis of a reinforced embankment will have to take the following modes of failure (a) Block sliding on the geotextiles: A vertical crack or other type of failure through the embankment isolates a block of soil which slides outward on geotextiles . A simple analysis would assume horizontal active earth pressures pushing outward and soil fabric friction resisting the process. Figure 20.1 file:///D|/Dr.patra/ground_improvement_techniques/lecture20/20_2.htm (1 of 2) [10/12/2011 10:41:52 AM] Objectives_template Module 7:Geotextiles and Geomembranes Lecture 20:GeneralApplications of Geotextiles and Geomembranes Geotextile and Geomembrane (b)Failure along a slip surface: Figure 20.3 ● Slip surface is assumed to be circular either within the embankment or through the geotextile ● Fabric provides an additional stabilizing force T at the point of intersection with the failure surface. Stabilizing moment due to the fabric For circular failure surfaces (c) Overall bearing failure: (Terzaghi’s or Hansen’s Bearing capacity) ● The bearing capacity of an embankment foundation is unaffected by a geotextile contained within or just below the embankment ● Overall bearing capacity could be improved if a mattress like reinforced surface layer of larger extent is provided at the base of the embankment . (c) Excessive settlement : Due to consolidation of the sub soil the embankment undergoes large settlement and the presence of the fabric may reduce differential settlement. file:///D|/Dr.patra/ground_improvement_techniques/lecture20/20_4.htm (1 of 2) [10/12/2011 10:41:52 AM] Objectives_template Because of the drainage effect of nonwoven fabrics consolidation of the subsoil may be accelerated with a consequent gain in strength where deformation criteria require high strength, high –modulus woven fabrics the drainage function may be provided by the Geocomposits . Edge reinforcement also helps to reduce erosion and may assist in the establishment of vegetation. file:///D|/Dr.patra/ground_improvement_techniques/lecture20/20_4.htm (2 of 2) [10/12/2011 10:41:52 AM] Objectives_template Module 7:Geotextiles and Geomembranes Lecture 20:GeneralApplications of Geotextiles and Geomembranes Geotextiles and geomembrane Unpaved roads: ● Reinforcing action of geotextile can be used in unpaved roads for economic advantages. ● Geotextiles also fulfill additional basic functions such as separation, filtration and drainage. ● Nonwoven and woven fabrics are used in road construction. Unpaved roads without fabric Hammit (1970) proposed a formula for determining the thickness of aggregate required for unsurfaced roads and air fields so as to produce a rut depth less than 3 - in (75mm). The design thickness is a function of the number of coverage N of an equivalent single wheel load and the tire contact area . The unreinforced aggregate depth required for is Where Aggregate depth unreinforced,m Axle load, KN Undrained cohesion of the sub soil file:///D|/Dr.patra/ground_improvement_techniques/lecture20/20_5.htm [10/12/2011 10:41:53 AM]