Role of Case Histories on Geotechnical Engineering Teaching and Practice

Geotechnical engineering teaching can be made more interesting with the use of modern methods of teaching and learning aids, visits to construction projects, case studies etc. A faculty at an university/technical institute, who is actively involved in geotechnical designs and consultancy works, will have enough case studies, with the examples of which he, will be able to deliver his lectures more effectively and make a good impression upon the students. The universal mantra nowadays is ‘learning should be made more student centric’. At the author\u27s institute, where a post-graduate and doctoral programme in geotechnical engineering are being successfully run for the past two decades, some of his experiences in effectively teaching geotechnical engineering subjects are being explained in the following paragraphs, with the help of a number of case histories on geopractices

Bearing Capacity of Interfered Adjacent Strip Footings on Granular Bed Overlying Soft Clay: An Analytical Approach

In the present paper, the interference effects on bearing capacity of two and three closely spaced strip footings resting on granular bed overlying clay are being studied. A simple analytical model is proposed to predict the load-carrying capacity and the interference factor of an interfered footing, when adjacent strip footings are optimally placed on the surface of a Granular Bed (GB) overlying clay and both the footings are simultaneously loaded. A punching shear failure mechanism is envisaged in the analytical model. The load-carrying capacity of the footing is taken as the sum of total shearing resistances along the two vertical planes through the edges of the strip footing in the upper granular layer and the load-carrying capacity of the soft clay beneath the GB. Insights gained from finite element simulations are used to develop the new modified punching shear model for interfering footing. Bearing capacity can be easily calculated by using the proposed punching shear model for interfering footing. The analytical model is validated with numerical analyses and previous experimental results and found to be in reasonably good agreement. The influence of different parameters such as granular bed thickness, width of footing, number of footings are carried out in this study. Doi: 10.28991/cej-2021-03091723 Full Text: PD

Numerical Modelling Study of Behaviour of Consolidated Strata Around Tunnel

Tunnelling in densely populated areas and under existing buildings is common in most of the cities around the world. Upon excavation there are changes that take place in the soil /rock mass and these changes can have an impact on the surface structures. In this paper an attempt is made to assess the behavior of the tunnel in given environment and the associated displacements due to tunneling in a highly consolidated soil/rock mass with two different conditions of earth pressure coefficient. A case study of a tunnel in South India was taken up for studies. 3-dimensional Distinct Element Modelling code was used for the analysis. In the first stage, earth pressure coefficient Ko of 2.2 was taken for the top layers and 1.8 for bottom layers. In the second stage, a value of 2.2 was considered throughout the model. In the third stage displacement generated in the transverse direction, in the presence and absence of the building load was taken into consideration and analysed. Vertical displacements were found to be of considerable magnitude at the crown, showing a decreasing trend towards the surface. Horizontal displacements were of negligible magnitude along the depth. However, maximum displacement was noted at the springing level of the tunnel. Models incorporating weight of buildings showed no noticeable increase in the settlements, as the soil/rock mass is already consolidated.Keywords: Numerical modeling; 3 Dimensional; Distinct Element code; Earth pressure coefficient

Case Study of Landslide in NH –13 at Kethikal Near Mangalore – India

The disastrous slope failure occurred at the Kethikal hill, in the outskirts of Mangalore city in NH 13, India, during the month of June 1998 soon after the heavy and continuous monsoon rains. Many closely built dwelling houses at the top of hill are damaged and the traffic along the road is also diverted for some duration. Typical stratified slope with three layers is considered for the stability analysis and the general computer program is developed in C language for optimization of factor of safety. The factor of safety is calculated using Janbu’s generalized procedure of slices and Davidon-Fletcher-Powel (DFP) technique for optimization. The road is acting as a berm in Kethikal slope. The program gives factor of safety and the co ordinates of critical slip surface. The program is modified to take the effect of tension crack and the effect of berm. The automated stability analysis program gave least value of factor of safety in base failure with tension crack and a berm. The obtained result matches with the field observation. Kethikal landslide is due to the development of high pore pressure in soil

Composition and Properties of Fibre Extracted from Pseudostem of Banana (Musa Sp.)

Pseudostem waste from five commercial cultivars of banana was used to extract fibre in order to study its properties. Fibre was extracted by decortification of sheath either manually or using Raspador machine. Yield of fibre in cultivars varied from 0.548% to 0.891%. There was no significant difference in the yield of fibre from different layers of sheath although differences among cultivars were significant. Cellulose was the major component of the fibre at about 60% while lignin levels were nearly 20%. The strength characteristics of Nendran fibre like, mean breaking load, mean breaking extension and tenacity were comparable to those reported for other naturally occurring plant fibres such as pineapple, jute and sisal. The study highlighted the importance of exploiting banana pseudostem after harvest of banana bunch for fibre production on a commercial scale

Assembly of sol-gel-grown Li<SUB>x</SUB>CoO<SUB>2</SUB> nanocrystals through electromagnetic irradiation

We report the fabrication of assembled nanostructures from the pre-synthesized nanocrystals building blocks through optical means of exciton formation and dissociation. We demonstrate that Lix CoO2 nanocrystals assemble to an acicular architecture, upon prolonged exposure to ultraviolet-visible radiation emitted from a 125 W mercury vapor lamp, through intermediate excitation of excitons. The results obtained in the present study clearly show how nanocrystals of various materials with band gaps appropriate for excitations of excitons at given optical wavelengths can be assembled to unusual nanoarchitectures through illumination with incoherent light sources. The disappearance of exciton bands due to Li xCoO2 phase in the optical spectrum of the irradiated film comprising acicular structure is consistent with the proposed mechanism of exciton dissociation in the observed light-induced assembly process. The assembly process occurs through attractive Coulomb interactions between charged dots created upon exciton dissociation. Our work presents a new type of nanocrystal assembly process that is driven by light and exciton directed

Investigation of Plasmon Resonance Tunneling through Subwavelength Hole Arrays in Highly Doped Conductive ZnO Films

Experimental results pertaining to plasmon resonance tunneling through a highly conductive zinc oxide (ZnO) layer with subwavelength hole-arrays is investigated in the mid-infrared regime. Gallium-doped ZnO layers are pulsed-laser deposited on a silicon wafer. The ZnO has metallic optical properties with a bulk plasma frequency of 214 THz, which is equivalent to a free space wavelength of 1.4 μm. Hole arrays with different periods and hole shapes are fabricated via a standard photolithography process. Resonant mode tunneling characteristics are experimentally studied for different incident angles and compared with surface plasmontheoretical calculations and finite-difference time-domain simulations. Transmission peaks, higher than the baseline predicted by diffraction theory, are observed in each of the samples at wavelengths that correspond to the excitation of surface plasmon modes