G. V. Ramana

Stability Enhancement of Landfills on Sloping Ground Using Earthen Berms at the Toe

This paper presents the results of a study undertaken to enhance the stability of a landfill on sloping ground of a hilly region. The base of the landfill has a significant elevation difference from one end to the other causing an overall inclination of the base with the horizontal. The study highlights the influence of the following factors on the base sliding stability along the geomembrane interface as: (a) leachate head; (b) pore water pressures in wet waste; (c) seismic forces and (d) smooth versus textured geomembrane (GM). Limit equilibrium methodology is adopted for analyses and three types of failure surfaces are analysed – circular, planar (single straight line) and planar (two straight lines). The study reveals that stability against sliding along liner is low, whenever (a) pore pressures/leachate head are high; (b) earthquake forces are large and (c) smooth GM are used. Usually planar failure surface (two straight lines) is observed as the critical surface.

Effect of Embedment on Dynamic Response of Block Foundation Under Coupled Vibration

The dynamic response of a block foundation under machine-induced vibration depends on several parameters such as the shape and size of the foundation, depth of embedment, static load, dynamic excitation frequency and other geological parameters. In this present study, the dynamic response of embedded block foundation of aspect ratio L/B = 1.5 under coupled mode of vibration for different depth of embedment (D = 0, 0.25 and 0.5 m) has been studied. A number of block vibration tests are carried out using a Lazan-type mechanical oscillator under four different eccentric moments (We = 0.2, 0.8, 1.4 and 2.0 Nm) for a static load of 6.6 kN. The frequency amplitude responses of the block foundation for both translational and rotational motion for different embedded condition are also obtained using the half-space theory. The theoretical results are compared with the response obtained from the experimental investigations. The comparison showed encouraging agreement between the experimental test results and that obtained from the analysis. The frequency amplitude response of embedded block foundation indicates that as the embedment depth increases, the resonant amplitude decreases and resonant frequency increases.

Feasibility of Reuse of Bottom Ash from MSW Waste-to-Energy Plants in India

Incineration of municipal solid waste (MSW) is relatively new in India. The process results in generation of residues, bottom ash (BA) and fly ash which are presently dumped back in landfills. The study investigated the properties of MSW incineration (MSWI) BA from two MSW waste-to-energy (WtE) plants in Delhi and the results have been compared with coal bottom ash (CBA) from a local thermal power plant and two local soils, namely: Delhi silt and Yamuna sand. MSWI BA with particle size predominantly in the sand size range was found to be coarser to CBA and local soils making it suitable for earthworks. The chemical composition revealed that SiO2 in the form of quartz is the major constituent of MSWI BA. The organic content was more than regulatory levels for earthworks. Dissolved solids, chlorides and sulfates were very high in comparison to CBA and local soils. The above findings indicate that MSWI BA can possibly be reused in embankments or filling of low-lying areas, provided some environmental control measures are adopted at site or pre-treatment is undertaken to attenuate the leaching of salts and reduce organic content.

Investigations on fine fraction of aged municipal solid waste recovered through landfill mining: Case study of three dumpsites from India:

Reclamation of the dumps/landfills having huge quantities of decades-old garbage (aged waste or legacy waste) in an environmentally sound manner is one of the major challenges faced by the developing nations in general and in particular by urban local bodies in India. The article presents the feasibility of landfill mining operation specifically to recover soil-like material at old dumpsites of India for re-use in geotechnical applications. Aged municipal solid waste was collected from three dumpsites of India and initial tests were conducted on the soil-like material of the municipal solid waste. Initial tests results of grain size distribution, compositional analysis, organic content, total dissolved solids, elemental analysis, heavy metal analysis and colour of the leached water from finer fraction of aged municipal solid waste are presented. From the preliminary investigation, it was found that organic content in 15–20-year-old dumpsites varies between 5%–12%. The total dissolved solids ranges between 1.2%–1.5%. The dark coloured water leaching out from aged waste, with reference to local soil, is one of the objectionable parameters and depends on the organic content. The concentration of heavy metals of the finer fraction were compared with the standards. It was found that copper, chromium and cadmium are present at elevated levels in all the three dumpsites. The study concluded that the bulk of the soil-like material from aged municipal solid waste landfills can be used as cover material for landfills at the same site. However, some treatment in terms of washing, thermal treatment, blending with local soil, biological treatment, etc., is required before it can be re-used in other geotechnical applications.

Capacity Enhancement of Landfills on Sloping Ground Using Engineered Berms at the Toe

In the present study, a hazardous waste (HW) landfill on a sloping ground is considered. The base profile of the landfill exhibited significant elevation difference from one end to the other. Due to the inclined base and fixed waste footprint area, the waste retaining capacity of the landfill decreases significantly in comparison to a same plain base area. As a consequence, an engineered berm is provided at the lower end to act as a stabilizing berm and also to increase the waste filling space.

A Stress-Strain Model for Geomaterials Subjected to Air-Blast

The engineering design of underground protective structures subjected to blast loading requires an appropriate stress-strain relationship for surrounding geomaterials. The behaviour of geomaterials under blast loading depends upon strain rate, stress level and interaction among the three phases. A few advanced constitutive models are proposed in the literature to model stress-strain behavior. However, a less accurate but simple alternative is to use functional forms for capturing the experimental stress-strain curves. In this paper, the functional form of stress-strain curve of geomaterials subjected to air-blast (uniaxial high strain-rate loading) is proposed based on the deformation mechanism of geomaterials. The proposed model consists of two different expressions for loading and unloading and requires only three parameters. The physical meaning of the three model parameters is discussed and the procedure for their evaluation is outlined. It is found that the proposed functional form captures the experimental stress-strain curves very well.

Uncertainties of a Nuclear-Air-Blast Induced Ground Displacement Model

Scenario based design of strategic underground structures is increasingly becoming important with increasing capacities of nuclear warheads. The ground displacement caused by nuclear-air-blast is an important design parameter for such structures. A simplified model to compute ground displacement, proposed earlier by authors, is recommended for preliminary designs in professional practice. This paper quantifies the uncertainties associated with this simplified model as well as its input parameters namely P-wave velocity, strain recovery ratio, velocity ratio, and constrained modulus, while estimating the nuclear blast induced ground displacement. The model uncertainty quantification is generally accomplished using sampling based Bayesian updating techniques. However, this is a computationally time-consuming process and not suitable with increasing number of model parameters. To circumvent this, an alternate simplified model uncertainty characterization approach is developed based on Taylor’s series approximation. The validity of the proposed approach is established by comparing the results for a simple case of an earth pressure problem, routinely encountered in geotechnical engineering, against Bayesian approach. Subsequently, this simplified approach has been used to quantify the model uncertainties of air-blast induced ground displacement model and it is observed that this model is biased towards conservative side.

Influence of Unit Weight of Slurry-Deposited Coal Ash on Stability of Ash Dykes Raised by Upstream Method

In this paper efforts have been made to understand the influence of unit weight of slurry-deposited coal ash on the slope stability of ash dykes raised by upstream method. Using the geotechnical properties of compacted ash as well as slurry-deposited ash, a series of stability analysis have been carried out to identify the critical factor of safety for incrementally raised ash dykes. A 19 m high ash pond in Eastern India had been incrementally raised to its current elevation, by upstream method in four raisings. The ash pond was to be further raised by providing two raisings (5th and 6th) of 3 m each making the ash pond 25 m high.

A Designer’s Approach for Estimation of Nuclear-Air-Blast-Induced Ground Motion

A reliable estimate of free-field ground displacement induced by nuclear-air-blast is required for design of underground strategic structures. A generalized pseudostatic formulation is proposed to estimate nuclear-air-blast-induced ground displacement that takes into account nonlinear stress-strain behaviour of geomaterials, stress-dependent wave propagation velocity, and stress wave attenuation. This proposed formulation is utilized to develop a closed-form solution for linearly decaying blast load applied on a layered ground medium with bilinear hysteretic behaviour. Parametric studies of closed-form solution indicated that selection of appropriate constrained modulus consistent with the overpressure is necessary for an accurate estimation of peak ground displacement. Stress wave attenuation affects the computed displacement under low overpressure, and stress-dependent wave velocity affects mainly the occurrence time of peak displacement and not its magnitude. Further, peak displacements are estimated using the proposed model as well as the UFC manual and compared against the field data of atmospheric nuclear test carried out at Nevada test site. It is found that the proposed model is in good agreement with field data, whereas the UFC manual significantly underestimates the peak ground displacements under higher overpressures.