Pathmanathan Rajeev

Monitoring of pressure transients in water supply networks

Ageing water infrastructure is one of the major problems faced by water utilities around the world at present, and urgent solutions are required in order to maintain the integrity of the water supply network. In order to use pipe failure prediction models, accurate information about loads acting on these pipes is important. Water pressure (steady-state and transient) is one of the key loads that needs to be estimated accurately in order to improve the predictability of pipe failures. This paper reports the results of a pressure monitoring program, which was conducted to measure pressure fluctuations during events of pressure transients in three selected network sections in Australia. Pressure measurements were conducted in network sections which were considered as susceptible to pressure transients. Potential sources of pressure transients were identified, and high speed data loggers were installed in selected locations of each network to measure and monitor pressure transients. Pressure transients that were generated during normal operation were measured for a period of one month in each selected section. Further, some of the pressure transients were manually made to simulate the different pressures due to pump start-ups within the network. Pressure fluctuations that could potentially lead to pipe failures were measured at many locations during the monitoring program (several selected failures were reported in this article). Therefore, the effect of pressure transients must not be ignored in pipe failure prediction.

Experimental Study on Contact Erosion Failure in Pavement Embankment with Dispersive Clay

AbstractSoft subgrades are not strong enough to provide the required degree of compaction for a pavement embankment’s foundation. Therefore, it is required to treat the subgrade soil or construct a working platform on top of the soft subgrade to ensure proper compaction of the subsequent layers. The constriction sizes of the granular materials used for a working platform are comparatively higher to restrict the erosion of overlying embankment materials. This condition would lead to severe material loss in the embankment layer in cases where the embankment is constructed with dispersive soil, which becomes structurally unstable in wet conditions and appears to disperse in water. This paper investigates the contact erosion failure at the foundation of a pavement embankment constructed with dispersive soil as a result of groundwater fluctuation. Experimental studies were conducted on a laboratory model test apparatus designed to simulate the conditions in the pavement embankment’s foundation. The experimenta...

Effects of vertical irregularities and construction quality in seismic fragilities for reinforced concrete buildings

Seismic fragility of buildings is often developed without consideration of irregularities and material qualities that can underestimate the prevalent vulnerability. This study demonstrates effect of vertical irregularities (VIs) and construction/design quality (CQ) on seismic fragility curves of reinforced concrete (RC) frames. A six-story three-bay RC moment resisting frame designed for seismicity of Vancouver, BC, Canada, according to the 2005 National Building Coded of Canada, is considered. Three sets of 15 ground motions, corresponding to the 2%, 5%, 10% probability of exceedence in 50 years hazard level, are matched to Vancouvers mean response spectrum at the natural period of the structure and used for nonlinear time history analyses. Sensitivity of seismic demand (i.e., interstory drift and story shear) on VI and CQ is studied. Finally, the interaction effects of VI and CQ in seismic demand of a structure is considered.

Contribution of Cement Mortar Lining to Structural Capacity of Cast Iron Water Mains

Cast iron water mains represent a significant component of the water pipe networks in many cities across Australia. Such pipes are usually furnished with an internal cement mortar lining, mainly to act as a physical barrier to flowing liquids to reduce internal corrosion and to reduce energy losses. Although the lining is not intended to resist internal and external loadings to the pipe, recent observations of corroded cast iron water mains showed that the cement lining can withstand some internal water pressure on its own. This reveals that the lining may contribute to the structural capacity of deteriorated pipes, although the level of this contribu- tion is unknown. This paper investigates the likely contribution of cement lining to the structural capacity of deteriorated pipes. This research is undertaken through numerical modeling of pipe-liner- soil interactions. The properties of cement linings were obtained by testing actual specimens obtained from field pipes and casting simulated lining specimens of cement-sand mixtures. The study revealed that, depending on the level of pipe corrosion, cement lining can reduce pipe stress by as much as 5 to 12% or 10 to 25% if the lining tensile strength is 1 or 4 MPa (145 or 580 psi), respectively.

The use of restrained ring test method for soil desiccation studies

Tensile failure in soils caused by desiccation cracking is of great importance in many geotechnical applications such as earth dam engineering, design of clay liners for waste contaminant systems, agricultural engineering, and environmental remediation. Currently, the majority of tests used for tensile strength measurement are based on external loading and few studies have measured soil tensile strength during the desiccation process. This study uses the restrained ring test as a method to determine the tensile strength in desiccating clay soils by isolating the initiation of a single crack. Four clay soils with varying shrink/swell potentials were tested and analyzed to predict their tensile strength during desiccation. Using image correlation or particle image velocimetry, information on shrinkage displacement and void ratio development were examined. An incremental non-linear elastic analytical model was used to explain the experimental behavior successfully.

Average Vertical Stresses in Underground Mine Stopes Filled with Granular Backfills

Marston’s theory and its modifications are being used to determine the average vertical stress variation with depth within a cavity with vertical wall, backfilled with granular material. In the past, this has been applied in trenches, mine stopes and silos of different cross sections. In all situations, at very large depths, the vertical stresses become asymptotic. The laboratory model tests clearly suggest that this is not the case and that the average vertical stresses continue to increase. In this paper, an attempt is made to improve Marston’s model, in the light of laboratory test data. It is shown that the problem with Marston’s equation is its inability to model the shear stress correctly, which leads to an asymptotic vertical stress after a certain depth. The proposed equation is of the same form as Marston’s equation, and has two coefficients α and β that have to be determined from a laboratory model test.

Modelling of Climate Induced Moisture Variations and Subsequent Ground Movements in Expansive Soils

Expansive behaviour of soil in response to moisture changes is a significant issue for lightly loaded structures. Recent reports have shown more than 4000 houses in Victoria, Australia have been damaged due to abnormal moisture changes beneath footings. For design purposes, the moisture change due to climate is crucial. This paper provides details of modelling of climate induced soil moisture changes and subsequent ground movements. The soil moisture variation due to climate was modelled using Vadose/w for two sites in Melbourne, Australia. The model was validated against the regular measurements from the field. The predicted soil moistures from the Vadose/w model were used to predict the possible ground movement using FLAC3D. The predicted ground movements were also validated using the field monitored ground movements at the sites. Further, the model was used to determine the possible ground movements due to long-term climate conditions. The model results demonstrate the reductions of soil moisture and shrinkage movements during the millennium drought. The model predictions also suggest that the soils have not been able to fully recover that moisture deficit through the drought breaking rains in 2010 and 2011. This model can be used to observe expectable ground movements due to climate changes and hence can greatly assess the footing performance for different climate scenarios.

Lateral Variation of the Vertical Stress in Underground Mine Stopes Filled with Granular Backfills

Abstract Marston’s theory and its modifications are widely used to predict the average vertical stress variation with depth within mine stopes. However, this does not model the lateral variation in vertical stress at a particular depth. In this study, a mathematical expression to simulate the vertical stress variation is developed using the experimental shear stress data of granular backfill. The developed model is validated against average vertical stress measured in the experiment. Therefore, the developed model has the advantage of determining both the average vertical stress and its distribution respectively, at a particular depth and a cross sectional area of the mine stope.

Estimating apparent thermal diffusivity of soil using field temperature time series

Reliable estimates of soil thermal properties such as heat capacity, thermal conductivity, and diffusivity are important in analysis of heat transmission through soils in applications such as shallow geothermal applications, buried electrical conduits, and in general heat/fluid flow analyses. A number of analytical, numerical and experimental methods are available to determine the soil thermal properties. In this paper, the analytical and numerical methods developed on the basis of one-dimensional heat conduction equation are used to estimate the apparent thermal diffusivity of soil. Three of the four analytical methods, Amplitude, Phase, and Arctangent provide explicit equations for the apparent thermal diffusivity. Two methods, Harmonic and Numerical, make use of large number of temperature measurements to implicitly solve for the apparent thermal diffusivity. The temperature time series data monitored at different depths in two field sites in Melbourne, Australia for more than 2 year period were used to estimate the apparent thermal diffusivity of soil down to 2 m depth. The apparent thermal diffusivity was calculated using all five methods and compared with laboratory experimental results. The effectiveness of each method in predicting the thermal diffusivity was compared and observed discrepancies were discussed. Finally, the observed soil temperature data for a 12 month period are used to model the temperature variation in the ground analytically using Harmonic method and the model prediction for the following 12 month was compared independently with the field measurements. The analytical model prediction is found to be in good agreement with the field monitored data.

A Modified Mohr-Coulomb Model to Simulate the Response of Buried Pipes Subjected to Large Ground Displacement

At the present time, it is very common practice (in industry as well as in research) to utilize Mohr-Coulomb to simulate the soil behaviour in the application of soil-structure interaction problems. The model is often chosen considering its simplicity, ease of use, reasonable computational time and the high level of understanding among the engineers. However, the linear elastic-perfectly plastic Mohr-Coulomb model is unable to predict the softening behaviour of material and hence unable to predict the pipe load accurately when subjected to large soil movements such as from landslides or earthquakes. A user defined modified Mohr-Coulomb model is developed to capture the strain softening behaviour of soil and to simulate the pipeline response subjected to large ground deformation. The softening behaviour of the model has been calibrated on the basis of direct shear test data, and triaxial test data have been used for calibrating the yielding and flow characteristics of the model. The calibrated model has been applied to simulate the response of HDPE pipeline undergoing different ground displacements. Finally, the model response was used to develop a strain demand model for buried pipelines facilitating the risk assessments.