L. K. Sharma

Stability investigation of hill cut soil slopes along National highway 222 at Malshej Ghat, Maharashtra

The section of about 12 km of National highway 222 passing through the Malshej Ghat experience frequent slope failure due to complex geological condition, heavy rainfall and slope geometry. The area is part of Western Ghat Deccan trap and slope masses are made of basalt and its weathered crust (debris/soil). The soil slope failure problem mainly occur in rainy seasons due to induced pore water pressure and reduced strength of the slope mass. The present study has been carried out to investigate the slope forming material and assess the stability of soil slopes by numerical approach. For the identification of the vulnerable zones, field study has been carried out and five vulnerable soil slopes identified namely MGS1, MGS2, MGS3, MGS4 and MGS5 on the basis of degree of weathering and slope geometry. The laboratory experiments were carried out to determine the strength properties of the geomaterials. All the input variables acquired from the field and laboratory experiments have been used for numerical simulation, which was performed with the help of limit equilibrium method (LEM) and finite element method (FEM). Numerical analysis provides understanding of the slope behaviour and illustrates that MGS1 and MGS3 are stable slopes, MGS2 and MGS4 are critically stable, whereas, slope MGS5 is unstable. This study recommend the protection of soil slopes and suggest that more detailed investigation is required for long term remedial measures to prevent risk of damage in Malshej Ghat.

Geotechnical Characterization of Road Cut Hill Slope Forming Unconsolidated Geo-materials: A Case Study

Geotechnical characterization of the unconsolidated geo-materials (which are mainly soils) is one of the major concerns for geotechnical engineers, administration and city planners. Recently, large scale highway projects in hilly regions leads to increase the road cut hill slope (RCHS) frequency. The slope failure along these RCHS is an uninterrupted source of suffering for human habitants and keeping human life in danger. The stability of these cut slopes mainly depends upon the geotechnical characterization of slope forming geo-materials. The present study was carried out to evaluate the geotechnical properties of unconsolidated geo-materials (i.e. basaltic soils) of Malshej Ghat, located in Maharashtra, India. Malshej Ghat is one of the most vulnerable hilly region, composed of basaltic rock and soils of Deccan plateau and suffers frequent RCHS failures, which block the National Highway-222 very frequently. A number of tests such as natural moisture content (NMC), specific gravity, grain size analysis, Atterberg limits, compaction, unconfined compressive strength and triaxial compression test were conducted to evaluate the geotechnical properties of unconsolidated geo-materials. The result of these tests indicates that the soils collected from five representative locations show high variability in geotechnical properties. Thus, the parameters from one location are not sufficient for the characterization and analyses of complete section of RCHS. For the quantification and numerical modeling of the RCHS, the geotechnical parameters of each location needs to be analyzed scientifically.

Regression-based models for the prediction of unconfined compressive strength of artificially structured soil

Unconfined compressive strength (UCS) of soil is a critical and important geotechnical property which is widely used as input parameters for the design and practice of various geoengineering projects. UCS controls the deformational behavior of soil by measuring its strength and load bearing capacity. The laboratory determination of UCS is tedious, expensive and being a time-consuming process. Therefore, the present study is aimed to establish empirical equations for UCS using simple and multiple linear regression methods. The accuracy of the developed equations are tested by employing coefficient of determination (R2), root mean square error (RMSE) and mean absolute percentage error (MAPE). It has been found that the developed equations are reliable and capable to predict UCS with acceptable degree of confidence. Among all the developed models, model-I consist of lime content, curing time, plastic limit, liquid limit, potential of hydrogen, primary ultrasonic wave velocity, optimum moisture content and maximum dry density as independent parameters shows highest prediction capacity with R2, RMSE and MAPE are 0.96, 25.89 and 16.59, respectively.

Soil slope instability along a strategic road corridor in Meghalaya, north-eastern India

The road widening carried out along National Highway-40, a strategic road corridor of north-eastern India, to ease the traffic snarls for geopolitical developments in the region. The newly exposed in situ soil slopes along National Highway-40 are on the verge of shear instability, and slope failures occur due to heavy earth cuttings. As a consequence, the road corridor witnesses several geotechnical failures during rainy seasons. The blasting activities initiated and propagated the soil creeps and falls resulting road blockades. Even a small rain shower is enough to undercut and uproot trees and transport boulders and surrounding earth materials up to the corridor. Besides, landslides are also prone to damage demographic areas and settling house units, thus invites for preventive measures towards hill slope management as these slopes make the highway corridor unsafe to the commuters. Therefore, the present study is aimed to investigate the stability of the hill cut soil slopes and to suggest possible stabilisation measures. The study also highlighted that steep soil slopes with high moisture content are prone to landslides mainly due to infiltration, and water flows on the slopes during high and prolonged rainfall. The highly plastic soils rich in silt and clay size particles with high moisture content cause soil/debris slide and flow. The numerical modelling of slopes using Fast Lagrangian Analysis of Continua (FLAC) codes (version 4.0) indicates failures in excavated high angle cut slopes. The re-excavation and benching of unstable slopes with geonets or bionets or jute matting to promote vegetation growth were suggested as stabilisation measures by field investigation, laboratory studies and numerical analysis of slopes.

Development of novel methods to predict the strength properties of thermally treated sandstone using statistical and soft-computing approach

The knowledge of thermally modified strength properties is crucial in processes such as underground coal gasification, disposal of radioactive wastes in deep geological reservoirs and restoration of fire-damaged structures. However, due to the unavailability of dedicated laboratory equipment, scientists and engineers need to go across various laboratory facilities for testing their desired sample. Further, it delays the process and increases the cost of the project. Since there is a lack of empirical equations that can provide the strength of a thermally modified rock from the strength at room temperature, new predictive models have been developed using multivariate regression analysis (MVRA), artificial neural network and adaptive neuro-fuzzy inference system (ANFIS), to predict the uniaxial compressive strength (UCS) and tensile strength (TS) of both uncooled (NC) and heat-treated (WC) samples of a fine-grained Indian sandstone that has been widely used as a major building material in most of the Indian monuments. The UCS and TS of NC and WC samples have been predicted from the physical properties, viz. temperature (T), density (D), porosity (P), thermal expansion coefficients (EL and EV) and ultrasonic wave velocities (VP and VS). The performance and prediction efficiency of the models have been compared on the basis of performance indices, namely the correlation coefficient (R2), the mean absolute percentage error, the root mean square error and the variance account for. Based on the comparative study, it was concluded that ANFIS provides a relatively closer estimation as compared to MVRA.

Assessment of Durability and Weathering State of Some Igneous and Metamorphic Rocks Using Micropetrographic Index and Rock Durability Indicators: A Case Study

Weathering and durability are the key factors of the rock in the suitability and usefulness of different construction materials, building materials and engineering structures. A single test never predicts the entire factor for suitability of rock stone and aggregate in different uses. Thus, variety of physical, mechanical and chemical tests and indices of rocks are widely used to estimate and evaluate the rocks for the suitability of the required purpose. In all the cases, knowledge of durability and weathering properties are the most important along with the strength of the rock. Micropetrographic index and rock durability indicators (dynamic and static) are the one of the best methods to evaluate the rock for weathering and durability. To estimate these indices, variety of tests are performed such as petrographic examination test, point load index, sulfate soundness test, water absorption test, modified aggregate impact value test and test for specific gravity. Slake durability index and impact strength index tests were also performed for correlation with static and dynamic rock durability indicators due to its application and usefulness in the durability and strength of the rock materials. Micropetrographic index was obtained by petrographic examination test and correlated with all the physical and mechanical properties used for find out the durability indicators. The present study is to express the usefulness of these three indices in the classification of weathering and durability classes and estimation of durability indices by slake durability index, impact strength index and micropetrographic index.

Parametric study of factors affecting fluid flow through a fracture

Understanding the flow behavior through fractures is critically important in a wide variety of applications. In many situations, the fluid flow can be highly irregular and non-linear in nature. Numerical simulation can be employed to simulate such conditions which are difficult to replicate in laboratory experiments. Therefore, a parametric study has been conducted on the fluid flow through micro-fracture over a large range of inlet pressure, fluid density, fluid viscosity, temperature, joint roughness coefficient (JRC), and fracture using finite element analysis. Irregular fracture profiles were created using Barton’s joint roughness coefficient. The Navier-Stokes (NS) equation was used to simulate the flow of water in those micro-fractures. The result showed that the fracture, fluid, and ambient conditions have a wide and varied effect on the fluid flow behavior. The interrelationship between these parameters was also studied. The model simulation provided result in the form of velocity and pressure drop profile, which can be used to determine the behavior of flow under different condition. The volumetric flow was calculated for each condition and has been plotted against the corresponding parameter to study the interrelationship.

Assessment of Potential Alkali Aggregate Reactivity for Siliceous and Carbonate Aggregates: A Case Study

Alkali-aggregate reactivity (AAR) involves a reaction between the pore solution of concrete and certain minerals found in some aggregates. To assess the potential AAR various physical and chemical tests are available and extensively used. The petrographic examination is the initial assessment that decides the further investigation for potential reactivity of an aggregate. A chemical approach is another option to assess the aggregate for potential AAR. The accelerated mortar bar method and concrete prism tests are other very important tests for determination of potential AAR of aggregates samples. However, a combination of the results of all the techniques provides most reliable results for potential AAR in aggregates. Moreover, each test represents the stepwise investigation and provides the decision for the test of next approach. Petrographic examination and chemical test methods are the quick decision-making methods for the estimation of potential AAR. In some cases, by these two methods, the aggregate can be selected and rejected confidently. However, for critical values or doubtful aggregates, further tests are necessary to develop a higher confidence level of the results. The present study comprises of the assessment of the alkali-reactivity of siliceous and carbonate aggregates using petrographic and chemical approaches. X-ray diffraction analysis was used as a complementary method to the petrographic evaluation. Moreover, under chemical approach, two separate test methods were used for siliceous and carbonate aggregates. The study also included a comparison between the petrographic examination and chemical analysis for the same aggregate samples and found significant results.