M. Ahmad

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.

Instability investigations of basaltic soil slopes along SH-72, Maharashtra, India

Mahabaleshwar is one of the most attractive and important destinations for tourists in Maharashtra, India, which experiences frequent slope failure due to high-intensity rain and complex geological conditions. The litho unit of the area is the Deccan Trap Basalt, the most famous consecutive basaltic flows during the late Cretaceous to Tertiary periods. The area is very susceptible to weathering, different degrees of alteration, formation of soils and occurrences of bole beds in between two consecutive basaltic flows. Soil formation process in this area is one of the most influencing factors for slope failure; in addition to this, joints, sub-vertical-to-vertical slopes, heavy rainfalls, etc. also play a pivotal role in instability. These transformed soils create instability on the slopes and ultimately converge to slope failures. Five types of soils have been identified during field investigations, petrographic study and X-ray diffraction that indicate change in composition and colour variations. Geomechanical properties viz. bulk density, grain size analysis, Atterberg limit, uniaxial compressive strength, cohesion and angle of internal friction were calculated for five types of soil samples. Effects of these soils on slope stability have been depicted with the help of numerical program Slide 6.0 based on limit equilibrium method.

Rockfall risk assessment for pilgrims along the circumambulatory pathway, Saptashrungi Gad Temple, Vani, Nashik Maharashtra, India

This paper mainly describes the assessment of rockfall risk for the large number of pilgrims along the parikrama path (circumbultory or pathway around the shrine) at the Saptashrungi Gad Temple, Vani, Nashik, Maharashtra, India. The temple is constructed on moderately weathered and fractured basaltic terrain along the steep high hill slope. The loose rockmass from the top of the hill occasionally fall, bounce, roll and slide down along the slope of the temple with some rockmass blocks landing on or passing the parikrama path. This leads to risk while taking parikrama along the hill. A quantitative risk assessment (QRA) was undertaken to determine the risk for the pilgrims performing parikrama along the parikrama paths struck by rockfalls and the risk reduction capabilities of various remedial work. The obtained QRA results indicate that, the societal risk cannot be acceptable.

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.

Rockfall Hazard Rating System along SH-72: a case study of Poladpur–Mahabaleshwar road (Western India), Maharashtra, India

Construction of railways, highways and roads around steep slopes is a challenging assignment and require special investigations by geologists and geotechnical engineers that help to identify critical slopes. Rockfall Hazard Rating System for India (RHRSI) is a modified scheme for Indian subcontinent and used to define overall stability of slopes in mountainous region or rock cut slopes. Once this rating system identifies critical zones, proper protection measures can be applied to prevent rockfalls. In this article, RHRSI is adopted to identify slopes, prone to rockfalls so that proper preventive measure can be proposed to mitigate loss. State Highway-72 (SH-72) connecting Poladpur to Mahabaleshwar, is an important transportation corridor supporting high vehicle traffic within the well-known tourist area is chosen for rockfall hazard rating. Field observations show that up to 15 km corridor from Mahabaleshwar town has frequent rockfall problems with two most rockfall locations situated at about 12 and 6 km from Mahabaleshwar town. Also, an attempt has been made to focus on risk-consequence analysis for rockfall locations. To this aim, the RHRSI is applied to SH-72 corridor on two locations which are identified as very prone to rockfall hazard.

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.