Ashutosh Kainthola

Estimation of elastic constant of rocks using an ANFIS approach

The engineering properties of the rocks have the most vital role in planning of rock excavation and construction for optimum utilization of earth resources with greater safety and least damage to surroundings. The design and construction of structure is influenced by physico-mechanical properties of rock mass. Youngs modulus provides insight about the magnitude and characteristic of the rock mass deformation due to change in stress field. The determination of the Youngs modulus in laboratory is very time consuming and costly. Therefore, basic rock properties like point load, density and water absorption have been used to predict the Youngs modulus. Point load, density and water absorption can be easily determined in field as well as laboratory and are pertinent properties to characterize a rock mass. The artificial neural network (ANN), fuzzy inference system (FIS) and neuro fuzzy are promising techniques which have proven to be very reliable in recent years. In, present study, neuro fuzzy system is applied to predict the rock Youngs modulus to overcome the limitation of ANN and fuzzy logic. Total 85 dataset were used for training the network and 10 dataset for testing and validation of network rules. The network performance indices correlation coefficient, mean absolute percentage error (MAPE), root mean square error (RMSE), and variance account for (VAF) are found to be 0.6643, 7.583, 6.799, and 91.95 respectively, which endow with high performance of predictive neuro-fuzzy system to make use for prediction of complex rock parameter.

Correlation Between Point Load Index and Uniaxial Compressive Strength for Different Rock Types

Uniaxial compressive strength (UCS) is one of the most significant geomechanical properties of rock, being of importance in civil engineering, mining, geotechnical, and infrastructure projects, etc. The UCS is a useful approximate parameter when considering a variety of issues encountered during blasting, excavation, and supporting in engineering works (Hoek 1977). UCS values are also employed in geomechanical classification of rock mass, viz. the rock mass rating (RMR) and Q system, which are used in designing and planning of underground works (Bieniawski 1976; Barton et al. 1974). There are standard methods for determination of UCS, proposed by various scientific agencies (ASTM 1984; ISRM 1979 1985), but all of them are tedious, time consuming, and expensive. Moreover, obtaining core samples of the desired geometry is often not possible, particularly in soft or highly jointed rock masses. Therefore, indirect tests such as the determination of the point load strength index (PLI) are widely used and accepted for estimation of the UCS value. Point load tests are preferred, as the test is quite flexible in terms of the sample to be used, ease of testing, and applicability in the laboratory as well as in the field. A number of researchers have attempted to provide empirical relations between UCS and PLI (D’Andrea et al. 1964; Broch and Franklin 1972; Bieniawski 1975; Hassani et al. 1980; Gunsallus and Kulhawy 1984; Panek and Fannon 1992; Singh and Singh 1993 and Kahraman 2001). These equations give quite similar results, although a few of them show wide variation. However, there is a need for more experimental work for better correlation, particularly for Indian rocks. The main objective of this study is to test and verify the empirical relation between PLI and UCS for some Indian rocks. All tests were performed on NX-size core samples of ten different rock types of igneous, sedimentary, and metamorphic origin from seven different lithostratigraphic units. A total number of 318 core samples were tested, and the average of three test results for each rock was used for analysis to reduce variation in the dataset.

The stability of road cut cliff face along SH-121: a case study

Rockfall is one of the major concerns along highways, settlements and forests around the globe. Amboli road cut hill is one such region which is highly vulnerable and suffers from recurrent rockfall mostly in the rainy season, which blocks the State Highway 121 for considerable period of time. The steep and highly jointed slope along the road makes the zone prone to failure due to rainwater action. This road experiences heavy traffic throughout the year as it is the only road connecting Goa to Satara and Kolhapur via Sawantwadi in Maharashtra State, India. Therefore, an attempt has been made in this study to understand the stability of the cliff face. A combination of field study and 2D computer simulation was performed to assess surface characteristics of the cliff face. Bounce height, translational kinetic energy, translational velocity and factor of safety for saturated condition have been estimated. The result of this study shows that the rock face is highly unstable taking into consideration the environmental condition and daily traffic. Proper preventive measures have also been suggested to arrest the movement of falling rocks before reaching the roads or valleys. It is a belief that if proper care is taken, then further uncertain rockfall hazards can be prevented.

Rock mass assessment along the right bank of river Sutlej, Luhri, Himachal Pradesh, India

The study involves the characterization of rock mass along the right bank of river Sutlej, Luhri, Himachal Pradesh. This road connects to several important locations and therefore blockage due to slope failure may cause several problems. Lack of proper geotechnical/geological investigations has led to cutting of the natural hill slopes with improper design. The subsequent road cut slope has made this zone highly vulnerable and a threat to local commuters. The concerned area has varying lithology which are highly jointed and exposed all along the road cuts. The unrestrained slope in this zone is prone to recurrent failures due to high precipitation and seismicity, eventually causing loss of life and property. Therefore, the study helps in understanding the behaviour and mode of failure of the cut slope through geometrical relationship between structural discontinuities and surface topography. Several important parameters were determined to quantify the region based on available and widely used rockmass characterization techniques to develop a proper understanding. This will ultimately help in designing appropriate remedial measures to such vulnerable zones that will prevent further slope failure and resulting damage.

Stability analysis of potential failure zones along NH-305, India

The national highway (NH-305) is crucial since it is used as the only alternative connectivity for transportation of goods and other materials for military purpose during the closure of other highway. A number of slope failures were reported in the past therefore hazard zonation map is prepared using five commonly used parameters to identify the potential susceptible areas of failure. This was followed by detailed field investigations for collection of rock engineering parameters and geomechanics classification. Several locations were identified from hazard zonation map and subsequent field investigations for stability analysis. Hazard zonation clearly demarcates the steep cut slopes along the right bank of river Sutlej as potential failure zones, which is also confirmed by low values of slope mass rating. Finite element method was later used to investigate the deformation mechanism associated with such slope failures. The safety factor value is on a higher side indicating the slopes to be stable but the displacement contours and shear strain concentration near the toe of the slope suggests otherwise.

Indirect estimation of compressive and shear strength from simple index tests

Uniaxial compressive and shear strength are two of the very important parameters, commonly required in the initial stages of planning and design of rock engineering projects. So, an attempt has been made in this study to predict compressive and shear strength (output) of rocks from some simple and easily determinable parameters in laboratory viz., point load index, tensile strength, unit weight and ultrasonic velocity (input). Failure modes have also been studied and correlated with their ultrasonic velocity. The study uses two of the most commonly used predictive mathematical techniques: statistical analysis and neural networks to predict the strength parameters. The regression analysis shows that the rock quality parameters are very well correlated with the ultrasonic velocity except for the unit weight. Unlike few researchers in the past, a linear correlation was best suited for the rock quality parameters in this study. On the other hand, Artificial Neural Network (ANN) was able to predict the same strength parameters with a better reliability than regression analysis. The study shows that the proposed method for the prediction of UCS and shear strength is acceptable and can be reliably applied in various rock engineering problems.

Comparative study of the deformation modulus of rock mass

The deformation modulus of a rock mass (Em) is an important parameter in rock mechanics and engineering and its determination is a difficult task. Therefore, several equations were proposed using regression analysis of Em and rock mass class. Among them, widely used equations based on Q and RMR were selected for the calculation of Em values for different rock types which are encountered along the tunnel alignment of the Kulekhani III Hydroelectric Project, Nepal. From the results, it is found that some of the equations show Em value to be highly sensitive to the rock mass class while others show less sensitivity. Different values of Em were obtained from different equations for the same class and eight different rock types. Even a small change in RMR causes large variation in Em value. Maximum differences in obtained values are about 5–30 GPa for same rock class. In such condition, it becomes very difficult to choose deformability value to design engineering projects in rock mass. The graphs obtained from different equations show linear to fluctuating pattern depending upon the sensitivity of equation towards rock class.

Protection measures on the failed cut-slope along the free expressway, Chembur, Mumbai, India

The present work summarizes the investigations made during the stability analysis of a cut slope across the basaltic rock mass of the Deccan traps. Kinematic analysis was done to understand the relation between the structural discontinuities and surface topography and to determine the probable modes of failure. The concerned slope was in very poor condition because of the discontinuity ornamentation and other construction activities in the vicinity. Due to steep cut slope and blocky nature of rock mass, rockfall investigation was done to identify the rockfall trajectory, bounce height and kinetic energy in order to design proper support systems against falling mass. Material model was later simulated using the Hoek and Brown parameters in a finite element method considering different structural discontinuities. The safety factor at this state was less than one, the result of which was the recurrent slope failure and hassled traffic movement along the expressway. Finally, with the help of field observations, investigations from rockfall analysis and numerical simulation, necessary remedial measures were suggested and implemented that showed tremendous results in terms of safety and stability.

Rockfall analysis along transportation corridors in high hill slopes

The paper discusses the problems pertinent to rockfall activities in highly jointed rock cut slopes, excavated without detailed geotechnical and geological investigations along the right bank of river Sutlej, Luhri, Himachal Pradesh, India. The cut slopes are near vertical to sub-vertical and overhangs are ubiquitous at several locations. Initially, probable zones of slope failure were identified from field inspection and kinematic analysis. The study then uses 2D rockfall analysis for estimating loss of energy due to the impact of falling blocks on the slope face and subsequently on the road. Several parameters were also assessed from the study viz. bounce height, travel distance, kinetic energy and translational velocity. The result from rockfall analysis shows that the energy and velocity achieved by the falling blocks are considerably high, capable enough to cause severe damage. In relation to energy and velocity, bounce height achieved is not very large. Because of removal of trees from the slopes face and no measures to capture falling blocks, the problems have been aggravated and therefore, most of the rock covers very large distance to reach up to the valley crossing the roadways endangering travelers and infrastructures. Based on the results, preventive measures have been suggested to prevent future rockfall hazards.

Stability Analysis of an Open Cut Slope in Wardha Valley Coal Field

Open cast mines are the prime source of coal production in India. Due to an increase in coal demand, deeper surface mines are being planned to ensure better productivity with enhanced safety of these mines. The safe working environment and continuous production of the coal calls for the safe and stable design of cut slopes. The stability analysis of this slope requires in depth geotechnical investigation which are aided by result orientated stability assessment using empirical methods and numerical simulation. In the present study, a slope was examined to understand the mechanism and comparisons were made with field observations. The investigation has involved a 32m high cut slope from an open cast mine in Wardha valley coal field which has been analyzed using a two dimensional numerical simulation. The bench slope consisted of a low strength sandstones, shales and clay sequence. Hoek-Brown strength parameters established and used as input parameters in the model. The results indicate that the slope is critically stable and may lead to failure without warning and needs proper attention.