Geotechnical Strength Parameters Research Articles

Determination of stochastic shear strength parameters of a real landslide by back analysis

One of the most hazardous phenomena leading to enormous monetary loss and threatening human life is slope instability. The major contributors to such disasters are slope geometry, slope material strength, geohydrological condition, structural discontinuity, weathering, development of weak zones, lithological disturbance, and heavy rainfall. As the accuracy of parameters obtained from geotechnical investigations is vital for a practical understanding of the geotechnical project, the back analysis is a pragmatic approach to forecast and control landslide and slope instability. The current paper presents a stochastic back analysis of a recent landslide near a highway located in the south of Iran. Some background information has been gathered through air photos, field observations, and photographs indicating slope failure is pretty recent, and some boreholes were drilled to obtain the required geotechnical parameters of the soil media. Due to the uncertainties in these parameters, the stochastic back analysis approach was adopted. To this end, soil strength parameters have been calculated using the FEM program coded in MATLAB. Results that properly aligned with the findings of the post-event investigations showed a computationally more efficient back analysis approach. The improved knowledge of the geotechnical strength parameters gained through the stochastic back analysis better elucidated the slope failure mechanism, which provides a basis for a more rational selection of remedial measures.

Stress-strain behavior of blue marls from the Guadalquivir river basin in Spain

This paper describes the geotechnical behavior of the Blue Marls from the Guadalquivir River Basin in Southern Spain, defined as high-plasticity clays that behave as a stiff, over- -consolidated clayey soil. These Blue Marls are, in general, classified as an inadequate material for reuse in various earthworks. In this study the comparison between the geotechnical properties of its natural and compacted remolded state, with and without additives, is studied based on different laboratory tests. A great variety of laboratory tests were performed, including triaxial tests under consolidated undrained conditions. Three types of samples were tested in triaxial tests to define different stress-strain behaviors: undisturbed and remolded samples of the in-situ clay material, as well as remolded clay samples mixed with lime. Lime stabilization is frequently used to improve the geotechnical properties of clayey soils for application in different earthworks. The back-analysis of the slope stability is performed for a comprehensive assessment of the condition of the slopes consisting of these remolded materials mixed with lime as well as without lime. The results of the retrospective analysis of man-made slopes permit an analysis of the operational geotechnical strength parameters necessary in the design of slopes as well as its comparison with the results of the triaxial consolidated undrained tests. The improvement of the strength parameters for the slope-stability analysis is confirmed under remolded conditions with and without the addition of the small amount of lime.

INTEGRATION OF SPT (N-VALUE), MACKINTOSH PROBE (M-VALUE) AND RESISTIVITY VALUES FOR SOFT SOIL ASSESSMENT

2-D resistivity method has been used in association with Mackintosh probe and Standard Penetration Test (SPT) to investigate the ground properties at Universiti Sains Malaysia, Pulau Pinang. The purpose of this study was to determine the resistivity value of the subsurface material together with N-value and M-value of the particular location. The study also aimed to evaluate whether there is any correlation could be made by the parameters measured. Borehole record revealed that two types of soil exist up to 13 m; loose sand and stiff sandy silt. The loose sand recorded N-value of 8 and M-value of 170 having resistivity value of 790 Ohm.m. On the other hand, stiff sandy silt recorded N-value of 9-11, M-value of 135-170 and showing resistivity value of 415-785 Ohm.m. The results showed no clear relation between those geotechnical strength parameters with the resistivity imaging result. It is due to non-existence of distinctive differences in the electrical conductivity of the mentioned ground material when they are in the low strength bracket. However, the resistivity result suggested the presence of higher resistance material that is dry loose sand. The resistivity result was able to detect the water saturated zone near the ground surface, which showed low N-value and M-value

Prediction of Strength Parameters of Himalayan Rocks: A Statistical and ANFIS Approach

The knowledge of geomechanical properties of rocks is essential for planning and design of structures in civil, mining, and other allied industries. Direct assessment of these properties is quite expensive and time consuming. It also requires fine precision in sample preparation and high-end testing instruments. To overcome these problems, 597 rock samples of four different Himalayan rock types have been tested for their strength attributes in a laboratory. The test results were correlated with their P-wave velocity using linear regression analysis for estimation of compressive, tensile, cohesive strengths and angle of internal friction. Subsequently, an adaptive neuro-fuzzy inference system (ANFIS) technique was applied to find its efficiency as a predictor against normal regression system. The results indicated that the ANFIS is comparatively better at prediction of geotechnical strength parameters when pitted against regression techniques.

Design and Application of Rock Bolt Foundation in Mountain Cable Crane

Restricted by the construction environment, the cable crane is an effective means to resolve the transportation of materials and component in the mountainous area. Compared with traditional gravity anchor base, cable crane fixed on the rock bolt foundation can take advantage of the bearing capacity of bedrock, and the construction method is simple and of good economic benefit. With the effect of the construction methods, design theory of geological conditions, and other factors, however, force calculation is much complicated. By analyzing the failure modes of rock bolt foundation, anchor foundation bearing capacity factors and multi anchorage effect on anchoring force, we studied the design process of rock bolt foundation, geotechnical strength parameters and the safety coefficient of reference value. Further, a construction way is proposed to improve the basic bearing capacity of rock bolt. Combing with engineering examples, we also demonstrated the security and reliability of the design method .

Risk analysis of building damage induced by landslide impact disaster

Assessing building damage in a geological landslide is a dynamic process in which the event can be regarded as the combined effect of the landslide impact and the building’s response. In conventional models, a landslide mass is typically assumed to be rigid, and standard energy principles are used to calculate equivalent impact loads. Because the disintegration phenomenon of a landslide mass is being ignored, the conventional method often leads to a larger impact force than observed in reality. Based on a case study of a critical landslide, this paper applies a granular discrete element method to investigate landslide processes. First, macroscopic and meso-structural parameters are calibrated through biaxial simulation tests. Second, energy conversion laws between the impact force, geotechnical strength parameters and the outrun distance of the landslide are studied, providing a more realistic load curve of the landslide impact. Finally, a distressed building model is established through a loading curve analysis to study the structural damage state with different parameters. Numerical results show that building damage can be characterised through an equivalent impact force and that the precise calculation of dissipated energy in a landslide is greatly improved by taking into account both the energy dissipation at the slipping surface and the internal friction in the rock mass. The proposed evaluation factor of the damage degree of buildings shows great promise in analysing landslide motion and assessing the safety of building structures.

Probabilistic back analysis of slope failure – A case study in Taiwan

In this paper, the authors present a probabilistic back-analysis of a recent slope failure at a site on Freeway No. 3 in northern Taiwan. Post-event investigations of this failure found uncertain strength parameters and deteriorating anchor systems as the most likely causes for failure. Field measurement after the event indicated an average slip surface of inclination 15°. To account for the uncertainties in input parameters, the probabilistic back analysis approach was adopted. First, the Markov Chain Monte Carlo (MCMC) simulation was used to back-calculate the geotechnical strength parameters and the anchor force. These inverse analysis results, which agreed closely with the findings of the post-event investigations, were then used to validate the maximum likelihood (ML) method, a computationally more efficient back-analysis approach. The improved knowledge of the geotechnical strength parameters and the anchor force gained through the probabilistic inverse analysis better elucidated the slope failure mechanism, which provides a basis for a more rational selection of remedial measures.

Evaluating the effects of the magnitude and amplification of pseudo-static acceleration on reinforced soil slopes and walls using the limit equilibrium Horizontal Slices Method

The effects of horizontal and vertical pseudo-static forces on reinforced soil structures are investigated in the paper. In particular, the effects of the magnitude and amplification of the ground acceleration on the seismic stability of reinforced soil slopes and walls have been investigated using the Horizontal Slices Method (HSM). The HSM is a limit equilibrium method for the analysis of reinforced soil structures, which offers a number of benefits over conventional vertical slice methods. First, a parametric study using acceptable geotechnical, geometrical and design parameters was undertaken. The results of the parametric analysis are presented in dimensionless form relating to the force required to maintain stability of the slope ( K) and the required length of the reinforcements ( L c/ H). Different rotational and planar slip surfaces are shown for various slopes and walls with different geotechnical strength parameters. Second, the capability of the HSM to consider the effect of earthquake amplification on the stability analysis of reinforced soil structures was considered. It has been shown that the effect of horizontal seismic acceleration on the response of reinforced slopes and walls depends mainly on the geotechnical strength parameters. The effect of vertical seismic acceleration on the performance of reinforced slopes is not significant for low values of horizontal seismic acceleration. It has been concluded that ignoring the effect of the amplification phenomenon could result in an underestimated design.

Partial factors and non-linear ground–structure interaction

Challenges associated with the application of partial factors to non-linear ground–structure interaction were studied for some case history examples. For some nonlinear ground–structure interaction systems, the selection of geotechnical strength parameters for calculating the movement at service condition can be important but problematic. In the calculation of action effects for structural strength design, the application of partial factors needs to simulate the trigger or path to various modes of instability, both geotechnical and structural. To avoid inconsistency, the partial factor for the self-weight of soil that is part of the interaction system needs to be set at unity. For some complex soil–structure interaction systems, the design action effects on a structural element depend on the potential failure mode examined.

Geotechnical strength parameters from geophysical logs

ABSTRACT The development of three separate algorithms for predicting geotechnical strength parameters from geophysical logs in sedimentary rock formations is outlined. The geotechnical and geophysical data were obtained from drillholes which penetrated both coal and non-coal deposits to depths up to 80 m at two operating surface coal mines in western Canada. The strength parameters for the different lithologies were determined from back-pressure saturated, consolidated-undrained triaxial tests with pore pressure measurement. The digitized suite of geophysical logs included gamma, caliper, density, resistivity, sonic and neutron logs. The algorithms consist of exponential expressions relating the effective across-bedding friction angle, φ to various combinations of geophysical logs.

A statistical method to study the variability in strength parameters in an open pit

A method is introduced to determine the homogeneity/heterogeneity of slope material at different locations and depths of an open pit mine. In this method, it is ascertained that geotechnical strength parameters are significantly variable or not, using a two-way analysis of variance technique. This study is important during the division of a mine into different statistically homogeneous design sectors and the selection of a suitable method for stability analysis. This technique was successfully used during the stability analysis of a copper open pit mine.

Study of the variation in strength parameters prior to slope analysis

A new approach is introduced for study of the behaviour of geotechnical strength parameters prior to slope analysis to ascertain whether strength parameters of slope materials are homogeneous or heterogeneous at different mine depths. The strength parameters used for the study are uniaxial compressive strength, tensile strength and shear strength. The analysis is based on statistical analysis of variance technique for one-way classification. The application of the technique is given through a case study in an openpit limestome mine.