Abstract
Discontinuities are an intrinsic characteristic of rock masses, and they appear at every scale of a technical survey. Issues related to the procedure’s duration and the operator’s safety ...during the survey have encouraged the development of non-contact methods: images and digital models serve as representations of the rock mass for surveying the geometric features of discontinuities. In particular, various automatic and semi-automatic trace sampling methods were developed in the last decade, focused on estimating persistence and the degree of fracturing. A review of these methods is presented in this paper, highlighting their strengths and disadvantages.
A new automatic method for discontinuity traces mapping and sampling on a rock mass digital model is described in this work. The implemented procedure allows one to automatically identify ...discontinuity traces on a Digital Surface Model: traces are detected directly as surface breaklines, by means of maximum and minimum principal curvature values of the vertices that constitute the model surface. Color influence and user errors, that usually characterize the trace mapping on images, are eliminated. Also trace sampling procedures based on circular windows and circular scanlines have been implemented: they are used to infer trace data and to calculate values of mean trace length, expected discontinuity diameter and intensity of rock discontinuities. The method is tested on a case study: results obtained applying the automatic procedure on the DSM of a rock face are compared to those obtained performing a manual sampling on the orthophotograph of the same rock face.
► A new method for discontinuity traces mapping and sampling on a rock mass model. ► Automatic identification of discontinuity traces to estimate degree of fracturing. ► Quantitative evaluation of rock mass quality based on photogrammetry/laser scanner. ► Method to quickly analyze huge amount of trace data. ► This is part of a research ongoing at University of Parma from 10 years.
The design of flexible barriers against debris flows is a complex procedure because of the large number of parameters involved. In order to face this difficult task, the Authors have developed a ...simplified approach. The proposed simplified model involves the determination of parameters related to both the mobilized material and the various mechanical portions of the structure. A calibration phase is required to appropriately model the deformation of the net and the load transfer that occurs between the net and the horizontal structural cables. The determination of the parameters required to set up the analytical model is discussed in the first part of the paper. Tests carried out to calibrate the transfer function that allows the deformation behavior of the barrier to be reproduced using the analytical model are then reported.
•A full scale test simulating a debris flow impacting on a barrier is presented.•Impact forces were recorded and deformations were obtained from stereoscopic images.•A test for calibrating the cable deformation function was performed on a barrier.•Deformations and tensions from full scale test and analytical model are compared.
Abstract
It is well known that the mechanical behaviour of rock discontinuities strongly influences the stability of slopes and fractured rock walls. With this end, particular attention must be paid ...to the analysis of the roughness of natural discontinuities, which represents a peculiar geometric feature strongly influencing their shear strength. The paper describes an experimental procedure carried out at laboratory scale on natural rock discontinuities to measure the shear strength and the roughness of their surfaces to analyse the progressive damage of the asperities during shearing process. The direct shear tests along discontinuities were coupled to photogrammetric surveys of the surfaces carried out before the tests (natural surfaces), after the first cycle and at the end of the last cycle. This allowed the reconstruction of the digital surface models of the intact and degraded surfaces. Through analytical procedures, the data obtained were processed to obtain geometric descriptors and adequately estimate the Joint Roughness Coefficient (JRC), analysing several profiles extracted along the direction in which the mechanical tests were conducted. The comparison between the experimental results and the roughness surface direct measure showed that discontinuities, even at the small scale, have an inhomogeneous roughness and that discontinuity degree of damage is a progressive process influenced by the state of confinement applied during the tests.
Effect of uncertainties on block volume estimation Carriero, M T; Ferrero, A M; Migliazza, M R ...
IOP conference series. Earth and environmental science,
01/2023, Volume:
1124, Issue:
1
Journal Article
Peer reviewed
Open access
Abstract
The combination of the aleatory nature of the rock mass structure and the epistemic errors related to the survey methods make rock mass characterization a challenge despite the remarkable ...evolution of the survey tools and the research on the subject. In particular, significant uncertainties affect block volume estimation: the need for simplification connected to the engineering approach to rockfall problems, for instance, risks to mask the ripple effect of uncertainties on the reliability of the results. Even considering a simplified shape of the block created by three sets of discontinuities (i.e., a prism), the uncertainties on the geometrical characteristics of the discontinuities (orientation, spacing, and persistence) greatly influence the resulting volume distribution. It is a fact that a single value of the volume cannot be representative of the rock mass: the In Situ Block Size Distribution (IBSD) should be built to describe the variability of block volumes. Many statistical distribution functions can be used for fitting spacing data (i.e., gamma, negative exponential, log-normal, Weibull). The choice of the function must follow a rigorous evaluation of the goodness of fit. This research aims to assess the influence of the uncertainties related to the discontinuities sets, with particular reference to spacing samples, on block volume estimation. Through numerical examples and a case study, this research shows that a reduction of uncertainty can be reached by rigorous statistical processing of the data.
This paper discusses the applicability and the limitations of an approach to the limit states design of flexible barrier in which the soil/rock strength are factored as required in the European ...construction code. It shows as this approach has different implications if it is applied to the same kind of structure when loaded by different phenomena (rockfall and debris flow in particular). Flexible barriers are common countermeasures to protect from rockfall hazard and to restrain debris flow events. Even if an intense scientific production has demonstrated the difference between the two phenomena, the protection systems are still often designed in the same way. Additionally, the Eurocode 7 (EC7), which is the European Standard concerning geotechnical design, has not been conformed to these kinds of structures and consequently a relationship between the reliability of the system and the partial factors does not exist. Since most of the parameters that rule these systems are not even considered in the code, the Authors propose the study of two cases, in which rockfall and debris flow occur, respectively, to analyse the applicability and the limitations of EC7 principles to design the suitable kind of structure.
Abstract
Many methods for calculating the volume of rock blocks have been developed in the last decades. The first attempts to estimate such crucial quantity produced analytical equations to ...calculate the mean and variance of volume, considering blocks created by three discontinuity sets with a certain spacing probability distribution. From then, the research community followed three kinds of approaches for calculating block volume: the fully analytical one (e.g., Palmstrøm’s formula), the fully probabilistic one (e.g., Discrete Fracture Network generators), and the mixed one (e.g., In Situ Block Size Distribution). In this paper, a comparison among the different methods is presented, supported by numerical examples, highlighting their strengths and disadvantages in terms of reliability and repeatability.
This article presents a multidisciplinary research devoted to correlate estimation of the rock mass characteristics with parameters and features obtained by the use of digital photography. The data ...obtained from remote slope analysis are then undertaken to a statistical analysis of discrete data samples comparing different survey areas in terms of shape and dimension of the sampling window. The method is developed by an application to the North rock face of the Aiguilles Marbrées (Mont Blanc). This slope was chosen as case of study since it represents an important high mountain location from the environmental and touristic point of view, where the severe working condition led to the application of innovative methodology. This site is monitored by a local authority (Fondazione Montagna Sicura) devoted to the territory safe control since a rock fall of considerable size occurred in September 2007. After a photogrammetric survey, an orthophotograph has been created; circular windows have been materialized on the orthophotograph to perform area sampling. Statistical analysis of the obtained data enables us to calculate parameters and estimators for rock mass classification.
Abstract
Physical and mechanical properties of building stones can vary due to different degradation mechanisms caused by temperature and chemical agents. The problem of chemical and thermal ...weathering on marble rocks is an important issue to consider for designing building façades since it may cause sugaring, bowing, cracking and spalling. Moreover, an accurate comprehension of induced damages is required for restoration and conservation of heritage monument purposes. While thermal weathering has been widely studied in the last years, the combined effect of thermal and chemical weathering (that here is intended as the combined action of rainwater and atmospheric pollutants) is still poorly understood. In this study, no-destructive (ultrasonic pulse velocities) and destructive tests (bending tests) were performed on Carrara marble slabs in natural and after thermal (with target temperatures respectively of 50 and 90°C) and thermo-chemical treatment. Thermo-chemical treatments were performed by soaking the specimens in a 5×l0
−6
mol/l solution of sulphuric acid at pH=5 to simulate the acid rain behavior, at constant target temperatures, for one week. In general, for each weathering mechanism, progressive degradation of the physical and mechanical properties of marble specimens was observed. In particular, a marked drop in flexural strength, mirrored by a wide variation in P- and S-wave velocity, was found in specimens chemically treated at target temperature equal to 90 °C.
Several high-altitude slope instability phenomena, involving rock blocks of different volumes, have been observed in recent years. The increase in these phenomena could be correlated to climatic ...variations and to a general increase in temperature that has induced both ice melting with consequent water seepage and glacial lowering, with a consequent loss of support of the rock face. The degradation of the high-altitude thermal layer, which is known as “permafrost”, can determine the formation of highly fractured rock slopes where instabilities can concentrate. The present research has developed a methodology to improve the understanding and assessment of rock slope stability conditions in high mountain environments where access is difficult. The observed instabilities are controlled by the presence of discontinuities that can determine block detachments. Consequently, a detailed survey of the rock faces is necessary, both in terms of topography and geological structure, and in order to locate the discontinuities on the slope to obtain a better geometric reconstruction and subsequent stability analysis of the blocky rock mass. Photogrammetric surveys performed at different times allow the geostructure of the rock mass to be determined and the rock block volumes and detachment mechanisms to be estimated, in order to assess the stability conditions and potential triggering mechanisms. Photogrammetric surveys facilitate both the characterisation of the rock mass and the monitoring of slope instabilities over time. The methodology has been applied in a case study pertaining to the North Face of Aiguilles Marbrées in the Mont Blanc massif, which suffers from frequent instability phenomena. A slope failure that occurred in 2007 has been back-analysed using both the limit equilibrium method (LEM) and 3D distinct element modelling (DEM). The method has been supported and validated with traditional in situ surveys and measurements of the discontinuity orientation and other rock mass features.
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