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ABSTRACT ABSTRACT : This paper presents a theoretical approach to establish a suitable law to describe the hydromechanical behavior of shales. Because of microscopic chemo-hydro-mechanical interactions, the poroelastic theory cannot be simply applied to these rocks. The proposed approach uses chemical potentials as variables for non-solid phases. Moreover, local microscopic thermodynamical equilibrium is assumed so that liquid water and vapor can be gathered into a unique "water" phase. Thus, hydro-mechanical behavior of both saturated and unsaturated shales can be modelized with the same partially linearized elastic law. Then, drying effects on a tunnel structure are studied. Analytical and three-dimensional numerical calculations are performed : they show that high tensile stresses appear and that convergence is significantly increased. It seems to explain the apparition of a regular spaced network on the Tournemire gallery front faces after their excavation.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.97)
ABSTRACT ABSTRACT: Rock fracturing and failure in the walls and vaults of large underground openings and especially at the intersections of different caverns, tunnels, adits, etc., are commonly associated with stress concentrations due to the rock mass unloading during the excavation/reinforcement process and with dynamic effects of drill-and-blast operations. Observations in-situ provide an integrated information and it is usually difficult to obtain a differential understanding of the influence of static and dynamic factors. On the contrary, numerical modeling provides the possibility to explore the influence of different phenomena in the same way as in the laboratory experiments. A brief summary of experience in 3D numerical modeling is presented here.
- Asia (0.96)
- North America > United States (0.47)
- Europe > Russia (0.31)
ABSTRACT ABSTRACT: Observations of brittle failure at the laboratory scale indicate that the brittle failure process involves the initiation, growth and accumulation of micro-cracks. Around underground openings observations have revealed that brittle failure is mainly a process of progressive slabbing resulting in a new stable geometry that in most cases is a V-shaped notch. Continuum models with traditional failure criteria, (Hoek-Brown or Mohr-Coulomb) based on the simultaneous mobilization of cohesion and friction, have not been successful in predicting the extent and depth of brittle failure. This has lead to a variety of continuum and discontinuum modeling approaches, with varying degrees of success. A brittle cohesion-friction model is introduced that demonstrates that continuum models can be used to simulate brittle failure provided a constitutive model is utilized that captures an essential component of brittle failure: cohesion weakening and frictional hardening as a function of plastic strain.
ABSTRACT ABSTRACT: The reliability and effectiveness of underground constructions depend on the reliability of prediction of the rock mass strength. Traditional introduction of the corrective factors in laboratory strength, during the design phase, is not effective in most cases. Due to high labor cost, rock mass tests in situ are not done as extensively enough to ensure reliable results. Back Analysis Methods are more effective. The author has developed a method of evaluating the angle of internal friction of fractured rock mass, based on a theoretical hypothesis and data analysis of short-term displacement measurement.
ABSTRACT ABSTRACT: Cement-based grouting technique is normally applied to the crown area of the shallow tunnel so that the instant reinforcement and the long-term stability of a tunnel are assured. However, the assessment of the reinforcement effect has not been fully understood so far and engineering rules-of-thumb are still used in some cases. In this paper, two seismic test methods are performed in the construction field to investigate the soil reinforcement; specifically, Crosshole test and Spectral-Analysis-of-Surface-Waves (SASW) test are used to gain information on the tunnel site before and after the grouting injection. As a result, it is found that the shear moduli of the injection area are increased up to 20%. Also, investigated in this paper is the numerical analysis scheme to quantify the reinforcement effect. For this, a permeation grouting theory is assumed and the joint stiffnesses of the rock masses are selected as the main parameters to be determined. The so called back analysis shows that, after grouting, the stiffnesses of the filled joint are increased up to 6 times compared with those of the fresh joint.
ABSTRACT ABSTRACT: This paper presents a case study on the optimum design of excavation and support system of a shallow tunnel which is faced with the unexpected bad geological condition during excavation, The detailed geological investigation shows that the rock mass in the region of concerns is heavily weathered and fractured with RMR value less than 20. Considering this, the concept of the new design is focused on the reinforcement of the ground preceding the excavation and two design patterns are suggested. One is L W -grouting & fore-poling with pilot tunnelling and the other is the steel pipe reinforced grouting. Numerical analysis by FLAC shows that these two patterns maintain the roof ground stable during the whole excavation process while the original pattern causes tensile failure around the tunnel and the severe floor heaving. This process of the design assessment can be a good guide in the construction of the tunnels in heavily fractured rock mass.
ABSTRACT: During the Exploratory Studies Facility (ESF) construction, steel sets were used as a means of ground support while advancing the tunnel through the difficult ground conditions. The steel sets were assembled at the tunnel face and jacking loads were used to expand the sets in place and generate possibly uniform stress at the contact between the sets and rock mass. This analysis provides an example of the assessment of the data collected from the field measurements. Steel set strain gage data are used to assess the magnitude of ground loads acting on an individual set. Numerical modeling utilizing the FLAC program is used to examine steel set response to such factors as the installation procedure and the design value of jacking load, impact of non-uniform lagging, and range of possible design tolerances. 1 INTRODUCTION January 1995 through February 1997, forty steel sets fabricated from a 248 MPa (36 ksi) structural steel The Exploratory Studies Facility (ESF) is currently were instrumented with strain gages, with the purpose under development at the Yucca Mountain, Nevada. of monitoring their performance over time.
- Energy (0.94)
- Water & Waste Management > Solid Waste Management (0.46)
- Government > Regional Government > North America Government > United States Government (0.31)
ABSTRACT ABSTRACT: There is a fairly common belief that any rock excavation task can be accomplished with explosives if standard cautious blasting formulas are used appropriately, especially when accompanied by vibration limits Unfortunately, that conclusion is often not true. In some cases, that approach will not give satisfactory results, and vibration restrictions may serve no purpose but to shut down the job. At times, the sequence of the work is at least as important as the blast designs. Sometimes, success may depend on the method of excavation. And in some cases, the rock excavation task could not be accomplished by any means whatever, without some extra mechanical stabilization. Successful work in sensitive rock requires a careful study of the geological and physical characteristics of the site and a determination of the potential failure mechanisms involved. This paper describes several case histories to illustrate some of these important issues.
ABSTRACT: A simulated roekburst experiment was conducted underground at a deep lcvel gold mine in South Africa. The rockburst was simulated by means of a explosion detonated in solid roek dose to a tunnel sidewall. The experiment involved the design of a seismic source using numerical modeling and empirical equations, seismic monitoring by a fairly dense seismic array, high speed video filming and the study of rock mass conditions (fractures, joints, rock strength etc.) before and after the experiment. Special investigations were carried out to evaluate the mechanism and the magnitude of damage, as well"as the support behaviour under excessive dynamic loading. 1 INTRODUCTION In some cases part of the excavations lies Underground.mining One panel in a longwall The current level of rock burst studies is limited by may be severely damaged, while an adjacent panel the lack of strong ground motion data recorded in (perhaps even doser to the focus of the seismic the immediate vicinity of large seismic sources. In particular, it was found that ct al. (1993) commented: "Many investigators ground motion measured at points about I m apart have devciIoped direct relationships betwecn damage on the stope hangingwall showed variations of up to levels and ground motion parameters.
- Geology > Geological Subdiscipline > Geomechanics (0.66)
- Geology > Mineral (0.48)
- Materials > Metals & Mining (1.00)
- Energy > Oil & Gas > Upstream (1.00)
ABSTRACT:This paper describes a case study involving the design of a 10 meter diameter tunnel spillway in marl, including support design and excavation methods. The results of analytical techniques and finite element analysis were used for the design of the structure. The accuracy of the analysis was controlled by applying theoretical results during the construction of the two 5 meter diameter diversion tunnels. Swelling phenomenon is a time dependant The type of the ground is cretaceous marl behavior which causes movement of the rocks which consists of amonites. These amonites are toward the tunnel.