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Keywords: collapse line

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Proceedings Papers

Paper presented at the ISRM International Symposium - EUROCK 2002, November 25–27, 2002

Paper Number: ISRM-EUROCK-2002-086

... Reservoir Characterization mechanical collapsible rock soft clay

**collapse****line**consolidation pressure energy consumption law Serrano theoretical model Madrid equation Upstream Oil & Gas uriel critical load parametric equation stress path consumption law adjustment upper...
Abstract

Volcanic rocks, and particularly those of common occurrence in Canary Islands, do exhibit a special mechanic behaviour that makes them mechanically collapsible. Under a low stress level they behave as rocks, with high deformability modulus. However, when the stress level is high its internal structure may be destroyed and its deformability may increase greatly, thus causing it to behave as a soil. A theoretical model of collapse based on energetic criteria is presented. An "energy expand law" is proposed for these mechanically collapsible rocks as well as the parametric equations for the collapse lines, all for a non associative flow rule. 1. INTRODUCTION Low-density volcanic agglomerates can be regarded as a typical example of macroporous rocks. Their mechanical behaviour is very special. When stress levels are low they behave like real rock with very high deformability moduli. By contrast, when stress levels are high their structure is destroyed and their deformability increases greatly, causing them to behave like a soil (Uriel and Serrano, 1973 and 1976). This phenomenon is referred to as mechanical collapse, and the materials that are subjected to this process are known as mechanically collapsible rocks. Two types of theoretical model's have been proposed: structural models (Uriel & Bravo, 1970; Uriel & Serrano, 1973) and energetic models (Serrano, 1976; Serrano, 1996; Aversa & Evangelista, 1998). This second kind of model is the one analysed here. 2. ENERGETIC BEHAVIOUR MODEL 2.1. Behaviour domains The behaviour pattern shown in Fig.l could be established in the stress space (q, p). There is a domain in that space that contains the origin, within which the material behaves elastically in a normal load process. For stresses within this domain the agglomerate behaves as a rock. The boundary for the elastic domain is what is referred to as the lower collapse line. When the stresses reach this line, destruction of the structure of the material starts to take place, in such a way that when the lower collapse line is crossed, the transition zone is entered and this, in turn, is externally limited by the upper collapse line. The failure occurs within this transition zone. By the time the stress reaches the upper collapse line the structure of the material has already been completely destroyed. The material can now actually be regarded as a soil. From this time the material will behave as a soil and could thus have one peak strength and another residual strength. The behaviour will either be stable or unstable and this will depend upon what point it has arrived when it reaches the upper collapse line. Where homogeneous materials are concerned, the lower and upper collapse lines are in exactly the same place, and the transition zone disappears. The presence of both upper and lower collapse lines has been postulated in this description; that is to say, it has been assumed that the material is heterogeneous. These lines, which are in fact no more than the boundaries for the behaviour domains, depend upon the stress path.

Proceedings Papers

Paper presented at the ISRM International Symposium - EUROCK 93, June 21–24, 1993

Paper Number: ISRM-EUROCK-1993-119

... the same as yield condition according to Von-Mises hypothesis. In the point of view of plastic theory, the boundary line or the envelope of slip lines denotes the interface of strain speed. Reservoir Characterization class line limit equilibrium state

**collapse****line**equition Soil...
Abstract

ABSTRACT: Based on the thought of limit equilibrium equition of granular medium, this paper makes an effort to study the caving rules of the roof of the undercut stope deep buried in granular medium, and furthermore, connected with the calculation of the collapse of the powder ore of Jinshandian mine, the result of this paper is compared with that of pomogb kob's theory. So far, most of problems which are being studied in granular mechanics are such as bearing capacity of foundations, stability of slope engineering and earth retaining structure. etc. There has been hardly one who paid his attention on the collapse of roof of underground opening deep buried in granular medium so much as he done in foundation and slope engineering in granular mechanics. The current method concerned with this problem is still the pomogb kob's theory which was put forward as early as 1908. This theory is based on the granular structure mechanics and supposes the arch which is formed after the collapse as parabola, so, it is gained by primary method on the basis of some hypothesis. Compared to this, we try to solve this problem by numerical method for partial differential equitions based on the limit equilibrium equition of granular medium which has been widely used in soil mechanics. The characteristic method for solveing limit equilibrium equitions In granular mechanics, the limit equilibrium state of a point can be determined by the characteristic stress σ and the characteristic angle θ, their physic meaning are such as fig (l). By difference method, we can get M" first, and then M', and then M, so as to gain M from the known M1 and M2. The classify of surrounding area of undercut stope by the velocity of slip. According to plastic theory, the slip field surrounding a rectangular cave in an infinit area is such as figer (4). In this paper, the slip lines are logarithmic spiral within the curve zone. There is no sense in talking about strain when the limit equilibrium state has been reached, because that all points must have been plastic flow state then, and their strain will expend continuouslly without the increasing of stress. So, the velocity of strain makes sense rather than strain itself. In fact, the true solution of our problem must make the velocity field satisfy the boundary condition of velocity· It will be very difficult to do so, most of us haven't done so up to now. To the problem of this paper, the gravity will produce tensile stress due to the vacancy below the roof, and the roof must be collapsing when the stress exceeds its ultimate capacity. So, it is enough to do only qualitative analysis in the velocity field. Generally, plastic potential function f can be assumed as the same as yield condition according to Von-Mises hypothesis. In the point of view of plastic theory, the boundary line or the envelope of slip lines denotes the interface of strain speed.