ABSTRACT:

In this paper, we propose a set of basic equations of elastic-viscoplastic block theory which takes the prestressed anchors, piles and shear keys into account. A computer program has been compiled and an numerical example is studied.

Resume:

Dans cet article, nous proposons un group d'equations fondamentales basees sur la theorie de block elasto-viscoplastique qui prend la presence d'ancrages precontraints, de piliers et de talons en consideration. Un program pour ordinateur a ete etabli et un example numerique est etudie.

Zusammenfassung:

In dieser Arbeit leiten wir einen Satz grundsatzlicher Gleichungen her, der auf der elasto-viscoplastischen Block Theorie und vorgespannte verankerungen, Pfahle und Absatze beruecksichtigt. Ein Rechnerprogramm wurde erstellt und an einem Beispiel getested.

1 INTRODUCTION

Prestressed anchors, piles and shear keys are widely used as reinforcement measures in geotechnical engineering. There are two main analysis methods for such complicated foundation: the Rigid Body Method (RBM) and the Finite Element Method (FEM). The REM is simpler and easier for engineers, but its basic assumption is too rough. The FEM can calculate and design the reinforced foundation more reasonably, but if the number of the considered discontinuities and reinforced components lies in medium range, the calculation work will be difficult, neither the equivalent continuum nor the special element approaches can give out satisfied results conveniently. The Elastic-viscoplastic Block Theory (EVBT) has the advantages of the both REM and FEM - simplicity and accuracy. Only a few of geological and mechanical parameters of discontinuities are required to complete the calculation in personal computer. In recent years the author have been working in this area and an algorithm of elastic- viscoplastic analysis for rock block system in natural state has been established(Chen & Xiong 1991, Chen 1991, Chen 1992). In the following paper, we will take the influences of reinforced components into account and develop a new analysis method of reinforced rock foundation on the base of EVBT.

2 BASIC FORMULATIONS
2.1 Assumptions

To simplify the problem, the following assumptions are necessary:

1. The rock materials are rigid bodys, but the discontinuities have elastic-viscoplastic property;

2. The discontinuities are regarded as plans;

3. The anchors, piles and keys are regarded as lines;

4. At the cross section of anchor or pile, the stresses are uniform, along the width of key the stresses are uniform, too.

2.2 Geometry analysis of reinforced block system

The goal of geometry analysis is to get informations such as the position, shape and size of each block, the intersecting points of reinforced components with discontinuities, ect. A typical block is shown in Figure 1, it is delimited by seven discontinuities, the strikes, dips and emerging points of each discontinuty can be decided through geological investigation. Let the X-axis of global coordinate system point to North and keep horizontal; the Y-axis point to West and keep horizontal, too; the Z-axis be upright.

3 NUMERICAL EXAMPLE

An ideal profile of a gravity dam is shown in Fig.3, the foundation has three discontinuities: Fl, F2 and F3, their parameters for computation are listed in Table 1.

4 CONCLUSION

The elastic-viscoplastic block theory can be generalized into reinforcement case for rock masses efficiently, it has the advantages of both the Rigid Body Method and Finite Element Method ----- simple and rational. On the other hand, because the proposed method has taken the compatibility of the elastic-viscoplastic deformations between discontinuities and reinforcement components, it is a more reasonable approach to the real work state of reinforced discontinuous rock masses than REM.

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