This paper introduces the application of the stochastic method for prediction of ground surface movements and deformations due to near surface excavation in urban areas of large cities. The prediction method for two and three dimentional problem are given in detail with the PC computer programs. A lot of history cases are given.
Cet article nous introduit L application d'ume methode stochastique pour la predication de deplacement et de deformation de surface de la terre à couse de I excavation aupres de la surface de la terre en ville. La mèthode de predication est presentee en detail pour les problimes de deux et trois dimensions avec Ie programme du PC ordinateur èlectronique. Ouelqves exemples are donnès daus cet article. ZUSAMENFASSUNG: Im vorliegenden Arbeit wird eine Anwendung das Stochastisch Method fuer Rechnung der fagesoberflache Bewegung und Deformation bei Untergrundbahnbauen im Schdadt Die 2 and 3 dimentionen Problem fuer Rechnung und PC Berechnungsprogramm mit tatsachlich Beispiel ist im dem Arbeit geben.
An extensive research program has been conducted in China to predict the ground surface movements induced by near surface excavation. The aim is to minimize the damage to surface structures in the urban areas from infeuemce of excavation. Recently an increasing of the need for improved transportation. conservation of surface areas and ecological aspects has led to increased use of underground space for railways, storage and shopping centers. These excavations are placed close to the ground surface for low cost and convenience of use. However, caving into these spaces is liable to damage existing surface structures and services. In some cases the potential surface damage was estimated to be so great that the planned underground project was either changed or canceled.
An example is shown in Fig. 1 of an underground excavation of depth H. A sulfficiently large area of excavation can be treated as being composed of infinite numbers of infinitesimal elementary excavations which have the same influences on the ground surface. Consider an extreme case where the underground excavation has totally collapsed. The maximum ground surface subsidence will be reached after an infinite time following the total collapse. In this case the elementary subsidence we induced by the elementary excavation can be obtained from .
A long horizontal subway of arbitary cross-section is excavated at depth H from the ground surface. It is clear that the problem can be reduced to that of a plane strain state (Fig. 2). Experience in subway engineering show that when the subway is excavated and supported correctly only small movements develop in the surrounding rock (soil). Hence, ground surface movement is depending on the nature and extent of the displacements over the cross-section of the subway. In the hard soil or soil with broken rocks the cross-section of the subway takes the arch and wall form. The radial displacement of the surrounding rock mass was measured and illustrated in Fig. 5. For practical problem a simplified boundary geometries can be used. The horizontal strain of ground surface is given by (8). A calculation program of prediction of surface movements and deformation SUBWAY 2 has been developed for PC computer for arch and wall cross-section of subway. Five other history cases in the grey-yellow uniform soil region were monitored the same way. The comparison between the observed results with the prediction are shown in Fig. 7.