Failure modes and face instability of shallow tunnels under soft grounds

Abstract

For shallow tunnels under soft grounds, it is very difficult to gain a complete understanding on all the load-bearing arch effects during excavation, since such tunnels can easily deform or even collapse. Among these effects, the tunnel face stability plays the most important role and has not been understood and handled very well; therefore, the design and construction of such tunnels under soft grounds remain as a challenge. In this work, the different failure models of face instability of the shallow tunnels were established based on the upper-bound theorem of limit analysis for the formation of clayey and sandy soils, respectively, and the analytical equations for determining the limit support force for the face stability were also derived. Furthermore, the influences of various factors on the stability were analyzed and compared. For the sandy soil formation, an equivalent pressure coefficient was proposed for the tunnel faces of bolt reinforcement. Finally, taking the face stability of the shallow tunnels in sandy soils as an example, a complete numerical simulation was conducted to verify the accuracy and effectiveness of the analytical results based on the theoretical models as well as their application conditions.

Displacement and Stress Characteristics of Tunnel Foundation in Collapsible Loess Ground Reinforced by Jet Grouting Columns

“…In recent years, geological hazards happened frequently [1][2][3], and with the development of rock engineering [4,5] and civil engineering [6][7][8][9], a substantial number of tunnel projects have been constructed in complex geological areas as western development strategies have been implemented in China [10][11][12][13][14][15][16]. e construction of loess tunnels has become a focus of the tunnel field, and many relevant practical experience and theoretical results have been obtained [17][18][19][20][21][22][23].…”

Stress Field Distribution and Deformation Law of Large Deformation Tunnel Excavation in Soft Rock Mass

“…It is inevitable more long tunnels will be built in soft and weak surrounding rock areas [8][9][10][11][12][13][14]. Large deformation of soft rock mass is one of the common geological hazards when a tunnel passes through soft rock mass [15][16][17], and is also a long-term problem plaguing tunnel construction [18][19][20][21]. If the deformation of surrounding rock cannot be effectively controlled, the deformation will continue to grow and exceed the allowable value, which will often lead to the destruction of the rock mass structure and support structure of tunnel and bring great potential safety hazards and economic losses to the project [22][23][24][25][26].…”

The Prevention and Control Mechanism of Rockburst Hazards and Its Application in the Construction of a Deeply Buried Tunnel

“…With the development of transportation and economy, it is inevitable to build long large tunnels in deep underground space [1][2][3][4][5]. At present, the maximum depth of the civil tunnel has exceeded 2500 m. The increasing number of long, large and deep buried tunnels has brought great challenges to the construction and operation of projects [6][7][8][9][10][11][12]. However, rockburst is a common problem in the construction of deep tunnels, which occurred widely in Australia [13], Canada [14], South Africa [15,16], China [17][18][19] and other countries [20][21][22].…”