Modelling of Dip-Slip Normal Fault Rupture and Segmental Shallow Tunnel in Geotechnical Centrifuge

The use of urban tunnels is increasing to accommodate lifelines such as roads, railroads, subways, sewer systems and high-voltage electrical cables. Many cities sit on sedimentary deposits and faulting zones, which presents challenges for the construction of these tunnels. One type of probable damage is that caused by permanent ground displacement (PGD). Severe earthquakes can cause such displacements to appear at the ground surface and cause fractures called surface faulting. The interaction of surface faulting at ground structures such as bridges, dams, and buildings or underground structures such as tunnels and pipelines can result in major damage to them. Comprehensive studies have been conducted to fully understand this phenomenon [1-11].
 The building codes of many countries recommend avoiding construction in the vicinity of active faults, but at times the construction of a tunnel intersecting a fault is inevitable [4]. It is not always possible to avoid the construction of a tunnel near an active fault. Tunnels are at the risk of faulting due to their long length. This can affect the design of the tunnel lining. Such a tunnel must be capable of resisting fault displacement so that it will suffer only minor damage.
When designing tunnels located in the areas with the potential for surface fault rupture, it is necessary to consider the effects of loads caused by fault rupture in addition to other types of seismic loads [12]. Researchers have developed specific criteria to account for the effect of seismic wave loading. However, the effect of fault rupture loads has not been considered in comprehensive design methods.
Highly active faults can cause significant damage to a tunnel. Fault displacement can produce extreme stresses on the lining of the tunnel. The study of tunnel behavior passing through a fault zone during an earthquake is practically unknown because it has been experienced less study and investigations. Physical modeling by the use of geotechnical centrifuge provides the possibility of investigating the up-mentioned geotechnical phenomenon.
The current study investigated the effects of normal faulting on shallow segmental tunnels using physical modeling in a geotechnical centrifuge. This article describes the details of physical modeling of a normal fault, a segmental tunnel in a centrifuge, and the results of six centrifuge tests.
One of the most important and applicable results obtained from the faulting tests is an understanding of the failure modes. It was possible to discern vulnerable areas in the segmental tunnels by determining the failure modes and designing methods to mitigate tunnel damage. The present study conducted a series of centrifuge model tests on segmental tunnels subjected to normal faulting. Results indicate the probable rupture mechanisms. Results show that segmental tunnels can tolerate superficial faulting. However, as the faulting displacement increases, oval shapes in segmental ring occur in the faulting zone and finally tunnel collapse happen. However, the results indicated the absence of sudden collapse of segmental tunnels under normal faulting and improvement of function in response to an increase in the overburden of the tunnel. The angle of the fault affected tunnel behavior. Despite large displacement faulting, structural damage to the segments was very low because of the adequate geometric functioning of the segments and their joints. The length of the zone affected by faulting in the tunnel decreased as the overburden increased, but the severity of damage increased in response to localization of fault displacement. Sinkhole formation upon the collapse of soil into the tunnel is likely at the ground surface. Special attention must be paid to the effect of sinkholes on ground structures in the vicinity of the tunnel.
The results of this paper can be used to determine the pattern of rupture where a tunnel intersects a fault. Obviously, the pattern derived from this modeling can play an important role in developing analytical analysis and numerical methods.
The results can be used for better understanding of segmental tunnel behavior where it intersects a fault zone; it can also be used to specify the locations affected by the faulting and to adopt preventive strategies as well.
References

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