In the process of tunnel construction under high
stress, the problem of large deformation of weak surrounding rocks is severe.
Although large deformation can be controlled and improved by support to a
certain extent, the selection of the support type in actual engineering is
difficult. Accordingly, the support types commonly used in the current soft
rock tunnels with large deformation are summarized, namely, strong,
prestressed, and yielding supports. According to the various bearing
characteristics of a support system, these support types are classified into
two: active and passive supports. Then, based on the deformation law of the
surrounding rocks after tunnel excavation under various support strengths, the
applicability of the passive support mode is explored. A selection method of
active and passive support modes with the extrusion factor 〖WT5《TNR#I》〗N〖WT5《TNR》〗c as the control index is proposed.
When 〖WT5《TNR#I》〗N〖WT5《TNR》〗c≥0.2, the current strong support mode can
effectively support the surrounding rocks, and when 〖WT5《TNR#I》〗N〖WT5《TNR》〗c<0.2, the active support can be
considered according to the deformation of the surrounding rocks on the site.
Additionally, based on the material characteristics of the anchorage system,
further analysis of the applicability range of active support shows that a
prestressed anchor bolt system can be used when the applied prestress does not
exceed 200 kN, whereas a prestressed anchor cable system is recommended when
the applied prestress exceeds 200 kN. Based on the prestressed anchor cable
system, a selection method of active and activeyielding
support types with the cable elongation 〖WT5《TNR#I》〗ε〖WT5《TNR》〗a as the control index is proposed. That is, the active support can
be used when 〖WT5《TNR#I》〗ε〖WT5《TNR》〗a in a
working state does not exceed 2.3%, and when it exceeds 2.3%, it is suggested
to adopt the activeyielding support with greater
deformation capacity. Besides, relying on the typical large deformation section
of the Muzhailing highway tunnel, the support types were selected based on the
aforementioned basis and corresponding field tests were performed. The results
somewhat verify the feasibility of the proposed selection basis.
WANG Bo
,
YU Wei
,
ZI Xin
,
CHENG Xingyuan
,
GUO Xinxin
,
FAN Yong
. Rationality of Various Support Types of Muzhailing
Highway Tunnel in Soft Rocks with Large Deformation[J]. Tunnel Construction, 2023
, 43(1)
: 36
-47
.
DOI: 10.3973/j.issn.2096-4498.2023.01.004