An underground interchange tunnel is proposed to be
built at the intersection of Lu′ao Road and Haicang Shugang channel
in Xiamen. The tunnel bifurcation directly transitions from a singlehole fivelane largespan section to a small cleardistance
section of the main tunnel with three lanes and a ramp with two lanes. The
directtransition method is adopted without a multiarch section. The maximum excavation span reaches 30.46 m, and the
maximum excavation area reaches 450.41 m2. The design
of the construction and supporting structure of the bifurcated tunnel suffers
from many difficulties. First, the direct transition of the bifurcated tunnel
from the longspan section to the small cleardistance section results in complicated process transformation
during the construction process as well as in difficult control of the
construction mechanics. Second, the surroundingrock
stress of the bifurcated tunnel is affected by the clear distance of the tunnel
and its crosssectional form. Thus, triaxial test and
numerical analysis are conducted to investigate the construction mechanics of
the junction between the largespan and small cleardistance sections and the small cleardistance
tunnel. The following conclusions are drawn. (1) The granite samples collected
on site are elastic and brittle rocks. The strength and stability of the rock
in a triaxialstress state are much greater than those
in a biaxialstress state. The elastic modulus of the
granite sample is positively correlated to the confining pressure. The HoekBrown and MohrCoulomb strength criteria are
used to modify the triaxial test results to obtain the physical and mechanical
parameters of the rock mass. (2) The surrounding rock at the junction between
the largespan and small cleardistance
sections will ultimately be sealed. It is recommended to use highperformance shotcrete and an Ibeam support
to ensure that the surrounding rock will enter the triaxialstress state as soon as possible. (3) Tunnel excavation in the small
cleardistance section mainly affects the crosssectional displacement at the end of the largespan section along the vertical direction, and it causes different
degrees of internalforce changes at the end of the
largespan tunnel. The internal force changes at the
left and right arch feet are the most dramatic. The influence range of the maintunnel construction on the internal force and displacement of the
largespan tunnel is 16 m behind the tunnel face, and
that of the ramp is 12 m behind the tunnel face. (4) During the construction of
the small cleardistance section, the optimal
longitudinal excavation distance between the main and ramp tunnels is 16 m.
When the clear distance between the main and ramp tunnels is more than 6 m,
they can be designed and constructed as independent single tunnels.
ZHANG Junru
,
WANG Zhiyong
,
GONG Yanfeng
,
XU Xiangdong
,
ZHANG Hang
,
YE Lun
.
Construction Mechanics of Transition Connection
between a SingleSpan
FiveLane Highway Tunnel and Small ClearDistance Tunnel with
ThreeLane Main Tunnel and TwoLane Ramp
[J]. Tunnel Construction, 2021
, 41(2)
: 185
-198
.
DOI: 10.3973/j.issn.2096-4498.2021.02.004
