To investigate the stress transfer path and the
pattern of stress system transformation during the underpinning process when
using a castinsitu tunnel structure to support an
operational bridge, a specific case is examined, focusing on the cutandcover tunnel beneath the Fangzhong road
of the Xiamen 2nd East Passage(Xiang′an bridge), which
passes beneath an operational BRT viaduct. The investigation involves the
establishment of an automatic monitoring system for vertical displacement in
bridge abutments, tunnel structures, and reinforcement stress on piles. This
system is designed to assess the settlement of bearing platforms and abutments
as well as the forces acting on the top plate, middle sidewall, bottom plate,
and endbearing piles at the middle wall of the tunnel.
Then, the transfer paths of the underpinning load and the stress transformation
pattern of the tunnel structure are revealed. Subsequently, a simplified loadstructure calculation model incorporating prestress considerations
is developed to analyze internal force changes in the tunnel structure under
the underpinning load and assess the prestress effect. The key findings are as
follows: (1) The settlement of the two underpinned piers is measured at 3.30 mm
and 4.22 mm. Notably, the neighboring pier experiences settlement before the
underpinned piers due to the influence of bridge deck stiffness. Post
underpinning, the bridge pier may undergo continued slow settlement for a
certain period before stabilizing. (2) Following underpinning, the entire
bridge load is not borne by the entire tunnel; instead, the primary load is
supported by the top slab of the tunnel on the underpinned side, subsequently
transferring to the pile foundation through the middle wall and adjacent
sidewalls. (3) The deformation and force results are calculated by the
simplified calculation model of tunnel loadstructure
which considering prestress align well with the monitoring outcomes. In
comparison to scenarios neglecting prestress, the inclusion of prestressed
cables leads to an approximate 25.7% reduction in settlement.
LIN Lihua
. Stress System Transform of Operational BRT Viaduct
Piles Underpinned by Cast-in-Situ Tunnel Structure of Xiamen 2nd East Passage[J]. Tunnel Construction, 2023
, 43(11)
: 1896
-1907
.
DOI: 10.3973/j.issn.2096-4498.2023.11.009
