TECHNICAL | MINED TUNNELING
Temporary decking (schematic)
Eglington Avenue West Existing TTC Spadina box TTC box joint Unit 1604
gallery C
SEM L
elevation varies Springline
Extended gallery 1A
Gallery 1A
Gallery 3
Gallery 2
Gallery 4
Gallery 1B
gallery C
SEM L
gallery C
SEM L
TTC box joint
Unit 1608
gallery C
SEM L
gallery C
SEM L
gallery C
SEM L
TTC box joint TTC box joint Unit 1612
Needle beam (indicative) Bracing not shown for clarity
Springline elevation varies
Temporary vertical prop
Existing TTC spadina box
Temporary vertical props Bracing not shown for clarity
T/R
CL
CL T/R 1300mm caisson
SEM gallery springline
Approx. 10110 Above, figure 3: Combined plan view and transverse section of the completed galleries under the TTC box
Dewatering of the permeable soil layers was
implemented using deep wells prior to underground excavation in order to lower the groundwater level and to control groundwater inflow, mainly as part of the subsequent, main station excavation works. The geotechnical properties used in the design are summarized in Table 1.
UNDERPINNING SYSTEM The underpinning system consisted of a series of needle beams transverse to the alignment, installed through the six mined galleries. The two ends of the needle beams were supported during construction on temporary steel girders founded on caissons, and in the permanent configuration were connected to reinforced concrete wall-beams integral to the station structure. A jacking system provided the means to adjust the elevation of the needle beams and compensate for potential excessive movements, based on the real-time monitoring of the TTC box. Six mined galleries were constructed in total, as
shown in Figure 3, supported by a continuous lining of fibre reinforced shotcrete (FRS) at the sides, structurally connected to the invert slab. Each of the six galleries was divided longitudinally into eleven advances,
14 | Winter 2023
typically 1.1m-long, excavated simultaneously from both sides. Galleries 1A, 1B, and 2 which were excavated first,
were 4m-wide by 2.75m-high, U-shaped with a cross section as shown in Figure 4. The walls were supported by a 100m-thick shotcrete lining, following a concave shape, increasing to 300mm at the top connections to the TTC box. A first, 100mm-thick shotcrete layer was applied immediately against the sides of the exposed ground concurrently with the full thickness of the invert, whereas the completed profile of the sides was applied in a subsequent step. The invert slab was FRS, 350mm- thick, cast-in-place. Gallery ‘1A Extended’ was essentially an enlargement
of Gallery 1A with a concurrent removal of its left-side wall and shares the same geometrical characteriztics. Only its left side was supported by the full shotcrete lining whereas the invert slab is similar to the other galleries. Galleries 3 and 4 were excavated between the
completed Galleries 1A, 1B and 2, and they did not require side support. A 50mm-thick shotcrete layer (flashcrete) was
sprayed against the exposed excavation faces in all galleries.
SOUTH SIDE
NORTH SIDE
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