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| Excavation and Shoring |
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| Shoring is necessary whenever earth is excavated more than a few feet deep. Without shoring, the sides of an excavation can collapse. |
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| The shoring for City Hall was installed by digging piles around the perimeter of the building, spaced 8 feet apart and cementing 40 foot long steel "I" beams into these post holes. When the earth between the posts is cleared during excavation heavy timbers are inserted in between the "I" beams and the earth is filled in behind the timbers. The shoring is then able to hold back the weight of the earth safely. |
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| Once the area has been completely excavated work on the moat can commence. |
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| Post hole is being readied. |
Posts holding heavy timbers. |
The excavation is completed, allowing work in the basement
to be performed safely. |
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| Framing the Moat |
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| Once the shoring system was in place a slab could be poured at the bottom of the moat and reinforcing steel could be placed. The reinforcing steel takes on the frame or skeleton of the moat wall. Wall forms are then built and concrete is poured to complete the next wall |
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Footings for the moat wall
are poured and reinforcing
steel anchors installed. |
A reinforcing steel structure is constructed on the concrete
footing. |
Reinforcing steel is framed. |
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| Pouring the Moat |
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Reinforced concrete wall is
poured on first street side |
Wall is poured on
Spring St. side |
A section of forms during the concrete pour of the west
side moat facing Spring Street |
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| Back filling the moat |
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| The back filling operation of the west retaining wall (at right). The entire back filling operation is done in “lifts” which can be no greater than 12 inches. The wall is up to 24 feet tall. |
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| After enough soil is placed in the moat a “thumper” packs the soil. Then the soil is tested, and if it passes the compaction test the process is repeated until the back filling operation is completed. |
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Photo at right: Back filling the outer perimeter wall of the moat along Spring Street. In the foreground, a soil technician performs a compaction test to verify that the soil has been adequately compacted as required by code. |
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| Before |
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After |
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Footing slab is poured. |
Moat outer wall poured and water-proofed. |
The north west face of
the City Hall moat with
the outer moat wall completely back filled. |
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