Soldier pile & lagging · Tiebacks · Street permissions
Holding a garage excavation along a city street, with tiebacks under the public way
A developer's six-storey building sits on a one-level parking podium that runs right to the sidewalk, and the cut is about sixteen feet. Along the street, a tieback wall keeps the excavation open and free of bracing. But every tieback crosses the property line under a public street full of utilities, and that needs the City's permission before anyone drills.
Illustrative example — composite site, not a completed ESC project.
- Building
- Six storeys over a one-level garage
- Lot
- 100 ft × 120 ft
- Cut
- About 16 ft below the sidewalk
- Street side
- Garage wall just inside the front lot line
- Neighbor
- Two-storey commercial building 5 ft past the side line
- Ground
- Fill over sand and gravel over glacial till; water below the cut (typical; confirm by borings)
The situation
The garage runs to the front of the lot. Its wall sits just inside the property line, with the sidewalk, a parking lane and the usual water, gas, sewer and electric lines under the street beyond.
On the left, a two-storey commercial building on shallow footings stands five feet past the side line. To the right and at the rear the lot stays open, with room to lay the cut back.
At sixteen feet, a cantilever wall would need heavy piles and would move more than a street full of utilities should. A braced excavation would fill the garage with struts. Tiebacks keep the hole open, if they are allowed to go under the street.
What drives the design
Permission to go under the street
Tiebacks that leave the lot need the City's approval (in Boston that goes through the Public Improvement Commission) as well as street-opening and occupancy permits. That process sets the schedule, so it starts early.
The utilities
Every tieback has to pass each pipe and duct bank under the street with room to spare. Utility records and test pits fix their positions before the anchor layout is drawn.
The neighbor's side
No anchor goes under the neighbor's building without a written agreement. That side is braced from inside the hole with rakers instead.
What happens afterwards
Once the building holds the wall, the City may require the tiebacks to be de-tensioned or cut free so nothing is left loaded under the street.
Soldier pile and lagging on the street and neighbor sides, one row of tiebacks under the street, rakers on the neighbor's side, and slopes where the lot is open.
- Drilled HP12 soldier piles about seven feet apart along the street and the neighbor's side, set from existing grade before the dig starts.
- Timber lagging in lifts as the excavator comes down.
- Street side: one row of tiebacks about six feet below the sidewalk, drilled at a downward angle to pass beneath the utilities and bonded in the sand and gravel beyond the soil wedge that pushes on the wall. Each one tested and locked off.
- Neighbor's side: a waler and rakers braced to footing blocks in the excavation, set out to clear the garage structure.
- Right side and rear: laid back where the open ground allows.
Illustrative example — composite site, not a completed ESC project.
- Note 1: Property line: the street side of it is public way
- Note 2: Utilities under the street, located and cleared before any drilling
- Note 3: Tieback: free length through the wedge that loads the wall, bond length beyond it
- Note 4: Waler and anchor head, tested and locked off
- Note 5: HP12 soldier pile in a drilled hole, with timber lagging
- Note 6: Garage subgrade about 16 ft below the sidewalk
Illustrative example — composite site, not a completed ESC project.
- Lot line
- Neighboring building
- New building footprint
- Soldier pile & lagging (piles drilled, not driven)
- Tieback under the public way (if permitted)
- Raker brace inside the excavation
- Cut laid back — no support
- Gap that decides the design (measured on the drawing)
- Synthetic lot for illustration: 100 × 120 ft, with the garage against the street and the left side.
- Street wall about 97 LF, full height for about 73 LF and tapering where it meets the right-side slope. Left wall full height for about 93 LF, braced by rakers, then tapering into the rear slope.
- Tiebacks drawn one per pile, reaching about 37.5 ft past the property line under the sidewalk and street (plan length of a 40 ft tieback at 20°).
- No anchors under the neighbor. The slopes use the lot's own open ground on the right and at the rear.
The order of work
- 01Months ahead. Tieback layout, utility test pits and the City application. The permission, not the drilling, sets the start date.
- 02Weeks 1–2. Drill and set the soldier piles from grade on the street and neighbor sides.
- 03Weeks 3–5. Lag in lifts; stop at the tieback level to drill, grout, test and lock off the row; carry on down, with rakers on the neighbor's side as the dig reaches them.
- 04Then. The wall stays for the garage walls, and the tiebacks are released if the permit requires it.
Who carries what
ESC
the earth-support subcontractor
- Soldier piles, drilled and set
- Lagging as the excavator digs
- Tiebacks: drill, grout, test, lock off
- Waler and rakers on the neighbor's side
General contractor
or the builder
- Street-opening and occupancy permits, traffic control
- Utility test pits and locates
- Garage walls cast against the lagging
Excavator
often the GC's own crew
- Excavation in lifts, to the tieback level and below
- Slopes on the open sides
- Spoils off site
Engineer of record
designs and signs
- Wall, tieback and raker design
- Test loads and lock-off values
- Movement limits for the street and the neighbor
Others
- City: approval for tiebacks under the street
- Utility owners: clearances
- Monitoring consultant: survey points on the street and the neighbor
Budget range
Budget range · budget, not a quote
$420,000–$740,000
Computed from ESC’s published unit prices, book rev 1 issued September 14, 2026 and valid through December 13, 2026: the low quantities at the book’s low rates to the high quantities at its high rates, rounded out to the nearest $5,000. It is a budget for this composite site, not a quote for yours.
The basis, line by line
Drill rig for the soldier piles, one visit
$23,750–49,250
1 LS × $23,750–49,250
One continuous visit for the pile drilling.
Book row MOB-DRILL-LOCAL
Soldier piles on the street side (HP12 class, 24 in holes)
$91,000–166,050
350–410 LF × $260–405 per LF
About 15 piles: 11 at full height (26 to 30 ft) and 4 shorter where the wall tapers.
Book row SPL-PILE-24
Soldier piles on the neighbor's side (HP14 class, 30 in holes)
$154,050–261,000
474–522 LF × $325–500 per LF
About 14 full-height piles at 30 to 33 ft, plus 3 shorter ones where the wall tapers.
Book row SPL-PILE-30
Timber lagging, left in place
$92,625–170,800
2,850–3,050 SF × $32.50–56 per SF
About 73 LF of street face and 93 LF beside the neighbor at 16 ft, plus the tapering ends where each wall meets a slope.
Book row SPL-LAGGING-LIP
Waler on the neighbor's side, one level
$21,600–31,960
90–94 LF × $240–340 per LF
The length of the raker-braced wall.
Book row SP-WALE
Rakers, budgeted at the book's strut rate
$37,200–59,150
6–7 EA × $6,200–8,450 per EA
One raker at every other pile, about 14 ft apart, along the full-height wall.
Book row SP-STRUT
Tiebacks under the street, with testing and any later release
Priced per job
The current book prices anchors to about 20 ft; these run about 40 ft. Priced per job once the City's conditions and the utility positions are known.
Not in this range
- Excavation in lifts, slopes and spoils (excavator)
- Utility test pits, street-opening and occupancy permits, traffic control (builder)
- The City application for the tiebacks (owner's team)
- Wall, tieback and raker design (engineer of record, or the design-build option if the contract delegates it)
- Monitoring of the street, the utilities and the neighbor (owner's consultant)
Where a real job lands
The wall is priced from the book; the tiebacks are not. The City's conditions (how many, how deep, and whether they must be released later) set their price.
Low end: open site, repetitive work, good ground, larger quantities. High end: tight access, obstructions, variable ground, small quantities. Book rates carry prevailing wage.
Every rate in the published bookWhat we’d need to firm it up
- Garage plans with the wall line and subgrade levels
- Borings along the street side
- Utility records and test-pit results under the street
- The City's conditions for tiebacks in the public way
- The neighbor's footing depth, and any agreement on access
More on the techniques
Send us the address and drawings
We'll send back how we'd approach yours: the support we'd use, the order of work, and a budget range from our published prices. We work for builders, GCs and developers.
Or email plans to bids@earthsupportcorp.com