Retaining Wall Excavation in Christchurch
Top Retaining Walls Christchurch does the excavation that goes with retaining work. Cutting the bench a wall sits on, battering back a face so it can be worked safely, trenching for footings and drainage, and removing or reusing the spoil.
- Benched and battered so the face stays safe
- Services located before the machine starts
- Spoil removed or reused on site
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Excavation is the highest risk part of this trade and it is the part most often underestimated in a cheap quote. An unsupported face in loess can stand perfectly well for days and then fail without warning once it dries out or gets wet, which is exactly the property that makes people underestimate it.
Working a retaining wall excavation face safely in loess
Batter or bench, do not just cut vertical
A vertical face is only safe if it is supported. Battering the face back to a stable angle, or benching it into steps, is how an open excavation is kept safe while the wall is built.
Work in sections
On a wall replacement we open a section, build it, backfill it and move on rather than exposing the whole run. It takes longer and it is the reason the bank stays where it is.
Loess is deceptive
Undisturbed dry loess holds a near vertical face with high apparent cohesion. Wet, that changes. Never judge a Port Hills face by how it looks on the day it was cut.
Locating services before a retaining wall excavation
Every job starts with service location. Power, gas, water, fibre and stormwater all run where somebody put them rather than where the plan says, particularly on older properties and along boundaries.
We locate before we dig and hand dig where anything is close. Hitting a service is expensive at best and dangerous at worst.
Spoil from retaining wall excavation, reused or removed
A retaining wall excavation generates more material than most people expect, and where it goes is a real cost line. Reusing it on site as fill is cheapest where it is suitable, but topsoil and organic material cannot go behind a wall.
We tell you in the quote whether the spoil is going or staying, because discovering six truckloads was not allowed for is not a good day for either of us.
Excavation at a glance
- Face support
- Battered or benched, worked in sections rather than opened at once
- Loess
- Holds a near vertical face dry, behaves very differently wet
- Services
- Located before digging, hand dug where anything is close
- Spoil
- Reused on site where suitable, otherwise removed and priced
- Not reusable behind a wall
- Topsoil and organic material
- Plant
- Sized to the access, which on hill sites is the limiting factor
Excavation in Christchurch: common questions
Why can you not just cut a vertical face?
Because an unsupported face fails without warning, especially in loess once moisture changes. Battering or benching is how it stays safe.
Do you locate services?
Yes, before any machine starts, and we hand dig where anything is close.
What happens to the spoil?
Reused on site where it is suitable, otherwise removed. Either way it is in the quote.
Can the dug material go back behind the wall?
Sometimes, but not topsoil or organic material, and it has to be placed in compacted layers.
How close to a boundary can you excavate?
Close, provided the face is supported and the neighbour's ground is not undermined. What matters is not the distance but whether the excavation falls within the zone of influence of anything on the other side. On tight sites we do a pre construction condition survey of the neighbouring property so there is no argument later.
Do you locate underground services before digging?
Every time, before any machine starts, and we hand dig where anything is close. Power, gas, water, fibre and stormwater all run where somebody put them rather than where the plan says, particularly on older properties and along boundaries.
Can the excavated soil be reused as backfill?
Above the drainage zone, often yes, provided it is not topsoil, not organic and not saturated clay, and provided it is placed in compacted layers rather than pushed back in. In the drainage zone directly behind the wall it never can be, because that zone has to be free draining aggregate.
Recent Christchurch jobs
Boundary wall between us and the neighbour on a new build. Sorted the levels, the consent question and the fence on top in one job. Turned up when they said and left the site clean every night.
Builder here. I use them on subdivision work because the paperwork comes back complete. PS1 up front, PS4 at the end, no chasing.
Wall failed after the big rain and took part of the bank with it. Made safe within two days and rebuilt a month later with real drainage behind it.
Terraced the back lawn into two levels. Fast, tidy, fair price, and the drainage was done properly.
Get a price for excavation in Christchurch
Free site visit, a fixed written quote, and a straight answer on what the wall actually needs.
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