Hi this is a follow-on from my Gabion
Retaining Walls video which was Part One of the Steep Driveway to Flat Driveway series.
During the early stages of our retaining wall investigation we knew we needed a tall
retaining wall that was about 2m in height. We also knew that we wanted a natural look
to the wall as we we live in a rural lane, we're surrounded by trees and hedges, it made
sense to keep it made from natural products. Other things to consider were the proximity to
the road, plus the space we had available for the driveway project and easy access to the wall
for any future repairs. We'd also seen a number of retaining walls in the local area that were
being pushed over by water pressure due to the lack of weak holes or render popping off due to
the wetness which we definitely wanted to avoid. The first option which i'm sure lots
of people investigate is a dense block wall or hollow block wall with reinforced rebar
and concrete down the centre. This would have required a structural engineer to get involved
due to the height we required, plus we knew that the finish in brick would be costly. Render
wasn't an option as we knew it would need regular maintenance due to the damp conditions.
Quotes we got were also very high between £10,000-£20,000. So we then looked at a more natural
sleeper retaining wall. We absolutely love the vertical sleeper look. However, you would need
to put a third of your sleeper in the ground and as we had already reached the chalk, rock
and flint layer due to the removal of the trees, digging a trench another meter down was just not practical. So we also looked at horizontal sleeper
walls. This could be an option, but they would require some sort of stabilization both with
vertical rebar attachments down into the ground and also horizontal securements across the backs
of the sleepers for the size of wall we were after. This is something we could do ourselves which
would save hugely on labour costs, however, at some point the sleeper wall would need to be
replaced - a sleeper would need to be replaced or even the whole wall would need to
be replaced once the sleepers had had enough. As the new garage wall would be near the
retaining wall we felt this was possible, but not likely a probable solution. It just wouldn't
give us the access that we would need to replace 2.5m length sleepers. So then I
started looking at gabion retaining walls. Now this system really did interest me. Especially
as they could be faced with natural materials to give us the look we wanted, but use any heavy
material placed inside them to do the retaining. Also they're a porous structure so the issue of
water heaving out the wall would be alleviated. There would also be nothing to rot over time
and therefore would have less maintenance than a sleeper wall. We had been saving the brick rubble
from our internal house renovations for the actual driveway base, but now we could
use them as a recycled infill for the gabions. It was also something else that I could build
alongside my husband without the need of getting contractors in except for the initial digging
of course. The only negative about the gabions is that they take up a lot more space than the
other retaining wall solutions, but as a 2m tall by 1m deep wall would still
leave us with around 8m of usable space for the garage in the driveway, we felt it
was okay to give over the extra space required. Now that I knew which type of retaining wall
I was going to build, I came up with a design that I mocked up in excel. I
had worked out what we needed was a 9m length approximately 2m tall with a short dog-leg return on the end, and then a 5m length section 1.5m tall. Then finally, a 4m section 1m tall. Even though the baskets would reduce in height, this is to take into account the gradient
uphill back towards the drive entrance. The actual level of the baskets is maintained at 1.5m for that second 9m section. Now that I had my design worked out, I started to
look at the gabion construction in more detail. I came across a highly informative website called
Fine Mesh Metals. The quality of their gabions, the abundance of sizes, the vast amount
of case studies and installation guidance easily persuaded me to
purchase my gabions from them. They were very helpful when I emailed them my
design and guided me on what I needed to purchase. I decided to go with 4mm fronts to
help reduce the sagging (as I was an amateur and needed all the help I could get!) I also had to be
very careful that I chose the correct orientation of the baskets and that they were opening on
the correct face. I wasn't sure whether to go with the traditional gabion limestone or give the
baskets a more modern look with Scottish cobbles, so I purchased the corresponding hand
laying partitions to allow me to do that. Lastly, I selected the helicoils and some lacing wire that came for constructing the baskets to join them together. The website explained that the baskets should start about 50cm below your finish level,
placed at a five to six degree angle against the soil you're retaining, and they
should be placed on firm level ground. For our retaining wall construction, we
knew that the completed driveway would finish part way up the gabions, so we started at
the ground level that resulted from the digger. When he removed the tree stumps, one rookie mistake we made is that the digger followed the line of our boundary
as opposed to cutting in square to the house. This means our retaining wall is at a
slight angle to the house and could lead to visual issues once the garage is squared up to
the house. But fast forward this didn't actually cause a huge issue visually and i think this was
down to the fact that the gabion wall was along our boundary. Not all boundaries are square to
your house so the the slight skew is forgiven. If the wall had been lower down, the retaining
part of our driveway for example, then it really should be square to the house otherwise it will
look funny once completed at an angle. To stabilize the ground further we
laid down the black woven geotextile. At this point, I wasn't clued up on
the different types of geotextile. We had used the black woven textile under the
house rubble as we had read it was perfect for stabilization under a driveway. However,
further research showed that the non-woven geotextile actually has better filtration
and drainage qualities for our purpose. Both are good for ground stabilization. So we
continued to use the black woven geotextile under the baskets to help prevent any uneven sinking
once the the 2m high structure is full. We also laid them on 20mm of pea gravel to
help even out any slight undulations and to aid drainage. The baskets arrived part made up. You
just need to lay them down flat and lift the sides and secure with short pieces of the lacing wire in multiple places up and down every join. So about every two or three squares
is ideal to help reduce the bulging. On the front face, we were using
the slightly thicker 4mm mesh panels and we secured the front face with the helicoils. They are
more visible than the little pieces of wire you can cut, but in our opinion a neater finish
to the front of the baskets. The 2m wide baskets also have a partition in the middle that
needs securing down the centre of the basket. Again with the helicoil at the front, but just the
pieces of lacing wire at the back. Lay out the baskets on the gravel and geotextile.
You must check that they're level across ways, but also have that five to six degree slope from
front to back, into the slope, to aid the retaining. We used a string line for the front of the
baskets to ensure they were all in line. Space had to be left behind the baskets for
the 80mm by 25m perforated drainage pipe that we had bought. This was wrapped in
a portion of that white non-woven geotextile. It was originally purchased at 4.5mx11m in size, but we cut it in half providing two 2.25mx11m pieces.
We wrapped the pipe in that 0.25m of spare geotextile laid it down the back behind
the gabions, securing it by placing some gravel on top. The geotextile prevents
the soil from entering the drainage pipe. The excess of the geotextile is then pulled up vertically to line the back of the gabion wall. Now the lower level of baskets in line, we then started filling the baskets. Initially
we used the traditional limestone fill to face the front, but I couldn't use the hand
laying partitions at the front of the basket as the limestone was just too large and uneven that you just could not use them. I used brick to support the
limestone against the front, but you could see the brick through some of the gaps. I quickly changed
my mind and I moved on to the Scottish cobbles. The cobbles we bought were 80-120mm in size
to ensure that they didn't fall through the holes. Before adding the cobbles, I
cut a piece of black woven geotextile just larger than the meter square for each basket. I then
placed it inside the basket against the partition- inside the main section of the basket not inside
the little thin partition itself. As I added the cobbles, I found that the partition moved out towards the middle of the basket. With the different sizes of cobbles, each one pushed out the base as it wasn't secured at the bottom. So, in order to stabilize the partition,
I realized that lining the back of the partition with the bricks first kept the
partition in its place and made it a nice tight fit for the cobbles. As i slotted them down
into the partition, about a third of the way up i would put a piece of wire tie from front
to back and then also left to right across the the length of the gabion. The 3mm lacing wire
was cut off the reel about 1.5m in length threaded through in the same place in each gabion. So four spaces up four spaces from the left and then from the other
side four spaces up four spaces from the right etc. Then loop the wire back through the way you
came catching the basket on the other side of the the space and twisting the wire itself around
to prevent it coming loose in the middle of the basket. If it wasn't tight enough, as it needs to be taut, take a set of pliers, grip the middle of the wire and
twist them inside the basket. This puts a kink in the wire enough
to make it taut and maintain the gabion shape. When it's filled, it's important to do
this both ways- though I have to say I did fewer side to side, it was mainly front to back
that were the most important to stop the bulge. Also remember to only use the helicoils along
the front joins of the baskets. In the beginning we we forgot about this. As I'd
only just ordered enough to do the fronts of the baskets, we ended up running out as we'd
started using them to secure the partitions! We had to get more delivered to finish off
the job. Of course you can't get them out once you fill the basket! So we just had to
accept that we'd used about 10 incorrectly. We filled the main portion
of the baskets with the brick rubble that we had from our house renovations. It
was old retaining walls, an old fireplace, broken concrete garden ornaments- anything that we could
find in the garden that was heavy and solid. However, we did have to order extra recycled brick
which we managed to find from Mainland Aggregates online. It was perfect- whole and part bricks. They don't
seem to offer the same product anymore, but I did see an alternative on their website called
Recycled Gabion Fill which is bits of brick concrete & asphalt. It's perfect if you're going
to use the facing partitions with the cobbles. Remember to make sure that the baskets are filled
right to the top before adding the second layer. The weight of the material in the top baskets
will sink down into the bottom layer and misshape the base of your gabion. The lid of the basket
of the bottom layer must also be secured well. Before adding that second layer remember to add 2-3 bits of lacing wire curled around along the three sides of the gabion basket and then the
helicoil along the front join to seal the lid. You must also secure that front helicoil into the
base of the second layer. I always left that as the last job. Once
we started the second layer, we then threaded the helicoils through so it attached the top basket
to the bottom basket and secured the lid of the bottom basket. You repeat filling the baskets on
the second layer exactly like you did on the first. As the second layer gets more stable and full, I
then started to back fill behind the gabions. The non-woven geotextile is pulled up taut behind the
basket so that soil cannot enter the gabions. If this isn't done, it could be washed through to the front of the basket and would look unsightly. There was the second layer of black woven geotextile, but it's not as good at filtration as the white non-woven geotextile. So it's important you
pull that up behind before you start your backfill. The 90 degree return baskets at the end of
the run also need to be placed at that 5-6 degree angle back into the bank. This meant I
had to support the right side of the baskets as you look
at them with other flat stones underneath to help keep the basket at the correct angle.
The section of baskets to the left of the main 2m high
section were definitely the most tricky part, I had to make sure that the tops of the baskets
were maintained at the same height as it was the bottom level that changed. I had to dig
this out by hand to make sure it was accurate. Unfortunately, I ran out of the brick fill for this
section so I tried something new and ordered a couple of ton of the 20mm shingle gravel with lots of large and small woven rubble bags. I would fill a bag 3/4 full and then tie it off with a cable tie. The large bags were too heavy to lift into place
so I started them off with a few scoops of gravel before placing them inside the basket to
finish filling them up. I used a couple of old black flower pots fitted together so that you
couldn't see the holes and I would just scoop it out of the tonne bag, then scoop it straight
into my rubble bags. I used the small bags to fill in the gaps between the large bags. I have to say
that the this method did make inserting the cross wires (bracing wires) much more difficult. I also found that the top smaller baskets did move when the earth was backfilled at a later date as they just
weren't heavy enough to retain the soil in situ. In hindsight, this would be fine for a small low
wall, but not for anything over 1m tall. It's also very important to tie the backs of
the baskets on an upper layer to the one below it at the back, which i had forgotten to do on
this lower level which contributed them moving forward when the earth was backfilled. Annoyingly,
my lovely straight line as seen in the original image now has a slight curve in it. The
solution to resolve this is to dig out the fill, push the baskets back, connect them properly
and then fill back, but I'll do that another day! With regards to finishing the tops of the
baskets, I didn't in the end lay another piece of black geotextile and a layer of cobbles on
the top. I found this look very uneven as there were dips in the layers of bricks underneath the
black geotextile and the cobbles of course are all different sizes. It also was a massive
leaf trap with all the hedges that we have and it would mean that I would have to
fish out leaves all the time from the gaps. So instead, what I plan to do, is lay some of
the white non-woven geotextile over the top. I will then put a thin layer of soil over that
geotextile and grow rockery-type plants near the edge so that they can drape over in time. This is
definitely a project for a keen DIY-er and you can do it! Remember, you just need that level starting
point, make sure you've got the correct angle slope back towards the soil, and then it's just a case
of filling them up and securing them properly. All together we spent approximately £5000 on that 20m long retaining wall at 9m by 2m tall and the rest at 1.5m tall. This included the tree removal, the man and his digger, the
gabion baskets and their bits, the drainage pipe, the geotextile sheets and bags, the
gravel, the recycled brick and the Scottish cobbles. That was a saving of between £5-£15000 because we did it ourselves! I hope you found this useful. Please feel free
to leave any questions in the comments and I'll do my best to answer them. Remember we're just
DIY-ers doing it our way in our set of circumstances. Thanks for watching. I hope to get the next
part of the Driveway Series out soon which will involve all the groundworks that
we did to get it level and retained.
