what is the ideal retaining system for your project this is a very specific question we
can talk about aesthetics and architecture but in this video i will just assume you are here because
you're building on a tight budget let's start with the question why you would need a retaining wall
well you might be building your house on a sloping ground and you need to cut and fill the side so
you can have a flat surface to build the pad of your house that means you will need a retaining
wall on the cut side and also one on the field side or you may want to cut a sloping ground next
to your place so you can have a space to install a trampoline for the kids and also a pool on the
other side the way i would choose a retaining wall is based on the soil type it could be clay
sand suit rock or a mix of them all the height to be retained the space i have available and the
logistics of the works in other words if there is access for machines the more area available
the cheapest the retaining wall will be and i'll explain you why now firstly the cheapest material
you can get is the one already existing on your side and that is the soil itself so if you have
sufficient space you can cut the slope at the soil angle of repose which is the angle where the soil
will hold itself and this angle is generally between 25 and 45 degrees for clay and sand
and voila your retaining wall is actually the soil itself it cannot get cheaper than that the second
cheapest option is not exactly a wall but a system that can be built with different types of walls
i'll let this one for the end of the video because we're gonna go through the types of walls that can
be used in this system and it will be easier to understand jumping to the third option there are
the gravity walls these types of walls rely on their self weight for stability here we
have a boulder wall a gabian wall or a crib wall a lateral earth pressure tries to overturn and slide
the wall and at the same time the self weight of the structure is counteracting these forces to
keep the system stable again area available might be a problem with this system walls over four
meters high will require a really wide basis which might be impracticable besides that since they are
really heavy structures the soil under the wall must have reasonable bearing capacity in terms
of costs of materials you can use a gabien wall which is a steel wire cage filled with rocks you
can use boulders and then if you use mastery blocks or concrete it gets a little bit more
expensive if you choose a concrete gravity wall you will need form work and all these things
will add up to the final cost of the project the fourth option would be a timber slipper retaining
wall which could be as cheap as the previous solution however i would only use this type of
retaining walls for landscaping like garden walls or just a feature wall the height limit is around
1.5 meters and they will last approximately 15 years or more depending on the timber treatment
if you're looking for something similar that will last longer you can go for a concrete
sleeper retaining wall this system is comprised of concrete slippers spanning horizontally between
steel posts which are cast into a board pier it's one of the thinnest retaining walls you can get
if your goal is to maximize the use of your land and you can possibly go as high as six meters if
you use a really robust design but just remember the higher you go the deeper the board piers needs
to go therefore if you're on a rocky side for example it might be impracticable to dig holes
deep enough in terms of engineering the lateral earth pressure will put the concrete slippers
into bending which in turn will transfer these forces to the ub or uc steel posts these posts can
deliver out of a concrete board pier which should be embedded deep enough into the soil to resist
the bending moment by passive pressure the steel posts can go all the way down the board pierce
or a cheaper option would be lapping the steel post with reinforcement the next
option is reinforced concrete mainstream can deliver retaining wall this system consists of
a reinforced concrete footing which anchors the wall against overturning and sliding
and a stem of concrete mastery blocks the stem is reinforced with steel bars placed vertically to
resist bending moment and horizontal bars for cracking control all blocks are filled with a
semi-fluid concrete known as grout walls over 2.2 meters high will require a portion of the stem to
be 209 wide blocks and for walls over 4 meters high we would be looking to add some sort of
buttresses or counter forts spaced a length equal or less than the wall height depending on the side
that your property is located you might have the heel extended under the soil or you might have the
toe extended in front of the stem usually having the heel extended under the soil is preferable
as the weight of the soil will help to prevent overturning and sliding on the other hand if the
toe extends in front of the stem there is no soil to counteract the overturning and sliding forces
therefore depending on the height of the wall and type of soil you might have to build a base
key to prevent sliding this wall is designed as a cantilever beam fixed to the concrete footing
you will have to check for overturning sliding and soil bearing pressure reinforced concrete
mainstream basement walls are also another good use for concrete blocks so let's imagine you're
building a concrete slab on top of a retaining wall and this concrete slab might be able to
restrain the top of the wall and prevent movement so now the wall is designed as a simply supported
beam instead of a cantilevering and we can use a strip footing instead of a large typical retaining
wall footing you will have to ensure that the base and top slab can transfer the reactions and really
restrain the system a timber floor for instance might not be able to restrain the top of the wall
another important point to consider with basement wall is that they need to be propped until the
concrete slab has achieved its full strength in the case you cannot prop the wall you're better
off designing a normal cantilever retaining wall by the way guys i'm putting together another ebook
where i go through the actual design of some of these retaining walls step by step a complete
design you know footings and everything else so stay tuned and i'll let you know when it's ready
and finally the second option that i left for the end of the video which is not exactly a wall but
a series of walls they are the tiered walls or cascading walls in this system the walls will be
stacked one behind another so instead of building a single super high wall which could be quite
intimidating in a normal environment you would be building a series of small walls again space could
potentially be an issue especially because there needs to be a minimum distance from wall to wall
so that the walls above do not surcharge the walls below otherwise you will have to design these
walls below to take the extra loads let's use some numbers to understand why this system might be
more advantageous when we work out the lateral earth pressure we know that the load increases
uniformly from top to bottom forming a triangle and the pressure is the density of the soil
times the earth pressure coefficient k times the height of the wall the bending moment diagram for
a cantilever beam subjected to triangular loading is a curve like this one and the maximum bending
moment is given by w squared divided by six that means w times the height of the wall squared
divided by 6. if we substitute w for the lateral earth pressure the factor height is now to the
power of 3. in other words if we double the height of the wall the bending moment we need to design
this wall for will be multiplied by a which means more material and larger structural elements in
the project anyway this was just a fun way that i wanted to show you that you can actually analyze
prices by running simple equations obviously you would have to have a chat with your contractor and
confirm the actual costs behind building an extra role but in terms of engineering the numbers don't
lie and it would be cheaper there are a lot more types of retaining walls out there a few of them i
didn't mention in this video because they require a more specialized design and they're usually more
expensive and not worth it for smaller projects thanks again for watching if you learned something
new here give the video a like and subscribe to the channel and i will see you next time