How To Level a Backyard with Uneven Ground – Bumps, Holes, Lumps and Dips
There are many reasons why you would want to level your backyard. Maybe you just bought a new single-family home in a nice neighbourhood, but the backyard was in bad shape, with bumps, holes, lumps and dips all over the place. Maybe you have been looking to renovate and flatten your yard for a long time, but you were not sure that you could do it on your own, and you thought hiring a professional landscaper might be expensive, so you left it as it is. Levelling your yard is not a hard job if you are a DIY person with time on their hands. Neither is it expensive because the equipment you need can be hired on affordable daily rates.
The first step in levelling your backyard is clearing the ground of all rubbish, growths and obstacles that you don’t want. This includes removing litter, grass, bushes, shrubs, hedges, trees, leaves, any type of vegetation and grubbing up roots. Cart away the rubbish to a nearby dump. After clearing the site, remove big stones that are clearly visible and distorting the landscape.
If you have to dig up the vegetation and roots, make sure that you call the Dig Safe Number 811 in your state to get all utility operators to identify and mark the positions of underground services on your private property. Hitting a utility line in the course of digging is hazardous and you may be fined for the damage. To avoid problems with utility lines, dig safely and cautiously around the markings.
Clearing the site of all vegetation, shrubs, bushes etc, gives you a true picture of the natural ground and terrain. The terrain is the feature that we want to level, so you have to analyze its gradient or topography.
Setting Out Levels on Site with Profile Boards and Stringlines
Setting out levels on your backyard is easy because you already have existing structures like your house, garage, boundary fence, inspection chambers or street curb that you can use as a bench mark or reference point for marking the positions of horizontal and vertical lines. Horizontal lines are marked by stringlines made of nylon or cotton string, vertical lines (including corners) are marked by sharp wooden pegs or stakes which are hammered into the ground.
The best option is to use the house ground floor level (plinth level) as the reference point because it has its baseline with the breadth of the backyard area. Check to see if the foundation plinth is visible on the outer side of the external walls. The foundation plinth is usually visible on elevated houses with concrete floor slabs. On houses with timber floors and stud walls, the plinth level might be hidden and covered by wall cladding. The plinth might also be hidden by bushes, grass, shrubs and hedges. Over time, weather elements can deposit soil, leaves and organic matter on the sides of the walls, submerging the plinth line. If this is the case, you can remove the deposits using a shovel to expose the plinth.
To set out profiles and stringlines, start by driving two pegs or stakes into the ground. The first peg must be driven into the ground at the corner of the existing house. Using a spirit level, make sure the peg is plumb (vertical). If you are using a profile board (a set of two or more pegs attached by a ledger or batter board), make sure the batter board is horizontally level using a spirit level. The profile boards installed on all points on the ground must have their batter board tops level with each other. In this case, use a high precision levelling tool like a laser or optical level to see if the batterboard tops are in the same horizontal line. Drive in the second peg into the ground on the other end of the wall elevation, then set a stringline between the two points, making sure the string is taut.
Since you are working on uneven ground with bumps and dips, you will need to set profile stringlines on all four sides of the backyard space. This is assuming that your yard or residential lot is rectangular in shape. If your residential lot is polygonal or irregular in shape, then you should set stringlines on all sides.
Slotting, Levelling and Compacting the Ground
The next step after fixing in the profile boards and stringlines is dividing your backyard into sections or rows which are separated by excavated slots (300 to 1000mm wide) at 4 to 5 metre centre to centre spacing. Slots are grooves or narrow trenches which are dug down to the desired finished level (subgrade level). Previously, we mentioned that the tops of batter boards for each and every profile board must be level with each other. This horizontal level line between the profile boards is known as the line of sight. To ensure that the workers, scarifying machine or bull dozer doesn’t dig too deep beyond the subgrade level or too high above the finished level, you must use a traveller profile board which is placed vertically on the slot bottoms. The travelling profile board has a fixed height which is equal to the height between the line of sight and the subgrade level. This board is used as a yardstick or measurement tool for checking vertical deviations from the line of sight. As you are digging slots and preparing the final finished level, check to see that the travelling profile ledger has its top level with the line of sight. If the travelling profile is below the line of sight, you have dug too deep, so you may need to fill the slot with excavated earth. If the travelling profile is higher than the line of sight, you have dug too shallow, so you must dig a little bit deeper to reach the subgrade level.
After digging slots, you can proceed to excavate the site to strip level using a pick or hired mini bulldozer. Alternatively, if the soil is light and medium, and free from rock, you can use a scarifier to break up the topsoil at a depth of up to 300mm. This involves wetting the ground if the earth is dry and hard, scarifying to a suitable depth, breaking down oversize material, adding suitable material where necessary, and compacting the ground in 150mm layers to 95% Mod AASHTO density.
The pre-dug slots on prepared ground provide the bulldozer operator with a suitable reference depth to be stripped, so he will set the blade to that depth, ensuring a level stripped surface.
After excavating the site to strip level, the ground will look fairly flat but not to perfection. There will be pockets, holes and sunken areas that you have to fill with excavated material, as well as humps and lumps of soil that you have to break up into smaller particles and distribute evenly on the ground. A rake, shovel and hoe will be useful in this regard. Use a rammer to compact the soil after filling in the holes.
Once the holes are filled and lumps are broken, your next step is wetting and compacting the ground with a vibratory roller to 95% Mod AASHTO density. You will need to add more soil from excavated material stored on the site, compacting it in 150mm layers until you have firm and stable ground.
Ground Cover and Protection
Now that you have a flat and even surface, it’s not recommended to leave it bare and exposed to the elements. You could cover all ground with the exception of cultivation areas for plants, vegetables, trees, shrubs and hedges. Bare ground is susceptible to soil erosion caused by rain, wind and surface runoff. There are many soil covering materials that you can use to protect your yard from soil erosion. This includes lawn, ground cover plants, brick, stone and precast concrete pavers.
Design of Backyard
Even though you want a flat and level backyard, your yard should be designed to properly and efficiently drain surface water runoff away from the house and into a drainage channel. The problem with a flat and level surface is that it has poor drainage qualities, causing stagnant puddles of water after a rainfall. If your yard is to meet civil engineering requirements, it must be slightly sloping towards a drainage channel to prevent flooding and pooling of water in your yard. Waterlogged yards are a great mess, and poor site drainage may reduce the value of your home.
If you have a yard that is sloping towards the house on any wall elevation, then it might be a good idea to flatten the yard and reverse the slope to reduce the water pressure against your walls and the possibility of water seeping through.
The average lawn yard size in the USA ranges from 4386 square feet (Nevada) to 73,979 square feet (Vermont). Let’s say you have a house in South Carolina where the average lawn yard size is 17,320 sf and the lot size is 19,166 sf. If your house is 82ft long x 42.65ft wide and sitting on a square lot size 138.4 x 138.4 ft, then your total yard size will be about 15657 square feet or 1740 square yards. So we have to flatten this area (1455 square metres in metric units).
Tools and Machines You Will Need for Levelling Your Backyard
You will need the following tools for the job:
Setting Out Levels on Site:
Timber profile boards or pegs,
Nylon string for stringlines,
Laser or Optical Level,
Slotting, Levelling and Compacting the Ground:
Backfill tamper or rammer,