Here at MLS Contractors, we detail the basic guidelines for ground preparation, which are essential for a large proportion of our work.
The initial step, regardless of the size of your concrete pour, is to adequately prepare the ground before commencing the project. After obtaining all necessary planning permissions, utilise wooden pegs and string to restrict the designated area for the concrete pour, ensuring an additional 75mm allowance for the formwork that secures the wet concrete during the drying process.
Subsequently, excavate the foundations to the specified depth: strip footings typically require excavation to undisturbed, stable ground, while individual footings and floor slabs necessitate additional depth for the sub-base (100mm) and damp-proof membrane (DPM), in addition to the concrete. If feasible, use a small mechanical excavator to expedite this stage. Clear the site of debris, stones, and vegetation before compacting the soil to create a level surface.
Once the sub-base is in place, compact it again. For most residential concrete footings, such as extension foundations, a 100mm layer of base aggregates suffices. Install a DPM, ensuring the edges are turned up to form a tray, overlaps are sealed, and joints are taped to shield the concrete from rising dampness and chemical exposure from groundwater while regulating moisture levels to enhance strength and prevent cracking.
Proceed to construct the formwork using sturdy 25mm timber planks to contain the concrete until it cures. The formwork should match the depth of the concrete slab design.
Verifying the evenness of the formwork using a laser or spirit level is crucial, as it dictates the final level of the concrete surface.
Ground preparation before foundation digging is a crucial phase in construction, ensuring that the site is ready for accurate measurements and stable foundations. Using a theodolite to set the foundation helps ensure precise alignment and levelling. Here’s our step-by-step guide on ground preparation, along with instructions on how to utilise a theodolite for setting out the foundation:
Step 1: Site Clearing – ground preparation
Remove Obstacles: Clear the site of any vegetation, debris, rocks, and existing structures. This may involve using bulldozers or manual tools.
Level the Ground: If the site is uneven, you may need to level it to ensure proper drainage and access for machinery and workers.
Step 2: Soil Investigation – ground preparation
Soil Testing: Conduct soil tests to evaluate soil type, bearing capacity, and any potential issues (like contamination).
Determine Foundation Type: Based on soil conditions and load requirements, decide on the type of foundation to be constructed (e.g., shallow, deep).
Step 3: Layout Preparation – ground preparation
Obtain Plans: Get the architectural and engineering plans for the project, including dimensions and specifications for the foundation.
Identify Reference Points: Establish reference points on-site that will be used for measurements. These could be existing structures, property lines, or control points established in earlier surveys.
Step 4: Setting Out with a Theodolite – ground preparation
Using a theodolite is essential for precise alignment and measuring angles on the site. Here’s how to set out using a theodolite:
Setup the Theodolite:
Place the theodolite on a stable tripod at an appropriate height to avoid obstruction of view.
Ensure its level by adjusting the three levelling screws until the bubble is centred in the level vial.
Establish a Benchmark:
Set out a benchmark (known elevation point) on the site using known reference elevations. This benchmark will help in achieving the correct elevation for foundation footings.
Mark the benchmark clearly for easy reference.
Measure Angles and Distances:
Using the engineer’s plans, set up any required angles between different foundation points. Input the angles and distances into the theodolite.
Align the theodolite to the first reference point and rotate the telescope to sight the next benchmark or marker using the horizontal and vertical circles on the device.
Mark Out Points:
Use wooden stakes or paint to mark the layout of the foundation on the ground. Ensure that all distance and angle measurements are accurately transferred to the site.
Verify that all marked points correspond with the construction plans.
Check Squareness:
Use the 3-4-5 triangle method to check that corners are square. Measure 3 units along one edge, 4 units along the other, and ensure that the diagonal between these two points is 5 units. Adjust as needed.
Step 5: Final Verification – ground preparation
Review Layout: After marking out according to the plans, have the engineer or site supervisor review the layout for accuracy.
Additional Measurements: Recheck distances and angles after marking. It’s better to identify any issues at this stage before excavation begins.
Step 6: Preparation for Excavation – ground preparation
Notify Utilities: Before excavation starts, contact utility providers to ensure that there are no underground utilities, and obtain necessary clearance.
Set Up Site Safety: Establish safety measures on-site to protect workers and ensure proper access for machinery.
Ground preparation before foundation digging is critical for ensuring a solid and stable foundation. Using a theodolite for layout assists in achieving high accuracy in measurements and alignment, which is essential for the success of the construction project. Always collaborate closely with a professional engineer throughout this process to uphold safety and compliance with building codes.
If you require any help with your next groundwork project, please contact Max Stevens here at MLS Contractors.
