Civil engineering

What interviewers look for

• You can take quantities from a drawing and turn them into a priced BoQ, with units, rates and a contingency, and explain every line.
• You know what makes concrete strong or weak on a real site: the mix, the water, compaction, the cover to the steel, and curing.
• You inspect before you approve: a checklist before each pour, test results on file, a site diary, and photos with dates.
• You can use a level or total station and AutoCAD well enough to set out a building and update a drawing, and you say honestly what you have not used.
• For WASH posts: you understand how a borehole, pump, tank and pipe network work together, and what to test before handover.

Questions they ask

1. 1“How would you prepare a BoQ for a two-classroom block from the drawings?”

   Why they ask: Whether you have a method: measuring each element from the drawings, using the right units, pricing with current local rates and checking the total. Many candidates only copy an old BoQ.

   How to answer

   • Name the order you follow: preliminaries, substructure, superstructure, roof, finishes, doors and windows, electrical and plumbing, external works.
   • Show you know the units: m³ for concrete and excavation, m² for blockwork, plaster and paint, kg or tonnes for steel, a count for doors.
   • Explain where your rates come from: recent quotations from suppliers near the site, labour rates, transport to site, and a contingency.
   • End with how you check it: a second person reviews it, and you compare the cost per m² with similar buildings.

   I start from the architectural and structural drawings and measure element by element: excavation and foundations, the ground slab, blockwork, columns and beams, the roof, then finishes, doors, windows and services. I keep the units strict: cubic metres for concrete, square metres for walls and plaster, kilograms for steel from the bar schedule. For rates I ask two or three suppliers in the nearest town for current prices and add transport, because moving blocks to a rural site can change the cost a lot. I add the contingency the client agrees, and my senior engineer reviews it before it goes out.

2. 2“What do you check before you allow a concrete pour?”

   Why they ask: Whether you understand that a pour cannot be undone. The panel wants a clear pre-pour checklist, not “I make sure everything is fine”.

   How to answer

   • Formwork: right size and level, strong props, clean inside, and tight joints so the cement paste does not leak.
   • Steel: bar sizes, number and spacing against the drawing, laps, ties, and spacers so the steel has its cover.
   • Materials and plan: cement, sand, aggregate and clean water on site, a working vibrator, enough workers, and a curing plan for afterwards.
   • Sign it: a pour checklist signed before work starts, and cubes taken during the pour.

   Before any pour I walk the area with the contractor's foreman and a checklist. I check the formwork dimensions, levels and props, and that it is clean inside. Then the steel: bar sizes and spacing against the drawing, lap lengths, tied joints, and spacer blocks under the bottom bars. On a school slab in Burao I found the spacers missing along one side, so we lifted the mesh and fixed it before we poured. I also confirm the materials, the vibrator and the curing plan, then I sign the checklist and we take cubes during the pour.

3. 3“The 7-day cube results came back lower than expected. What do you do?”

   Why they ask: Whether you stay calm, check the facts and follow the process, instead of ignoring the result or ordering demolition the same day.

   How to answer

   • Explain that the 7-day strength is only part of the 28-day strength, so compare it with the expected 7-day value, not the final one.
   • Check the records: which pour, the mix, any water added, and how the cubes were made, stored and cured.
   • Hold further pours with the same materials until you know the cause, and inform your senior engineer or the designer.
   • Wait for the 28-day results; if they also fail, the designer decides on further tests such as cores, strengthening or removal.

   First I would not panic, because concrete keeps gaining strength and the 7-day result is only part of the 28-day strength. I would compare it with the expected 7-day value for that mix. Then I check the pour records: the batch, any water added on site, and how the cubes were made and cured, because cubes left in the sun can give low results. I would pause pours with the same cement or aggregate, inform my senior engineer, and wait for the 28-day results. If those fail too, the structural engineer decides on cores or other tests.

4. 4“How do you know the soil is good enough for the foundations?”

   Why they ask: Whether you know the basics of soil and foundations, and when to call the design engineer instead of guessing.

   How to answer

   • Start with what the design assumed: the soil report, or the bearing capacity written on the drawings.
   • On site: dig trial pits, check the depth to firm ground, and look for fill, loose sand, soft clay, water, or cracks in clay.
   • If the ground is different from the design, stop and report to the designer before any concrete goes in.
   • Under slabs and roads: compact the fill in thin layers at the right moisture, then test it.

5. 5“How would you set out a building on a new site?”

   Why they ask: Whether you can move a drawing onto the ground accurately. A building set out in the wrong place is one of the most expensive mistakes on a site.

   How to answer

   • Start from the reference points: the boundary, the benchmark for levels, and the grid on the drawing.
   • Use a total station, or a tape and a level; fix corner pegs and profile boards outside the digging area.
   • Check the corners are square with the diagonals or the 3-4-5 method, and check levels back to the benchmark.
   • Have a second person check it and sign before excavation starts.

   I start by finding the benchmark and the boundary pegs, and I confirm them with the client's surveyor. With the total station I set out the main grid lines, then fix profile boards outside the trench area so the lines survive the digging. I always check the diagonals: if both diagonals of a rectangle are equal, the corners are square. On small buildings I also use the 3-4-5 method with a tape. I carry levels from the benchmark, record everything, and ask my supervisor to check before we excavate.

6. 6“A detail on the drawing cannot be built as shown. What do you do?”

   Why they ask: Whether you respect who is responsible for the design, and whether you record changes so the as-built drawings tell the truth.

   How to answer

   • Do not change a structural detail yourself on site; send the designer a written query (RFI) with a photo or sketch.
   • Suggest a solution if you have one, but wait for written approval.
   • If it changes cost or time, treat it as a variation, agreed in writing before the work is done.
   • Mark the change in red on the site copy of the drawing, so the as-built drawings are right at handover.

   On a clinic project the drawing showed a drainage pipe passing through a column footing. I stopped that part of the work, took photos, and sent a written query to the design engineer with a sketch moving the pipe half a metre. She approved it by email the next day. Because it added a short length of pipe, I recorded it as a variation with the project manager's approval. I marked the change in red on our site drawing, and it went into the as-built drawings at handover.

7. 7“You are supervising a borehole with a solar pump and an elevated tank. What do you check before handover?”

   Why they ask: For WASH posts: whether you know the whole system and the tests that prove it works, not only the building work.

   How to answer

   • The borehole: drilling log, casing and screen depths, gravel pack, development, and a pumping test that sets a safe pumping rate.
   • Water quality results from a laboratory before people drink the water.
   • Pump, solar and tank: the pump set below the lowest pumping water level from the test, the tank stand inspected, the pipeline pressure tested, and no leaks.
   • Handover: as-built drawings, the O&M manual, spare parts, and training for the water committee.

   I would start with the drilling log and the pumping test report, because they tell me the safe yield and where the pump should sit. I check that the pump is installed below the lowest pumping water level, that the solar array matches the pump, and that the water quality results are back from the lab. Then I fill the tank, pressure test the pipeline and walk every tap stand looking for leaks. At handover I give the water committee the as-built drawings and the O&M manual, and train them on cleaning the panels and reading the water meter.

Example answers are in English, the language most panels use. Say it in your own words.

Topics to revise

• Bill of Quantities (BoQ)A list of every work item with its unit, quantity, rate and amount, measured from the drawings. Panels ask you to find errors in a BoQ, explain where a rate came from, or measure one item, such as the concrete in a strip footing.
• Concrete mix and water-cement ratioNominal mixes such as 1:2:4 (cement : sand : aggregate, by volume) are common on small sites; larger works use a designed mix. More water makes concrete easier to place but weaker, so “the mason added water” is a classic interview question.
• Slump test and cube testThe slump test uses a metal cone to check how workable fresh concrete is. Cubes are made during the pour, cured in water and crushed at 7 and 28 days; the 28-day result is compared with the specified strength.
• Curing in hot weatherConcrete needs moisture to gain strength. Keep it wet for at least seven days with wet hessian, plastic sheets or water ponded on slabs. In hot, dry, windy weather start curing early and avoid pouring in the hottest hours.
• Reinforcement: cover, laps and spacingCover is the concrete between the steel and the surface; it protects the steel from rust and fire and is kept with spacers. A lap joins two bars and has a minimum length set by the specification. Check bar sizes and spacing against the drawing before every pour.
• Steel weight (d²/162)The weight of a round bar in kg per metre is about the diameter in mm, squared, divided by 162. A 12 mm bar is about 0.89 kg/m and a 16 mm bar about 1.58 kg/m. You use it to turn a bar bending schedule into kilograms or tonnes.
• Foundations (strip, pad, raft)Strip footings carry walls, pad footings carry columns, and a raft spreads the load of the whole building on weak ground. Know that the foundation must reach firm ground and that the design assumes a certain bearing capacity.
• Compaction and CBRFill under slabs and roads is compacted in thin layers at the right moisture content. The Proctor test gives the target density, a field density test checks it on site, and CBR measures the strength of road layers.
• Setting out and levellingMoving the drawing onto the ground with a total station, tape and profile boards, and carrying levels from a benchmark with an automatic level. Know reduced levels and how to check squareness with diagonals.
• AutoCAD and Civil 3DAutoCAD for plans, sections and details, with layers and the right scale. Civil 3D builds a ground surface from survey points, then road alignments, profiles, cross-sections and cut-and-fill volumes. Say honestly which parts you have used.
• Borehole design and pumping testA borehole has casing, a screen where water enters, and a gravel pack around it. After drilling it is developed and pump tested: a step test and a constant rate test show the safe yield and the drawdown, which decide the pump size and depth.
• As-built drawingsDrawings that show what was really built, including every change. During the work, changes are marked in red on the site copies; at the end they are drawn up properly. They are needed for maintenance and extensions, and are often a condition of handover.

Practical tasks you may get

1. 1Written test (60–90 minutes), quantities by hand: concrete in footings and slabs, blocks per square metre, steel weight from a bar schedule, simple levelling. Practise with a calculator, and always show the formula, the working and the units, because marks are given for method.
2. 2BoQ or drawing review: a bill or drawing with planted mistakes, such as a wrong unit, a total that does not add up, or a beam size that disagrees with the section. Practise by checking an old BoQ of your own line by line and looking for exactly these errors.
3. 3AutoCAD test (30–60 minutes): draw a simple floor plan or foundation layout with layers, dimensions and text, and plot it to scale. Practise with a timer before the day so you are not slowed down by commands you rarely use.
4. 4Site walk or photo test: they walk you round a site or show photos and ask what is wrong. Look for exposed or rusty steel, missing spacers, honeycombed concrete, dry slabs not being cured, an unsupported trench, and workers without PPE.

Portfolio questions

• Bring two or three drawings you made yourself, and be ready to explain the layers, the scale and one decision you took.
• Show dated site photos of stages you supervised, such as steel before a pour, formwork and the finished building, and say which part was your responsibility.
• If you show a BoQ or report from an employer, ask permission first and remove prices or client details that are confidential.

Mistakes to avoid

• Giving numbers without units, or mixing m² and m³ in the written test.
• Saying extra water on site is fine because it makes the concrete easier to work.
• Claiming Civil 3D, ETABS or SAP2000 when you have only seen them in a class.
• Changing a structural detail on site without the designer's written approval.
• No records to prove the work: no site diary, no test results, no dated photos.
• Quoting a rate from memory or an old project without saying where and when it came from.

Quick check

5 questions. Answer each one to see the explanation.