Civil engineering interviews test your knowledge of structural design, concrete technology, soil mechanics, surveying and site practice, often with reference to Indian Standard codes. These questions suit site engineers, design engineers and PSU or government recruitment interviews.
Fundamentals, definitions and simple scenarios. Good for freshers and warm-ups.
It is the compressive strength of 150 mm concrete cubes tested at 28 days below which not more than 5% of test results are expected to fall. The grade name gives it directly: M20 concrete has a characteristic strength of 20 N/mm². IS 456 sets the minimum grade by exposure condition, for example M20 for mild exposure in reinforced concrete.
Dead loads from the self-weight of the structure and permanent parts; live or imposed loads from people, furniture and equipment; wind loads; seismic (earthquake) loads; snow loads in some regions; and effects of temperature, shrinkage and settlement. In India these are covered by IS 875 (Parts 1 to 5) and IS 1893 for earthquakes, and are combined using load factors in design.
Curing keeps concrete moist and at a suitable temperature so that cement hydration continues, which develops strength and durability and reduces shrinkage cracking. Without curing, the surface dries out, becomes weak and porous, and cracks. Methods include ponding, wet coverings, sprinkling and curing compounds. IS 456 recommends at least 7 days of moist curing for ordinary Portland cement, and longer for blended cements or in hot, dry weather.
It depends on the ratio of the longer span to the shorter span. If the ratio is greater than 2, the slab is one-way: it bends mainly along the short span, so the main reinforcement runs in that direction with distribution bars the other way. If the ratio is 2 or less, the slab is two-way: it bends in both directions, so main reinforcement is provided both ways.
Applied problems, trade-offs and questions about your own projects.
The water-cement ratio is the weight of water divided by the weight of cement in a concrete mix. A lower ratio gives higher strength and durability and lower permeability, but makes concrete less workable. Typical structural concrete uses about 0.4 to 0.55. Adding extra water on site to improve workability weakens the concrete, so superplasticisers are used instead.
The working stress method assumes elastic behaviour and keeps stresses under service loads below permissible values, applying a factor of safety only on material strength. The limit state method designs for both the limit state of collapse (strength) and the limit states of serviceability (deflection and cracking), using partial safety factors on both loads and materials. It is more rational and economical, and is the primary method in IS 456:2000.
On fresh concrete: the slump test for workability, plus the compaction factor, Vee-Bee and flow table tests. On hardened concrete: the cube compressive strength test at 7 and 28 days, split tensile and flexural strength tests, and non-destructive tests such as the rebound hammer and ultrasonic pulse velocity. Core cutting is used when the strength of an existing structure is in doubt.
Shallow foundations, such as isolated footings, combined footings, strip footings and raft (mat) foundations, are used when good bearing soil is near the surface. A raft is used when the soil's bearing capacity is low or loads are heavy, to spread the load and reduce differential settlement. Deep foundations, such as piles and well foundations, are used when good soil is far down, loads are very heavy, or for bridges over rivers.
System design, deep internals, leadership and tough follow-ups.
I study the drawings and specifications, then take off quantities item by item: earthwork, PCC, RCC (concrete, steel and formwork), masonry, plastering, flooring, doors and windows, finishes and services. Each item is priced using the schedule of rates or a rate analysis covering materials, labour, equipment, overheads and contractor's profit. The abstract of cost adds these up, with contingencies and work-charged establishment added.
First I identify the type of crack from its pattern, location and width: plastic shrinkage, drying shrinkage, thermal, settlement or structural. I monitor whether it is growing, using tell-tales or crack-width gauges. I investigate the cause by reviewing the design, checking workmanship and materials, testing the concrete non-destructively and, if needed, investigating the soil. Non-structural cracks are sealed or injected with epoxy; structural problems need strengthening such as jacketing or fibre-reinforced polymer wrapping.
Terzaghi's principle states that effective stress equals total stress minus pore water pressure: σ' = σ − u. The strength and compressibility of soil are controlled by effective stress, not total stress. When pore water pressure rises, for example during heavy rain or an earthquake, effective stress falls, which can cause slope failures or liquefaction, where saturated sandy soil temporarily behaves like a liquid.
For quality: a QA/QC plan, testing of incoming materials, cube tests, inspection checklists and approvals at each stage (for example, before concrete is poured), method statements, and documented corrections of non-conformities. For safety: PPE for everyone, safe scaffolding and edge protection, work permits for high-risk tasks such as working at height, daily toolbox talks, safety inspections and incident reporting, with the authority to stop unsafe work.