Mat settlement on expansive clay after a water leak in Vanadzor
A five-storey reinforced-concrete frame building in Vanadzor sits on a 1.2 m thick mat foundation at 2.5 m depth. The soil is a clay with plasticity index 35 and seasonal moisture variation. A buried water main beneath the parking area has leaked for at least two years. The building now shows diagonal cracks of 3 to 8 mm in ground-floor beams, separation of a facade panel, and a measured tilt of 1/450 toward the street. The owner wants to inject epoxy into the cracks and reopen the ground-floor clinic. The contractor proposes enlarging the mat without further investigation.
1. Diagnose the likely mechanism and decide whether the building is safe for the clinic to reopen.
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The leak has probably wetted the expansive clay under part of the mat, causing differential heave or softening and a rotation toward the street. The tilt of 1/450 exceeds common serviceability thresholds and, more importantly, the 3 to 8 mm diagonal beam cracks indicate structural distortion, not just finish damage. Reopening a clinic, which concentrates occupancy and adds live load, is not justified before a geotechnical and structural assessment. The assessment should include a level survey grid, crack monitoring over at least several weeks, boreholes with swell and consolidation testing on both wet and dry sides, and a foundation model using measured stiffness. The key question is whether the cracks are caused by settlement that has stabilized or by continuing movement. Epoxy injection alone would hide the symptom and could crack again; enlarging the mat without addressing the water source and soil movement could make differential effects worse.
2. Outline a remediation and monitoring sequence, including what must be verified before final structural acceptance.
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First, stop and reroute or repair the leak, then dewater and control surface drainage away from the mat. Install a monitoring array: precise levelling points, tiltmeters, crack gauges and piezometers. Second, excavate inspection pits to confirm mat thickness, reinforcement and soil condition. Third, design remediation according to the mechanism: if swelling is dominant, moisture control and a structural slab separation may be enough; if bearing loss is dominant, underpinning or compensation grouting may be needed. Any mat enlargement must be tied to the existing mat with designed dowels and checked for load transfer. Fourth, repair structural cracks only after movement has stabilized; use injected repairs where the crack width and cause are known. Final acceptance should require stable monitoring over a defined period, calculated crack widths within durability limits, tilt within an agreed threshold, and verification cores or non-destructive testing of repaired concrete.