Stability of Existing Structures – Which external factors can disturb it? For an existing building or structure, which of the following external changes in the environment can adversely affect its stability and serviceability?

Introduction / Context:
Structures are designed for a set of assumed boundary conditions and soil–structure interactions. Changes around a building can disrupt those assumptions, leading to distress, differential settlements, and even instability. Recognizing these external risk factors is crucial for asset management and urban construction planning.

Given Data / Assumptions:

• Existing structure with foundations bearing on soil strata.
• Neighbouring works or environmental changes may occur after construction.
• No special underpinning or protection unless implemented proactively.

Concept / Approach:

Rising water tables reduce effective stress and increase pore pressures, potentially lowering bearing capacity and causing buoyancy issues in basements. Traffic-induced vibrations can fatigue connections, loosen masonry, or aggravate settlement in loose granular soils. Mining or tunnelling creates ground movements and subsidence troughs. Adjacent excavations remove lateral confinement and can trigger basal heave or wall movements, transmitting settlements to nearby foundations.

Step-by-Step Solution:

Verification / Alternative check:

Case histories show façade cracking and tilt near deep excavations; structures near subway or traffic corridors often require vibration monitoring; groundwater control is a standard part of basement design and asset protection.

Why Other Options Are Wrong:

Each single choice omits other real hazards; “All” best captures the breadth of risks.

Common Pitfalls:

Underestimating cumulative effects; ignoring time-dependent consolidation after groundwater changes; failing to instrument adjacent structures during construction.

Final Answer:

All of the above