Which factors influence active earth pressure on a retaining wall?

Which factors influence active earth pressure on a retaining wall?

• A. Depth of water table only.
• B. Ambient temperature and humidity.
• C. Wall movement, soil friction angle, wall height, and backfill properties.
• D. Concrete strength and reinforcing steel yield.

Answer: (C)

Active earth pressure is the lateral pressure that soil can mobilize on a retaining wall as the wall moves away from the backfill. The amount of that pressure depends on four interrelated factors: how far the wall moves, the soil’s friction angle, the wall height, and the backfill properties. When the wall moves, the soil’s shear strength is mobilized and the active state develops, so movement directly controls how much pressure can be generated. The soil’s friction angle matters because higher friction resists sliding; increasing phi’ tends to reduce the active pressure, since the soil can mobilize more shear strength before failure. Wall height matters because the lateral pressure distribution is roughly triangular with height, so taller walls experience a larger total force. Backfill properties, including unit weight, moisture content, compaction, and drainage, set the driving stress and how much of that stress the soil can sustain; heavier or less-drained backfill increases lateral pressure, while well-drained, lighter backfill reduces it. Depth of the water table affects pore pressures but is not the sole determinant of active earth pressure, and factors like ambient temperature, humidity, or concrete strength and reinforcement do not govern the active lateral pressure on the soil–wall interface.

Active earth pressure is the lateral pressure that soil can mobilize on a retaining wall as the wall moves away from the backfill. The amount of that pressure depends on four interrelated factors: how far the wall moves, the soil’s friction angle, the wall height, and the backfill properties.

When the wall moves, the soil’s shear strength is mobilized and the active state develops, so movement directly controls how much pressure can be generated. The soil’s friction angle matters because higher friction resists sliding; increasing phi’ tends to reduce the active pressure, since the soil can mobilize more shear strength before failure. Wall height matters because the lateral pressure distribution is roughly triangular with height, so taller walls experience a larger total force. Backfill properties, including unit weight, moisture content, compaction, and drainage, set the driving stress and how much of that stress the soil can sustain; heavier or less-drained backfill increases lateral pressure, while well-drained, lighter backfill reduces it.

Depth of the water table affects pore pressures but is not the sole determinant of active earth pressure, and factors like ambient temperature, humidity, or concrete strength and reinforcement do not govern the active lateral pressure on the soil–wall interface.