Lateral earth pressure is primarily caused by the gravitational forces acting on the soil mass, which result in the soil particles exerting pressure on each other and on any structure or object in contact with the soil.

The magnitude of lateral earth pressure is influenced by various factors, including the soil type, soil density, and depth of the soil. Different soil types exhibit different frictional and cohesive properties, which affect the magnitude of lateral earth pressure. Soil density also plays a role, as denser soils exert greater pressure. Additionally, the depth of the soil influences the magnitude of lateral earth pressure, as the weight of the overlying soil contributes to the pressure exerted.

Active earth pressure is the pressure exerted by the soil on a structure that is moving away from the soil, such as a retaining wall that is rotating or sliding. Passive earth pressure, on the other hand, is the pressure exerted by the soil on a structure that is resisting movement, such as a retaining wall that is fixed in place.

Rankine's earth pressure theory is commonly used for the design of retaining walls due to its simplicity and ease of application. It assumes that the soil is cohesionless and fails along a plane of rupture. Rankine's theory provides equations for calculating both active and passive earth pressure.

A surcharge load applied on the soil surface increases both active and passive earth pressure. The increase in active earth pressure is due to the additional weight of the surcharge, which increases the gravitational forces acting on the soil mass. The increase in passive earth pressure is due to the increased resistance provided by the surcharge, which prevents the soil from moving away from the structure.

Weep holes are small openings provided in a retaining wall to allow water to drain from behind the wall. This prevents the buildup of hydrostatic pressure, which can lead to the failure of the wall. Weep holes also help to reduce the lateral earth pressure acting on the wall by allowing the water to escape.

There are several methods for reducing lateral earth pressure on a retaining wall. These include using a stepped or battered wall design, which reduces the height of the wall and the resulting earth pressure; installing a drainage system behind the wall to remove water and reduce hydrostatic pressure; and using a retaining wall with a curved or sloping face, which reduces the amount of soil that is in contact with the wall.

The coefficient of earth pressure at rest (K0) is the ratio of lateral earth pressure to vertical earth pressure. It represents the earth pressure that exists in a soil mass before any external forces are applied.

The Coulomb wedge is used to determine earth pressure in cohesive soils, which exhibit both cohesion and friction. The Rankine wedge, on the other hand, is used to determine earth pressure in cohesionless soils, which exhibit friction but no cohesion.

Backfill material is placed behind a retaining wall to serve multiple purposes. It provides drainage and prevents hydrostatic pressure buildup by allowing water to drain away from the wall. It also increases the stability of the wall by adding weight and reducing the lateral earth pressure acting on the wall.

Hydrostatic earth pressure is not a type of lateral earth pressure. It is the pressure exerted by water on a submerged structure or object.

Wall friction between the soil and the retaining wall reduces active earth pressure and increases passive earth pressure. This is because the friction between the soil and the wall resists the movement of the soil, reducing the active earth pressure and increasing the resistance to movement, which in turn increases the passive earth pressure.

Retaining walls serve multiple purposes. They support a soil mass and prevent it from collapsing, creating a level surface for construction, and preventing erosion of soil.

Gravity walls, cantilever walls, and sheet pile walls are all common types of retaining walls. Gravity walls rely on their own weight to resist lateral earth pressure, cantilever walls are supported by a foundation below the ground surface, and sheet pile walls are constructed using interlocking steel sheets.

The primary difference between a gravity wall and a cantilever wall is the method by which they resist lateral earth pressure. Gravity walls rely on their own weight to resist the pressure, while cantilever walls are supported by a foundation below the ground surface.