Problems

This diagram shows two types of failures. On the left side is a debris flow, on the right side is a bedding plane failure within the bedrock.

Debris flows involve the soil on the slope, a layer of soil and bedrock mix commonly called colluvium and the weathered bedrock. During periods of heavy rainfall an elevated temporary water table is created in the slope. This saturation weakens the soil, colluvium and weathered bedrock which fails along a planar surface generally parallel to the slope face. This material moves rapidly down slope as viscous saturated slurry.

The bedding plane failure within the bedrock occurs in bedrock materials with layers that are not supported at the base of the slope. The bedrock materials that are most times involved in this type of failure consist of shale, clay stones, siltstones and slates.


This figure shows an overview of the types of failures that can occur in slopes.  The diagrams (a) and (d) are basically thin wedges of materials that fail as a result of rainfalls that create an artificial water table which weakens the materials causing this type of failure

Figure (b) is a failure that would occur within clay like materials because of a weaker or stronger soil material at the base.

Figures (c) and (e) are deep seated failures which can occur over a stronger material located at depth.  These failures can occur in bedrock materials that have bedding or layering that has weaker materials, such as clayey bedrock, siltstone bedrock, slate bedrock, or shale bedrock.


This diagram is a depiction of the Heave and Creep phenomenon.
The top two show heave, the bottom one shows creep.

Heave within a site can be the result of bedrock or soils that have differing rates of expansion as they become wet.  Bedrock that has layers of expansive material, such as claystone and non expansive materials such as sandstone if uplifted and bent by tectonic forces can create a building pad that has zones of expansive bedrock and zones of non expansive bedrock.  Depending on how the structure is placed across the site these zones over a short period of time can cause significant damage to the structure.

Creep occurs on slopes built of expansive earth fills or expansive soils.  These materials become wet during periods of rainfall and expand volumetrically, like a balloon.  When the rains are over and the slope begins to dry the soils and fills shrink as they dry.  During the drying process the fill and or soil follow the direction of gravity and move down the slope.  This causes the slow movement of the slope which over time causes movement of the building pad and movement of structures built near the top of the slope or over the creep zone.

This a photo of a crack monitor placed across a wall that is moving. This monitor is affixed to each side of the crack and can accurately measure the amount and direction of the movement.

This structure was affected by soils that are subject to settlement upon saturation. The roof assembly is trying to resist the settlement occurring in another portion of the structure.

This is a another angle of the above photo.

Distress to interior wall. This type of movement could be the result of slope creep, differential settlement and or differentially expansive bedrock beds exposed beneath the building pad. The exact mechanism can be determined by a detailed geotechnical evaluation.

This shows the affects of expansive soils on a slab footing connection.

This is a close-up of the above photo.

This distress could be the result of creep effects of a nearby descending slope or settlement of a fill pad. This wall is built perpendicular to a descending slope and is easily affected by either condition. The mechanism of failure can only be determined by a detailed geotechnical evaluation.

This shows the amount of movement that can occur to a structure as a result of slope creep, fill settlement or slope relaxation.
Click on the image to view sample test reports.