Sealing tension cracks

Category: MODIFYING THE SURFACE WATER REGIME – Surface drainage

Description

In the context of landslide mitigation, it  is always necessary and beneficial to prevent the infiltration of surface water into the ground in or close to existing or potential landslides. Good surface drainage is therefore necessary in these areas. This is particularly significant where failure has already occurred, because the runoff water may flow into cracks and fissure in or at the boundary of the unstable soil mass, especially at tension cracks at the head of the slope (Figure 1). This would give rise to the following unfavourable effects:

  • Raise piezometric levels in the unstable mass, reducing effective stress and consequently shera strength on the slip surface;

  • Provide additional driving force by means of the hydrostatic pressure of free water in tension cracks at the head of the slide.

Figure 1: Tension cracks, 2009 reactivation, Petacciato Landslide, Italy (source: SGI-MI Project files)
Figure 1: Tension cracks, 2009 reactivation, Petacciato Landslide, Italy (source: SGI-MI Project files)

The most common methods for sealing cracks (Figure 2) consists of filling them with puddle clay or other impervious fill; it is often sufficient to excavate a trench along the tension crack and to backfill it with the excavated impervious material, possibly adding small quantities of bentonite or other natural material to reduce permeability further, and shaping the ground so that surface water does not pond in the area. If necessary, an impervious membrane may be added at or near the surface.

Figure 2: Sealing tension cracks – typical detail
Figure 2: Sealing tension cracks – typical detail

Impervious membranes may be used by themselves as an emergency or temporary measure, while arrangements are being made for the works to be carried out.

Regular inspection and maintenance is required in case of continued movement, since it may cause previously sealed cracks to reopen.


Design methods

Will be updated


Functional suitability criteria

Type of movement

Descriptor Rating Notes
Fall 0 Most suited to all types of slides. In spreads, only useful as remediation, not as a preventive measure.
Topple 0
Slide 8
Spread 3
Flow 1

Material type

Descriptor Rating Notes
Earth 9 Mainly applicable to landsliding involving earth and only to a lesser extent in debris. Applicability in rock limited by typical slope geometry and failure mode, but note that in deep seated rock slides tension cracks propagating through the surface cover would also benefit.
Debris 6
Rock 4

Depth of movement

Descriptor Rating Notes
Surficial (< 0.5 m) 8 Typically applicable to landslides of any depth, but relative effectiveness decreases with increasing depth of movement.
Shallow (0.5 to 3 m) 8
Medium (3 to 8 m) 6
Deep (8 to 15 m) 3
Very deep (> 15 m) 0

Rate of movement

Descriptor Rating Notes
Moderate to fast 1 Can be carried out without special difficulty when the rate of movement is slow (5 cm/day) or less, but may be disrupted and will require additional maintenance or reconstruction as a result of continued movement. May be applicable, with special precautions and limited effectiveness due to continuous disruption, to moderately fast movements.
Slow 6
Very slow 8
Extremely slow 8

Ground water conditions

Descriptor Rating Notes
Artesian 6 Applicable irrespective of groundwater conditions. Effects on groundwater levels only indirect through reduced infiltration. Potential difficulties in carrying out in areas of high or artesian groundwater levels, depending on the depth of local excavation required.
High 6
Low 7
Absent 8

Surface water

Descriptor Rating Notes
Rain 7 Water courses should be diverted.
Snowmelt 7
Localized 7
Stream 3
Torrent 0
River 0

Reliability and feasibility criteria

Criteria Rating Notes
Reliability 8 Effects on stability only indirect. The reliability in the long term may be impaired by further movement or poor maintenance.
Feasibility and Manageability 10 Simple technique. Potential benefits and limits of applicability are well established.

Urgency and consequence suitability

Criteria Rating Notes
Timeliness of implementation 10 Easily implemented with widely available equipment.
Environmental suitability 6 will be updated
Economic suitability (cost) 10 Low, where applicable.

References

Will be updated

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