Remediation of Landslides

The characterised mountain and highland relief of the Vsetín district, together with the extensive Mesozoic and Tertiary complexes of flysch belts are extreemly prone to erosion and therefore landslide activation. Various research organisations registered over 250 localities with developing slope failures in the Vsetín district. Extensive and damaging landslides occurred in the villages of Ružd‘ka, Mikuluvka and Bystřička as well as the towns of Vsetín and Valašske Meziříčí.In the majority of cases, the landslides were activated as early as Monday 7^th July, 1997. The fastest slides occurred between the 7-8^th July. Less intensive slides occurred due to the increased rainfalls between the 18-20^th of July.

see Figure - Total daily rainfall with the corresponding activation of Landslides

    Classification of Landslides

The Vsetín District Authority categorised the landslides into three different groups:

1) None or negligible damage

2) Damage possible but no serious risk

3) Serious damage, should have remediation

The areas where most damage has occurred are, Ružd‘ka, Mikuluvka and Bystřička. However, out of the total number of landslides in the Vsetín region, over 75 of them are of  category 3.  This causes a huge financial problem for the remediation work to be carried out and so money goes to the most needed cases, as stated above.

    Methods of Remediation

    1.Piles

Piles can be used from a variety of different materials depending on  factors such as soil type, location, accessibilty, type and size of structure and cost.

The different types of piles attainable are:

The piles are used to stabilise the landslide in critical places. They are usually used in cojunction with retaining walls for extra support, or anchored walls. In general, driven piles tend to be used in gravels, sands and silts. Bored piles are mostly used in clays.

    2.Retaining Walls

There are 2 types of retaining walls:

a)Rigid Retaining Walls

These walls are usually made of reinforced concrete and have a broad base for stability. Failure of these walls ussually occurs through slope movement, and therefore the wall slides. Crib walls use an open frame which relies for stability on the acting weight of the soil contained in the frame. Aside from this fact, it is much the same principle as the rigid wall.

see Figure - Types of Retaining Walls 

b)Flexible Retaining Walls  

Sheet piling provides a simple base for the construction of flexible retaining walls of roughly 5m high. Height required above this becomes uneconomic unless an anchored system is used as well.

    3. Anchored Walls

Anchored walls are not only supported by there broad base and the passive force of the soil infront, but also anchored rods which support the top of the wall as well. Anchored sheet pile walls are suitable for retaining depths of soil up to about 10-12m.  Figure 18 shows the various methods of anchoring the retaining wall and the respective failure planes for each kind.

see Figure - Types of Anchored Wall fixings

    4. Sand and Gravel Tamped Piles

These methods are used to de-water the landslide and at the same time, strengthen areas such as the transportation zone and places of most movement. Vertical sand piles are placed at the tips of horizontal dewatering boreholes. This technique draws water from the saturated slope into the vertical sand piles and then out through the drainage boreholes away from the landslide. This dewatering method increases the consistency and friction strength of the surrounding material. The same principle is used with the gravel tamped piles. These piles are of a large diameter and are present in a large belt across the landslide. The piles are filled with gravel and then compacted with a heavy weight or hammer. The amount of piles used depends on the size of the landslide, but generally the belt will stretch across the width to draw water away and increase the overall strength of the slide.

    5. Open Drainage

When a landslide occurs, there is usually a great deal of water present on the surface, such as springs, streams, open water tables etc. It is important to drain this surface water and this is done by open drainage ditches.

    6. Monitoring

This is a very important part of the remediation process of landslides. This is done by inclinometric boreholes, bench marks, recording of water table levels via wells and geological borehole data. Also the yeilds of the horizontal dewatering boreholes can be measured.