LANDSLIDES IN LITHUANIA - lgt.lt · PDF file17 LANDSLIDES IN LITHUANIA V. MARCINKEVICIUS 1, R.B. MIKŠYS2, V. MIKULENAS3 Geological Survey of Lithuania, Lt. 2600

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LANDSLIDES IN LITHUANIA

V. MARCINKEVICIUS1, R.B. MIKŠYS2, V. MIKULENAS3

Geological Survey of Lithuania, Lt. 2600 Vilnius, st S. Konarsko 35, Lithuaniae-mail: 1vytautas.marcinkevicius@lgt.lt, 2bonifacas.miksys@lgt.lt , 3vidas.mikulenas@lgt.lt

Slope landsliding is the most importantengineering geological process on the territoryof Lithuania. There are known historical facts aboutthe slope failures starting with the 16th century.These are landslides of Gediminas and Bekešashills in Vilnius. The Seredžius bricked church waswashed down by Nemunas River stream, andcollapsed into the valley 1829. The principal partof large slope failures of the past are remainedunknown. Ca. 85–90 landslides have been studiedor described during the last century (1937 andlater). It is noteworthy mention, that about 60 %of landslides are fixed in Lithuania jointly.

Landslide studies in Lithuania started beginningwith the 19th century. Systematic engineeringgeological research of slope failures in the cityof Kaunas was carried out by Prof. M.Kaveckissince 1937. Engineers geologists from KaunasUniversity of Technology (F.Norkus, A.Žiedelis,P.Masiulis) performed research of slopes of thelargest rivers in Lithuania 1960–1964. Since 1966,specialists from the Department of Hydrogeologyand Engineering geology of Vilnius Universityperform study of landslides. R.Stulpinas,R.B.Mikšys, V.Vaitiekunas are interested witha problem of archaeological monuments - hillforts -slope stability and an application of engineeringmeans to stabilise these historical sites. Recentlyspecialists from the Geological Survey and Instituteof Geology are able to apply quantitative orqualitative methods of landslide hazard assessment.

Landslides damage both natural and artificialslopes. Natural: due shore abrasion of the BalticSea, Kuršiu Marios lagoon and lakes, bankundercutting by artificial water reservoirs, erosionof rivers and ravines, etc. Artificial: slopes inexcavations and causeways (roadbeds) of trafficroads, walls of quarries of natural resources, slopesof the largest dumps; slopes of archaeologicalmonuments. The landslide activity is related tolocation of the largest cities (Vilnius, Kaunas,Alytus and others) in the deep valleys of the largestrivers Nemunas, Neris and others. Due to humaneconomic activity, with a construction on the slopesand their nearest environment, the stability andnatural moisture balance of soils are oftendisturbed. During these works, when the strengthproperties and strength stress state of soil havechanged, landslides could occur on the alreadyurbanized areas. According to economicalsignificance and their danger (by significance forthe land-use), landslides could be subdivided into:1. Urban areas; 2. Traffic roads; 3. Depositsof natural resources; 4. Protected areas and

monuments; 5. Dumps of waste materials; 6. Othereconomically significant territories.

Favourable engineering geological conditionsfor the landslide occurrence (geological structure,hydrogeological, geomorphological,technogenical),generally effecting a whole complex of naturalenvironment, where the slope failures form anddevelop are as follows:geological structure - slope failures develop in the

series of Quaternary sediments, formedof differently sized sand, sandy loam, loam andclay. Landslides develop sometimes on thetraffic roads especially due to deformationsof peat and silt. The most unstable slopes arecomposed of stripped clay characterised byliquid plastic or soft plastic consistency, orincompletely densed artificial grounds. Theirbest examples are landslides of Kuksa, Taurage,Rašnava clay deposits, also Vilkpede in Vilniusand Gandinga hillfort.

hydrogeological (and hydrological) –caused bysurface and underground water influenceconditioning changes in consistency andstrength parameters of clayey soils, or byhydrogeodynamical pressure, or whena filtrational stream effects the soil in the basicfrontal part of slope. The last is very importanton Lithuanian territory, becausehydrodynamical forces provoke the unstabillityof slopes in the walls of natural resourcedeposits. The influence of hydrogeologicalfactors is very often linked to suffosion process.

geomorphological – Slopes are unstable in thenatural geomorphological conditions due toerosional and abrasional strips, where the basicfrontal part of slopes is washed out by waterstream, and the steepnes of slopes increases tillthe stability limit.

technogenical – Landslides are happened inTonribis, Kuksa, Taurage and Rašnava quarries(pit) due to vibration, and on the areas of testingexploitation. They also occur duringconstruction works, when practically usedretaining-walls raise the local future changes ofhydrogeological conditions to become worseparameters of soil strength. Very frequentcauses are an increaseof slope stepness by digging-off of their lowerpart, extra loading of slopes, damages ina water-supply system, removal of vegetation onslopes for building, etc.

The landslide research at the time being isprovided according to these topics:

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1) to stabilise the landsliding process hazard forbuildings, communications and for objectsof historical heritage; 2) for the needs of territorialplanning.

An ordinary means for slope stabilisation areincluded for technical projects in most cases. Mainaim of all projects – to eliminate impacts andcauses might disturb a balance of slopes in mostsimplified ways and with minimal tools. Meansapplied most frequently in Lithuania for a replaceof slope balance with certain factor of safety are asfollows: 1. The angle of slope is decreased if it ispossible; 2. The embankments are constructedat the base of erodable slopes; 3. The basesof unstable slopes are loaded by additional ballast;4. Intensive drainage of the landslide body;5. The surface water stream is directed away to thebottom of slope; 6. In case of hydrodynamicalpressure – necessary engineering means are appliedto minimize this factor.When the landslides damage very important objectsor slopes slope failures develop in urban areas: 1.Retaining-walls are built to hold an active groundpressure; 2. Anchor systems are equipped(reinforcement of former landslides at the slopesof Gediminas hill in Vilnius and at the baseof Vytautas hill in Kaunas); 3. The terracing

of the slopes surface; 4. Constructionof installations for drainage; 5. Steel sheet pilling.The modern concept: To use most simplified andleast expensive engineering and economic meansfor the landslide stabilisation in Lithuania. They areaimed not for a stop of certain processes, but todirect the landslide development in that way, whichitself will eliminate their arising causes.The engineering – geological invasion intolandslide processes have to stimulate a naturalrebuilt of slope stability. Moderate and delicatelyincludable functional constructions of naturalmaterials are devoted to neutralise principalerosional factors and to direct the naturaldevelopment processes of slopes for a suppressionof dynamically active deformation hotbeds.

Becomes apparent regularity: The landslidesoccur most frequently in places of distinctlyeconomically impacted natural environment.

The research topicality of slopes is nowadaysconfirmed by a large landslide (ca. 50 000 m3

of ground have slided down according topreliminary data – see photo fig.) occurredsuddenly late evening 11th August 2000 on thefactory site of Lithuanian capital. The losses apartfrom the rebuilt work make up over 1 million USD.