Geological Quar terly, 2021, 65: 42 DOI: http://dx.doi.org/10.7306/gq.1611
The en gi neer ing geo log i cal and geotechnical con di tions of Gediminas Hill (Vilnius, Lith u a nia): an up date
arñnas SKUODIS1, *, Dainius MICHELEVIÈIUS2, Aldona DAMUYT#3, Juozas VALIVONIS1, Jurgis MEDZVIECKAS1, Arnoldas ŠNEIDERIS1, Aidas JOKUBAITIS1 and Mykolas DAUGEVIÈIUS1
1 Vilnius Gediminas Tech ni cal Uni ver sity, Fac ulty of Civil En gi neer ing, De part ment of Re in forced Con crete Struc tures and Geotechnics, al. SaulÅtekio 11, LT-10223 Vilnius, Lith u a nia
2 Vilnius Uni ver sity, In sti tute of Geosciences, Fac ulty of Chem is try and Geosciences, De part ment of Hydrogeology and En - gi neer ing Ge ol ogy, M.K. Èiurlionio 21/27, LT-03101, Vilnius, Lith u a nia
3 Lith u a nian Geo log i cal Sur vey, Di vi sion of En gi neer ing Ge ol ogy, S. Konarskio 35, LT-03123 Vilnius, Lith u a nia
Skuodis, ., Michelevièius, D., DamuëytÅ, A., Valivonis, J., Medzvieckas, J., Šneideris, A., Jokubaitis, A., Mykolas Daugevièius, M., 2021. The en gi neer ing geo log i cal and geotechnical con di tions of Gediminas Hill (Vilnius, Lith u a nia): an up - date. Geo log i cal Quar terly, 2021, 65: 42, doi: 10.7306/gq.1611
We pro vide an up date of en gi neer ing geo log i cal and geotechnical con di tions at Gediminas Hill in Vilnius (Lith u a nia) from 1955 till 2020, which al lows eval u a tion of the sta bil ity of its slopes. Ac tive geo log i cal pro cesses are still ob served on Gediminas Hill. The lat est land slides ap peared on March 22, 2004 and on March 8, 2008 on the east ern slope above the hik - ing trail, as well on Feb ru ary 11, 2016 and Feb ru ary 13, 2016 on the north ern part of the slope. The lat est land slide (in volv ing
~40 m3 of soil) took place on March 7, 2017 be tween the east ern and south ern slopes. Eight hydrogeological units were dis - tin guished in 2017. Dur ing 2019–2020 many en gi neer ing geo log i cal and geotechnical in ves ti ga tions have al lowed de ter mi - na tion of the pos si bil i ties and meth ods of slope sta bi li za tion.
Key words. Gediminas Hill, ge ol ogy, geo log i cal con di tions, geotechnical in ves ti ga tions, land slide, slope sta bil ity.
INTRODUCTION
Through out his tory, civil en gi neers have made many ad - mi ra ble and en dur ing stud ies that high light the mer its and of their pro fes sion (Buhler, 2016). Each re gion has its own his tor - i cal mon u ments, which have been in ves ti gated con tin u ously over de cades. For ex am ple, many en gi neer ing geo log i cal and geotechnical in ves ti ga tions have fo cussed on the tower of Pisa in It aly (Sarti et al., 2012; Squeglia et al., 2018), in Spain – there is the Sa grada de Fa milia church in Bar ce lona (Katzen - bach et al., 2013; Ladesma and Alnoso, 2017), in Egypt – the Mustafa Kamil Ne crop o lis un der ground tombs (Hemeda et al., 2015), in Saudi Ara bia – the Madâin Sâlih sand stones (Medini and Arbi, 2018), in In dia – the nat u ral stone sculp tures (Shar - ma, 2019), in Ne pal – the Kathmandu Val ley (Kumar et al., 2019), and so on.
An im por tant his tor i cal mon u ment in Lith u a nia, in cluded in the UNESCO World Her i tage List since 1994 (MikulÅnas et al., 2016), is Gediminas Hill with the re mains of the cas tle (Skuodis
and Ng, 2018) and nearby Ca the dral of Vilnius (Mackevièius, 2013; Gadeikis et al., 2016). Land slides on the slopes of Gediminas Hill have oc curred from olden times up to the pres - ent (Kitkauskas, 2001; MorkñnaitÅ and Èesnulevièius, 2005;
Satkñnas et al., 2008; Vaièiñnas, 2010; Skuodis et al., 2017;
adzevièius et al., 2018; Jonaitis et al., 2019). While gen er ally there is a low risk of land slides in Lith u a nia, ac cord ing to land - slide and risk map ping (Jelinek et al., 2007), Gediminas Hill has been ex ten sively in ves ti gated (Katalynas and Vaitkevièius, 2001; Maèiulis, 2005; Vaitkevièius and KiëkienÅ, 2010; Antana - vièienÅ, 2012; BaubinienÅ et al., 2015; Markelionis et al., 2017).
The most de tailed en gi neer ing geo log i cal and geotechnical in ves ti ga tions on Gediminas Hill were con ducted in 1955–1959 and 1968–1973, with ad di tional in ves ti ga tions in 1980, 1995–1997, and 2017 (JSC Geobaltic, 2020). All these in ves ti - ga tions are im por tant, but not all the re sults can be used in mod - ern en gi neer ing geo log i cal and geotechnical eval u a tion. Of the in ves ti ga tions or ga nized in 1959, 44% of the re sults are doubt - ful (or not re li able) and from 1973 in ves ti ga tions only 10% are un cer tain (or not re li able). Doubt ful re sults are due to sev eral rea sons: dif fer ent nor ma tive doc u ments re lat ing to in ves ti ga - tions to day and in ear lier times; av er age Vilnius city me chan i cal prop er ties be ing used if the true val ues were not de ter mined dur ing ear lier in ves ti ga tions, co or di nates sys tem dis crep an cies, and so on. This study up dates in for ma tion on en gi neer ing geo - log i cal and geotechnical in ves ti ga tions re al ized dur ing
* Corresponding author, e-mail: sarunas.skuodis@vilniustech.lt Received: June 4, 2021; accepted: July 30, 2021; first published online: September 9, 2021
2019–2020 (JSC Geobaltic, 2020). Dur ing these in ves ti ga tions, bore holes (ver ti cal and with in cli na tion of 35–40°) were drilled on the top of Gediminas Hill to col lect un dis turbed soil sam ples (the term “soil” here be ing used in an en gi neer ing sense, to in - clude un con sol i dated geo log i cal de pos its). Bore hole lengths var ied from 31.8 to 57.0 m. The in for ma tion pro vided al lows up - dat ing of ex ist ing data on soil lay ers, their thick ness, depth and phys i cal and me chan i cal prop er ties. A slope sta bil ity anal y sis is made based on that data.
ARCHIVAL
RESEARCH – SHORT REVIEW
In 1955, the Cit ies and Villagies Con struc tion De sign In sti - tute car ried out geo log i cal in ves ti ga tions of Gediminas Hill, on top of which 3 bore holes up to 45 m depth, and a few bore holes on the slopes, were drilled. Un for tu nately, the re port of these in - ves ti ga tions is miss ing and in for ma tion about them is found only in the 1973 Engineeering In ves ti ga tions In sti tute re port. Up to 2019 these 3 bore holes pro vided the main geo log i cal in for - ma tion about the Gediminas Hill li thol ogy. The Gediminas Hill in ves ti ga tions in 1959 fo cused on in ves ti ga tions of the slopes.
These were di vided into 6 lev els at dif fer ent al ti tudes across the whole hill. 87 shal low bore holes of 4–5 m depth were drilled on the slopes, on the ba sis of which geo log i cal cross-sec tions were com piled. The strata en coun tered in these bore holes were de scribed lithologically, with out de ter mi na tion of me chan i - cal prop er ties, or in for ma tion about any lab o ra tory in ves ti ga - tions.
In 1968–1973 the En gi neer ing In ves ti ga tions In sti tute con - tin ued the geo log i cal stud ies (1973). These in ves ti ga tions went fur ther than those of 1959, with 79 bore holes drilled up to 10 m depth, and sam ples for lab o ra tory test ing be ing col lected to de - ter mine phys i cal prop er ties. Six un dis turbed soil sam ples for in - ves ti ga tions of me chan i cal prop er ties were also pre pared. On the path to Gediminas Hill cone pen e tra tion tests were made in 2 places. In to tal, 3 geo log i cal cross-sec tions in dif fer ent ori en - ta tions were com piled, in clud ing use of in for ma tion from the 3 deep bore holes drilled in 1955. In these cross-sec tions en gi - neer ing geo log i cal lay ers with me chan i cal prop er ties (co he sion, an gle of in ter nal fric tion, Young’s modulus) were de lin eated.
How ever, me chan i cal prop er ties de scribed in the 1973 in ves ti - ga tions re port were de ter mined with in di rect in ves ti ga tion meth - ods ap plied to other Vilnius city stud ies with sim i lar en gi neer ing ge ol ogy prop er ties of soils.
To check the bound ary al ti tudes de ter mined in all the ar chi - val bore holes, the ad e quacy of their X, Y, and Z co or di nates for con tem po rary co or di nates sys tems was eval u ated, by com par - ing the LKS-94 co or di nate pro jec tions and their ab so lute heights at the pres ent sur face with the ab so lute heights given for the bore holes in the in ves ti ga tion re ports. One can have high con fi dence in a bore hole if the ab so lute height dif fer ence is
<1 m, but where there is >1 m ab so lute height dif fer ence, the bore hole was re garded as un re li able and not used in these in - ves ti ga tions. Based on the this cri te rion, 44% of bore holes in the 1959 in ves ti ga tions were un re li able, though only 10% from the 1973 re port. Given the amount of un re li able re sults for 1959, it was de cided not to use in for ma tion from them to con - strain the depths of lithological bound aries. And, in for ma tion from the 1973 in ves ti ga tions were used where the de scrip tion of soil lay ers was scant in the 2019–2020 in ves ti ga tions.
Later, in 1980, 1995–1997 and 2017, other en gi neer ing geo - log i cal and geotechnical in ves ti ga tions into in di vid ual as pects of the Gediminas Hill de sign were con ducted, though these added
lit tle new geo log i cal in for ma tion. The ar chi val data up to 2019 com prises 1089 bore holes of var i ous depth, though de scrip tions of 470 of them are miss ing. In for ma tion from at least 628 bore - holes is re li able, but only 200–300 bore holes are de scribed suf fi - ciently for the in for ma tion to be used by ge ol o gists and/or con - struc tion de sign ers. The deep est bore hole, drilled in 1955 on the Gediminas Hill top, is 45 m deep. Most of the rest each 12–15 m in depth, with shal low bore holes reach ing 2 m. Up to 2018, the Gediminas Hill in ves ti ga tions are listed in 167 doc u ments, while the ar chi val ma te rial bib li og ra phy com prises 119 doc u ments (https://atviras.vilnius.lt/gedimino-kalnas).
ENVIRONMENTAL CONDITIONS
Gediminas Hill is lo cated in the cen tral part of Vilnius in the area of the Na tional Mu seum of Lith u a nia. Ab so lute heights in en gi neer ing geo log i cal and geotechnical doc u men ta tion ranges from 92.7 to 141.0 m (Fig. 1). Slope in cli na tion is mainly 28–33°, but in a few places reaches 43° and rarely 54° (Skuodis and Ng, 2018). The Gediminas Hill in ves ti ga tion area is of one ge netic type of re lief, with technogenic soil pre vail ing through - out, the depth of which var ies from 0.7 to 7.4 m. Parts of the slopes (the main south east ern slope, and parts of the south ern and west ern slopes) are sta bi lized with tem po rary antislide so - lu tions (bal last lay ers, an chors, steel grids, drain age). The north slope is sta bi lized with ga bi ons and drain age.
The yearly av er age tem per a ture is 6.1–6.7°C (low est re - corded tem per a ture –37.2°C, high est re corded tem per a ture 35.4°C), an nual pre cip i ta tion is 610–690 mm (av er age 658 mm/year), the pe riod with snow cov er age is 90–105 days (max - i mum re corded thick ness of snow 52 cm) and du ra tion of sun - shine is 1690–1770 hours/year (Skuodis and Ng, 2018). Ac - cord ing to prog no sis, by 2100 pre cip i ta tion will in crease by 50 mm/year in the Vilnius area. Pre cip i ta tion in ten sity will also in - crease and max i mum pre cip i ta tion quan tity may in crease by 15%. The larg est pre cip i ta tion in cre ment will be dur ing win ter (up to 24%). Due to ris ing av er age tem per a tures, in creas ing amounts of win ter pre cip i ta tion will be driz zle and sleet. In the Vilnius re gion, ac cord ing to RSN 156-94 (1995), the max i mum soil freez ing depth each ten year pe riod may reach 1.34 and 1.70 m each 50-year pe riod. The Gediminas Hill sea sonal soil freez ing depth for sandy soil may reach 1.2 m, and for clay 1.5 m.
GEOLOGICAL STRUCTURE AND HYDROGEOLOGICAL CONDITIONS
Geomorphologically, Gediminas Hill is lo cated on the north - west ern edge of the Medininkai High land that is a part of the Aëmena Up land formed dur ing the last Mid dle Pleis to cene Gla - ci ation (GuobytÅ, 2010). Geo log i cally, Gediminas Hill is made of de pos its of sev eral Mid dle Pleis to cene glaciations. Ac cord ing to strati graphic scheme of the Qua ter nary cur rently ap proved for use by the Lith u a nian Geo log i cal Sur vey, the de pos its be - long to the Dainava For ma tion (rep re sent ing the Elsterian 2 Gla cial of Eu ro pean stra tig ra phy), and the Žemaitija (= Saalian Gla cial) and Medininkai (= Warthian Gla cial) sub formations (GuobytÅ and Satkñnas, 2011; Fig. 2). The Mid dle Pleis to cene de pos its are af fected by deluvial pro cesses and hu man ac tiv i - ties on the hill slopes (Fig. 3). Ac cord ing to soil per me abil ity cri - te ria, up to 8 dif fer ent hydrogeological lay ers may be dis tin - guished in the Gediminas Hill struc ture (Fig. 4). The phys i cal
arñnas Skuodis et al. / Geological Quarterly, 2021, 65: 42 3
Fig. 1. Re lief map: A – gen eral map of in ves ti ga tion site lo ca tion;
B – Gediminas Hill 3D re lief and wind di rec tions
Fig. 2. Geo log i cal model of Gediminas Hill
tIV – Ho lo cene technogenic soils; de pos its of the Mid dle Pleis to cene Medininkai (Warthian) Subformation: fIImd – glaciofluvial;
gdIImd – gla cial (deformational till); de pos its of the Mid dle Pleis to cene Žemaitija (Saalian) Subformation: lgIIžm – glaciolacustrine; gdIIžm – gla cial (de for ma tion till); lgIIdn – glaciolacustrine de pos its of the Mid dle Pleis to cene Dainava (Elsterian 2) For ma tion. Red lines show lines of geo log i cal cross-sec tion, while red ver ti cal and di ag o nal lines on the geo log i cal cross-sec tions rep re sent bore holes
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Fig. 3. Weak soil lay ers be neath the technogenic soil layer
Fig. 4. Sche matic hydrogeological cross-sec tion V–V’
1 – tIV – per me able strata (k = 0.4 m/d), 2 – gdIImd – im per me able strata, 3 – fIImd – per me able strata (k = 9m/d), 4 – lgIIžm – rel a tively im per me able strata, 5 – lgIIžm per me able strata (k = 0.3 m/d,; 6 – lgIIžm per me able intermoraine
de pos its (k = 5.4 m/d), 7 – gdIIžm – im per me able strata, 8 – lgIIdn – per me able strata (k = 2.3 m/d)
T a b l e 1 Sum mary of phys i cal and me chan i cal prop er ties
1 – soil layer iden ti fi ca tion with (1973) means ar chi val data taken from 1973 in ves ti ga tions; 2 – soil layer iden ti fi ca tion is the same as in Fig ures 5–8
arñnas Skuodis et al. / Geological Quarterly, 2021, 65: 42 7
Sa, Si,
E – cal cu lated ac cord ing to CPTU (qt) re sults given in Ta ble 1
T a b l e 2 Sum mary of Young’s modulus mea sure ments
and me chan i cal prop er ties of the dif fer ent lay ers are char ac ter - ized sep a rately and are shown in Ta bles 1 and 2. The soil lay - ers were dis tin guished us ing bore hole, CPTU and lab o ra tory data.
The Mid dle Pleis to cene Dainava (Elsterian 2) Gla ci ation left the glaciolacustrine de pos its at the foot of the hill. The thick - ness of these de pos its (lgIIdn) reaches up to >15 m. A wide lithological va ri ety is pres ent in side this layer, with fine-grained sand and hor i zon tal bed ding pre dom i nat ing. The up per part of this unit is char ac ter ized by interlayers (thick ness var ies from 0.3 to 4.9 m) of fine-grained brown sand, lo cally silty or clayey, and by interlayers of sandy silt (thick ness 0.2–0.6 m). The de - pos its of the lower part of the unit are rep re sented by interlayers of grey sand (thick ness up to 5 or more metres) al ter nat ing with silt interlayers (which can ex ceed 1.8 m). The silt is green - ish-grey, coarse, sandy in some places, mas sive. Interlayers (thick ness 0.2–0.3 m) of green ish-grey sandy gravel or a sin gle well-sorted gravel layer of car bon ate rocks up to 30 mm across were found in the mid dle part of the layer. A small ad mix ture of finely dis persed or ganic mat ter and a rel a tively high con cen tra - tion of black min er als are spe cific fea tures of this layer.
The glaciolacustrine de pos its of the Dainava (Elsterian 2) For ma tion (lgIIdn) com prise a suc ces sion of wa ter-per me able strata. Due to wide lithological di ver sity, the per me abil ity of the de pos its var ies from 0.08 to 15 m/d, av er ag ing 2.9 m/d.
Ground wa ter was found only in a sin gle bore hole DZ2914, at a depth of 5.05 m (90.05 m ab so lute height).
The glaciolacustrine de pos its of the Dainava (Elsterian 2) For ma tion are over lain by the Žemaitija (Saalian) Subformation which is di vided into ad vance (the lower part) and re treat (the up - per part) de pos its. The gla cial ad vance de pos its are be tween 2.0 and 2.2 m thick and are com posed of dark grey-brown and brown till, which be comes dark grey, coarse, dense, and mas - sive at the base. In ter ca la tions of sand, clay and gravel are char - ac ter is tic fea tures of this till layer. The gla cial ad vance and re - treat de pos its are sep a rated by a layer of glaciolacustrine de pos - its (lgIIžm), 1.1–1.5 m thick, com pris ing dense, plas tic, mas sive, dark red dish grey and grey-brown clay (thick ness 0.5–0.9 m) in its up per part and fine silty, car bon ate-feld spar-quartz, light brown ish, grey or brown sand in its lower part. The gla cial re treat de pos its (thick ness from 4.20 to 4.45 m) com prise till: brown in its up per part and grad u ally be com ing grey and then dark grey in its lower part. The till is coarse, dense, mas sive, lo cally with light brown spots, and in cludes gravel.
Glaciolacustrine de pos its (lgIIžm) of the Žemaitija (Saalian) Subformation ac cu mu lated in a melt wa ter ba sin and are 3.65–4.2 m thick. These de pos its vary in their par ti cle size dis - tri bu tion and com po si tion. Their low er most part (thick ness 0.2 m) is com posed of fine-grained, silty-clayey, dense and mas - sive, car bon ate-feld spar-quartz, brown and yel low ish-brown sand. This sand is over lain by 0.2–0.4 m thick of dense, plas tic, finely lay ered brown clay. Units of fine-grained and clayey-silty sand (thick ness up to 1.1 m), fine-grained sand (thick ness up to 1.1 m), and fine-grained silty sand (thick ness up to 0.7 m) oc cur above this clay. Lam i nated brown sand (thick ness from 0.9 to 1.7 m) oc curs at the very top of this glaciolacustrine suc ces sion.
Two per me able lay ers are pres ent within the Žemaitija (Saalian) Subformation. The lower of these is de vel oped be - tween two till lay ers (gdIIžm) of this subformation, while the up - per aqui fer is pres ent within the glaciolacustrine de pos its (lgIIžm). The per me abil ity of the lower aqui fer var ies from 0.05 to 0.8 m/d, the av er age value be ing 0.3 m/d. The up per per me - able layer con sists of slightly silty clayey sand (fSa) with rare low-plas tic ity clay-silt in clu sions. The per me abil ity of the main li - thol ogy var ies from 2.6 to 11 m/d, with an av er age of 5.4 m/d.
Due to the undulose ge om e try of the till lay ers be low and a
sharp de pres sion on the east ern slope, a ground wa ter dis - charge (source) was formed there.
The high est part of Gediminas Hill is rep re sented by de pos - its of the Medininkai (Warthian) Subformation (gdIImd). The up - per most part of these de pos its is miss ing, while the thick ness of the re main ing gla cial de pos its is 1.3–5.3 metres. A deforma - tional till layer is rep re sented by com pacted, mas sive, red - dish-brown till, and lo cally by morainic sand. The de for ma tion till is rich in sand, silt, and clay beds, also in boul ders. An ad mix - ture of me dium and poorly rounded gravel with clasts 2–50 mm across com prises ~5%. This is the first sur face aquitard; with poor per me abil ity, wa ter can move only through it via frac tures and per me able lenses or as an ini tial pres sure gra di ent.
The glaciofluvial sed i ments (fIImd) of the Medininkai (Warthian) Subformation lie be neath the gla cial layer. Their thick - ness var ies from 4.6 m in the north west ern part to 9.8 m in the south ern part of the Hill. These de pos its are lithologically gen er - ally uni form: car bon ate-feld spar-quartz brown sand, vary ing in grain size dis tri bu tion, lo cally with grav elly sand or gravel. They are per me able, per me abil ity rang ing from 1.0 to 16.0 m/d, av er - age – 9 m/d. Rain fall per co lates through them into deeper lay ers.
The en tire nat u ral sur face of Gediminas Hill is mod i fied by hu man ac tiv ity. The thick ness of ar ti fi cial de pos its – techno - genic soil (tIV) – var ies from 2.4 to 4.6 m. They com prise hu - mus-rich clayey sand and diamicton of var i ous grades, as well as gravel, gravel and brick de bris, pieces of car bon ate ce ment, bur ied cul tural lay ers, etc. The prev a lence of weak soil lay ers ex posed be low technogenic struc tures is shown in Fig ure 3, and a hydrogeological cross-sec tion in Fig ure 4.
ANALYSIS OF TEST RESULTS
Soil phys i cal and me chan i cal prop er ties used in slope sta - bil ity cal cu la tions were taken from the lat est en gi neer ing geo - log i cal and geotechnical in ves ti ga tions in 2019–2020 (JSC Geobaltic, 2020). Dur ing these in ves ti ga tions 6 ver ti cal bore - holes and 9 bore holes with an av er age in cli na tion of 35–40o were drilled at the top of Gediminas Hill to col lect un dis turbed soil sam ples. Bore hole length var ied from 31.8 to 57 m. Close to ver ti cal bore holes, cone pen e tra tion tests with pore pres sure mea sure ment (11 tests) and with out pore pres sure mea sure - ment (5 tests) were con ducted. In or der to find the technogenic soil layer thick ness on the slopes me chan i cal drill ing by hand (134 tests of av er age 4.1 m depth) and me chan i cal dy namic pen e tra tion (119 tests of max i mum 10 m depth) were per - formed. Also, 40 pits for eval u a tion of foun da tions were dug. In the lab o ra tory 361 par ti cle size dis tri bu tion tests, 165 wa ter per - me abil ity tests, 355 wa ter con tent tests, 347 unit weight tests, 251 plas tic and 231 liq uid limit tests, 353 par ti cle solid den sity tests, 160 di rect shear tests, 110 oedometer tests and 14 uni ax - ial com pres sion tests were con ducted.
Me chan i cal prop er ties were de ter mined for un dis turbed sam ples us ing di rect shear, triaxial and oedometer de vices. Un - dis turbed sam ples were taken us ing col umn bor ing. Elletarri EK 200 equip ment was used for drill ing ver ti cal bore holes with a three-sec tion col umn pipe (with plas tic shell), outer di am e ter – 116 mm, in ner di am e ter – 93 mm, length – 3 m. When drill ing in coarse soils “Denison” type equip ment was used. Af ter lift ing, the soil is re moved to gether with the in ner plas tic pipe. The pipe is sealed with pro tec tive caps. On site the soil left on the bor ing crown was used only for vi sual de ter mi na tion of soil type. A de - tailed de scrip tion of the soil was made in the lab o ra tory. Part of the soil ob tained from the pipe was sent to the lab o ra tory where it was de scribed and clas si fied. The other part was col lected in boxes and sent to a stor age site.
Based on all en gi neer ing geo log i cal and geotechnical in - ves ti ga tion re sults, for slope sta bil ity anal y sis each layer soil unit weight g, ef fec tive an gle of in ter nal fric tion j’, ef fec tive co - he sion c’, co he sion un der un drained con di tions cu, and Young’s modulus was used (Ta ble 1). Ac cepted ma sonry unit weight is 30 kN/m3, pos si ble dis trib uted load on the paths is 10 kPa.
Young’s modulus is shown sep a rately in Ta ble 2, where it was cal cu lated from CPTU re sults given in Ta ble 1 and from oedometer tests. Oedometer test loads ap plied ac cord ing to nat u ral soil weight with the pos si bil ity of stress in cre ments due to re con struc tion of the Gediminas cas tle re mains. More de - tailed in for ma tion about the phys i cal and me chan i cal test re - sults are given in the JSC Geobaltic (2020) En gi neer ing geo - log i cal and geotechnical in ves ti ga tions re port, which can be found in the Lith u a nian Ge ol ogy Sur vey.
SLOPE STABILITY
Gediminas Hill slope sta bil ity was cal cu lated us ing the Morgenstern-Price method (Zhu et al., 2005) with a po lyg o nal slip sur face. The so lu tion of the slope sta bil ity prob lem adopt ing a po lyg o nal slip sur face is based on the de ter mi na tion of the limit state of forces act ing on the soil body above the slip sur - face. To in tro duce these forces, the slip sur face above is sub di - vided into blocks by di vid ing planes. Slope sta bil ity cal cu la tions were con ducted with the GEO5 (2020) slope sta bil ity pro gram.
Morgenstern-Price is a gen eral method of slices de vel oped on the ba sis of limit equi lib rium. It re quires a sat is fac tory equi lib -
rium of forces and mo ments act ing on in di vid ual blocks. The blocks are cre ated by di vid ing the soil above the slip sur face into di vid ing planes. In these cal cu la tions the slope uti li za tion fac tor is de fined as the ra tio of the destabilizing and sta bi liz ing ef fects (Bond and Har ris, 2008) ex pressed in %. Slope sta bil ity equi lib rium is reached when uti li za tion is equal to 100%. If uti li - za tion is <100%– slope sta bil ity is sat is fac tory, if uti li za tion is
>100%, slope sta bil ity is not sat is fac tory. Cal cu la tions were pro - vided ac cord ing to tech ni cal re quire ment STR 2.05.21:2016 ap - ply ing third (III) de sign ap proach.
The Gediminas Hill slope sta bil ity eval u a tion was made on cross-sec tions shown in Fig ure 2 with a worst case sce nario, when technogenic soil sat u ra tion is 90%. In Fig ure 2 the north - ern slope is marked as III, east ern slope – V’, south ern – III’, west ern – V. The re sults of slope sta bil ity anal y sis are shown in Fig ures 5–8 (stra tig ra phy in dex and soil layer iden ti fi ca tion is the same as in Ta ble 1). The uti li za tion fac tor of slope sta bil ity ob tained is:
in the north ern part – 82.5%, east ern part – 75.8%, south ern part – 79.4%, west ern part – 71.9%.
Cal cu lated slope sta bil ity is high enough for such steep slopes, where slope in cli na tion is from 28 up to 57°. More over, soil sta bil ity is usu ally not sat is fac tory for technogenic soil lay - ers, where the for ma tion of shal low land slides is ob served. An ex am ple of such a shal low land slide is shown in Fig ure 6, where a dis trib uted 10 kPa load on the path is eval u ated.
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Fig. 5. North ern slope sta bil ity anal y sis
In re cent years, shal low land slides in the techogenic soil layer have ap peared on the east ern slope in 2004 and re curred in 2008, and on the north ern slope in 2016 (Skuodis and Ng, 2018). These land slides ap peared due to ex treme weather con - di tions with very large rain fall. The re sults shown in Fig ures 5–8 also show that the nat u ral Gediminas Hill soil lay ers are sta ble enough. Also, since 2020, the Gediminas Hill top pre cip i ta tion wa ter col lec tion and re moval sys tem has been com pleted. This partly helps to col lect rain wa ter from the technogenic soil layer and avoids deeper soil sat u ra tion.
CONCLUSIONS
We pro vide an up date of en gi neer ing geo log i cal and geo - technical in ves ti ga tions of Gediminas Hill re al ized in 2019–2020, when new re sults re lated to geo log i cal lay ers and geotechnical
and hydrogeological pa ram e ters were ob tained. The en tire nat u - ral sur face of Gediminas Hill has been mod i fied by hu man ac tiv ity and cov ered with technogenic soil (tIV). The Mid dle Pleis to cene de pos its are af fected by deluvial pro cesses and hu man ac tiv i ties on the slopes of the hill. Dur ing this re search, weak nat u ral soil lay ers be neath the technogenic soil were found. Technogenic soil layer thick ness var ies from 0.6 up to 9.7 m. The thick est technogenic soil de pos its are in the south ern slope bot tom (5.5–9.7 m). The thin nest layer of technogenic soil (0.6–2.5 m) was found on the west ern slope, around the hill on gla cial (gdIIžm) de pos its and to wards the hill top. In the mid dle of Gediminas Hill stiff nat u ral soil lay ers were iden ti fied. Low and me dium wa ter con tent is see in the main part of the soil lay ers, that are char ac ter ized by var i ous par ti cle size dis tri bu tions, with coarse and fine soils.
Six nat u ral soil lithological types were found, namely: tIV – Ho lo cene technogenic weak soils and stiff de pos its of the Mid - dle Pleis to cene Medininkai (Warthian) Subformation: fIImd – Fig. 6. East ern slope sta bil ity anal y sis
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Fig. 7. South ern slope sta bil ity anal y sis
Fig. 8. West ern slope sta bil ity anal y sis
glaciofluvial; gdIImd – gla cial (de for ma tion till); Žemaitija (Saalian) Subformation: lgIIžm – glaciolacustrine; gdIIžm – gla cial (de for ma tion till); lgIIdn – glaciolacustrine de pos its of the Mid dle Pleis to cene Dainava (Elsterian 2) For ma tion. Ac - cord ing to per me abil ity cri te ria, up to 8 dif fer ent hydro - geological lay ers were dis tin guished in the Gediminas Hill struc ture, with 5 of these be ing per me able:
tIV (k = 0.4 m/d), fIImd (k = 9 m/d),
lgIIžm (k = 0. 3m/d, intermoraine k = 5.4 m/d), lgIIdn (k = 2.3 m/d);
3 are im per me able: gdIImd, lgIIžm and gdIIžm.
Po ten tially, zones with low slope sta bil ity cor re late with weak soils, their main con cen tra tions be ing on the north ern slope (at the top and bot tom), also on the east ern and west ern slopes. De tailed slope sta bil ity anal y sis was ac com plished with up dated en gi neer ing geo log i cal and geotechnical data.
The uti li za tion fac tors of slope sta bil ity were: in the north ern part 82.5%, east ern part – 75.8%, south ern part – 79.4%, west ern part – 71.9%. In the east ern part of Gediminas Hill the low est slope sta bil ity uti li za tion was found in the technogenic soil layer. This slope is mostly un sta ble and shows the larg est prob a bil ity of new shal low land slides if the technogenic soil layer be comes fully sat u rated. From the Gediminas Hill land - slide his tory, the technogenic soil layer de vel ops shal low land - slides af ter se vere pre cip i ta tion with rel a tively high sat u ra tion lev els.
Ac knowl edge ments. The au thors sin cerely thank the Na - tional Mu seum of Lith u a nia, JSC Hidroterra and JSC Geobaltic for al low ing pub li ca tion of this re search work, and anon y mous re view ers for their con struc tive com ments and sug ges tions for im prov ing the qual ity of this ar ti cle.
REFERENCES
AntanavièienÅ, R., 2012. Ur ban de vel op ment in Vilnius dur ing the Sec ond World War. Art and ar tis tic life dur ing the two world wars. Vilnius: Lietuvos kultñros tyrim÷ institutas: 319–350.
BaubinienÅ, A., MorkñnaitÅ, R., Bauûa, D., Vaitkevièius, G., Petrošius, R., 2015. As pects and meth ods in re con struct ing the me di eval ter rain and de pos its in Vilnius. Qua ter nary In ter na - tional, 386: 83–88.
Bond, A., Har ris, A., 2008. De cod ing Eurocode 7. 621.
Buhler, D., 2016. Mon u ments of civil en gi neer ing and the World Her i tage. En gi neer ing His tory and Her i tage, 169: 181–194.
Gadeikis, S., Dundulis, K., DaukëytÅ, A., GadeikytÅ, S., 2016.
The ca the dral of Vilnius: prob lems and fea tures of nat u ral con di - tions. In: Pro ceed ings of 13th Bal tic Sea Geotechnical Con fer - ence His tor i cal Ex pe ri ence and Chal lenges of Geotechnical Prob lems in Bal tic Sea Re gion“, Vilnius, Lith u a nia: 9–21.
GEO5. 2020. Slope sta bil ity anal y sis. En gi neer ing man ual No. 8.
Up dated: 01/2020. 13.
GuobytÅ, R., 2010. GeomorfologinÅs sritys ir rajonai // Lietuvos gamta (in Lith u a nian). Vilnius: Mokslo ir enciklopedij÷ leidybos centras: 16–18.
GuobytÅ, R., Satkñnas, J., 2011. Pleis to cene glaciations in Lith u a - nia. De vel op ments in Qua ter nary Sci ence, 15: 231–246.
Hemeda, S., Pitilakis, K., Bandis, S., 2015. Geotechnical, geo - phys i cal in ves ti ga tions and seis mic re sponse anal y sis of the un - der ground tombs in Mustafa Kamil Ne crop o lis, Al ex an dria, Egypt. Meditterranean Ar che ol ogy and Archaeometry, 15:
191–207.
Jelinek, R., Hervas, J., Wood, M., 2007. Risk Map ping of Land - slides in New Mem ber States. Eu ro pean Com mis sion Joint Re - search Cen tre In sti tute for the Pro tec tion and Se cu rity of the Cit - i zen.
Jonaitis, B., Antonoviè, V., Šneideris, A., Boris, R., 2019. Anal y - sis of phys i cal and me chan i cal prop er ties of the mor tar in the his toric re tain ing wall of the Gediminas Cas tle Hill (Vilnius, Lith - u a nia). Ma te ri als, 12: 1–15.
JSC Geobaltic, 2020. III geotechninÅs kategorijos projektini÷ IGG tyrim÷ visoje Gedimino kalno teritorijoje ataskaita (in Lith u a - nian).
Katalynas, K., Vaitkevièius, G., 2001. Vilniaus plÅtra iki XV amûiaus (in Lith u a nian). Kultñros paminklai, 8: 68–76.
Katzenbach, R., Leppla, S., Vogler, M., Seip, M., Kurze, S., 2013.
soil-struc ture-in ter ac tion of tun nels and su per struc tures dur ing con struc tion and ser vice time. Procedia En gi neer ing, 57:
35–44.
Kitkauskas, N., 2001. Gedimino kalno vakarinÅs papÅdÅs pirmykëtis reljefas ir ankstyvieji statiniai (in Lith u a nian). Lietuvi÷
katalik÷ mokslo akademijos metraëtis, 19: 213–242.
Kumar, A., Hughes, P.N., Toll, D.G., Coningham, R.A.E., Da vis, C., Sarhosis, V., Wilkinson, S., Joshi, A., Weise, K., Maskey, P.N., Acharya, K.P., Kunwar, R.B., 2019. Dam age as sess ment within the Kathmandu val ley’s World Her i tage Mon u ment Zones af ter 2015 Gorkha Earth quake. In: Pro ceed ings of the XVII ECSMGE-2019 Geotechnical En gi neer ing foun da tion of the fu - ture: 1–9.
Ladesma, A., Alonso, E.E., 2017. Pro tect ing sen si tive con struc - tions from tun nel ling: the case of World Her i tage build ings in Bar ce lona. Geotechnique, 67: 914–925.
Lietuvos kvartero stratigrafijos schemos aprašas (in Lith u a nian).
2009 m. birželio 17, Vilnius.
https://www.lgt.lt/uploads/1242304244_kvartero_str_scema2-2.pdf Mackevièius, R., 2013. Pos si bil ity for sta bi li za tion of grounds and
foun da tions of two valu able an cient ca the drals on weak soils in Bal tic Sea re gion with grout ing. Procedia En gi neer ing, 57:
730–738.
Maèiulis, A., 2005. Vilniaus ûemutinÅs pilies pirmavaizdûio aliuzija (in Lith u a nian). Acta Academiae artium Vilnensis. DailÅ, 38:
115–130.
Markelionis, M., MiltinytÅ, G., Popovas, D., Aksamitauskas, V.È., 2017. In ves ti ga tion of Vilnius Up per Cas tle ver ti cal de for ma - tions. 10th In ter na tional Con fer ence “En vi ron men tal En gi neer - ing”, 27–28 April 2017, Vilnius Gediminas Tech ni cal Uni ver sity, 1–7. Lith u a nia, Vilnius.
Medini, H.K., Arbi, M., 2018. Chem i cal and phys i cal anal y sis of sand stone and re la tion ship with weath er ing dam age of Madâin Sâlih mon u ments. Jour nal of Taibah Uni ver sity for Sci ence, 12:
37–45.
MikulÅnas, V., Minkevièius, V., Satkñnas, J., 2016. Gediminas’s Cas tle Hill (in Vilnius) case: slopes fail ure through his tor i cal times un til pres ent. Pro ceed ings of World Land slide Fo rum 4, May 29–June 2, Ljubljana.
MorkñnaitÅ, R., Èesnulevièius, A., 2005. Re cent in ves ti ga tions of the pe cu liar i ties of Vilnius re lief dy nam ics. Pro ceed ings of the Es to nian Acad emy of Sci ences: Ge ol ogy, 54: 191–203.
Sarti, G., Rossi, V., Amorosi, A., 2012. In flu ence of Ho lo cene strati graphic ar chi tec ture on ground sur face set tle ments: A case study from the City of Pisa (Tuscany, It aly). Sed i men tary Ge ol - ogy, 281: 75–87.
Satkñnas, J., Mikëys, R.B., MikulÅnas, V., Minkevièius, V., 2008.
Geodinaminiai procesai Vilniaus pili÷ teritorijoje: ëlait÷ defor - macijos (in Lith u a nian). Lietuvos pilys: 62–68.
Sharma, V.K., 2019. Her i tage stones in In dia. Geo log i cal So ci ety Spe cial Pub li ca tions, 486: 325–341.
Skuodis, Š., Kelevišius, K., Žaržojus, G., 2017. Vi bra tions mea - sure ment of the fu nic u lar gen er ated vi bra tions on Gediminas Hill north part slope. 10th In ter na tional con fer ence „En vi ron - men tal En gi neer ing“, 27–28 April 2017, Vilnius Gediminas Tech ni cal Uni ver sity: 1–8. Lith u a nia. Vilnius.
Skuodis, Š., Ng, P.L., 2018. Slope res to ra tion and top o graph i cal mon i tor ing for her i tage pres er va tion of Gediminas Hill and Cas - tle Tower in Lith u a nia. Pro ceed ings of the 38th An nual Sem i nar Geotechnical Di vi sion, The Hong Kong In sti tu tion of En gi neers
“Geotechnical en gi neer ing for in fra struc ture de vel op ment”, 18 May 2018, Geotechnical Di vi sion the Hong Kong In sti tu tion of En gi neers: 121–133.
Squeglia, N., Stacul, S., Abed, A.A., Benz, T., Leoni, M., 2018.
m-PISE: A novel nu mer i cal pro ce dure for pile in stal la tion and soil ex trac tion. Ap pli ca tion to the case of Lean ing Tower of Pisa.
Com put ers and Geotechnics, 102: 206–215.
STR 2.05.21:2016 Geotechninis projektavimas. Bendrieji reikala - vimai“ (in Lith u a nian).
Šadzevièius, R., Vyèius, Ž., Damulevièius, V., 2018. Gedimino kalno iaurÅs Vakar÷ ëlait÷ stabilumo modeliavimas (in Lith u a - nian). InûinerinÅs ir edukacinÅs technologijos, 1: 114–122.
Vaièiñnas, G., 2010. Gedimino kalno ëlait÷ stabilumo vertinimas (in Lith u a nian). Lietuvos pilys, 6: 65–75.
Vaitkevièius, G., KiëkienÅ, M.L., 2010. Kreivasis miestas (in Lith u - a nian). Miest÷ praeitis, 2: 1–21.
Zhu, D.Y., Lee, C.F., Qian, Q.H., Chen, G.R., 2005. A con cise al go - rithm for com put ing the fac tor of safety us ing the Morgenstern - -Price method. Ca na dian Geotechnical Jour nal, 42: 272–278.
arñnas Skuodis et al. / Geological Quarterly, 2021, 65: 42 13
