Engineering geological problems in loess regions of hungary

Quaternary International, Vol. 24, pp. 25-30, 1994. Copyright © 1994 INQUA/Elsevier Science Ltd. Printed in Great Britain. All fights reserved. 104045182/94 $26.00

Pergamon

E N G I N E E R I N G G E O L O G I C A L P R O B L E M S IN LOESS REGIONS OF H U N G A R Y P. Fodor* and B. Klebt *Central Geological Office, Budapest, Hungary tDepartment of Mineralogy and Geology, Budapest Technical University, Budapest, Hungary Throughout Hungary periglacial conditions were widespread in the Pleistocene. As a result, one-third of the country is covered by loess and its subtypes. From an engineering geological point of view the major problems concerning these areas are the erosion and landslide bluffs and the collapsing of cellars dug in the loess. The length of cellar network in the studied settlements reaches 100 kin. The engineering geological studies therefore were concentrated on these two major problems. From a geological viewpoint the territory of Hungary forms a part of the Carpathian basin surrounded by mountain ranges of the Alps, the Carpathians and the Dinarids. Geomorphologically, the area of the country (93,030 square km) is of basin character, dominated by plains (68.8 per cent), with only limited vertical dissection. As far as the superficial geological formations are concerned, the loose, clastic deposits of Quaternary age are dominant. Some 43.8 per cent of these are of fluvial origin (including lacustrine and pasudal) and 42.0 per cent are of aeolian origin.

Local circumstances of the accumulation and those of the subsequent impact on the deposited duct and on the resultant

DISTRIBUTION OF LOESS AND ITS MAIN TYPES Throughout Hungary periglacial conditions (those typical regions surrounding the glaciated areas) prevailed during the Pleistocene. In cool and dry intervals, dust (the initial material of the loess) was deposited over vast areas (Fig. 1).

loess, however, are manifested in their differentiation. In this way engineering geological characteristics of the formations vary considerably. Zones of the mid-mountains also occur in the higher parts of the lowlands (state altitudinal range). Its thickness varies significantly, from 2 to 10 m in the plains up 21"

14" 17'

2o"

l

/

22"

,s

111"

o .~S.......s.$ J !

/

II

typical loess sandy loess loess loam, brown clayey loess 0

25

SO

I

I

I

lOOkm I

I

FIG. 1. The distribution of loess and its main types in Hungary.

25

silty, infusion loess

26

P. Fodor and B. Kleb 19'

f

/o,o2_o, osm~xx, x

18' 48* CZEc' ~ SLOVAK'~'~ Jr

/ \\ /

BUD,!EST

s°dicl°ess"~'~//dri fI sond~l~X

< 0,0Zmm ~

> 0,05mrn

50*/,

47*

Ip%

~,

r , ~

sodicIo~ +~+ ' ;~ ,

,o

.....

,o,ss,o'~m,d: '~/ / 2° .ri.g: ; ~ s s {infusion ~

o

0

20

I 40

1924 Racatmo --I964 1960 DunutJjvoros'~--~1946 19501963

60

PaRs~-~L-1975

B0WL%

_

N

°°°°=" : k

''/"

FIG. 2. Grain size composition and plasticity of loess by types (using data by T. Ung~r).

~-,~..2 ,~ ,o to 50 to 90 m in the southeast part of the Transdanubian hills. Typical loess is of pale yellow colour. Its characteristic feature is a macroporous structure, a skeleton of pipelets cemented by carbonate. Typical loess has a significant carbonate content but, due to its high permeability, it is frequently dissolved by water through the surface layers. Typical characteristics are as follows: CaCO3 = 14-27% Dm = 0.046--0.050 m m e = 0.65-1.1 n = 39-52%

~:

~oR~

FIG. 3. Location of loess bluffs along the Danube. 1 = bluff in the immediate vicinity of the river; 2 = bluff, distant from the river; 3 = date of considerable mass movements.

WE = 31--42% Wp = 20-25% Ip = 4-22%

Typical loess is a product of sequential development and so is not a homogeneous formation. In thick profiles intercalated fossil soils of reddish brown colour occur. Such loamy horizons mixed with loess result in raw material of medium plasticity suitable for the production of bricks of low stability. Many brickyards of Transdanubia use this mixture. Due to its unique structure, loess forms bluffs in which columns become isolated along vertical joints. When dry, loess is very stable. Development of wetland loess in certain locations, has resulted from dust deposition in moist areas or places covered by water. It is a characteristic formation over the Trans-Tisza Region where the thickness of loess rarely exceeds 1 to 3 m. The deeper horizons of the loess are of greyish colour and generally have a fine stratification. Particle distribution differs from that of typical loess, being mixed with flood plain silt and clay. It has a low .plasticity index, organic matter is frequently encountered (Fig. 2), and carbonate

FIG. 4. Slip plane in a loess bluff, D u n a f t l d v ~ 1970.

EngineeringGeologicalProblems

27

HG. 5. In front of the failed blufflandslide lobes piled up into shoalsin the river bed, Dtmaf01dvgr1970.

content is variable. Typical values of this material are listed below.

mentioned above, and typical properties include the following;

CaCO3 = 12-38% Dm= 0.025-0.052 mm e = 0.59-0.73 n = 37-42%

CaCO3 = 10-15%

WL = 17-22%

Dm= 0.058-0.066 mm e = 0.52-0.59 n = 34-37%

Wp = 11-17% Ip = 5-10%

WL = 22--42% Wp -- 15-23% Ir = 7-23%

Fine dust sedimented in depressions, under the influence of alkaline soil solutions can be fixed by salt accumulation resulting in 'alcalic' loess. This type of loess is highly compressed with the prevalence of the silt fraction. Loess of the detrital sediments and sand dunes also differs from the typical loess since it has rounded sand particles in abundance and is called sandy loess. It is yellow in colour turning into greyish towards the deeper layers. This type of loess occurs in undulating landscapes o f the Great Plain and Transdanubia. On average, particles are coarser than those of the types

In hill landscapes and in areas marginal to the mountains which have higher precipitation and more abundant vegetation, and so more intense weathering and more advanced soil formation, the initial loess structure has undergone transformation into clayey loess. Loess loam thus formed has an increased mineral content, is leached and of a darker colour, as well as being more compact and consolidated. When dry, loess loam is hard, but when moistened it becomes plastic. Its properties include the following;

28

P. Fodor and B. Kleb

FIG. 6. Bank protection in Dunatijv~os. Terraced in situ loess, with bank protection establishment in the front, built in the Danube (1968).

CaCO 3 = 2-10% D m = 0.02-0.055 m m

e = 0.50-1.22 n = 33-55%

WL = 33-50% Wp = 18-25% Ip = 17-30%

THE P R O B L E M OF LOESS BLUFFS As is widely known, a characteristic feature of typical loess is its vertical joint systems. The steep loess bluffs of the

FIG. 7. Opened collapse of loess cellars at Nagymaros.

Engineering GeologicalProblems

29

19" 100

18"

48°

~

,~0

agy b6rzsony

p

kPo 300

~d=1,/,7 g/cm3 e - 0,81

2

Nagymoros N ~Kosd

SL V~ 'v'\b''

loading 200

s -0.29

/.00 s 55,0 % w 13,1% a 31,9%

5-

Velence--

_n~,

n "

i

Es"&A--~E"/,,6 MPa izholombGlto

10-

o.....~ fI00 d~tn9

~.,.~

_~

Szekesfel'~r~ 1 /, 7*

~

~

FIG. 10. Compressibility and collapsibility of loess.

~Dlunaujvaros

.

uu 1

II~gocs

"L''J

B~taap6ti t.6"

~ I

~ ( t

( /

Ju

o v o s LIAr

I~A

'

50km '

'

FIG. 8. Settlements with cellar problems on record. 1 = collapse on record; 2 = engim¢ring geological mapping under way in settlements under hazard.

e 0,6

(~7

0,8

5 E

0,9

-

oI

lO

compression module 5

~

I . .:'/

"Io 1 6 ~

.'Eqt .-.;" "~.

E

I'lL

}1o

-

NPa

15 I

150

o =~o. o" I

50-

5

10

~5

plasticity index

20 ~ %

FIG. 9. Changingof the physicalparametersof loess with thickness.

Danube pose an engineering geological problem. These high bluffs stretch along the eastern margin of Transdanubia over a distance of 200 km from Budapest southward to Moh~ics. The length of the bluffs total 50 km and in some places they reach 50 to 60 m in thickness (Fig. 3). Steep bluffs of different height consist mainly of the loess series. Apart from the typical loess these sequences consist of fossil soils and fine-grained, bedded sand. Experience shows that intensive surface movements endangering buildings and other structures occur in those places where the bluff extends close to the river channel or is connected to the bank with a waste mound of earlier landslides. In such locations, direct effects of underwash by the Danube must be taken into account especially as fluctuations of the water level of the river may reach 10 m. This inevitably leads to variations in groundwater pressures, degrees of saturation and drainage within the loess deposits. Among several mass movements, a classic landslide occurred recently, initially as a vertical failure and the loess deposits displaced during this slide accumulated as a bank in the Danube (Figs 4 and 5). Such mass movements pose a particular hazard since some large industrial works and settlements have been developed on the edge of the bluffs and an increased probability of the occurrence of landslides has resulted from seeping of water from public utilities. The most serious landslide took place on February 29, 1964 at Dunadjvfiros. This affected a section of the bluff 1300 m length and 15 to 25 m in width. Total displacement was 10 million m 3 of loose deposits. The damage involved costs of about 1 billion forints. Bluff protection measures started with terracing of the in situ loess. Other bank protection measures included the construction of a bank revetment (Fig. 6). A training wall was built along the Danube and connected with the bank through transverse dykes and the area between them filled back by loess and gravel. Groundwater is collected by dewatering wells, drainage tunnels and desiccating shafts. To catch surface waters a belt ditch system was constructed. Other areas threatened by mass movements along the river have not been given protection on such a scale. Nevertheless, preventive measures are still considered important.

30

P. Fodor and B. Kleb

P R O B L E M S O F CELLARS CUT INTO LOESS Loess is easy to excavate. For this reason, construction of wine-cellars in loess is a widespread phenomenon in Hungary. Initially these cellars used to be dry due to the favourable ventilation qualities of loess which provide a stable average temperature all year long. In recent years, however, intensive urbanization and the construction of public utilities networks have posed a growing hazard associated with seeping waters, so that cellars in loess have collapsed in several places (Fig. 7). Similar problems have been reported from about 40 settlements. The total length of deep galleries in the country amounts to 500 kin. Of this total, those hollowed in loess make up 80 to 100 km (Fig. 8). This explains why current engineering geological mapping extends almost exclusively to settlements with cellars. An example is the town of Paks, under which as many as 1800 cellars exist. Since these galleries occur under establishments such as buildings and public roads, any damage constitutes a hazard situation. The main source of problems in these areas is the development of a public water supply coinciding with desiccation schemes without an appropriate construction of sewerage systems, as well as the dynamic load caused by the public transport system. Large sums of money are currently spent to secure their safety by special stowage at Szekszgtrd and Nagymaros.

PROBLEMS OF FOUNDATIONS AND EARTHWORKS It follows from the above discussion that loess and its main variant facies are widespread in Hungary and pose particular problems in foundation and civil engineering. The area affected by damage to buildings constitutes a mere 2% of the territory covered by loess. In dry conditions loess has a considerable load strength (and a related high value of compressibility). Its great thickness is an advantage from a civil engineering point of view (in some places amounting to several tens of metres) especially as its bulk density and compaction increase with thickness (Fig. 9). With a rise in moisture content, however, collapse becomes a hazard to any buildings or structures (Fig. 10).

Subsidence is attributed to an abrupt destruction of soil structure upon moistening, its character and extent depending on the initial voids ratio and moisture content of the deposits, on the amount of load and the water added. As a rule,if the initial voids ratio (e0) remains below 0.8, smallscale collapse is to be expected. For safety reasons, inflow of a large amounts of water should be prevented. Since a considerable part of the country is covered by loess it would be useful to consider its use in large-scale earthworks (i.e. motorway and dike construction). However, this is problematical because, due to low Ip values of loess, even a minimum increase in moisture content leads to creep as occurred during the construction of the M 1 motorway and the subsequent serious damage.

REFERENCES Fodor, T., Horv~ith,Zs. et al. (1981). Ingenieurgeologische Kartierung und Stabili~tsuntersuchung des Donau-Hochufers zwischen Dunaf61dv(tr und Paks. FOldtani Ki~zli~ny,111(2), 258-280 (in Hungarian). Fodor, T. and Kleb, B. (1986). Magyarorszdg m~rnb'kgeol6giai dttekinMse (Engineering-geological survey of Hungary). F01dtani Int6zet kiadvftnya, Budapest, 119 pp. (in Hungarian). Galli, L. (1951). A 16sztalajok keletkez6se 6s tulajdons~iguk m6ro0ki szemponth61 (The formation of loess soils and their properties from an engineering point of view). M61y6pft6studom(myi Szemle, 1(5), 270-274 (in Hungarian). Kar~tcsonyi, S. and Scheuer, Gy. (1972). A dunai magaspartok ~pft6sf01dtani probl6m(ti (Engineering-geological problems of high bluffs along the Danube). FiJldtani KutaMs, 15(4), 71-83 (in Hungarian). Kleb, B. (1988). Engineering-geological test on settlements with cellar difficulties. Periodica Polytechnica, 32(3-4), 99-129. Kleb, B. (1988). Geological-technical catastering of areas with surface movement. Periodica Polytechnica, 32(3-4), 131-149. P6csi, M. and Scheuer, Gy. (1979). Engineering-geological problems of the Dunaujv(tros loess bluff. Acta Geologica Acad. Sci. Hung. XXII(1-4), 345-353. P~csi, M., Schweitzer, F. and Scbeuer, Gy. (1979). Engineering-geological and geomorphological investigation of landslides in the loess bluffs along the Danube in the Great Hungarian Plain. Acta Geologica Acad. $ci. Hung. XXII(1-4), 327-343. R6th~iti,L. (1977). Altalaj eredefi lpaletkdrok (Building damages of subsoU origin). Akad6mial I¢dad6, Budapest, 251 pp. (in Hungarian). R6nal, A. (1979). Geological mapping of the Hungarian Plain. Acta Geologica Acad. Sci. Hung. XXII(1--4), 355-365. Ung~r, T. (1964). Physical properties of loessic soils. Hidrol6giai Kt~zh~ny. 44(12), 537-545 (in Hungarian).