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Settlement predictions in the Anatolian Motorway, Turkey

Suleyman Dalgc a,*, Orhan Simsekb

aIstanbul University, Faculty of Engineering, 34850 Avclar, Istanbul, TurkeybIC Consulenten, Zollhouse weg No. 1 Bergheim, Salzburg, Austria

Received 19 February 2001; accepted 20 May 2002

Abstract

The Anatolian Motorway through the Asarsuyu Valley passes across the landslides which have been extensively disturbed

by past fault movements. The Asarsuyu Valley is the most important crossing of the motorway between Istanbul and Ankara

route. Along the Asarsuyu Valley, about 7 km of the roadway is still under construction. In this study, the magnitude and the rate

of the settlement over consolidated clays in lacustrine deposits within the Asarsuyu Valley were compared with each other. On

the basis of field observations and laboratory test results, it was determined that the lacustrine deposits were eroded up to 15 m

by the river in the valley bottom. As results of unloading and desiccation process, the clay layers are overconsolidated.

Settlement calculations indicate that the amount of clay layers has caused the intolerable consolidation settlement under the

concrete structures and motorway embankment. In this respect, preloading embankment on clay and silty clay deposits was

projected and constructed. On the basis of evaluations, estimated values of settlement are lower than those realized. However,

the predicted settlement quantities are found reliable and comparable to field measurements. On the other hand, significantdifferences were observed between calculated and measured rate of the settlement. The high rate of the settlement, which was

measured during preloading, was caused by the viscoelastic strain due to the relatively high load and sandy pockets available in

the clay layers, but was not detected by the drilling and the micro/macro texture of the clay layers.

D 2002 Elsevier Science B.V. All rights reserved.

Keywords: Landslide; Clay; Consolidation; Settlement; Predictions; Measurements

1. Introduction

This study was carried out in the Asarsuyu Valley

crossing of the Anatolian Motorway (Fig. 1). The

Asarsuyu crossing is located next to the Bolu Tunnel

crossing (Dalgc, 2000). The engineering geological

problems were observed both in the Asarsuyu cross-

ing and in the Bolu Tunnel of the motorway. One of

these geotechnical problems in the Asarsuyu Valley of

the Anatolian Motorway is the overconsolidated claylayers, which are encountered in the recent fluvial

deposits. Investigations reveal that the deposition of

the clay layers is associated with the Bakacak land-

slide blocking the valley front. In the area, other huge

landslides, which were caused by the North Anatolian

Fault, such as the Bakacak landslide, are available.

The horizontal and vertical extensions of the clay

layers in the lake deposits were investigated by a total

number of 16 boreholes. The natural unit weight,

grain unit weight, grain size distribution, Atterberg

0013-7952/02/$ - see front matterD 2002 Elsevier Science B.V. All rights reserved.P I I : S 0 0 1 3 - 7 9 5 2 ( 0 2 ) 0 0 1 5 4 - 0

* Corresponding author. Fax: +90-212-5911997.

E-mail address: [email protected] (S. Dalgc).

www.elsevier.com/locate/enggeo

Engineering Geology 67 (2002) 185199


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Limits and Consolidation tests were performed on the

undisturbed samples extracted from boreholes. These

tests were conducted in accordance with ASTM stand-

ards in the laboratories of Astaldi, the contractor firm

of Gumus ova Gerede Motorway, and the General

Directorate of State Highways. According to settle-

ment calculations performed by the authors on the

basis of results of 16 consolidation tests, preloading

embankment was found to be necessary and thecontractor firm implemented it. Following the pre-

loading fill, settlement measurements were controlled

with 5 magnetic settlement columns and 15 settlement

plates. This study indicated that there is an 88%

consistency between the settlement values determined

by calculation and in situ measurement. However,

some differences were observed in rate of the con-

solidation. The reason for this is the viscoelastic strain

due to the relatively high load and the micro and

macro textures of the clay that cannot be determined

easily in the laboratory conditions, and also clay

layers containing some sandy pockets in the field.

Most of the literatures about the consolidation

properties of the clays are for the determination of

the relations between compression index and index

properties (Ansal, 1987; Gunduz and Onalp, 1996;

Bowles, 1979; Herrero, 1980). In addition, estimation

of the compression index, depending on the minera-

logic composition of the soils and the geographicalposition, changes one region to another. In this study,

therefore, the value for the compression index of the

clays was evaluated with respect to results obtained

from odometer tests.

2. Lithology of the Asarsuyu Valley

The Asarsuyu Valley route passes through land-

slides formed in weak zones related to paleotectonic

Fig. 1. Location map.

S. Dalgc, O. Simsek / Engineering Geology 67 (2002) 185199186


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thrustfaults and the neotectonic North Anatolian Fault

Zone (Dalgc, 1998a). The Yedigoller formation con-

sists of metamorphic rocks and is the oldest unit

present at the Asarsuyu Valley. It is tectonicallyoverlain by the metamorphic Ikizoluk formation of

Devonian age. Above these strata the upper Creta-

ceous to upper Eocene sedimentary units are encoun-

tered. These formations are overlain by alluvium,

colluvium and lacustrine deposits (Figs. 2 and 3).

Alluvium deposits are generally composed of

rounded, subrounded, pebbly sand, blocky pebblysand and blocky pebbles derived from weakly altered,

intermediately softvery compact amphibolite, meta-

granite and other rocks. Thickness of these deposits at

Fig. 2. Evaluation of the Asarsuyu Valley before the clay deposits.

S. Dalgc, O. Simsek / Engineering Geology 67 (2002) 185199 187


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Fig.

3.

Longitudina

lcross-sectionoftheAsarsuyuValley.



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the downstream of Asarsuyu river is about 20 m.

Investigation boreholes drilled at the upstream part of

the river indicate that thickness of alluvium lowers to

6 8 m. Grain size of the deposits decreases fromupstream to downstream. Among the alluvium depos-

its, there are lens or wedge-shaped, weakly plastic,

intermediately compact, green silt and sandy silt

together with clay, silt and silty clay deposits with a

total thickness between 3 and 5 m.

Within the alluvium deposits, there are also plastic,

brownish grey coloured, overconsolidated, cohesive,

fissured clay and silty clays with thickness of 211 m.

There are two suggestions for the occurrence of these

deposits (Dalgc, 1994). They are: (1) alluvial depos-

its; (2) lacustrine deposits formed as a result of

blocking of the Asarsuyu Valley by the Bakacak

landslide.

The first suggestion indicates that, due to geo-

technical characteristics, these deposits cannot be

fluvial sediments. As will be explained further in

detail, these deposits are composed of overconsoli-

dated, cohesive, fissured, plastic clay and silty clay

(CH). The second suggestion is based on blocking of

Asarsuyu Valley by the Bakacak landslide, which

formed a lake behind the valley. Findings supporting

this suggestion are given below.

Cutting of landslide material in exploratory drill

holes. The motion of Bakacak landslide at south has

changed Asarsuyu riverbed. Remnant of the landslide material encountered at

northern side of the valley. Soil characteristics of the clayey deposits.

Considering the field characteristics given above, it

was believed that these sediments were deposited in

the lake that was formed behind the landslide dam.

3. Slope failure in Asarsuyu Valley

The Bakacak landslide, which gave rise to the

formation of lacustrine deposits in the study area,

has a length of 4 5 k m and a width of 1.5 km and

is still active (Fig. 4). As the toe of this landslide is

Fig. 4. Landslides areas in the Asarsuyu Valley.



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4. Seismicity of the Asarsuyu Valley

The magnitude of the earthquakes causing the

fault movements in the Asarsuyu Valley is estimatedto be around 7.0 (Dalgc, 1994). It can therefore be

assumed that earthquakes in the region have con-

tributed to several of the landslides when the hori-

zontal and vertical earth accelerations have affected

slopes in a critical condition (Dalgc, 1998b). Like-

wise, during the 12 November 1999 Duzce earth-

quake of M= 7.2, a landslide occurred in the

Asarsuyu Valley triggered by the earthquake. In

addition, Ambraseys (1988) records that the 1957

Abant earthquake triggered several landslides in the

region. These events support the blocking of the

Asarsuyu Valley by the Bakacak landslide and the

formation of the lake deposits.

5. Geotechnical properties of the lake deposits

Clayey layers in the lake deposits were evaluated

with the use of the data from 16 geotechnical

investigation bore holes drilled by Astaldi, the main

contractor of the Asarsuyu passage in the Gu-

musWovaGerede Motorway. In addition, in accord-

ance with ASTM (1985) standards, natural unitweight (cn), grain unit weight ( Gs), grain size dis-

tribution, and Atterberg limits of 16 undisturbed

samples from the boreholes were determined. The

consolidation properties were conducted by odometer

tests and the shear strengths of the soil have also

been measured.

6. Index properties

The grain size distribution of the disturbed andundisturbed clayey samples from the lake deposits of

the Asarsuyu Valley was determined by sieving from

number 4, 10, 40, and 200 sieves and, silt and clay

size remaining from the 200 sieves was determined

by the hydrometer test (Table 1). On the basis of

results, 6080% of the lake sediments are made of

clay and silt. The remaining part (11% and 39%) is

composed of silt, and a little part is sand. However,

there are also sites that have not been sampled during

drillings. Therefore, it can be stated that the sand ratio

of these deposits is high. Moreover, standard error

and standard deviation values given in Table 1 are

also high. This may indicate that grains are of differ-

ent sizes.

The specific gravity of the clays does not vary to

any great extent, ranging between 2.60 and 2.67, with

a mean value of 2.62. Test results from the exami-

nation of the clay layers are that an average value of

the water content, the degree of saturation and unit

weight are 45%, 79%, 1800 kg/m3, respectively. Theaverage values of liquid limit, plastic limit and

plasticity index for these clays are 75%, 31%, and

45%, respectively (Table 2). The liquid limit varies

from 49.6% to 94%, the plastic limit from 24% to

37% and the plasticity index from 25% to 67%. The

liquidity index is always very low indicating that the

value of natural moisture content is never above that

of the plastic limit. This is typical of highly over-

consolidated clays (Fig. 5). The range of liquidity

index varies from 0.12 to 0.92 with an average value

of 0.34. The consistency indices suggest that this isstiff clay (Table 2).

7. Undrained shear strength

Triaxial tests with unconsolidatedundrained shear

parameters were determined on 16 clay and silt

samples. The range of undrained cohesion varied from

40 to 219 kN/m2 with an average value of 83 kN/m2.

Variation of test results with respect to depth is shown

Table 2

Consistency limits (Atterberg limits) of clay layer

Consistency

limits

Min. Max. Average

value (x)

Standard

error (SE)

Standard

deviation

(SD)

Water content

(%)

27.07 89.42 45.71 12.4 13.8

Liquid limit

[LL] (%)

49.6 94.0 74.77 13.79 14.32

Plastic limit

[PL] (%)

24.0 36.8 30.75 4.61 4.78

Plasticity index

[PI] (%)

24.9 67.2 44.72 11.48 11.91

Liquidity index

[LI] (%)

0.12 0.92 0.34 0.25 0.27

Consistency index

[CI] (%)

0.07 0.87 0.64 0.25 0.27



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in Fig. 6. Results show that unconsolidated un-

drained parameters of clay and silty clays increase

from top to bottom. Changing of values may be

explained by overconsolidation of upper layers. How-

ever, strength values obtained from SPT tests indicate

no significant difference between surface and bottom

sections (Fig. 7).

8. Consolidation properties

Consolidation properties of the clays were per-

formed on 16 undisturbed samples, taken from the

surface to a depth of 11.25 m, using the odometer

device based on ASTM (1985) standards. Using the

data obtained from tests, graphics of pressure (log-

arithmic) void ratio and settlement-time relation of

clays were drawn. Consolidation coefficient (Cv),

volumetric compression coefficient (Mv) and com-

pression indices (Cc and Cr) were determined from

these graphics. Also using the relation between

preconsolidation pressure (Pc) and initial effective

vertical stress (Po), overconsolidation ratio (OCR)

was computed. Preconsolidation pressure and com-

pression indices (Cc = compression index and Cr=re-

compression index) were graphically determined(Table 3).

The preconsolidation pressure has been deter-

mined from the laboratory curves by the procedure

proposed by Casagrande. The preconsolidation char-

Fig. 7. Variation of N SPT values with depth.

Fig. 6. Undrained cohesion for cohesive soil.



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acteristics of the lake deposit profile are expressed in

terms of the consolidation ratio (OCR) versus depth

plot, as shown in Fig. 8. Evaluations reveal that Pcvalues in first meters are extremely high in compar-

ison to Po. Overconsolidation ratio (Pc/Po) values in

silty clays drop from 14 to 3 from the surface to a

depth of 12 m. These values indicate that the upper

clay and silty clays above are more overconsolidated

in comparison to those underlying.

The coefficients of consolidation (Cv) obtained

from the laboratory tests for various sublayers are

shown in Fig. 9. For a pressure interval of 14 kg/

cm2, an average (Cv) value for consolidation settle-

ment time is taken as 0.003 cm2/s. The Cv values are

Fig. 8. The variation of the overconsolidation ratio with depth.

Table 3

Consolidation parameters

Sample Chainage (km) Depth (m) Po Pc OCR eo Cr Cc

M345-UD1 9 + 650 to 9 + 800 2.4 19.2 240 12.5 1.326 0.087 0.62M345-UD5 4.2 33.6 250 7.44 1.116 0.072 0.52

M346-UD2 9 + 800 to 9 + 860 2.5 20.0 280 14 1.148 0.044 0.34

M346-UD4 3.7 29.6 300 10.13 1.275 0.080 0.45

M346-UD9 7.7 61.6 300 4.87 1.043 0.090 0.66

M346-UD11 9.3 74.4 320 4.30 0.955 0.055 0.35

M304-UD2 9 + 860 to 9 + 900 5.0 40.0 250 6.25 1.245 0.064 0.61

M304-UD3 9.0 72.0 280 3.88 1.009 0.049 0.24

M304-UD4 10.75 86.0 400 4.65 0.900 0.062 0.46

M347-UD2 9 + 900 to 10 + 000 3.25 26.0 200 7.69 1.234 0.029 0.36

M347-UD4 4.75 38.0 250 6.57 1.044 0.038 0.27

M347-UD9 8.75 70.0 300 4.28 1.147 0.082 0.52

M347-UD11 10.25 82.0 320 3.90 1.039 0.072 0.48

M305-UD1 10 + 00 to 10 + 060 9.25 74.0 280 3.78 0.838 0.072 0.42

M344-UD2 9.25 74.0 350 4.72 1.385 0.12 0.54M306-UD2 11.25 90.0 280 3.11 1.155 0.060 0.31

Po = effective pressure (kN/m2); Pc = preconsolidation pressure (kN/m

2); OCR = overconsolidation ratio; Cc = compression index; Cr= recom-

pression index; eo = void ratio.



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within the range of 0.00150.014 cm2/s and do not

show any relationship with depth.

9. Geological evolution and preconsolidation

pressure

In the case of the preconsolidation pressure (Pc)

being higher than the present overburden pressure,

one of the following conditions may be the cause:

(a) Thicker soil overburden, which has since been

removed or eroded

(b) Change in the groundwater level (Kenny, 1964)

(c) Desiccation of soil (increasing of Pc with respectto Po).

Besides the general conditions mentioned above,

cementing, a change in the ion concentration,

oxidation (Bjerrum, 1972), depositional conditions,

and mineralogic composition are the other impor-

tant factors increasing the preconsolidation pressure

(Pc).

At normal conditions, consolidated clay and silty

clay are expected in recent fluvial deposits. However,

considering the geologic model of the valley (Figs. 2, 3

and 4), the Bakacak landslide closed this part of valley

and gave rise to the formation of clay and silty clay

layers. By the erosion of landslide materials in front ofthe lake deposits, the part of the geologic load was

unloaded from the upper part of the clayey deposits

and, as a consequence, the clay layers were over-

consolidated. After the erosional phenomena, desicca-

tion processes also took place to contribute to the

overconsolidation of clay layers. Preconsolidation

pressure (Pc) values (200400 kN/m2) also indicate

that erosion is about 15 m. This is also supported by

uneroded remnants of the landslide in the valley.

10. Settlement calculation

Accurate determination of Pc values of the clay is

vital for the accurate settlement analyses and for

determining the geological evolution. In the situations

where

(1) Pc =Po (normal consolidation)

(2) If P+Po Pc (overconsolidated clay).

Fig. 9. The variation of consolidation coefficient (Cv) with applied pressure.



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As stated above, clay and silty clays in the study

area are overconsolidated. The sum of embankment

load (DP) and the overburden load (Po) exceed

preconsolidation pressure (Pc), and therefore, thethird case is valid. A small part of the calculated

and measured settlements support the second case.

Consolidation settlements of clay and silty layers

under the embankment were computed at 19 points.

Primary settlements were taken as the total of each

sublayers settlement. The following equation was

used in this approach (Das, 1983).

S HCr

1 eolog

Pc

Po H

Cc

1 eolog

DP PoPc

1

where S= total settlement; H= thickness of clay

layer; Cr= recompression index; eo = initial void

ratio; DP= applied load; Pc = preconsolidation pres-

sure; Cc = compression index of normal consolidated

clay.

Summary of these results are given in Table 4. The

consolidation settlement time (t90%) is calculated in

accordance with the Terzahgi consolidation theory.

The time factor (Tv) was established for consolidation

degree U= 90%.

Where

t90% Tv1=2h2Cv

11. Settlement monitoring

Preloading embankment was constructed at heights

between 12 and 19 m in order to provide preconso-

lidation for solid clay and silty clay encountered under

motorway embankment and concrete structures. The

height of preloading fill was projected on the basis of

calculated total settlement, settlement amount toler-

able for concrete structure (15 cm) and 90% settle-ment time. In situ settlement measurements were

implemented with 15 settlement plates and 5 magnetic

settlement columns. Settlement plates measure total

settlement from the soil surface while magnetic settle-

ment columns measure settlements on different levels.

Settlement was taken for an observation period lasting

380 days. Measurements taken with settlement col-

umns and settlement plates in this period are consis-

tent. Minimum and maximum values obtained for the

Table 4

Predicted and monitored settlement rate

Chainage

(km)

Thickness of

comp. layer

(m)

Height of preloading

embankment (m) as

constructed

Predicted

settlement

(a) (cm)

Monitored

settlement

(b) (cm)

a/b=rate

(%)

9 + 650 3 14 21 21 100

9 + 675 4 16 29 20 70

9 + 700 5 16 35 28 80

9 + 730 5.5 14 32 26 82

9 + 760 5 13 26 28 100

9 + 790 5 13 26 24 92

9 + 820 8 13 24 14 60

9 + 850 10 13 31 32 100

9 + 880 8 13 24 22 91

9 + 920 11.5 12 31 25 80

9 + 935 11.5 13 37 33 89

9 + 965 8 10 16 17 100

9 + 990 8 13 25 21 80

10 + 015 8 16.8 40 36 90

10 + 045 5 18.5 28 24 85

10 + 075 4.5 19 28 25 89

10 + 095 5 19 28 26 93

10 + 130 4.5 19 20 26 100

10 + 152 5 19 21 18 85



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Fig. 10. Predicted and monitored settlement along preloading embankment.

Fig. 11. Typical theoretic and monitored settlements curve in the embankment.



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ment of a time-dependent consolidation process

requires a material method relevant to water flux in

soil voids (such as Darcy Law), an equation for

permeability void ratio and a stress-unit deformationequation for the grain phase of the soil. Some

assumptions in the Terzaghi uniaxial consolidation

theory are not realistic and are inconsistent with

application cases. At unstable conditions, depending

on the effective stress level, soil characteristics may

change in a nonlinear shape (Barden, 1969; Ladd et

al., 1977). As a result, considering the settlement

time relation determined from odometer tests con-

ducted in the laboratory, if a geotechnic design is

implemented for important projects, different results

might be obtained in practice (Saglamer and Ylmaz,

1998). However, close agreement between observed

and predicted behaviour was obtained when field

parameters were used in the analyses. Although

substantially overestimating the time required for

completion of primary settlements, the finite element

predictions of the magnitude and the rate of settle-

ments are considered satisfactory (Al-Shamrani and

Dhowian, 1996).

Investigations reveal that consolidation in the study

area was rapidly developed when compared to that in

the laboratory. Fissured structure in the clay layer

compressible during the loading, which could not bedetermined sensitively during the field investigations,

silt and sand levels together with the size of consol-

idation device, that is unsuitable to reflect the field

conditions, accelerated the consolidation process.

Because drainage lengths are not sufficiently known,

consolidation coefficients (Cv) indirectly calculated

from the field data are not meaningful. Instead, t90or t50 values should be respected.

13. Conclusions

Overconsolidated clay layers were encountered

within recent lake deposits in the Asarsuyu Valley

pass at the Bolu mountain part of the Anatolian

Motorway. Field and laboratory investigations indi-

cate that overconsolidated clay was deposited in a lake

environment, which is formed as a result of blocking

of the valley by the Bakacak landslide. It was deter-

mined that these clay deposits gained an overconso-

lidated character with erosion, and drying processes

prevailed in a later stage as also shown by a 15-m

eroded part in the valley.

Consolidation tests conducted on these deposits

reveal that settlement values tolerable for concretestructures may be exceeded. In this respect, the soil

improvement by preloading is found to be necessary.

Preloading embankment of height ranging from 12 to

19 m has been constructed on clay and silty clay

deposits and in situ settlement measurements were

checked with the use of 5 magnetic rings and 15

settlement plates.

The measured settlements compare well with those

predicted by using consolidation parameters averaged

from laboratory data. Investigations indicate that there

is an 88% consistency between the settlement magni-

tude calculated on the basis of field and laboratory

data.

Settlement rates determined in the field are higher

than those obtained in the laboratory. This could be

attributed to the viscoelastic strain and the insufficient

size of tested samples determined in the laboratory,

which could not adequately represent micro and

macro texture of the clays and clay laminations and

associated sandy layers that could not be sufficiently

determined with drilling techniques. In order to exam-

ine this negative effect, consolidation tests should be

conducted on bigger samples or Cv should be eval-uated in the field.

Acknowledgements

The authors acknowledge the help of Astaldi, the

main contractor of the GumusWovaGerede Motorway

and Yuksel-Rendel, the Control Engineer on behalf of

the client, for their help in the preparation of this

manuscript.

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