PERFORMANCE OF SOIL-NAILED AND ANCHORED WALLS BASED ON FIELD-MONITORING DATA IN DIFFERENT SOIL CONDITIONS IN ISTANBUL
Dogan Qetin
Yildiz Technical University, Civil Engineering Department Davutpasa Campus, Esenler, Istanbul, Turkey E-mail: dogancetin56@hotmail.com
Keywords
deep excavation, wall displacement, soil formation, soil-nailed wall, anchored wall
Abstract
In this study, data on the lateral wall displacements of 28 deep excavations in Istanbul soil from over 90 field monitors were collected and analysed. The most commonly used retaining walls for deep excavations in Istanbul are soil-nailed shotcrete walls (SNPWs) and contiguous pile walls (CPWs). Other types of retaining walls include anchored micropile walls (MPWs), diaphragm walls (DWs), concrete walls (CWs) and secantpile walls (SPWs). The analyses were performed under two main headings: analysis of soil-nailed walls' data and analysis of anchored walls' data. The data of S^max generally range from 0.05%H to 0.35%H with an average value of 0.20%H in the soil-nailed projects. The data of Sh,max generally range from 0.043%H to 0.32%H with an average value of 0.155%H in anchored pile wall projects. Some factors affecting the deformation of deep excavations, such as nail density, embedded wall ratio and wall stiffness, were studied based on field-monitoring data. Wall movements were also compared with observations in some case histories from around the world.
1 INTRODUCTION
Due to the city's rapid economic growth, a number of deep excavation projects for high-rise buildings, shopping malls and metro systems have been carried out in Istanbul during the past two decades [1]. Estimates of the wall movements and ground deformations induced by deep excavations are critically important in urban areas in order to be able to provide safety for adjacent structures and buildings [2, 3]. Understanding the behaviour of excavation bracing is a complicated issue because of the number of factors affecting the performance of wall systems, such as soil type, base stability, compression and rebound, consolidation, wall-system stiffness, construction procedures, and workmanship [3, 4]. Any of these factors can contribute to the overall movement of a supported excavation. Therefore, great concern has been shown with respect to deep excavations since the report initiated by Peck [5]. Numerous researches have been performed to understand and evaluate the behaviour of retaining walls. Because of the difficulties in making a direct analysis of the performance of wall systems and the behaviour of ground deformation [3,6,7], case studies have been a better way to obtain information about deep excavations and retaining walls. Case studies performed by Ma et al. [3], Hwang and Moh [6], Finno and Bryson [8], Ou et al. [9], Hou et al. [10], Wong and Chou [11] can be given as examples.
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D. Qetin: Performance of soil-nailed and anchored walls based on fleld-monltoring data in different soil conditions In Istanbul
Databases prepared by Goldberg et al. [12], Mana and Clough [13], Clough and O'Rourke [14], Ou et al. [15], Wong and Patron [16], Carder [17], Fernie and Suckling [18], Wong et al. [19], Hsieh and Ou [20], Long [21], Yoo [22], Moormann [23] and Leung and Ng [24] present comprehensive information about the performance of in-situ walls constructed in urban areas in terms of different soil conditions, adjacent structures and utilities.
In this study, data from field monitors on the lateral displacement of the walls from some 28 deep excavations in Istanbul soil were collected. The notation for the symbols and parameters used in this study is shown in Figure 1. The magnitudes of the lateral displacement for different types of retaining systems were compared with each other and also compared with relevant case histories worldwide. Furthermore, some factors affecting the deformation of deep excavations were studied.
Figure 1. Definition of the wall and support parameters in a deep excavation.
H is the excavation depth, Hemb is the embedded wall length, sv is the vertical distance between the anchors or soil-nailing levels, Hw is the depth of the ground-water level from the surface, Sh,max is the maximum wall displacement and ft is the wall inclination from the vertical in Fig.1.
2 GENERAL SOIL CONDITIONS IN PROJECT FIELDS
A very comprehensive and detailed geotechnical survey carried out by the Metropolitan Municipality of Istanbul between 2005 and 2009 for very large areas of both the Asian and European sides of the city [25, 26] was used to explain the soil profile and general soil properties in the project fields. As a result of that intensive work, 24 different local soil formations were identified on both the Asian and European sides. If the project fields are placed on the map of the microzonation work, it can be seen that 7 of the 24 local formations were encountered in deep-excavation projects. These local formations can be called Fill, Alluvium, Gungoren, Gurpinar, Bakirkoy, Cukurcesme and Trakya. The alluvium in the investigated areas mainly consists of clay-type materials of soft-to-medium stiffness. Sand layers are also present at different depths. The Gungoren formation is composed of clay and sand layers that are very stiff and dense. The over-consolidated clay layers in this formation show claystone properties. The Gurpinar formation generally consists of consecutive clay-claystone and/or sand-sandstone layers. The Bakirkoy formation contains limestone layers, but this formation also has clay-sand layers within the limestone layer. The Cukurcesme formation in the investigated areas is mostly composed of gravel and/or sand of different fractions and forms. The Trakya formation is the general name of the claystone-sandstone-mudstone in Istanbul. The upper level of this formation can be seen mostly as highly fractured and/or weathered. Therefore, the upper levels in the Trakya formation can be defined as clay or sand, depending on the main fraction of the material. Figure 2 shows the borders of the investigation areas. The investigation work can be classified as in-situ tests and laboratory tests.
According to the soil-investigation works carried out by the related department of the Metropolitan Municipality of Istanbul, the ground-water level is generally between 1 m and 20 m from the ground surface in the investigated area depending on the altitude of the point at which the measurement of the ground-water level was made.
2.1 In-situ Tests
The geological investigation and geophysical measurements were carried out as in-situ tests. The geological investigation consists of normal borehole, deep borehole, liquefaction borehole, landslide borehole and CPT. Table 1 shows the content of the geological survey.
Table 2 shows the content of the geophysical investigation.
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Table 1. Content of the geological survey.
Type of investigation work	Number of borehole Number of borehole points for Asian Side points for European Side		Total quantity of boreholes for Asian Side (m)	Total quantity of boreholes for European Side (m)
Normal Borehole	4426	2830	98681	86840
Deep Borehole	122	27	11594	4201
Liquefaction Borehole	433	764	6683	12344
Landslide Borehole	10	608	227	18144
CPT Test	?	663	4076	8769
Table 2. Content of the geophysical investigation.				
Number points measured for Number points measured for Measurement method , . „. , „ „. , Asian Side European Side				Total quantity (m)
Seismic refraction	4132		2762	435093
Seismic reflection	-		-	34105
PS-Logging	504		201	10997
Array microtremor	30		30	-
Electric resistance	80		2625	-
Figure 2. Location of the projects and the border of the geotechnical investigation area in Istanbul.
2.2 Laboratory Tests
Laboratory tests included whole basic soil tests such as Atterberg limits, sieve analysis, unaxial and triaxial compressive strength tests, natural water content tests, hydrometer tests and consolidation tests. According to the reports of the microzonation works [25, 26],
for natural water content tests ASTM D2216, for sieve analysis ASTM D422, for hydrometer tests ASTM D4221, for Atterberg Limits tests ASTM D4318, for unconfined compression tests ASTM D2166 and for Triaxial Compression tests ASTM D2850 standards were followed. Table 3 shows the content of the laboratory tests.
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D. Qetin: Performance of soil-nailed and anchored walls based on fleld-monltoring data in different soil conditions In Istanbul
Table 3. Content of the laboratory tests.
Side
Natural water content tests
Determination of the grain size distribution
Sieve analysis Hydrometer Tests
Atterberg Limits
Unaxial Compressive Tests
Triaxial Tests
Consolidation
Asian
29072
29071
6867
21608
572
214
1339
European
53938
53938
124
46432
1120
462
2315
Table 4. Average soil properties of the local soil formation.
Particle size distribution
Local formation name	Definition of the formation	Wn (%)	WL (%)	Wp (%)	Ip (%)	Clay and Silt (%)	Sand (%)	Gravel (%)	Cu (kPa)
Fill	New and old fill material	23.8	46.5	13.2	33.3	48.4	28.3	23.3	85
Alluvium	Sandy soft to stiff clay	32.2	50.3	13	37.3	68.1	26.4	5.5	69
Trakya	Mudstone, sandstone, claystone (from fractured to extensively fractured)	14.6	35.5	15.3	20.2	35.2	37.7	27.1	93
Gurpinar	Alternating sandy stiff clay-claystone	24.6	56.1	15.7	40.4	73.6	23.4	3	127
Gungoren	Soft-to-medium sandy clay	28.9	60.6	16	44.5	79.1	17.7	3.2	98
Bakirkoy	Limestone with clay strip	24.1	47.1	15.2	31.9	62.8	18	19.2	78
Cukurcesme	Clayey gravely sand	17.8	41.3	13.5	27.8	36.6	54.2	9.2	164
As a result of a comprehensive geotechnical investigation, 24 different local soil formations were identified on the Asian and European sides of Istanbul. As can be seen from Figure 2, most of the projects were carried out bordering the geotechnical investigation area. Therefore, the soil formations encountered in the project files were identified using the results of the geotechnical investigation. Selected projects were conducted in 7 different local soil formations. The properties of the soil formation and a brief explanation of the local soil formation are given in Table 4.
3. SUMMARY OF INFORMATION FROM COLLECTED DATA
For the database, data from 28 individual projects in Istanbul were collected. Almost all of these projects were carried out in the past two decades. The data were mainly extracted from conference proceedings, PhD theses and a company database that contains a lot of valuable unpublished data. In each case, the measured wall displacement was analysed in terms of the wall type, the support system and its geometric configuration, the embedded wall ratio, the soil-nailing density, the wall stiffness and the soil type.
The most common method for measuring wall deflection is the use of vertical inclinometers, instruments for measuring the relative horizontal displacements through a borehole casing placed behind the wall. The bottom must be embedded to the zero displacement zone. An
inclinometer is read using a probe. The probe measures the tilt, which can be converted to a horizontal movement. The inclinometer probe is connected to a power source and readout unit to enable the measurements. The electrical cable linking the probe to the readout device is usually marked in 0.5-m increments so the shape of the casing can be measured at consistent depths. The measurements are taken starting at the bottom of the inclinometer. Subsequent readings are made of the casing as the probe is raised incrementally, usually at 0.5-m intervals, to the top of the casing. This process is conducted shortly after the casing is installed to determine the initial shape of the casing, i.e., to obtain the zero reading. The difference between the zero and the subsequent readings is used to determine the change in the shape and position of the initially vertical casing [27].
Two sets of casing grooves allow the inclinometer probe to be oriented in either of two planes set at 90° to each other. Therefore, the horizontal components of movement, both transverse and parallel to any assumed direction of movement, can be computed from the inclinometer measurements [28]. The measurement accuracy is generally to hundredths of a mm.
The most commonly used retaining walls for deep excavations in Istanbul are soil-nailed shotcrete walls (SNPWs) and contiguous pile walls (CPWs). Other types of retaining walls include anchored micropile walls (MPWs), diaphragm walls (DWs), concrete walls (CWs) and secant pile walls (SPWs). Summarized information about the projects is given in Table 5.
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►B-axls
vA-axis Suction ji-x
(a)
Figure 3. (a) Principles of an inclinometer. Configuration of inclinometer parts. (b) Illustration of inclinometer process.[28]
(b)
A L"Li-LLLI almr.mL'nl of
guide casing (exaggerated) -
Table 5. Summary information of the projects.
No. Project District Name
Support ..	Soil ,	H Hw
„	Wall type	formation
System	profile
name
Hemb Sv Sh n (m/
(m) (m) (m) (m) (m) m2)
EI
(kNm2 n /m)
h max Reference (mm)
Baumax , ., 1	Avcilar
AVM
Multi anchored
80 cm Clayey diameter sand-bored pile Hard clay
7.9
Gung-oren
15.8
6.7 2.4
312500 4
25.3 18.9
36.3
Unpublished data
Karabulut 2 Textile Kagith-Factory ane Project
Multi an-chored+ strut
65 cm diameter Silty soft secant clay pile
Alluvium 8
-2
2 1.2
172300 2
18.4 Unpublished 30 data
							21.6	3.7				49.7	
	Busi-	Bahce-lievler	Multi anchored	65 cm	Clayey sand-clay	Gung-oren	21.6	3.7				68.5	Unpub-
3	nessPort			diameter			21.6 -	3.7	2.5 1.8	- 115000	5	43.2	lished
	AVM			bored pile			19	4.1				34.2	data
							18	4.5				19.8	
4	Taksim	Sisli	Multi	25 cm diameter	Mud-stone-sandstone	Trakya	19.65			- 1070	2	19.65	Cetin et
	Residence		anchored	micro pile			18.70					16.8	al. [29]
			Multi anchored	25 cm	Fractured sandstone		26	2.5				43.3	
5	Bomonti	Sisli		diameter micro pile		Trakya	22.8	2.1	2.5 1.5	- 2350	2	42.5	Unpublished
Soil nailing
Shotcrete Fractured wall sandstone
Trakya 22
1.5 1.5
5.5
1 14.60
data
25
45
Tekfen	Soil nail-
6 _	Levent
lowers	ing
Highly Shotcrete fractured
24
wall
gray-wacke
Trakya 20
1.5 2
2.85
14.4 10
19.50 24
9.75 19.2
" Yilmaz et - al. [30]
7 Otoport Esenyurt
Multi anchored
80 cm Clayey diameter sand-san-bored pile dy clay
Gung-oren
25
7.2
21
-6
2.3 2
312500 2
51.7 Unpublished data
Setat
8 2002 LeVent
Soil nailing
Shotcrete wall
Dense fill Fill
9.50 10
10 13
7.6
1.5 2
2.4
10
10
_ Yilmaz et al. [30]
22.1
1
6
5
6
4
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D. Qetin: Performance of soil-nailed and anchored walls based on fleld-monltoring data in different soil conditions In Istanbul
Table 5. Summary information of the projects (Continued).
No. j District Support Name	System
Wall type
Soil profile
Soil formation
H Hw Hemb Sv Sh n (m/ (m) (m) (m) (m) (m) m2)
EI
(kNm2 n /m)
$h, max Reference (mm)
T, . _ . 100 cm ,	Cuku-ideal Gazios- Multi .. sand
. . . . diameter . .	rcesme
Hospital manpasa anchored . .. overlying	_ .
bored pile '	irakya sandstone
29.2
4.4
2.92.5-2
1.2
699850 1
Unpub-18.9 lished data
Metal Co. 10 Factory Catalca Project
Multi anchored
65 cm diameter secant pile
Sandy
gravely ? clay
9.25
5.25
6.75 2.5 1.8
3.75 1.7
123240 2
16.2 Unpublished 4.1 data
11 B;K FUya Besiktas Complex
Soil nail-
tag
Exten-Shotcrete sively wall fractured sandstone
Trakya
18.50 25
32.5
3.4
1.5 1.8
5.3
? 3
4.9
14.8
22.5 Keskin ~ [1]
Saglik
12 Hotd Bey0glu Project
Single prop
65 cm diameter secant pile
7.4
Alluvium Alluvium 6.1
5.9
172300 2
7.9
Unpublished data
Erdem „ .. Multi 13	. . Gunesli , ,
Hospital	anchored
65 cm diameter bored
.. Medium- Gung-hard clay oren
reinforced concrete wall
16.3
16.3
0.91.8
122570 2
45.5
13.7
Unpublished data
Filiz Con-14 struction Ikitelli Co.
Multi anchored
80 cm diameter bored pile
Medium- Gung-hard clay oren
18.2
312500 4
Unpub-7.95 lished data
Besler 15 Co. Ware- Pendik house
Soil nailing
Shotcrete wall
Extensively fractured Trakya grey-wacke
14.7 16.2
18.4
2.3
2.4
2.7
10.3
17.8	Keskin
12.9	[1]
Ozbas
Cons. Co. 16 „ .. Kadikoy Residence
Project
Multi anchored
25 cm diameter micro-pile+ 40 cm concrete wall
Highly fractured sandstone overlying Highly fractured limestone
Trakya Bakirkoy
22.9
25.9
25.9
22.7
9.1
2.1 1.8
233940 4
30.7 Unpub-
- lished
40.3 data
35.7
10
1.7
27
10
2.8
22
17
Isti- Istinye-nyepark Sariyer
Soil nailing
Shotcrete wall
Extensively fractured Trakya gray-wacke
12
12
14
1.5 2
16
18
20
22
2.9
2.7 3.1
3.2 3.4
? 9
37.2 25.2
19.6 44.8
55.8 80
96.8
Keskin [1]
14
3.1
28
15.7
18.8
3.1
18 Kanyon Levent
Soil nailing
Shotcrete wall
21.3
Extensively
fractured Trakya 25.3
gray-wacke
1.5 2
26.3 28.3
28.3 28.3
4.3 4.7
4.9 5.0
5.0
5.1
? 9
45.5 31.9 68.2 58.2 86.8 53.7 67.9 96.2
Keskin
[1]
9
2
3
1
3
3
2
2
3
4
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Table 5. Summary information of the projects (Continued).
No. project District Name
Support Wall type Soil J°L H Hw Hemb Sv Sh n (m/ (kNn2
System	profile	(m) (m) (m) (m) (m) m2)
name	/m)
Sh,
. max Reference (mm)
Zeytin-burnu Municipality _
19 Under- Z.eytin-burnu
ground Parking Lot Project
Lime..	45 cm
Multi ..	stone „ , . , ,, „
. . diameter . . . Bakirkoy 11.3 anchored . ... with clay bored pile .
layers
B.7 2.6 2.1
29240 6
28.5 34
6.9 Unpub-8 8 lished - data
26.6
20.1
Alper Co. 20 Company Umra-Residence niye Project
Soil nail- Shotcrete ing wall
Fractured Sand- Trakya stone
15.2
15.2
1.6 1.4
24.9 Unpub-
- lished
34.5 data
Mashat-21 tan Resi- Maslak dans
Soil nail- Shotcrete
ing
wall
Extensively
fractured Trakya 18.3 gray-wacke
1.5 1.6 2.8
1 58.6
Keskin
[1]
22 Terrace- Esenyurt Mix
80 cm
soft-
11.5
12
Multi . diameter medium Gurpinar-
anchored , . .. .	r 13.4
bored pile clay
12
9.6
2.2 1.25
312500 4
13.4
9.6
10.4 15.3
26.9 17.2
Unpublished data
		Exten-	7		2.4	5.6	
Tepe	Soil nail-	Shotcrete sively	9		5.3	16.2	Keskin
23 Shopping Maltepe Mall	ing	fractured Trakya wall	9	1.5 1.8	3.1	4 15.3	[1]
		gray-wacke	10		5.3	24	
24
Cultural Sultan-
Center
gazi
Multi anchored
65 cm diameter
Fill
-Sand-
Fill
17.6
bored pile stone Trakya 17.6
2 1.7
146000 2
4.5 Unpub-
- lished
6.7 data
25
Hotel Kucuk- Soil nail- Shotcrete
Radisson cekmece ing
wall
clay-sand-limestone-
Gung-oren
7.5
over
consoli- Bakirkoy 7.5 dated clay
2 2
15.4
38.4
Durgu-noglu and Olgun [31]
Axis 26 Shopping Mall
Kaig-thane
single
. . Dia- „ r . Gung-anchored .	Soft clay
, . phragm . . oren 17 +multi	„ overlying _ .
. wall	irakya
propped
1280000 1
Durgu-100 noglu et al. [28]
27
Faco
Medicine Levent-Factory Besiktas Project
65 cm diameter Multi bored pile Gray-anchored 25 cm wacke diameter micropile
Trakya
22
18
1.5 3.2 1.95	115000 1
1.5 2.7 2.1
2350 1
45
36
Adatepe et al. [33]
Siya-vuspasa Under-28 ground Parking Lot Project
Bahce-lievler
. . 80 cm Fill	„.„ „
Multi .. , .	Fill Gur-
. . diameter overlying	. 11
anchored . . TT . .	pinar bored pile Hard clay
3 2.25 1.7 - 312500 4
Unpub-10.1 lished data
n
2
3
3
2
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D. Qetin: Performance of soil-nailed and anchored walls based on fleld-monltoring data in different soil conditions In Istanbul
H is the excavation depth, Hw is the depth of the underground water level from the surface, Hemb is the embedded wall length, Sv is the vertical distance between the anchor or soil-nailing levels, Sh is the horizontal distance between the anchor or the soil nailing, q is the nail density (m/m2), EI is the wall stiffness, n is number of the inclinometers in a project, S^max is the maximum lateral wall displacement in Table 5.
The anchor properties in the anchored wall projects are given in Table 6.
4 DATA ANALYSIS_
4.1 Analysis of soil-nailed wall data
Soil nailing is a useful technique for constructing excavations by reinforcing with fully bonded steel
bars. The reinforced surface is stabilized with sprayed concrete, which creates a zone similar to a conventional gravity retaining wall. However, this sprayed concrete face does not play a vital role in the structural stability of the soil-nailed wall system. The inclination to the vertical of the wall, the soil condition, the excavation depth and the nail density per unit length of the wall (m2/m) can be considered important factors affecting the performance of the wall system. Figure 4 shows the relationship between the maximum lateral displacement of the wall (Sh,max) and the excavation depth (H) for soil-nailed shotcrete wall systems. The data shown in Figure 4 are from projects 5, 6, 8, 11, 15, 17, 18, 20, 21, 23 and 25.
There is a clear relationship between Sh,max the maximum lateral displacement and the excavation depth. The data of Sh,max generally range from 0.05%H to 0.35%H
Table 6. Anchor Properties for anchored walls.
		Excavation Depth		Number	Anchor Length			Tendon	EA (kN/m)	Allowable
Project No	Project Name		(m)	of Anchor		(m)		Diameter		Tensile Ca-
		Min.	Max.	Rows	Min.		Max.	('')		pacity (KN)
1	Baumax AVM		15.80	6	20		25	0.6	112000	728
2	Karabulut Textile Factory		8	3	20		14	0.6	84000	545
3	BusinessPort	18	21.60	5-8	12		22	0.6	84000	545
4	Taksim Residence	18.7	19.65	?	?		?	0.6	84000	545
	Bomonti Hotel									
5	and Congress Center	22.8	26	11	12		28	0.6	84000	545
7	Otoport	21	25	10		35		0.6	84000	545
9	Ideal Hospital		29.2	11	18		32	0.6	140000	910
10	Metal Co. Factory	5.25	9.25	3-4	13		19	0.6	84000	545
13	Erdem Hospital		16.3	7	19		30	0.6	84000	545
14	Filiz Co. Factory		18.2	6	14		25	0.6	84000	545
16	Ozbas Residence	22.7	25.9	12	13		35	0.6	84000	545
19	Zeytinburnu Parking lot		11.3	4	14		20	0.6	84000	545
22	Terramix	11.5	13.4	4-5	14		26	0.5	59200	385
24	Cultural Center		8-17.6	3-8	12		19	0.6	84000	545
27	Faco Medicine Factory	18	22	7-9	13		22	0.6	84000	545
28	Siyavuspasa Parking lot		11	4	14		21	0.5	59200	385
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Figure 4. Relationship between maximum wall displacement and excavation depth for soil-nailing data.
with an average value of 0.20%H. Except for projects 8 and 23, all the data shown in Figure 4 were obtained from projects carried out in the Trakya formation that is mainly composed of claystone-sandstone-mudstone, from extensively fractured to highly fractured. With a few exceptions, it can be said that the distribution of the data is within very reasonable limits. The data outside the limit are from Projects 17 and 25. Project 17 was conducted in the Gurgoren formation, which, composed of soft clay layers, is a weak soil formation in comparison to the Trakya formation. The excavation depth and the maximum wall displacement as a percentage of excavation depth were 7.5 m and 0.51%H, respectively, for project 17. It can be said that the wall movement beyond the maximum limit was due to the weak soil condition. In project 25 there were 9 inclinometers. The data from 7 inclinometers are within the limits, while the data from only 2 inclinometers are outside the limits. Sometimes, unexplained, excessive wall movement can be seen in projects that have very long facades.
Generally, the inclination of the wall varies between 5° and 11° to the vertical in soil-nailing projects. This inclination has some positive effects on the performance of the wall, such as a lower earth pressure, a lower soil density and a better safety factor in comparison with the condition of a zero wall inclination to the vertical. Mittal [34] conducted a study on the effects of the variation of some design parameters, such as the nail length, the nail inclination and the wall inclination, on the safety of the wall. It was found that the safety factor of the wall system increases uniformly with an increasing wall inclination up to 20° to the vertical. Beyond this angle, the dimension of the increase of the safety factor of the wall system is very high.
Figure 5. Relationship between nail density and excavation depth.
4.1.1 Influence of nail density
The nail density can be calculated as follows:
q = L/sv sh [1, 35] (1)
where q is the nail density, L is the average nail length, sv is the vertical distance between the nail levels and Sh is the horizontal distance between the nails.
Figure 5 shows the relationship between the nail density and the excavation depth. The nail density increases with the height of the soil-nailed wall. With the exception of a few points, the data are evenly distributed on both sides of the slope line.
Figure 6 (next page) shows the relationship between the nail density and maximum wall displacement.
The data are scattered over a wide range. Increasing the nail density is a natural consequence of increasing the excavation depth. Therefore, the nail density should be considered in conjunction with the excavation depth. It can be said that increasing the nail density is not a decisive factor solely on the performance of the wall.
4.2 Analysis of anchored wall data
The data for five different wall types were collected and analysed. Figure 7 shows the relationship between the maximum wall displacement and the excavation depth depending on the type of wall.
Similar to the soil-nailing data, there is a clear relationship between the maximum lateral displacement and the excavation depth. The data of Sh,max generally range
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D. Qetin: Performance of soil-nailed and anchored walls based on fleld-monltoring data in different soil conditions In Istanbul
100 90 80 70 60 50
E
«f 40
30 20 10 0
• •
•a*
v
Nail density (m/m )
0.45
0.4
0.35
0.3
1 0.25 :
E 0.2
.c
o
0.15 0.1 0.05
Nail density (m/m ) (b)
Figure 6. Relationship between nail density and maximum wall displacement.
from 0.043%H to 0.32%H with an average value of 0.155%H. With a few exceptions, it can be said that the distribution of the data is within very reasonable limits.
The data from project 26 were obtained from soft clay overlying sandstone. The excavation depth was 17 m, which can be considered as a large depth. Although the wall type was a diaphragm wall, which has a high wall stiffness, the weak soil conditions combined with the
large excavation depth may have caused high wall movements in practice.
The secant pile wall and the diaphragm wall systems are used to prevent water flow into the excavation site if the underground water level is above the final excavation depth. Although the data for the secant pile wall (SCW) and the diaphragm wall (DW) are
•	Contiguous pile Micropile
□ Concrete wall+micropile
♦	Diaphragm wall ▼ Secant pile
^h.m^min
10	15	20
Excavation Depth (m)
Figure 7. Relationship between maximum wall displacement and excavation depth depending on the type of wall.
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very limited, it can be seen in Fig. 7 that the Sh,max values from the SCW and DW projects are close to or over the max line. This limited data indicate that the underground water level should be taken into account very carefully in the design stage of the wall. MPW and MPW+CW data show that this type of wall has a very good performance in the soil conditions mentioned. As for contiguous pile walls (CPW), the data are generally between the maximum line and minimum line up to an excavation depth of H=20 m. However, for excavation depths greater than H=20 m, the data are above the average line and below the maximum line. An excavation depth of 20 m can be considered as a threshold for a CPW.
Table 7 shows the results obtained from projects 1, 2, 7 and 13 and the results given by some researchers for soft clay soil conditions regardless of the construction method or wall type.
Table 7. Comparison of this study's results with other studies for soft-to-stiff clay condition.
Study	$h,max / H	Soil Con-	Note
	Min. Avg. Max.	dition	
This study (project 2, 7, 13, 22)	0.09 0.18 0.37	Soft-to-stiff clays	Four different project results
Goldenberg et al. [20]	0.90	Soft-to-stiff clays	Case histories collection
Bentler [37]	0.452	Soft-to-stiff clays	Case histories collection
Wang et al. [36]	0.452	Soft-to-stiff clays	Case histories collection
Kung et al. [38]	0.39	Taipei clay	Case histories collection
Ou et al. [15]	0.40	Taipei soft soil	Case histories collection
As can be seen in Table 7, the average limit of lateral movement for soft-to-stiff clays is 0.18%H. This is smaller than the values given by Goldenberg et al. [20], Bentler [37], Wang et al. [36], Kung et al. [38] and Ou et al. [15].
Long [21] presented a database consisting of about 300 case histories collected from different soil conditions with different wall and support types. As a result of an
intensive analysis, it was found that the normalized maximum lateral movement values, S^max, are mostly between 0.05%H and 0.25%H, where H is the excavation depth. In this paper, for soil-nailing data, the maximum lateral movement values range from 0.05%H to 0.35%H with an average value of 0.20%H, and for anchored wall data, the maximum lateral movement values range from 0.043%H to 0.32%H with an average value of 0.155%H. The maximum lateral values presented by Long [21] and the maximum lateral values presented in this study differ only slightly from one another.
Tomlinson [40] reviewed 34 case histories of deep excavations conducted with different methods. The results were grouped into three major categories of ground condition. For soft-to-firm NC clays, S^max ranges from 0.08%H to 0.58%H with an average value of 0.30%H, for stiff-to-hard OC clays, Sh,max ranges from 0.06%H to 0.30%H with an average value of 0.16%H and for sands and gravels, Sh,max ranges from 0.04%Hto 0.46%H with an average value of 0.19%H. Projects 1, 10, and 14 were conducted in hard clay. For these projects, Sh,max ranges from 0.04%H to 0.23%H with an average value of 0.12%H, which are close to the values reported by Tomlinson [40] for hard clays.
A total of 536 case histories were collected and analysed by Moorman [23]. These case histories were classified into five categories in terms of the ground condition. For stiff clays in Moorman's database, the upper limit of the maximum lateral movement is 1%H and most of the data are under the 0.5%H limit. These values are higher than the values obtained from projects 1, 10 and 14 in this study. For very limited data from a deep excavation conducted in rock, the upper limit of the maximum lateral movement is 0.5%H and most of the data are under the 0.25%H limit. In this study, most of the data for the maximum lateral movement obtained from projects conducted in a rock formation are under 0.20%H, which is very close to the value for a deep excavation conducted in a rock formation presented by Moorman [23].
4.2.1 Influence of embedded depth ratio
The embedded depth ratio can be expressed as follows,
Remb = Hemb / H (2)
where Hemb is the embedded depth of the wall and H is the excavation depth (m). This ratio is an important factor that reflects the economy of the wall [36]. Figure 8 shows the relationship between the maximum wall displacement and the embedded depth ratio of the wall.
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D. Qetin: Performance of soil-nailed and anchored walls based on fleld-monltoring data in different soil conditions In Istanbul
Figure 8. Relationship between maximum wall displacement and the embedded depth ratio of the wall.
The dimensions of the maximum wall displacement are shown in mm units in Fig. 8(a), while they are shown as a percentage of S^max /H in Fig. 8(b). Although the dimensions of the maximum wall displacement were expressed in two different ways, it can be seen that there is a clear trend that the embedded ratio increases while the lateral displacement, or S^max /H ratio, decreases in accordance with the inclination line (Fig.8 (a) and (b)).
Projects 2 and 22 have a higher embedded ratio. Project 2 was conducted in very soft clay soil conditions. There was a risk that the anchors would not work because of the soft soil conditions. Therefore, the embedded ratio selected was very high. Similarly, project 22 was conducted in clay soil that had a landslide risk. Thus, the embedded ratio selected was more than 1. According to the displacement value of the wall, it can be said that a
110i-
100 90 80
70 .
I 60
Is
E 50- • " «
40 30 20 10
I1'

0.7
0.6
0.5
0.4
c 0.3
0.2
0.1
10
15

• ••
J.! si

0	5	10	15
Wall stiffness, EI(kNm2/m) x -|05
Wall stiffness, EI(kNrrr/m) x 10 Figure 9. Relationship between maximum wall displacement and wall stiffness.
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high embedded ratio is a strong parameter to prevent excessive displacements provided that selection of high wall stiffness in soft soil conditions.
4.2.2 Influence of wall stiffness
Wall stiffness can be expressed as EI, where E is the elasticity modulus of the concrete and I is the moment of inertia of the wall. Figure 9 shows the relationship between the maximum wall displacement and the wall stiffness.
There is no definite information about the thickness of the shotcrete walls. The wall stiffness of the anchored walls was considered in this analysis. Figure 9 shows the data obtained from projects with large-diameter pile walls. Except for projects 9 and 26, the wall stiffness of the anchored pile walls is less than 500,000 kNm2/m and the data from anchored pile walls vary from 0.05%H to 0.45%H. There is a large scatter in the data. It can be said that there is no direct or no linear relationship between the wall stiffness and the movements. Hence, it can be interpreted that the wall movements are mainly independent of the wall stiffness. This result is consistent with those reported by Moormann [23], Moormann [39] and Long [21].
This study is the first attempt to prepare a deep-excavation database for Istanbul. Although there are limited data for some analyses, this database provides a good idea about the dimensions of wall movement. This database can be improved by collecting additional data in the future.
4.2.3 Influence of soil type
All the anchored wall data were plotted in Figure 10 in terms of the main soil type in which the projects were conducted.
The data for the Gungoren formation are around the average line up to an excavation depth of 20 m, after which the data are between the maximum and average lines. For the alluvium data, although the excavation depths are low, the data are between the maximum and average lines. The data for the Gurpinar formation are around the average line. The data from the Trakya formation are far from the maximum line even though the excavation depths are greater than 20 m. Because the data for the fill overlying Trakya formation and the Trakya-Bakirkoy formation are very limited, no interpretation can be made. However, it can be said that the data for the Trakya formation are the best results, regardless of soil type, wall type and support type.
5. CONCLUSIONS
On the basis of the results from this study, the following conclusions can be drawn:
- The results obtained show that successful wall performance can be obtained under a wide variety of soil conditions provided that suitable wall and/or support systems are chosen in the design phase.
120 r
100
80
•	Gungoren Formation ▼ Alluvium
Gurpinar Formation □ Trakya Formation
♦	Bakirkoy Formation
*	Trakya+Bakirkoy Formations Fiil +Trakya Formations
(6. )max=0.32%H
10	15	20
Excavation Depth(m)
Figure 10. Relationship between maximum wall displacement and excavation depth depending on soil type.
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D. Qetin: Performance of soil-nailed and anchored walls based on fleld-monltoring data in different soil conditions In Istanbul
The maximum lateral displacement of the wall increases with an increasing excavation depth for all types of walls. The data for the SCWs and DWs are close to or over the max line. These limited data show that the underground water level should be taken into account very carefully in the design stage. The data for the MPWs and MPWs + CWs show that these types of walls perform well. The data for CPWs are generally between the max line and min line up to a H=20 m excavation depth. However, for an excavation depth over H=20 m, the data are above the average line and between the average and maximum lines. An excavation depth of H=20 m can be considered as a critical excavation depth for CPWs.
The data for Sh,max generally range from 0.05%H to 0.35%H with an average value of 0.20%H in soil-nailed projects. The data for Sh,max generally range from 0.043%H to 0.32%H with an average value of 0.155%H in anchored pile wall projects The nail density increases with the height of soil-nailed walls. It should average 2.2 m/m2 for H=10 m, 3.5 m/m2 for H=20 m and 4.8 m/m2 for H=30 m, according to the data obtained from projects conducted in Istanbul.
With regard to soil-nailing shotcrete wall systems, it can be said that a soil-nailed shotcrete wall system is a very suitable system in rock conditions if there is no adjacent structure or infrastructure. Wall inclination to the vertical is an important factor to be able to obtain good performance for soil-nailing projects.
In light of the analysis, there is a clear trend that the maximum wall displacement decreases with an increasing embedded ratio. Especially in soft soil conditions, a high ratio should be chosen to be able to prevent excessive soil and wall movements. However, this ratio is also related to the economics of the project. Therefore, this ratio should provide both safety and economy at the same time. There is no linear relationship between the wall stiffness (EI) and the wall movements (Sh,max). A number of different Sh, max values can be seen for the same EI values. In this case, the excavation depth is a more important parameter than the embedded ratio. Soil type has an important influence on the dimensions of wall movement. The project conducted in the Trakya formation had the best results in terms of wall movement. Down to an excavation depth of 20 m, the wall movements for the projects conducted in the Gungoren formation are around the average line. However, beyond an excavation depth of 20 m designers should be careful in the design process for projects in the Gungoren formation.
Acknowledgements
The author would like to thank C.E. Mahmut Candan and Geoform Engineering and Consultancy Company for their help with the data collection.
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