Safety Assurance for Challenging Geotechnical Civil Engineering Constructions in Urban Areas

doi:10.4236/ojce.2013.33B006

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Open Journal of Civil Engineering, 2013, 3, 33-38

http://dx.doi.org/10.4236/ojce.2013.33B006 Published Online September 2013 (http://www.scirp.org/journal/ojce)

Safety Assurance for Challenging Geotechnical Civil

Engineering Constructions in Urban Areas

Rolf Katzenbach, Christiane Bergmann, Steffen Leppla

Technische Univers ität Darmstadt, Institute and Laboratory of Geotechnics, German y

Email: [email protected] -darmstadt.de

Received July 2013

ABSTRACT

Safety is the most important aspect during design, construction and service time of any structure, especially for chal-

lenging projects like high-rise buildings and tunnels in urban areas. A hi gh level design considering the soil -structure-

interaction, based on a qualified soil investigation is required for a safe and optimised design. Due to the complexity of

geotechnical co nstructions the safety assurance guaranteed by the 4-eye-principle is essential. The 4-eye-principle con-

sists of an independent peer review by publicly certified experts combined with the observational method. The paper

presents the fundamental aspects of safety assurance by the 4-eye-principle. The application is explained on several

examples, as deep excavations, complex foundation systems for high-rise buildings and tunnel constructions in urban

areas. The experiences made in the planning, design and construction phases are explained and for new inner urban

projects recommendations are given.

Keywords: Natural Asset; Financial Value; Neural Network

1. Introduction

A safety design and construction of challenging projects

in urban areas is based on the following main aspects:

• qualified experts for planning, design and construc-

tion;

• interaction between architects, structural engineers

and geotechnical engineers;

• adequate soil investigation;

• design of deep foundation systems using the Finite-

Element-Method (FEM) in combination with en-

hanced in-situ load tests for calibrating the soil para-

meters used in the numerical simulations;

• quality assurance by an independent peer review

process and the observational method (4-eye-prin-

ciple).

These facts will be explained by large construction

projects which are located in difficult soil and ground-

water conditions.

2. The 4-Eye-Principle

The basis for safety assurance is the 4-eye-principle. T his

4-eye-principle is a process of an independent peer re-

view as shown in Figure 1. It consists of 3 parts. The

investor, the experts for planning and design and the

construction company belong to the first division. Plan-

ning and design are done according to the requirements

of the investor and all relevant documents to obtain the

building permission are prepared. The building authori-

ties are the second part and are responsible for the build-

ing permission which is given to the investor. The third

division consists of the publicly certified experts. They

are appointed by the building authorities but work as

independent experts. They are responsible for the tech-

nical supervision of the planning, design and the con-

struction.

In order to achieve the license as a publicly certified

expert for geotechnical engineering by the building au-

thorities intensive studies of geotechnical engineering in

university and large experiences in geotechnical engi-

neering with special knowledge about the soil-structur e-

inter acti on have to b e proven.

Figure 1 . Inde pendent peer review proces s .

R. KATZENBACH ET AL.

The independent peer review by publicly certified ex-

perts for geotechnical engineering makes sure that all

info rmation includi ng the re sults o f the s oil inve stigation

consisting of laboratory and field tests and the boundary

conditions defined for the geotechnical design are com-

plete and correct.

In the case of a defect or collapse the publicly certified

expert for geotechnical engineering can be involved as an

independent expert to find out the reasons for the defect

or damage and to develop a concept for stabilization and

reconstruction [1].

For all difficult pr ojects an independ ent peer review is

essential for the successful realization of the project.

3. Observational Method

The observational method is practical to projects with

difficult boundary conditions for verification of the de-

sign during the construction time and, if necessary, dur-

ing service time. For example in the European Standard

Eurocode 7 (EC 7) the effect and the boundary condi-

tions of the observational method are defined.

The application of the observational method is rec-

ommended for the following types of construction pro-

jects [2]:

• very complicated/complex projects;

• projects with a distinctive soil-structure-interaction,

e.g. mixed shallow and deep foundations, retaining

walls for deep excavations, Combined Pile-Raft Foun-

dations (CP RFs);

• projects with a high and variable water pressure;

• complex interaction situations consisting of ground,

excavation and neighbouring bui l dings a nd str uctures;

• projects with pore-water pressures reducing the sta-

bility;

• projects on slopes.

The observational method is always a combination

of the common geotechnical investigations before and

during the construction phase together with the theo-

retical modeling and a plan of contingency actions

(Fig ure 2). Only monitoring to ensure the stability and

the servi ce ability of the structure is not sufficient and,

according to the standardization, not permitted for this

purpose.

Overall the observational method is an institutiona-

lized controlling instrument to verify the soil and rock

mechanical modeling [3,4].

The identification of all potential failure mechanisms

is essential for defining the measure concept. The con-

cept has to be designed in that way that all these me-

chanisms can be observed. The measurements need to be

of an adequate accuracy to allow the identification of

critical tendencies. The required accuracy as well as the

boundary values need to be identified within the design

phase of the observational method.

Conti ngency a ctions needs to be planned in the design

phase of the observational method and depend on the

ductility of the systems.

The observational method must not be seen as a poten-

tial alternative for a comprehensive soil investigation

campaign. A comprehensive soil investigation campaign

is in any way of essential importance. Additionally the

observational method is a tool of quality assurance and

allows the verification of the parameters and calcula-

tions applied in the design phase. The observational

method helps to achieve an economic and save con-

struction [5].

4. In-Situ Load Test

On project and site related soil investigations with core

drillings and laboratory tests the soil parameters are de-

termined. Laboratory tests are i mportant and essentia l for

the initial definition of soil mechanical properties of the

Figure 2 . Observat io n al met ho d.

R. KATZENBACH ET AL.

soil layer, but usuall y not su fficient for an e ntire and re a-

listic capture of the complex conditions, caused by the

interaction of subsoil and construction [6].

In order to reliably determine the ultimate bearing ca-

pacity of piles, load tests need to be carried out [7]. For

pile load tests often very high counter weights or strong

anchor systems are necessary. By using the Osterberg

method high loads can be reached without installing

anchors or counter weights. Hydraulic jacks induce the

load in the pile using the pile itself partly as abutment.

The results of the field tests allow a calibration of the

numerical simulations.

The principle scheme of pile load tests is shown in

Figure 3.

5. Examples for Engineering Practice

5.1. Classic Pile Foundation for a High-Rise

Building in Frankfurt Clay and Limestone

In the downtown of Frankfurt am Main, Germany, on a

construction site of 17,400 m2 the high-rise building

project “PalaisQuartier” has been realized (Figure 4).

The cons truct ion was f i nishe d in 20 10.

The complex consists of several structures with a total

of 180,000 m2 floor space, thereof 60,000 m2 under-

ground (Figure 5). The project includes the historic

building “Thurn-und Taxis-Palais” whose façade has

bee n preser ved (Unit A). The o ffice buildi ng (Unit B) ,

which is the highest building of the project with a

height of 136 m has 34 floors each with a floor space

of 1 340 m2. The hotel build ing (Unit C) has a height of

99 m with 24 upper floors. The retail area (Unit D)

runs along the total length of the eastern part of the

site and consists of eight upper floors with a total

height of 43 m.

The und er gro und p ar ki ng gar a ge wit h fi ve fl oo r s sp a ns

across the complete project area. With an 8 m high first

sublevel, partially with mezzanine floor, and four more

Figure 3 . Principle sche me of pile load tests.

Figure 4 . “Palai sQuartier”, Frankfurt am Main, Germany.

Figure 5. “PalaisQuartier”, Frankfurt am Main, Germany:

plan v iew ( top) and cr oss section A-A (bottom).

sub-levels the foundation depth results to 22 m below

ground level. Thereby excavation bottom is at 80 m

above sea level (msl). A total of 302 foundation piles

(diameter up to 1.86 m, length up to 27 m) reach down to

R. KATZENBACH ET AL.

depths of 53.2 m to 70.1 m. above sea level depending on

the structural requireme nts.

The pile head of the 543 r etaining wall piles (dia meter

1.5 m, length up to 38 m) were located between 94.1 m

and 99.6 m above sea level, the pile base was between

59.8 m and 73.4 m above sea level depending on the

structural requirements. As shown in the sectional view

(Figure 6), the upper part of the piles is in the Frankfurt

Clay and the base of the piles is set in the rocky Frank-

furt Li me s t o ne.

Regarding the large number of piles and the high pile

loads a pile load test has been carried out for optimiza-

tion of the classic pile foundation. Osterb erg -Cells

(O-Cells) have been installed in two levels in order to

assess the influence of pile shaft grouting on the limit

skin friction of the piles in the Frankfurt Limestone

(Figure 6). The test pile with a to tal length of 12.9 m and

a diameter of 1.68 m consist of three segments and has

been installed in the Frankfurt Limestone layer 31.7 m

below ground level. The upper pile segment above the

upper cell level and the middle pile segment between the

two cell levels can be tested independently. In the first

Figure 6 . Pile l oad test setup.

phase of the test the upper part was loaded by using the

middle and the lo wer part as abutment. A limit of 24 MN

could be reached (Figure 7). The upper segment was

lifted about 1.5 cm, the settlement of the middle and

lower part was 1.0 cm. The mobilized shaft friction was

about 830 kN/m2.

Subsequently the upper pile segment was uncoupled

by discharging the upper cell level. In the second test

phase the middle pile segment was loaded by using the

lower segment as abutment. The li mit load of the middle

segment with shaft grouting was 27.5 MN (Figure 7).

The skin fric tion was 1040 kN/m2, this means 2 4% high-

er tha n wit ho ut s haf t gr o ut in g. B a se d o n the r esul t s o f t he

pile load test using O-Cells th e majority of the 290 foun-

dation piles were made by applying shaft grouting. Due

to pile load test the total length of was reduced signifi-

cantly.

5.2. CPRF for a High-Ris e Bu ilding in Clay Marl

In the scope of the project Mirax Plaza in Kiev, Ukraine,

2 high-rise buildings, each of them 192 m (46 storeys)

high, a shopping and entertainment mall and an under-

ground parking are under construction (Figure 8). The

Fig ure 7. Load di splace ment curve of tes t phas e 1 (t op) and

test phase 2 (bottom).

R. KATZENBACH ET AL.

area of the project is about 294,000 m2 and cuts a 30 m

high nat ura l s lo pe .

The geotechnical investigations have been executed 70

m deep. The soil conditions at the construction site are as

follows:

• fill to a depth of 2 m to 3 m

• quaternary silty sand and sandy silt with a thickness

of 5 m to 10 m

• tertiar y silt and sand ( Charko w a nd P olta w formatio n)

with a thickness of 0 m to 24 m

• tertiar y clayey silt and cla y marl of the Kiev and B ut-

schak formation with a thickness of about 20 m

• tertiary fine sand of the Butschak formation up to the

investigation depth

The ground water level is in a depth of about 2 m be-

low the ground surface. The soil conditions and a cross

section of the project are shown in Figure 9.

For verification of the shaft and base resistance of the

deep foundation elements and for calibration of the nu-

merical simulations pile load tests have been carried out

on the construction yard. The piles had a diameter of

0.82 m and a length of about 10 m to 44 m. Using the

results of the load tests t he back analysis for verification

of the FEM simulations was done. The soil properties in

accordance with the results of the back analysis were

partly 3 times higher than indicated in the geotechnical

report. Figure 10 sho ws the r esults o f the load test No. 2

and the numerical back analysis. Measurement and cal-

culation show a good accordance.

The obtained results of the pile load tests and of the

executed back analysis were applied in 3-dimensional

FEM-simulations of the foundation for Tower A, taking

advantage of the symmetry of the footprint of the build-

ing. The overall load of the Tower A is about 2200 MN

and the area of the foundation about 2000 m2 (Figure

11).

The foundation design considers a CPRF with 64 bar-

rettes with 33 m length and a cross section of 2.8 m × 0.8

m. T he raft of 3 m thick ness i s loca ted in K iev Clay Mar l

at about 10 m depth below the ground surface. The bar-

rettes are penetrating the layer of Kiev Clay Marl reach-

ing the Butschak Sand s.

The calculated loads on the barrettes were in the range

of 22.1 MN to 44.5 MN. The load on the outer barrettes

was about 41.2 MN to 44.5 MN which significantly ex-

ceeds the loads on the inner barrettes with the maximum

value of 30.7 MN. This behavior is typical for a CPRF.

The outer deep foundation elements take more loads be-

cause of their higher stiffness due to the higher

Figure 8 . Mi rax Plaza Ki ev: ani matio n tower A a nd B (l eft),

tower A under construc tion (right).

Figure 9 . Soil conditions and cross secti on of the proj ect area.

R. KATZENBACH ET AL.

Figure 10. Results of the in-situ load test and the nu merical

si mulati ons.

Figure 11. FEM-model of the CPRF of Tow er A and calcu-

lated settlements in [cm].

volume of the activated soil. The CPRF coefficient is

αCPRF = 0.88. Maximum settlements of about 12 cm were

calculated due to the settlement-relevant load of 85% of

the total design load. The pressure under the foundation

raft is calculated in the most areas not exceeding 200

kN/m2, at the raft edge the pressure reaches 400 kN/m2.

The calculated base pressure of the outer barrettes has an

average of 5100 kN/m2 and for inner barrettes an aver-

age of 4130 kN/m2. The mobilized shaft resistance in-

creases with the depth reaching 180 kN/m2 for outer bar-

rettes and 150 kN/m2 for inner barrettes.

During the construction of Mirax Plaza the observa-

tional method according to EC 7 is applied. Especially

the distributio n of the loads bet ween the barrettes and the

raft is monitored. For this reason 3 earth pressure devices

were installed under the raft and 2 barrettes (most loaded

outer barrette and average loaded inner barrette) were

instrume nted over the length.

In the scope of the project Mirax Plaza the new al-

lowable shaft resistance and base resistance were defined

for t ypic al soi l layer s in K iev. T his uni que e xper ienc e wil l

be used fo r the skyscra per s of new generation in Ukraine.

The CPRF of the high-rise building project Mirax

Plaza represents the first authorized CPRF in the Ukraine.

Using the advanced optimization approaches and taking

advantage of the positive effect of CPRF the number of

barrettes could be reduced from 120 barrettes with 40 m

length to 64 barrettes with 33 m length. The foundation

optimization leads to considerable decrease of the uti-

lized resources (cement, aggregates, water, energy etc.)

and cost savings of about 3.3 Million US$.

REFERENCES

[1] R. Katzenbach, S. Leppla, A. Weidle and D. Choudhury,

“Aspects Regarding Management of Soil Risk,” 4th In-

ternational Seminar on Forensic Geotechnical Engineer-

ing, Bengaluru, 10-12 Januar y 2013, p. 12 .

[2] R. Katzenbach, A. Weidle and S. Kurze, “Baugrund und

Grundwasser Erkundungsproblematik, Baugrundrisiko

und Technische Risiken,” 39. Baurechtstagung der Arge

Baurecht des Deutschen Anwaltsvereins, Berlin, 16-17

March 2012, p. 22.

[3] W. Rodatz, J. Gattermann and T. Bergs, “Results of Five

Monitoring Networks to Measure Loads and Deforma-

tions at Different Quay Wall Constructions in the Port of

Hamburg,” 5th International Symposium on Field Mea-

surements in Geomech anics, Singapore, 1-3 December

1999, p. 4.

[4] R. Katzenbach, A. Schmitt and J. Turek, “Co-Operation

between the Geotechnical and Structural Engineers—

Experien ces fro m P rojects in Frankfurt ,” COST Action C7,

Soil-Structure-Interaction in Urban Civil Engineering,

Thessaloniki, 1-2 Octobe r 19 99, pp. 53 -65.

[5] R. Katzenbach, G. Bachmann, S. Leppla and H. Ramm,

“Chances and Limitations of the Observational Method in

Geotechnical Monitoring,” 14th Danube-European Con-

ference on Geotechnical Engineering, Bratislava, 2-4

June 201 0, p. 13.

[6] R. K atzen bach , “Opt imised Desi gn of High-Rise Building

Foundations in Settlement-Sensitive Soils,” International

Geotechnical Conference of Soil-Structure-Interaction, St.

Petersburg, 26-28 May 2005, pp. 39-46.

[7] J.-L. Briaud, M. Ballouz and G. Nasr, “Static Capacity

Prediction by Dynamic Methods for Three Bored Piles,”

Journal of Geotechnical and Geoenvironmental Engi-

neerin g, Vol. 126, ASCE, Reston, Virginia, USA, July

2000, pp . 640-649.