Design of 20 m Deep Excavation With Permanent Anchored

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Design of 20 m Deep Excavation with Permanent Anchored Secant Bored Pile Wall (SBPW) and Contiguous Bored Pile... Conference Paper · May 2014 DOI: 10.13140/2.1.2959.5520

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Proceedings of the World Tunnel Congress 2014 – Tunnels for a better Life. Foz do Iguaçu, Brazil.

Design of 20 m Deep Excavation with Permanent Anchored Secant Bored Pile Wall (SBPW) and Contiguous Bored Pile Wall (CBPW) as Retaining Structure of Cut and Cover Tunnel O. Kokten Temelsu International Engineering Services Inc. , Ankara, Turkey.

G. Gungor, S. Kiziroglu, A. Sirin, S. Kucukaslan General Directorate of Turkish Highways, Ankara, Turkey

ABSTRACT: Deep excavations are common for tunnel constructions in urban areas nearby existing structures. In this paper, design of deep excavation of cut and cover tunnel for Portal of dual tube Konak Tunnel in the Konak Square in İzmir, is presented. The maximum height of excavation is 20 m. At the right side of excavation section with maximum height, adjacent 5 storey masonry museum building is located. For the staged excavation of cut and cover tunnel structure, secant bored pile walls (SBPW), contiguous bored pile walls (CBPW) with and reinforced concrete deck (RCD) are designed as components of portal structure. Jet grout columns are designed at excavation basement level and under nearby museum building foundation. According the analysis results, stability of cut and cover tunnel, displacements closed the excavation, internal forces in retaining structures and settlements under nearby structure foundations are computed and checked with acceptable limits in design state. 1 INTRODUCTION

against heave and under nearby structure foundation against settlements.

The design of deep excavation of cut and cover tunnel for Portal of Konak Tunnel in the Konak Square in İzmir, is presented. Nowadays the excavations of cut and cover tunnel has been started. The cut and cover excavation area is approximately 60m x 42m and is shown in Figure 1. The maximum height of the critical excavation section is 20 m. At the right side of excavation section with maximum height, adjacent 5 storey masonry museum building is located and shown in Fig 2. The groundwater level has been observed in excavation area under ground surface. For the staged excavation of cut and cover tunnel structure, 1000 mm diameter secant bored pile (SBPW) walls are designed at outside boundary of excavation. At the inner side 1200 mm diameter contiguous bored piles (CBP) with center to center spacing of 1600 mm and reinforced concrete deck are designed as components of portal structure. SBPW and CBPW are supported with permanent soil anchors. Before the start of the excavation, jet grout columns are designed at excavation basement level for the stability

Figure 1.Cut and cover structure plan, secant and bored piles application plan 1


The stability of cut and cover tunnel, displacements closed the excavation, internal forces in retaining walls and settlements under nearby structure foundations are computed with using PLAXIS 2D, MIDAS 3D and SAP2000 finite element simulations.

The clay deposits range in consistency from a medium stiff to stiff and corresponding undrained shear strengths from UU tests, su= 45kPa to 163kPa, respectively. The clays are lightly over consolidated, but no consolidation tests were performed for this project. In the longitudinal profile of excavation plan and in some cross sections, sand and gravel layers were found, lying between clay and rock layers. These sand and gravel layers contain pressured water and they have relatively high permeability values, k = 1.2 m/day according to index properties with literature assessments. The blocky, gravelly sand layers were classified as very dense layers based on SPT data. Groundwater conditions were measured by a series of piezometers, within the underlying sands, till and rock layers and all borehole observations. These data consistently confirm the groundwater observation at below the ground surface level. The masonry museum building, immediately adjacent to connection of the east piled wall row and the beginning of excavation tunnel as shown in Figure 3. Museum building is founded on uncontrolled fill overlying clay layer without any areal mat or strip foundation. The building is founded on separate under column and wall footings.

Figure 2.Excavation Area

1.1 Site description The original site investigation comprised a series of 14 deep borings is opened within the excavation area and footprint of the existing museum building. In-Stu tests were performed both conventional SPT blow count and pressuremeter test. There was a limited program of laboratory tests (index properties, water content and UU strength testing in the clay, and particle size distributions for the granular layers) while permeability properties were reported from lugeon tests. Figure 4 summarizes the soil profiles, lateral earth support systems and ground improvements for the most critical excavation cross-sections included existing masonry museum building. The subsurface profile comprises 1m - 2m of uncontrolled fill material overlying the medium stiff and stiff clay layer on sedimentary claystone, sandstone and siltstone bedrock layer. The bedrock was described as very weak to weak, completely to slightly weathered rock according to pressuremeter test results, net limit pressures PL*=8.3-38.5 kg/cm2 for very weak PL*=15.4-61.1 kg/cm 2 for weak rock. RQD values of rock varies between RQD = 0% - 64%

Figure 3.Museum Building

So this foundation is unexpected to distribute the ground movements and hence, is most likely to suffer serious damage during excavation to building. 2


1.2 Ground improvements Changes in groundwater level that can lead the unexpected effective stress increments and it could be the result of unwanted consolidation settlements under masonry museum building founded on uncontrolled fill and underlying clay layer and the surrounding other structures foundation. For the purposes of prevention in changes groundwater level under museum building and surrounding structures foundation in the city center, 80 cm diameter and 10 cm overlap intersecting with 5m and 7m thick jet grout columns was designed at the base elevation of excavation shown in Figure 4. Whereby the movement of ground water and the possibility of basement heave were prevented against excavations under ground water level. Another in a useful of jet grout columns in excavation basement level is to behave such an embedded pressure element (strut) and to prevent the base deformation of wall elements, possibility of kick of failure of system and the close the frame structure with reinforced concrete top deck. For the purposes of increasing shear strength of museum building foundation soil and to preventing displacements can be caused by excavations soil improvement was designed with consolidation and jet grouting.

Figure 4.Idealized soil profile, support system and ground improvements

The tieback anchors were also specified with zero tolerance against water leakage in order protects the steel tendons from long term corrosion problems according to FHWA-IF-99-015, 1999 and CIRIA C580, 2003. Each anchor was inclined at 20° with minimum fixed anchor lengths of 10m in the bond soil and weak rock zone. Horizontal spacing of the anchors ranged from 0.80m to 1.6m and each tendon comprised from 3 strands of 1.5cm diameter high tensile strength steel. The vertical distances of anchors are 2m. The lock-off loads for each level of anchors around the excavation is designed as 35 tons. It should be noted that the two levels of anchors just below and above the reinforced deck are most critical levels and in this region the anchors horizontal distance is designed as 0.8m.

1.3 Lateral earth support system and ground improvements For the permanent lateral earth support system of cut and cover tunnel, 1000 mm diameter secant bored pile walls (SBPW) are designed at outside boundary of excavation. At the inner side 1200 mm diameter contiguous bored piles walls (CBPW) with center to center spacing of 1600 mm and reinforced concrete deck are designed as components of portal structure. In most critical excavation section, walls are supported with ten levels of post grouted soil anchors was designed to resist the lateral earth and pore water pressures, seismic loads and surcharge loads from construction equipment and adjacent structures.

1.4 Measurement program for excavation The excavation performance of Konak Tunnel cut and covers structure all excavation sections will be monitored by topographic measure points and tilt meters of museum building settlements. The deflections of SBPW and CBPW will be monitored by readings from a series of inclinometers. The pore water pressures in soil and weathered rock and ground water level changes during excavations will be monitored by vibrat3


ing wire piezometers. Axial forces in the post grouted pre-tensioned anchors will be monitored by load cells in all anchor levels. 1.5 Finite element simulations and model parameters A series of finite element simulations have been carried out to obtain better insight into the performance of the excavation support system for the Konak Tunnel cut&cover structure excavation. The deformation calculations and the performance of lateral support systems and deformation based calculations have been carried out with all using the plane – strain models in PLAXIS 2D and 3-D continuum models in MIDAS 3D finite element package programs. The large number of prepared finite element 2D and 3D models for excavation cross sections representing the behavior of all sides of the excavations. The other interesting point in this project design stage, modeling the structural behavior of SBPW, CBPW and RCD frame system. Because the structural modeling of adjacent SBPW and CBPW piles is required to define imaginary constrained elements to interface surfaces of walls in numerical models. In this way it is possible to catch real bending behavior of both pile walls together. For this purpose the structural design of reinforced concrete SBPW, CBPW and deck was designed with using SAP 2000 finite element models. The finite element model representing the behavior of lateral support systems and defining the displacement levels that will occur due to excavation is given below in Figure 5., Figure 6., Figure 7., Figure 8. and Figure 9. The staged construction modeling of excavation was model in more than 30 stages in PLAXIS 2D and MIDAS 3D.

Figure 6.PLAXIS 2D finite element model at 14th. stage

Figure 7.PLAXIS 2D finite element model at 30th. final stage

Figure 8.MIDAS 3D finite element model

Figure 9.MIDAS 3D finite element model

Figure 5.PLAXIS 2D finite element model 4


The excavation in Konak Tunnel cut and cover tunnel have been started recently. The recent construction stages are shown in Figure 10., Figure11. and Figure 12. below.

Soil deformation parameters and shear strength properties was selected according to index properties and UU test results from boreholes samples, pressuremeter test results and literature survey of similar site properties. Each of the soil layers have been simulated using the Mohr – Coulomb model due to lack of parameters for hardening soil model. The stress and strain relations of Mohr – Cloumb model is given below in Figure 13. and Figure 14.

Figure 10.Excavations under cut and cover structure Figure 13.Yield surface in principal stress space in Mohr – Cloumb model

Figure 14.Elastic, perfectly plastic Mohr – Coulomb model Figure 11.Excavations under cut and cover structure

For clay layer undrained behavior was defined in PLAXIS with Undarained-B loading for using UU test results in analyses. The stress path is given below in Figure 15. for UndrainedB loading in PLAXIS 2D.

Figure 12.Excavations under cut and cover structure

Figure 15.Undrained-B loading in PLAXIS 2D 5


The shear strength and elastic properties is characterized for very weak rock overlying weak rock layer for drained loading condition such an assuming dense sand layer. For weak rock layer shear strength properties was assessed from RMR rock classification system. The drained elastic parameters for input were defined from using the relation given by according to relation between over consolidation ratio OCR, plasticity index and E u/su by Duncan and Buchignani, 1976 in Figure 16.

The model parameters were assumed in finite element models is given below Table 1. Table 1.Model parameters in finite element models

M-C UndrainedB Loading

Very weak rock M-C Drained Loading

Weak rock M-C Drained Loading

18

20

22

20

21

23

30

35

250

0,38 40

0,35 5

0,30 200

-

35

20

Parameter

Clay

Material model Material loading type Unit weight, 3 kN/m Saturated unit 3 weight, kN/m Drained elasticity modulus, MPa Poisson ratio Cohesion, kPa Angle of friction, o

The elasticity modulus of jet grout columns were defined as Ejg=500 MPa by using table given by Durgunoglu, 2004. The grid spacing of jet grout columns was assessed for wanted elasticity modulus for soilcrete elements by using relation given by Saurer et all. 2011. 1.6 Finite element simulations results Figure 16.Eus/su versus OCR

The initial settlement of museum building before the start of excavation was calculated as 3.5 cm given below in Figure 17. This back analysis result value is consistent with the building investigations. Also some differential settlement cracks were observed on museum building walls in site investigations.

The drained elasticity modulus is assessed with using Equation 1: E d ' =

2(1 + ν ' ) E u 3

where v is the drained poisson ratio and E d’ is the drained elasticity modulus. The elasticity very weak rock layer is selected from table given from Bowles. The elasticity modulus of weak rock layer is defined by using Equation 2: given by Hoek, Torres, Corkum, 2002.

⎛ ⎝

E m (GPa ) = ⎜ 1 −

D ⎞

σ

ci 10 ⎟ 2 ⎠ 100

((GSI −10 ) / 40 )

Figure 17.Initial settlements of museum building before the start of excavations, PLAXIS 2D

where σci is the uniaxial compressive strength of rock sample, GSI is the geological strength index, D is the disturbance factor and E m is the rock mass elasticity modulus.

The most critical level was the excavation stage under reinforced concrete deck. This stage 6


is fourteenth stage of model and fourth anchors level of construction. In this level, maximum total displacements were obtained as 6.5 mm at nearest corner of foundation to excavation border is given in Figure 18.

In the final stage of excavation the maximum wall deflections of SBPW and CBPW walls was calculated as 7.3 mm is shown in Figure 21.

Figure 21.Horizontal displacements of SBPW and CBPW elements at final stage, tenth anchor level, PLAXIS 2D

According to the 3 dimensional Midas 3D analysis results, at final stage the maximum total displacements were obtained as 1.3 cm at under museum building foundation is given in Figure 22.

Figure 18.Settlements of museum building at fourteenth stage, fourth anchor level, PLAXIS 2D

In this stage of excavation the maximum wall deflections of SBPW and CBPW walls was calculated as 7.3 mm is shown in Figure 19.

Figure 19.Horizontal displacements of SBPW and CBPW elements at fourteenth stage, fourth anchor level, PLAXIS 2D

Figure 22.Settlements of museum building at final stage, tenth anchor level, Midas 3D

The final stage of excavation, maximum total displacements were obtained as 1.0 cm at nearest corner of foundation to excavation border is given in Figure 20.

In the final stage of excavation the maximum wall deflections of SBPW and CBPW walls was calculated as 7.1 mm is shown in Figure 23.

Figure 20.Settlements of museum building at final stage, tenth anchor level, PLAXIS 2D

Figure 23.Horizontal displacements of SBPW and CBPW elements at final stage, tenth anchor level, MIDAS 3D 7


The structural model, obtained deformation curve and bending moment diagram of cut and cover structure from SAP 2000 analyses is given below in Figure 24., Figure 25. and Figure 26.

Deep excavations for the Konak Tunnel cut and cover structure were designed to support by a permanent lateral earth support system com prising a 1000 mm diameter SBPW and 1200 mm CBPW, reinforced concrete deck and up to 10 levels of prestressed postgrouted against corssion protected soil anchors. Before the start of excavation stages, the ground improvements systems as a jet grout columns and grouting was designed to prevent and mitigate the changes in ground water level and deformations. According to analysis results, the lateral earth support system was very successful in controlling lateral wall movements of walls and total displacements that may occurred under museum building. The 2D and 3D analysis results are in well compliance. The results show that, at the final stage of excavation the maximum wall deflection is about 7.3 and 7.1 mm. And under museum building the maximum total displacement is 1 and 1.3 cm. These values show that the settlements values of both wall and museum building foundation soils are with in expected and accaptable ranges. Analysis results also shows that, designing jet grout columns under excavation basement layer and soil improvement under museum building prevent and mitigate the changes in groundwater level. The permanent pre-tensioned anchor loads remain under design lock loads in all excavation stages. The reinforced concrete design of walls and deck was made in reasonable limits. But it should be remembered that, these analysis results is not confirmed from field instrumentation data. The excavation in Konak Tunnel cut and cover tunnel have been started recently. The analysis will be verified by the detailed instrumentation results.

Figure 24.SAP 2000 structural finite element model

Figure 25.Deformation curve in cut and cover structure, SAP 2000

Figure 26.Bending moments in cut and cover structure, SAP 2000

REFERENCES

2 CONCLUSION

Bowles, J. E. ;.2005. Foundation Design and Analysis, Fifth Edition, The Mc-Grawhill Company Inc. CIRIA C580 ; 2003. Embedded Retaining WallsGuidance for Economic Design, London. Hoek, E. ; Carranza, C. ;Torres & Corkum, B. 2002. Hoek-Brown Failure Criterion-2002Edition. In: Proceedings of the NARMS-TAC Conference on Soil Mechanics and Geotechnical Engineering. Toronto

Konak Tunnel is one of the major transportation projects in Turkey. The project area is located in the city center of İzmir. The adjacent buildings to excavation area, high groundwater level, traffic density and the urgency of project are the major difficulties. 8


Holtz, R. D. ; Kovacs, W. D. ; Sheahan, T. C. 2011. An Introduction to Geotechnical Engineering, Second Edition, The Prentice Hall Company Inc. Midas / GTS. 3D Finite Element Code, 2012. Getting Starting Manual. Midas / GTS. 3D Finite Element Code, 2012. Analysis Case Manual. Plaxis 2D Finite Element Code, 2012. Material Models, Netherlands. Plaxis 2D Finite Element Code, 2012. Reference Manual, Netherlands. Sauer, E. ; Marcher, Th., T.B. ; Lesnik, M. 2011. Grid space optimization of jet grouting columns. In: Proceedings of the 15th European Conference on Soil Mechanics and Geotechnical Engineering. Netherlands: IOS Press Temelsu International Engineering Services Inc. 2012. Konak Tunnel and Connection Road, Konak Portal Geological Study Report . Ankara. Temelsu International Engineering Services Inc. 2013. Konak Tunnel and Connection Road, Konak Portal Final Design Report . Ankara. U.S.Department of Transportation Federal Highway Administration;1999. Geotechnical Engineering Circular No.4, Ground Anchors and Anchored Systems, Washigton.

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Design of 20 m Deep Excavation With Permanent Anchored

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