Proceedings of the Wo 1 INTRODUCTION The current and future expansi Paulo Metro System will construction of several shafts stations, accesses, emergency ex and construction support. Late shotcrete supported shafts as prim the CMSP, proved to be a si constructive method, minimizin and economically competitive c traditional methods in open cuts (2012). The monitoring of settlements for the successful construction supported shafts, which can Sequential Excavation Method (S in the vertical direction. This paper intends to analyze supported shafts instrumentation over the years by the CMSP see practical results for the des structures. 1.1 The Analyzed Shafts Though there are dozens of shaft the authors decided to use 3 shaft Settlements due to the C.C. Dias Infra7 Consulting and Engineerin F.P. Hirata São Paulo Metropolitan Company F.M. Kuwajima Infra7 Consulting and Engineer Brazil. ABSTRACT: This work presents several shotcrete supported shafts Using data present in SACI: moni software, a statistical analysis an under study are built with the Seq of the ground, furthermore the geological scenarios that cover th others Metro system all around th orld Tunnel Congress 2014 – Tunnels for a better Life. Foz do Igua 1 ion of the São demand the to utilize as xits, ventilation, ely the use of mary support by imple and fast ng settlements compared with Bilfinger et al. is a key aspect n of shotcrete be termed as SEM) or NATM some shotcrete data, collected eking to obtain sign of these ts from CMSP, fts from Line 4- Yellow and 7 shafts from recent Lines built by the C the location of the shafts. Figure 1.Location of the shaft Paulo: Google E Table 1 presents the Line and function of eac Excavation of Shafts in São P ng, São Paulo, Brazil. y - CMSP, São Paulo, Brazil. ring & Technological Institute of Aeronaut a study of the settlements registered during t s built by the São Paulo Metropolitan Comp itoring system and iterative control of instrum nd a methodology to estimate settlements are quential Excavation Method taking full advan shafts have different diameters, depth and he main spectrum of the type of shafts built b he world. açu, Brazil. m Line 5-Lillac, the most CMSP. Figure 1 shows . ts analyzed in the city of Sao Earth®, 2013. information about the ch analyzed shaft by the Paulo. tics - ITA, São Paulo, the excavation phase in pany - Metrô (CMSP). mentation of the CMSP e presented. The shafts ntage of the arch effect d are built in distinct by the CMSP and many
Transcript
Proceedings of the World Tunnel Congress 2014
1 INTRODUCTION The current and future expansion of the São Paulo Metro System will demand the construction of several shafts stations, accesses, emergency exitand construction support. Lately shotcrete supported shafts as primary supportthe CMSP, proved to be a simple and constructive method, minimizing settlements and economically competitive compared with traditional methods in open cuts Bilfinger (2012).
The monitoring of settlements is a key aspect for the successful construction of shotcrete supported shafts, which can be termed Sequential Excavation Method (SEM) or NATM in the vertical direction.
This paper intends to analyze supported shafts instrumentation over the years by the CMSP seeking to obtain practical results for the design of these structures.
1.1 The Analyzed Shafts
Though there are dozens of shafts from CMSP, the authors decided to use 3 shafts from Line 4
Settlements due to the Excavation of Shafts in São Paulo
C.C. Dias Infra7 Consulting and Engineering
F.P. Hirata São Paulo Metropolitan Company
F.M. Kuwajima Infra7 Consulting and Engineering & Technological Institute of AeronauticsBrazil.
ABSTRACT: This work presents a study of the several shotcrete supported shafts built by the São PaulUsing data present in SACI: monitoringsoftware, a statistical analysis and a methodology to under study are built with the Sequential Eof the ground, furthermore the shafts have different diameters, depth and are built ingeological scenarios that cover the main spectruothers Metro system all around the world.
Proceedings of the World Tunnel Congress 2014 – Tunnels for a better Life. Foz do Iguaçu, Brazil.
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The current and future expansion of the São ystem will demand the
to utilize as , emergency exits, ventilation,
Lately the use of as primary support by
simple and fast , minimizing settlements
and economically competitive compared with cuts Bilfinger et al.
The monitoring of settlements is a key aspect for the successful construction of shotcrete supported shafts, which can be termed as Sequential Excavation Method (SEM) or NATM
some shotcrete data, collected
by the CMSP seeking to obtain practical results for the design of these
Though there are dozens of shafts from CMSP, 3 shafts from Line 4-
Yellow and 7 shafts from Line 5recent Lines built by the CMSP.the location of the shafts.
Figure 1.Location of the shafts analyzed in the city of Sao Paulo: Google Earth
Table 1 presents the Line and function of each analyzed shaft b
Settlements due to the Excavation of Shafts in São Paulo
Infra7 Consulting and Engineering, São Paulo, Brazil.
Metropolitan Company - CMSP, São Paulo, Brazil.
Infra7 Consulting and Engineering & Technological Institute of Aeronautics
This work presents a study of the settlements registered during the shafts built by the São Paulo Metropolitan Companymonitoring system and iterative control of instrumentation of the CMSP
analysis and a methodology to estimate settlements areunder study are built with the Sequential Excavation Method taking full advantage of the arch effect of the ground, furthermore the shafts have different diameters, depth and are built in
hat cover the main spectrum of the type of shafts built by the CMSP and many system all around the world.
Tunnels for a better Life. Foz do Iguaçu, Brazil.
ellow and 7 shafts from Line 5-Lillac, the most recent Lines built by the CMSP. Figure 1 shows
.
Figure 1.Location of the shafts analyzed in the city of Sao Earth®, 2013.
Table 1 presents the information about the unction of each analyzed shaft by the
Settlements due to the Excavation of Shafts in São Paulo.
Infra7 Consulting and Engineering & Technological Institute of Aeronautics - ITA, São Paulo,
the excavation phase in Company - Metrô (CMSP).
system and iterative control of instrumentation of the CMSP are presented. The shafts
ethod taking full advantage of the arch effect of the ground, furthermore the shafts have different diameters, depth and are built in distinct
m of the type of shafts built by the CMSP and many
Proceedings of the World Tunnel Congress 2014 – Tunnels for a better Life. Foz do Iguaçu, Brazil.
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region they are distributed: 3 in west, 5 in south-central and 2 in south.
Table 1.Summary information of the analyzed shafts.
Shaft MetroLine Purpose* Region
Incor 4 V.E.E. Pinheiros Jardins 4 Access J. Paulista Ferreira de Araujo Domingos de Morais Joel Jorge de Melo Magalhães Jesuino Maciel Roque Petrella Alexandre Dumas Paulo Eiró
4 5 5 5 5 5 5 5
V.E.E. Access V.E.E. V.E.E. E.E.
V.E.E. V.E.E. V.E.E.
J. Paulista V.Mariana V.Mariana V.Mariana
C. Belo C. Belo
S. Amaro S. Amaro
*E.E. = Emergency Exit; V.E.E. = Ventilation and Emergency
Exit.
1.2 Shotcrete Supported Shafts
The shafts analyzed in this paper were constructed using the Sequential Excavation Method (SEM) or NATM in the vertical direction. This method takes full advantage of the arch effect in the ground making the soil a constitutive part of the support, reducing the thickness of the lining to a minimum. The shape of the excavation should be circular or similar (elliptical) to maximize the arch effect. Figure 2 shows simplistically the main phases of the method. To better represent the phases, Figures 3 and 4 show construction site procedures to the Access Shaft Jardins.
Figure 2.Main phases for the excavation sequence of a shaft done by the SEM method, Dias et al. (2013).
i. The 1st phase can involve ground water table (GWT) variations or not and the GWT lowering can happen before (as shown in Fig. 2) or while
the excavation takes place. At the same time the construction of the capping beam takes place;
ii. Excavation of the 1st ring; iii. Application of the shotcrete of the 1st ring; iv to vi. Repeat phase ii and iii to the
remaining rings ending with the excavation of the last ring (v) and application of the respective shotcrete (vi).
Figure 3.Excavation of a ring and installation of wire
mesh in Access Jardins, October 2012.
Figure 4.Application of the shotcrete in Access Jardins, October 2012.
Despite the recommendations which indicate a form ideally circular, the use of multi-shafts secants is increasingly used in São Paulo, as examples Luz, Celestino et al. (2009), and Vila Prudente, Cecílio Jr. et al. (2010), Stations from CMSP. These innovations are due to architectural requirements and are made possible by combining structural solutions; recently completed the Adolfo Pinheiro Station required the construction of five secant shafts.
Brazil has been a forerunner in innovations in the constructive method presented here.
Proceedings of the World Tunnel Congress 2014 – Tunnels for a better Life. Foz do Iguaçu, Brazil.
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2 SETTLEMENTS DUE TO EXCAVATION OF SHAFTS
The construction of shafts leads, like any other excavation, to settlements at the surface, the prediction of settlements in the design phase is indispensable for instrumentation design.
2.1 Methods of Estimating Settlements
There are several methods of settlements prediction that were defined using data from real excavations instrumentation, they could be empirical, e.g. Peck (1969), or semi-empirical, e.g. Bowles (1984). The majority of the available methods refer to structures implemented in plane strain deformation, and the excavation of a shaft leads to an axisymmetric condition. While in open cuts the support is built before excavation starts, in shotcrete supported shafts is made by steps becoming difficult the direct application of the estimation methods mentioned above.
Although increasingly used, shafts evolutionary numerical calculations may estimate results close to the ones measured by the instrumentation, as example Kuwajima et al. (2004), but are not always available or easily presented. Although it is recognized each time, the numerical methods will continue to gain more prominence, we should use the results of numerous instrumentations available and learn from case histories.
2.2 Local Geology
The geology in the regions of the shafts can be divided into three major geological units: Precambrian, Resende and São Paulo Formations. Next, a simplified geological presentation of materials found in the regions where the shafts were constructed. Precambrian composed by granite and gneiss residual soils.
Resende tertiary formation corresponds to a sequence of low sandy gray clay, and gray and yellow silty sand, generally little argillaceous.
São Paulo tertiary formation occurs predominantly above an elevation of 760 m and is composed of two main litofacies. The first one is compose of rough sandstone, sometimes conglomeratic and graded, the second one is composed of sandstone with average to rough grains, also graded, up to claystone and siltstone, with plain-parallel horizontal stratifications and
great side persistence, Riccomini & Coimbra (1992).
2.3 Data Analysis Instrumentation
The data used in the analysis were collected from SACI: monitoring system and iterative control of instrumentation, Kuwajima (2012). With the help of an online database, SACI, running (online) instrumentation, the collection of data has been simplified.
The selection of shafts was made keeping following points in mind: representativeness and availability of instrumentation data use of the SEM and circular shape, Table 2 shows the technical characteristics of the selected shafts.
Table 2.Technical characteristics of the Shafts.
Shaft Start of Excavation
End of Excavation
Diameter [m]
Incor 09/2005 12/2005 19.5 Jardins 06/2005 02/2006 19.5 F. de Araujo D. de Morais J. J. de Melo Magalhães Jesuino Maciel Roque Petrella A. Dumas Paulo Eiró
for the end of excavation. Settlements data were collected by ground
pins totaling 161 measurements (Fig. 6). Analyzed shafts had 1 to 2 ground pins per instrumentation axis; data from leveling pins were not used because of the interference from the stiffness of the buildings.
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Figure 5.Shotcrete supported shafts parameters. Settlements in distorted scale.
For the construction of graphs, two indicators were used: W/H defines the ratio of settlement extension to the excavation height and S0/H defines the ratio of maximum settlement at the shaft wall to the excavation depth. where S0 = maximum surface settlement, H = maximum height of the excavation, W = width of settlements curve and D = excavation diameter.
Figure 6.Settlements data collected.
Figure 7 shows the data from Figure 6 evidencing geological units.
Figure 7.Settlements data collected classified by
geological unit.
To classify the data by granulometry and stiffness (Fig. 8) the following table was considered.
Table 3.Classification criteria for sands and clays.
Material NSPT Classification
Sands < 9 Soft to little compact ≥ 9 Compact to very compact
Clays < 11 ≥ 11
Soft to medium Stiff
Figure 8.Settlements data collected classified by
granulometry and stiffness.
3 RESULTS
To the analyzed shafts the position of the water table initially changes between 4 to 10 m (Table 2) and all the shafts had a total water table lowering. As a result of that the analyzed settlements occur due to increase on the effective stress associated with the excavation and lowering of water table. The water table registered above believed to be a hydraulic usual condition for São Paulo soils, in shafts excavations without water table lowering the results here presented are conservatives.
The data presented in Figure 6 were subjected to statistical analyzes which assumed that the curve of settlements is a quadratic equation. In order to minimize the influence of instrumentation errors it was considered that the settlement curves are the upper limits of 95% of the data. The equations of the curves were then determined to the Resende and São Paulo Formations, and soft to medium and stiff clays. To Precambrian and compact to very compact sands, was not possible to set the equations due to the small number of data. Furthermore the layers of the Resende and São Paulo Formations are rather interspersed, and in São Paulo Formation the sand is considerably argillaceous.
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It was considered that the geomechanical behavior of sandy-clays or clayey-sands is represented as clays.
Figure 9 presents the equation upper limit of settlements for the Resende Formation instrumentation data. This and the next graphs show that the highest concentration of points occurs for W/H smaller, due to placing the ground pins very close to excavation.
Figure 9.Equation upper limit of settlements, considering the Resende Formation data.
Next the upper limit equation settlements (Fig. 10), was defined to the São Paulo Formation instrumentation data.
Figure 10.Equation upper limit of settlements, considering the São Paulo Formation data.
Considering granulometry and stiffness, the data were divided into soft to medium clays and stiff clays, both presented in the Resende and São Paulo Formations. Figure 11 shows the resulting equation from application of the methodology for soft to medium clays data.
Figure 11.Equation upper limit of settlements, considering soft to medium clays data.
Figure 12 shows the resulting equation from
the stiff clays data analysis.
Figure 12.Equation upper limit of settlements, considering stiff clays data.
To conclude all the obtained equations where
set in Figure 13 and some considerations were made.
Analyzing the width of settlements basin we note that this is smaller than twice the excavation total height, for soft to medium clays, and once, for stiff clays. Comparing with Peck (1969), a classical open cuts settlements estimation method, the results were 4 times and twice, respectively. These differences results from the particularities of the construction methods and demonstrate that we should take care while choosing the method for estimating settlements.
For the maximum settlement can be observed that 0.23% of the total height is an upper limit for the analyzed data.
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Figure 13.Equations upper limits of settlements, considering geological units, granulometry and stiffness.
The obtained curves for geology and granulometry and stiffness seem to create two groups, the first Resende Formation and stiff clays had similar results; and second, the São Paulo Formation and soft to medium clays the same. It occurs due to in Resende Formation, predominate very compact sands and stiff clays while in the São Paulo Formation, the predominant data was from soft to medium clays. The differences between São Paulo and Resende settlements have a ratio of a 1/3.
4 CONCLUSION
Considering São Paulo geology it was demonstrate that the settlements due to shafts excavation are almost three times bigger in the São Paulo Formation comparing with the Resende Formation.
The study of more than 150 settlements instrumentation data had led to obtaining an empirical method of estimating settlements due to shafts excavations executed by the sequential method and using shotcrete as support. This method considers the axisymmetric condition, excavation/support installation by steps and water table lowering. Although simple and empirical, the method showed interesting results that may be use in similar cases for instrumentation design.
ACKNOWLEDGEMENTS
The authors would like to thank the authorization to publish and facilities conceded by São Paulo Metropolitan Company - Metrô (CMSP).
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