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Drainage behavior of two-layered water-sealing polymeric systems
Polymer Testing 23 (2004) 43–49 www.elsevier.com/locate/polytest
Test Apparatus
Drainage behavior of two-layered water-sealing polymeric systems M. Farshad ∗, P. Flu¨eler Department of Polymers/Composites, EMPA, Ueberlandstrasse 129, Du¨bendorf, Switzerland Received 12 February 2003; accepted 9 April 2003
Abstract In this contribution, the results of development work on testing of water isolation systems to be used in tunnels is reported. For this purpose, a testing system capable of testing rectangular samples having dimensions of 1.0 × 1.5 m was designed and built. This testing device was able to apply lateral compression up to 2.0 MPa and in-plane shear displacement up to 10 mm on the samples, independently. The contact surface had the same roughness as would occur during grouting of the tunnel rock. The samples were tested for the tunnel environment up to 45 °C. The experiments included short-term and long-term water-tightness as well as drainage capacity tests. The multi-layer water isolation systems consisted of water-tight membrane and surface drainage layers. The sample groups tested included surface drainage layers with knob geometry, irregularly meshed polymeric fibers, and structured mesh. It was found that the knobbed membrane systems had better drainage capacity than other types of drainage materials. To simulate the behavior of the testing system, numerical finite element analysis was performed. Furthermore, a simple theoretical model of the drainage behavior was derived. With the help of this model trends observed in the real experiments were reproduced. 2003 Elsevier Ltd. All rights reserved. Keywords: Drainage systems; Water-insulation; Tunnels
1. Introduction Water isolation systems are used in various civil engineering installations including tunnels, reservoirs, waste depositories, and buildings. The embedded membranes normally provide water isolation. The main function of the water isolation membrane is to isolate the inside from the water-containing outer environment. To fulfill this function, the water isolation membrane should remain intact and free of perforations. The joints between the membrane sheets should also be water-tight. In some cases, the water behind the system, which to be isolated, may be under pressure. It may be required
∗ Corresponding author. Tel.: +41-1-823-4491; fax: +41-1821-6244. E-mail address: [email protected] (M. Farshad).
that no pressure should be built up behind the system. In such case the water should be continuously drained. For this purpose, in addition to the water isolation membrane, a drainage mechanism is also required. One means of continuous drainage is the so-called “surface drainage”. Surface drainage consists of a layer or layers of draining sheets, which are place behind the water isolation membrane. The water flows through these sheets and is collected and transported by drainage pipes or conduits. As the result, no substantial pressure will be built up behind the system which is to be isolated. A combination of the surface drainage layer(s) and the water-tightness membrane will be referred to herein as the water isolation system. Some of the research and development activities relating to the systems are reported in Refs. [1,2].
0142-9418/$ - see front matter 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0142-9418(03)00060-6
44
M. Farshad, P. Flu¨ eler / Polymer Testing 23 (2004) 43–49
2. Practical aspects A multi-layered polymeric water isolation system is placed between the outside objects such as tunnel rock, trenches or excavation and the internal installation such as tunnel shell, building or stored material. Hence, a confined multi-layered water isolation of this sort is expected to be subjected to lateral pressure as well as shear action at higher temperatures during longer time periods. In addition to that, the operation environment of some of these systems include not only mechanical actions, but also high temperatures and aggressive media. For example, the water isolation system used in the tunnels may be subjected to temperatures up to 50 °C. In addition, they be under the influence of the high alkaline content of concrete as well as the action of microorganisms and even an acid environment. A water isolation system should function properly in the long-term. The required service life of some of such systems may amount to about 100 years. Some of the requirements of the water isolation system may be expressed in quantitative terms, while others, such as water-tightness, must be qualitatively assured. The decision on the choice of an appropriate water isolation system is normally based on several aspects. The technical aspects include functional requirements and the practical considerations. The functional requirements include long-term water isolation property and drainage capability under lateral pressure, shear action, water pressure, high temperature, and chemical as well as biological actions.
3. Laboratory investigation of water-insulation systems Some of the functional aspects of the water isolation system may be investigated in a laboratory atmosphere. This investigation should be complemented by appropriate field tests, which take into account some of the practical aspects such as connection of the sheets and their fixation. Moreover, theoretical correlation such as longterm extrapolations and numerical simulations of tests and correlation of the experimental data should accompany the experimental program. The laboratory investigation carried out included the chemical and biological resistance tests and the mechanical tests on the constituent elements of the water isolation system as well as the system as a whole.
4. Compression–shear testing system To simulate the functional behavior of the water isolation system, a compression–shear testing system was built. The conceived testing system was intended to
simulate the behavior of the water isolation samples in the tunnel conditions. Specimens having dimensions of 1 m × 1.5 m could be tested by this system. This testing system consisted of two parallel concrete plates which contained the testing sample in between. The testing system was capable of applying lateral compression and inplane shear independently. It also included a heating device, so those samples could be conditioned at the desired temperature. The compression–shear testing system built consisted of two parallel plates, which could be pressed against each other and could also be displaced relative to one another. The lateral force was applied via two hydraulic cylinders, each of which would be capable of applying up to 300 kN. The horizontal displacement of up to 30 mm (corresponding to 700 kN) was produced by a third hydraulic cylinder. The experimental set-up described in this paper was designed for comparative testing of a number of water isolation systems. The aim was to construct a testing system which could reasonably simulate the reality. In the real situation in tunnels, grouting first stabilized the bored rock. The shotcrete profile of the tunnel would normally be wavy and relatively rough. For this purpose, an additional cast metal plate with surface roughness of about 3.1 mm was attached to the bottom of the compression block. This surface roughness corresponded with the roughness achieved in the tunnel by the application of fine-grain shotcrete to the excavated rock profile. The water isolating system would be placed on this profile in such a fashion that the surface drainage layer would face the rock. Further operation would be to build a cast-in-place concrete layer, which would act as the structural profile. Application of the fresh concrete on the water isolating system would push the layer system against the grouted rock. As a result, the concrete surface on the face of the water-insulation membrane would adjust itself to the rock surface, but would be not as rough as the grouted rock surface. To simulate this situation, a negative roughened surface was provided on the upper part of the lower compression block. This was supposed to simulate the mild uneven surface which would result from the load bearing concrete cladding in the tunnel. To incorporate the surface roughness in the testing system, additional cast iron plates having the same roughness as the shotcrete surface and the opposite concrete surface were made and were place between the loading blocks. Fig. 1 shows the lateral view of the compression–shear testing system and Fig. 2 is a photograph of the apparatus. The behavior to be investigated consisted of water isolation capability and the drainage capacity of the system under lateral compression and in-plane shear at higher temperature up to 50 °C. The applied lateral compression amounted to 2.0 MPa and the shear displacement amounted to 10 mm.
M. Farshad, P. Flu¨ eler / Polymer Testing 23 (2004) 43–49
45
Fig. 1. Lateral view of the compression–shear testing system.
Fig. 2.
A picture of the compression–shear testing system.
5. Experimental program The experimental program consisted of short-term as well as long-term (up to 14 days) drainage and water isolation tests. These tests were carried out on the preconditioned and heated samples of various water isolation systems. Table 1 summarizes the experimental program, which was executed in the laboratory.
6. Materials and samples The samples had typical dimensions of 1.0 × 1.5 m. Each sample consisted of a water isolation membrane and a surface drainage layer. In some cases, the surface drainage layer itself consisted of two sub-layers.
The samples were preconditioned in the testing system for at least 4 h. They were placed between two preheated concrete blocks via two rough surfaces. To assure the thermal contact during this time, a small amount of lateral load of about 0.1 MPa was applied. 7. Compression–shear tests Compression and shear tests were performed on the samples according to the testing program outlined in Table 1. The preconditioned samples were subjected to short-term and long-term compression tests. Shear tests were performed in the short-term and were also performed at the end of the compression tests. In the following section, only the results of the short-term experiments on the water isolation systems will be reported.
46
M. Farshad, P. Flu¨ eler / Polymer Testing 23 (2004) 43–49
Table 1 Experimental program for the compression–shear tests on the water isolation systems Testing module
Purpose of the test
1
Lateral pressure = 1.5 MPa combined with an in-plane shear displacement of up to 3 mm Short-term drainage at high lateral Lateral pressure up to 2 MPa pressure combined with an in-plane shear displacement of up to 3 mm
2
Short-term water-tightness under high lateral pressure
3
Short-term water-tightness test under high in-plane shear
4
Long-term water drainage test (7day test) at high lateral pressure
Testing parameters
Measurements
(1) Vertical compression of the water isolating sample; (2) relative horizontal displacement of two plates (1) Required water pressure for a given drainage capacity; (2) vertical compression of the water isolating sample; (3) relative horizontal displacement of two plates Lateral pressure = 0.3 MPa (1) Vertical compression of the water combined with an in-plane shear isolating sample; (2) relative displacement of up to 10 mm horizontal displacement of two plates Lateral pressure of 1.5 MPa at the (1) Required water pressure for a end combined with an in-plane shear given drainage capacity; (2) vertical displacement of up to 3 mm compression of the water isolating sample; (3) relative horizontal displacement of two plates
8. Experimental results Fig. 3 shows one of the results obtained from the compression–shear tests on various water isolation systems. This figure shows the water pressure gradient which is required to force a specified water volume. In this case, the specified water volume fed into the system for all samples was 10 l/min. Four general groups of surface drainage systems were included in these tests. The water isolation membrane was made of 2–3 mm thick thermoplastic material, but the material was not the same for all systems. The four types of surface drainage included knobbed membranes with different geometry mesh, with and without fleece, and fleece alone. Fig. 3 shows a general trend of increase of the water pressure gradient as a function of lateral compression. With increase of the lateral compression, the sample would be further compressed and hence the drainage
capability would be reduced. Fig. 3 shows that the knobbed drainage membranes have a better drainage capacity than the other types of surface drainage materials. It also shows that some types of irregularly meshed materials (spaghetti type mesh) show a better performance in comparison with the structured rigid mesh.
9. Theoretical model 9.1. Finite element simulation of the compression– shear behavior To simulate the compression–shear tests on the watertight systems with the testing rig, numerical finite element (FE) simulation was carried out. For FE simulation of the compression–shear behavior of the watertightness system, the features of the experimental set-up shown in Fig. 1 were used. Accordingly, for the FE model, the following assumptions were made: Dimensions of two concrete blocks: length 1500 mm, thickness 300 mm, width 1000 mm Original distance between two concrete blocks: 20 mm Material properties of two blocks: E = 500 000 N / mm2, v = 0.2 Dimensions of the water-tight samples: 1500 mm, thickness 300 mm, width 1000 mm Average material properties of the sample: E = 300 N / mm2, v = 0.3
Fig. 3. Drainage behavior of various water isolation systems. The water pressure gradient required for the water volume of 10 l/min which is fed into the system.
FE model: Number of elements: 132
M. Farshad, P. Flu¨ eler / Polymer Testing 23 (2004) 43–49
Boundary conditions: the top block is fixed against horizontal displacement; lower block can move horizontally, but is restrained against rotation Vertical load: total compressive force equal to 450 kN on the top block equivalent to a uniformly distributed pressure of 3 bar. The total force is applied through two cylindrical load cells, each having a diameter of 300 mm. These cylinders are placed on the top of the upper concrete block (see Fig. 1) Horizontal action: a 10 mm shear displacement applied to the lower block Type of analysis: non-linear contact analysis Software: COSMOS/M, version 2.5. 9.2. Results of FE analysis Fig. 4 shows the normal stress field in the two concrete blocks between which the samples are placed. As we expect, due to concentrated action of two loading cylinders, the normal stress will not be uniformly distributed. However, the spatial variation of the normal stress tends to become smaller as we approach the lower surface of the upper block. Hence, the assumption that the vertical load is uniformly distributed at the level of the sample is justifiable. Fig. 5 shows the shear stress field in the two concrete blocks between which the samples are placed. Again, as expected, the shear stress distribution in the concrete blocks due to an applied shear displacement will not necessarily be uniform. Fig. 5 shows locations of maximum shear stress. However, the local variation in the shear stress field is assumed not to affect the drainage capacity. 9.3. Hydraulic model of the drainage function In order to achieve a theoretical estimation of the drainage function of the water-insulation systems, an
Fig. 4.
47
analytical model was used. The model employed the Bernoulli energy equation for a non-viscous fluid. This theory relates the pressure difference at the water-inlet to the compression–shear testing system and the outlet from this system to the kinetic energy of the fluid flow. In this calculation, the head lost due to friction was neglected. Under these assumptions, the Bernoulli equation was written as: ⌬p ⫽ (g / 2g)Q2(1 / A22 ⫹ 1 / A21)
(1)
In which, ⌬p: pressure difference of the drainage water at the inlet and the outlet of the testing system in MPa, herein so-called water pressure; Q: volume of water in mm3/s; A1: section of the drainage system at the water-inlet in mm2; A2: section of the drainage system at the water-outlet in mm2; g : density of water N/mm3; g: acceleration of gravity in mm/s2. Due to the lateral compression applied to the water isolation system, the drainage sections at the inlet and the outlet to the system (A1 and A2) will be reduced. The reduction of the flow section can be related to the lateral compression in the following fashion: A2 ⫽ Ld(1⫺F /AE)
(2)
where L is the length, d is the original height, A is the area, E is the elasticity modulus of the drainage layer, and finally F is the total lateral compressive force. Due to the structured configuration of the drainage layer, it was assumed that only part of the drainage layer should be accounted for as the effective flow section. Furthermore, the lateral compressive stress was calculated by dividing the total force F by the effective load carrying structured drainage layer. For the calculations, which follow the numerical values of d = 10 mm and E = 10 N / mm2 were chosen. Substitution of the Eq. (2) into Eq. (1) results in a relation among various parameters including lateral compression, F, drainage volume, Q, and the pressure differ-
Distribution of the normal stress field in the vertical direction in the concrete blocks.
48
M. Farshad, P. Flu¨ eler / Polymer Testing 23 (2004) 43–49
Fig. 5.
Distribution of the shear stress field in the two concrete blocks.
ence ⌬p. If the drainage volume Q is prescribed, then the relation of the pressure gradient required for the flow ⌬p and the lateral compressive stress is derived. Fig. 6 shows the trend of variation of the water pressure required for a drainage volume of 10 l/min as function of the lateral compressive stress. This trend, which is also intuitively plausible, is quite compatible with the measured data of Fig. 3. The quantitative changes in water pressure with the lateral compression depend on the particular structure of the drainage layer as depicted in Fig. 1. If, instead of the drainage volume, the pressure gradient ⌬p is prescribed, then the relation of the water pressure required for the water flow ⌬p and the lateral compressive stress is derived. Fig. 7 shows the trend of variation of the drainage volume as a function of the lateral compressive stress for the prescribed pressure gradient of 0.001 MPa. The quantitative changes in water pressure with the lateral compression depend on the particular structure of the drainage layer as depicted in Fig. 1.
Fig. 6. Theoretical variation of the water pressure required for a drainage volume of 10 l/min as function of the lateral compression (see Fig. 1).
Fig. 7. Theoretical variation of the drainage volume as function of the lateral compression (see Fig. 1) for a pressure gradient of 0.001 MPa.
10. Discussion and conclusions In this paper, an experimental system for testing of two-layer water isolation systems used in tunnels is described. In construction of this testing system, effects like tunnel temperature, lateral pressure due to rock, shear action due to concreting, and roughness of the media at both sides of the water isolation layers were taken into consideration. Various tests, including shortterm and long-term water-tightness experiments and drainage function were carried out. In this paper only the results of the short-term drainage experiments were reported. To simulate the behavior of the testing system, numerical FE analysis was performed. Furthermore, a simple theoretical model of the drainage behavior was derived. With the help of this model trends observed in the real experiments were reproduced. The experiments performed with the described testing system have a plausible relation with reality. The theoretical models presented in this contribution predict the general drainage behavior observed in the tests. How-
M. Farshad, P. Flu¨ eler / Polymer Testing 23 (2004) 43–49
ever, the models should be refined to take into account the structural features of the individual water isolation systems. Furthermore, the results of these laboratory experiments need to be correlated with field tests.
49
systems and execution of the experiments. In this connection, special thanks are due to Andreas Brunner.
References Acknowledgements The authors would like to thank the financial support provided by the AlpTransit Authorities of Switzerland. They also express their thanks to many EMPA colleagues who contributed to the construction of the testing
[1] P. Flu¨ eler, Ch. Lo¨ we, M. Farshad, P. Zwicky, H. Bohni, The sealing of deep-seated Swiss Alpine railway tunnels— new evaluation procedure for waterproofing systems, Conference Proceedings 9 dbcm Brisbane, Australia, 2002, p. 9. [2] Ph. Rietman, P. Flu¨ eler, P. Zwicky, Test methods for sealing systems, Tunnel 10 (2002) 13–15.
Test Apparatus
Drainage behavior of two-layered water-sealing polymeric systems M. Farshad ∗, P. Flu¨eler Department of Polymers/Composites, EMPA, Ueberlandstrasse 129, Du¨bendorf, Switzerland Received 12 February 2003; accepted 9 April 2003
Abstract In this contribution, the results of development work on testing of water isolation systems to be used in tunnels is reported. For this purpose, a testing system capable of testing rectangular samples having dimensions of 1.0 × 1.5 m was designed and built. This testing device was able to apply lateral compression up to 2.0 MPa and in-plane shear displacement up to 10 mm on the samples, independently. The contact surface had the same roughness as would occur during grouting of the tunnel rock. The samples were tested for the tunnel environment up to 45 °C. The experiments included short-term and long-term water-tightness as well as drainage capacity tests. The multi-layer water isolation systems consisted of water-tight membrane and surface drainage layers. The sample groups tested included surface drainage layers with knob geometry, irregularly meshed polymeric fibers, and structured mesh. It was found that the knobbed membrane systems had better drainage capacity than other types of drainage materials. To simulate the behavior of the testing system, numerical finite element analysis was performed. Furthermore, a simple theoretical model of the drainage behavior was derived. With the help of this model trends observed in the real experiments were reproduced. 2003 Elsevier Ltd. All rights reserved. Keywords: Drainage systems; Water-insulation; Tunnels
1. Introduction Water isolation systems are used in various civil engineering installations including tunnels, reservoirs, waste depositories, and buildings. The embedded membranes normally provide water isolation. The main function of the water isolation membrane is to isolate the inside from the water-containing outer environment. To fulfill this function, the water isolation membrane should remain intact and free of perforations. The joints between the membrane sheets should also be water-tight. In some cases, the water behind the system, which to be isolated, may be under pressure. It may be required
∗ Corresponding author. Tel.: +41-1-823-4491; fax: +41-1821-6244. E-mail address: [email protected] (M. Farshad).
that no pressure should be built up behind the system. In such case the water should be continuously drained. For this purpose, in addition to the water isolation membrane, a drainage mechanism is also required. One means of continuous drainage is the so-called “surface drainage”. Surface drainage consists of a layer or layers of draining sheets, which are place behind the water isolation membrane. The water flows through these sheets and is collected and transported by drainage pipes or conduits. As the result, no substantial pressure will be built up behind the system which is to be isolated. A combination of the surface drainage layer(s) and the water-tightness membrane will be referred to herein as the water isolation system. Some of the research and development activities relating to the systems are reported in Refs. [1,2].
0142-9418/$ - see front matter 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0142-9418(03)00060-6
44
M. Farshad, P. Flu¨ eler / Polymer Testing 23 (2004) 43–49
2. Practical aspects A multi-layered polymeric water isolation system is placed between the outside objects such as tunnel rock, trenches or excavation and the internal installation such as tunnel shell, building or stored material. Hence, a confined multi-layered water isolation of this sort is expected to be subjected to lateral pressure as well as shear action at higher temperatures during longer time periods. In addition to that, the operation environment of some of these systems include not only mechanical actions, but also high temperatures and aggressive media. For example, the water isolation system used in the tunnels may be subjected to temperatures up to 50 °C. In addition, they be under the influence of the high alkaline content of concrete as well as the action of microorganisms and even an acid environment. A water isolation system should function properly in the long-term. The required service life of some of such systems may amount to about 100 years. Some of the requirements of the water isolation system may be expressed in quantitative terms, while others, such as water-tightness, must be qualitatively assured. The decision on the choice of an appropriate water isolation system is normally based on several aspects. The technical aspects include functional requirements and the practical considerations. The functional requirements include long-term water isolation property and drainage capability under lateral pressure, shear action, water pressure, high temperature, and chemical as well as biological actions.
3. Laboratory investigation of water-insulation systems Some of the functional aspects of the water isolation system may be investigated in a laboratory atmosphere. This investigation should be complemented by appropriate field tests, which take into account some of the practical aspects such as connection of the sheets and their fixation. Moreover, theoretical correlation such as longterm extrapolations and numerical simulations of tests and correlation of the experimental data should accompany the experimental program. The laboratory investigation carried out included the chemical and biological resistance tests and the mechanical tests on the constituent elements of the water isolation system as well as the system as a whole.
4. Compression–shear testing system To simulate the functional behavior of the water isolation system, a compression–shear testing system was built. The conceived testing system was intended to
simulate the behavior of the water isolation samples in the tunnel conditions. Specimens having dimensions of 1 m × 1.5 m could be tested by this system. This testing system consisted of two parallel concrete plates which contained the testing sample in between. The testing system was capable of applying lateral compression and inplane shear independently. It also included a heating device, so those samples could be conditioned at the desired temperature. The compression–shear testing system built consisted of two parallel plates, which could be pressed against each other and could also be displaced relative to one another. The lateral force was applied via two hydraulic cylinders, each of which would be capable of applying up to 300 kN. The horizontal displacement of up to 30 mm (corresponding to 700 kN) was produced by a third hydraulic cylinder. The experimental set-up described in this paper was designed for comparative testing of a number of water isolation systems. The aim was to construct a testing system which could reasonably simulate the reality. In the real situation in tunnels, grouting first stabilized the bored rock. The shotcrete profile of the tunnel would normally be wavy and relatively rough. For this purpose, an additional cast metal plate with surface roughness of about 3.1 mm was attached to the bottom of the compression block. This surface roughness corresponded with the roughness achieved in the tunnel by the application of fine-grain shotcrete to the excavated rock profile. The water isolating system would be placed on this profile in such a fashion that the surface drainage layer would face the rock. Further operation would be to build a cast-in-place concrete layer, which would act as the structural profile. Application of the fresh concrete on the water isolating system would push the layer system against the grouted rock. As a result, the concrete surface on the face of the water-insulation membrane would adjust itself to the rock surface, but would be not as rough as the grouted rock surface. To simulate this situation, a negative roughened surface was provided on the upper part of the lower compression block. This was supposed to simulate the mild uneven surface which would result from the load bearing concrete cladding in the tunnel. To incorporate the surface roughness in the testing system, additional cast iron plates having the same roughness as the shotcrete surface and the opposite concrete surface were made and were place between the loading blocks. Fig. 1 shows the lateral view of the compression–shear testing system and Fig. 2 is a photograph of the apparatus. The behavior to be investigated consisted of water isolation capability and the drainage capacity of the system under lateral compression and in-plane shear at higher temperature up to 50 °C. The applied lateral compression amounted to 2.0 MPa and the shear displacement amounted to 10 mm.
M. Farshad, P. Flu¨ eler / Polymer Testing 23 (2004) 43–49
45
Fig. 1. Lateral view of the compression–shear testing system.
Fig. 2.
A picture of the compression–shear testing system.
5. Experimental program The experimental program consisted of short-term as well as long-term (up to 14 days) drainage and water isolation tests. These tests were carried out on the preconditioned and heated samples of various water isolation systems. Table 1 summarizes the experimental program, which was executed in the laboratory.
6. Materials and samples The samples had typical dimensions of 1.0 × 1.5 m. Each sample consisted of a water isolation membrane and a surface drainage layer. In some cases, the surface drainage layer itself consisted of two sub-layers.
The samples were preconditioned in the testing system for at least 4 h. They were placed between two preheated concrete blocks via two rough surfaces. To assure the thermal contact during this time, a small amount of lateral load of about 0.1 MPa was applied. 7. Compression–shear tests Compression and shear tests were performed on the samples according to the testing program outlined in Table 1. The preconditioned samples were subjected to short-term and long-term compression tests. Shear tests were performed in the short-term and were also performed at the end of the compression tests. In the following section, only the results of the short-term experiments on the water isolation systems will be reported.
46
M. Farshad, P. Flu¨ eler / Polymer Testing 23 (2004) 43–49
Table 1 Experimental program for the compression–shear tests on the water isolation systems Testing module
Purpose of the test
1
Lateral pressure = 1.5 MPa combined with an in-plane shear displacement of up to 3 mm Short-term drainage at high lateral Lateral pressure up to 2 MPa pressure combined with an in-plane shear displacement of up to 3 mm
2
Short-term water-tightness under high lateral pressure
3
Short-term water-tightness test under high in-plane shear
4
Long-term water drainage test (7day test) at high lateral pressure
Testing parameters
Measurements
(1) Vertical compression of the water isolating sample; (2) relative horizontal displacement of two plates (1) Required water pressure for a given drainage capacity; (2) vertical compression of the water isolating sample; (3) relative horizontal displacement of two plates Lateral pressure = 0.3 MPa (1) Vertical compression of the water combined with an in-plane shear isolating sample; (2) relative displacement of up to 10 mm horizontal displacement of two plates Lateral pressure of 1.5 MPa at the (1) Required water pressure for a end combined with an in-plane shear given drainage capacity; (2) vertical displacement of up to 3 mm compression of the water isolating sample; (3) relative horizontal displacement of two plates
8. Experimental results Fig. 3 shows one of the results obtained from the compression–shear tests on various water isolation systems. This figure shows the water pressure gradient which is required to force a specified water volume. In this case, the specified water volume fed into the system for all samples was 10 l/min. Four general groups of surface drainage systems were included in these tests. The water isolation membrane was made of 2–3 mm thick thermoplastic material, but the material was not the same for all systems. The four types of surface drainage included knobbed membranes with different geometry mesh, with and without fleece, and fleece alone. Fig. 3 shows a general trend of increase of the water pressure gradient as a function of lateral compression. With increase of the lateral compression, the sample would be further compressed and hence the drainage
capability would be reduced. Fig. 3 shows that the knobbed drainage membranes have a better drainage capacity than the other types of surface drainage materials. It also shows that some types of irregularly meshed materials (spaghetti type mesh) show a better performance in comparison with the structured rigid mesh.
9. Theoretical model 9.1. Finite element simulation of the compression– shear behavior To simulate the compression–shear tests on the watertight systems with the testing rig, numerical finite element (FE) simulation was carried out. For FE simulation of the compression–shear behavior of the watertightness system, the features of the experimental set-up shown in Fig. 1 were used. Accordingly, for the FE model, the following assumptions were made: Dimensions of two concrete blocks: length 1500 mm, thickness 300 mm, width 1000 mm Original distance between two concrete blocks: 20 mm Material properties of two blocks: E = 500 000 N / mm2, v = 0.2 Dimensions of the water-tight samples: 1500 mm, thickness 300 mm, width 1000 mm Average material properties of the sample: E = 300 N / mm2, v = 0.3
Fig. 3. Drainage behavior of various water isolation systems. The water pressure gradient required for the water volume of 10 l/min which is fed into the system.
FE model: Number of elements: 132
M. Farshad, P. Flu¨ eler / Polymer Testing 23 (2004) 43–49
Boundary conditions: the top block is fixed against horizontal displacement; lower block can move horizontally, but is restrained against rotation Vertical load: total compressive force equal to 450 kN on the top block equivalent to a uniformly distributed pressure of 3 bar. The total force is applied through two cylindrical load cells, each having a diameter of 300 mm. These cylinders are placed on the top of the upper concrete block (see Fig. 1) Horizontal action: a 10 mm shear displacement applied to the lower block Type of analysis: non-linear contact analysis Software: COSMOS/M, version 2.5. 9.2. Results of FE analysis Fig. 4 shows the normal stress field in the two concrete blocks between which the samples are placed. As we expect, due to concentrated action of two loading cylinders, the normal stress will not be uniformly distributed. However, the spatial variation of the normal stress tends to become smaller as we approach the lower surface of the upper block. Hence, the assumption that the vertical load is uniformly distributed at the level of the sample is justifiable. Fig. 5 shows the shear stress field in the two concrete blocks between which the samples are placed. Again, as expected, the shear stress distribution in the concrete blocks due to an applied shear displacement will not necessarily be uniform. Fig. 5 shows locations of maximum shear stress. However, the local variation in the shear stress field is assumed not to affect the drainage capacity. 9.3. Hydraulic model of the drainage function In order to achieve a theoretical estimation of the drainage function of the water-insulation systems, an
Fig. 4.
47
analytical model was used. The model employed the Bernoulli energy equation for a non-viscous fluid. This theory relates the pressure difference at the water-inlet to the compression–shear testing system and the outlet from this system to the kinetic energy of the fluid flow. In this calculation, the head lost due to friction was neglected. Under these assumptions, the Bernoulli equation was written as: ⌬p ⫽ (g / 2g)Q2(1 / A22 ⫹ 1 / A21)
(1)
In which, ⌬p: pressure difference of the drainage water at the inlet and the outlet of the testing system in MPa, herein so-called water pressure; Q: volume of water in mm3/s; A1: section of the drainage system at the water-inlet in mm2; A2: section of the drainage system at the water-outlet in mm2; g : density of water N/mm3; g: acceleration of gravity in mm/s2. Due to the lateral compression applied to the water isolation system, the drainage sections at the inlet and the outlet to the system (A1 and A2) will be reduced. The reduction of the flow section can be related to the lateral compression in the following fashion: A2 ⫽ Ld(1⫺F /AE)
(2)
where L is the length, d is the original height, A is the area, E is the elasticity modulus of the drainage layer, and finally F is the total lateral compressive force. Due to the structured configuration of the drainage layer, it was assumed that only part of the drainage layer should be accounted for as the effective flow section. Furthermore, the lateral compressive stress was calculated by dividing the total force F by the effective load carrying structured drainage layer. For the calculations, which follow the numerical values of d = 10 mm and E = 10 N / mm2 were chosen. Substitution of the Eq. (2) into Eq. (1) results in a relation among various parameters including lateral compression, F, drainage volume, Q, and the pressure differ-
Distribution of the normal stress field in the vertical direction in the concrete blocks.
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Fig. 5.
Distribution of the shear stress field in the two concrete blocks.
ence ⌬p. If the drainage volume Q is prescribed, then the relation of the pressure gradient required for the flow ⌬p and the lateral compressive stress is derived. Fig. 6 shows the trend of variation of the water pressure required for a drainage volume of 10 l/min as function of the lateral compressive stress. This trend, which is also intuitively plausible, is quite compatible with the measured data of Fig. 3. The quantitative changes in water pressure with the lateral compression depend on the particular structure of the drainage layer as depicted in Fig. 1. If, instead of the drainage volume, the pressure gradient ⌬p is prescribed, then the relation of the water pressure required for the water flow ⌬p and the lateral compressive stress is derived. Fig. 7 shows the trend of variation of the drainage volume as a function of the lateral compressive stress for the prescribed pressure gradient of 0.001 MPa. The quantitative changes in water pressure with the lateral compression depend on the particular structure of the drainage layer as depicted in Fig. 1.
Fig. 6. Theoretical variation of the water pressure required for a drainage volume of 10 l/min as function of the lateral compression (see Fig. 1).
Fig. 7. Theoretical variation of the drainage volume as function of the lateral compression (see Fig. 1) for a pressure gradient of 0.001 MPa.
10. Discussion and conclusions In this paper, an experimental system for testing of two-layer water isolation systems used in tunnels is described. In construction of this testing system, effects like tunnel temperature, lateral pressure due to rock, shear action due to concreting, and roughness of the media at both sides of the water isolation layers were taken into consideration. Various tests, including shortterm and long-term water-tightness experiments and drainage function were carried out. In this paper only the results of the short-term drainage experiments were reported. To simulate the behavior of the testing system, numerical FE analysis was performed. Furthermore, a simple theoretical model of the drainage behavior was derived. With the help of this model trends observed in the real experiments were reproduced. The experiments performed with the described testing system have a plausible relation with reality. The theoretical models presented in this contribution predict the general drainage behavior observed in the tests. How-
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ever, the models should be refined to take into account the structural features of the individual water isolation systems. Furthermore, the results of these laboratory experiments need to be correlated with field tests.
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systems and execution of the experiments. In this connection, special thanks are due to Andreas Brunner.
References Acknowledgements The authors would like to thank the financial support provided by the AlpTransit Authorities of Switzerland. They also express their thanks to many EMPA colleagues who contributed to the construction of the testing
[1] P. Flu¨ eler, Ch. Lo¨ we, M. Farshad, P. Zwicky, H. Bohni, The sealing of deep-seated Swiss Alpine railway tunnels— new evaluation procedure for waterproofing systems, Conference Proceedings 9 dbcm Brisbane, Australia, 2002, p. 9. [2] Ph. Rietman, P. Flu¨ eler, P. Zwicky, Test methods for sealing systems, Tunnel 10 (2002) 13–15.