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Subway construction is Stuttgart under protection of a frozen soil roof
Engineering Geology, 13 (1979) 425--428
425
© Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
SUBWAY CONSTRUCTION IN STUTTGART UNDER PROTECTION OF A FROZEN SOIL ROOF
GEORG-PETER JONUSCHEIT
Philipp Holzmann Aktiengesellschaft, Frankfurt am Main (G.F.R.) (Received June 15, 1978)
ABSTRACT Jonuscheit, G-P., 1979. Subway construction in Stuttgart under protection of a frozen soil roof. Eng. Geol., 13: 425--428. Experiences gained on the building of the City Railway turning loop, Stuttgart, Section 12, are described, where the new Austrian tunneling method is used in connection with the freezing technique. The Metro-tunnel lies in leached-out gypsum 'marl and unleached zones, respectively. In a section of this tunnel within the leached-out gypsum marl the excavation was protected by a frozen soil roof in order to keep away any water seepage which could be dangerous for the excavation itself and for the buildings superimposed as well The drilling for the freeze pipes, the installation and operation of the freezing system and the tunnel driving including the erection of the final support are described. A point of special interest is the application of the shotcrete method as the shotcrete has to adhere to the frozen soil and has to harden sufficiently before the hardening process is interrupted by frost penetration. INTRODUCTION
The following notes of a lecture on the new Austrian tunnelling method in conjunction with the freezing process describe the experience gained on the building of the City Railway turning loop, Stuttgart, Section 12. GEOLOGICAL AND SUBSOIL CONDITIONS
The underground turning installation is entirely in layers of the middle gypsum bed. At the same time, the front part is in the leached-out ~Tpsum marl. CONSTRUCTION
When choosing the method of construction, consideration had to be given to buildings in the neighbourhood. There had to be as little settlement as possible. This could not be achieved without additional temporary construc-
426
tions, as no adequate standing time was available for tunnel roofs and walls and there was no question o f shield or blade drive because of the sharply changing g e o m e t r y of the c o n s t r u c t i o n work. There are some interesting cross-sections; n o t a b l y the tongued wall with the branch c o n n e c t i o n t o the Hasenberg -- here the tunnel expands from 8 to 13 m -- and the t r u m p e t s of the two-track area with their excavation diameters o f 14.5 m. On general, it was planned t o start the freezing of the tunnel roofs and walls f r o m a freezing shaft and tunnels over b o t h railway tunnels t hrough freezing lances drilled vertically or at an angle. This was modified by a special proposal f r om the Philipp H ol zm a nn Company. In this m e t h o d the vertical freezing lances were replaced by horizontal freezing lances. By rearrangement o f the freezing lances an umbrella-shaped frozen area was achieved over the tunnel roofs. The cube of the frost c o n t e n t was reduced f r o m 35,000 m 3 to a b o u t 9000 m 3 by this m e t h o d . However, this m eant increased c o m b i n e d risk in the construction. The m ost significant being the enlargement o f the standard cross-section for the a t t a c h m e n t of the freezing lances. F o r the standard cross-section, an enlargement from 50 metres to 70 m 2 was necessary, as well as great accuracy in horizontal drilling for the refrigerant tubes. Variations of m or e than 1% in the length of the borehole would certainly have led to the frozen area n o t being closed, or drilling tubes running into th e excavation.
The drilling process After a great deal o f consideration and e x p e r i m e n t a t i o n the superimposed drilling m e t h o d was chosen, as this produces the greatest directional accuracy F o r this it was necessary to c o n s t r u c t a special drilling rig. During c o n s t r u c t i o n it was f o u n d useful to predrill with the auger and to follow up with the core drilling tube. The direction of the borings was controlled by automatic, adjustment, using a drilling template with sleeves 1.5 m long, so th at the drilling rig, m o u n t e d on a hydraulic excavator, needed only a rough alignment. The distance between drilling tubes varied from 0.6 to 1.3 m. The tubes were bet w e e n 0.5 and 1 m away from the edge o f the excavation. F o r the first section to be drilled a drilling length of 30 m was decided on. The subsequent survey showed m a x i m u m variations o f 30 cm, t h e r e f o r e the drilling lengths for f u r t h e r sections could be fixed at 40 m for the following sections and 60 m for the branch line t o the Hasenberg. The horizontal stratification o f the subsoil to be worked on had a favourable influence on the accuracy of the drilling. In only one case did the drilling penet r a t e the cross-section o f tunnel excavation. The following points should be not ed: (1) The core drilling tubes of t e m p e r e d steel with a diameter of 101 m m and a wall thickness of 8.0 m m acted as freezing tubes.
427
(2) The watertight threads must allow transference of the turning m o m e n t s arising from drilling. (3) After being sunk into position the freezing tubes were impacted against the soil and tested for excess water pressure at approximately 8 atm. (4) After the brine delivery tube was connected, each freezing t u b e was connected separately. (5) The connection tubes were insulated against cold losses by expanded polystyrene lagging.
Freezing power plant The p o w e r requirement of the freezing power plant was determined by the repetitive m e t h o d of driving and of freezing the tunnel roofs. While one area was being frozen and built up, excavation of the previously frozen area could be begun. The installed freezing o u t p u t was a b o u t 500,000 dcal/h at an average brine temperature of -- 20°C. During active freezing time the brine could be frozen to -- 40°C, b y means of which the freezing times could be reduced in comparison with earlier work. Within six to eight days the frozen area was built up to its required strength. The freezing process was monitored b y temperature-measuring chains built equidistant between two freezing lances. With these, both the build-up Of temperature and later the temperature to be maintained could be measured. The refrigerant used was calcium chloride with a strength o f 31.5 ° Baum~. The cooling limit shows that at brine temperatures of --40°C the calcium chloride c o n t e n t must be gauged exactly, as even with minor variations the danger exists that the machine will freeze up. The interdependence of ground temperature and the o u t p u t required from the freezing equipment, split up into kilocalories per hour and energy usage in kilowatts per day, are illustrated in the diagram for the first section to be frozen. After constant temperatures are achieved, the interdependence of individual factors becomes clear. Especially n o t e w o r t h y is the narrow temperature difference of 4°C and less between the flow and return of the brine. DRIVING
Driving under the protection o f the frozen area This area of operations was constructed b y the new Austrian tunnel method, with 25-cm gunite, tunnel arches and t w o layers of steel mesh reinforcement. In the standard section, with an excavation diameter of 8.10 m, the work° ing face was benched into three terraces, and in the trumpet-shaped area, with an excavation height of 12.6 m, into four terraces. For normal excavation hydraulic excavators were used. However, the frozen tunnel roof, with a temperature of --5°C at the edge of the excavation, had to be cut o u t with a p o w e r cutter. The cylinder compressive strength of the frozen area was in the
428 region of 100 kp/m 2 . Two problems had to be solved before gunite work could begin. They were (1) application to frozen soil, and (2) application to soil with surface-water seepage. The gunite must adhere to the frozen ground surfaces and harden sufficiently before the curing process is interrupted by frost penetration. The temperature behaviour of the gunite was measured with temperature sensors which were built into the external load-bearing gunite shell after the application of a 2-cm-thick seal. The diagram shows that the temperature of the gunite applied at 80°C rises to a b o u t 19°C as a result of hydration heat, then slowly sinks and does not reach the 0°C limit until after four and a half days. In its application in Stuttgart, the freezing process can be evaluated as follows: (1) The standing time of the tunnel roofs was given. (2) The compatibility of frozen soil and gunite protection could be proved. (3) A risk to safety from breakdown of the freezing plant did not arise, as the immediate protection of the cavity was ensured by the reinforced gunite and by the tunnel arches. (4) All w o r k was carried o u t within the resources of the joint venture and integrates fully into the building programme.
425
© Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
SUBWAY CONSTRUCTION IN STUTTGART UNDER PROTECTION OF A FROZEN SOIL ROOF
GEORG-PETER JONUSCHEIT
Philipp Holzmann Aktiengesellschaft, Frankfurt am Main (G.F.R.) (Received June 15, 1978)
ABSTRACT Jonuscheit, G-P., 1979. Subway construction in Stuttgart under protection of a frozen soil roof. Eng. Geol., 13: 425--428. Experiences gained on the building of the City Railway turning loop, Stuttgart, Section 12, are described, where the new Austrian tunneling method is used in connection with the freezing technique. The Metro-tunnel lies in leached-out gypsum 'marl and unleached zones, respectively. In a section of this tunnel within the leached-out gypsum marl the excavation was protected by a frozen soil roof in order to keep away any water seepage which could be dangerous for the excavation itself and for the buildings superimposed as well The drilling for the freeze pipes, the installation and operation of the freezing system and the tunnel driving including the erection of the final support are described. A point of special interest is the application of the shotcrete method as the shotcrete has to adhere to the frozen soil and has to harden sufficiently before the hardening process is interrupted by frost penetration. INTRODUCTION
The following notes of a lecture on the new Austrian tunnelling method in conjunction with the freezing process describe the experience gained on the building of the City Railway turning loop, Stuttgart, Section 12. GEOLOGICAL AND SUBSOIL CONDITIONS
The underground turning installation is entirely in layers of the middle gypsum bed. At the same time, the front part is in the leached-out ~Tpsum marl. CONSTRUCTION
When choosing the method of construction, consideration had to be given to buildings in the neighbourhood. There had to be as little settlement as possible. This could not be achieved without additional temporary construc-
426
tions, as no adequate standing time was available for tunnel roofs and walls and there was no question o f shield or blade drive because of the sharply changing g e o m e t r y of the c o n s t r u c t i o n work. There are some interesting cross-sections; n o t a b l y the tongued wall with the branch c o n n e c t i o n t o the Hasenberg -- here the tunnel expands from 8 to 13 m -- and the t r u m p e t s of the two-track area with their excavation diameters o f 14.5 m. On general, it was planned t o start the freezing of the tunnel roofs and walls f r o m a freezing shaft and tunnels over b o t h railway tunnels t hrough freezing lances drilled vertically or at an angle. This was modified by a special proposal f r om the Philipp H ol zm a nn Company. In this m e t h o d the vertical freezing lances were replaced by horizontal freezing lances. By rearrangement o f the freezing lances an umbrella-shaped frozen area was achieved over the tunnel roofs. The cube of the frost c o n t e n t was reduced f r o m 35,000 m 3 to a b o u t 9000 m 3 by this m e t h o d . However, this m eant increased c o m b i n e d risk in the construction. The m ost significant being the enlargement o f the standard cross-section for the a t t a c h m e n t of the freezing lances. F o r the standard cross-section, an enlargement from 50 metres to 70 m 2 was necessary, as well as great accuracy in horizontal drilling for the refrigerant tubes. Variations of m or e than 1% in the length of the borehole would certainly have led to the frozen area n o t being closed, or drilling tubes running into th e excavation.
The drilling process After a great deal o f consideration and e x p e r i m e n t a t i o n the superimposed drilling m e t h o d was chosen, as this produces the greatest directional accuracy F o r this it was necessary to c o n s t r u c t a special drilling rig. During c o n s t r u c t i o n it was f o u n d useful to predrill with the auger and to follow up with the core drilling tube. The direction of the borings was controlled by automatic, adjustment, using a drilling template with sleeves 1.5 m long, so th at the drilling rig, m o u n t e d on a hydraulic excavator, needed only a rough alignment. The distance between drilling tubes varied from 0.6 to 1.3 m. The tubes were bet w e e n 0.5 and 1 m away from the edge o f the excavation. F o r the first section to be drilled a drilling length of 30 m was decided on. The subsequent survey showed m a x i m u m variations o f 30 cm, t h e r e f o r e the drilling lengths for f u r t h e r sections could be fixed at 40 m for the following sections and 60 m for the branch line t o the Hasenberg. The horizontal stratification o f the subsoil to be worked on had a favourable influence on the accuracy of the drilling. In only one case did the drilling penet r a t e the cross-section o f tunnel excavation. The following points should be not ed: (1) The core drilling tubes of t e m p e r e d steel with a diameter of 101 m m and a wall thickness of 8.0 m m acted as freezing tubes.
427
(2) The watertight threads must allow transference of the turning m o m e n t s arising from drilling. (3) After being sunk into position the freezing tubes were impacted against the soil and tested for excess water pressure at approximately 8 atm. (4) After the brine delivery tube was connected, each freezing t u b e was connected separately. (5) The connection tubes were insulated against cold losses by expanded polystyrene lagging.
Freezing power plant The p o w e r requirement of the freezing power plant was determined by the repetitive m e t h o d of driving and of freezing the tunnel roofs. While one area was being frozen and built up, excavation of the previously frozen area could be begun. The installed freezing o u t p u t was a b o u t 500,000 dcal/h at an average brine temperature of -- 20°C. During active freezing time the brine could be frozen to -- 40°C, b y means of which the freezing times could be reduced in comparison with earlier work. Within six to eight days the frozen area was built up to its required strength. The freezing process was monitored b y temperature-measuring chains built equidistant between two freezing lances. With these, both the build-up Of temperature and later the temperature to be maintained could be measured. The refrigerant used was calcium chloride with a strength o f 31.5 ° Baum~. The cooling limit shows that at brine temperatures of --40°C the calcium chloride c o n t e n t must be gauged exactly, as even with minor variations the danger exists that the machine will freeze up. The interdependence of ground temperature and the o u t p u t required from the freezing equipment, split up into kilocalories per hour and energy usage in kilowatts per day, are illustrated in the diagram for the first section to be frozen. After constant temperatures are achieved, the interdependence of individual factors becomes clear. Especially n o t e w o r t h y is the narrow temperature difference of 4°C and less between the flow and return of the brine. DRIVING
Driving under the protection o f the frozen area This area of operations was constructed b y the new Austrian tunnel method, with 25-cm gunite, tunnel arches and t w o layers of steel mesh reinforcement. In the standard section, with an excavation diameter of 8.10 m, the work° ing face was benched into three terraces, and in the trumpet-shaped area, with an excavation height of 12.6 m, into four terraces. For normal excavation hydraulic excavators were used. However, the frozen tunnel roof, with a temperature of --5°C at the edge of the excavation, had to be cut o u t with a p o w e r cutter. The cylinder compressive strength of the frozen area was in the
428 region of 100 kp/m 2 . Two problems had to be solved before gunite work could begin. They were (1) application to frozen soil, and (2) application to soil with surface-water seepage. The gunite must adhere to the frozen ground surfaces and harden sufficiently before the curing process is interrupted by frost penetration. The temperature behaviour of the gunite was measured with temperature sensors which were built into the external load-bearing gunite shell after the application of a 2-cm-thick seal. The diagram shows that the temperature of the gunite applied at 80°C rises to a b o u t 19°C as a result of hydration heat, then slowly sinks and does not reach the 0°C limit until after four and a half days. In its application in Stuttgart, the freezing process can be evaluated as follows: (1) The standing time of the tunnel roofs was given. (2) The compatibility of frozen soil and gunite protection could be proved. (3) A risk to safety from breakdown of the freezing plant did not arise, as the immediate protection of the cavity was ensured by the reinforced gunite and by the tunnel arches. (4) All w o r k was carried o u t within the resources of the joint venture and integrates fully into the building programme.