Large-scale freezing work for subway construction in Japan

Engineering Geology, 13 (1979)397--415 397 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

LARGE-SCALE FREEZING WORK FOR SUBWAY CONSTRUCTION IN JAPAN

MICHIO MIYOSHI, TSUNEO TSUKAMOTO and SHIRO KIRIYAMA

Tokyo Metropolitan Government, Tokyo (Japan) Tekken Construction Co. Ltd., Tokyo (Japan) Seiken Co. Ltd., Osaka (Japan) {Received June 15, 1978)

ABSTRACT

Miyoshi, M., Tsukamoto, T. and Kiriyama, S., 1979. Large-scale freezing work for subway construction in Japan. Eng. Geol., 13: 397--415. In this freezing work four parallel tunnels, Line No.10, Line N o . l l and two utility tunnels, are being constructed simultaneously by the freezing method under a river in the central part of Tokyo. Over the proposed tunnels there exists an old concrete arch bridge across the river. In addition, in the river there are piers of an expressway viaduct quite close to the tunnels to be constructed. Under such conditions, this freezing work is being carried on with great care, taking safety measures as described below. (1) Prevention of excessive growth of frozen zone. (a) Installation of heating pipes; (b) partial application of steel pipe wall for earth retaining instead of ground freezing. (2) Minimization of damage caused by expansion of frozen soil. (a) Rationalization of freezing procedure to prevent confined freezing; (b) extraction of surplus ground water by vacuum pumps; (c) use of stabilizing liquid to reduce frost expansion pressure. (3) Strict watch for frozen soil. (a) Installation of instruments for measuring soil temperatures and displacements; (b) constant observation by a centralized control/watch system. INTRODUCTION The Transportation Bureau of the Tokyo Metropolitan Government ( T . B . T . M . G . ) is r e s p o n s i b l e f o r t h e c o n s t r u c t i o n a n d o p e r a t i o n o f f o u r o f t h i r t e e n s u b w a y lines p l a n n e d t o b e c o n s t r u c t e d in t h e T o k y o t r a f f i c area, n a m e l y , L i n e s N o s . 1 , 6, 10 a n d 12. T w o lines, L i n e s N o s . 1 a n d 6, are a l r e a d y in o p e r a t i o n , L i n e N o . 1 0 is u n d e r c o n s t r u c t i o n , a n d L i n e N o . 1 2 is b e i n g p l a n n e d . L i n e N o . 1 0 n o w u n d e r c o n s t r u c t i o n originates a t T a m a N e w T o w n , r u n s w e s t to e a s t t h r o u g h t h e c e n t r a l p a r t o f T o k y o f o r 91 k m , a n d t e r m i n a t e s at C h i b a N e w T o w n . T h e c e n t r a l s e c t i o n ( 1 4 . 6 k m ) line is n o w b e i n g c o n s t r u c t e d b y t h e T . B . T . M . G . , a i m i n g a t c o m p l e t i o n in M a r c h 1 9 8 0 .

398

General: Section name Location Section length Undertaken by Constructed by Details of work

Kudanshita, 2nd Section From 2, Kudankita 1-chome, to 2, Kandajinbocho 3-chome, Chiyoda-ku, T o k y o 232.5 m Rapid Transit Railway Construction Headquarters, Transportation Bureau o f T o k y o Metropolitan Government Tekken Construction Co., Ltd. ( S u b ~ o n s t r u c t o r Seiken Co., Ltd.) Station tunnel 38.0 m Under-river tunnel 70.5 m (Soil-freezing section 47.2 m) Running tunnel 124.0 m Incidental work for utility tunnel 240.0 m

Main figures of freezing work: Volume o f frozen soil Total length o f freezing pipes Temperature o f brine Total freezer capacity

37,700 13,747 --20°C 100 hp 200 hp

m3 m (75 kW) × 11 sets (150 kW) × 2 sets

Between Kudan and Jinbocho in central T o k y o , Line No.10 runs parallel to Line N o . l l (T.R.T.A. line, under construction) and t w o utility tunnels. As the T.B.T.M.G. has been commissioned to construct these tunnels simultaneously with Line No.10, the scale of the construction work is extremely large. At Kudanshita 2nd Section between Kudan and Jinbocho, these tunnels have to be built under the Nihonbashi River, and there the ground-freezing method has been applied on a large scale for their construction. PRIMARY REASONS

FOR EMPLOYING

THE GROUND-FREEZING

METHOD

Metropolitan Avenue 302, under which Line No.10 is constructed, intersects the Nihonbashi River at Manaita Bridge. This bridge, a fixed reinforced concrete arch, was built in 1928 (Fig.l). Over the Nihonbashi River runs Metropolitan Expressway No.4, whose viaduct piers stand on both upstream and downstream sides of the river. At the planning stage, taking account of the above geographical conditions, the unusual width of the excavation and the restricted construction time, the following were considered to be the main restrictions on the construction work. (1) The traffic on Manaita Bridge was t o o heavy to effect substantial traffic control. (2) The Nihonbashi is a tidal river with a difference in water level of a b o u t 2 m between high and low water. In addition the water level is subject to

399

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Subway L i ne No. 10 Subway Line No.ll Subway Lines Fig.1. Sketch of subway network.

sudden rises caused by heavy rainfall. Accordingly, the present crosssectional area cannot be reduced. (3) It was necessary to provide enough space for navigation of ships. (4) The vertical alignment o f the tunnel allowed only a very small a m o u n t o f earth cover. (5) There is a densely built-up area on the right-hand side of the river. (6) An expressway runs overhead. (7) The tunnel must be constructed in such a way so as n o t to interfere with future restoration of the bridge. The freezing m e t h o d was adopted because the above restrictions made unfeasible any of the m e t h o d s given below. (1) Open c u t with the river water bypassed. (2) Trench excavation with the flow of river water diverted to a t e m p o r a r y culvert. (3) Building tunnel structure with the river water partially cut off. (4) Tunnelling by the shield m e t h o d . (5) Tunnelling by the pipe r o o f m e t h o d or similar. EXPERIENCES IN GROUND F R E E Z I N G

In Japan ground freezing was first applied in 1962 at Moriguchi, Osaka, for the construction o f a water main.

400 The first application for a large~liameter tunnel was made by the T o k y o Metropolitan Government to construct Subway Line No.1 beneath the Furukawa River. Since then seven freezing projects have been carried out for under-river subway construction. In addition, the freezing m e t h o d has also been employed for shaft sinking, sewer and water line construction, etc., and the total n u m b e r of its applications to underground construction works now exceeds 100. The primary purposes of the application of the freezing m e t h o d can be divided into the following items. (1) Solidification and stabilization of soft ground. (2) Prevention o f water inflow or leakage. PREPARATORY INVESTIGATIONS In the freezing m e t h o d the most difficult pro.blem to deal with is the expansion o f freezing ground. In this work, taking account of its tremendously large scale, detailed preparatory investigations were conducted on frost expansion pressures in freezing soils and their displacements (Fig.2). As a result o f these investigations the following facts were confirmed. For the stiff cohesive stratum between depths o f 12 and 14 m below ground level: (1) The expansion pressure a t the freezing front is about 2 kg/cm 2. (2) The expansion pressure has a tendency to decrease with the distance from the freezing front. For sand strata at depths of 9--12 m and below 18 m the effect of frost expansion is virtually negligible at positions some distance away from the freezing front. Fig.2 shows the location o f the experimental ground freezing and its outline. OUTLINE OF CONSTRUCTION WORK The tunnel constructio'n under the Nihonbashi River was carried out as shown in Figs.3 and 4 in the following order. (1) Construction o f a vertical shaft on each side of the River (Manaita Bridge). (2) Horizontal boring from the two shafts and installation of freezing pipes. (3) Ground freezing. (4) Trench excavation and concreting using ice walls for earth retaining. The under-river tunnel at the Kudanshita 2nd Section, including the two vertical shafts, is 70.5 m in length, o f which 47.2 m is a frozen section. As previously mentioned, two subway lines, Nos.10 and 11, and two utility tunnels are to be constructed simultaneously, the width of the frozen zone ranging from 36 to 40 m (Fig.5). Moreover, the volume of the frozen earth is as large as 37,700 m 3, and ground freezing on such a scale has not yet been experienced in Japan. The engineering quantities, work schedule and

401

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Fig.2. Experimental ground freezing.

construction procedure are shown in Tables I and II and Fig.6 respectively. In the following an outline of the construction procedure is given.

Vertical shafts As seen in Fig.3, two vertical shafts (10.5 m X 44.8 m, 12.0 m X 43.7 m) were built, one on each side o f Manaita Bridge. The two shafts have the same depth o f 24.0 m. The retaining walls o f the t e m p o r a r y structures consisted of cast-in-place concrete diaphragm walls o f 60 cm thickness, and, where building such walls was impossible due to such obstructions as buried pipes and the like, the retaining walls were formed b y placing reinforced concrete in position with the progress o f shaft excavation, with the aid o f chemical grouting previously performed.

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Owing to ground conditions and the fact that the shafts were quite close to the river, it was feared that the shaft construction would be affected by river water. Therefore, in order to prevent bentonite slurry from dispersing and running thin, chemical injection with sodium silicate and calcium chloride was performed in the sections abutting on the river from ground level down to a depth o f 13 m. In addition, during shaft excavation, chemical grouting was injected into the sections beneath the bridge abutments and around the shafts to prevent leakage o f river water. As a result, shaft excavation was successfully carried out, installing struts (H -- 3 0 0 × 3 0 0 × 1 0 / 1 5 ) and wales ( H - - 350 × 357 × 1 9 / 1 9 ) without any water inflow.

Renewal of superstructure of Manaita Bridge Manaita Bridge, a reinforced concrete fixed arch, was built in 1 9 2 8 and is vulnerable to the differential settlements o f the ground. Accordingly, its superstructure was replaced by new steel decks and simply supported

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405 TABLE

I

Schedule

of engineering

Wor ks

quantities

O,u a n t i t i e s

C a s t in Place Concrete Piles Cast inPlace Diaphragm Wall

L=540m.450#. 24Piles

Works

Quantities

Frozen Soil

V = 37 700 mj

A=3,072 m: 25.6m in depth Horizontal , 600mm in thicknes~ Freezing Pipes

Cast in Place Piles

L=150m. H-300x300. 6piles

in the Shaft

L=100m. L =208m. Steel Pile Driving L=918m. Intermediate L=189m Steel Pile Driving

H-400x408.4 piles H- 300x300.16piLes H-400x408.34piles H-300x300 7piles

Concrete ( Trench )

V= 3,530 m'

Chemical Grouting

V= 3,266 m"

Re mova I of the Bridge

V= 2,B60 m'

Superstructure of the Bridge

Street Decking

A = 1.166m'

Trench Excavated Soil

V = 10.740 rn~

Trench Bracing

W=414 t

Horizontal Steel Pipe Wall

L=720m, 600 II 15 Pipes

L= 11,620.8 m. 523 pipes

w = 505,6 t (Simple Girder Bridge with Steel Plate Floor)

TABLE II Progression chart of works Works Preparatory Work s

1977 12n ,

Date'& I I

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Period

( Thawing ) Withdrawal Allied Civil Engineering Works

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girders to avoid the risk o f unusual stress concentrations in the old concrete arch. This superstructure replacement was carried o u t by dividing the bridge width into three parts so as n o t to disrupt traffic flow across the bridge. In addition, in the course of the replacement work, t e m p o r a r y pedestrian bridges

406

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were built on either side of the old bridge; these included the various utilities which were a p e r m a n e n t feature of the former bridge.

Insulation/refrigeration board A total of 32 insulation/refrigeration (I/R) elements (Fig.7) were placed on the river b o t t o m for the following purposes:

407

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(1) To secure an adequate cross-sectional area of the river. (2) To prevent thawing o f the frozen ground caused by river water. (3) To freeze the river b o t t o m and prevent accidents due to water inrush during the horizontal boring operation f o r freezing-pipe installation. The upper part o f the I/R board was filled with insulating materials, thereby preventing heat conduction from the river water, and the freezing pipes, installed in the lower part o f the I/R board, freeze the ground beneath the board. The horizontal section o f the board was placed at the elevation of the planned dredging formation ( A P - - 1.8 m), and the t o p of the vertical section was located at the elevation A P + 2.7 m, which the river water will n o t reach except at an unusually high tide. The height o f each element was 4.9 m, and its length equal to half the width o f the river; and 3.2 m was chosen as its width for convenience o f transportation. As I/R board was manufactured at a remote factory, it was transported to the site by trailer cars. After placing each element on the river surface b y a mobile crane, it was

408

charged with ballast sand for stabilization, and then rehung and shifted by a crane on to a verge, and sunk on to the river b o t t o m . For permanent fixture o f the I/R bqard, the voids between the board and the bridge abutments were filled with concrete, and those between the board and the river b o t t o m were filled with cement mortar through the grout holes. The I/R elements were L-shaped, and when t h e y were fabricated on the river b o t t o m , U-shaped I/R board was formed according to the configuration of the river. It was first feared that the I/R elements would be pulled apart due to the expansion o f the freezing ground and that the invading river water would thaw o u t or wash the frozen ground. Therefore, along the edges of the elements, freezing pipes were increased in n u m b e r and cushions provided. In addition, the element joints were covered with rubber. Prior to the element-sinking operation, sheet steel piles were driven along both upstream- and downstream-side edges of the zone to be frozen, and concrete was placed there on the river b o t t o m to prevent the frozen soils from being washed by the river water.

Freezing equipment The freezers were placed separately in three different places because of available space and the time required for their setting. F o u r sets (150 kW X 2, 75 kW X 2) were placed on the upstream-side a b u t m e n t site of the Manalta Bridge, two sets (75 kW X 2) in the nearby building of the former metropolitan tax office, and seven sets (75 kW X 7) on the first floor of the adjacent station structure constructed through the reverse concreting procedure. The control center cabin to control this equipment was also located on the same a b u t m e n t site. In this control center cabin automatic digital recorders were also a c c o m m o d a t e d to obtain the ground temperatures measured by the approximately 700 thermometers installed in the ground. This equipment used for freezing and the overall freezing system are shown in Table III and Fig.8 respectively.

Freezing pipes and temperature-measuring pipes Horizontal boring from the vertical shafts was started when the thickness of the frozen zone, formed beneath the I/R board by its initial freezing, reached 80 cm. This boring operation was carried out downward from the upper to the lower parts. The length o f the freezing pipes is 24.6 m and t h e y were overlapped 2 m at the river center. Fig.5 shows the locations of the freezing and the control pipes. A freezing pipe consists of a 101.6-mm-dia. outer pipe (SGP pipe) with a closed lower end and a 48-mm-dia. polyethylene inner pipe. A control pipe consists o f a 60.5-mm-dia. carbon steel pipe closed at the lower end, and has the same length as a freezing pipe. Inside a control pipe four platinum resistance thermometers were installed at 6-m intervals.

409 TABLE III

Specification of Ref dgerating Plant l' Refrigerating

Unit

I 7 5 kw 7 5 kw

Screw Compressor

I 150 kw

1 1 (set)

2 (set)

150 k'w unit

unit

Rlefr)gerating Cap=city 90,000 kcal I h Evaporating Temp. -27"C

164~X)0 kcal I h -27"C

-Condensing Temp. °37=C

,37°C 150 kw 3,300V

Motor

75 kw

Condenser

Coo~ir~j Surface Area31/,l~'

62.1 M=

Brine Cooler

Cooling Surface Aree39A~

6z5~'

Brine Temperature

3,300V

Brine Pump

80~x 11kw

Water Pump

125ox 7.5 kw

Cool i ng Tower

-21.5"(: -18.5%

out -21,5'C i n -18.5"C

Cooling Capacity Air Te_~ature Water Temperature Fan

125~ x 22 kw 585,000 kcall h .27"C .37"C 3.7 kw

Control le r Safety Controller

1

1

Specification of Temperature Measuring System Digital

Recorder

Temperature Aiarm System Sensor

5 (sets) 1 (set) (Platinum Resistance Bulb 100D.) 800 (points)

Horizontal steel pipes As the distance between the upstream-side piers of the expressway and the tunnel structure is only 10 m, it was expected that the distance between the piers and the frozen zone would be a b o u t 5 m. Though the result of the experimental freezing indicated that no harm would be done to the piers b y the expansion of the freezing ground, it was decided n o t to apply freezing on the upstream side and, instead, to use

410 Re~riaerat ino System

Fig.8. Overall freezing system.

horizontal steel pipes with a diameter of 600 mm for earth retaining, taking account o f the following: (1) The scale o f the experimental freezing cannot be compared with that of the real freezing. (2) The expressway viaduct is curved and built of three-span continuous bridges with a m a x i m u m span length o f 70 m. Jacking o f the horizontal pipes was done when the frozen zone developed to some extent, and prior to jacking the adjacent part of the ground was consolidated b y chemical injection. These horizontal pipes were jacked from the Kudan-side vertical shaft and filled with mortar to increase their stiffness and watertightness.

Control of freezing Freezing was first started in the upper sections and then extended to the lower sections. The process of freezing was carefully determined to avoid confined freezing, in which unfrozen sections are left within the frozen ground. If this occurs, cracking in frozen softs and fractures of freezing pipes take place, with serious effects on subsequent operations. Presuming the freezing rate from the real ground composition, it was t h o u g h t inevitable that confined freezing would take place in some sections under the prevailing economic and time restrictions. Under such circumstances, and to relieve excessive pore water and expansion pressures in confined parts, filter pipes were installed, through which surplus groundwater had been extracted. In addition, to relieve expansion pressures, a special stabilizing liquid with cellulose added, was injected into the ground around

411

the boreholes before the freezing tubes were inserted. This liquid was used in expectation that, with increased viscosity, it would b e c o m e more difficult for the groundwater to be absorbed from the frozen parts and that, consequently, possible expansion pressures would be reduced to a certain extent. With regard to groundwater movement, it had been observed that the groundwater was flowing from Kudanzaka to the Nihonbashi River at the rate of 1.6 m/day. However, endorsed by the experimental ground freezing, it was concluded that such a rate o f groundwater flow would n o t obstruct the growth o f the frozen ground, and no special measures were taken to expedite freezmg. Instead, as such groundwater movements can be discovered b y observing the changes in the ground temperatures, a system has been estabfished in which timely countermeasures against unusual states can be taken.

Excavation and concreting Excavation and concreting are carried o u t b y the t r e n c h ~ u t method, and H -- beam (150 X 150 X 70 X 7/15) bracings are installed at 1-m intervals. The temporary work structures have been designed so that the ground pressures can be withstood b y the ice walls, except in the case Of the upstreamside trench with a steel pipe wall, where H -- beam (300 × 300 X 10/15) bracings are installed at 1-m intervals. The process of the excavation and concreting is shown in Fig.9. As is generally known, the strengths o f frozen softs vary according to their properties and temperatures. The figures shown in Table IV were taken for the design strengths, and the thickness o f the ice walls of below --5°C was considered adequate in the temporary structure design. Concreting is carried o u t immediately after each trench excavation is finished. Because o f m a n y uncertainties as to the plasticity o f frozen soils, groundwater movements, etc., rapid-hardening concrete is used. As thick w o o d forms are used and concreting is done with high-strength, rapidhardening cement, no frost damage is expected. Concrete o f an ordinary proportion is used, and heaters are n o t used except in the inverted part where heating wires are e m b e d d e d in the ~.0-cm-thick base concrete placed in two layers and which protect the concrete against freezing. As the concrete slabs and walls are very large, the temperature gradient across them will also be fairly large. Therefore, it is feared that contraction cracks will appear in the concrete and lead to groundwater leakage. Therefore, the use o f non-contracting c e m e n t is being examined for parts around placing joints, especially for those in the upper slabs.

Care o f surrounding structu res In the freezing m e t h o d , it is quite difficult to carry o u t construction works w i t h o u t causing damage to surrounding structures b y frost expansion. In this case it was realized that damage m a y be caused to the bridge, the piers o f the expressway viaduct, or buried utilities, and therefore, the follow. ing precautionary measures were taken.

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of T r e n c h E x c a v a t i o n ]

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o

o

'._ 2 5 7 5 ]

o

o

o o

o

413 TABLE IV Design strength of frozen soil Cohesive Soil

Sandy Soil

Temperature of Frozen Soil

18 kglcrR

25 kg/crrf

- 5"c

30 kg/cm'

45 kg/cm'

-10°c

Compressive Strength

Shearing Strength

15 kglcrrf

Bending Strength

18 kg/cm'

-10'c

(1) Conversion o f the fixed concrete arch into a simply supported steel girder bridge with steel decks. (2) Measurements on the changes in the bridge and the expressway viaduct. (3) Protection o f the bridge and the expressway piers on the left-hand side of the river b y building a separation wall (cast-in-place concrete pile wall). (4) Replacement of the utilities fixed to the old bridge. (5) Protection of the expressway piers by the heating pipes from frost damage. (6) Use of a horizontal steel pipe wall on the side close to an expressway pier. The changes in the bridge and the expressway have been measured by the use of the settlement meters and clinometers attached to the bridge abutments and the viaduct piers. In addition, displacements and pressures in the ground have been measured b y installing clinometers, earth-pressure meters and pore-water pressure meters in the ground between the expressway piers and the frozen zone (Fig.10). As the expressway pier and the bridge a b u t m e n t were connected solidly by the concrete river bank on the left-hand side of the Nihonbashi River, it was thought possible that the pier would be damaged by the lateral displacem e n t o f the a b u t m e n t caused b y differential ground upheaval. Accordingly, a part o f the concrete bank was removed, and sandbags were packed therein to form a buffer zone. Such utilities fixed to the old bridge as gas pipes, water pipes, electric p o w e r cables, telephone cables, etc., were resited on the new temporary bridges built on both upstream and downstream sides of the old bridge. For the protection o f the expressway piers the heating system has also been e m p l o y e d to minimize damage. In this heating system, heating pipes are p u t into the boreholes located between the piers and the frozen zone.

The D e t a i l of P a r t ( Cross Section) (Bridge)

IF, Board)

The D e t a i l of

Part (~

x Dr~,~ - wav

~P • :ross

nome~pr

Sect ion )

I

( Freezing Board) ]

~

(Shall) _

rig.

10. Location of measuring equipment.

.....

&L W L . ,

u ~(Freezing Pipes.)

• u

--

Clinometer Settle,ment Measuring Equipment ~water level system) Earth Pressure Cell 8, Pore Water Pressure C e t l & C l i n o m e t e r in Pipe

415

The voids between the heating pipes and the surrounding ground are expected to relieve frost expansion pressures in the ground, and, by circulating warm water through the heating pipes, the growth of the frozen zone can be controlled. Locations of the heating pipes and equipment for the heating system are shown in Fig.10 and Table V respectively. Owing to the various precautionary measures mentioned above, no serious effect on surrounding structures has taken place, except that the bridge has shown some displacement due to ground uplift. CONCLUSION

The section discussed above is one of the most difficult from a construction viewpoint in the Subway Line No.10. The work at this section was started in May 1975, and the growth of the frozen zone has now reached 70% of its full scale. So far, any problems of prohibitive damage to adjacent existing structures have not yet arisen. However, although most of the problems in the early stages of application of this method have been solved, there are still several problems outstanding. This freezing work has been the greatest one in scale in Japan, and may be in the future, too. Because of this, in thecourse of this work, we may encounter various problems hitherto not experienced. But, by developing new techniques from experience obtained in the previous freezing works in the construction of the metropolitan subway lines and others, we are sure that we will be able to cope with such problems with confidence. The following are the two representative problems to be encountered in this section in the near future. (1) Settlement at the time of ground thawing. (2) Reconstruction of Manalta Bridge. We are currently examining several ways of solving these problems. Finally, we would like to note that this freezing work is being quite successfully carried on, aiming at completion in 1979. TABLE V

Specification o f thawing plant

Quant it ies 2 sets

Heater

Pump

( 11 kw, ~125)

2 sets

Controller

2 sets

Water Tank

2 sets