HK Cavern Construction Masato Shiozawa (UTokyo) T2HKK Workshop - PowerPoint PPT Presentation

HK Cavern Construction Masato Shiozawa (UTokyo) T2HKK Workshop November 21, 2016 1

• Overview of Hyper-K cavern design and excavation is given in my talk • Thanks to J.Yamatomi, S. Nakayama, and Hide Tanaka for many slides • More details in the Hyper-K Design Report • KEK Preprint 2016-21, ICRR-Report-701-2016-1 2

76000 (cavern) 78000 (cavern) 60000 (water tank) Cavern dimension: 76m( ϕ ) x 78m(H) Tank dimension: 74m( ϕ ) x 60m(H) 74000 (water tank) 3

Detector location • The detector site � � locates in Tochibora Mine under � Mt. Nijugo-yama (25- yama) • ~8km south from Super-K • Identical baseline � (295km) and off-axis angle (2.5deg) to J- PARC beam � � • Overburden ~650m � � (~1755 m.w.e.) � � � 4

Candidate site 25yama 1,156m a.s.l. � 0M=845m a.s.l. � overburden ! 648m � Hyper-K � -300M � ← 553m a.s.l. -370M � ← 483m a.s.l. 508m a.s.l. � -430M � ← 423m a.s.l. Surrounded by many drifts at various levels which enable us to perform geological surveys 5

Maruyama: disposal place � The peak was collapsed due to past mining activity. The capacity of rock disposal is estimated ~2 million m 3 . × 6

坑口 和佐保堆積場 （ずり仮置場） 円山陥没地 地図に道がないので 適当に線（点線）を 書いています Waste rock disposal • 2.1km long access Maruyama collapsed Mt. tunnel between HK site and Wasabo accumulation place. • Waste rock (570 kilo Rock m 3 /Tank) will be transportation 1 4 e road transported by tracks t u HK o R from HK to Wasabo, ( 地下 ) and then Maruyama. Access tunnel 和佐保坑道 • Maruyama collapsed ( 地下 ) (2.1km) mountain peak, Entrance Wasabo capacity of ~2 M m 3 accumula tion place Kamioka downtown 7

Geological surveys • Identified candidate site w/ 300m × 300m intersected by major faults • 553m above sea level(asl),300mL(~level of tank top) - use existing drift for geological investigation, rock mass classification, and in-situ stress measurement - 250m drilling hole for discontinuity survey and rock deformability measurement • 483m asl,-370mL(~level of tank floor) - Use existing drifts for geological mapping - At drilled 4 boreholes w/ total length of 600 m, borehole discontinuity survey and rock mass classification, insitu stress measurements were performed. • 423m asl, -430mL(level below the tank) - D rift was opened and cleared, and geological mapping was conducted 8

Summary of Geological study Initial stres ess Bor oreh ehol ole e No. o.4 mea easurem emen ent (4 (483 m a.s.l a.s.l.) .) � (4 (483 m a.s.l a.s.l.) .) � Tunnel el No. Initial stres ess o.3 Tunnel (483 m a.s.l (4 a.s.l.) mea easurem emen ent (423 m a.s.l (4 el No. .) � (483 m a.s.l (4 a.s.l.) .) � o.4 a.s.l.) .) � ������������� o.2 .) � e No. a.s.l.) (483 m a.s.l ole ehol oreh Bor o.3 (5 (553 m a.s.l oreh e No. .) � Bor a.s.l.) ehol (483 m a.s.l (4 ole ole ehol e No. a.s.l.) oreh Bor o.1 .) � (4 Initial stres ess mea easurem emen ent (5 (553 m a.s.l a.s.l.) .) � o.1 Tunnel el No. o.2 el No. Tunnel .) � a.s.l.) (483 m a.s.l (4 a.s.l.) .) � (553 m a.s.l 9 (5

Summary of Geological study Initial stres ess Bor oreh ehol ole e No. o.4 mea easurem emen ent (4 (483 m a.s.l a.s.l.) .) � (4 (483 m a.s.l a.s.l.) .) � Tunnel el No. Initial stres ess o.3 Tunnel (4 (483 m a.s.l a.s.l.) mea easurem emen ent • Dominated by Hornblende Biotite and Migmatite in the (4 (423 m a.s.l el No. .) � (4 (483 m a.s.l a.s.l.) .) � o.4 a.s.l.) .) � state of sound, intact rock mass ������������� • Rock mass classification (according to the classification o.2 .) � e No. a.s.l.) (483 m a.s.l ole defined by Japanese Central Research Institute of ehol oreh Bor o.3 (5 (553 m a.s.l oreh e No. .) � Bor a.s.l.) Electric Power Industry (CRIEPI)) ehol (483 m a.s.l (4 ole ole ehol e No. a.s.l.) oreh Bor o.1 .) � • Define rock distribution models for stability analysis by (4 referring the obtained data. Initial stres ess mea easurem emen ent (5 (553 m a.s.l a.s.l.) .) � o.1 Tunnel el No. o.2 el No. Tunnel .) � a.s.l.) (483 m a.s.l (4 a.s.l.) .) � (553 m a.s.l 10 (5

� � � � Cavern stability analysis (1) Summary of rock classification CM-class CH-class A~CH CM~D Model-1 classes classes 24.305° 24,190° � → Ref. for � 553m a.s.l. 65.695° 6 5 >95% <5% , 8 Model-1 � � � 1 0 (-300mL) ° � ~68% ~32% → Ref. for 483m a.s.l. CH 78 (57~78%) (43~21%) (-370mL) Model-2 ( uniform ) • Model-1 Assume the rock mass consists of 100% of CH-class rock Model-2 • Model-2 24.305° CH 2 4 , 1 9 0 ° � (17m) Assume rock mass consist of a mixture 65.695° 65,810° � CM (14m) of CH-class (64%) and CM-class (36%) rocks CH (50m) • 78 To be conservative, CM-class rock intentionally allocated at the structurally CM (21m) weaker portion (dome and bottom barrel CH (10m) sections) of the cavern CM 11 (13m)

����������� ���������������������������� �� ���� � � � � � �������� Cavern stability analysis (2) Cavern geometry Excavation steps 3D model for ���������������������� ����������� ���������������������������� �� 24,190° � 24.305° stability analysis ���� 6 6 5 5 . , 6 8 1 9 0 5 ° ° � 78 (ex. at an excavation step) ����������������������������������� � �������� • Carried out the cavern stability analyses with Model-1 and � ������� ������� Model-2 rock conditions • Adopt the measured initial stress of the rock ���������������������� • 3D finite element analysis adopting Hoek-Brown model • A model to treat the elastic and inelastic behaviors of rock • Step-by-step excavation taken into account in stability analysis • Evaluate plastic region depth and design cavern support 12 ����������������������������������� � ������� �������

� � � � � � Cavern stability analysis (3) � � � �� ������� ����������� ������� � ������� � � � � Plastic region depth CM-class CH-class � Cavern support (PS-anchors) (without support) 24.305° 24,190° � � 65.695° 65,810° � � � � � � 12m Model-1 Model-1 � CH � 78 � ( uniform ) � 7m 4.5m � � � ���� � �������� � � � ���� (45° slice) (45° slice) � �� ���������������������� � �� ���������������������� �������� � � CH 24,190° � 24.305° (17m) 65.695° 65,810° � CM (14m) 14m 12m 14m CH Model-2 Model-2 (50m) 78 10m 9m 10m CM 9m (21m) CH (10m) CM (45° slice) (45° slice) (13m) • Model-2 has a larger plastic region and requires more support than � � � �� ���������������������� � �� ������������������������ Model-1 • Confirmed the cavern can be constructed with the existing technologies for both Model-1 and Model-2 rock mass conditions 13

Cavern construction Approach tunnels Wasabo access tunnel (one cavern) N Upper access tunnel Lower access ‘Wasabo’ access tunnel 1st water tunnel Dome section room Upper access tunnel approach tunnel Outer incline 2nd water tunnel room Top level approach tunnel 2nd level approach tunnel Outer incline tunnel 4th level approach tunnel Lower access tunnel Wasabo access tunnel 1 km • Cavern construction begins with tunnels construction • ‘Wasabo access tunnel’ construction → approach tunnels & cavern construction • Wasabo tunnel used for access the detector site and used for the waste rock transportation • Cavern excavated from top to bottom • Dome section → barrel section 14