¹Institute of Oceanic Research and Development, Tokai University

Shimizu, JAPAN

tsuruya@scc.u-tokai.ac.jp

　

²Yokohama Research and Engineering Office for Port and Airport

Kanto Regional Development Bureau

Ministry of Land, Infrastructure and Transport, JAPAN

　

³Kobe REOPA, Kinki RDB, MLIT, JAPAN

⁴Nagoya REOPA, Chubu RDB. MLIT, JAPAN

⁵Coastal Development Institute of Technology, JAPAN

　

　

Three types of floating disaster prevention bases (FDPB) have been constructed in 2000 and disposed at the base ports in Tokyo, Ise, and Osaka Bays. The shell structures adopted for the bases are steel, PC-hybrid and RC-hybrid types. Details of the structures from the construction to the present situation are described. After the completion of FDPD, training exercises have been conducted. Improvement proposals acquired from the experiences are also shown in the present paper.

　

　

The Great Hanshin-Awaji Earthquake has occurred at 17 January 1995 and 6,400 people have been killed or missing. Houses partially or completely destroyed in the quake reached 240,954 and the financial cost of total damages are estimated approximately ten trillion Japanese Yen. Because of the heavy damages of infrastructures and buildings, human and urban activities are forced to be stagnant for a long time. Through many types of experiences for relief and restoration works, it has been recognized that the relief activities especially from sea side are quite important and effective especially during about two weeks from just after the occurrence of a disaster to the genuine relief and rescue operations are put into practice.

　

After the Great Hanshin-Awaji Earthquake, the Ministry of Transport has drawn up the Basic Principle for the Construction of Countermeasures for the Big Earthquake Disaster in Port Area. Based on the principle, the Second, the Third, and the Fifth Port Construction Bureaus of the Ministry of Transport have decided to construct floating disaster prevention bases as complementary facilities of the high-performance quay walls against earthquake, which had been intentionally constructed but still be insufficient. Because of the reorganization of the central government of Japan in 2001, the Ministry of Transport has changed its name to the Ministry of Land, Infrastructure and Transport, and the Second District Port Construction Bureau to the Kanto Regional Development Bureau, the Third Port Construction Bureau to the Kinki RDB, and the Fifth PCB to the Chubu RDB. The present paper describes the sequence of the construction of three types of floating disaster prevention basis and improvement proposals based on the training exercises.

　

　

　

The basic design concept of each basis has been explained by Kozawa et al. (2000). Three types of the bases are planned to be disposed in Tokyo, Ise, and Osaka Bays. In a disaster, the floating disaster prevention basis will be towed by a ship to the neighboring stricken district and fully used for relief activities.

　

The basic design concept of the floating basis learned from the relief activities from seaside at the Hyogoken-nanbu earthquake disaster is as follows (Kozawa et al., 2000):

　

The advantages of a floating structure are that it is unaffected by earthquakes, transportable, and that inside space of it is available. Generally, they are used as a floating wharf for vessels. Once a disaster occurs, it will be taken in tow to the suffering district from the base port and support relief works. Images for the general use and relief works during disaster are expressed in Figure 1.

　

　

　

　

　

Structure type and size should be appropriately determined according to the site condition and the purpose of usage not only for an emergency but for usual use. The common specification for each structure type is that the length of the float should be 80 m to enable a 1,000 DWT class cargo ship come alongside it. According to the Technical Standards for Port and Harbor Facilities in Japan, the apron width of a pier will be 20 m for 7.5 m berth water depth. Kozawa et al. (2000) have already explained the detailed design conditions and structures. Here we describe the completed FDPBs.

　

Tokyo Bay

The FDPB is moored at Yokohama Port central harbor for small craft as shown in Figure 3. The size of the FDPB is 80 m in length, 25 m in width, and 4 m in height. Both sides are double decked and serviceable for both small and large vessels. The regular width of an apron for public use is 20 m as described before. Adding 5 m to the fundamental apron width 20 m, the width of the FDPB here is estimated to be 25 m so that mooring pillars do not disturb takeoff and landing for medium and small size helicopters. Inside the floating body, 1,000 tons water for human use can be stored. Usually, it is moored with chains and dolphins with rubber fenders. The weight of the connecting bridge is 50t and that of the hatch for carrying in supporting materials is 4t (totally 5t taking into account the bonding force for waterproof).

　

　

Osaka Bay

The size of the FDPB is 80 m in length, 40 m in width, and 4 m in height. Ordinary, as both sides of the FDPB can be used as berths for passenger boats, the width is estimated as 40 m taking into account the safety of passengers. Generally, it is moored at the Universal City Port in Osaka City and used as a wharf for passenger and cruise ships (Fig.4(a)).

　

In relief works, cargo handling is possible on both sides of the FDPB as the width of it is 40 meters. It has available space for a large helicopter (35 m*30 m). Ordinarily, a roof tent for passengers is set. It introduces combined mooring system of chain and rubber fenders to suppress the motion. Four anchors are prepared as emergency anchoring at the suffering district. A 25t truck crane and a 4t truck can travel on the deck, and a 4t truck can pass the connecting bridge. Relief goods can be stored on the deck about 1,600 ton and that of about 3,000m³ equivalent to the weight 400t can be stored inside the float.

　

　

　

Ise Bay

The structure of the FDPB is RC-Hybrid type. It is separable in two parts, namely A (40m*40m) and B (20m*40m) sections. It can be used as a single structure by linking the two sections with slide guides. The section B and inside view of the section A is shown in Figure 5. The reasons that the RC-Hybrid structure has been selected here are;

　

Table 1 shows the specifications of each FDPB. The PC and RC-Hybrid structures have less displacement during disaster condition than the ordinary condition. In ordinary time, they are used as wharves for passenger and cruise ships. In order to adjust the freeboard as 1 m or 1.1 m for small ships, the displacements are increased in ordinary use to pour water into the ballast tank.