Coastal Protection in Earthquake-Prone Areas

The coastline of Japan has experienced earthquake and earthquake-induced tsunami disasters. Especially the 2011 Great East Japan Earthquake and tsunami disasters revealed the vulnerability of gravity-type coastal protections. Based on these experiences, design concept for the protection has changed, ensuring serviceability for earthquakes with high probability of occurrence during design life and reparability for earthquakes with low probability. Reinforcement and upgrading of existing protection by a resilient structure such as embedded double sheet pile walls or embedded tubular pile walls are becoming popular.

Reinforcement of Coastal Levee to Prepare For Future Earthquakes and Tsunamis

For the event of a huge earthquake at plate boundary off the coast, a series of events and their consequences must be examined carefully. In the 1946 Nankai Earthquake, due to the displacement and deformation of the earth’s crust, Kochi City settled 1-2 m and strong earthquake motion attacked the city almost simultaneously and then increased water level arrived at the damaged shore protections. Most of the Kochi city was inundated for about a month period and 200,000 people were affected.

Along the coastline of Kochi Prefecture, existing coastal protections are being reinforced to cope with anticipated huge earthquake and tsunamis in near future. An example shown in Figure 4.12 is a reinforcement of coastal levee at Nino coast, Kochi Prefecture. The existing protection is vulnerable to earthquake-induced liquefaction and may lose its function before the arrival of tsunami. The selected solution here is reinforcing the existing sea wall by double steel sheet pile walls (Ishihara et al., 2020).

As shown in the figure, U sheet piles are installed through liquefiable layer down to non-liquefiable layer, so that the protection maintains its design height in the event of huge earthquake and tsunami overflow. The press-in piling assisted by simultaneous inner augering was selected to reduce the adverse influence of vibration and to penetrate existing boulder with diameter ranging from 500 to 800 mm underneath the current sea wall.

Restoration of Coastal Defense Damaged By Tsunamis

The length of the totally or partially collapsed coastal defense sections due to 2011 Great East Japan Earthquake Tsunami reached 190 km out of 300 km coast line spanning Iwate, Miyagi, and Fukushima prefectures according to the Cabinet Office, Japanese Government. Almost all the fishery ports (about 260 ports) suffered from catastrophic failures. The failure of coastal protection inside the Ryoishi Port is one of such examples.

In the 2011 Great Tohoku Earthquake, 80m long stretch of the seawall at the Ryoishi Port was failed under tsunami wave force by overturning toward protected side. Figure 4.13 shows the failed section and original gravity-type seawall can be observed. Cantilevered wall by tubular piles with 1,500mm diameter and 24mm thick was selected for upgrading the seawall. As shown in Figure 4.14, 27.5 m long tubular piles were installed in front of the original seawall and the top elevation of the seawall was increased from +9.3 to +12 m. The road behind the seawall will be raised on the backfill. As the pile tips were required to be installed several meters into sandy rock layer penetrating through gravel and weathered rock layers, tubular piles with cutting edges were used and pressed in by the rotary press-in piling (Gyro Piler). Figure 4.15 shows the pile installation work in progress.

Beach Protection

A wide beach can dissipate energy of waves and tides and protect the structures behind the beach. Such beaches have been threatened by erosion by various reasons including reduced supply of sand from rivers or from longshore transport, the increased

Renovation of coastal defense, typical cross section

Figure 4.14 Renovation of coastal defense, typical cross section.

The pile installation work in progress

Figure 4.15 The pile installation work in progress.

intensity of hurricanes, and the sea level rise. When beach itself has the value in ecosystem or for recreation, the construction of huge seawall is not always a good solution. Beach nourishment by detached breakwaters or groins may be useful option if properly undertaken taking into account the use of the coastline and the ecosystem in the surrounding areas. The embedded wall may contribute in such undertakings.

For the emergent protection of residence or facilities behind the beach, embedded wall construction has been carried out. Shown in Figure 4.16 is an example of emergency seawall at the town of Lantana, Florida.

Z-shaped steel sheet piles (PZC26), 10.7 m long, were penetrated into very stiff sand layer as shown in the soil profile in Figure 4.17. The project owner specified the press-in piling assisted by simultaneous inner augering in order to minimize the influence on the nearby structures and reduce noise and vibration impacts during construction on restaurant patrons and park visitors.

Emergency seawall under construction at the Town of Lantana, Florida

Figure 4.16 Emergency seawall under construction at the Town of Lantana, Florida.

Emergency sea wall

Figure 4.17 Emergency sea wall.

Seismic Reinforcement of Various Infrastructures by Sheet Pile Wall Enclosure

Seismic design standards for various structures have been revised by responsible authorities around 10-20 years interval based on the lessons learned from disasters caused by huge earthquakes. Old structures were constructed to meet the requirements of then-available design standard and are recommended or required to retrofit. Therefore, renovation or upgrading of old structures often accompany the seismic retrofitting as shown earlier in the coastal defense in the previous section and bridges in Bangladesh described in Chapter 3.

The following example is a seismic retrofitting of oil tank in the Japan’s coastal industrial areas. By the government ordinance issued in 1994, the improvement of large oil tanks against liquefaction was mandated within a certain transitional deadline. The preferred countermeasures taken to liquefiable foundation soils were ground improvement by grouting, ground water lowering, and steel sheet pile ring method.

Steel sheet pile ring is a continuous embedded wall surrounding the tank foundation as shown in Figure 4.18. The functions of embedded steel sheet pile wall are: restraining the shear deformation of loose soil beneath the tank and reducing the excessive pore pressure generation, preventing lateral flow of foundation soil and local slip failure at the periphery of tank, and shutting off pore pressure propagation to the confined soil even if the soil outside the ring liquefied. Steel sheet pile ring is constructed by installing straight steel sheet piles down to non-liquefiable layer. Especially in densely developed areas, the retrofitting works have to overcome the spatial constraints and the influence of noise and vibration.

is the actual construction of the steel sheet pile ring around a petroleum tank at Shimonoseki, Japan, owned by the Chugoku Electric Powe

Figure 4.19 is the actual construction of the steel sheet pile ring around a petroleum tank at Shimonoseki, Japan, owned by the Chugoku Electric Power Co., INC. Due to the spatial constraints and the necessity to eliminate the adverse influence of vibration and displacement. Silent Piler was used together with the Non-staging system comprising clamping crane and pile runner.

Sheet pile wall enclosure can be applied to variety of structures above ground or underground as illustrated in Figure 4.20. The floating up of light-weight underground structures such as utility tunnels can be effectively prevented by the enclosure. Road/ railway embankments can be seismic retrofitted by means of a pair of sheet pile walls at the toes of embankment.

East Japan Railway Company has been undertaking seismic reinforcement of various facilities against an anticipated earthquake directly beneath the Tokyo

Construction of steel sheet pile ring around a petroleum tank

Figure 4.19 Construction of steel sheet pile ring around a petroleum tank.

Sheet pile wall enclosure for a variety of structures

Figure 4.20 Sheet pile wall enclosure for a variety of structures.

metropolitan area which include embankment and cut slopes, bridges, tunnel, and stations. Figure 4.21 is one of such examples; a seismic reinforcement of embankment between Higashi Kanagawa and Ohkuchi of JR Yokohama Line. Double steel sheet pile wall is constructed on toes of embankment and connected each other at upper portion by tie w'ire to increase its stability and reduce settlement during earthquake.

Seismic reinforcement of railway embankment

Figure 4.21 Seismic reinforcement of railway embankment.

Bike Commute Infrastructure – Underground Automated Bicycle Stands

Bicycle commuting is popular in developing countries because of economy. Bike also attracts commuters in developed countries, especially in European cities, because it is good for fitness and also it reduces the air pollution and traffic congestion in the city. Even in Japan, where public transportation system including rapid trains, light rails, subways, and city buses is highly developed, bike commute from home to the nearest departing station and the arriving station to work places or schools is quite common. Bike commute, how'ever, has increased crash with motor vehicles and/or pedestrians. Parked bikes in great number in the public squares and the sidewalks obstruct other people’s passages, especially of wheel chairs. To cope wfith these difficulties, advanced cities are investing in bicycle infrastructures such as bike lanes, bike-sharing systems, and bike parking stands.

Scarcity of available land in densely populated city has prevented the development of sufficient parking space for bicycles. “Eco-Cycle” developed in Japan is a fully automated storage and retrieval system for bicycles, which provides bicycle stands on multiple levels underground by minimizing the use of land space as shown schematically in Figure 4.22.

Construction is carried out in a limited space without noise and vibration following a simple construction sequence as showm in Figure 4.23. A vertical cylindrical shaft is constructed by installing steel sheet piles down to required depth. Basement concrete slab and internal ring beams are installed to complete vertical shaft. Steel sheet piles function to retain surrounding soils and to shut off ground water. A fully automated

Eco-Cycle - underground automated bicycle stands

Figure 4.22 Eco-Cycle - underground automated bicycle stands.

Construction sequence of Eco-Cycle

Figure 4.23 Construction sequence of Eco-Cycle.

storage and retrieval system for bicycles is assembled in the shaft. Finally, the ground floor slab and compact bicycle entrance booth is constructed at grade. After completion, valuable space at ground surface can be left open for public use or for other purposes.

Currently available standard model of Eco-Cycle, which accommodates 204 bicycles, requires inside dimensions of the vertical shaft with only 8.1m diameter and 11.9m depth. Storage and retrieval of bicycle is computer controlled with the aid of IC (Integrated Circuit) user card and IC tag attached to the bicycle. Average retrieval time is only 13 seconds.

As of August 2018, 52 units of Eco-Cycle have been adopted at 22 locations in Japan, which include the locations near the railway station, city hall, park, shopping district, school, and rent-a-cycle depot. Figure 4.24 shows the construction of Eco-Cycle in Minato-ku, Tokyo.

Other Interesting Applications

Preservation of Historic Structures

Historic structures, especially those made of stone or brick founded on shallow foundations, are vulnerable to vibration and displacement. Adjacent construction such as foundation work and excavation needs to be carefully planned taking the structural characteristics of historic structures into account. Regarding pile installation, the press-in piling with low vibration is superior to the ordinary vibratory or impact hammering methods.

Underground automated bicycle stands in Minato-ku, Tokyo

Figure 4.24 Underground automated bicycle stands in Minato-ku, Tokyo.

San Juan de Ultra is a fortress overlooking the port of Veracruz, built by the Spanish Empire in the middle of 16th century on a sandy island. The port of Veracruz is one of the busiest ports in Mexico. Due to the expansion of navigation channel and increased number of vessels, the foundation soil of the fortress has experienced erosion. Structures such as ramparts that face the navigation channel were threatened with collapse by settlement and tilting.

To restore the undermined wall foundation and to prevent further erosion, U sheet piles, LX 32 were installed down to 18 m and the foundation soil was reinforced by concrete filling. The protective steel sheet pile wall was constructed on the bay side of the fortress as shown in Figure 4.25.

The requirements for the pile installation work were minimizing vibration to restrain adverse influence on the wall structure and minimizing the space for construction barges and temporary structures to restrain adverse influence on traffic near the fortress. The press-in piling by the Silent Piler was adopted as shown in Figure 4.26.

Restoration of undermined wall foundation by embedded wall, (a) Pile layout (plan), (b) Machine layout (cross-section)

Figure 4.25 Restoration of undermined wall foundation by embedded wall, (a) Pile layout (plan), (b) Machine layout (cross-section).

Protection of residence from secondary disaster near the sink hole

This is an example of emergent stabilization of slope created by sinkhole. The location is Orland, Florida, where bedrock is mostly limestone and susceptible to sinkholes. The photograph on the left-hand side of Figure 4.27 shows the slope close to the apartment covered tentatively by plastic sheet to prevent erosion by rain. To prevent the secondary disaster, permanent retaining wall was constructed by tubular piles with interlocking device, with 900 mm diameter and 15 m length as shown in Figure 4.28. Considering the safety of the building foundation and the unstable ground itself, the press-in piling assisted by simultaneous inner augering was adopted. Nam (2019) and Takuma (2019) provide further information on the mechanisms of sinkhole formation and countermeasures.

Press-in piling at San Juan de Ultia

Figure 4.26 Press-in piling at San Juan de Ultia.

Protection of Woodhill apartment complex close to the sinkhole

Figure 4.27 Protection of Woodhill apartment complex close to the sinkhole.

The typical cross-section and the bore hole log

Figure 4.28 The typical cross-section and the bore hole log.

Sheet piling to control settlement due to adjacent construction

Adjacent construction would more or less affect the surrounding environment and nearby structures. Especially the embankment construction on soft clay deposit influences larger extent outside of its right-of-way. Figure 4.29 illustrates such a problem and expected effect of one of the possible countermeasures. The sheet pile wall confines the propagation of additional stresses induced by embankment loading underneath the embankment and protects the nearby structures from the settlement. The initial idea was the construction of continuous sheet pile wall down to the bearing stratum underneath the compressible layer as shown in the figure.

Problem associated with adjacent construction and countermeasure by sheet piling (Otani, 2017). (a) Without countermeasures and (b) with sheet pile countermeasures

Figure 4.29 Problem associated with adjacent construction and countermeasure by sheet piling (Otani, 2017). (a) Without countermeasures and (b) with sheet pile countermeasures.

When the compressible layer is thick, the cost of sheet piling becomes enormous. The Kyushu University and the Japan’s Ministry of Construction (now, Ministry of Land, Infrastructure, Transport and Tourism) conducted collaborative research to reduce the construction cost even in the thick deposit of Ariake Clay, which is famous for its high sensitivity and the thickness as large as 40 m. The proposed method is illustrated in Figure 4.30, which is called Partial Floating Sheet-Pile method, PFS.

An in-situ full-scale test was conducted on Ariake Clay site in Kumamoto city. Figure 4.31a shows the soil profile and the specification of PFS wall which comprises a combination of one end-bearing steel sheet pile for five floating steel sheet piles. Figure 4.31b shows the observation of settlement due to embankment load during 4years and 1 month. By reducing the number of end-bearing steel sheet piles, the cost and construction time are reduced while the settlement of nearby structure was effectively controlled.

In September 1999, a typhoon (a tropical cyclone) attacked Ariake Bay at the time of high water of spring tide and caused a storm surge which inundated approximately 20ha spanning Kumamoto City to Uto City along downstream of Midorigawa River and Hamadogawa River. The Renovation Project of Storm Surge Barriers along these rivers to reinforce by raising and widening the levees is being undertaken by the Ministry of Land, Infrastructure, Transport and Tourism. Figure 4.32 shows a renovation plan of a levee on the right bank of Hamadogawa River at Hashirigata Machi, Uto City. Shaded area is the additional fill on the existing levee. Prior to the additional filling, two sheet pile walls were installed at both sides of the levee.

Sheet pile wall on the left-hand side is constructed by installing 26.5 m long U sheet pile SP-IVw with 600 mm effective width which is expected to function as a cantilevered wall to maintain the stability of levee during additional filling. The sheet pile wall on the right-hand side is the PFS wall to control settlement outside the levee’s foot print. The PFS wall comprises a combination of an end-bearing steel sheet pile about 40m long for nine floating steel sheet piles about 27 m long. By using Hat-shaped steel sheet pile SP-25H with 900 mm effective width, number of piles were reduced in comparison with ordinary U sheet pile and resulted in reduced construction cost and time.

Partial floating sheet pile method (Otani, 2017)

Figure 4.30 Partial floating sheet pile method (Otani, 2017).

An in-situ full-scale embankment to investigate PFS wall (Otani, 2017)

Figure 4.31 An in-situ full-scale embankment to investigate PFS wall (Otani, 2017).

(a) Soil profile and PFS wall specifications, (b) Settlement observation.

Renovation of storm surge barrier by embedded walls

Figure 4.32 Renovation of storm surge barrier by embedded walls.

References

Arikawa, T., Oikawa, S., Moriyasu, S., Okada, K., Tanaka, R., Mizutani, T., Kikuchi, Y., Yahiro, A. and Shimosako, K. (2015) Stability of the breakwater with steel pipe piles under tsunami overflow, Technical Note of Port and Airport Research Institute, 46 p. (in Japanese)

Hiiragi, S. (2006) Zoom-up: Renovation of navigation channel at Miike Port, Nikkei Construction Vol. 12, Issue 22, pp. 72-75 (in Japanese).

Ishihara, Y., Yasuoka, H. and Shintaku, S. (2020) Application of press-in method to Coastal Levees in Kochi Coast as countermeasures against liquefaction, Geotechnical Engineering Journal of the SEAGS & AGSSEA, Vol. 51, Issue 1, pp. 79-88.

Kikuchi, Y., Kawabe, S., Taenaka, S. and Mori3'asu, S. (2015) Horizontal loading experiment on reinforced gravity type breakwater with steel walls, Proceeding of 15th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering, pp. 1268-1271.

Kimura, Y. (2012) Renovation of sea wall, Construction Machinery and Equipment, Vol. 2, pp. 7-12 (in Japanese).

Moriyasu, S., Tanaka, R., Oikawa, S., Tsuji, M., Taenaka, S., Kubota, K. and Harata, N. (2016) Development of new type of breakwater reinforced with steel piles against a huge tsunami, Nippon Steel & Sumitomo Metal Technical Report No. 113, December 2016, pp. 64-70

Nam, B.H. (2019) Detection and geotechnical characterization of sinkhole: Central Florida case study, IPA Newsletter, Vol. 4, Issue 3, pp. 9-14.

Otani, J. (2017) A new steel sheet pile method for countermeasures against the settlement of embankment on soft ground -development of PFS method-, IPA Newsletter, Vol. 2, Issue 3,

pp. 8-10.

Takuma, T. (2019) Mitigation of sinkhole with press-in Piles, IPA Newsletter, Vol. 4, Issue 3, pp. 15-18.

 
Source
< Prev   CONTENTS   Source   Next >