History of land reclamation using dredged soils at Tokyo Haneda Airport

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1 Japanese Geotechnical Society Special Publication The 15th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering History of land reclamation using dredged soils at Tokyo Haneda Airport Yoichi Watabe i) and Shinji Sassa ii) i) Soil Mechanics and Geo-environment Group, Port and Airport Research Institute, Nagase, Yokosuka , Japan. ii) Soil Dynamic Group, Port and Airport Research Institute, Nagase, Yokosuka , Japan ABSTRACT The Tokyo Haneda Airport has been developed by land reclamation since When we look back its history, dredged soils have been effectively used at the offshore expansion project ( ) and the D-runway project ( ). In the offshore expansion project, a dredged clay deposit in ultra-soft state was converted into an airport island. Because of softness of the dreaded soil, continuity of the vertical drains under large consolidation settlement, as well as large lateral soil movement, had to be concerned. In the D-runway project, lightweight treated soils of dredged clay were effectively used to reduce earth pressure on the seawall. To efficiently conduct large-scale placement, pneumatic mixing method was very useful. At the joint structure between the reclamation and piled pier sections, air-foam treated lightweight soil was placed as backfill, because more lightness was strongly required to ensure the stability. Keywords: reclamation, dredged clay, lightweight soil, cement treated soil, air foam 1 INTRODUCTION The development of the Tokyo Haneda Airport (official name is the Tokyo International Airport) is a history of land reclamation since In the year of Tokyo Olympic in 1964, a parallel runway of about 3000 m (original C-runway) was inaugurated, and then in 1971, crosswind runway (original B-runway) was extended to 2500 m. Since then, from 1971 to 1984, development of the Tokyo Haneda Airport was temporary suspended, because all the international flights moved to a new airport named as the Tokyo Narita Airport (official name is the Narita International Airport) in To respond to significant increase of domestic passenger demand, the government decided to expand the airport facilities to an offshore side and a project named as offshore expansion project was started in This project was consisted of three stages as shown in Figure 1; (a) the 1st phase: new A-runway inaugurated in 1988, (b) the 2nd phase: the terminal 1 inaugurated in 1993, and (c) the 3rd phase: new C-runway inaugurated in 1997, new B-runway inaugurated in 2000 and the terminal 2 inaugurated in 2004 and its extension in 2007 as well. After the completion of the offshore expansion project, the further expansion project named as D-runway project (Figure 2) was commenced. This project was aimed at meeting a strong social demand to redevelop international airline routes from Tokyo Haneda Airport. The D-runway, as well as a new international terminal, was constructed to increase the airport capacity to be approximately 1.5 times in aircraft movement from approximately 300,000 annual flights to approximately 450,000 annual flights. This paper summarizes the core technologies used in the offshore expansion project and D-runway project at the Tokyo Haneda Airport, namely effective use of dredged soil for the reclamation of the airport island. 2 OFFSHORE EXPANSION PROJECT The offshore expansion project was started from ultra-soft soils reclaimed by dumping of dredged soils and construction waste soils. The waste reclamation facility for those soils in ultra-soft state (Figure 3) was converted into the airport island in overconsolidation state by installing vertical drains and applying preload. Because the slurry state soils were unstable with high fluidity, selection of drain materials in consideration of flexibility and continuity were the key factors in this project. Preliminary work for surface treatment such as shallow mixing method with cement or lime and sand fill with geotextile was required before installing vertical drains to ensure the trafficability. In the original seabed soil in deeper portion, normal sand drains with 300-mm diameter were installed; however, in the slurry state deposit in shallower portion, continuity of the sand drains was of concern because of significant fluidity and settlement. Therefore, packed sand drains, in which each sand drain was wrapped by fiber-synthetic, were installed to ensure the continuity

2 (a) (b) Figure 3. Surface treatment on the ultra-soft state soil at the Tokyo Haneda Airport. (c) (d) (a) Cross-sectional arrangement of vertical drains Figure 1. Construction stages in the offshore expansion project at the Tokyo Haneda Airport. Figure 2. Aerial photo of the Tokyo Haneda Airport taken when D-runway was almost completed (in July 2010). (Katayama, 1991). The volume of sand used for packed drains was able to be reduced by decreasing the (b) Planar arrangement of vertical drains. Figure 4. Illustration of vertical drains installed in the offshore expansion project. diameter of sand drains, compared to the normal sand drains. The spacing of both the sand drains and packed drains were 2.5 m in a square arrangement; however, additional drains were required in the slurry state deposit to shorten the construction period. Therefore, prefabricated vertical drains (PVD) provided as an industrial plastic product were additionally installed as shown in Figure 4. The spacing of the PVD was 1.0 m in a square arrangement at the center of the square arrangement of the packed sand drains. In consideration of residual settlement of manmade island, engineers generally compare two concepts: one is inauguration after minimizing the residual settlement and the other one is inauguration with tolerating the residual settlement. These two concepts are in trade-off between an expensive construction cost with long 1785

3 Figure 5. Surface profiles along the center of C-runway. construction period resulting in a low maintenance cost and a low construction cost with short construction period resulting in an expensive maintenance cost. Decision from these two depends on the feature of the project. In the offshore expansion project, aiming at early inauguration, they decided to tolerate a certain level of residual settlement. In the offshore expansion project, very significant differential settlement was concerned (Tanaka et al., 2002) because of existence of partitions, different reclamation period, and heterogeneity of dumped soils. On the basis of the results of ground investigation and reclamation history, consolidation settlement was calculated, and then finial filling height was decided considering the predicted residual settlement. Surface profile at the center of C-runway is shown in Figure 5. Here, the drawings correspond to fundamental design, final elevation of filling work, prediction at 10-year later, and observation at 13 years later. The observed profile at 13 years later indicates that there were some significant settlements in the regions of the north half and the south end of C-runway; however, the slope gradients were smaller than the criteria written in the technical standard for airport facilities. However, some scheduled maintenance such as overlaying pavement to adjust the level will be required in a future. 3 D-RUNWAY PROJECT 3.1 Outline of D-runway The D-runway is characterized as a hybrid structure consisted of offshore reclamation fill and piled pier in the river mouth of the Tama River (Figure 2). Another remarkable feature is an elevation higher than A.P m that is significantly higher than normal reclamation fills, so that an airplane can overpass a large container ship navigating in the vicinity. Note here that A.P. is a sort of chart datum that is often used in construction in Tokyo Bay. Adopting the piled pier section reduced the volume of sand required for the high reclamation fill. On contrary, if piled pier was adopted in whole area of D-runway, huge amount of steel products would be required, resulting in harmful impact on the other demands of steel products. Adopting the hybrid structure exquisitely solved these problems in procurement of the materials. 3.2 Ground improvement for soft seabed clays The D-runway was constructed in the further offshore sea of the airport facilities developed by the offshore expansion project. Construction period was from March 2007 to October The water depth at the construction site was approximately 19 m. The surface seabed soil layer was a homogeneous soft high-plastic clay layer with a thickness of approximately 15 m. Therefore, this project can be generally characterized as reclamation work on a soft ground. Below this layer, some clay, sand, and gravel layers were deposited alternately. Detailed results from ground investigation are written with stratigraphy in Watabe and Noguchi (2011). To overcome the very soft and thick clay layer, ground improvement was required to ensure the stability of the seawall and to minimize the residual settlement of the landfill. In other words, geotechnical issues caused from the shallow soft clay layers were able to be overcome by concentrating the wisdom of mankind, i.e. ground improvement technologies. This means that geotechnical engineering can actively control the natural condition. A typical cross section of the seawalls is shown in Figure 6. Because a short construction period was required for the 17-m high reclamation (equivalent to 36-m high landfill on the seabed), the technologies used in the offshore expansion project, such as vertical drains with preload after dumping of the slurry soils, were difficult to be applied to the D-runway project. In the ground improvement for the original seabed clays under the high landfill, the most useful technology was to accelerate the consolidation, and the solution was the conventional sand drains. In this regard, the technology used in the ground improvement for the original seabed clays was the same as that used in the offshore expansion project. In the ground improvement for the original seabed clays under the rubble seawall, the required technique was not only accelerating the consolidation but also strengthening by soil replacement, and the solution was the sand compaction piles (SCP) with low replacement ratio of 30% (Watabe and Noguchi, 2011). In comparison with the Kansai International Airport, in which the original seabed soils under the rubble seawall were improved by only sand drains (Watabe et al., 1786

4 Figure 6. A typical cross-section of the rubble seawall of the D-runway 2002; Furudoi, 2010) because sufficient construction period could be ensured, it can be understood that the reason of installing sand compaction piles in the D-runway instead of sand drains were to meet the short construction period. 3.3 Seawall structure using lightweight soils To ensure additional stability of the seawall, cement treated dredged soils were backfilled (Figures 6 and 7). The material soils were dredged in front of the seawall and other area in Tokyo Bay. The trough after dredging in front of the seawall was filled by sandy material whose unit weight was larger than that of the original seabed deposit, to be a counterweight against the slip failure. The unit weight of the cement treated dredged soil backfilled to the seawall was smaller than that of normal sandy/gravely backfill and the fill material itself became solidified; consequently these facts contribute to increase the stability of the seawall. Using the cement treated dredged soil as the reclamation fill material also contributed to reduce the volume of mountain sands which were a little difficult to obtain in Tokyo Bay area. Cement treated soil was one of the ideal fill materials in the D-runway project, because the strength can be adjusted corresponding to the mix proportion. In addition, it is notable that the required curing period is much shorter than the required consolidation period in ground improvement with vertical drains. Staged construction with a curing period after each layered placement can reduce lateral mud pressure on the seawall, even in construction of a very high landfill. Despite these advantages, it was impossible to reclaim the D-runway Island by using only lightweight soils due to the construction period caused by low construction efficiency, because the region to place the mixture had to be surrounded by dikes (main seawall and partition) before placing the cement treated soils. Comprehensively assessing the advantages and disadvantages, the cross-section where the pneumatic mixing cement treated soil to be placed was decided. The maximum height of pneumatic mixing cement treated soil was set to be A.P m. Pneumatic mixing method was useful to efficiently place the cement mixture. This method was originally developed and used in the north part of the Central Figure 7. (a) A placement site of the pneumatic mixing cement treated soil; (b) aerial photo showing the placement site between the rubble seawall and partition. Japan International Airport (Nagoya Airport) (Kitazume and Satoh, 2003). The pneumatic mixing cement treated soil was a mixture of dredged soil and cement. Water was first added to the dredged soil to make it slurry with high fluidity, and then a certain amount of cement was added and the mixture was pumped with pressured air, then it was automatically mixed by plug flow, and then placed from the outlet. Its unit weight varies according to the soil physical properties and amount of added water. In the design of the seawall, the unit weight was set to be 15 kn/m 3. The pneumatic mixing cement treated soil of approximately 4,700,000 m 3 was placed over one year. Because a sufficient curing period for the pneumatic mixing cement treated soil prior to loading to the design overburden stress was ensured, the quality was controlled by the properties at 91 days, instead of 28 days, which is ordinarily used in many projects. Detailed mix proportions of the pneumatic mixing cement treated soil used in this project are summarized in Watabe et al. (2012). The field compressive strength in design was set to be 360 kn/m 2. Unconfined compressive strength and bulk density for the samples collected by confirmatory boring were examined. Average unconfined compressive strength was 693 kn/m 2 with a defective percentage of 11.7%, and unit weight was kn/m 3. These values met the required 1787

5 Figure 8. Cross section of the joint section. specifications for the target. As mentioned above, in the reclamation of the D-runway, not only ground improvement technologies but also new material technologies were efficiently used. This feature clearly seen in the joint section between the reclamation and piled pier sections (Figure 8). The joint section is a very important structure, which takes the role of both the seawall of the manmade island and abutment for the joint girder. In this project, a steel pipe pile foundation, which consisted of steel pipe piles arranged as rectangle cell. This kind of foundation has a good track record in bridge foundations and abutments. The steel pipe pile foundation has consecutive 24 rectangle cells consisting of two parallel steel pipe sheet piles as the out envelope and 25 orthogonal steel pipe sheet piles. To ensure the stability of the steel pipe pile foundation, which was embedded into the bearing stratum, it was required to utilize lightweight backfill such as pneumatic mixing cement treated soil and air-foam treated lightweight soil (Tsuchida and Egashira, 2004; Watabe et al., 2004). The lightweight backfill can contribute to decreasing the lateral earth pressure, consolidation settlement, and lateral soil movement. In addition, the soft deposit in front of the structure was improved by SCP with high replacement ratio (78%), to decrease the lateral displacement of the structure. Also, a rubble mound was filled in front of the structure as a counterweight. The key technology was the air-foam treated lightweight soil. The air-foam treated lightweight soil is a mixture of dredged clay, cement, and air-foam. Water was first added to the dredged soil to make it slurry with high fluidity, and then some cement and air-foam were added and mixed in a plant. Note here that the pneumatic mixing method was not applicable for air-foam treated lightweight soil, because high-level of quality control was required. The air-foam is consisted of very fine bubbles whose diameter was approximately Figure 9. Microscope photograph of air-foam treated lightweight soil. 200 μm. Note here that each air bubble is independent from others as shown in Figure 9 (Watabe et al. 2004) to avoid from durability issues. In the design of joint section, the unit weights above and below residual water level were set to be 10.0 kn/m 3 and 11.5 kn/m 3, respectively. Note here that the residual water level was assumed to be A.P m (equivalent to the high tide level) in the design. Because long-term bulk density was expected to increase by 0.5 kn/m 3 below water level, the target bulk density in the placing work was set to be 11.0 kn/m 3 instead of 11.5 kn/m 3. The section where the soil was placed above the water level and would be submerged (because of consolidation settlement of subsoil) was classified as below water level. The actual residual settlement at the backfill of the steel pipe pile foundation (retaining wall) was calculated to be approximately 1 m during 100-year in-service period. An unconfined compressive strength greater than 200 kn/m 2 in design was required in order to avoid consolidation yielding under the overburden effective stress. Average unconfined compressive strength was 322 kn/m 2 and 449 kn/m 2 with percent defective of 10.0% and 6.2% above and below the residual ground water level, respectively. Average unit weight was

6 kn/m 3 and kn/m 3 above and below the residual ground water level, respectively. These values met the required specification in design (Watabe and Noguchi, 2011; Watabe et al., 2012). The air-foam treated lightweight soil of approximately 790,000 m 3 was placed using two groups of plant ships taking over 6 months. Before this project, approximately 520,000 m 3 of air-foam treated lightweight soil had been used for various coastal construction projects in Japan for 13 years since its development. The amount of soil volume placed within six months in this project was equivalent to 1.5 times of this previous volume. 5) Watabe Y, Noguchi T., Site-investigation and geotechnical design of D-runway construction in Tokyo Haneda Airport. Soils and Foundations 51(6), ) Watabe Y, Tsuchida T, Adachi K., Undrained shear strength of Pleistocene clay in Osaka Bay. Journal of Geotechnical and Geoenvironmental Engineering, ASCE. 128(3), ) Watabe Y, Itou Y, Kang M-S, Tsuchida T., One-dimensional compression of air-foam treated lightweight geo-material in microscopic point of view. Soils and Foundations, 44(6), ) Watabe Y, Noguchi T, Mitarai Y., Use of cement-treated lightweight soils made from dredged clay. Journal of ASTM International. Paper ID: JAI SUMMARY Effective use of dredged soil has been attempted in construction of manmade island for airport facilities in Japan. A typical case history was studied in the present paper through the reclamation works of the Tokyo Haneda Airport. In the offshore expansion project ( ), a dredged clay deposit in ultra-soft state was converted into an airport island with prefabricated vertical drains. In the D-runway project ( ), which can be characterized by a hybrid structure consisted of reclamation and piled pier sections, as well as a high elevation of 17.1 m, lightweight treated soils of dredged clay were effectively used. Cement treated soil was placed along the seawalls surrounding the reclamation section. To efficiently conduct large-scale placement, pneumatic mixing method was useful. In addition, air-foam treated lightweight soil of dredged clay was placed as backfill at the joint structure between the reclamation and piled pier sections, because more lightness was strongly required to ensure the stability. ACKNOWLEDGEMENTS The author would like to thank Dr. Takatoshi Noguchi of Kanto Regional Development Bureau, Ministry of Land, Infrastructure, Transport and Tourism, Japan for his kind cooperation to write this technical report. REFERENCES 1) Furudoi T., The second phase construction of Kansai International Airport considering the large and long-term settlement of the clay deposits. Soils and Foundations. 50(6), ) Katayama T., Meeting the challenge to the very soft ground the Tokyo International Airport Offshore Expansion Project. Proceedings of the International Conference on Geotechnical Engineering for Coastal Development, GEO-COAST 91, Yokohama, ) Kitazume M, Satoh T., Development of pneumatic flow mixing method and its application to Central Japan International Airport construction. Ground Improvement. 7(3), ) Tsuchida T, Egashira K, editors., Lightweight Treated Soil Method. A. A. Balkema, Rotterdam. 1789