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Development and improvement effectiveness of sand compaction pile method as a countermeasure against liquefaction
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ScienceDirect Soils and Foundations 57 (2017) 980–987 www.elsevier.com/locate/sandf
Development and improvement effectiveness of sand compaction pile method as a countermeasure against liquefaction Kenji Harada ⇑, Jun Ohbayashi Geotechnical Department, Fudo Tetra Corporation, Japan Received 19 October 2016; received in revised form 16 June 2017; accepted 3 August 2017 Available online 11 November 2017
Abstract The sand compaction pile (SCP) method was developed in Japan to improve soft grounds. One of the major features of the SCP method is that it can be applied to all soil types found in Japan, from sandy to clayey soils; and therefore, it has been widely used for the improvement of soft grounds. Recently, the SCP method has been mainly adopted as a countermeasure against liquefaction, and its effectiveness in preventing liquefaction has been confirmed through past large earthquakes. This paper provides an outline of the conventional SCP method, including its principle, history, equipment, and implementation, and also describes other methods derived from the SCP method as liquefaction countermeasures. Furthermore, several examples are reported to confirm the effectiveness of the methods through past large earthquakes. Ó 2017 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BYNC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Keywords: Ground improvement; Sand compaction pile; Countermeasure against liquefaction
1. Introduction The sand compaction pile method (hereinafter abbreviated as the SCP method) is a method for improving soft grounds by means of installing well-compacted sand piles in the ground. It combines such fundamental principles for ground improvement as densification and drainage. It can be applied to all types of soil found in Japan, from sandy to clayey soils, by commonly using a single piece of equipment; therefore, it has been widely used for the improvement of soft grounds. In sandy grounds, the SCP method is mainly used as a countermeasure against liquefaction, and its effectiveness in preventing liquefaction has been confirmed through past large earthquakes, show-
ing that this method is one of the most reliable ground improvement methods in Japan. This paper describes the principle, the history, and the equipment of the conventional SCP method as well as outlines two other methods derived from the SCP method in accordance with the needs of the times as liquefaction countermeasures including the procedure, the equipment, and the material used for each method. Some cases are also shown that demonstrate the difference between an unimproved ground and a ground improved by the SCP method based on the degree of damage brought about by past large earthquakes. 2. Outline of SCP method 2.1. Principle and purpose of the SCP method
Peer review under responsibility of The Japanese Geotechnical Society. ⇑ Corresponding author. E-mail addresses: [email protected] (K. Harada), jun. [email protected] (J. Ohbayashi).
The SCP method is effective in improving the performance of all the types of ground for different reasons. The reasons for such effectiveness in three representative
https://doi.org/10.1016/j.sandf.2017.08.025 0038-0806/Ó 2017 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
K. Harada, J. Ohbayashi / Soils and Foundations 57 (2017) 980–987
soil types, i.e., sandy grounds, clayey grounds and soft clay deposits which is typically formed at offshore sites, are described. The principle of the SCP method for clayey grounds is based on the theory for composite grounds proposed by Murayama (1957). Composite grounds consist of soft cohesive grounds and compacted sand piles formed therein; the composite ground formed has high shear strength and drainage capability owing to the presence of the sand piles. Through the formation of these compacted sand piles, the bearing capacity of the ground can be increased due to ‘‘replacement effect” and ‘‘stress concentration effect”. ‘‘Stress concentration” means that external load is concentrated mainly on the sand piles, as shown in Fig. 1(a). Furthermore, by including ‘‘drainage effect” (see Fig. 1(a)), an increase in the stiffness of the whole ground as well as a decrease in lateral spreading and in consolidation settlement can be expected. On the other hand, the principle of the SCP method for sandy grounds is primarily to decrease the void ratio and to densify the ground as a result of the sand pile installation, as shown in Fig. 1(b). Accordingly, the purpose of the SCP method is to increase the bearing capacity, to decrease the compression settlement, to prevent the occurrence of liquefaction, and to increase horizontal resistance. For sandy grounds, Ogawa and Ishido (1965) suggested a practical design procedure related to the increase in density due to the installation of sand piles. Conversely, for soft clay deposits which are typically encountered in offshore works, thicker sand piles are installed into the clay at the sea bottom, as shown in Fig. 1(c). ‘‘Forced replacement” is the major principle for the improvement of offshore works, rather than the formation of ‘‘composite ground” where the sand piles replace the cohesive soils. In such cases, the objectives of the improvement are to increase the bearing capacity, to reduce the consolidation settlement, and to increase the horizontal resistance.
Fig. 2. Vibratory SCP equipment.
Fig. 3. Installation procedure for vibratory SCP method.
Fig. 1. Concept for installation of compacted sand piles.
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2.2. Equipment and implementation process An on-land type equipment for the vibratory SCP and its installation procedure in a soft ground are illustrated in Figs. 2 and 3, respectively. The procedure is as follows. (1) Positioning: Set the casing pipe at the predetermined place. (2) Penetration of a casing pipe: By operating the vibrator, penetrate the casing pipe into the ground. (3) Feeding sands through a hopper: After the casing pipe has reached the required depth, feed sand into the casing through the upper hopper. (4) Drawing up the casing pipe: By drawing up the casing pipe, the sand in the pipe is forced out through the void by compressed air. (5) Re-driving the casing pipe: Re-drive the casing while compacting the sand pile pressed out by the vibrations, resulting in its enlargement. (6) Completion: Form each compacted sand pile to reach the ground surface by repeating the above procedure.
3. Development of SCP method as liquefaction countermeasure 3.1. Development of liquefaction countermeasures Liquefaction countermeasures in Japanese engineering practice are roughly classified according to three principles, i.e., compaction (densification), solidification, and drainage (pore water pressure dissipation). Table 1 summarizes the history of major liquefaction countermeasures in Japan based on the aforementioned principles. As shown in the table, the densification method using vibratory hammers was first introduced in the 1950 s as a ground reinforcement method. In 1964, the Niigata earthquake resulted in significant damage due to liquefaction. After the 1964 Niigata earthquake, the SCP method was recognized as an effective countermeasure against liquefaction (Fudo Construction Co., Ltd., 2003). The gravel drain method, which is one of a number of drainage methods, was
developed in the 1970s as an environment-friendly measure with low noise and vibrations. The lattice-type deep mixing method, a shear strain restraint method, was developed as an economical countermeasure in the 1980s. The SCP method was recognized as a liquefaction prevention/mitigation method after its effectiveness was verified by many case histories during large earthquakes, such as the 1978 Miyagi-ken-Oki Earthquake and the 1983 Nihonkai-Chubu Earthquake. Examples of such case histories are presented later in this paper. However, the drawbacks of this method are the noise and the vibrations generated by the vibro-hammer. Thus, it became necessary to improve the SCP method such that it would have no adverse influence on the surrounding environment. To meet this demand, two new types of SCP methods, the non-vibratory SCP method (Harada et al., 2004) and the sand injection-type SCP method (Imai et al., 2009), have been developed, as explained in the next section. 3.2. Methods derived from conventional SCP method 3.2.1. Non-vibratory SCP method In the conventional SCP method (Vibratory SCP method), the vibromotive force of a vibratory-hammer is used for the ground penetration of a casing pipe, and a winding wire is used to withdraw it. As the vibratoryhammer causes excessive noise and vibration, the vibratory SCP method cannot be used in urban areas. A nonvibratory SCP method can form sand piles statically in the ground. Instead of a vibratory-hammer, withdrawal and re-driving of casing pipes are achieved by a forced lifting/driving device that rotates the casing pipe, as shown in Fig. 4. The operating procedure for the non-vibratory SCP method, shown in Fig. 5, is identical to that of the vibratory SCP method. A casing pipe, 400–500 mm in diameter, is used to create well-compacted sand piles, 700 mm in diameter, and the surrounding ground is densified as a result. The system for the implementation of this method involves the application of vertical movement of the casing pipe, as indicated by a wave pattern with a shorter wave
pin rack
rack
Table 1 History of liquefaction prevention.
Sprocket (a) Pin rack and sprocket type
pinion gear (b) Rack and pinion type
Fig. 4. Main components of forced lifting/driving device.
K. Harada, J. Ohbayashi / Soils and Foundations 57 (2017) 980–987
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(b)
(a)
10cm
40cm
Rod
Casing
Withdrawal
Redriving
Compaction
Compaction Enlarging
Withdrawal Compaction
Compaction
Enlarging
Existing sand pile Existing sand pile 70cm
Fig. 5. Installation procedure for non-vibratory SCP method.
length than the one of a vibratory SCP, as shown in Figs. 3 and 5. The recordings of noise and vibration levels associated with the vibratory SCP and the non-vibratory SCP methods made at five sites, A to E, are shown in Fig. 6. It is clear from the figure that both noise and vibration levels are greatly reduced in the non-vibratory method compared with the vibratory SCP method, making it suitable for applications in urban areas and at sites close to existing structures. 3.2.2. Sand injection-type SCP method The sand injection-type SCP method is a method to densify the target ground by pumping and injecting fluidized
70cm
Fig. 7. Mechanism for installation of compacted sand piles.
sand into the ground through a small-sized equipment. A mixture of sand and a fluidizing reagent is forcibly ejected by pumping from the tip of the rod which is penetrated into the ground to densify the surrounding ground. To form a dense ground, the fluidity of the ejected sand is wellcontrolled. The fluidity gradually disappears due to the combination of dehydration of the mixture and chemical process of the retarding plasticizer. Fig. 7 shows a comparison of the mechanism for enlarging the diameter of the sand piles between (a) the vibratory/non-vibratory SCP method and (b) the sand injection-type SCP method. The procedure for applying the sand injection-type SCP method is as follows (see Fig. 8): (1) Positioning: Set the rod at the prescribed position and insert it into the ground. (2) Feeding the fluidized sand through a rod: After the rod has reached the required depth, pump out the fluidized sand.
(Position Set) (Penetration Complete) (Pile formation completed) Move Penetration Pile formation
Rod Equipment
trace of rod
Fig. 6. Decrease over distance of noise and vibration with non-vibratory SCP method.
Fig. 8. Installation procedure for sand injection type of SCP method.
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Percentage finer by weight (%)
90
Performance range
80 70
Performance range
60 50 40
Achievement of SCP
30 20 10 0
Grain size D (mm)
Fig. 9. Grain distribution curves of used material.
Photo 1. Examples of implementation under limited space.
4. Verification of effectiveness of method through past earthquakes 40m
Fig. 11 shows the epicenter locations and characteristics of the 1964 Niigata Earthquake and eleven other largescale earthquakes in Japan, including the 2011 Off the Pacific Coast of Tohoku Earthquake, as well as information on the performance of SCP-improved grounds during these earthquakes. As shown in the figure, there has been no report of any major damages to the structures constructed on SCP-improved ground, such as by vibratory and non-vibratory SCP methods, confirming in a qualitative sense the effectiveness of the compaction-type ground improvement techniques against strong earthquakes. Detailed information for some of these cases is given below.
30m
20m
10m
Vibratory SCP Non-vibratory SCP Sand injection type SCP
4.1. Example of tank foundation (Fudo Construction Co., Ltd, 1994)
Fig. 10. Equipment of each SCP method.
(3) Drawing up the rod: Draw up the rod to the next step. (4) Completion: Form each compacted sand pile up to the surface by repeating the above procedure. Fig. 9 indicates the grain size distribution curves of several kinds of sand used for this method at numerous sites, in order to compare the applicable grain size range of the sand injection-type SCP method and the conventional SCP method (PHAJ, 2007). Fig. 10 shows the size of the equipment used in the vibratory, the non-vibratory, and the sand injection-type SCP methods. Recently, a smallsized equipment has been developed for use in narrow spaces, such as under bridge girders and/or close to existing structures. In such cases, only the sand injection-type SCP is applicable. Photo 1 shows an example of the sand injection-type SCP method being used at a narrow space where it is surrounded by an existing factory building and a revetment.
Following the 1994 Hokkaido Toho-Oki Earthquake, a remarkable difference was observed between the areas of improved ground, including the SCP-improved tank foundation ground, and the adjacent unimproved areas. Fig. 12 shows the locations of the sand boil trace in the improved tank foundation ground and in the adjacent non-improved ground areas. The tanks themselves were installed on a ground improved against liquefaction by the vibratory SCP method and did not suffer any damage. However, evidence showed that sand boil was observed at a location just 10 meters away from the improved section. The improvement specifications consisted of a triangular arrangement with the spacing of 1.8 m (replacement ratio as = 15%) and the pile length of 8–10 m, similar to the depth of the reclaimed layer. The increase in SPT Nvalues was over 10 at this site, as shown in Fig. 13. An area close to this site was hit again by the Tokachi-oki earthquake in 2003. The unimproved areas liquefied again, in stark contrast to the non-occurrence of liquefaction in the improved areas.
K. Harada, J. Ohbayashi / Soils and Foundations 57 (2017) 980–987
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Hokkaido Toho-oki Earthquake (Oct.'94;M=8.1)
Hokkaido Nansei-oki Earthquake (July'93;M=7.8) Effectiveness of SCP improvement for
Effectiveness confirmed of SCP method at site where it was adopted for restoration work after '93 Kushiro-oki earthquake (Nishikawa (Nishikawa et et al., al., 1995) 1995)
storage tank site at Hakodate confirmed. (Fudo, 1993)
Nihonkai Chubu Earthquake (May'83;M=7.7)
Kushiro-oki Earthquake (Jan'93;M=7.8)
Effectiveness of SCP improvement for Okitate storage tank site confirmed. (JSCE, 1986) 1986)
Effectiveness confirmed of SCP and gravel drain method used for Kushiro's West Harbor (Iai et al., 1993) SCP used in restoration work of Kushiro and Tokachi Rivers (Sasaki (Sasaki et et al., al., 1995) 1995)
Niigata Earthquake (Jun.'64;M=7.5) Effectiveness of vibro floatation for Tank at Ohse confirmed. (Watanabe, 1966)
Nemuro-Hando-oki Earthquake (Nov.'04;M=7.1)
Hyogo-ken Nambu Earthquake (Jan.'95;M=7.2)
Tokachi-oki Earthquake (Sep.'03;M=8.0)
Earthquake-resistant effect of ground improvement confirmed(Yasuda (Yasudaetetal., al.,1996) 1996)
Effectiveness of vibratory SCP improvement for quaywall at Hanasaki Port confirmed(Iida (Iidaetetal., al.,2005) 2005)
Sanriku Haruka-oki Earthquake (Dec.'94;M=7.5) Effectiveness of SCP improvement confirmed at Hachinohe storage tank site (JGS, (JGS, 1996) 1996)
Off the Pacific Coast of Tohoku Earthquake (Mar.'11;M=9.0) Effectiveness of SCP Vibratory and non-vibratory SCP improvement for residential area at Urayasu and Koto-ku confirmed(Yasuda (Yasudaetetal., al.,2012) 2012)
Miyagi-ken-oki Earthquake (Jun.'78;M=7.4) Tottori-ken Seibu Earthquake (Oct.'00;M=7.3) Effectiveness of non-vibratory SCP improvement for embankment at Abe Sanryu line confirmed. (Fudo, (Fudo, 2000) 2000)
Effectiveness of SCP improvement confirmed at storage tank site near Ishinomaki fishing port (Ishihara (Ishihara et et al., al., 1980) 1980)
Fig. 11. Case histories verifying the effectiveness of compaction methods through past earthquakes (modified after Ohbayashi et al. (1998)).
15m
27m Depth (m) 0
approx.10m 5m
Soil profile
00
10
SPT N-values 20 30
40
50
Sand boil
8m
average
SCP spacing: 1.8m
2
Sand pile
4
Sand (Fill) 6
before improvement after improvement
Sand boil
8
10 Fig. 12. Plane and cross section of the site.
4.2. Example of quay wall backfill (Iida et al., 2005) Fig. 14 shows the distribution of improved and unimproved grounds and locations where liquefaction was observed behind the quay wall at Nemuro Port after the 2003 Tokachi-Oki Earthquake. The vibratory SCP method was adopted at this site as a liquefaction countermeasure. The improvement specifications consisted of a square arrangement of sand piles with spacing of 1.9 m (as = 10.6%) in Area A and 1.3 m (as = 22.7%) in Area B. The increase in SPT N-values was from 10 to 15 at the site,
Fig. 13. SPT N-values before and after improvement.
as shown in Fig. 15. The area of improvement extends about 30 m from the normal line of the quay wall with the maximum pile length of 8.5 m. Traces of sand boils were observed at locations about 50 m from the quay wall along a line running roughly parallel to it. In other words, there was a gap of some 20 m between the boundary of the improved zone and the liquefied unimproved area. In the following year, the 2004 Nemuro Hanto-oki Earthquake occurred near the site. In spite of the re-liquefaction of the unimproved areas, there was no damage observed at the improved area.
K. Harada, J. Ohbayashi / Soils and Foundations 57 (2017) 980–987
Apron
1.9m×1.9m
Boring before application and after application
Boring before application
Road No.1
13m 17m 30m
1.3m×1.3m
Asphalt pavement
A
Improved area Area B 185m
Area A 57m
Boring before application and after application
50m
986
Sand boil
Boring after application
No.3
No.2
A´ (A-A´ section) approx. 50m approx. 30m
approx. 20m
SCPs spacing: 1.9m caisson
max=8.5m
Sand boil
backfill
Fig. 14. Plane and cross section of the site.
Depth (m) 0
Soil profile
00
SPT N-value 10 20
30
injection-type SCP method are presented, in addition to the conventional SCP method. Therefore, the SCP method is now applicable for various soil types, such as sandy or clayey grounds and soft clay deposits, as well as for narrow working spaces.
2
References 4
Silty Sand (Fill)
Sand pile
6
8
Clay
before improvement (Boring No.2) after improvement (Boring No.1)
10 Fig. 15. SPT N-values before and after improvement.
5. Summary This report deals with progress and improvement of the sand compaction pile (SCP) method in Japan. At first, the SCP method was developed in 1950s as a ground reinforcement method. But several case histories in Japan show that the SCP is effective as a countermeasure against soil liquefaction, because no major damages due to those large earthquakes were reported so far. Now, the SCP is recognized as a leading countermeasure against soil liquefaction. Two case histories are explained in this paper to support this claim. For wider application of the SCP method, two modified versions, i.e., the non-vibratory SCP method and the sand
Fudo Construction Co., Ltd, 1994. Investigative Report on the 1994 Hokkaido Toho-oki Earthquake (in Japanese). Fudo Construction Co., Ltd, 2003. History of Fudo’s Ground Improvement – Compozer (in Japanese). Harada, K., Tsuboi, H., Tanaka, Y., Takehara, Y. and Fukada, H., 2004. Case histories and recent development of the sand compaction pile method as a countermeasure against liquefaction, Proceedings of the 5th International Conference on Case Histories in Geotechnical Engineering, CD 8.43. Iida, K., Kogai, Y. and Ohbayashi, J., 2005. Improvement effectiveness of sand compaction pile method as a countermeasure against liquefaction at Nemuro Port. In: Proceedings of 40th Technical Meeting of the Japanese Geotechnical Society, 2191–2192 (in Japanese). Imai, Y., Ohbayashi, J., Fukushima, S., Itoh, T., 2009. Improvement effectiveness and application example of sand ejection type SCP. In: Proceedings of 54th Symposium for Japanese Geotechnical Society (in Japanese). Murayama, S., 1957. Soil improvement by sand compaction pile (Compozer method). Semin. Rep. Osaka Constructors Assoc., 1–11 (in Japanese) Ogawa, M., Ishido, T., 1965. Application of vibro-compozer methods on sandy ground. Tuchi-to-kiso 13 (2), 77–82 (in Japanese). Ohbayashi, J., Harada, K., Yamamoto, M., Sasaki, T., 1998. Evaluation of liquefaction resistance in compacted ground. In: Proceedings of 10th Japan Association for Earthquake Engineering Symposium, 1411– 1416 (in Japanese). Ports and Harbors Association of Japan, PHAJ, Technical Standards for Port and Harbour Facilities in Japan, 729 (in Japanese).
Further reading Fudo Construction Co., Ltd, 1993. Investigative Report on the 1993 Hokkaido Nansei-oki Earthquake (in Japanese).
K. Harada, J. Ohbayashi / Soils and Foundations 57 (2017) 980–987 Fudo Construction Co., Ltd, 2000. Investigative Report on the 2000 Tottori-ken Seibu Earthquake (in Japanese). Iai, S., Matsunaga, Y., Morita, T., Sakurai, H., Ohishi, H., Ogyra, H., Ando, Y., Tanaka, Y., Kato, M., 1993. Effects of remedial measures against liquefaction at 1993 Kushiro-oki Earthquake. In: Proceedings of the 5th US-Japan Workshop on Earthquake Resistant Design of Lifeline Facilities and Countermeasures against Soil Liquefaction. Ishihara, K., Kawase, Y., Nakajima, M., 1980. Liquefaction characteristics of sand deposits at an oil tank site during the 1978 MiyagikenOki Earthquake. Soils Found. 20 (2), 97–112. Japanese Geotechnical Society, JGS, 1996. Investigative Report on the 1996 Sanriku Haruka-oki Earthquake (in Japanese). Japan Society of Civil Engineering, JSCE, 1986. Investigative Report on the 1983 Nihonkai-chubu Earthquake (in Japanese).
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Nishikawa, J., Kamata, T., Kaji, M., 1995. Damage to highways, railways and river embankments from the 1994 Hokkaido Toho-oki Earthquake. Tuchi-to-kiso 43 (4), 7–10 (in Japanese). Sasaki, Y., Tamura, T., Yamamoto, M., Ohbayashi, J., 1995. Soil improvement work for river embankment damaged by the 1993 Kushiro-oki Earthquake. In: Proceedings of the 1st International Conference on Earthquake Geotechnical Engineering, pp. 43–48. Watanabe, T., 1966. Damage to oil refinery plants and a building on compacted ground by the Niigata Earthquake and their restoration. Soils Found. 6 (2), 86–99. Yasuda, S., Harada, K., Ishikawa, K., Kanemaru, Y., 2012. Characteristics of the liquefaction in Tokyo Bay Area by the 2011 Great East Japan Earthquake. Soils Found. 52 (5), 793–810. Yasuda, S., Ishihara, K., Harada, K., Shinkawa, N., 1996. Effect of soil improvement on ground subsidence due to liquefaction. Spec. Issue Soils Found., 99–107
Available online at www.sciencedirect.com
ScienceDirect Soils and Foundations 57 (2017) 980–987 www.elsevier.com/locate/sandf
Development and improvement effectiveness of sand compaction pile method as a countermeasure against liquefaction Kenji Harada ⇑, Jun Ohbayashi Geotechnical Department, Fudo Tetra Corporation, Japan Received 19 October 2016; received in revised form 16 June 2017; accepted 3 August 2017 Available online 11 November 2017
Abstract The sand compaction pile (SCP) method was developed in Japan to improve soft grounds. One of the major features of the SCP method is that it can be applied to all soil types found in Japan, from sandy to clayey soils; and therefore, it has been widely used for the improvement of soft grounds. Recently, the SCP method has been mainly adopted as a countermeasure against liquefaction, and its effectiveness in preventing liquefaction has been confirmed through past large earthquakes. This paper provides an outline of the conventional SCP method, including its principle, history, equipment, and implementation, and also describes other methods derived from the SCP method as liquefaction countermeasures. Furthermore, several examples are reported to confirm the effectiveness of the methods through past large earthquakes. Ó 2017 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BYNC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Keywords: Ground improvement; Sand compaction pile; Countermeasure against liquefaction
1. Introduction The sand compaction pile method (hereinafter abbreviated as the SCP method) is a method for improving soft grounds by means of installing well-compacted sand piles in the ground. It combines such fundamental principles for ground improvement as densification and drainage. It can be applied to all types of soil found in Japan, from sandy to clayey soils, by commonly using a single piece of equipment; therefore, it has been widely used for the improvement of soft grounds. In sandy grounds, the SCP method is mainly used as a countermeasure against liquefaction, and its effectiveness in preventing liquefaction has been confirmed through past large earthquakes, show-
ing that this method is one of the most reliable ground improvement methods in Japan. This paper describes the principle, the history, and the equipment of the conventional SCP method as well as outlines two other methods derived from the SCP method in accordance with the needs of the times as liquefaction countermeasures including the procedure, the equipment, and the material used for each method. Some cases are also shown that demonstrate the difference between an unimproved ground and a ground improved by the SCP method based on the degree of damage brought about by past large earthquakes. 2. Outline of SCP method 2.1. Principle and purpose of the SCP method
Peer review under responsibility of The Japanese Geotechnical Society. ⇑ Corresponding author. E-mail addresses: [email protected] (K. Harada), jun. [email protected] (J. Ohbayashi).
The SCP method is effective in improving the performance of all the types of ground for different reasons. The reasons for such effectiveness in three representative
https://doi.org/10.1016/j.sandf.2017.08.025 0038-0806/Ó 2017 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
K. Harada, J. Ohbayashi / Soils and Foundations 57 (2017) 980–987
soil types, i.e., sandy grounds, clayey grounds and soft clay deposits which is typically formed at offshore sites, are described. The principle of the SCP method for clayey grounds is based on the theory for composite grounds proposed by Murayama (1957). Composite grounds consist of soft cohesive grounds and compacted sand piles formed therein; the composite ground formed has high shear strength and drainage capability owing to the presence of the sand piles. Through the formation of these compacted sand piles, the bearing capacity of the ground can be increased due to ‘‘replacement effect” and ‘‘stress concentration effect”. ‘‘Stress concentration” means that external load is concentrated mainly on the sand piles, as shown in Fig. 1(a). Furthermore, by including ‘‘drainage effect” (see Fig. 1(a)), an increase in the stiffness of the whole ground as well as a decrease in lateral spreading and in consolidation settlement can be expected. On the other hand, the principle of the SCP method for sandy grounds is primarily to decrease the void ratio and to densify the ground as a result of the sand pile installation, as shown in Fig. 1(b). Accordingly, the purpose of the SCP method is to increase the bearing capacity, to decrease the compression settlement, to prevent the occurrence of liquefaction, and to increase horizontal resistance. For sandy grounds, Ogawa and Ishido (1965) suggested a practical design procedure related to the increase in density due to the installation of sand piles. Conversely, for soft clay deposits which are typically encountered in offshore works, thicker sand piles are installed into the clay at the sea bottom, as shown in Fig. 1(c). ‘‘Forced replacement” is the major principle for the improvement of offshore works, rather than the formation of ‘‘composite ground” where the sand piles replace the cohesive soils. In such cases, the objectives of the improvement are to increase the bearing capacity, to reduce the consolidation settlement, and to increase the horizontal resistance.
Fig. 2. Vibratory SCP equipment.
Fig. 3. Installation procedure for vibratory SCP method.
Fig. 1. Concept for installation of compacted sand piles.
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2.2. Equipment and implementation process An on-land type equipment for the vibratory SCP and its installation procedure in a soft ground are illustrated in Figs. 2 and 3, respectively. The procedure is as follows. (1) Positioning: Set the casing pipe at the predetermined place. (2) Penetration of a casing pipe: By operating the vibrator, penetrate the casing pipe into the ground. (3) Feeding sands through a hopper: After the casing pipe has reached the required depth, feed sand into the casing through the upper hopper. (4) Drawing up the casing pipe: By drawing up the casing pipe, the sand in the pipe is forced out through the void by compressed air. (5) Re-driving the casing pipe: Re-drive the casing while compacting the sand pile pressed out by the vibrations, resulting in its enlargement. (6) Completion: Form each compacted sand pile to reach the ground surface by repeating the above procedure.
3. Development of SCP method as liquefaction countermeasure 3.1. Development of liquefaction countermeasures Liquefaction countermeasures in Japanese engineering practice are roughly classified according to three principles, i.e., compaction (densification), solidification, and drainage (pore water pressure dissipation). Table 1 summarizes the history of major liquefaction countermeasures in Japan based on the aforementioned principles. As shown in the table, the densification method using vibratory hammers was first introduced in the 1950 s as a ground reinforcement method. In 1964, the Niigata earthquake resulted in significant damage due to liquefaction. After the 1964 Niigata earthquake, the SCP method was recognized as an effective countermeasure against liquefaction (Fudo Construction Co., Ltd., 2003). The gravel drain method, which is one of a number of drainage methods, was
developed in the 1970s as an environment-friendly measure with low noise and vibrations. The lattice-type deep mixing method, a shear strain restraint method, was developed as an economical countermeasure in the 1980s. The SCP method was recognized as a liquefaction prevention/mitigation method after its effectiveness was verified by many case histories during large earthquakes, such as the 1978 Miyagi-ken-Oki Earthquake and the 1983 Nihonkai-Chubu Earthquake. Examples of such case histories are presented later in this paper. However, the drawbacks of this method are the noise and the vibrations generated by the vibro-hammer. Thus, it became necessary to improve the SCP method such that it would have no adverse influence on the surrounding environment. To meet this demand, two new types of SCP methods, the non-vibratory SCP method (Harada et al., 2004) and the sand injection-type SCP method (Imai et al., 2009), have been developed, as explained in the next section. 3.2. Methods derived from conventional SCP method 3.2.1. Non-vibratory SCP method In the conventional SCP method (Vibratory SCP method), the vibromotive force of a vibratory-hammer is used for the ground penetration of a casing pipe, and a winding wire is used to withdraw it. As the vibratoryhammer causes excessive noise and vibration, the vibratory SCP method cannot be used in urban areas. A nonvibratory SCP method can form sand piles statically in the ground. Instead of a vibratory-hammer, withdrawal and re-driving of casing pipes are achieved by a forced lifting/driving device that rotates the casing pipe, as shown in Fig. 4. The operating procedure for the non-vibratory SCP method, shown in Fig. 5, is identical to that of the vibratory SCP method. A casing pipe, 400–500 mm in diameter, is used to create well-compacted sand piles, 700 mm in diameter, and the surrounding ground is densified as a result. The system for the implementation of this method involves the application of vertical movement of the casing pipe, as indicated by a wave pattern with a shorter wave
pin rack
rack
Table 1 History of liquefaction prevention.
Sprocket (a) Pin rack and sprocket type
pinion gear (b) Rack and pinion type
Fig. 4. Main components of forced lifting/driving device.
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(b)
(a)
10cm
40cm
Rod
Casing
Withdrawal
Redriving
Compaction
Compaction Enlarging
Withdrawal Compaction
Compaction
Enlarging
Existing sand pile Existing sand pile 70cm
Fig. 5. Installation procedure for non-vibratory SCP method.
length than the one of a vibratory SCP, as shown in Figs. 3 and 5. The recordings of noise and vibration levels associated with the vibratory SCP and the non-vibratory SCP methods made at five sites, A to E, are shown in Fig. 6. It is clear from the figure that both noise and vibration levels are greatly reduced in the non-vibratory method compared with the vibratory SCP method, making it suitable for applications in urban areas and at sites close to existing structures. 3.2.2. Sand injection-type SCP method The sand injection-type SCP method is a method to densify the target ground by pumping and injecting fluidized
70cm
Fig. 7. Mechanism for installation of compacted sand piles.
sand into the ground through a small-sized equipment. A mixture of sand and a fluidizing reagent is forcibly ejected by pumping from the tip of the rod which is penetrated into the ground to densify the surrounding ground. To form a dense ground, the fluidity of the ejected sand is wellcontrolled. The fluidity gradually disappears due to the combination of dehydration of the mixture and chemical process of the retarding plasticizer. Fig. 7 shows a comparison of the mechanism for enlarging the diameter of the sand piles between (a) the vibratory/non-vibratory SCP method and (b) the sand injection-type SCP method. The procedure for applying the sand injection-type SCP method is as follows (see Fig. 8): (1) Positioning: Set the rod at the prescribed position and insert it into the ground. (2) Feeding the fluidized sand through a rod: After the rod has reached the required depth, pump out the fluidized sand.
(Position Set) (Penetration Complete) (Pile formation completed) Move Penetration Pile formation
Rod Equipment
trace of rod
Fig. 6. Decrease over distance of noise and vibration with non-vibratory SCP method.
Fig. 8. Installation procedure for sand injection type of SCP method.
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Percentage finer by weight (%)
90
Performance range
80 70
Performance range
60 50 40
Achievement of SCP
30 20 10 0
Grain size D (mm)
Fig. 9. Grain distribution curves of used material.
Photo 1. Examples of implementation under limited space.
4. Verification of effectiveness of method through past earthquakes 40m
Fig. 11 shows the epicenter locations and characteristics of the 1964 Niigata Earthquake and eleven other largescale earthquakes in Japan, including the 2011 Off the Pacific Coast of Tohoku Earthquake, as well as information on the performance of SCP-improved grounds during these earthquakes. As shown in the figure, there has been no report of any major damages to the structures constructed on SCP-improved ground, such as by vibratory and non-vibratory SCP methods, confirming in a qualitative sense the effectiveness of the compaction-type ground improvement techniques against strong earthquakes. Detailed information for some of these cases is given below.
30m
20m
10m
Vibratory SCP Non-vibratory SCP Sand injection type SCP
4.1. Example of tank foundation (Fudo Construction Co., Ltd, 1994)
Fig. 10. Equipment of each SCP method.
(3) Drawing up the rod: Draw up the rod to the next step. (4) Completion: Form each compacted sand pile up to the surface by repeating the above procedure. Fig. 9 indicates the grain size distribution curves of several kinds of sand used for this method at numerous sites, in order to compare the applicable grain size range of the sand injection-type SCP method and the conventional SCP method (PHAJ, 2007). Fig. 10 shows the size of the equipment used in the vibratory, the non-vibratory, and the sand injection-type SCP methods. Recently, a smallsized equipment has been developed for use in narrow spaces, such as under bridge girders and/or close to existing structures. In such cases, only the sand injection-type SCP is applicable. Photo 1 shows an example of the sand injection-type SCP method being used at a narrow space where it is surrounded by an existing factory building and a revetment.
Following the 1994 Hokkaido Toho-Oki Earthquake, a remarkable difference was observed between the areas of improved ground, including the SCP-improved tank foundation ground, and the adjacent unimproved areas. Fig. 12 shows the locations of the sand boil trace in the improved tank foundation ground and in the adjacent non-improved ground areas. The tanks themselves were installed on a ground improved against liquefaction by the vibratory SCP method and did not suffer any damage. However, evidence showed that sand boil was observed at a location just 10 meters away from the improved section. The improvement specifications consisted of a triangular arrangement with the spacing of 1.8 m (replacement ratio as = 15%) and the pile length of 8–10 m, similar to the depth of the reclaimed layer. The increase in SPT Nvalues was over 10 at this site, as shown in Fig. 13. An area close to this site was hit again by the Tokachi-oki earthquake in 2003. The unimproved areas liquefied again, in stark contrast to the non-occurrence of liquefaction in the improved areas.
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Hokkaido Toho-oki Earthquake (Oct.'94;M=8.1)
Hokkaido Nansei-oki Earthquake (July'93;M=7.8) Effectiveness of SCP improvement for
Effectiveness confirmed of SCP method at site where it was adopted for restoration work after '93 Kushiro-oki earthquake (Nishikawa (Nishikawa et et al., al., 1995) 1995)
storage tank site at Hakodate confirmed. (Fudo, 1993)
Nihonkai Chubu Earthquake (May'83;M=7.7)
Kushiro-oki Earthquake (Jan'93;M=7.8)
Effectiveness of SCP improvement for Okitate storage tank site confirmed. (JSCE, 1986) 1986)
Effectiveness confirmed of SCP and gravel drain method used for Kushiro's West Harbor (Iai et al., 1993) SCP used in restoration work of Kushiro and Tokachi Rivers (Sasaki (Sasaki et et al., al., 1995) 1995)
Niigata Earthquake (Jun.'64;M=7.5) Effectiveness of vibro floatation for Tank at Ohse confirmed. (Watanabe, 1966)
Nemuro-Hando-oki Earthquake (Nov.'04;M=7.1)
Hyogo-ken Nambu Earthquake (Jan.'95;M=7.2)
Tokachi-oki Earthquake (Sep.'03;M=8.0)
Earthquake-resistant effect of ground improvement confirmed(Yasuda (Yasudaetetal., al.,1996) 1996)
Effectiveness of vibratory SCP improvement for quaywall at Hanasaki Port confirmed(Iida (Iidaetetal., al.,2005) 2005)
Sanriku Haruka-oki Earthquake (Dec.'94;M=7.5) Effectiveness of SCP improvement confirmed at Hachinohe storage tank site (JGS, (JGS, 1996) 1996)
Off the Pacific Coast of Tohoku Earthquake (Mar.'11;M=9.0) Effectiveness of SCP Vibratory and non-vibratory SCP improvement for residential area at Urayasu and Koto-ku confirmed(Yasuda (Yasudaetetal., al.,2012) 2012)
Miyagi-ken-oki Earthquake (Jun.'78;M=7.4) Tottori-ken Seibu Earthquake (Oct.'00;M=7.3) Effectiveness of non-vibratory SCP improvement for embankment at Abe Sanryu line confirmed. (Fudo, (Fudo, 2000) 2000)
Effectiveness of SCP improvement confirmed at storage tank site near Ishinomaki fishing port (Ishihara (Ishihara et et al., al., 1980) 1980)
Fig. 11. Case histories verifying the effectiveness of compaction methods through past earthquakes (modified after Ohbayashi et al. (1998)).
15m
27m Depth (m) 0
approx.10m 5m
Soil profile
00
10
SPT N-values 20 30
40
50
Sand boil
8m
average
SCP spacing: 1.8m
2
Sand pile
4
Sand (Fill) 6
before improvement after improvement
Sand boil
8
10 Fig. 12. Plane and cross section of the site.
4.2. Example of quay wall backfill (Iida et al., 2005) Fig. 14 shows the distribution of improved and unimproved grounds and locations where liquefaction was observed behind the quay wall at Nemuro Port after the 2003 Tokachi-Oki Earthquake. The vibratory SCP method was adopted at this site as a liquefaction countermeasure. The improvement specifications consisted of a square arrangement of sand piles with spacing of 1.9 m (as = 10.6%) in Area A and 1.3 m (as = 22.7%) in Area B. The increase in SPT N-values was from 10 to 15 at the site,
Fig. 13. SPT N-values before and after improvement.
as shown in Fig. 15. The area of improvement extends about 30 m from the normal line of the quay wall with the maximum pile length of 8.5 m. Traces of sand boils were observed at locations about 50 m from the quay wall along a line running roughly parallel to it. In other words, there was a gap of some 20 m between the boundary of the improved zone and the liquefied unimproved area. In the following year, the 2004 Nemuro Hanto-oki Earthquake occurred near the site. In spite of the re-liquefaction of the unimproved areas, there was no damage observed at the improved area.
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Apron
1.9m×1.9m
Boring before application and after application
Boring before application
Road No.1
13m 17m 30m
1.3m×1.3m
Asphalt pavement
A
Improved area Area B 185m
Area A 57m
Boring before application and after application
50m
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Sand boil
Boring after application
No.3
No.2
A´ (A-A´ section) approx. 50m approx. 30m
approx. 20m
SCPs spacing: 1.9m caisson
max=8.5m
Sand boil
backfill
Fig. 14. Plane and cross section of the site.
Depth (m) 0
Soil profile
00
SPT N-value 10 20
30
injection-type SCP method are presented, in addition to the conventional SCP method. Therefore, the SCP method is now applicable for various soil types, such as sandy or clayey grounds and soft clay deposits, as well as for narrow working spaces.
2
References 4
Silty Sand (Fill)
Sand pile
6
8
Clay
before improvement (Boring No.2) after improvement (Boring No.1)
10 Fig. 15. SPT N-values before and after improvement.
5. Summary This report deals with progress and improvement of the sand compaction pile (SCP) method in Japan. At first, the SCP method was developed in 1950s as a ground reinforcement method. But several case histories in Japan show that the SCP is effective as a countermeasure against soil liquefaction, because no major damages due to those large earthquakes were reported so far. Now, the SCP is recognized as a leading countermeasure against soil liquefaction. Two case histories are explained in this paper to support this claim. For wider application of the SCP method, two modified versions, i.e., the non-vibratory SCP method and the sand
Fudo Construction Co., Ltd, 1994. Investigative Report on the 1994 Hokkaido Toho-oki Earthquake (in Japanese). Fudo Construction Co., Ltd, 2003. History of Fudo’s Ground Improvement – Compozer (in Japanese). Harada, K., Tsuboi, H., Tanaka, Y., Takehara, Y. and Fukada, H., 2004. Case histories and recent development of the sand compaction pile method as a countermeasure against liquefaction, Proceedings of the 5th International Conference on Case Histories in Geotechnical Engineering, CD 8.43. Iida, K., Kogai, Y. and Ohbayashi, J., 2005. Improvement effectiveness of sand compaction pile method as a countermeasure against liquefaction at Nemuro Port. In: Proceedings of 40th Technical Meeting of the Japanese Geotechnical Society, 2191–2192 (in Japanese). Imai, Y., Ohbayashi, J., Fukushima, S., Itoh, T., 2009. Improvement effectiveness and application example of sand ejection type SCP. In: Proceedings of 54th Symposium for Japanese Geotechnical Society (in Japanese). Murayama, S., 1957. Soil improvement by sand compaction pile (Compozer method). Semin. Rep. Osaka Constructors Assoc., 1–11 (in Japanese) Ogawa, M., Ishido, T., 1965. Application of vibro-compozer methods on sandy ground. Tuchi-to-kiso 13 (2), 77–82 (in Japanese). Ohbayashi, J., Harada, K., Yamamoto, M., Sasaki, T., 1998. Evaluation of liquefaction resistance in compacted ground. In: Proceedings of 10th Japan Association for Earthquake Engineering Symposium, 1411– 1416 (in Japanese). Ports and Harbors Association of Japan, PHAJ, Technical Standards for Port and Harbour Facilities in Japan, 729 (in Japanese).
Further reading Fudo Construction Co., Ltd, 1993. Investigative Report on the 1993 Hokkaido Nansei-oki Earthquake (in Japanese).
K. Harada, J. Ohbayashi / Soils and Foundations 57 (2017) 980–987 Fudo Construction Co., Ltd, 2000. Investigative Report on the 2000 Tottori-ken Seibu Earthquake (in Japanese). Iai, S., Matsunaga, Y., Morita, T., Sakurai, H., Ohishi, H., Ogyra, H., Ando, Y., Tanaka, Y., Kato, M., 1993. Effects of remedial measures against liquefaction at 1993 Kushiro-oki Earthquake. In: Proceedings of the 5th US-Japan Workshop on Earthquake Resistant Design of Lifeline Facilities and Countermeasures against Soil Liquefaction. Ishihara, K., Kawase, Y., Nakajima, M., 1980. Liquefaction characteristics of sand deposits at an oil tank site during the 1978 MiyagikenOki Earthquake. Soils Found. 20 (2), 97–112. Japanese Geotechnical Society, JGS, 1996. Investigative Report on the 1996 Sanriku Haruka-oki Earthquake (in Japanese). Japan Society of Civil Engineering, JSCE, 1986. Investigative Report on the 1983 Nihonkai-chubu Earthquake (in Japanese).
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Nishikawa, J., Kamata, T., Kaji, M., 1995. Damage to highways, railways and river embankments from the 1994 Hokkaido Toho-oki Earthquake. Tuchi-to-kiso 43 (4), 7–10 (in Japanese). Sasaki, Y., Tamura, T., Yamamoto, M., Ohbayashi, J., 1995. Soil improvement work for river embankment damaged by the 1993 Kushiro-oki Earthquake. In: Proceedings of the 1st International Conference on Earthquake Geotechnical Engineering, pp. 43–48. Watanabe, T., 1966. Damage to oil refinery plants and a building on compacted ground by the Niigata Earthquake and their restoration. Soils Found. 6 (2), 86–99. Yasuda, S., Harada, K., Ishikawa, K., Kanemaru, Y., 2012. Characteristics of the liquefaction in Tokyo Bay Area by the 2011 Great East Japan Earthquake. Soils Found. 52 (5), 793–810. Yasuda, S., Ishihara, K., Harada, K., Shinkawa, N., 1996. Effect of soil improvement on ground subsidence due to liquefaction. Spec. Issue Soils Found., 99–107