SPECIAL ISSUE OF SOILS AND FOUNDATIONS 189-200, Jan. 1996 Japanese Geotechnical Society

FOUNDATION DAMAGE OF STRUCTURES

TAMOTSU MATSUIO and KAZUHIRO ODAii)

ABSTRACT The 1995 Hyogoken-Nambu earthquake caused heavy damage to many super- and sub-structures of elevated highways in the , Ashiya, and area. The majority of the elevated highways are founded on piles, most of which are cast-in-place reinforced large diameter concrete bored piles. The bore-hole television (BHTV) system was the most reliable method applied to the inspection of the soundness of cast-in-place bored piles. It was revealed that some cracks occur not only around the top of a pile but also between the pile top and tip. It was also noted that the degree of pile damage does not necessarily correspond to that of super- and sub-structures. In addition, the lateral resistance of damaged piles is discussed herein, based on the results of an available full-scale static load test on a pile group. Some case histories of raft foundations, caisson foundations, steel pipe pile foundations and precast prestressed concrete pile foundations are presented. Finally, it was concluded that the foundation damage to structures is sometimes caused not only by seismic force of super- and sub-structures, but also by liquefaction and/or lateral flow of the subsoil below the ground surface.

Key words: caisson, cast-in-place pile, deep foundation, earthquake damage, foundation, pile, shallow foundation, (IGC: H1)

geotechnical engineering, but also including considera- INTRODUCTION tion of the methods of restoration. The 1995 Hyogoken-Nambu earthquake was the larg- est to occur so far in a highly urban area. The earth- DAMAGE OF ELEVATED HIGHWAYS quake consisted of horizontal and vertical motion of short duration and of greater severity than anticipated. The damage of super- and sub-structures of elevated These shocks resulted in extensive damage to the social highways due to the Great -Awaji Earthquake infrastructure, including highways, railroads and harbor Disaster is summarized in Table 1, and a damage location facilities, to name a few of the civil engineering struc- map is presented in Fig. 1. Highway routes which tures. suffered extensive damage are 1) All structures are, in some way, supported by subsoils. No. 3 , 2) Hanshin Expressway No. 5 Bay Because most civil engineering structures are heavy, the Route, 3) , 4) Chugoku Expressway, foundation that supports the super- and sub-structures 5) Harbor Highway and 6) Hamate Bypass of the Nation- plays a crucial role in maintaining their integrity. A al Highway Route 2. Damage to the four highway routes sound structure, therefore, is one with a good founda- of 1), 2), 5) and 6) was more severe, because they are lo- tion as well as integrated super- and sub-structures. cated near the area of very strong seismic intensity and Most visible damage was observed in both the super- were constructed on soft alluvial deposits along the north- and sub-structures. It is very possible for the foundation ern part of the Bay. Highway routes 2), 5) and 6) to suffer invisible damage that is then the cause of visible particularly are constructed on reclaimed soft subsoils. damage to both the super- and sub-structures. Based on this view, the authors attempted to evaluate the founda- tions damage to the structures mainly focusing on elevat- FOUNDATION TYPES OF ELEVATED HIGHWAYS ed highways, including effect of displacement or deforma- The foundation types adopted for these six routes se- tion to the surrounding subsoil caused by liquefaction or verely damaged are shown in Fig. 2. The majority of the lateral flow of soils. In addition, the purpose is to deter- foundations for each route were pile foundations, mostly mine the "damage mechanism" of foundations based on cast-in-place reinforced concrete bored piles of more

i) Professor, Dept. of Civil Engineering, Osaka University, Yamadaoka 2-1, , Osaka 565. ii) Research Associate, ditto. Manuscript was received for review on August 18, 1995. Written discussions on this paper should be submitted before August 1, 1996 to the Japanese Geotechnical Society, Sugayama Bldg. 4F, Kanda Awaji-cho 2-23, Chiyoda-ku, Tokyo 101, . Upon request the closing date may be extended one month.

189 190 MATSUI AND ODA

Table 1. Damage to super- and sub-structures of elevated highways

Fig. 1. Damage location map for super- and sub-structures of elevated highways FOUNDATION DAMAGE OF STRUCTURES 191

Fig. 2. Foundation types than one meter in diameter. In some cases, large diameter advantage of BHTV system is to be able to directly ob- steel pipe piles were adopted. Caisson foundations were serve cracks, followed by accurately confirming their posi- used for some long span highway bridges spanning water- tion, direction and width even at a deeper position. ways between reclaimed land areas, whereas raft founda- Photograph 1 shows an example of the picture image tions were used for ramp with relatively lower piers or observed by BHTV system, a development plan of a founded on shallow bearing layers. The damage of cast- bore-hole wall. Even hair cracks can be distinguished by in-place bored piles is described below, because they are the BHTV image. Figures 5 (a), (b) and (c) illustrate three the prevailing foundation type. typical examples of damage to piles observed by BHTV system. In all types, cracks are concentrated at around the top of the pile where the maximum moment occurs. DAMAGE OF CAST-IN-PLACE BORED PILES In types (b) and (c), some cracks also occur between the In order to inspect the soundness of cast-in-place pile top and tip. It is considered that the reasons why bored piles, some of the methods listed in Table 2 were these cracks occur in the middle to lower portion of the used. Fig. 3 shows an example of inspection data for the pile might be 1) Position at which the density of reinforce- Hanshin Expressway No. 3 Kobe Route, where the bore- ment bars changes, 2) Position of the second largest mo- hole television (BHTV) system and direct observation ment, or 3) Interface zone between soft and hard soil lay- were most reliable. The outline of BHTV system is illus- ers. trated in Fig. 4 (Kamewada et al. , 1990). This method Figure 6 shows a pier of the Harbor Highway with was originally developed to investigate the condition of damaged cast-in-place bored piles. The inspection of the cracks in a rock mass by observing a bore-hole wall. The pile shaft surface is shown by the photos, in which some cracks are confirmed. A BHTV image of these piles is shown in Photo. 1. In order to understand the general Table 2. Methods for inspecting soundness of cast-in-place bored view of pile damage, classification as shown in Table 3 piles was used. In Table 3, the restoration methods are also shown corresponding to the classification of the founda- tion damage. Figure 7 shows the results of pile damage classification for the Hanshin Expressway No. 3 Kobe Route and No. 5 Bay Route. The piles investigated were selected at random corresponding to damage of both the super- and sub-structures. On the Kobe Route, most of the piles investigated were classified in rank D (no damage) and 16% of those were classified in rank C (light- 192 MATSUI AND ODA

Fig. 3. Example of inspection data for Hanshin Expressway No. 3 Kobe Route

Meishin and Chugoku Expressways, although some piles investigated have small cracks, all the piles were classified in rank D (no damage), whereas on the Harbor Highway and the Hamate Bypass, the majority of the piles investi- gated were classified in rank D (no damage) and rank C (lightly damaged), but no rank A (severely damaged), in a similar manner as on the Hanshin Expressway No. 5 Bay Route. Comparing the degree of foundation damage men- tioned above with that of super- and sub-structures as shown in Table 1 and Fig. 1, it is noted that for exten- sively damaged super- and sub-structures, the founda- tion damage was not necessarily extensive. Generally, the foundation damage corresponds to the subsurface condi- tions, that is, foundations on soft subsoil such as reclaimed lands sometimes suffer heavier damage. This is due to the effect of liquefaction and/ or lateral flow of subsoils than seismic motion of the structure itself. Cast- in-place bored piles are subjected to lateral flow pressure of the subsoils during earthquake. Such piles are called "passive piles during earthquake" (Matsui T ., 1993). In contrast, piles subjected to only seismic force of the su- per- and sub-structures are called "active piles". It is Fig. 4. Measurement fundamentals for BHTV system (Kamewada et al., 1990) pointed out, therefore, that a systematic design method for both passive and active piles is desirable for cast-in- place bored piles subjected to lateral flow pressure during ly damaged). On the Bay Route, the majority of the piles an earthquake. investigated were classified in rank D (no damage) and Finally, the capacity of lateral resistance for damaged rank C (lightly damaged), 52% and 37%, respectively. piles is discussed. A full-scale lateral load test on a pile There were no rank A (severely damaged). On the group was carried out by the Hanshin Expressway Public FOUNDATION DAMAGE OF STRUCTURES 193

(a)

(b)

Photo. 1. BHTV picture image

(c) Corporation in 1993 before the 1995 Hyogoken-Nambu earthquake took place (Kimura et al., 1994). Figure 8 il- lustrates the plan of the pile group, consisting of nine cast-in-place bored piles (1 m in diameter). Figure 9 shows the relationship between the lateral load and dis- placement in a static load test. In the loading curve envel- ope, lateral load gradually increases with increasing later- al displacement even after a large lateral displacement of 40 cm occurred. Pile cracks occurred at a lateral displace- ment of less than 10 cm. With regard to the load bearing capacity, the piles subjected to a large lateral displace- ment (more than 40 cm) have still retained sufficient capacity of lateral resistance . Photograph 2 shows cracks around the top of the pile which were observed af- ter the completion of a load test, that is, after large defor- mation (more than 40 cm) took place. This pile damage seems to correspond to rank B (heavily damaged) as shown in Table 3, which was also supported by BHTV data. This fact suggests that even a heavily damaged pile can retain sufficient capacity of lateral resistance. It Fig. 5. Typical examples of damage to piles by BHTV system 194 MATSUI AND ODA

Pile A

File b

Fig. 6. A pier of Harbor Highway with damaged cast-in-place bored piles

a) Hanshin Expressway b) Hanshin Expressway No. 3 Kobe Route No. 5 Bay Route

Fig. 7. Results of pile damage classification for Hanshin Expressway No. 3 Kobe Route and No. 5 Bay Route FOUNDATION DAMAGE OF STRUCTURES 195

Pile group-1 Pile group-2 Pile group-3

Fig. 8. Plan of pile group (Kimura et al., 1994)

Fig. 9. Relationship between lateral load and lateral displacement Photo. 2. Cracks around pile top after large deformation (more than (Kimura et al., 1994) 40 cm)

Table 3. Classification of pile damage 196 MATSUI AND ODA

should be noted that this load test was carried out using Caisson Foundation static one-way cyclic loading. Most of long span bridges crossing open waters or rivers are supported on caisson foundations. These foun- dations are constructed near a revetment or as a revet- CASE HISTORY OF OTHER TYPES OF ment. Figure 10 illustrates a schematic drawing of typical FOUNDATION DAMAGE damage to a revetment and caisson foundation. The foun- Raft Foundation dation was subjected to lateral earth pressure due to later- An example of damage to a raft foundation of a al flow of the surrounding subsoils caused by the collapse "flyover" structure on the National Highway Route 171 of the revetment and/or liquefaction during the earth- is shown in Photo. 3. Some cracks occurred in the pier quake. around the footing which had no damage. This damage Two typical examples of damage to caisson founda- was caused by the seismic motion of the superstructure. tions are shown below. Photograph 5 (JGS, 1996) shows The restoration was carried out by injection filling the cracks with an epoxy-resin. Another example of damage to a raft foundation on an elevated approach span to the Kobe Bridge on Jetty No. 4 of the Kobe Port is shown in Photo. 4 (JGS, 1996). The right and left piers have raft and pile foundations, respec- tively. The right raft foundation, which was supported on an artificially reclaimed rubble-mound layer (about 8 m in thickness), settled and tilted due to the liquefaction of the surrounding subsoils, followed by settlement and inclination of the pier and cross beam. This structure will be rebuilt by using a pile foundation.

a) Cross section

Photo. 3. Damage to raft foundation on National Highway Route 171

b) Plan

Fig. 10. Schematic drawings of typical damage to revetment and caisson foundation

Photo. 4. Damage to raft foundation of elevated approach to Kobe Photo. 5. Collapse of a girder connected with Nishinomiya-Ko Bridge Bridge FOUNDATION DAMAGE OF STRUCTURES 197

Photo. 7. Damaged revetment and piers with steel pipe piles on West Photo. 6. Support of Kobe Bridge on Kobe side and damage to the Jetty at Maya Wharf surrounding area

elevated approach span to the Second Maya Bridge were the collapse (failure) of a girder connected with the exposed. It is suggested, therefore, that the steel pipe Nishinomiya-Ko Bridge. The caisson foundation of the piles were subjected to lateral flow pressure of subsoils bridge was located about 23 m away from the revetment. during the earthquake, that is, they became "passive Large traces of sand spouting caused by liquefaction piles during earthquake". Photograph 8 shows a field in- were found in the inland area, and the revetment moved spection of a steel pipe pile for approximately the top 2 about 2 m in the direction of open water. Consequently, meters, in which direct observation and X-ray inspection the caisson foundation was subjected to lateral flow pres- (see in Photo. 8) were carried out. As a result, it was sure and possibly a more severe condition for foundation confirmed that the steel pipe piles investigated ex- deformation was imposed during the earthquake. Photo- perienced no damage even for the "passive piles during graph 6 (JGS, 1996) shows the support of the Kobe earthquake". Bridge on the Kobe side. The abutment of the caisson foundation, which was also used as a revetment, moved about 60 cm toward open water. This displacement was partly attributable to movement of another abutment with a fixed shoe on the Port Island side. Except adjacent to the bridge abutment, the jetty edge revetment moved about 1.5 m toward open water and also subsided about 1 m. The backfill behind the abutment subsided about 1 m. Most of the caisson foundation damage, as mentioned above, was due to the movement and inclination toward open water resulting from lateral flow pressure acting on the foundation due to the lateral movement of subsoils. No damage of the caisson was observed in those caisson foundations investigated by BHTV system. It should also be pointed out that a systematic design method should be developed for caisson foundations, considering the effect of the lateral flow pressure from ground movement which occurs during an earthquake. The damaged cais- son foundations will be restored mainly by improving the surrounding subsoils.

Steel Pipe Pile Foundation For elevated highway foundations, large-diameter steel pipe piles are used particularly for cases of foundations off shore or near shore where cast-in-place bored piles are not suitable to be installed. Photograph 7 shows a damaged revetment and piers with steel pipe piles (1 m in diameter) on the West Jetty at the Maya Wharf. The jetty revetment moved toward the sea and footings of the Photo. 8. Direct observation and X-ray inspection of steel pipe pile 198 MATSUI AND ODA

Figure 11 shows a cross section of a landing pier with of the river revetment with precast prestressed concrete steel pipe piles (70 cm in diameter), which was located piles. These are friction piles (35 cm in diameter) which near a seawall and damaged during the earthquake. Since were installed in an alluvial loose sand layer. Along the the landing pier was constructed away from the revet- riverside area, sand spout traces were observed due to liq- ment, the movement of the revetment was not directly uefaction and ground surface subsidence as well. The affected by pile deformation. Figure 12 shows the defor- revetment tilted toward the river by 2 to 3 degrees, and mation of damaged piles which were pulled out after the the crown of the retaining wall subsided 30 to 40 cm. Pho- earthquake. All piles were indented at almost the same depth which approximately coincides with position of the replaced sand layer below the revetment. These facts sug- A B C D gest, therefore, that some of the replaced sand liquefied around the piles during the earthquake and moved toward open water. As a result, the piles became the "pa- ssive piles during earthquake", followed by bending piles.

Precast Concrete Pile Foundation Precast concrete piles are usually used as foundations for relatively light structures, some of which also suffered earthquake damage. An example of damage to a revet- ment with piles against storm surge on the Kanzaki River in Osaka is shown below. Figure 13 shows a cross section

Fig. 11. Cross section of a landing pier with steel pipe piles located near seawall Fig. 12. Deformation of damaged piles

Fig. 13. Cross section of river revetment with precast prestressed concrete piles FOUNDATION DAMAGE OF STRUCTURES 199

Photo. 9. Cracks in three piles around pile top

foundation of a pedestrian bridge around the Harbor Highway. The footing was broken and the integrity of the connection to the pile top can not be assured.

CONCLUSIONS In this paper, the authors tried to evaluate foundation damage to structures from the Great Hanshin-Awaji Earthquake Disaster, focusing mainly on elevated high- ways, together with revealing the damage mechanism for each type of foundation. The main conclusions are sum- marized as follows: 1) Elevated highways, which are located at around the area of very strong seismic intensity and/ or on soft alluvi- al deposits along shore lines, were more heavily damaged. 2) In order to inspect the soundness of cast-in-place bored piles, which are the prevailing foundation type for elevated highways, the bore-hole television (BHTV) sys- tem and direct visual observations provided the most reliable data. 3) Cracks in cast-in-place bored piles occurred near the top of the pile and in the middle to lower portion of the pile length. The former is the position of maximum mo- ment, while the latter might be the position at which the density of reinforcement bars changes, the position of the second largest moment or the interface zone between

Photo. 10. Damage of precast prestressed concrete piles soft and hard soil layers. 4) Foundations on soft ground such as reclaimed land sometimes suffer heavy damage due to the effect of liq- tograph 9 shows some cracks in the three piles around the uefaction and/ or lateral flow of ground. The piles some- pile top, which occurred at some intervals in the vertical times became "passive piles during earthquake", and direction. This damage was caused mainly by liquefac- subjected to lateral flow pressure of subsoils. It is pointed tion and lateral flow of loose sand, followed by a reduc- out, therefore, that a systematic design method for both tion in the bearing capacity. The damaged part of the passive and active piles is desirable. revetment against storm surge was removed and rebuilt. 5) The full-scale field test data by static one-way cyclic Photograph 10 shows another example of damage to loading suggests that even heavily damaged piles have precast prestressed concrete piles, which were used as the still maintain sufficient capacity for lateral resistance. 200 MATSUI AND ODA

6) Most damage to caisson foundations resulted from the movement and inclination toward open water due to REFERENCES lateral flow pressure acting on the foundation from the 1) Japanese Geotechnical Society (1996): "Selected photographs on the lateral ground movement. It is also pointed out that a sys- damage caused by the 1995 Hyogoken-Nambu earthquake," Soils tematic design method should be developed for caisson and Foundations, Special Issue on the 1995 Hyogoken-Nambu earthquake. foundations, considering the effect of lateral flow pres- 2) Kamewada, S., Hu, S. G., Taniguchi, S. and Yoneda, H. (1990): sure. "Application of borehole image processing system to survey of tun - 7) Large-diameter steel pipe piles (more than 1 m in di- nel", Proceedings of the International Symposium on Rock Joints, ameter) were not damaged even in the "passive piles dur- pp. 51-58. ing earthquake", whereas relatively small-diameter piles 3) Kimura, M., Kosa, K. and Morita, Y. (1994): "Full-scale failure tests on laterally loaded group piles", Proc. 3rd Int. Conf. Deep (both steel pipe and precast concrete), sometimes Foundation Practice Incorporating PILETALK International '94, suffered damage as "passive piles during earthquake". Singapore, pp. 147-154. 4) Matsui, T. (1993): "Case studies on cast-in-place bored piles and some considerations for design", Proc. 2nd Int. Geotech. Seminar on Deep Foundations on Bored and Auger Piles, Ghent, pp. 77-102.