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 Kobe, Ashiya, and Nishinomiya 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 Hanshin-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) Hanshin Expressway All structures are, in some way, supported by subsoils. No. 3 Kobe Route, 2) Hanshin Expressway No. 5 Bay Because most civil engineering structures are heavy, the Route, 3) Meishin Expressway, 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 Osaka 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, Suita, 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, Japan. 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).