Statistical results of the damage which occurred mainly in Hyogo Prefecture from “the 1995 Hyogoken-Nambu Earthquake” are given. Introduction of Hyogo Prefecture, earthquake overview, and earthquake damage and its recovery to lifeline, highway, railroad, and harbor are presented.

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More than 200 strong ground motions were observed during the 17 January 1995 Hyogoken-Nambu earthquake over a wide variety of subsurface ground conditions including rock and stiff or soft soils. Key parameters of the records, such as peak ground acceleration values (PGAs), were immeadiately published by many organizations, such as CEORKA (the Committee of Earthquake Observation and Research in the Kansai Area), JMA (the Japan Meteorological Agency), PWRI (the Public Works Research Institute, Ministry of Construction), PHRI (the Port and Harbour Research Institute, Ministry of Transport), RTRI (Railway Technical Research Institute, Japan Railway Companies), the Kansai Electric Power Co., Osaka Gas Co. and others. This paper presents a preliminary overview of strong ground motion characteristics using these records especially focussing on peak ground acceleration. The main results of this study are that (1) S wave radiation from strike slip fault can explain the regional distribution of PHGAs during this event, (2) High PGAs observed in the strike direction area have been strongly affected by the directivity effect and (3) The unusually small PHGA/ PVGA ratios near the fault rupture zone have resulted from the strong nonlinearlity of the subsurface soils.

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A number of civil engineering structures in a large area Kobe-Hanshin and Awaji in southwest Kinki, southwest Japan, were seriously damaged by the 1995 Hyogoken-Nambu earthquake. Geological studies were made to reveal both geological and geotechnical characteristics in and around the Osaka sedimentary basin. A geological map of the Osaka Plain and the surrounding area was compiled for the geotechnical engineering use.
A Bouguer gravity anomaly map is presented with additional gravity measurements for an evaluation of the subsurface geologic structure. Data on the depth of the basement rocks was collected from information on deep drilling for the geologic survey or hot springs, reflection seismic exploration and surface geological survey. A configuration map of the basement rock forming the bottom of the Osaka basin was also compiled from the depth data collected and an analysis of the correlation between the depth and the Bouguer anomaly was attempted to outline the relief image.
In order to assess the contribution of underground structure with faults to the distribution of structural damage, the focusing process of seismic wave was examined by using the ray theory applied to model the Uemachi Fault zone, which is located in a dense urban region in the Osaka area. As a result, the efficiency of the focusing based on a common underground structure with fault was substantiated qualitatively.

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Vertical array records obtained at Kobe Port Island during the Hyogo-ken nanbu earthquake were analyzed. Acceleration records at four different depths were obtained. The peak horizontal acceleration was minimum at the ground surface and increased with depth, whereas, the peak vertical acceleration, the peak horizontal velocity, and displacement all decrease with depth.
The de-amplification of the horizontal acceleration was due to non-linear effect of soils.The amplification of the vertical acceleration was caused by small P-wave velocity in the unsaturated fill layer which resulted in a large velocity contrast at the boundary between the unsaturated and saturated layer.
Using ground response analysis, the equivalent linear soil parameters were obtained for 50% of the rigidities of the shear wave velocity with PS-logging.
A method of synthesis of strong ground motion by summation's aftershock records was applied to simulate the main shock at the ground surface and at a depth at GL-83 m. Synthesized strong motion at GL-83 m compared relatively well to the recorded one. Strong ground motion synthesized at the ground surface indicated twice larger peak acceleration than the observed. The smaller amplitude observed at the ground surface was due to the non-linear effect of soils.

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During the 1995 Hyogoken-Nambu earthquake, strong acceleration records were obtained at several sites in and around Kobe city. At some of these recording sites, multi-level vertical arrays had to been installed, which demonstrated very peculiar nonlinear features of seismic amplification in reclaimed land areas and Holocene and Pleistocene deposits. The down-hole acceleration records on Port Island where one of the strongest accelerations was measured, have been analyzed with the inversion technique to estimate S-wave velocity and damping ratio corresponding to the main shock as well as a small aftershock. Records of three other down-hole sites with much different distances from the epicenter between them were also analyzed with the same technique. These studies disclosed effects of soil liquefaction and nonlinear soil properties on the peculiar seismic amplication mechanism at these sites.

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Landslides triggered by the 1995 Hyogoken-Nambu earthquake were reviewed based on air photo interpretation for their distribution. Landslides were almost linearly distributed along the line of aftershocks. Most landslides showed limited motion probably affected by less saturated soil condition due to the very dry season. The Osaka group layer, however, retained the ground water and rapid landslides took place there. The Nikawa landslide and the Takarazuka landslide were investigated as case histories. The undrained cyclic loading ring shear test suggested that this landslide showed a rapid motion due to the high pore pressure generation caused by grain crushing along the sliding surface. It can be called “sliding-surface liquefaction”.
The trench investigation for the Takarazuka landslide and the previous undrained loading ring shear test for the Sale landslide suggested that the high mobility of the Takarazuka landslide was caused by the undrained loading onto the saturated layer. The sliding surface was formed inside the saturated layer below the ground surface, and the landslide mass moved scraping the surface soil layer above the saturated layer.

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The results of an investigation of soil liquefaction caused by the 1995 Hyogoken-Nambu earthquake are described. Massive and extensive soil liquefaction occurred in the coastal areas of reclaimed land, in old river beds, in Holocene deposits and in areas reclaimed from old ponds. A man-made island of weathered granite, or “Masado, ” was also seriously damaged by soil liquefaction. The maximum distance from the epicenter to the liquefied sites was approximately 90 km. Several characteristics of liquefaction formation, strong earthquake motions recorded on Port Island, and damage to structures from this earthquake are discussed.

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This paper introduces an outline of liquefaction-induced large ground displacement and the damage to lifeline facilities, and foundations of buildings and bridges piles during the 1995 Hyogoken-Nambu earthquake. Some typical examples of large ground displacements which were measured by aerial survey are presented and the causal relationship of damage to buried pipes and foundation piles with ground displacement is introduced. In addition, the present paper outlines the soil and geomorphological conditions in the areas where the liquefaction and the large ground displacements occurred.

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Liquefaction occurred at many sites along Osaka Bay during the 1995 Hyogoken-Nambu earthquake (the Great Hanshin-Awaji earthquake disaster) and caused extensive damage to buildings, bridges, quay walls, etc. The authors conducted detailed site surveys at the liquefied sites and found a remarkable phenomenon. Some zones in two big artificial islands, Port Island and Rokko Island, in Kobe City, did not liquefy even though the zones surrounding the islands liquefied. Damage to buildings and ground subsidence in these zones were also less severe than the damage and subsidence in the surrounding zones. Based on a study of the soil conditions in these islands, it was found that the non-liquefied zones had been improved by several methods, including sand compaction piles, rod (vibro) compaction, sand drains and preloading, before buildings had been constructed on them. These ground improvement methods were effective in mitigating liquefaction even though the ground shaking was as extreme as more than 400 gals of maximum surface acceleration.

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Soil conditions in reclaimed islands which were devastated by extensive liquefaction during the Kobe earthquake are described together with the soil strength which was obtained from the laboratory tests on undisturbed samples. Interpretation of this soil strength is given in the light of back-calculated shear strength based on accelerations recorded on the ground surface.
Observed settlements of the ground surface resulting from liquefaction are described and evaluated in terms of the values estimated based on existing methodology. Finally, the outcome of an in-situ survey on permanent deformations of the land areas behind a quaywall or revetment is presented. As a result it was possible to identify the characteristic patterns of the displacements which vary with the distance from the waterfront inland.

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Many caisson type quay walls were damaged in Kobe Port during the 1995 Hyogoken-Nambu earthquake. Seaward displacements of the caisson walls were about 5 m maximum and 3 m average. Although the caisson walls also tilted and settled, they did not collapse or overturn and deformed quite uniformly maintaining almost straight face lines of the walls along the port front alignment (pier head).
The high seismic resistant quay walls of a caisson type, which were specifically designed for unloading emergency supplies, performed very well and resisted the strong earthquake motion.
Geotechnical investigations including in-situ soil freezing sampling and shake table tests were performed in order to understand the mechanism of deformation in the caisson walls. The displacements of the caisson obtained from the shake table tests agreed very well with those measured in Kobe Port after the earthquake. The results of these investigations suggested that the excess pore water pressure increase in the foundation soil underneath the caissons and in the backfill soil significantly increased the deformation of the caisson walls.

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The Hyogoken-Nambu earthquake hit Kansai area in the pre-dawn hours on January 17 1995. One of the worst affected areas was Kobe and its vicinity. Large scale damage brought on by the severity of the earthquake were observed due to soil failure, structural failure etc. Failure patterns have been classified especially for revetments, quaywalls and petroleum storage tanks. Emergency restoration was undertaken to bring back various facilities to normal operations. Some typical which have been restored sections are discussed in this paper. These restored sections may provide information on various aspects of countermeasures that can be taken in waterfront areas.

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Liquefaction and related phenomenon that occurred during the 1995 Kobe earthquake are discussed. The field investigation showed that the sites where liquefaction occurred are located in the area of recent reclamation near the sea. Although liquefaction occurred significantly in the harbor, there is no evidence of liquefaction near the quay walls which failed. It was also demonstrated that surface motion records can be used to estimate the thickness of liquefied subsoil. Shaking table tests were conducted on quay wall models to demonstrate a limited development of excess pore water pressure behind a wall. It seems that the large displacement of walls in Kobe Harbor can occur without liquefaction when the intensity of seismic inertia force is as strong as that which was experienced in 1995.

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The 1995 Hyogoken-Nambu earthquake severely damaged coastal facilities and reclaimed land in the Hanshin area. This report summarizes the outline of the reclaimed land at Naruohama on the basis of the previous investigations. And then this report discusses the damages caused by the earthquake to the reclaimed land at Naruohama by means of the leveling and the grain size analysis conducted by the authors. A summary of the damage is as follows; Sand boil due to liquefaction occurred mainly in the western part of the reclaimed land area, as well as in the part of the reclaimed land near the original shoreline. The degree of settlement caused by the earthquake ranged from 0.3 to 42.5 cm, and averaged 13.3 cm. The ratio of the degree of settlement due to the earthquake to the thickness of the sand stratum above the alluvial clay stratum ranged from 0.03 to 4.12%, and averaged 1.14%. No significant settlement caused by the earthquake was observed in buildings supported by approximate 30 m-long piles.

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This paper reports the deformation of composite breakwaters in the port of Kobe, due to the 1995 Hyogoken-Nambu earthquake. Two types of acoustical surveying technique were employed to characterize the underwater surface around breakwaters No. 6 South and No. 7. A multi-narrow beam sonar was used for geometrical measurements, and a side-scan sonar was used for revealing geological and dynamic features of the seabed. The cross section profiles obtained from surveying with a fan of multi-narrow beams are presented, showing a clear picture of the deformation that occurred in the rubble mound. Several circular depressions were found in the side-scan image showing the seabed about 10 m away from the toe of the rubble mound in breakwater No. 6 South. They appear to be sand boils. By comparing the side-scan images of breakwaters No. 6 South and No. 7 it can be seen that the surcharges over the sand surface should suppress the occurrence of liquefaction to some extent. The surcharge effect is discussed with emphasis on the stability of composite type breakwaters, referring to the results of shaking table tests conducted on the saturated sand deposits with model structures.

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The epicenter of the main shock of the 1995 Hyogoken-Nambu earthquake was very close to the construction site of the Akashi Kaikyo Bridge, which will be a three-span, two-hinge stiffening truss suspension bridge with a total length of 3,910 m upon completion. The bridge consists of tower foundations, anchorages, towers, cables and girder.
At the time of the earthquake, the main cable installation had been completed and the working had reached the stage of cable squeezing. Immediately after the earthquake, a structural inspection, a survey of pier locations using an optical distance measuring instruments and a global positioning system and a geotechnical investigation were conducted. The basic information and technical data related to the earthquake and its impact including the displacements of the foundations on the Akashi Kaikyo Bridge are described in this paper.

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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 around surface.

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An outline of the results of investigation into the damage and reconstruction of foundations of railway structures is presented in this paper prepared by committee members of the Japanese Geotechnical Society. The foundations of elevated bridges near a quay or a river levee moved and inclined due to the movement of the surrounding subsoils. Mat foundations for an elevated rigid frame bridge did not undergo damage whereas meshed cracks or complete shear failures were found in the piers below the ground surface. Cracks were found frequently at the top of the pile foundations for bridges supported on one-pier.

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A relatively large up-down vibration was recorded during the 1995 Hyogoken-Nanbu earthquake. Many people in Kobe area felt a strong up-down shock at the beginning of the earthquake. The effect of this vibration is not normally considered in the seismic design of bridge piers. Many different types of failure and damage of bridge piers were observed after the earthquake. Most of the concrete piers were damaged by bending or shear, or a combination of the two forces.
Some damages in a pier such as a racket type, however, seem to be affected by uniaxial tension. Seismic analysis of bridge piers was performed to check the effect of up-down vibration. Evaluation of up-down impact effect on bridge piers and chimneys was also attempeted. The time dependent dynamic analysis represented the shear or bending failure of the piers and the analysis confirmed that the up-down vibration recorded during the earthquake only had a minor effect on the failure.
Analysis of piers due to up-down impact load indicated the possibility that concrete bridge piers might be affected by the uniaxial tension which was imposed at the beginning of the earthquake. A strange failure associated with horizontal cracking which occurred near the top of bridge columns might have been affected by the up-down impact.

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An overview of the geotechnical aspects of the building damage in the 1995 Hyogoken-Nambu earthquake is presented. It is shown that (1) the damage to buildings was caused by either strong ground shaking or ground problems, each of which combined with inadequate design of buildings, and (2) the pattern, extent, and distribution of the damage were significantly affected by local soil conditions as well as ground failures including soil liquefaction. Typical features of the ground problems are settlement and/or tilting of buildings. Possible causes of the foundation damage include : (1) horizontal forces and overturning moments imposed on the foundation from the superstructures, (2) kinematic forces acting on deep foundations due to shear deformation of soils, (3) reduction in bearing capacity due to ground failures including liquefaction, and (4) lateral spreading. The damage to pile foundations caused by Categories (1) and (4) has posed particularly serious problems. Despite extensive soil liquefaction, the engineered buildings on Port and Rokko Islands performed relatively well, probably due to (1) ground surface motions attenuated by soil liquefaction, and (2) indirect effects of foundation designs related to consolidation settlement. The buildings for which remedial measures were undertaken to mitigate liquefaction hazards, were found to have performed well.

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Among the rivers damaged by the earthquake, two most severely damaged along the Yodo-gawa River are described. In the left levee, the settlement exceeded 2 m for a length of 1.4 km, with a maximum settlement of 3 m. Sand boils were observed extensively on the ground surface near the damaged dikes. Holocene sandy soil with an SPT N-value of 10 or less existed in the upper part of the subsoil profile. These facts indicate that liquefaction of the soil was the major cause of the embankment damage. The cyclic stress ratio required to cause liquefaction was 0.30 as determined from cyclic triaxial tests on undisturbed samples.

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Levees with masonry and concrete-block walls underwent collapse and destortion between the central Kobe and Nishinomiya where the most severe damage was sustaind. In a coastal area, levees sustained characteristic deformation of the soft ground. In a reclaimed land liquefaction of the fill brought about excessive deformation in revetments of levees. Levees in the Muko River on the eastern foot of Mt. Rokko suffered from settlement, distortion and cracks. The Ina, Mo, Kanzaki, nakajima, Samondo, Aji and Shorenji Rivers were damaged where a thick soft sandy deposits underlay and old meanders were also found in some locations. In a port area, excessive distortion and cracks occurred in levees, while heavy concrete revetments supported by long piles which resist against the storm surge were little damaged. This paper outlines the structural, geological and geotechnical aspects of earthquake damage to levees in Hanshin region but damage to the Yodo River is excluded.

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This paper summarizes the damage to several agricultural facilities during the 1995 Hyogoken-Nambu earthquake, namely, dams, farming ponds embankments, head works, farming roads and channels. Case histories on seven dams are dealt with; Tokiwa dam, Taniyama dam, Otani dam, Kojiya dam, Dondo dam, Okawase dam and Kamogawa dam. Details on the damage to each item are listed and their characteristics are discussed.

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As a result of the 1995 Hyogoken-Nambu earthquake, about 1,200 relatively small-scale earth dams used for irrigation suffered some sort of damage. Since there was such an enormous number of damaged areas, survey data have not yet been sufficiently compiled. Using the results of damage and soil surveys obtained so far, this paper describes and characterizes the damage sustained by earth dams.
Damage was seen in earth dams within a radius of 90 km from the epicenter, with most of it occurring within a radius of 30 km. Compared with previous earthquakes, major damage was of a greater extent from this 1995 occurrence. Damage in some of the earth dams subjected to soil surveys may have been caused by liquefaction. In fact, there is a strong possibility that liquefaction may have been responsible for large-scale damage such as “rupturing”.
Finally, data from this and previous earthquakes proved that a constant relationship exists between the anticipated maximum damage rate of earth dams and magnitude, which is a function of the average distance of a region from the earthquake's epicenter.

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Immediately after the earthquake, emergency inspections of dams were carried out in a wide area around the epicenter, and Public Works Research Institute made inspection visits to dam sites to investigate the effects on the dams. Their results are reported in this report. Emergency inspections and investigation by PWRI confirmed that there was no major damage to dams, excluding some slight effects, nor other problems seriously affecting dam safety or requiring immediate protective countermeasures.
Meanwhile many acceleration records were obtained at dam foundations, and they are also showed in this report.

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A detailed Reconnaissance survey was conducted at the Daikai subway station which is the first subway structure that completely collapsed due to the earthquake. The station is a box frame structure with columns at the center, measuring 17 m wide and 7.17 m high in the exterior dimensions, and 120 m long. A complete collapse occurred in more than half of the center columns, which resulted in the failure and collapse of the ceiling slab and subsidence of subsoils over the station by more than 2.5 m at maximum. Many diagonal cracks were also observed on the walls in the transverse direction.
Judging from the damage pattern, a strong horizontal force was imposed on the structure from the surrounding subsoils below the ground surface. The relative displacement of the surrounding soils between the ceiling level and base level during the earthquake and the inertia force of the overburden soil transferred to the ceiling slab are supposed to cause the damage. Evidence of damage due to vertical force was not clearly observed.

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There are over one hundred mountain tunnels in the hazard area of the 1995 Hyogoken-Nambu earthquake. Over thirty tunnels were affected by the quake including minor damage. About ten tunnels required countermeasures. In the Rokko Tunnel of the Shinkansen, many shear cracks occurred in the arch crown. In the Bantaki road Tunnel, a portion of the lining concrete in the arch and side wall fell down. In the Shioyadanigawa Water Tunnel, some cracks occurred and it slipped 8 cm due to movement of the Yokoosan Fault. Generally, compared to the catastrophic surface damage, tunnel damage was not severe and most of the damage was found in fracture zones.

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During the Hyogoken-Nambu earthquake of January 17, 1995, many conventional masonry and unreinforced concrete gravity-type retaining walls completely collapsed, whereas many modern cantilever-type reinforced concrete retaining walls were also seriously damaged. Geogrid-reinforced soil retaining walls having a full-height concrete facing with a total length of about 2 km performed very well. It should be noticed that a wall located in one of the most severely shaken areas deformed only slightly. The performance of geogrid-reinforced soil retaining wall, as documented, will foster future confirmation and development of aseismic design procedures.

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Earthquake damage to water supply pipelines during the 1995 Hyogoken-Nambu earthquake was investigated. An overview of the damage to water supply pipelines in the Hanshin area is presented and the relationship between the damage to water supply pipelines in Kobe city, geological features and damage to buildings is discussed. The damage is compared with that which occurred from past earthquakes. The study lead to the following conclusions. (1) The majority of failures occurred in pipelines of relatively small diameter. (2) The damage rates for asbestos cement pipe and vinyl pipe were high. The replacement of old pipe such as asbestos cement pipe is urgently required. (3) Joint separations were extensive. Joint separations for cast iron pipe occurred in the older lead and mechanical joints. (4) Liquefaction caused extensive damage to pipelines. The ductile cast iron pipelines with earthquake-proof joint did not suffer damage even in the liquefied area. The effect of earthquake proof joint was confirmed. (5) Since damage to the pipe fittings such as valves, hydrants, etc., was extensive, the strength of the pipe fittings should be improved.

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Damage to the public sewerage systems for six cities in the Hanshin area due to the 1995 Hyogoken-Nanbu earthquake was summarized as 140 km pipelines, 19 treatment plants and 32 pumping stations. Characteristic features of the damage compared to those in past earthquakes were as follows : 1) distribution of damaged pipelines in Nishinomiya was concentrated both in liquefied zones of the coastal area and in an area surrounded by two faults, 2) three large concrete pipelines were heavily cracked longitudinally, 3) internal concrete linings in sewerage shield tunnels were cracked causing water leakage, and 4) the Higashinada treatment plant suffered serious damage due to liquefaction, whereas the Port Island plant was sound due to soil improvement to increase the soil's resistance for liquefaction.

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The 1995 Hyogoken-Nambu earthquake of January 17, 1995 resulted in a devastating damages to the highly developed urbanized region of Kansai, and created a total of 20,000 Gg (20,000,000 ton) of debris. Debris clearance in two years became an urgent and difficult emergency management issue for the disaster managers in Kobe city and Hyogo prefecture. The status of debris clearance was reviewed for each of the demolition operation phase, transportation, crushing and separation at a temporary storage location, disposal at final landfill site phases in terms of problems and state of progress. In practice, most of the debris may be either disposed of at landfill sites or reused as materials for construction. Therefore the debris clearance operation should focus on the geotechnical engineering approach as an important post-disaster issue to control the quality of the incoming flow of potential soil materials. The importance of an emergency management perspective in this geotechnical approach which takes into account the different criteria related to the operation execution is proposed.

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