INTRODUCTION 1.1 General
2.7 Research outputs! Case studies related to Multi-stage actions
Muller-Rochholz (1994) studied the effects of dynamic loading. The tests showed that a dynamic loading has no significant influence on the creep performance. In fact, if peak load is constant, the dynamically loaded specimen shows less creep deformation. This kind of load history is close to the deformation of mean level of load.
The Combined Sustained-Cyclic Loading test on a range of uniaxial geogrids, carried
out by Khan (1999), have confirmed these results. Traffic flow may be either
frequent (without rest period between the vehicles passing) or rather less frequent
(with rest period). He selected the case with no rest period, as it happened to be the
2.7.2.1 Duration of Earthquake
2.7.2 Combined Sustained plus Earthquake loading
more critical than that with a rest period, because there would be more 'locked in' strain in the material without rest period than the material with a rest period.
Therefore, it may be suggested that dynamic loading can be conservatively simulated by and appropriate sustained loading regime. Further, the practice of considering the traffic load as a sustained load equivalent to the contact tyre pressure by different codes/methods seems to be conservative in contrast to the test results.
Further, it was shown that the strains at the end of Loading and Unloading Phases were close to the strain envelopes obtained from the creep tests at a load level of[ps+
O.SP,]. This means under a total combined sustained-cyclic loading of [Ps+P,J, the uniaxial geogrid behaved as ifit was subjected to a sustained load of[ps+ O.5P,].
Bommer et al (1999) showed that a seismic event is of a cyclic in nature; hence CRS testing is not essentially an appropriate test methodology. The duration of seismic events is important to obtain the realistic test results. During an earthquake, if a structure is deformed beyond its elastic limit, then the amount of permanent deformation would depend on how long the shaking is then sustained, Kupec (2000).
This shaking is defined as the Earthquke Strong Motion by Bommer et al (1999).
Therefore, it is important to ensure that the duration of the strong motion be consistent within the design scenario. The effective duration includes 91% of the total recorded energy released by the strong motion and also considers the rest period between sub-events in multiple events of this type. Khan (1999) showed that the creep deformation depends on these rest periods. A specimen is likely to show higher deformation when subjected to Cyclic Loading without rest periods.
The variation of strong motion duration with distance is complex, i.e. depends on the geology. On one hand, as the energy wave separates due to different propagation
2.7.2.3 Case studies
From these test results it was observed that after the removal of the Additional Short Term Load
[&,],
the geosynthetic is likely to show the same strain behaviour as that of a creep test under a load of25 kN/m, i.e. the sustained load alone. For lower levels of Additional Short Term Load [~P,], e.g. 10 kN/m and 20 kN/m, this was observed within 200 hours of the test. For higher levels of Additional Short Term Load[&,],
e.g. 30 kN/m and 40 kN/m, although this was not observed within 200 hours of the test but it was likely to be observed after a longer period of time.Khan (1999) performed the combined sustained-short term loading test on a uniaxial geogrid. Generally, the seismic shakings are cyclic in nature with irregular frequency.
To avoid the complexities of simulating the actual earthquake loading, it is represented by a uniform load applied over a short period of time.
2.7.2.2 Available test results
velocities and scattering, the duration will increase with increasing distance. On the other hand, energy will decrease with distance due to attenuation of the motion.
The review, of the recent major earthquakes at a distance of less than lOkm from epicenter for soil and rock sites including the Kushiro Offshore Earthquake (I 993) and the Northridge Earthquake (I 994), shows that, although there exist earthquakes with the Effective Durations of the Earthquake Strong Motion larger than 60 seconds, in most cases, they are below 20 seconds, Kupec (2000). This is the reason why the duration of the short-term loading was chosen to be 20 seconds.
White and Holtz (I 997), reported on the performance of seven geosynthetic- reinforced structures (three walls and four slopes) with varying types and methods of reinforcements located in the areas that experienced the shaking of Modified Mercalli Intensity (MMI) from V to VIII during the Northridge California Earthquake of January 17, 1994. In no case was a failure (neither any significant displacement nor
cracks) of the reinforced slope or wall observed, even in the areas where other nearby structures failed.
Similarly, Tatsuoka (1997) reported on the performance of reinforced soil structures during the January 17,1995 Hyogo-ken Nanbu (Kobe) Earthquake with a magnitude of 7.2 on Richter scale, Tables 2.1 and 2.2. It should be appreciated that in general, older RWs (retaining walls) were damaged more seriously while masonry, leaning type and gravity type unreinforced concrete RWs showed a very low stability against the strong seismic shaking. Further, many cantilever type or inverted T-shaped (reinforced concrete retaining walls) RC RWs, mostly without piles performed badly.
Further, a great number of RC (reinforced concrete) columns and piers collapsed by shear failure in a brittle manner.
On the other hand, a number of geogrid or metal-reinforced soil RWs performed satisfactorily. In particular, the geogrid-reinforced soil RWs with full height rigid (FHR) facings that were constructed in 1992 at Tanata did not collapse despite the fact that the site was located in one of the most severely shaken and damaged areas.
Based on these experiences, many damaged embankment slopes and conventional RWs were replaced with GRS-RWS with (full height rigid) FHR facings, Tatsuoka et al (1997).
One of the two (geotextile reinforced soil retaining walls) GRS-RWs without FHR facings that experienced the earthquake showed no problematic deformation despite the cracks with a maximum opening of 20cm appeared on the ground surface in front of the wall and unequal settlement of 20cm was observed. While in the case of another wall, the ground settled unevenly and large crack reached to the subsoil below the facing blocks due to liquefaction in the subsoil in front of the wall. Yet, the deformation of the facing was smaller than that in the subsoil.
Similarly, of the four GRS-RWs that experienced the quake, the three were located in the area where (Japanese Meteorological Agency seismic intensity) JMA scale was V or VI. In two cases, no deformation of the wall was observed, while in the third case the wall moved outward about 2cm maximum at the top ofthe facing. The GRS-RW
These GRSSs, thus survived, were designed as per limit equilibrium-based pseudo- static static analyses using relatively a low seismic coefficient k
h=0.20. Probably, this situation results from a consideration that in case soil structures in secondary applications are damaged, the influence of damage would not be vast and serious and they could be easily repaired. On the other hand, use of higher k
hvalues could lead to uneconomical structure. The seismic stability of the GRS-RWs was evaluated by the two-wedge method, Horii et ai, where the seismic loads are resisted mainly by the tensile force in the reinforcements and partly by the reaction force at the bottom of the facing.
located at Tanatata experienced the highest seismic load among the modern GRS- RWs and hence the scale of damage to this wall needs to be appreciated. The bottom of the wall moved outward on average about Scm relative to the supporting foundation subsoil, pushing the subsoil in front of the wall laterally. At the highest part of the wall, the largest outward displacement occurred, which was 26cm at the top of the wall and 10cm at the ground surface level. Despite the noticeable movement of the wall, the performance of the GRS-RWs were considered quite satisfactory, since in the areas adjacent to these GRS-RWs with FHR facings a number of wooden houses, railway and highway embankments and conventional types ofRWs were seriously damaged.
The design standard for railway earth structures (Ministry of Transport, 1992)
specified the minimum allowable length of grid reinforcement for GRS-RW system
to be the larger value of either 35% of the wall height or 1.5m. For most of the GRS-
RWs constructed so far, to be conservative, several reinforcement layers were made
larger than the others at lower levels. However, for Tanatata GRS-RW, all the
reinforcement layers were truncated to nearly the same length due to construction
constraints that is similar to that adopted in the design of modern GRSSs. This
truncation might have reduced the seismic stability of the wall, particularly in terms
of overturning.
Further, several GRSSs were found to maintain stability during the Lorna Prieta Earthquake in 1989 having a magnitude of 7.1, Collin et al (1992), and Kushiro Offshore Earthquake in 1993 having a magnitude of7.8, Fukuda et al (1994).
The GRSSs that survived the quakes, particularly the Kobe, were designed with a low seismic coefficient kh=0.20 and the reinforcements were curtailed to the same lengths (Tanatata) due to construction difficulties, i.e. the lengths were not as per the railways guidelines. Yet, they did not fail except with a noticeable displacement, although other structures in the vicinity were badly damaged. This indicates the conservatism inherent in the design of the GRS-RW. The above data lead to the conclusion that the GRSSs were in deed capable of taking greater loads, had it been applied rapidly.
The development of designs for GRSSs involving earthquake forces is presently empirical. Fukuda et al (1994) reported that until 1993, the GRSSs were designed for seismic forces on the basis of the procedure for design under ordinary static conditions, as given by Jewell et al (1984). In this procedure the long term creep rupture strength of geosynthetics was used as Reference Strength.
Later, it was suggested by Fukuda et al (1994), AASHTO (1994) and Jones (1996) that the Design Strength of geosynthetic for sustained loading condition should be increased by 1.5 times when designing for sustained loading plus short term earthquake loading. In the recent codes/methods, as more confidence is gained from the performances of GRSSs during recent earthquakes, factored short term CRS strengths of geosynthetics are suggested for use in designs against sustained loading plus short term earthquake loading, AASHTO (1997), NCMA (1997) and DIBt (1998). Nevertheless, the considerations of higher strengths of geosynthetics, from 1994 to 1998, were all empirical without any concrete justification.
An important aspect that may be noted that all these GRSSs were constructed very recently prior to the event, i.e. the time interval between the construction and the occurrence of the earthquake was not more than five years. This may be the possible reason for their survival of the shocks, since there would be more 'available' strain
and less 'locked in' strain during the initial phase of the operational life in the geosynthetics and the reverse during the later phase. Inother words, the GRSSs could take more loads in the initial part of its design life due to greater available strain but less load in the later stages of its design life due to lesser available strain. Therefore, it is unlikely that the GRSSs would be able to take the same amount of load throughout their design life regardless of the time of occurrence of the earthquake.
Those GRSSs might not have survived the earthquake, had they been hit during the later part of their design life. If it were so, considering the same design strength of geosynthetics over the entire operational life of the GRSSs is likely to be unsafe.
Facility SUe Location 'f)'pe of wall HeightlLength Subsoil Brief description of
of wall Condition damageIPennanent
restoration metbod
Railway MSI Between Setsu.Motoyamll & Mnsonry 4 m/50m - Total Collapse! GRS-RW
Sumiyoshi Slutions of m Kohc I,inc
Railway MS2 Adjacentof Hanshin Main Lineto Nlshi-Nada Station Masonry 3.4SOxlm !o3.8m! - Tiltingsctt1ement ofof uppercmbankmentJwall, GRS-RW
Road MS3 City Road Nishi-Nada-Harada & Masonry Max. about 5m1 - Vertical &Horizontal crocking
Rokko-.Sannomiya Lines o. 70m of wall, lateral deformation &
Iwayakila ] & 4-chome, Nada-
settlement of embankment Ku, Kobe city
Railway LTI BetweenSumiyoshi StationsSetsu-Motoyamaof JR Kobe& Leaning -type 2.6m1500m Pleistocenegravel Completebreakage at the level of subsoiloverturning, portia!
Line fN m surfaoet GRS-RW, RW with
=15-50up) embankment reinforced by large diameter nailinli!.
Railway LT2 Between Okamoto & Mikagc Leaning -type S.Om/500xlm - Tilting on both sides., cracking Stations ofHankyu Kobe Line
near the bottom, settlement of embankmentJ V-shaped RW
--. ---. filled with cement treated soil
Road LT3 City mad Higashi-Nada-Sato No Leaning -type Max. about 5m1 Vertical opening &horizontal
143 Line at Higashi-Nada. Ku, 160m sliding at construction joint/
Kobe city
partial reconstruction to increase wall heiAAt
Railway GTI Hanshin main lineAdjacent to Jshiyagawa Station of C'Ifavlty.type 5.0m/1OOx2m Holocene Tilting on both sides, partial sand (NSI'T breakage at construction joint
=1 ()-.]O) &overtumin21 viaduct Road GTl City road Ookubo No 18 line at GrllVity -type Mnx. 3.0/160m - Tilting, Longitudinal cracking
Ookubo-eho, Akashi city
of ernba:n.lanenV reconstruction of original RW
Railway CLl Betweenstations of JR Sanyo LineByogo & Shin-Nagata Cantilever-type 4.0m/400x2m - Tilting on both sides, settlement of embankment, defonnation of foot path!
reinforcement by anchoring &
tie rods
Railway CL2 AtSanyo lineShin-Nagata Station of JR Cantilever-type 4.1mfor overlying( +5.3m clayHolocenefN"" Tiltingthe middle height, settlement of&sliding,. Cracking at
emhankment,Y =5) embankmentJ GRS-RW,
200m Cantilever type R W with pile
foundation
Railway CLJ At TanatataKobe LineSetsu-MotoyamaBetweenstationsAshiya &of JR foundationCantilever.typew;th pile 5.4m150m HolocenesandfN &clay Tiltingembankment/reinforcement&sliding, settlement ofby
"" horizontal tie rods connected to
=25-50 & upper RW adjacent to RC box 10-25)
Railway CL4 Adjacent to Ishiyagawa Station ofHanshin main line Cantilever-type 5.0m/30m Holocene Tilting, crocking at the middle sand (NSPT height of a section without
=I()-.30) counterfortsl viaduct
Railway CL5 Between Higashi- NadaKou(freight branch)stations of JR Kobe Line& Kobe. Cantilever-type embankment)!4.5mfor overlying( +1.6m - bottom,embankmentJTilting, Crockingsettlementcut offnearsheettheof
50m piles with tie rods & upper
bock fiJI reinforeed by geogrid Road CL6 PrefacturalMondosou Linehighwayot Koma-No-Shiozc- Cantilever-type About 4m/80m (adjoiningwaterway) Subsidence, tilting & sliding ofwall, longitudinal fisswing of
Machi, Takarazuka city
embankment reconstruction of originalRW
restoration method
Rom! CL7 City road Yamatc Main Line at Cantilevcr.type About 3m160m - Tilting of wa1~ longitudinal
Yuminoki.I-Chome, Nada-Ku, fissuring of embankment! Terre
Kobe city Annee
Rom! CL8 City Road Nishi-Nada-Harada Cantilever - Max. about 5m/ - Tilting and vertical cracking of
""d Rokko-Sannomiya Lines at type? 250m wall, opening of vertical joint,
lwaya-Kita 3 & 4<nome, Nada- (not conlinncd) settlement of embankment/
ku, Kobe City TerreArmee
Rom! CL9 Regional Highway 13aiko- Cantilever- Max. 3.7m! - Tilting of wall (cracking of
Hamabcdori-Wakihama Line
.,
typc? 310m side wall of RC box culvertMasago-dori I &2<homc, Chou- ~not conlinncd) adjoining the wall).
ku, Kobe City Reconstruction of original
Rood CLI Regional Highway Sanroku Line Cantilever- Max. 4.5mJ Holocenc RW?Slicing of wall. Reinforcement 0 at Hiyodorigoc, Hyogo.ku, Kobe type? 40m "",d (N '" by earth anchor fixed to finn
City (not confirmed) =3-50) subsoil
Railway CLI Shioya Station of Sanyo Dentetsu Cantilever-type About 4m.l - Tilting of walV viaduct
I Line 360m
Rom! UBI City Road Ashiya-hama Line at V-shaped with About 2mJ - Uneven settlement and tilting!
Midori-cho, Ashiya City inner backfill 560m reconstruction of original RW,
correction of wall hei£ht Railway GRI At TanattJfJIbetween Ashiya & GRS with rigid Max:. 4.5mJ Holocene Tilting and sliding, partial
Setsu-motoyama Stations of JR facing 300m sand &clay cracking of facing at the
Kobe Line (N
'"
middle height, settlement of=5-50 &5) embankment! reinforcement by horizontal tie-rods connected to upper RW adjacent to RC box P",k GR2 In Maihama Park at Ashiya-hama, GRS with 5.3m ( +l.Om - Uneven settlement and opening
Ashiya City concrete-block for overlying of facing blocks (+extensive
facing embankment)! sand boil and fissures due to
90m liquefaction at the subsoil
surfa", )/'I
Rood GR3 Near approach road to Akashi GRS W'ith flex. Max. 4.0m! - 8light differential horizontal
Kaikyo Bridge (under Metal-mesh 9Sm movement of sound banier
construction) at Maiko, Tanuni- facing foundation at the lop of
ku, Kobe City
embankment (uneven
settlement & fissures at the subsoil~)
Railway GR4 Ncar Amagasaki Station of JR GRS with rigid Max. 8m (av. - No damage
Kobe Line facing 5my IOOOm
(including two abutments by GRS-RW)
Railway GR5 Near approach road
'0
Akashi GRS with rigid Max. 6.7mJ - No damageKaiyo Bridge (under com•.truction) facing 150m atMaiko, Tarumi-ku, Kobe City
Railway GR6 NearKone LineAmagasaki Station of JR DRS with rigid Max. 8m1400m - No damage
lacing
Rood MA Kita-Kobe Line of Hanshin Multiple- Max. 4.6mJ - Tilting of cap concrete without
Express way at Kami.Tanigami, anchor- 24m anchors at the top ofRWn
Yamada-eho, Kita-ku, Kobe City reinforced soil willi RC Ihcm2
Road TAl National Highway Route No.28 at Terre Armcc MaX:.8.9mI?m - Tilting of facing, partial
Hokulan-cho, Awaji Island cracking of facing at the
comer! reconstruction using lengthened metal-strip
orWlu Condition damageIPermanent restoration method
Pari< TA2 In Hoshi-ga-oka Park al Tarumi- Terre Arnlee Max. 5.1ml - Tilting and sliding of facing,
ku, Kobe City 43m partial cracking of facing at the
corner/?
Others TA3 In Midori-ga-oka Pool at Hami TcrrcAnncc Max. 33m! - Tilting of facing, partial
Cily 36m
cracking of facing at the oomer, settlement of embankment/?
Road TM Approach Road to Akashi Kaikyo Tl.'1Te Annee Max.6-7ml 1m - Noticeably compressing at the
Bridge (under construction) at bottom offacingf7
Maiko,Tanuni-ku, Kobe Citv
RW; retaining wa1I, GRS: geogrid.reinforccd soil, Terre Amlce: metal-strip reinforced soil with discrete RC facing
Fadlity Site Location Slope angle! Height! length Sublloil Brief description of damagel
facing condition of condition pennanent restoration
embankment method
Railway EM! Between Hyogo &Shin-Nagata 1:1.51 cas1-io- 4.4m! 450m - Settlement and lllteml
Stations of JR Sanyo Line place concrete (full deformation, sliding of
lattice and embankment) concrete facing/embankment
precast concrete partially reinforeed by
pancl gcogrid and covered with
, =embmne (artificial lawn Railway EM2 Between Higashi-Nada &Kobe- l :1.5/ vegetation 6.0m! 320m - Settlement and IlIleral
kou Stations of JR Kobe Line (full deformation, longitudinal
(freight branch) embankment) crack! embankment
reinforced by large diameter nailinlZ
Road EM3 Ookum-dani Interchange of the - 15m! 30m (full Soft clay Collapse of embenkm.ent/?
Second Shinmei Expressway embankment) and partial
sand (N,,.,.<S, fonner pond)
Road EM4 Regional Highway Kobe- 1:2.01 precast 7m! 1m (balf (existing Sliding of slope and filcingI Kakogawa-Himeji Line at concrete panel bank) pond at reinf=emcn! by sheet pile
Zenkai, Ikawadani-cho, Nishi- slope toe) driven at the middle of slope
ku, Kobe City
Road EMS Regional Highway Kobe- - Max. 8m! 1m (existing Collapse of embankment/?
Kakogawa-Him~i Line at (balfbank) pond at
Minami, Kande-cho, Nishi-ku,- slope toe)
Kobe City
Road EM6 Regional Highway Kobe- - ?mI?m (existing Sliding of slope/?
Kakogawa-Himeji Line at Wada, (balfbank) pond al
Oshibedani-cho, Nishi-ku, Kobe slope toe)
City
Road EM7 Miki CityCity Road Fukui Line at Fukui, - Max. 13m166m(full pond(existing at Collapseprotection ofworkembankment!against
embankment) slope toe) seepagc of waIer from existim! ncmd?
Road EMS Tovm. Road Urn No.105 Line atKusumoto,Tsuna DistrictHigashiura Town, - (balfbank)?m!1l6m (swamp) reconstructionCollapse of embankment!of original
embankment
Road EM9 Town Road Takataki Line at
-
Max. 7.5m! (swamp) Collapse of embankment!Ikuho, Tsuna Town, Tsuna 34m cast-in-place concrete lattice
District (balfbank) and partial drainage mat in
embankment
Road EMIO LineTown, Tsuna DistrictTownat Takayama,Road Hirata-ShitamichiIchinomiya - (balfbank)?mI39m - Collapsereconstructionof embankment!of original
embankment