Adis Skejic

This paper presents the details of experimental and numerical analysis performed on three 0.8 m-high reinforced earth model walls with strip footing surcharge near the wall facing. The study investigates how wire mesh strength and geometry affect the failure mechanism. All three walls were nominally identical, except for reinforcement strength and geometry. The displacement field of the entire cross section was captured by highresolution digital camera through transparent sidewall. The resulting images were analyzed using digital image correlation software. The results indicate that both reinforcement strength and aperture size influence the type of failure mechanism. Numerical modelling was also applied to assess the influence of sidewall friction (3D model) and reinforcement stiffness and strength (2D model) on the failure mechanism of the walls. The parameters for the numerical models were derived from independent tests and results, which were compared with the experimental observations. A good level of agreement with measurements was confirmed, even for the 2D model that excluded sidewall friction.

The existence of thick compressible clayey silt deposits along the Sava River provides major obstacle for design and construction of highway embankments in this region. To understand the consolidation and permeability characteristics of this alluvial layer and then to develop reliable soil parameters for earthwork design and construction, a comprehensive soil testing program was carried out. The program consisted of both in situ tests [e.g., standard penetration test borings, piezocone penetration test (CPT) soundings, Marchetti flat dilatometer test soundings, Lefranc test and CPT pore pressure dissipation tests] and laboratory tests (e.g., soil index tests, consolidation tests). The field and the laboratory test results showed that the clayey silt deposit was highly overconsolidated at the top and lightly overconsolidated at greater depths. The findings obtained from this study will be beneficial for future design and construction of Embankments along the Sava River.

Zbog topografskih odlika, kao i drugih prirodnih uslova kao što su obilne kišne padavine, klizišta predstavljaju kontinuirane i veoma prisutne hazarde u Bosni i Hercegovini te uzrokuju složene i sve veće probleme za zajednice i vlasti na svim nivoima. U procjeni rizika za BiH, koju je usvojilo Vijeće ministara 2012. godine, već je registriran veliki broj aktivnih klizišta u zemlji. 
Rat koji se desio u zemlji u periodu 1992–1995. godine također je uzrokovao obimne migracije stanovništva, što je povezano sa ilegalnom gradnjom stambenih objekata na padinskim područjima ili duž riječnih korita. Pored toga, nedostatak dokumentacije o prostornom planiranju zasnovane na geološkim analizama dovodi do neodrživog teritorijalnog razvoja i investicija u infrastrukturu što također dugoročno uzrokuje opasnosti od pojave klizišta. Pored toga, aktivnosti ljudi koje se odnose na širenje naselja ka nesigurnim lokacijama, rudarske aktivnosti koje nisu zasnovane na naučnim istraživanjima, rizična izgradnja puteva, nasipa i ignoriranje prirodnih karakteristika doprinose povećanju broja klizišta.
Obilne kišne padavine, koje su zadesile područje Balkana u maju 2014. godine, uzrokovale su značajnu pojavu klizišta i poplava koje su nanijele štete u Bosni i Hercegovini. Četvrtina teritorije BiH i oko milion ljudi, što je jednako 27% ukupnog stanovništva zemlje, bilo je pogođeno ovom katastrofom. 
Kako bi se unaprijedila trenutna situacija, UNDP provodi intervencije usmjerene na jačanje otpornosti, posebno u pogledu smanjenja rizika od klizišta i poplava u BiH. Kao dio napora UNDP-a, provedena je „Analiza situacije i procjena potreba za edukacijom u BiH“ 2015. godine, a rezultati su primijenjeni u ovom „Priručniku o upravljanju rizicima od klizišta“.
Svrha ovog priručnika je predstaviti čitateljima tehničke smjernice za prevenciju, istraživanje, analizu i saniranje klizišta te ublažavanje rizika. Namjera priručnika je da se koristi kao referentni priručnik za profesionalce u BiH koji se bave klizištima. Priručnik je izrađen kako bi osigurao strukturalna poboljšanja praksi upravljanja rizicima od klizišta u BiH, u skladu sa trenutnim najboljim praksama i domaćim i međunarodnim standardima.

A case study: cantilever retaining wall founded on concrete blocks (counterforts)

A large number of relatively high cantilever retaining structures in BiH were built in last 10 years. These walls were part of motorway route “Vc” project, regional road remediation project and in private sector as well. Many were constructed like cantilever walls founded on concrete block (so called counterforts). The construction phases for this type of retaining structures were defined in special chapter of this manual. Since these walls are found as cost effective solution that is adopted to local construction companies for more than 40 years, it is not surprising that it was involved in mentioned project as well. One of the walls is selected as case study for this manual. The details like construction sequence, geotechnical investigations, numerical analysis and practical construction details are presented in order to promote this type of structures. On the other side, the shortcomings of these structures are highlighted to draw the attention to practical engineers that will built these walls in the future.

Problemi obuhvaćeni ovom grupom riješenih zadataka su oni iz osnovnih oblasti mehanike tla, od zapreminskih odnosa, zbijanja i klasifikacije tla, preko principa efektivnih napona i procjeđivanja vode kroz tlo, do proračuna intenziteta i trajanja slijeganja, horizontalnih pritisaka tla, proračuna vertikalnih napona od dodatnog opteredenja i čvrstode tla, kao i osnovni principi proračuna stabilnosti kosina i dopuštenih napona u tlu. Obzirom da se teoretske osnove mogu pronadi u svakoj standardnoj literaturi vezanoj za Mehaniku tla, nisu posebno priložene teoretske osnove, a korišteni dijagrami i formule objašnjeni su pri samoj izradi zadataka, uz potrebne napomene.

The most often remediation measure for landslide stabilisation is the construction of drainage system that controls the underground water as most often trigger for soil failure. Deep gravity drains are usually designed to reduce hydrostatic water pressure. Since the named pressure influence the soil strength by reducing the effective stress, the concept of preventing high water levels along the slope is for a long time recognized as remediation measure in practical geotechnical engineering. The construction phases for this kind of remediation measures are well known in local practice. It consists of excavation of trench that is usually performed in segments. After the excavation, the lean concrete is poured, drainage pipe is installed and covered first by filter material wrapped around by geotextile and later by granular material. Finally, near the top of the excavation, natural fine grained soil is used as trench cover for preventing the infiltration of surface water into the drainage system. This remediation measure is found as relatively cost effective and practical solution that is known to local construction companies for a long time. One of the practical examples is selected as case study for this manual. The details like construction sequence, geotechnical investigations, numerical analysis and practical construction details are presented in order to share experiences with this concept of landslide remediation. On the other hand, the shortcomings of this remediation approach are highlighted to draw the attention to practical engineers that will design it and construct it in the future.

A large number cut slope failures were observed along the existing railway and motorway routes in coherent materials. Most of such a failures were trigged by heavy rainfall that causes increment of pore water pressure and reduces the soil strength by reducing the effective stress. The most practical and cost effective solution for remediation after this kind of failures is to perform the toe improvement by replacing the existing material with crushed stone granular material. This kind of material has favourable mechanical and hydraulic conductivity properties. Namely, along with slope draining, it provides additional shear resistance in comparing to in situ coherent material. The construction phases for this type of retaining structures will be defined by presenting the details of practical case study. Since this remediation measure is found as cost effective solution that is adopted to local construction companies for a long time, it is not surprising that it was involved in mentioned project as well. The details like construction sequence, geotechnical investigations, numerical analysis and practical construction details are presented in order to promote this type of landslides remediation meassure. On the other side, some shortcomings of this method are highlighted to draw the attention to practical engineers that will use it as design solution in the future.

It is not a rare practice that retaining structures in BiH are built as piles additionally supported by ground
anchors. These walls are often design in road engineering to support cut slopes and in private sector
for retaining of deep excavations. Designing the piles without anchors usually cannot provide
appropriate safety factor and cannot appropriately reduce displacements, since the piles flexural
capacity is quite limited. In many practical examples it is not possible to perform large diameter piles in
unstable areas (due to heavy equipment), so only small diameter piles (D < 600,0 m) must be used for
remediation. The construction phases for this type of retaining structures were defined in special chapter
of this manual. One of the walls is selected as case study for this manual. The details like construction
sequence, geotechnical investigations, numerical analysis, monitoring results and interpretations along
with the practical construction details are presented in order to get the insight to possibilities of these
structures. On the other side, the shortcomings of these structures are highlighted to draw the attention
to practical engineers that will built these walls in the future.

Identifikacija mehanizma sloma i općenito, istraživanje ponašanja zidova od armiranog tla pri velikim pomacima, privlači pažnju velikog broja istraživača u novije vrijeme. Ipak, ograničene su studije utjecaja interakcije između pojedinih elemenata zidova na način njihovog otkazivanja. Utvrđivanje nosivosti različitih geometrijskih konfiguracija zidova, obuhvaćajući pri tome interakciju pojedinih elemenata, provodi se u ovom radu primjenom numeričkih i fizičkih modela. U radu se detaljno istražuje interakcija armature i nekoherentnog zasipa u uvjetima pokusa izvlačenja i u zidovima armiranim mrežama.
Numeričkim 2D i 3D simulacijama pokusa izvlačenja u radu se istražuju utjecaji rubnih uvjeta na rezultat pokusa. U prvoj fazi istraživanja provodi se niz parametarskih analiza i usporedbi s eksperimentalnim istraživanjima. Model, koji uspješno simulira mehanizme interakcije u pokusu, iskorišten je za istraživanje utjecaja rubnih uvjeta na rezultate. Rezultati istraživanja uspostavljaju vezu između dimenzija sanduka, zbijenosti zasipa i granične otpornosti na izvlačenje. Radom se daju preporuke za oblikovanje i pripremu sanduka i armature koji se koriste pri provođenju pokusa izvlačenja.
Numeričkim 2D i 3D simulacijama zidova u radu se istražuje utjecaj interakcije armature i nekoherentnog zasipa na proračun stabilnosti zidova. U prvoj fazi istraživanja provodi se niz parametarskih analiza i usporedbi s eksperimentalnim istraživanjima. Model, koji uspješno simulira mehanizme interakcije u zidu, primijenjen je za istraživanje utjecaja geometrije armature, čvrstoće spoja zasipa i armature i čvrstoće temeljnog tla na mehanizam otkazivanja i faktor sigurnosti zidova. Rezultati analiza iskorišteni su za definiranje preporuka o načinu modeliranja pojedinih komponenti zidova i njihove interakcije.
Pored niza numeričkih simulacija u radu su objavljeni rezultati nekoliko umanjenih fizičkih modela zidova uz opažanje pomaka kompletnog zasipa digitalnom kamerom kroz prozirnu staklenu bočnu stijenku. Obrada digitalnih fotografija provodi se metodom korelacije digitalnih fotografija što rezultira pomacima kompletnog zasipa uz prednju bočnu stijenku. Rezultati mjerenja pokazuju vezu između čvrstoće i geometrije armature na jednoj i mehanizma sloma zida na drugoj strani. Pored toga, navedeni rezultati mjerenja predstavljaju bazu za verificiranje numeričkih modela jedne grupe geometrijskih konfiguracija zidova.