Investigation of liquefaction potential of sands from the subsoil at the HPP Brežice

Phenomenon of liquefaction is characteristic for loose, saturated, fine-grained cohesionless soils. These soils tend to compact under monotonic, impulsive or repeating load (e.g. earthquake) which leads to the increase of pore water pressures and consequently to the loss of shear strength. Using “in situ” and laboratory tests the susceptibility of liquefaction of fine-grained sands under the flood embankments of the hydropower plant Brežice is investigated in the presented thesis. Suitability of this local soil for the construction of these embankments is also checked. With regard to index values representative material for investigation of dynamic properties of the soil was selected. Effect of different parameters like void ratio, water content and cyclic stress ratio on the liquefaction of the abovementioned soil was checked in controlled conditions in the laboratory. Obtained results from the samples prepared in the laboratory were then compared to the results on intact samples taken from different layers of the full scale test embankment. Results of laboratory tests were used for the evaluation of the results of in-situ investigations. Characteristics of the fine-grained sand from the hydropower plant Brežice were finally compared to Toyoura sand as a reference material

Liquefaction potential of sands at the Krško-Brežice field, Slovenia

The Krško-Brežice field is one of the most seismically active areas in Slovenia. The most damaging recorded earthquake with an intensity of VIII (EMS) occurred on 29th January 1917. It caused damage and claimed two lives. In the last 100 years, 9 earthquakes with intensity higher than VI (EMS) have been recorded. At the investigated area, a top layer up to 5 m thick, consisting of recent deposit of very loose silts and sands (ML, SM, SP), covers the medium dense to dense Quaternary gravel, beneath which there are over-consolidated, uncemented Miocene silts and marls. The top layer could be prone to liquefaction, as reported for the close surroundings of Brežice, where the liquefaction phenomenon was observed during the Zagreb earthquake in 1880 and during the Kupa Valley earthquake in 1909. The paper presents the results of laboratory index tests, cyclic simple shear tests and field investigations (SPT, CPT, (S)DMT, vs measurements), which were carried out to assess the liquefaction potential of the top layer at the location of the Brežice Hydroelectric Power Plant (HPP). All results show that the top layer is prone to liquefaction for an earthquake with a 475 year return period. Cyclic simple shear test results show that the liquefaction potential of horizontal ground for an earthquake with a 475 year return period can be reduced by the densification of the top layer to at least 95% of maximum Proctor density.</p

TESTING METHODS FOR MECHANICALLY IMPROVED SOILS: RELIABILITY AND VALIDITY

A possibility of in-situ mechanical improvement for reducing the liquefaction potential of silty sands was investigated by using three different techniques: Vibratory Roller Compaction, Rapid Impact Compaction (RIC) and Soil Mixing. Material properties at all test sites were investigated before and after improvement with the laboratory and the in situ tests (CPT, SDMT, DPSH B, static and dynamic load plate test, geohydraulic tests). Correlation between the results obtained by different test methods gave inconclusive answers

Recognition of properties and sustainable management of sediments from water environments

V vodnih plovnih poteh in umetnih akumulacijah na kopnem se kopičijo sedimenti, ki izvirajo iz naravnega geološkega zaledja in so po mineralni in zrnavostni sestavi podobni zemljinam. Nakopičeni sedimenti zmanjšujejo obratovalno in funkcionalno varnost teh objektov, zato jih je potrebno redno odstranjevati in odlagati na drugem mestu. Odlaganje se lahko izvaja s premeščanjem znotraj vodnega telesa ali s skladiščenjem na kopnem. V umetnih akumulacijah na kopnem so uskladiščeni tudi industrijski mulji. Zaradi visoke vlage in rahle strukture je trdnost muljev praviloma nižja od trdnosti zemljin pri vlagi na meji židkosti, številni mulji imajo tiksotropen značaj. V disertaciji smo raziskovali ali so terenske in laboratorijske raziskave ter materialni modeli, uveljavljeni za zemljine, primerni tudi za identifikacijo lastnosti in napoved obnašanja muljev. Preiskovali smo reful iz Luke Koper in mulj kemične sadre, ki nastaja pri proizvodnji titanovega dioksida v Celju. Oba mulja sta skladiščena na kopnem v umetnih akumulacijah, ki predstavljajo omejitve pri načrtovanju razvoja infrastrukture in proizvodnje. Akumulacije refula so zgrajene za nizkimi obodnimi nasipi, akumulaciji mulja sadre pa za visokima nasutima pregradama Za Travnikom in Bukovžlak, ki sta objekta visokega tveganja. Lastnosti muljev smo identificirali s terenskimi in laboratorijskimi preiskavami. Rezultate smo izvrednotili v luči klasične geomehanike, upoštevaje posebnosti, ki izvirajo iz okolja nastanka in novega sedimentacijskega okolja. Raziskali smo vpliv soli na indeksne lastnosti refula, preverili omejitve terenske opreme in veljavnost semiempiričnih zvez, razvitih za zemljine, za vrednotenje terenskih raziskav mulja sadre. Z reološkimi raziskavami smo pokazali široko uporabnost ConTec Viscometra 5, razvitega za malte in betone, tudi na področju sedimentov. Ovrednotili smo občutljivost muljev in njihovo tiksotropno obnašanje. Raziskali smo možnost izboljšanja refula z anorganskimi vezivi. Iz rezultatov laboratorijskih preiskav in iz parametrov poskusnih tlačnih filtracij suspenzij muljev smo določili parametre za modelne izračune konsolidacijskega lezenja, sušenja v akumulacijah in tlačne filtracije. Ugotovili smo, da lahko konsolidacijsko lezenje v edometru dobro opišemo s Soft soil creep modelom v Plaxisu, da z 1D modelom, razvitim za sušenje plazine iz plazu Slano Blato, ne moremo ustrezno ovrednotiti sušenja muljev v akumulacijah in da lahko tudi s preiskavo stisljivosti v edometru zadovoljivo opišemo tlačno filtracijo.Sediments from natural geological hinterland accumulate inside waterways and man made accumulations on land. Their grain size distribution and mineral composition are comparable with soils. Accumulated mud reduces safe operation and functionality of these facilities. Thus, it should be permanently removed and disposed of inside the water body or on land. Industrial muds are also stored in man made accumulations on land. Due to high water content, strength of muds is usually lower than strength of soils with water content at liquid limit. Some muds exhibit thixotropic behaviours. In this thesis, the validity of in situ and laboratory test methods and material models, developed for soils, for the identification of mud properties and for the prediction of their behaviour, were investigated. Two muds were examined: dredged marine sediment – reful from the Port of Koper and red gypsum mud, which is by-product in the production of titanium dioxide in Celje. Both are deposited on land, in accumulations which present limitations in the planning of the infrastructure and production. Reful is deposited in shallow lagoons, while red gypsum mud is stored behind two large embankments Za Travnikom and Bukovžlak, which represents high risk facilities. Properties of muds were identified with in situ and laboratory investigations. Results were interpreted in the light of classical soil mechanics, taking into account the specificities which emanate from the mud origin and from new sedimentation environment. The influence of salty pore water on the index properties of reful was determined. The limitations of in situ measuring sensors for the investigation of muds were checked. The validity of semi empirical relationships, developed for evaluation of in situ tests in soils, for the description of red gypsum mud properties were analysed. ConTec Viscometer 5, designed for mortars and concrete, was recognized as suitable also for rheological investigations of muds. The sensitivity and thixotropic behaviours of muds were evaluated. The improvement of reful was investigated by mixing it with inorganic binders. From the results of laboratory tests and from trial pressure filtration tests, technological and material parameters for model description of consolidation creep, drying and pressure filtration, were estimated. Results show that Soft soil creep model is suitable for the description of consolidation creep, while basic 1D model, developed for the computation of the Slano Blato landslide drying, is not completely appropriate for the description of drying of mud in the accumulation and oedometer test is suitable also for the prediction of the pressure filtration parameters

Reološke lastnosti morskih sedimentov iz Luke Koper

Subaqueous, fine-grained, cohesive sediments are continuously fluidized by waves and other disturbances that cause their movement, which can be described with numerical models incorporating rheological parameters. The rheological behaviour depends on the soil (solid) type, the volume concentration, the salinity and the testing methods. In this study, rheological investigations of marine sediments from the Port of Koper were carried out by using two coaxial cylinder rheometers (DV3T HB, Brookfield and ConTec Viscometer 5). The influence of the specimen volume, the size of the gap and the type of measuring spindles were analysed and compared. The measured data were evaluated using the Bingham model. For each data set, the boundary between the sheared (“fluid”) and the un-sheared (“solid”) material was calculated and then the calculated boundary was used instead of the outer radius of the cylinder for the evaluation of the rheological parameters, where necessary. A good comparison of the results was found when using this approach. The results are also in agreement with the literature data. The ConTec Viscometer 5, primarily designed for mortars and concrete, was shown to be also suitable for the investigation of sediments.Sedimenti na morskem dnu so nenehno izpostavljeni valovanju in drugim motnjam, ki povzročajo njihovo premikanje. Premikanje lahko opišemo z numeričnimi modeli, ki vključujejo reološke parametre, odvisne od vrste zemljine (trdnine), volumske koncentracije, slanosti in preiskovalnih metod. Ta članek opisuje preiskave reoloških lastnosti morskega sedimenta iz Luke Koper. Raziskave so bile izvedene z uporabo dveh koaksialnih valjastih reometrov (DV3T HB, Brookfield in ConTec Viscometer 5). Analiziran je vpliv volumna vzorca, razdalje med notranjim in zunanjim valjem in vrste uporabljenih vreten. Meritve so analizirane z uporabo Bingham-ovega modela. Za vsako meritev je bila izvrednotena meja med materialom, ki teče in tistim, ki ne teče. Kjer je bilo potrebno, je bila za vrednotenje reoloških parametrov, namesto radija zunanjega cilindra uporabljena izračunana meja. Z uporabo te metode je bilo ugotovljeno dobro ujemanje rezultatov. Rezultati so primerljivi s podatki iz literature za podobne zemljine. ConTec Viscometer 5, ki je prvenstveno razvit za preiskave malt in betonov, je bil prepoznan, kot primeren tudi za preiskave sedimentov

Soil classifiation for engineering purposes in Slovenia – how to proceed?

Principles of engineering soil classifiation used in Slovenia since 1948 are analysed and compared with the newly accepted European soil classifiation principles. The main differences in terminology, symbols and index properties are emphasised. New Slovenian classifiation symbols and terminology are proposed and supported by practical examples of its use

TESTING METHODS FOR MECHANICALLY IMPROVED SOILS: RELIABILITY AND VALIDITY

A possibility of in-situ mechanical improvement for reducing the liquefaction potential of silty sands was investigated by using three different techniques: Vibratory Roller Compaction, Rapid Impact Compaction (RIC) and Soil Mixing. Material properties at all test sites were investigated before and after improvement with the laboratory and the in situ tests (CPT, SDMT, DPSH B, static and dynamic load plate test, geohydraulic tests). Correlation between the results obtained by different test methods gave inconclusive answers

TESTING METHODS FOR MECHANICALLY IMPROVED SOILS: RELIABILITY AND VALIDITY

A possibility of in-situ mechanical improvement for reducing the liquefaction potential of silty sands was investigated by using three different techniques: Vibratory Roller Compaction, Rapid Impact Compaction (RIC) and Soil Mixing. Material properties at all test sites were investigated before and after improvement with the laboratory and the in situ tests (CPT, SDMT, DPSH B, static and dynamic load plate test, geohydraulic tests). Correlation between the results obtained by different test methods gave inconclusive answers

Effect of Different Cellulose Fillers on the Properties of Xanthan-Based Composites for Soil Conditioning Applications

The aim of this study was to investigate the effect of different types of natural cellulose-based fillers on the properties of Xanthan gum (XG) in order to develop novel bio-based soil conditioners (SCs) that could be used in forestry and agricultural applications. Rheological measurements highlighted that SCs with cellulose fillers characterized by a high aspect ratio and low oxide ash content exhibited an average increase of 21% in yield stress compared to neat Xanthan gum. The presence of cellulose fillers in the composites resulted in a slower water release than that of neat XG, limiting the volumetric shrinkage during the drying process. Furthermore, an analysis of the water absorption and water retention capacity of soils treated with the different SCs was carried out, demonstrating that the addition of 1.8 wt.% of SC with optimized composition to the soil led to an increase in water absorption capacity from 34% up to 69%. From the soil water retention curves, it was observed that the addition of SCs significantly increased the amount of water effectively available for plants in the area between field capacity and permanent wilting point (100–1000 kPa). From practical experiments on grass growth, it was observed that these SCs improved the water regulation of the soil, thus increasing the probability of plant survival under drought conditions