Antonio Gens Solé

Liquefaction potential of hydraulic fills

A container terminal is under construction at the Port of Barcelona. The quay, 1.6 km long, is made of concrete caissons founded on granular rubble mounds. The natural soil is a sequence of normally consolidated fine-grained deltaic deposits that reach a thickness of over 60 m. The quay was backfilled with hydraulic fill dredged from the seabed soils in front of the caissons quay, deposited by a rainbowing technique. A failure of a section of the quay was attributed to the static liquefaction of the hydraulic fill. This failure prompted a field campaign to identify fill properties and its liquefaction potential. Standard and seismic CPTU´s and Marchetti dilatometer tests were performed as well as a programme of laboratory tests. Available indices to estimate liquefaction potential were calculated and compared. One of the relevant issues raised after the quay failure was the ability of preloading to eliminate the liquefaction potential of the fill. In situ tests were performed on the fill before and after a large scale preload test. Liquefaction indices at those two stages are compared showing, in some cases, a reduction of liquefaction potential after preloading.

Formulation for the THMC analysis of clayey materials: application to radioactive waste disposal

A fully coupled formulation combining reactive transport and an existing thermo-hydro-mechanical (THM) code is briefly described. Special attention has been given to phenomena likely to be encountered in clay barriers used as part of containment systems of nuclear waste. The types of processes considered in the chemical formulation include hydrolysis, complex formation, oxidation/reduction reactions, acid/base reactions, precipitation/dissolution of minerals and cation exchange. Both kinetically controlled and equilibrium-controlled reactions have been incorporated. The formulation has been implemented in the numerical code CODE_BRIGHT. An application is presented concerning the performance of a large scale in situ heating test simulating high-level nuclear waste repository conditions.

Observation of ventilation effects around a tunnel excavated in argillaceous materials

The nature-inspired concept of self-healing materials in construction is relatively new and has recently attracted significant attention as this could bring about substantial savings in maintenance costs as well as enhance the durability and serviceability and improve the safety of our structures and infrastructure. Much of the research and applications to date has focused on concrete, for structural applications, and on asphalt, with significant advances being made. However, to date no attention has been given to the incorporation of self-healing concepts in geotechnical and geo-environmental applications. This includes the use of concrete and other stabilising agents in foundations and other geotechnical structures, grouts, grouted soil systems, soil-cement systems and slurry walls for ground improvement and land remediation applications. The recently established Materials for Life (M4L) project funded by EPSRC has initiated research activities in the UK focussing on those applications. The project involves the development and integration of the use of microcapsules, biological agents, shape memory polymers and vascular networks as healing systems. The authors are exploring development of self-healing systems using mineral admixtures, microencapsulation and bio-cementation applications. The paper presents an overview of those initiatives to date and potential applications and presents some relevant preliminary results.By contrast to studies in petroleum geology and, despite their world-wide occurrence, geotechnical studies of ancient fluvial sediments are rare. This paper introduces the main characteristics of these sediments by reference to a classic UK example. Attention is then drawn to a number of major overseas examples where, although the principal features can be recognised, large differences arise as a result of factors such as the tectonic setting, the volume and mineralogy of the source material and the climate at the time the sediments were deposited. The first, over-riding problem for their engineering evaluation comes during the site investigation phase with the difficulty of deducing the geological structure and distribution of the widely varying lithologies.Strain accumulation in granular soils due to dynamic loading is investigated through long term cyclic triaxial tests and cyclic triaxial tests according to ASTM D 3999-91. Soil parameters, test equipment and loading conditions have a significant influence on strain accumulation, therefore a parameterization of the silica sand and a description of the cyclic triaxial test device are explained. Cyclic triaxial tests are performed and test results are presented illustrating the evolution of Young’s modulus during long term cyclic loading. The influence of the width of the stress-strain loop and the initial void ratio on strain accumulation is investigated and validated with existing accumulation models. The usefulness of Miner’s rule on sand subjected to cyclic loading is demonstrated by two tests with different packages of loading cycles.

EPB tunnelling in mixed geological formations: a case study

Tunnels for the new Barcelona Metro Line 9 are being constructed in a densely built urban area, close to sensitive structures. The paper presents a case history involving tunnelling in difficult mixed geological conditions belowan existing Metro Line (Line 4).Tunnelling was performed with a dual EPB boring machine and the closed mode of operation was prescribed beneath all sensitive structures. Despite this original prescription, an open mode excavation (with a partially filled pressure chamber) had to be adopted to avoid the interruption of the boring process in the area below the existing Metro Line 4. The paper describes the geological conditions of the site, presents some of the ground movement observations prior to the change of excavation mode and discusses the rationale that allowed the change in the prescribed tunnelling mode as well as the results obtained. Observations of displacements during the excavation in open mode confirmed that no soil inrush into the head chamber occurred and that in addition, with the new excavation procedure, ground movements were reduced significantly.

Preload improvement and monitoring in a newly reclaimed area

The paper describes the preload improvement of a newly reclaimed area that is part of the current development of the Barcelona Port. The area will provide the required surface of a new container terminal with a berth length of 1,600 m. The total surface area is 750,000 m2. The improvement affects both the hydraulic fill placed for the reclamation as well as the underlying soft natural ground. Improvement was required for both reducing subsequent settlements and providing an adequate level of stability during construction and quay commissioning. Special attention has been given to the reduction of the liquefaction potential of the hydraulic fill. The degree of improvement has been assessed comparing extensive site investigations performed before and after preloading. CPTu tests have proved especially useful in this regard. An extensive instrumentation scheme was deployed to observe the progress of preloading throughout the whole process. In some areas, preloading was supplemented by the installation of prefabricated vertical drains and by reinforcement using large-diameter gravel columns. The paper describes the ground improvement operations and the field monitoring observations performed during the works.

Simulation of expansive clay behavior under simultaneous heating-hydration for nuclear waste storage applications

The storage of nuclear waste is still an unresolved problem of the nuclear industry, being geological disposal the most favoured option. Most conceptual designs for the deep geological disposal of nuclear waste envisage placing the canisters containing the waste in horizontal drifts or vertical boreholes. The empty space surrounding the canisters is filled by an engineered barrier often made up of compacted swelling clay. A good understanding of thermo-hydro-mechanical (THM) issues is therefore necessary to ensure a correct performance of engineered barriers and seals. The conditions of the bentonite in a typical engineered barrier are being simulated in a mock-up heating test at almost scale. The evolution of the main Thermo-Hydro-Mechanical (THM) variables of this test are analyzed in this paper. Especial emphasis has been placed on the study of the effect of thermo-osmotic flow in the hydration of the clay barrier at advanced staged of the experiment.

Engineering assessment of jet-grouted structures

The treatment characteristics, quality control measures and outcomes of two different jet-grout based soil treatments are described in detail. In the first one, a jet-grouted slab was built to limit retaining wall movements in a cut-and-cover tunnel. Quality control relied on borehole core quality assessment and laboratory testing. Core quality was very sensitive to coring practices. The strength and stiffness of the jet-grouted slab were deemed adequate and the structure successfully contributed to minimal wall movements. In the second case, a jet-grouted treatment was designed to provide strengthening and impermeabilization around a tunnel excavated on silty sands below the water table and underneath another tunnel. Control was based on extensive coring, cross-hole seismic surveys and permeability tests. The results were generally favourable and where defects were detected, reparation was undertaken. However, in spite of all those actions, a number of deficiencies escaped detection and only became apparent during the excavation of the tunnel resulting in significant construction problems./ /Les caracteristiques de traitements, les mesures de controle de qualite et les resultats de deux differents traitements de sol par jet grouting sont expliques en detail. Dans l’un d’entre eux, on a construit une plaque par jet grouting pour limiter les mouvements des parois de soutenement d’une tranchee recouverte. Le controle de qualite s’appuyait sur l’evaluation de la qualite des carottes de sondage et des tests de laboratoire. La qualite des carottes etait tres sensible a la methodologie de forage. La resistance et la rigidite de la plaque par jet grouting ont ete considerees adequates et la structure a contribue avec succes a limiter les mouvements de parois. Dans l’autre cas, un traitement par jet grouting a ete concu pour renforcer et impermeabiliser la zone autour d’un tunnel excave dans des sables limoneux plus bas que le niveau phreatique et en-dessous d’un autre tunnel. Le controle etait base sur de nombreux forages, de la sismique cross-hole et des tests de permeabilite. Les resultats etaient generalement favorables et les defauts detectes ont ete repares. Malgre tous ces efforts, un certain nombre d’imperfections ont echappe a la detection et sont seulement devenus apparents lors de l’excavation du tunnel ce qui a produit des problemes de construction significatifs.