Eduardo Alonso Pérez de Agreda

Tracking degradation of argillaceous rocks using bender elements.

The results of a comprehensive experimental program focused on the study of progressive degradation processes on a low permeability argillaceous rock induced by hydraulic cycles is presented in the paper. Relative humidity cycles were applied with vapour transfer technique, and bender elements were used to evaluate the evolution of shear stiffness during the application of hydraulic paths. The characterisation of the material included the determination of the water retention properties (water retention curve), as well as the pore size distribution using mercury intrusion porosimetry, complemented with SEM micrographs and elemental analysis using X-ray spectroscopy to characterise micro-structural features and detect clayey and non-clayey constituents. Results showed cumulative and irreversible swelling of the samples with the application of relative humidity cycles. Regarding shear stiffness, an important reduction (around 80%) was observed at the end of the hydraulic paths applied. Evidence of rock degradation at macro-scale was linked to structural modifications at micro-level.

Microstructural evaluation of the water sensitivity of clayey rocks

The paper presents both macroscopic and microstructural evidence of the water sensitivity of a low porosity clayey rock from Northern Spain. Particular emphasis is focused on the effects of water sensitivity at micro level. Results obtained from Environmental Scanning Electron Microscopy (ESEM) using the common procedure of sample preparation show that this procedure of sample preparation is not enough to evaluate in a proper way the irreversible changes induced at micro level by hydraulic effects. An alternative procedure is described, which seems to improve the evaluation of rock degradation at micro scale.

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.

Reaction of a pile group against deep swelling

A singular case of development of deep soil expansions in the vicinity of pile groups supporting bridge pillars motivated the analysis. A semi-analytic procedure, which uses some available fundamental solutions for cavity expansion and the presence of concentrated loads in an elastic half-space, has been developed. The analysis requires an estimation of the soil displacements under the combined action of the stresses induced by the pile, the external loads and the volumetric deformations imposed by the soil expansion. “In situ” measurements provided an estimation of the deep volumetric deformations. The pile cap was also monitored and the evolution of its rotations and displacements was available. The analysis shows that all the piles of a group develop considerable bending stresses, which explain the cracking observed in the contact between the pile and the pile cap. The procedure developed predicts reasonably well the displacements and rotations experienced by the pile cap of the pile group.

Thermo-hydro-mechanical analysis for the simulation of rapid sliding process in a new and fast ring shear prototype

Vajont was a case of an extremely fast landslide and efforts to clarify the failure have been mainly concentrated in providing a consistent explanation taking into account this characteristic feature. Particularly in the case of Vajont landslide, attention has been essentially focused on the shearing properties of the sliding surface. An accepted explanation for the velocity reached is the thermo-hydraulic-mechanical coupling under saturated conditions, which induces thermal dilation and effective stress reduction due to pore pressure build-up. Nevertheless, lack of in situ and experimental information has become one of the main drawbacks when trying to explain these coupled processes. In situ information is difficult to obtain since temperature and pore pressure development during these fast processes are impossible of being measured. To overcome this limitation, a new fast sliding prototype -emulating a ring shear apparatus- has been recently developed at the Universitat Politecnica de Catalunya (Spain). This prototype can reach relatively high speeds along the sliding surface (up to 30 km/h) under relatively high total vertical stresses (up to 3 MPa). Temperature and pore pressure changes can be locally measured with miniature transducers located close to the shear band. The design of this complex prototype requires the use of simulation-aided techniques, to help with the interpretation of the coupled processes, as well as to estimate the maximum temperature and pore pressure changes. A thermo-hydro-mechanical formulation, applied to the ring shear test, is proposed in the paper to study pore water pressure build up and dissipation in a sliding surface being heated by the frictional work induced by the motion. Particularly, the proposed model is applied to simulate the evolution of the shear strength along the sliding surface during a fast sliding process.

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.

Rapid drawdown in embankment dams

Two real cases: the potential effect of an induced infiltration in the vicinity of an embankment founded on potentially collapsible natural silts and the effect of rainfall regime on a canal founded on cemented collapsible silts are discussed. Tests performed to determine the parameters of an elastoplastic constitutive model (BBM) for the unsaturated foundation materials are described. Hydraulic properties were also determined. The two cases are simulated through the computer program CODE_BRIGHT. The calculation scenarios aim at studying limiting cases, to establish the risk of embankment malfunctioning.The calculation of pore water pressure distribution in a slope partially submerged and subjected to a drawdown is analyzed in this chapter. Drawdown phenomenon is a critical situation for the stability of slopes of earth dams and bank rivers affected by variations of water level. The prediction of pore water pressure in two earth dams subjected to a drawdown event under different calculation hypothesis highlight that classical flow methods of analysis may overestimate or underestimate pore water pressures depending on several external condition and material properties. In particular, an instrumented dam is simulated and calculated results can be compared with field measurements. Finally, in the chapter, an incipient landslide (40 Mm3) in the left margin of a reservoir triggered by a drawdown is presented and analyzed.

Environmental effects on earth embankments

Two real cases: the potential effect of an induced infiltration in the vicinity of an embankment founded on potentially collapsible natural silts and the effect of rainfall regime on a canal founded on cemented collapsible silts are discussed. Tests performed to determine the parameters of an elastoplastic constitutive model (BBM) for the unsaturated foundation materials are described. Hydraulic properties were also determined. The two cases are simulated through the computer program CODE_BRIGHT. The calculation scenarios aim at studying limiting cases, to establish the risk of embankment malfunctioning.The calculation of pore water pressure distribution in a slope partially submerged and subjected to a drawdown is analyzed in this chapter. Drawdown phenomenon is a critical situation for the stability of slopes of earth dams and bank rivers affected by variations of water level. The prediction of pore water pressure in two earth dams subjected to a drawdown event under different calculation hypothesis highlight that classical flow methods of analysis may overestimate or underestimate pore water pressures depending on several external condition and material properties. In particular, an instrumented dam is simulated and calculated results can be compared with field measurements. Finally, in the chapter, an incipient landslide (40 Mm3) in the left margin of a reservoir triggered by a drawdown is presented and analyzed.