Expansion mechanisms in sulphated rocks and soils

Geological formations containing sulphates are commonly associated with the development of severe expansions when they are involved in tunnel excavation. The intensity of the observed expansive behaviour in these materials is greater than in other expansive soils and rocks free of sulphates. Swelling in sulphated formations can also occur in the rock mass although no tunnel is excavated, and also within fills made of compacted material from excavations in sulphated rocks. The functionality and stability of engineering works are affected in the majority of the cases. The prediction of strains and swelling pressures in sulphated formations is a difficult task. On that direction, the Thesis analyses and describes the mechanisms and conditions leading to expansions in sulphated rocks through the detailed investigation of three exceptional cases of damage induced by expansions involving sulphated formations in Spain. Lilla tunnel, the first case-history analysed, was excavated in Tertiary anhydritic claystone. Expansions developed led to severe tunnel floor heaving and to very high pressures against tunnel lining. The second case, a bridge founded on piles within an anhydritic claystone, Pont de Candí bridge, experienced an unexpected and sustained heave of the central pillars as a consequence of the development of swelling strains below the deep pile foundations. The third case, the compacted access embankments to another bridge, Pallaressos embankments, experienced a very significant volumetric expansion. As a result, the bridge was axially compressed and damaged. Mechanisms leading to swelling in tunnels in sulphated rocks have been described in the literature; however, an alternative interpretation is proposed. In the first two cases the development of swelling phenomena is explained by the precipitation of gypsum crystals in rock discontinuities. The presence of anhydrite plays a central role in the phenomenon because its dissolution leads to supersaturation conditions of groundwater in calcium sulphate with respect to gypsum, which will result into gypsum precipitation. The process of precipitation of gypsum in discontinuities is thought to act as local jacks inducing swelling strains. The maximum pressure exerted by crystal growth has been estimated under a thermodynamical point of view. Expansions in the third case analysed are a result of massive growth of ettringite and thaumasite minerals in embankments reinforced by Portland cement due to sulphate attack to cementitious materials. Mineralogical analysis and the simulation of the chemical reactions involved in sulphate attack have shown that expansions in this type of embankments would proceed for a long time because of the availability of the necessary components for ettringite and thaumasite formation. A finite element model of embankment swelling developed has shown that great loads can be generated due to swelling against rigid structures restraining the expansion in some direction. A coupled Hydro Mechanical and Chemical model formulated in a porous media has been developed to simulate volumetric expansions explained by gypsum precipitation. The model is consistent with field and laboratory observations and describes the kinetics of precipitation and dissolution of gypsum and anhydrite, the solute transport and the development of strains induced by crystallization. The model has been applied to interpret and simulate the heave experienced by Pont de Candí viaduct. Modelling capabilities were checked against the long term history of viaduct heave and also, against the foundation response when the vertical load from a surface embankment was added to counteract swelling.Las formaciones geológicas que contienen sulfatos están asociadas tradicionalmente al desarrollo de expansiones severas cuando son atravesadas por túneles. La intensidad del comportamiento expansivo observado en estos materiales es mayor que en otras rocas y suelos expansivos libres de sulfatos. El hinchamiento asociado a formaciones sulfatadas también puede ocurrir en el macizo rocoso aunque no se excave un túnel, y también en rellenos construidos con material compactado procedente de excavaciones en rocas sulfatadas. En la mayoría de casos la funcionalidad y estabilidad de las obras de ingeniería se ven afectadas. La predicción de deformaciones y presiones de hinchamiento en formaciones sulfatadas es una tarea difícil. En este sentido, la Tesis analiza y describe los mecanismos y las condiciones que conducen a expansiones en rocas sulfatadas, a través de la investigación detallada de tres casos excepcionales de daño debido a expansiones que involucran formaciones sulfatadas en España. El túnel de Lilla, el primer caso analizado, se excavó en arcillita anhidrítica. El desarrollo de expansiones condujo a un levantamiento severo de la solera y a presiones contra el revestimiento muy altas. El segundo caso, un puente cimentado en pilotes en una arcillita anhidrítica, el viaducto de Pont de Candí, experimentó un levantamiento inesperado de los pilares centrales debido al desarrollo de hinchamientos por debajo de las cimentaciones profundas. En el tercer caso, los terraplenes de acceso a otro puente, los terraplenes de Pallaressos, experimentaron una expansión volumétrica muy significativa y el puente resultó comprimido axialmente y dañado. Los mecanismos que conducen al hinchamiento en túneles en rocas sulfatadas se han descrito en la literatura; sin embargo, se propone una interpretación alternativa. La precipitación de cristales de yeso en discontinuidades de la roca explica el desarrollo de fenómenos de expansión en los dos primeros casos. La presencia de anhidrita juega un papel central en el fenómeno expansivo porque su disolución conduce a condiciones de sobresaturación del agua del macizo en sulfato cálcico respecto el yeso, que resulta en la precipitación de yeso. Se cree que el proceso de precipitación de yeso en discontinuidades actúa como gatos locales generando deformaciones. La presión máxima ejercida por crecimiento de cristales se ha estimado desde un punto de vista termodinámico. Las expansiones en el tercer caso son el resultado del crecimiento masivo de los minerales de etringita y thaumasita en terraplenes estabilizados con cemento Portland debido al ataque sulfático a los materiales cementantes. Ensayos mineralógicos y la simulación de las reacciones químicas involucradas en el ataque sulfático han mostrado que las expansiones en este tipo de terraplenes continuarían durante un periodo de tiempo largo, debido a la disponibilidad de los componentes necesarios para la formación de etringita y thaumasita. Un modelo de elementos finitos del hinchamiento del terraplén ha mostrado que estas expansiones pueden generar presiones muy altas contra estructuras rígidas. Se ha desarrollado un modelo acoplado Hidro-Mecánico y Químico formulado en medio poroso para simular expansiones volumétricas explicadas por la precipitación de yeso. El modelo es consistente con observaciones de campo y laboratorio y describe la cinética de la precipitación y disolución, el transporte de soluto y el desarrollo de deformaciones inducidas por cristalización. El modelo se ha aplicado para interpretar y simular el levantamiento experimentado por el viaducto. La capacidad de modelación se ha verificado frente a las medidas de levantamiento del viaducto en el tiempo y también, frente a la respuesta de las cimentaciones a la construcción de un terraplén en superficie para contrarrestar el hinchamient

Heave of a building induced by swelling of an anhydritic Triassic claystone

The final publication is available at Springer via http://dx.doi.org/10.1007/s00603-018-1503-4This paper describes the conditions leading to a sustained, low-rate, heave phenomenon affecting a building founded on hard Keuper anhydritic rock. The building was located in an abandoned gypsum quarry. Monitoring data as well as vertical profiles of gypsum and anhydrite content indicate that swelling was associated with the presence of a shallow level of anhydritic clay rock. This paper concludes that the initial quarry excavation as well as the additional building foundation work modified the original stress state and contributed to opening fractures at depth. It also resulted in a facilitated access of water to the upper rock levels, immediately under the foundation footings. Measured heave rates are substantially lower than other rates recorded in a few recent cases. An explanation is provided for the difference. This paper describes a comforting solution for the building.Peer ReviewedPostprint (author's final draft

Crystal growth under bridge foundation

W(H)YDOC PhD Prize 2012, durant el 4th International Workshop of Young Doctors in Geomechanics W(H)YDOC 2012.A high-speed railway viaduct experienced a sustained heave at high rates after its construction. The pillars of the bridge are founded on an Eocene hard anhydritic-gypsiferous claystone by means of massive foundations. Field investigations identified an active layer below the piles’ tips where expansions occur as a result of gypsum crystal growth in discontinuities from supersaturated aqueous solutions. The construction of the bridge is supposed to have triggered the swelling mechanism. An embankment, partially filling the valley, was built to slow the heave rate. The presence of soluble gypsum and anhydrite and inert materials is considered in the model developed to reproduce the observed expansive mechanism. The formulation describes the kinetics of dissolution and precipitation of minerals and the induced swelling strains by crystal growth. The calculated heave is compared with the field long-term vertical displacements measured before and after the construction of the embankment. A sensitivity study is also reported.Peer ReviewedAward-winningPostprint (published version

Hydro-chemo-mechanical modelling of tunnels in sulfated rocks

Permission is granted by ICE Publishing to print one copy for personal use. Any other use of these PDF files is subject to reprint fees.A modelling procedure to address the tunnel–anhydritic rock interaction is described in this paper. The model incorporates the basic physico-chemical phenomena involved in rock swelling, often observed during excavation and subsequent operation of tunnels. It includes (a) a provision for rock damage during tunnel excavation, (b) the precipitation of gypsum crystals in discontinuities and (c) a stress-dependent relationship between swelling strains and mass of gypsum precipitation. The model includes hydro-mechanical coupling and the transport of sulfate salts dissolved in the massif water. Rock damage is described by the development of a network of fractures that increases permeability and allows gypsum crystal growth. Field information, laboratory data and monitoring records available for Lilla tunnel, located in the province of Tarragona, Spain and excavated in Tertiary anhydritic claystone, were selected as a convenient benchmark case to test model capabilities. Predictions and measurements (swelling records of the unlined tunnel floor and swelling pressures against a structural invert) were found to agree reasonably well.Peer ReviewedPostprint (published version

Designing tunnel lining in anhydritic claystones: intensity and distribution of swelling forces

The measured swelling pressures against tunnel linings range between a fraction of one MPa and 6–7 MPa. A strong spatial heterogeneity is often observed. The paper integrates these considerations into a procedure to design tunnel linings in anhydritic formations. Three-dimensional effects and proper consideration of heterogeneity is shown to be consistent with monitoring data of lining reinforcement stresses. The calculation methodology is illustrated in the case of the Lilla tunnel lining, which was monitored for more than 6 years. The described procedure leads to a rational design away from the conservatism of the assumption of uniform pressures against lining and two-dimensional modelling of tunnel cross-section.The Spanish railway administration (ADIF) kindly provided the monitoring data of AVE Lilla tunnel analysed here. The authors are grateful for the support received from Prof. Gonzalo Ramos for some of the structural calculations reported and to Eng. Francesc Cervera for his continuous collaboration and help regarding the A27 Motorway case. The Grants PID2021-122733OB-I00 and RTI2018-094226-J-I00 funded by the Spanish MCIN/AEI/10.13039/501100011033 and by “ERDF (FEDER) A way of making Europe” Projects, and, also, the former financial support of Spanish Public Works Ministry are gratefully acknowledged. Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature.Peer ReviewedPostprint (published version

El túnel de Lilla

Las arcillas sulfatadas pueden experimentar fenómenos expansivos graves como consecuencia de excavaciones. La intensidad del comportamiento expansivo observado en estos materiales es mayor que en otras rocas y suelos expansivos libres de sulfatos. En la mayoría de casos la funcionalidad y estabilidad de los túneles se ven afectadas. Investigaciones de campo y ensayos de laboratorio muestran que, en general, el desarrollo de deformaciones y altas presiones en rocas sulfatadas está asociado al crecimiento de cristales de yeso en discontinuidades. El crecimiento de cristales de yeso es una consecuencia de la sobresaturación del agua del macizo en sulfatos. Los datos de campo que avalan esta interpretación tienen un ejemplo sobresaliente en el túnel de Lilla (Tarragona), que ha sufrido graves problemas de hinchamiento tras su construcción. Aunque el fenómeno de hinchamiento en túneles que atraviesan materiales yesíferos se ha descrito y analizado cualitativamente a menudo, la predicción de deformaciones y presiones de hinchamiento sigue siendo una tarea difícil. En el presente trabajo se ha desarrollado un modelo de cálculo hidro-mecánico acoplado que permite predecir hinchamientos en excavaciones en arcillas sulfatadas durante la etapa de diseño. Se concluye con una descripción del diseño de la sección resistente del túnel de Lilla, a partir de datos de campo de presiones experimentadas por el revestimiento en secciones de prueba.Postprint (published version

Analysis of ettringite attack to stabilized railway bases and embankments

Two cases of massive sulphate attack to cement treated embankments and track bases in a high speed railway line are described. In the first case, two large access embankments to a railway viaduct were treated with jet–grouting columns. In the second case a compacted cement treated soil was placed over a rigid concrete caisson. The treated layer, 1.5 m thick, expanded at a continuous rate of 0.9-1.3 mm/month. In the two cases the soil was excavated from nearby cuts in gypsiferous Tertiary (Oligocene) claystones. Ettringite and thaumasite crystals were found within the expanding levels. The chemical evolution of an interface between a cement treated body and a compacted soil is presented. Solutions adopted to remediate the created problem are briefly described.Postprint (published version

Mecanismos de expansión en rocas sulfatadas

Los mecanismos que conducen al hinchamiento en túneles en rocas sulfatadas se han descrito en la literatura; sin embargo, se propone una interpretación alternativa. La precipitación de cristales de yeso en discontinuidades de la roca. La presión máxima ejercida por crecimiento de cristales se ha estimado desde un punto de vista termodinámico. Se ha desarrollado un modelo acoplado Hidro-Mecánico y Químico formulado en medio poroso para simular expansiones volumétricas explicadas por la precipitación de yeso. El modelo se ha validado con el levantamiento experimentado por el viaducto

Mecanismos de expansión en rocas sulfatadas

Los mecanismos que conducen al hinchamiento en túneles en rocas sulfatadas se han descrito en la literatura; sin embargo, se propone una interpretación alternativa. La precipitación de cristales de yeso en discontinuidades de la roca. La presión máxima ejercida por crecimiento de cristales se ha estimado desde un punto de vista termodinámico. Se ha desarrollado un modelo acoplado Hidro-Mecánico y Químico formulado en medio poroso para simular expansiones volumétricas explicadas por la precipitación de yeso. El modelo se ha validado con el levantamiento experimentado por el viaducto.Postprint (published version

Mecanismos de expansión en rocas sulfatadas

Los mecanismos que conducen al hinchamiento en túneles en rocas sulfatadas se han descrito en la literatura; sin embargo, se propone una interpretación alternativa. La precipitación de cristales de yeso en discontinuidades de la roca. La presión máxima ejercida por crecimiento de cristales se ha estimado desde un punto de vista termodinámico. Se ha desarrollado un modelo acoplado Hidro-Mecánico y Químico formulado en medio poroso para simular expansiones volumétricas explicadas por la precipitación de yeso. El modelo se ha validado con el levantamiento experimentado por el viaducto