Laboratorio de Geotecnia
Landslide on the Lucena - Encinas Reales section of the Córdoba Highway
In 2003, the Laboratorio de Geotecnia carried on developing the great number of activities it was involved in the year before in the field of research, technological development and innovation, with respect to both improving laboratory techniques and devising mathematical models to explain soil and rock behaviour. The study into the effects of earthquakes on foundations lying on granular material was completed and progress was made on analysing stress/ strain behaviour prior to the failure of clays and on obtaining the dilatancy laws that govern the behaviour of rock anchorages. A calculation method was developed for rock slopes based upon the Limit State theorems with non-associated flow laws, and work continued on studying soil-geotextile interaction in the case of nonsaturated soils.
Where European thematic R&D&I networks are concerned, and as part of the GROWTH Programme, the Laboratory took part in the development of the SUPERTRACK Project for the conservation and maintenance of high-speed railway lines with ballast structures. As part of this project the necessary excavations were prepared for installing a test cell 20 m long, 5 m wide and 4 m deep, which will serve to provide a full-scale reproduction of the short- and long-term behaviour of a section of the high-speed rail link between Madrid, Zaragoza and Lérida that has already been instrumented; the cell has been constructed and the hydraulic equipment and load elements needed have been acquired with a view to simulating the passing of trains along that stretch at 350 km/h.
Landslide affecting sandy-silty clays forming a cutting on the A-7 Highway in Barcelona
The Laboratory also took part in the GEOTECHNET Project concerning the Eurocodes and in developing methodologies and construction procedures that make it possible to improve safety in geotechnical works. The Laboratory also played an active part in the annual meeting of ELGIP, the network of European excellency geotechnical centres association, of which it is a member.
In the field of technical assistance collaboration continued with the Directorates of the Ministries of Fomento, Environment and Education, Culture and Sport, and of Autonomous Communities, County Councils, Local Councils, Public Bodies, Associations and Companies.
Lower Cretaceous marly limestone folding in a cutting along the road CN-232
Technical assistance was given to the Dirección General de Carreteras (Ministry of Fomento) on the works for the Mediterranean Highway; also a study and recommendations to stabilise the landslides that affect an embankment located at Kilometre 420.3 on the Andalucía Highway, and two other reports, one of them concerned the excavated slopes on one of the A-7 Highway directions in Barcelona, and a second one involving the works carried out to convert the N-260 road into a highway along the Montagut-Olot section in the Pyrenees. A set of technical notes was also prepared with respect to the following tasks and pathologies:
- Stabilising works for the Lingotes Embankment along the Cigales-Arroyo section of the Castilla Highway in Valladolid.
- Pathologies detected affecting the embankments located between Kilometres 48.5 and 123 of the road CN-340.
- Stabilising works for the cuttings located at Kilometre 0.9 and between Kilometres 1.8 and 2.5 of the road N-629 between Oña and Trespaderne in the Province of Burgos.
- Works on the N-II Highway along the Cervera-Santa María del Camino Section.
- Geotechnical problems affecting two zones of the CN-420 in the Province of Tarragona.
- Pathologies observed in the South on León Bypass.
- Slope pathologies affecting the cuttings for the A-7 Motorway in Barcelona.
- Geotechnical problems affecting the new Cañeda Ring Road in Cantabria.
- A variety of pathologies affecting some sections of the road N-621 (Cantabria).
- Pathologies in the Viella Tunnel (Lérida).
- Slope stability problems affecting the cutting on the road CN-232 in the Province of Castellón.
- Adjustments to the cutting slopes between Kilometre 1.9 and 2.4 of the Castilla Highway
The second and final draft for the Technical Building Code referring to foundations was prepared for the Dirección General de la Vivienda, la Arquitectura y el Urbanismo (Ministry of Fomento).
Two six-monthly reports were issued for the Ente Público Gestor de Infraestructuras Ferroviarias (GIF), as part of the agreement to study the long-term behaviour of railway ballast structures; these reports contain the results of the in situ tests conducted with a view to geotechnically defining two embankment sections and one excavated section that had been pre-instrumented on the Madrid-Grajanejos section, at the Pilancones Ravine lying about 70 km from Madrid. The data obtained from static and dynamic tests conducted with a 120-tonne Rumanian diesel electric locomotive on one of the instrumented sections was also analysed.
Stabilising the slate and Palaeozoic sandstone cliffs with anchors near Castropol (Asturias)
Furthermore, and in fulfilment of another agreement entered into with the GIF, with a view to carrying out applied research, technical assistance and technological development activities of interest to the state-owned Spanish railway system, the following works were undertaken:
- Field tests using the spectral analysis of surface waves technique (S.A.S.W.) in transition earth structures, embankments and excavations at four locations on the high-speed rail link between Lérida and Barcelona.
- Dynamic tests in laboratory up to one million cycles in 9” diam. cells on micro-ballast with a maximum particle size of 4 cm.
- Improving a mobile Láser ray system for the in situ measurement of the absolute rail movements on high-speed and conventional railway tracks.
Dynamic compaction treatment by impact on urban waste-mounds
Work progressed for the Ente Público Puertos del Estado on the rockfill deformability study, with an analysis of the behaviour of the limestones in the Port of Málaga, for which the Laboratory's 1 m3 capacity direct shear box was used. As part of the port structures general technical assistance agreement that the above-mentioned company has with CEDEX, the Laboratory analysed the results of the tests conducted with a view to improving with jet-grouting, the foundation ground for the enlargement of the La Cabezuela Quay in the Bay of Cádiz.
The geotechnical problems detected at the Juan Gonzalo Quay in the Port of Huelva were also examined and solutions were proposed. Progress was also made on improving the Finite Differences programme for analysing the dynamic behaviour of breakwaters constructed with submerged caissons under exposure to waves.
A set of geotechnical recommendations to be taken into account when constructing the Bediesta Pool on the Island of La Palma were prepared for the Dirección General de Obras Hidráulicas y Calidad de las Aguas (Ministry of Environment), and several reports were issued concerning the movements detected in the fills in the Nafarrondo Quarry, which affect a section of the Guardián-Llodio Canal in Navarra.
The apparatus used to explore the Caspe Dam in Zaragoza was inspected and examined within the framework of the agreement for monitoring and exploration earth dams in the River Ebro Basin, and the results obtained from the exploration of the Calanda Dam in Teruel were analysed. A report was issued on the use of electrical techniques for detecting potential filtration links on the submerged faces of earth dams, as part of the agreement concerning the control and interpretation of the increase of water content in the cores of earth dams, with particular reference to the Canales Dam (Granada). A technical note was also issued about the documentation available on the reservoir and the heightening of Yesa Dam in Navarra.
Static barrier treatment against rockfalls on the road CN-629
Rockfall simulation on a section of the A-1 Highway
The Laboratory worked for the Dirección General de Calidad y Evaluación Ambiental (Ministry of Environment), on the technical development of Royal Decree 1481/2001 concerning waste disposal installations. Appendices I and II of that document were drawn up and a set of criteria were prepared for waterproofing and sealing waste dumps. The work was completed with a report on the use of geotechnical methods to sound and analyse zones with contaminated ground.
Several technical reports were prepared for the Gerencia de Infraestructuras y Equipamiento (Ministry of Education, Culture and Sport); one concerned the works involved in the enlargement to the Casón del Buen Retiro (Madrid); two reports contained the monitoring of the instrumentation for the Museo del Prado enlargement works, next to the Iglesia de Los Jerónimos; another one contained a study of the effects of those works on the groundwater table, and a final report dealt with the suitability of a solution based upon micropiles for enlarging the Museo Arqueológico in Córdoba.
A report on the stability of a slope in marls planned for the Las Cruces open-cast mine working in the Province of Sevilla was issued for the Regional Government of Andalucía and the final report was prepared concerning the filtration study on the Buenas Hierbas Dam in the Province of Córdoba
A report was issued for the Regional Government of Castilla and León that analysed the stability of the cuttings on the new layout for the Vivanco to Bercedo section of the Bilbao to Reinosa Highway.
A geological study was conducted for the Government of Islas Canarias that analysed the different lithotypes that constitute the weakly cemented pyroclasts.
Ties for retaining walls at the test cell excavations for the SUPERTRACK Project
Micropiles used to excavate the basements of the Casón del Buen Retiro (Madrid).
A final report was issued for Teruel County Council containing a study of the way in which cracks and earth movements have evolved and the effects of blasting upon on several houses and former barracks in the Municipality of Utrillas.
Stability problems were controlled for Castropol Local Council (Asturias) by anchoring the Palaeozoic slate and sandstone cliffs in that zone.
Final reports were issued for RENFE concerning the study of the effects of vibrations on two buildings in the Municipality of Montcada i Reixac (Barcelona), on a building on the Cuesta de San Vicente, on a tunnel in the "Railway Green Belt" in Madrid and on three houses in the Municipality of Alcobendas (Madrid).
Finally, and with respect to the technical assistance activities carried out for other public and private bodies, reference must be made to a study on Toledo Cathedral for the Cathedral Chapter, which analyses different options for waterproofing the ground in the vicinity of the San Blas Chapel. The laboratory has collaborated with the Instituto Eduardo Torroja on research work prior to establishing regulations in the Chapter on Foundations of the Building Technical Code. Work has also progressed on the agreement signed with Tierra Armada, S.A., which involves studying the behaviour of unconventional footing for prefabricated walls made of reinforced concrete, by means of full scale in situ tests.
Excavating the trench where the test cell will be installed for the SUPERTRACK Project
Monographic article
Equipment for studying anchorage in rock materials
Formulae that are merely experimental or empirical rules that deduce an anchor's resistance to pull-out from the fixed percentage of the unconfined compressive strength of the rock are often used to design the anchorage for rocky materials. Not only do these formulae fail to consider the properties inherent to each rock type or its failure criterion, they are also difficult to extrapolate from one environment to another; this fact, coupled with a lack of reliable data concerning a parameter such as dilatancy, which, in spite of this lack, is extensively used in the commercial calculation programs available on the market, has led to the need for analytical calculation methods to be developed that enable the user to obtain the tensile strength of an anchor in rock in a rational way.
Diagram of the tensometer
As part of its activities in the field of Rock Mechanics, the Laboratorio de Geotecnia is making a major effort to develop a theoretical model that will serve to calculate the tensile strength of the anchors and the general form that the failure takes, and to do so for any failure criterion in the ground, as well as to establish a law of plastic flow with variable dilatancy.
As part of this process, the equations for the model have been particularised for two different failure criteria, and the linear and non-linear behaviour cases have been analysed in that failure law using the Mohr-Coulomb and Hoek and Brown criteria, respectively. The research work that is being carried out at the Laboratorio de Geotecnia analyses anchors in rock by means of the theory of non-associated plasticity. The approach used is based upon the limit equilibrium theories, taking as a calculation variable the instantaneous angle of friction, and then minimising the failure stress by applying Euler's variational method.
This method is being validated with a series of tests that have to be conducted using a very specific item of equipment called a tensometer, which is composed of a tension device for the anchor tests, a computing system and a mould for manufacturing the pieces of mortar (See Figures 1 and 2).
The tensometer is used to alternately test parallelepiped concrete samples or rock samples 0.50 m high with a 1 m x 1 m base, subjecting them to an increased tension exerted by a jack, until failure takes place. The equipment is designed to be portable so that the tests can be performed in the field, but it was initially used to conduct laboratory tests.
Tensometer designed at the Laboratorio de Geotecnia (CEDEX)
This piece of equipment consists of two parts, which are described below:
- A strong mechanowelded structure with extremely rigid sections that minimise deformations during the test, with a 1 x 1 m support base on the sample. The hydraulic tension applier is fixed to this structure in the central shaft. The assembly is equipped with a grille to protect it from flying particles during the test.
- A 10-tonne vertical-load static hydraulic applier, attached to the load support structure with a flange; its maximum operating pressure is 210 bars, and it has a run of 100 mm.
- A coupling tool whose twofold purpose is to transmit the loads to the anchor and to align them.
- A hydraulic exchange that can produce up to 210 pressure bars with the capacity to activate the hydraulic applier, equipped with control and safety valves. The hydraulic exchanged is attached to the strong structure in such a way that the assembly can be easily moved and transported.
- An extensometric cell with a rated capacity of 10 tonnes, attached to the applier, for measuring the actual vertical load that is mobilised during the test
The following components are used to measure and transmit the data:
- A potentiometer transducer for measuring the movement, for directly measuring the deformation during the test, coupled to the hydraulic applier, and with a measuring range of 50 millimetres.
- An electric control and measurement assembly, including the measurement amplifiers, electrical connection devices, the control manoeuvring mechanism, and the auxiliary power supplies for measurement and control.
- Amplifier for extensometry, to prepare the signals for the extensometric cells to measure the strength, with an extensometric transducer.
- A conditioner for the potentiometer transducer, to prepare the transducer movement signals for measuring the deformation, with standard bridge connection.
Pull-out test in mortar
This equipment was used to carry out two types of test. The first ones were conducted using mortar as the base material for simulating the rock matrix (See Figure 3). The relevant scale ratios can be applied to these tests, which were carried out to scale, with a view to obtaining conclusions about the behaviour of the anchors used in engineering works carried out in rock. Other tests were conducted on rock, which enabled us to reach conclusions about the actual values of the dilatancy angle, by making comparisons with the theoretical model. Sandstone, limestone and granite (See Figure 4) were the types of rock selected to perform these tests, because these are the rock materials that are most commonly found in Spain.
A total of 60 pull-out tests were conducted, of which 32 were conducted on anchors inserted into eight different blocks of mortar with an unconfined compressive strength of about 14 MPa after 14 days; the rest of the test were carried out using rock material. Three blocks of sandstone, two blocks of limestone and two blocks of granite were used, on which 8, 10 and 10 tests, respectively, were conducted.
These tests were used to obtain the failure form and the force that was necessary to pull the anchors out of these materials. The results of the experiment were compared with the theory developed and succeeded in validating it. Furthermore, it was possible to deduce the actual dilatancy laws governing the rocks in question.
Pull-out test in granite