Geotechnical Design Lecture Notes PDF - 2023-2024

Dipartimento di Ingegneria Civile, Università di Salerno Corso di Geotecnica per l'ambiente ed il territorio MODULO II Indagi...

Dipartimento di Ingegneria Civile, Università di Salerno Corso di Geotecnica per l'ambiente ed il territorio MODULO II Indagini e monitoraggi geotecnici convenzionali e innovativi A.A. 2023-2024 Lesson n°2 7 March 2024 Prof. Dario Peduto 1 1/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Conventional investigations 2 2/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical soil characterization The geotechnical soil characterization encompasses: ❑ the definition of the detailed stratigraphy; ❑ the determination of the groundwater conditions; ❑ the identification of the current and past stress condition; ❑ the determination of the permeability characteristics; ❑ the determination of mechanical properties. The set of this information allows identifying the design criteria and related parameters. To obtain this information we use: LABORATORY TESTS IN-SITU INVESTIGATIONS 3 3/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical soil characterization A French study (Logeais, 1982) indicates that out of 2000 cases analyzed with construction problems, 80% of the problems are the consequence of erroneous geotechnical characterization. 4 4/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical soil characterization But when is Geotechnics needed? (i.e. what is the Geotechnical Engineer for?) Strictly speaking, any time a problem of soil-structure interaction is faced or, for instance, stabilization of slopes (also with non-structural techniques), subsidence (both localized and widespread) an appropriate geotechnical study would be needed. Obviously, the experience of Technicians and the complexity of the study will depend on the importance of the work. Unfortunately, we often remember Geotechnics only following failures due to a defect in a preliminary geotechnical study. 5 5/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical design GEOTECHNICAL DESIGN To deal with the study of a Geotechnical Engineering work, it is necessary to first define the physical medium to which to refer for the design choices. geotechnical system It includes: the works and interventions planned; the ground around them ("significant volume"); surface and deep waters that may be present; works or parts of works already existing on the ground and / or subsoil. 6 6/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical design GEOTECHNICAL DESIGN Particularly important role is played by the soil within the “Significant volume” This conditions the mechanical response (and therefore the behavior) to the applied actions of geotechnical works and related superstructures Lancellotta e Calavera (1999) The geotechnical system can change over time following the construction process. 7 7/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical design PURPOSE OF THE STUDY Design All factors that can influence the performance of the work, including extreme ones, are taken into consideration. Behavior prediction The behavior of the work is examined under the conditions that are most likely to occur in its life. Observation of behavior It is performed in the conditions to which the work is actually subjected. Therefore, in the design activity, reference will also be made to conditions of which, in principle, it will not be possible to observe the behavior, whereas in the forecast it will be sufficient to take into account only the actions and the boundary conditions that may actually affect the work. The deepening to be dedicated to each of the phases indicated above depends on the importance of the work itself. 8 8/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical design: the model THE MODEL Like in all engineering problems, also in the design of a geotechnical work it is necessary to resort to a procedure for reducing physical reality to a "model“. The model, characterized by more or less complex laws, must allow the quantitative analysis of the problem and provide its solution. Modeling is the core of the design problem: it is necessary to "gather" the essential information on the real problem, identifying quantities and parameters necessary for a model close to reality and yet sufficiently simple. The model must therefore be able to mediate between adherence to reality and simplicity of the model itself, in order to be easily usable. The identification of the most suitable model must therefore not pursue the aim of grasping all aspects of the problem ("exact" model); often it is sufficient and of greater use that it provides less information, which, however, allows to pursue a certain goal ("adequate" model). 9 9/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical design : the model Once the most suitable model has been identified, the constitutive laws to be used are defined, for which the parameters that characterize them must be chosen. DEFINED PROBLEM (IN GENERAL) IN CIVIL ENGINEERING A r.c. structure or in steel can be modeled almost always as a frame with elastic - linear or elastic-perfectly plastic behavior, constrained in a certain way and made up of materials (concrete, steel, composite materials) whose deformability and strength characteristics are known in advance (steel), or they can be assigned (concrete). The resolution of the problem is therefore reduced to a series of calculations, more or less expensive depending on the model chosen and the static scheme assigned, which can be tackled today with the aid of powerful automatic calculation means, which provide advanced design documents. 10 10/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical design : the model THE FIELD OF GEOTECHNICAL ENGINEERING REPRESENTS AN EXCEPTION TO THIS RULE… In fact, we have to deal with a material, the soil, which has some peculiarities: 1) it is a natural material…this implies the need not to be able to assume or assign the physical-mechanical properties, but to measure them; 2) it is a polyphase medium…this entails the need to first define the relationships between the phases in the mechanical response; 3) has a distinctly non-linear behavior…this concerns the stress-strain response (addressed in the course of Soil Mechanics). The first step of a geotechnical study is therefore to proceed with the soil classification 11 11/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical design The design of any Civil Engineering work requires the acquisition of series of information on the work and the area concerned, such as: geometric characteristics; characteristics of the materials; historical information; information on weather conditions. In the field of Geotechnical Engineering this requirement specializes in the need to characterize from the physical and mechanical point of view that part of the subsoil that influences the behavior of the work to be realized. In particular, it will be necessary to define: stratigraphy; groundwater regime; physical-hydro-mechanical properties of soils current and past stress state 12 12/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical design All the gathered information allows geotechnical soil characterization, which is propaedeutic to the definition of the geotechnical model of the subsoil GOAL OF GEOTECHNICAL INVESTIGATIONS AIM: reduce uncertainties and risks related to soil variability for a cost-effective design of civil engineering works. Everything should be tailored on the importance of the engineering work. Not always investigations are exaustive Wide and expensive investigations could result incomplete or even useless if not appropriately finalized. Any investigation should be planned and realized to address a specific technical problem: No question, no reason to survey/investigate (Dunnicliff, 1995) A SOLUTION NEEDS A PROBLEM! 13 13/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical design CONTRIBUTION OF GEOTECHNICAL SURVEY TO DESIGN DESIGN OF NEW WORKS Preliminary Phase Feasibility analysis: to carry out a feasibility analysis of the selected site for the work; Site selection: among different locations to highlight specific convenience of different options. Design Phase Support to design: to define model parameters; For an optimization of the design, under the technical and economical point of view, highligthing all critical issues related to the soil-structure interaction. To select the quarry for construction materials (e.g. for embankments, leeves, dams, etc.) 14 14/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical design CONTRIBUTION OF GEOTECHNICAL SURVEY TO DESIGN INTERVENTIONS ON EXISTING STRUCTURES Knowledge on the subsoil: to know soil properties whether not available from previous surveys; Soil characterization with respect to new construction works: to investigate a different soil volume that is relevant to new constructions. INTERVENTIONS FOLLOWING (SLOPE) INSTABILITIES Back analysis: to investigate the causes of the instability starting from current evidences; Soil characterization in the new conditions to design stabilization works. 15 15/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical design PLANNING A GEOTECHNICAL SURVEY To properly plan a geotechnical survey some preliminary data are needed. 1) Geology: knowledge of the geology of the area of interest is necessary to be informed on the possible problems. Its importance depends on the dimension and the complexity of the work. For works on non-complex subsoil, or of modest size, or for sites for which there is satisfactory bibliographic material, the geological study takes on secondary importance. For works of greater importance, with significant longitudinal development (roads, railways) or particularly complex ones (dams, tunnels) it is necessary to involve a Geologist who will be entrusted with the study. However, the current regulations require a Geological Report regardless of the importance of the work. 16 16/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical design PLANNING A GEOTECHNICAL SURVEY 2) Previous investigations: all available data obtained from previous investigations will be collected in order to better target the campaign to be carried out. 3) Inspections: the sites must be examined to verify the feasibility of the investigations and choose the most suitable equipment; in the absence of direct knowledge, information on the peculiarities of the places (e.g. dormant landslide) will be collected by technicians and inhabitants of the place. 17 17/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical design PLANNING A GEOTECHNICAL SURVEY The survey designer will define: 1) Extension of the investigation: it will be extended to all that volume that is believed to be influenced by changes in stress states and groundwater regime following the construction of the work. 2) Investigation equipment: the investigation program must be carried out having in mind the limits and potential of the tools used, on the basis of which aspects to be investigated will be chosen, checking the compatibility of each of them with the soil to be investigated. 3) Interpretation of results: for the interpretation of some in-situ tests, often empirical correlations formulated for a specific type of soil are used. For a correct interpretation, it is therefore necessary to identify the most appropriate experimental technique. 4) Significance of the results: the ground volumes investigated, even if very accurate, are extremely small compared to those involved in the work. The extension of the optimal investigation to make the extrapolation of the results more or less reliable is entrusted solely to the professional competence of the Technician. 18 18/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical survey KEY FEATURES OF THE SURVEYS An investigation program should be: Arranged over time (depending on the importance and size of the work to ensure the possibility of adaptations "in progress"); flexible (as information is acquired some evidence may be superfluous, and others, not provided for, useful and/or indispensable) timely (it is imperative that the results of the investigation are available at the time of design; since they take not negligible time, thus it would be a good rule planning and executing them well in advance) 19 19/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical survey STRUCTURE OF THE SURVEYS An investigation campaign can be divided into several stages: 1) Investigations in the Feasibility study Phase They are essential in cases where geotechnical factors can influence the location of the work (dams, tunnels); avoidable for minor works; greater extent since, as the work is not defined, the volume involved is not yet estimable Targets define stratigraphy; identify soils; identify the presence and position of any groundwater table. 20 20/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical survey STRUCTURE OF THE SURVEYS An investigation campaign can be divided into several stages: 2) Investigations in the Design Phase They must provide the designer with stratigraphic and physical- mechanical knowledge of the soils (geotechnical model of the subsoil); more limited extension (volume concerned defined) but higher density because knowledge of the subsoil must be more detailed; specific tests may be envisaged to test particular executive procedures (e.g. load tests, experimental fields, etc.). 3) Investigations in progress during the Construction Phase not always necessary; allow you to check the design hypotheses as the ground affected by the work is brought to light, which previously was not possible to investigate with sufficient approximation (e.g. tunnels); allow you to specify some aspects that may become clear during the works. 21 21/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical survey STRUCTURE OF THE SURVEYS An investigation campaign can be divided into several stages: 4) Monitoring it consists in controlling the variation over time of some quantities (pore pressures, displacements, stresses) in works in progress or completed; in the first case the results can be used as project data; in the second case, it verifies that the work has the expected behavior in the project and checks its functionality; it can also be used as a warning with respect to reaching serviceability limit states. The presence of one or more of these phases depends on the importance of the work. 22 22/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical survey COSTS They cannot be defined a priori They depend on the importance of the work They depend on the complexity of the subsoil 23 23/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical survey An example from some works in Naples area }preliminary Ramondini (2019) 24 24/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical survey An example from some works in Naples area Ramondini (2019) 25 25/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical survey COSTS In general they do not exceed the value of a few percentage units of the total cost of the work. The cost decreases in percentage as the latter increases. An error due to inadequate investigations can have very expensive consequences on the work itself. THEREFORE, AS MUCH AS POSSIBLE It is preferable planning surveys in a broader way (benefits >> increase in costs that they entail) 26 26/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical surveys EXTENSION OF THE SURVEY The investigations should be extended to that portion of the subsoil that will interact with the work to be carried out. This portion can be defined as that volume in which the changes in the stress state induced by the work produce not negligible consequences, called: “Significant volume” Strictly speaking, it depends on the characteristics of the foundation/structure and the soil involved (in particular the relative stiffness). 27 27/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical surveys EXTENSION OF THE SURVEY For a homogeneous ground there are general indications for the different types of works. 28 28/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical surveys EXTENSION OF THE SURVEY Example For foundation works, the significant volume can be assumed as the one in which the effective vertical stress increase Ds’z is greater than 15÷20% of the pre-existing vertical stress s’ z0. For stratified soils it is appropriate to investigate greater thicknesses as small increases in stress can have important consequences for layers of poor mechanical characteristics. 29 29/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical surveys TYPES OF SURVEYS The investigations necessary for the geotechnical characterization of the subsoil can be divided into two main categories: Site investigations Laboratory tests Each activity has advantages and disadvantages, but for characterization purposes they are to be considered complementary. 30 30/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical surveys Finalità AIM Mezzi d'indagine SURVEY TECHNIQUE diretti DIRECT indiretti INDIRECT pozzi SHAFTS indagini geofisiche GEOPHYSICAL SURVEYS STRATIGRAPHIC PROFILE Profilo stratigrafico trincee TUNNELS prove CONEpenetrometriche statiche PENETRATION TESTS (CPT) CPT TRENCHES cunicoli BOREHOLES sondaggi inLABORATORY laboratorio in sito IN-SITU Prove Tests su campioni indisturbati on undisturbed samples prove penetrometriche CONE PENETRATION TESTS statiche (CPT) CPT (edometro, (Eodometer, compressione triaxial tests, direct shear test) etc.) triassiale, taglio, prove penetrometriche STANDARD dinamiche PENETRATION TESTS (SPT) SPT Proprietà PHYSICALfisiche e meccaniche AND MECHANICAL prove scissometriche SCISSOMETRIC TESTS PROPERTIES DILATOMETER DMT prove dilatometriche DMT PRESSURE prove PLATEsu piastra di carico prove geofisiche GEOPHYSICAL (CH, (CH, SURVEYS DH,DH, SASW) SASW) inLABORATORY laboratorio IN-SITU in sito HYDRAULIC ProprietàPROPERTIES idrauliche prove di permeabilità su Permeabilityindisturbati tests on undisturbed prove di permeabilità in fori di campioni Permeability tests in wells and boreholes samples (permeameter, Eodometer, etc.) sondaggio, in pozzi ed in pozzetti (permeametri, edometri, etc.) LABORATORY in laboratorio in sito IN-SITU Regime idraulico GROUNDWATER REGIME PIEZOMETERS Misure in piezometrì 31 31/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024  Geotechnical surveys 32 32/32 Course of Indagini e monitoraggi geotecnici convenzionali e innovativi – A.A. 2023–2024 – Prof. Dario Peduto - Lesson II, 7 March 2024