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Gassy Soils ofF the Llobregat Delta: Impact on Geomechanical Characterization
Get PDFThe presence of biogenic gas in the soft soils of the Delta del Llobregat at the Port of Barcelona has already been reported by various authors based on geophysical investigations and in-situ tests. As the impact of gas presence on soil behaviour remains uncertain, it is of interest to describe the behaviour of these gassy soils as they may affect future expansions of the Port of Barcelona. Recently, in new geotechnical investigations at the Port of Barcelona, gas emissions have been observed, in several locations in the vicinity of the South breakwater, while performing in situ tests (CPTu and SDMT) or during borehole drilling. Samples were extracted from those boreholes that were subsequently used for laboratory tests. Given the potential impact on geotechnical properties, the results of the investigation were utilized to increase the understanding of gassy soils. Essentially, the focus was on detecting anomalies in geotechnical parameters at the points where gas was detected. These anomalies were also correlated with observations of soil structure obtained from microCT scanning X-ray images of undisturbed samples from the zones where gas was present
Comparative Analysis of DMT, CPTt And DPH for Soil Characterization of Granular Rhine Soil
Get PDFThis paper presents the results of direct and indirect field investigations carried out as part of a detailed soil investigation of granular Rhine soil in Germany. After a brief overview of the project and geological conditions in the project area, the results of the field investigations are shown in a compressed and comprehensive manner. Focus of the presented results are the DMT, which are a novelty for projects in Germany. The presented results clearly indicate the challenges regarding the interpretation of the test results in the mainly dense to very dense sands and gravels, as especially the results of the DMT tend to scatter a lot. Despite the interpretation challenges, a comparative analysis of the CPT and DMT is carried out showing possible relations between dilatometer modulus Ed, friction angle DMT , corrected cone resistance qt and relative density ID. The relations are discussed, and limitations are presented. Afterwards, a strength-based correlation between CPT and DMT to determine the effective friction angle as a function of the cone resistance is presented indicating reasonable results for the investigated soils in the project area. The paper finishes with a discussion of limitations of the DMT and conclusions
A Case Study for Data-driven Soil-layer Delineation
Get PDFIn the past, soil-layer delineation methods can usually only take a single type of input data, e.g., soil-type data at boreholes. However, this does not fit in the geotechnical engineering practice where multiple types of data are usually available during site investigation (e.g., borehole data and cone penetration test data are both available). This paper adopts a novel data-driven method for soil-layer delineation that accommodates multiple types of site investigation data. The basic idea is to include liquid limit (LL), plasticity index (PI), and fines content (FC) into the soil parameters of analysis. According to the Unified Soil Classification System (USCS), the information of (LL, PI, FC) can be used to determine whether the soil is sand, silt, or clay. As a result, the conditional random field simulation results for (LL, PI, FC) can be used to delineate sand, silt, and clay layers. If extra soil parameters (such as cone penetration test results) are incorporated, the novel method can accommodate multiple types of site investigation data. A real example of the Fucino Basin in Italy is adopted to demonstrate the application of the novel data-driven soil-delineation method
Inherent and CPTu-measured Scale of Fluctuation of Undrained Geomaterials: a Numerical Perspective
Get PDFThe vertical scale of fluctuation of soil parameters is often indirectly estimated through Cone Penetration Testing (CPTu) as the test provides nearly continuous and repeatable data. However, the variability quantified from CPTu might not be representative of a soil parameter intra-site variability, but rather the effect of the variability of soil measured through its response to the cone probe. The objective of this work -of an openly prospective nature- is to examine how the vertical inherent spatial variability of clay-like insensitive geomaterials propagates to the cone tip and friction sleeve resistance by means of numerical modelling. A total stress analysis is presented, in which the undrained shear strength is described according to random field theory. Numerical results show that the scale of fluctuation of the tip resistance and friction sleeve resistance is greater than the one assumed for undrained shear strength
Correlations Between The Pressuremeter And The Rigid Dilatometer Parameters In Soils
Get PDFThe Dilatometer Fondasol Test (DFT) is a unidirectional loading test in a borehole that provides an in-situ stress-strain curve. Two rigid shells are spread in the soil at a constant displacement rate by several small hydraulic jacks. First results using this probe in soils were obtained by Besson (2022) who also provided methods to compute from the stress-strain curve both a pseudo-elastic modulus and a limit stress. However, additional data were required to establish strong correlations between the dilatometer parameters and the pressuremeter parameters. This paper introduces new results obtained in various sites in France and synthetises all the results obtained so far. For each site, pressuremeter soundings and dilatometer soundings are carried out in pairs using the same drilling methods. DFT and PMT are performed at the same depths and at the same strain rate. For the computation of moduli and limit stresses, semi-automatic methods are employed to prevent subjective interpretations. Correlations are proposed between the dilatometer modulus and the pressuremeter modulus as well as between the dilatometer limit stress and the pressuremeter limit pressure. The established correlations, along with their limitations, are interpreted
How to get a good match for consolidation coefficient
No full textIt is difficult to get accurate magnitudes when dealing with consolidation coefficient, decisive when clays and clayey silts, are compressing, especially if secondary consolidation is in play. This is a typical condition in harbours when new areas are to be reclaimed to get more and more loading/unloading areas. There are several approaches to assess consolidation rate. The oedometer cell is the main lab test used to get the compressibility parameters. It is accepted that 24 hours is a good time for each pressure. However, some soils consolidate slowly, and they need more time. Especially when slope is far from horizontal. On the other hand, “true” consolidation coefficient is obtained when surpassing the preconsolidation pressure. Thus, values obtained below preconsolidation pressure are usually discarded. Horizontal coefficient of consolidation can be assessed with dissipation tests from piezocones. If piezometers are installed within the consolidating layer, comparing with the theoretical isochrones we may derive the “true” consolidation coefficient. If settlements are measured, a comparison with theoretical ones can be informed on the predominant consolidation phenomenon. Much care is to be applied and not misunderstand the process in play. Dissipation tests give way to much higher consolidation values than laboratory tests. This could be due to anisotropic effects, but the main reason is that dissipation occurs in a reloading process, while oedometer tests are in primary consolidation, at least from the preconsolidation pressure and on. This paper shows some ideas to properly assess the process involving consolidation
Engineering characterization of lacustrine soil deposits at the inner bay of Puno around Titicaca Lake
Get PDFThe inner bay of the city of Puno has been the subject of various investigations that seek to recover and enable floodprone areas, through strategic urban development projects (urban infrastructure) and protection works. On the other hand, the characteristics of soft soil deposits, such as those in the inner bay of Puno, represent a risk of problems with excessive settlement of the infrastructure. This study presents an engineering characterization of the lacustrine soil deposits in the inner bay of the city of Puno, around Lake Titicaca. The site lies around the Pier of Puno city at Lake Titicaca, the highest navigable lake in the world, approximately a few hundred meters in front of the National University of the Altiplano of Puno (UNAP) and a few hundred meters to the southward of the Pier of Puno city. Physical, strength, and deformation properties were determined from standard laboratory tests. The material studied corresponds to the shallow layers of the study area, corresponding to sedimentary soils of the lacustrine units and fluvial-alluvial deposits of the inner bay of Puno. These lacustrine soils are classified as highly plastic silts and organic clays (MH and OH). The results show the significant influence of the quality of soil samples, due to the sampling method and storage time, on consolidation and resistance parameters. Finally, this study provides valuable insights into the influence of sample quality on consolidation parameters and shear strength of the lacustrine soils in the inner bay of Puno city around Titicaca Lake
Offshore shear wave velocity measurements for the assessment of soil sampling quality
Get PDFShear wave velocity Vs is a critical soil parameter for several geotechnical and geophysical engineering applications including seismic site response analysis, liquefaction risk assessment and design of shallow and deep foundations. Moreover, the comparison of shear wave velocity between laboratory and in situ measurements has become a standard acceptance criterion for the assessment of sampling quality. Offshore in situ shear wave velocity testing is considerably more challenging than onshore, due to the difficulties in the correct deployment of the instrumentation as well as of the wave source, in absence of direct visibility of the ground level below water. This paper describes the methodology employed for offshore shear wave velocities (Vs) measurements in the harbour of Barcelona in September 2022. Medusa SDMT tests were performed in sea depths ranging between 15-17 m from a jackup and employing a drill rig to penetrate the probe down to 40 m below the seafloor. The paper includes examples of recorded S-wave seismograms, analyses of Vs repeatability for the same depth measurements and Vs profiles with depth. In the same test locations, carefully prepared specimens of undisturbed samples were tested after reconsolidation to the estimated in situ stress states in stress path triaxial cells with bender elements transducers. The obtained lab shear wave velocities were compared with the in situ values obtained with the Medusa SDMT tests to assess sample quality
Computational modeling of cutting disc-rock interaction in mixed ground conditions
Get PDFThis paper presents the performance of a simulation tool based on state-based peridynamic theory, developed to model the interaction between cutting discs of a Tunnel Boring Machine (TBM) and the ground being excavated. Compared to existing TBM performance prediction models, the current computational approach accounts for mixed ground conditions, different TBM and disc designs, as well as the direct coupling with wear models. The developed peridynamic model is thoroughly validated using several benchmarks, including indentation tests on sandstone specimens. Additionally, a full-scale Linear Cutting Machine (LCM) test conducted on Colorado Red granite is simulated, where cutting forces obtained from the computational model at various disc spacings are compared against experimental data. Excavation in mixed ground conditions, which can lead to excessive tool wear or failure due to rapidly changing cutting forces, was examined through an LCM experiment. Scaled-down peridynamic simulations show cutting force trends consistent with the LCM experiment results. Finally, to predict the influence of these varying cutting forces on tool life, an abrasive wear model is implemented in the peridynamic simulation framework
Critical planes analysis of the impact of porosities on the fatigue of metal solids
Get PDFIn this work, we take interest in the impact of defects present in metal solids manufactured by material fusion or by additive manufacturing on their fatigue life during cyclic loading. Indeed, we observe a more or less strong local plasticity around the defects even if the stresses remain below the elastic limit, which can strongly impact the fatigue life of such solids. In the case of a part obtained by steel casting, it is the retassures that make the part most vulnerable. In the case of solids obtained by additive manufacturing, the most damaging defects are surface roughness and porosities linked to a lack of fusion. In order to estimate the fatigue life of such solids, it is necessary to observe the states of stress and strain around the defects during a cycle. As stress levels can be relatively high locally, critical plane type criteria are relevant for estimating the fatigue life of such solids. In order to carry out a fatigue analysis of a part obtained by steel casting or by additive manufacturing, we propose to model it by finite elements, with a refinement of the elements around the porosities, then to calculate the local stress and strain states, and finally to implement a critical plane type criterion, like the Fatemi-Socie criterion. The critical planes are the planes on which the maximal shear strain amplitudes occur. The local stress and strain states can be highly multi-axial. So the determination of the critical planes can be very computationally and storage consuming. In the present work, an analysis in the space of deviators of the deformation tensor makes possible determination of such planes in each of the numerous nodes of the mesh. These three steps of calculation, correlated with experimental tests, makes it possible to envisage obtaining fatigue life laws for numerous metallic materials presenting defects