Geotechnical Model Research Articles

Seismic amplification maps of Italy based on site-specific microzonation dataset and one-dimensional numerical approach

Prediction of surface ground motion based on advanced approaches is a non-trivial task at large area. In fact, advanced approaches require a detailed geological and geotechnical subsoil model based on geological, physical and mechanical properties retrieved from in situ investigations and laboratory data, and to perform time consuming numerical simulation of the seismic site response. Bearing in mind that there is a lack of available site investigations and laboratory data at large area, simplified methods based on “soft data” are often adopted. On this regard, a methodology to perform seismic site response analyses at national scale is proposed in this paper, based on the following assumptions: 1) homogeneous areas were identified at national scale based both on morpho-geological and lithological properties, in order to classify and analyse site-data archived in the Italian database of seismic microzonation studies; 2) geotechnical subsoil one-dimensional models of the Italian site conditions were defined according to site-data; 3) in accordance with the reference seismic hazard levels, pseudo-acceleration response spectra were selected as input motions for numerical simulations.About thirty million numerical simulations of seismic site response were performed, and national maps of seismic shaking amplification factors were produced in terms of ratio of response spectra referred to three intervals of period. This estimation of surface ground motion based on the proposed procedure is a supporting tool for large area territorial and emergency planning.

Assessment of the Local and Global Stability of the Luzzone Arch Dam Including Visualisation of the Data Analysis

This study investigates the local and global stability of the Luzzone Dam. Two finite element models were built; one with foundation rock, the other without. The purpose of this was to demonstrate a potential gulf between rigid connection modelling, and rock–structure interaction (RSI). Strand7 is not a traditional geotechnical finite element model (FEM) program, though performed well when modelling radial displacement on the Luzzone Dam. Generally, the percentage between a rigid base and RSI model displacement was 10%. This result was validated against previous numerical models on the structure. Static loads produced a radial displacement on the crown structure of 9.01 cm. Uneven stress distributions at the base of the structure were shown to be the most unpredictable result. With rigid base connections, these loads produced peak tensile stresses of 10.7 MPa. This was greater than its dynamic counterpart, asking questions about fully fixed restraints. It is noted that this is above yield and should be investigated further. Special attention will be devoted to determining the failure criteria in the simulated dams to suggest better practical guide lines for the practical engineers on site.

Role of Geotechnical Engineering in BIM process modelling

BIM “Building Information Model” creates a significant step forward in the whole process of construction. The role of geotechnical engineering will be shown as for classical building engineering so for civil engineering structures. In the first case all upper structures are in interaction with ground (subsoil), when foundation structures are basic element of this interaction. The 3D Ground model and 3D Foundation structure model create therefore one of the first individual parametric elements around basic (coordinating) BIM model. Some specificity will be shown as the impact of step by step creation (nD dimension) of the Ground model for the earliest building conception. Roughly the same is valid for civil engineering structures. Some specificity will be shown for earth structures of transport engineering, as a selection of borrow pit, definition of soil compaction for fill, fill compaction or any other methods of soil improvement and its control as they create important elements for the safe and optimal embankment design and performance. Final 3D Ground model together with 3D Geotechnical structure model (real performance) create the important base for the future decision making, when some changes will occur.

Dualism of geology and geotechnical engineering: two parallel approaches to define lake water infiltration into an interlobate esker

This case study is a modern example of how geologists and engineers have worked together to reconcile groundwater abstraction from the Pispalanharju aquifer and urban planning of the shore of Lake Näsijärvi in the vicinity of the Hyhky pumping station, located in the Tampere region of southern Finland. The authorities have been concerned about the potential impact of urban development on the important aquifer system to which the lake shore region is possibly connected. Before the study, it was estimated by the authorities that the infiltration rate into the esker from Lake Näsijärvi could be up to 1000 m3/day, forming a significant source of groundwater. Two parallel studies were conducted to examine water infiltration from the lake to the esker. The effects of a proposed land reclamation project on the shore of Lake Näsijärvi were modeled with the finite element code Plaxis 2D. Coupled analysis was conducted to analyze both the flow conditions and deformations in these conditions caused by the fill. An essential part of the geotechnical modeling was the creation of the present state of the shore complex, which already includes manmade fills and structures and a low permeability lake bottom next to the esker. Combining observations with geological and geotechnical data was highly important in the task. The amount of water flow to the esker was estimated from the analysis, and the values were compared with the results of hydrogeological analysis. For the hydrogeological studies, thousands of soil investigations were interpreted by different methods to fit a geological concept that formed the basis of geological cross-section construction work (2.5D), which was then used for groundwater flow modeling by GMS. Both GMS and Plaxis modeling simulations predicted that, due to the low conductance of silt and clay materials found on the shore of Lake Näsijärvi, the amount of water infiltrating in the direction of the esker is very limited, being only 60 to 155 m3/day. Hence, the dualism of hydrogeology and geotechnical engineering hypothesized in this case study was confirmed by modeling results.

Validation of a 3D numerical model for piled raft systems founded in soft soils undergoing regional subsidence

Abstract In this paper a 3D numerical model using a software based on the Finite Element Method (FEM), was developed and validated using the results obtained in a geotechnical centrifuge model of a piled raft system founded in soft soils undergoing regional subsidence. The piled raft configuration had nine piles distributed in the center of the raft. The kaolin parameters were obtained, calibrated, and validated for the Hardening Soil Model (HSM), based on laboratory triaxial and oedometer test results. Also, a single pile load test was carried out in the centrifuge to get the resistance parameters used in the FEM. The developed numerical model reproduced satisfactorily soil and foundation consolidation displacements due, not only by the structural service load but also by the pore pressure drawdown. For load distribution on piles and raft, the model reproduces with good agreement the foundation behavior only for the structural service load, for pore pressure drawdown some adjustments on the embedded piles elements shaft and base resistance had to be done. The developed model allowed to identify the most sensitive parameters for this type of simulation, to define the types and stages of analysis that had the best fit for the physical model, and to obtain additional results to those measured in the physical model, e.g., the axial load distribution developed along the piles and therefore the magnitude of the negative skin friction, that is an important load that should be considered for the structural safety review of piled foundations subjected to this complex conditions.

Experimental investigation of cracking behaviors of ductile and brittle rock-like materials

The cracking characteristics of ductile rocks were studied by similar materials with sand, barite, epoxide resin, polyamide, silicone rubber and alcohol, while the cracking characteristics of brittle rocks were investigated by similar material with sand, barite, rosin and alcohol. In this paper, to enhance the application range of the rock-like materials in the field of geotechnical engineering model tests, the values of the elastic modulus and the compressive strength of the artificial rock-like materials are changed in a wide range by adjusting the amount of cementitious materials (epoxide resin, polyamide, rosin, etc). The elastic modulus, compressive strength and cracking characteristics were obtained from the complete axial stress–strain curves of the specimens made of similar materials, which were cast using the different mixture ratios. These experimental data can provide quantitative investigation on mixture ratios of similar materials of rocks to model the geotechnical engineering. Furthermore, the effect of mixture ratios on mechanical properties and crack propagation pattern of specimens were also investigated by the specimens with pre-existing flaws under uniaxial compressive tests

When do rock glacier fronts fail? Insights from two case studies in South Tyrol (Italian Alps)

AbstractThe fronts of two rock glaciers located in South Tyrol (Italian Alps) failed on 13 August 2014, initiating debris flows in their downslope channels. A multimethod approach including climate, meteorological, and ground temperature data analysis, aerial image correlation, as well as geotechnical testing and modeling, led to the reconstruction of the two events. An integrated investigation of static predisposing factors, slowly changing preparatory factors, and potential triggering events shed light on the most likely reasons for such failures. Our results suggest that the occurrence of front destabilization at the two rock glaciers can only partly be explained by the occurrence of heavy rainfall events. Indeed, antecedent hydrological and thermal ground conditions were characterized by a saturated active layer favored by a snow‐rich winter and extensive precipitation in late spring and summer. Also, the rising trend of air temperature during spring and summer months since 1950s might explain the concurrent marked displacement of the two rock glaciers. Indeed, geotechnical investigations have provided strong indications that one of the investigated rock glacier fronts was at a marginally stable state prior to 2014. As rainfall events more intense than the one that occurred in August 2014 were previously recorded in the same area without resulting failures at the studied rock glaciers, we propose that both predisposing and preparatory destabilizing factors have played a key role in the 2014 rock glacier front failures.

Energy dissipation of rammed earth-timber joints under cyclic loading

Rammed earth-timber joints without enlarged ends have been used in rammed earth buildings for several hundreds of years. Due to the embedment nature, the joint has a certain degree of flexibility, allowing the floor and roof beams to slide without damaging the rammed earth, enabling dissipating energy during earthquakes. The energy dissipation mechanism of rammed earth-timber joint has not yet been fully understood. This study studied the energy dissipation characteristic of eight rammed earth-timber joint specimens via cyclic pull-out/push-in experiments, investigating the effects of compressive loading, embedment length, and surface roughness on joint performance. Results show that the joint stiffness under cyclic loading was reduced nonlinearly with the increase of pull-out displacement until the occurrence of slippage. The high vertical compression from the upper level, the deformability of timber frames, and the plasticity of rammed earth were found to be the primary energy dissipators. A linear frictional and nonlinear geotechnical hysteretic model, combining frictional and soil mechanics theories, was established to represent the joint behavior. In addition, a simplified multi-linear hysteretic model was developed for the same purpose. The predictions and the measurements had good agreement, suggesting that geotechnical methods should be employed to analyze the joint, maintaining the assumption that both the timber frame and the rammed earth are linear-elastic.

Geotechnical parameters modelling and the radiation safety of expansive clayey soil treated with waste marble powder: a case study at west Gulf of Suez, Egypt

The present paper aims to reduce and detect the environmental impact of radioelement concentrations and waste marble powder (WMP) in the surrounding environment and additionally, improve the characteristics of the expansive soil and investigate the effect of stabilizers on the swelling soil to use a foundation layer. Different geotechnical laboratory tests have been performed on representative clay samples to define the physical and mechanical characteristics. The results indicate that the swelling pressure and swelling potential are reduced from (805.7 to 576 kN/m2) and (15.78 to 7.11%), respectively. The plasticity index decreased from 35.9% (high plasticity) to 19.4% (low plasticity), and the free swell index becomes zero by adding waste marble powder. Geospatial techniques have also been used to produce the distributions layers of different geotechnical characteristics and radioelements’ concentrations. These layers were integrated to produce a geospatial model. This model showed a noticeable improvement in the properties of clayey soils after the use of waste marble powder, which ranged from low expansion to high expansion. The radioelement concentrations of all samples are below an acceptable limit, except that the concentration of 40K is greater than the acceptable limit. This study recommends a 40% replacement of WMP. This amount is suitable and economical for this kind of treatment because of its positive solutions to protect the environment from pollution and reduce the cost of construction.

Analysis of earth pressure distribution on deep circular shafts in composite geological strata using centrifuge modelling

With the rapid development of urban underground space, the depth of working shaft has been gradually becoming deeper to accommodate the underground construction needs. The existing studies for earth pressure distribution of shafts are mainly focused on sandy soils within 30 m. There is a strong need to investigate the earth pressure distribution on deep shafts (more than 30 m) in complicated soil conditions using centrifuge modelling to fill the knowledge gap and provide experimental basis for design. In this paper, geotechnical centrifuge modelling was used to investigate the earth pressure distribution along deep circular shaft structures (with a depth of 100 m) in composite geological strata. Three centrifuge tests on model shafts in layered ground with different thickness of clay and sand were carried out, respectively. Drainage method was used in the experiment to simulate the unloading effect caused by excavation of soils inside the shaft model. The earth pressure distributions along the shaft lining before and after the excavation were investigated. The results were analysed and compared with other existing earth pressure theories. This research provides valuable insights for earth pressure distribution for design of circular deep shafts (e.g. 100 m) in composite geological strata.

PRELIMINARY STUDY ON PLASTICINE AS A SUBSTITUTE COHESIVE MATERIAL FOR GEOTECHNICAL PHYSICAL SOIL MODELING

<p>Plasticine is an artificial material made from solids such as gypsum, lime, mixed with petroleum jelly or micro wax and acid fat. The properties of plasticine are likely similar to natural clay and is influenced by oil content. The information about mechanical properties of plasticine is still very rare, and as such the study on it is riquired and must be conducted intensively. The preliminary laboratory study has been conducted to understand the behaviour of plasticines. Microwax and petroleum jelly based plasticines were utilised with the variation of oil content, whereas kaolin clay with the variation of water content is utilised as a reference material. The study is focusing on the stress-strain behaviour for both microwax and petroleum jelly based plasticines compared to the stress-strain behaviour of kaolin clay. This paper reports the result of preliminary investigation regarding the use of plasticine as an alternative artificial material for substitution of clay in soil modeling. Some engineering properties from unconfined compression strength (UCS) test and hand penetrometer are shown. The result indicates that the stress-strain behaviour of plasticine resembles the stress-strain behaviour of kaolin clay. The plasticine is suitable as a substitute cohesive material and it has a potential to be utilised for geotechnical material modelling in the future.</p>

PRELIMINARY STUDY ON PLASTICINE AS A SUBSTITUTE COHESIVE MATERIAL FOR GEOTECHNICAL PHYSICAL SOIL MODELING

Plasticine is an artificial material made from solids such as gypsum, lime, mixed with petroleum jelly or micro wax and acid fat. The properties of plasticine are likely similar to natural clay and is influenced by oil content. The information about mechanical properties of plasticine is still very rare, and as such the study on it is riquired and must be conducted intensively. The preliminary laboratory study has been conducted to understand the behaviour of plasticines. Microwax and petroleum jelly based plasticines were utilised with the variation of oil content, whereas kaolin clay with the variation of water content is utilised as a reference material. The study is focusing on the stress-strain behaviour for both microwax and petroleum jelly based plasticines compared to the stress-strain behaviour of kaolin clay. This paper reports the result of preliminary investigation regarding the use of plasticine as an alternative artificial material for substitution of clay in soil modeling. Some engineering properties from unconfined compression strength (UCS) test and hand penetrometer are shown. The result indicates that the stress-strain behaviour of plasticine resembles the stress-strain behaviour of kaolin clay. The plasticine is suitable as a substitute cohesive material and it has a potential to be utilised for geotechnical material modelling in the future.

Stability Analysis of a Landslide: A View with Implications of Microstructural Soil Characters

The 2015 Devrek landslide is one of the largest and most puzzling features on the Devrek-Eregli Highway in Zonguldak Province, in the north-west of Turkey. The landslide which was activated in March, was about 700 m long, 110 m wide with a volume of 1,100,000 m3. In order to assess the landslide hazard in a systematic way, we have employed several techniques such as geotechnical, microstructural and finite elements (FE) modelling. X-ray diffraction and X-ray fluorescence studies show low clay content in the crown section and the amounts of illite and sepiolite do not exceed 25% where there is detrital sand indicating that there is continuous sliding activity. The main sliding body demonstrates implications of liquefaction according to the amount of fine sand and clay obtained by laboratory measurements. The most active clay group prevailing the landslide formation are illite and sepiolite. Furthermore, rounded fine quarts have increased sliding and rolling activity risk according to their physical structures combined with high-seasonal rainfall rate. The FE method was used for both static and dynamic slope stability investigations. Since the landslide region are in a very active tectonic region, earthquake-triggered landsliding strongly correlates with measured peak ground acceleration. Therefore, we have tested the model in numerical dynamic analysis, and the results show a deterioration in landslide stability during seismic loading which puts the study area at risk. All analysis carried out for the landslide assessment shows a continued landslide hazard for the residential areas close to the landslide foot zone.

Geo-environmental monitoring and 3D finite elements stability analysis for site investigation of underground monuments. Horemheb tomb (KV57), Luxor, Egypt

The Valley of the Kings (KV) is a UNESCO world heritage site with more than thirty opened tombs. Since the first tombs were constructed, at least 24 historical flash flood events has been identified, each of which has been contributed to the destruction and deterioration of the tombs. Recently, most of these tombs have been damaged and inundated after 1994 flood. In order to understand the Geo-environmental impact mainly the past flash floods due to the intensive rainfall storm on the valley of kings and the long-term rock mass behavior under geostatic stresses in selected Horemheb tomb (KV57) and its impact on past failures and current stability, Remote sensing, GIS, LIDAR, 3D finite element stability analysis and rock mass quality assessments had been carried out using advanced methods and codes. Our work provides environmental satellite space views via landviewer Erath Observation System (EOS) Platform with passive and active sensors which include the Normalized Difference Vegetation Index (NDVI), Soil-Adjusted Vegetation Index (SAVI), Atmospherically resistant vegetation index (ARVI), Green Chlorophyll Index (GCI), Normalized Burn Ratio (NBR), Normalized Difference Snow Index (NDSI), Light Detection And Ranging (LIDAR) images, Terrain (DEM) Digital Elevation Models, 3D geological maps. In other hand experimental and numerical geotechnical evaluations and modeling of the rock mass of these underground structures and their surroundings have been executed. We estimated the rock mass quality of the different members within the Thebes limestone and Esna shale formations using the mechanical testing and Rock Mass Rating (RMR), rock quality system (Q-system) and Geological Strength Index (GSI) systems. Our recent analyses show that the KV57 rock- cut tomb at Luxor has been cut into poor to very poor quality marl shale masses due to the impact of flash foods. Rock failures of ceilings and pillars were frequently facilitated by local, unfavorably oriented persistent discontinuities, such as tension cracks and faults. Other failures were related to the disintegration of the marl limestone and Esna shale Formations into individual nodules upon weathering. Our data suggest that, in ancient Egypt monumental tomb construction, low-strength rock masses rarely resulted in modifications of the planned tomb design in order to minimise the risk of rock falls and to prevent collapses. The current flood protection measures are not enough. For this two following measures are proposed 1—to rise the current wall by 50 cm. 2—to fill the depression by reshaping bathymetry.

BIM – AN APPLICATION IN GEOTECHNICAL ENGINEERING

BIM model represents a significant step forward within the frame of the overall process of construction. This new approach goes from the assumption that up to date praxis, which is represented by different sets of 2D or 3D drawings of drawings, technical reports and calculations does not cover all problems of the above mentioned overall process of construction. Basic principles of BIM will be discussed, not only from the view of 3D models of the structure design. The utilization of the BIM model during life time structure expectancy will be stressed - from the initial phase (investigation, design) via the phase of structure execution, maintenance and ending with structure demolition at the end of life time expectancy. Specificity of the geotechnical engineering is in this entire process fundamental, as each construction is in the interaction with ground. 3D model of the ground (geotechnical model) is therefore one of the basic individual parametric elements from which BIM model consist. Ground model is time dependant as geological profile and geotechnical properties are refinement during each phase of ground investigation as well during geotechnical structure construction. Final 3D Ground model together with 3D model of geotechnical structure represents a first significant step of the overall BIM model. In the case of underground or earth structures such output can be primordial element of the BIM model with parametric elements around it. Finally some other possibilities or practical applications are mentioned.

Centrifuge Modeling of Soft Soil Reinforced with Granular Columns

This paper presents a geotechnical centrifuge model of an embankment built in stages, over a 6.0 m layer of soft soil reinforced with nine floating granular columns arranged in a 3 × 3 square grid. The container was divided in two compartments where reinforced and unreinforced soil were tested simultaneously for comparison purposes. The load was applied by means of a 4 m high sand embankment (prototype dimensions) built in three steps. For each step, the centrifuge was stopped to allow the placement of the embankment layer and then re-accelerated up to 26 g and the excess of pore pressure was allowed to dissipate after each step. The instrumentation, comprised of total stress cells, pore pressure transducers and displacement transducers, was configured to collect information about the load transfer mechanism between the soil and the instrumented central column for each loading step during pore pressure dissipation. Results showed that despite representing only 30% of the total load, the first step provoked almost 70% of total vertical displacement. Finally, the columns were exhumed for a detailed and comprehensive visual analysis aiming to support and explain the results obtained.

Development of Data Integration and Sharing for Geotechnical Engineering Information Modeling Based on IFC

With the rapid development of infrastructure construction, geotechnical engineering has always been worthy of attention due to its complexity and diversity. Accelerating the informatization of geotechnical engineering will contribute to the project management, but the information contained in geotechnical engineering cannot be well integrated because of the lack of unified data standards. Building Information Modeling (BIM) has been considered as an effective technology to manage information, and Industry Foundation Classes (IFC) in BIM serves as a neutral and open standard for the exchange of information. However, it was found that BIM cannot express the information of some structure objects and geological objects well during the construction process of geotechnical engineering. Combined with the characteristics of geotechnical engineering, taking advantage of the good extensibility of IFC, this paper proposes a “Built‐In Generation Schema” for geotechnical structure models and a “Plug‐In Extension Schema” for three‐dimensional (3D) geological models, ultimately forming the basic data system of geotechnical engineering information models based on IFC. Applying extended IFC to the modeling process, the BIM‐based modeling method of geotechnical models is proposed. In addition, an IFC‐based platform is developed to integrate geological models and structure models for further displaying and analyzing of geotechnical engineering models. The work in this paper provides a feasible way and technical support for promoting the integration and sharing of geotechnical engineering information and enhancing the multiprofessional collaborative work.

Comparisons of Two Approaches for Geotechnical Model Calibration with Scarce Data

Geotechnical models are usually built upon assumptions and simplifications, inevitably resulting in discrepancies between model predictions and measurements. To enhance prediction accuracy, geotechnical models are typically calibrated against measurements by bringing in additional empirical or semiempirical correction terms. Different approaches have been used in the literature to determine the optimal values of empirical parameters in the correction terms. When measured data are abundant, calibration outcomes using different approaches can be expected to be practically the same. However, if measurements are scarce or limited, calibration outcomes could differ significantly, depending largely on the adopted calibration approach. In this study, we examine two most commonly used approaches for geotechnical model calibration in the literature, namely, (1) purely data‐catering (PDC) approach, and (2) root mean squared error (RMSE) method. Here, the purely data‐catering approach refers to selection of empirical parameter values that minimize coefficient of variation of model factor while maintains its mean value of one, based solely on measured data. A real case of calibrating the Federal Highway Administration (FHWA) simplified facing load model for design of soil nail walls is illustrated to thoroughly elaborate the differences in practical calibration and design outcomes using the two approaches under scarce data conditions.

ВЫДЕЛЕНИЕ КЛЮЧЕВЫХ ЗОН КОНТРОЛЯ В СИСТЕМЕ ГЕОТЕХНИЧЕСКОГО МОНИТОРИНГА

In this paper, we propose an algorithm for identifying key zones of geotechnical monitoring based on the data of an information and analytical system. The proposed algorithm is based on the analysis of the stability of individual sections of the geotechnical system, group stability using a neural network approach and a basic model. The training sample is formed on the basis of the geotechnical system model and a priori information. To isolate homogeneous reactions of a geotechnical system at different values of its parameters, the data clustering procedure is used. The correction of the permissible limits of the output of the controlled parameters is proposed to be carried out taking into account the results of the bifurcation analysis. The practical verification of the proposed algorithm was carried out on the monitoring data of a three–story building. The results obtained during the processing of the data of the information and analytical system of geotechnical monitoring by the proposed algorithm are consistent with the measurement and modeling data.

I-BIM based approach for geotechnical and numerical modelling of a conventional tunnel excavation

Very recently the Building Information Modeling (BIM) design approach has landed in the infrastructure field, giving life to the I-BIM, the BIM for the infrastructures, including geotechnical underground works likes tunnels. In this framework, the present paper shows an application in the field of geotechnical engineering of the BIM based design approach to the case of an underground line. It is a tunnel excavated by means of traditional method, currently under construction. The project defines, in a central BIM model, a detailed tunnel structure model integrated with geological-geotechnical information for the definition of the subsoil 3D model. Once the BIM model of the tunnel stretch under study was completely defined, it was imported into a finite element (FE) model to perform deformation analyses. Thus, BIM-to-FEM-to-BIM interoperability was exploited in order to verify the maturity level of the BIM approach in the field of application for geotechnical infrastructures. Finally, the BIM fourth dimension (4D) was also implemented in the central model for the time management of the tunnel excavation process, synchronized with the numerical model. The BIM based procedure proposed in the present work can be considered as a case study in the technical literature of I-BIM for tunnels, putting in evidence limitations and advantages: i) a high level of BIM maturity was not yet achieved in the infrastructures field; ii) the BIM-to-FEM interoperability seems to be not fully effective and many operations still require the manual intervention; iii) the FEM-to-BIM interoperability brings back all geotechnical choices and hypothesis to the central BIM model, linking the models into a continuously interoperable circuit; iv) an important part of the design of civil infrastructures consists of addressing geotechnical aspects, hence the inclusion of ground conditions and geotechnical data into the BIM model can improve the quality and the usefulness of the model, not only during the design phase but also, and in particular, during the construction and the lifecycle management of the infrastructure, as a support to decision making process especially in urban context.