Documents published in Scipedia

• Paired in situ tests for site characterization and geotechnical design optimization

  D. Berisavljević*, N. Božović, N. Stanić

  ISC2024.

  
  

  Abstract

  The paper shows recent experience in performing and interpreting the three most common in situ tests for site characterization: cone penetration test (CPT), seismic dilatometer test (SDMT) and Menard pressuremeter Test (MPT). It is shown that an adequate selection of in situ test methods for site characterization can be used to correctly predict the pile head load-settlement curve. Menard pressuremeter design rules, which were established in the 1st and a draft version of the 2nd generation of Eurocodes, can be applied to SDMT readings to obtain the pile bearing capacity. It was found that corrected lift-off pressure p0 obtained in the SDMT test is similar to the Menard limit pressure pl in clay, while pressure p1 (SDMT) is similar to pl in sand. All results used in the analysis are obtained on a large-scale project where investigations are strictly controlled and performed in accordance with Eurocode standards.

  Abstract
  The paper shows recent experience in performing and interpreting the three most common in situ tests for site characterization: cone penetration test (CPT), seismic dilatometer [...]

  • 0
  •  read

• On the Effectiveness of MOSTAP Sampling in Tailings

  P. Oelofse*

  ISC2024.

  
  

  Abstract

  The MOSTAP sampling apparatus is a popular tool in geotechnical investigation, since MOSTAP sampling can be done efficiently and cost effectively with the same rig used for CPT testing. Although few publications exist discussing the nuances and application of the MOSTAP sampler in practice, it is generally found that the MOSTAP sampler provides lower quality undisturbed samples when compared to piston tube or block samples. This paper discusses the experiences and learnings from geotechnical investigations where the MOSTAP sampler was employed in platinum and discard sand tailings in Southern Africa. A comparison between different sampler diameters at the same site showed significant improvements in sample recovery with larger diameter samplers. Ancillary equipment such as a core catcher and nylon stockings have significant effects on sample recovery and quality. The soil type and degree of saturation of samples also have a significant effect on sample recovery and sample quality. Transportation and storage of samples were identified as major contributors in moisture loss and sample disturbance. Even with the potential challenges in obtaining a representative sample at depth, MOSTAP samples are shown to be greatly beneficial in evaluating a soil profile and density determination with high confidence, especially when paired with index tests. The opportunity is identified where diligent sample measurement and tracking can provide reliable and invaluable information about a relevant soil stratum. Advanced laboratory testing (e.g., triaxial and oedometer tests) is not recommended on undisturbed MOSTAP samples, these should rather be remolded for critical state line testing, if relevant.

  Abstract
  The MOSTAP sampling apparatus is a popular tool in geotechnical investigation, since MOSTAP sampling can be done efficiently and cost effectively with the same rig used for [...]

  • 0
  •  read

• Combining penetration resistance and shear-wave velocity to quantify soil microstructure for liquefaction assessment

  R. Andrus*

  ISC2024.

  
  

  Abstract

  This paper discusses two ratios involving penetration resistance and shear-wave velocity (VS) that have been proposed for quantifying the influence of microstructure in aged and cemented soils for liquefaction assessment. The first ratio is the small-strain shear modulus (Gmax) divided by the cone penetration test tip resistance (qc). Because Gmax/qc is dimensionless, it can be expressed as a ratio of measured VS divided by a function of qc with velocity units. The second ratio is the measured VS divided by an estimated VS from penetration resistance-VS relationships for relatively young sand deposits (MEVR). The advantages and limitations of both ratios are discussed. The influence of various fines content (𝐹𝐹𝐹𝐹) corrections on 𝑉𝑉𝑆𝑆, penetration resistance-𝑉𝑉𝑆𝑆 relationships, and a relationship between MEVR and the liquefaction cyclic resistance ratio correction factor for microstructure (𝐾𝐾𝐷𝐷𝐷𝐷) is evaluated using two published datasets. The results show the 𝐹 𝐹𝐹𝐹 correction to 𝑉𝑉𝑆𝑆 is minimal in the range for which the correction was derived. The 𝐹𝐹𝐹𝐹 corrections to qc and standard penetration test blow count are significant for silty soils, having a net effect of lowering the penetration resistance-𝑉𝑉𝑆𝑆 relationships and increasing the slope of the 𝑀𝑀𝑀𝑀𝑉𝑉𝑀𝑀-𝐾𝐾𝐷𝐷𝐷𝐷 predictive relationship

  Abstract
  This paper discusses two ratios involving penetration resistance and shear-wave velocity (VS) that have been proposed for quantifying the influence of microstructure in aged [...]

  • 0
  •  read

• Site characterization of large hydropower projects

  T. Trick*, K. Kontar, G. Klee, M. Stolz

  ISC2024.

  
  

  Abstract

  Hydropower plays an important role in the context of the energy transition contributing to the reduction of the CO2 emission through a permanent power production as run-of-river scheme as well as for energy storage as pump-storagescheme. Nowadays large hydropower plant designs comprise tunnel, cavern and shaft excavation work known as head race and pressure tunnel or pressure shaft. The powerhouse is often placed within a large underground cavern. The results of a ground investigation phase including the determination of in-situ parameters derived from tests in boreholes drilled from the surface are crucial for a preliminary design of the hydropower plant. Additional in-situ measurements are frequently carried out within an exploratory tunnel to confirm the first predictions and to characterize in detail the mechanical and hydraulic properties of the rock mass. Solexperts portfolio of in-situ well tests comprise the assessment of hydraulic properties vs. depth through hydraulic testing of isolated borehole sections along the borehole axes, the determination of geomechanical parameters like deformation- and Young’s modules through borehole dilatometer tests and rock stress measurements conducting hydraulic mini-frac tests. Plate load tests which use surficial loading are performed in small tunnels or test adits to measure the deformation characteristics of a rock mass on a larger scale.

  Abstract
  Hydropower plays an important role in the context of the energy transition contributing to the reduction of the CO2 emission through a permanent power production as run-of-river [...]

  • 0
  •  read

• Ground Model Workflow with DAARWIN

  I. Jaqués, C. Cano, J. Llopart*, B. Solà, I. Aliguer

  ISC2024.

  
  

  Abstract

  Structural geological models are used to understand and visualize how geological materials are organized below the Earth surface. This technique is crucial in different fields of geomechanics such as mining to identify mineral deposits and to plan mining operations, environmental engineering to assess the contamination of soil and groundwater and to design remediation strategies, and civil engineering to design foundations, tunnels and other underground structures. In this sense, ground models allow the engineer to understand and to visualize the spatial organization of subsurface geological structures and, additionally, it is possible to evaluate the spatial distribution of material properties which is essential in any geomechanical study prior to any project. In this context, SAALG Geomechanics through DAARWIN web platform provides a suitable software tool for the geotechnical engineer to perform the complete ground model workflow. The process starts introducing borehole data from different sources and then, the engineer can visualize and interpret borehole logs, define geomechanical units and assign parameters from in-situ and laboratory tests, as well as assign units’ geometry from geological layers. Finally, the user can feed this information to the system to obtain a 2D cross-section, that can be exported to the commercial Finite Element software PLAXIS and use this PLAXIS model for geotechnical design and more advanced analyses such as Sensitivity analysis and Back-Analysis, which are also implemented in DAARWIN.

  Abstract
  Structural geological models are used to understand and visualize how geological materials are organized below the Earth surface. This technique is crucial in different fields [...]

  • 0
  •  read

• Combined resistivity and seismic measurements along linearly extended earth structures - acquisition and interpretation approaches

  C. Comina*

  ISC2024.

  
  

  Abstract

  Geotechnical parameters of linearly extended earth structures, such as embankments and earth dams, are usually obtained from localized investigations through drilling or penetration tests, commonly time and cost consuming. Non-invasive geophysical investigations may be considered an alternative approach for the geotechnical characterization of these structures, given their surveying speed and their depth and length of investigation. Particularly, new acquisition approaches with the use of appropriate streamer cables could strongly reduce the acquisition times making geophysical surveys ideal for a preliminary screening of these structures. Specifically, resistivity and seismic methods can be adopted given that these two methodologies could offer complementary information with respect to the pore fluid properties (resistivity methods) and the solid skeleton characteristics (seismic methods). Also, through specific correlations, relevant geotechnical parameters for the evaluation of the stability of these structure and its efficiency (i.e. hydraulic conductivity, porosity and others) can be obtained. In this paper a review of the methodologies developed in recent years for data acquisition along linearly extended earth structures is reported with special focus on the use of combined electric and seismic streamer cables. Suggestions with respect to interpretation approaches and data elaboration are also analysed.

  Abstract
  Geotechnical parameters of linearly extended earth structures, such as embankments and earth dams, are usually obtained from localized investigations through drilling or penetration [...]

  • 0
  •  read

• Long-Term ERT Monitoring Data Analysis to Set Slope Instability Attention Thresholds Based on Water Level Fluctuations

  R. Bianchi*, F. Brambilla, A. Hojat, G. Tresoldi, L. Zanzi

  ISC2024.

  
  

  Abstract

  In this paper, we discuss the results of long-term electrical resistivity tomography (ERT) monitoring of a critical slope located on an important high-speed railway gallery. Data were acquired by a customized ERT system from 24 March 2022 until 31 august 2023 and were analysed with the final objective of defining thresholds of attention for resistivity changes derived from water table fluctuations after heavy rainfalls. This helps the authorities in reducing the hydrogeological risk impacts related to potential slope instabilities triggered by extreme meteorological conditions. In order to continuously observe water level changes, five piezometers were also integrated with the ERT monitoring system which is also accompanied by a meteorological station. All datasets were inverted using a time-lapse algorithm that was optimized to minimize artifacts generated by the subsurface complex geology of the site. Due to the long period considered, seasonal temperature corrections on resistivity values were also explored by calibrating a seasonal model of soil temperature versus depth and evaluating the corresponding effects on the resistivity tomographic maps. Finally, the correlation between resistivity values and piezometric levels was studied by producing scatterplot graphs for a selected subzone of the ERT sections. Based on this analysis, a preliminary threshold of attention was defined.

  Abstract
  In this paper, we discuss the results of long-term electrical resistivity tomography (ERT) monitoring of a critical slope located on an important high-speed railway gallery. [...]

  • 0
  •  read

• Early Screening for Improved Management of Geo-risks

  R. Eddies*, R. Wood, M. Staring

  ISC2024.

  
  

  Abstract

  Across several sectors including medicine and agriculture and the extractive industries, availability of early information from screening delivers disproportionate downstream benefit to key stakeholders. With the aim of reducing uncertainty to manage geo-risks in the subsurface, site characterisation for geotechnical engineering is mainly executed following a project owner’s final investment decision (FID) and continues to rely predominantly on conventional investigation techniques that inform both the geotechnical design and construction phases of infrastructure development. However, historical project performance of capital works developments tells us that geo-risks continue to play a role in unwanted engineering business outcomes in the form of schedule and cost overrun associated with earlier cost underestimation. Fundamentally, we recognise that the construction sector would benefit from earlier, faster, and better representation of the subsurface in the top 50 m to 100 m using techniques with a light footprint and low permitting requirements at the earliest stages of project development. We describe an example early-phase screening solution based on adapted ambient noise tomography. Screening at feasibility and planning phases can help to mitigate the impact of human bias arising from epistemic uncertainty in the subsurface and can improve early decision-making where the opportunity to influence project outcome is greatest and at lowest cost. Screening coupled with an optimised conventional intrusive investigation during the execution phase can complete the information set for full project design at considerably reduced levels of subsurface uncertainty leading to improved engineering business outcomes. The industry is encouraged to promptly incorporate the screening philosophy into feasibility and planning activities and into design codes for geotechnical design and construction.

  Abstract
  Across several sectors including medicine and agriculture and the extractive industries, availability of early information from screening delivers disproportionate downstream [...]

  • 0
  •  read

• Interpretation of geotechnical data from an upstream dam for preparation of the site response analysis

  W. Durval Soares de Carvalho, T. Andrade, R. Viola, J. Ccotohuanca, M. Neto, D. Eloi*

  ISC2024.

  
  

  Abstract

  Despite seismic studies in Brazil not being common in the engineering practice as Brazil is a tectonically stable continental region, recent Brazilian regulations require seismic evaluation as supporting studies for decommission and decharacterization projects. Although there exist some critical issues such as limited laboratory data because of sampler processes related to the upstream raised tailings dams, standard tailings and soil foundation characterization, in addition to the field investigation including piezocone (CPTu), seismic piezocone (S-CPTu) and geophysical surveys are the main sources for supporting the characterization of the dynamic properties of the geostructures. This paper presents a brief discussion about the main aspects concerning to the site response analysis carried out for an upstream raised tailings dam (case study), located in Minas Gerais, Brazil. Frequency domain 1-D amplification analyses were conducted by relating local-like representative seismic records and dynamic natural characteristics of the soil profiles to evaluate the seismic response of the case study. Results showed that the maximum accelerations along the profiles are greatly influenced by the presence of the soft foundation tailings layers, and the level of amplification or attenuation is strongly influenced by the tailings layer thickness as well as the frequency content of the applied ground motions. The study pointed out that the site-specific response can support the definition of the appropriate seismic parameters to be used in engineering projects in Brazil.

  Abstract
  Despite seismic studies in Brazil not being common in the engineering practice as Brazil is a tectonically stable continental region, recent Brazilian regulations require [...]

  • 0
  •  read

• New processing methodology of televiewer data for the definition of geotechnical and structural domains

  M. Heredia Bilbao*, R. Sánchez Marín, R. Cano Martín, A. Deu Lozano, P. Martínez Diaz

  ISC2024.

  
  

  Abstract

  Six structural domains were defined using data from acoustic televiewers and oriented boreholes as part of the reopening of the old Aznalcóllar mining site in Sevilla, southern Spain, by Minera Los Frailes (MLF). Additionally, geotechnical subdomains were defined within each structural domain, classifying the subdomains based on geotechnical parameters obtained from the geotechnical logging of boreholes and through correlations. The methodology used to define the domains allows mine design and planning to be done with enough accuracy to determine the underground excavation needs and the systematic methodology. The main source of this new structural information was acoustic borehole image televiewers (ABI) and, on a much minor scale and as a complement for ABI data, oriented boreholes. This paper describes the methodology used for this definition, some of the challenges encountered during the investigation, the main results obtained and the utility of these defined structural domains in the development of the MLF mining site reopening. Additionally, a preliminary approach to an updated methodology in the definition of structural domains with the combination of televiewer data, both acoustic and optical, with data obtained from other downhole probes is also included.

  Abstract
  Six structural domains were defined using data from acoustic televiewers and oriented boreholes as part of the reopening of the old Aznalcóllar mining site in Sevilla, southern [...]

  • 0
  •  read