Documents published in Scipedia

• Passive Seismics Monitoring Applied to Rock Block Stability in the Montserrat Massif

  M. Janeras*, A. Macau, J. Andrés, F. Parera

  ISC2024.

  
  

  Abstract

  The Montserrat Massif (Catalonia, NE of Spain) is a natural and cultural heritage where rockfall risk arises. Therefore, a risk mitigation plan is underway, including rockfall monitoring at different scales using different techniques. Particularly, the rock block A3-6, menacing the rack railway leading to the monastery, has been monitored since 2010 by extensometers that show the cyclic movement due to the annual thermal cycle, which is mainly recoverable, but small residual plastic derivations have been detected in a varying amount, along years. At the end of 2021, stabilization work has been carried out. The block has been monitored with passive seismic techniques before, during, and after these works in order to detect signs or evidence of evolving stability similar to previous experiences in the Alps. Two main results have been found. On the one hand, a slight difference in the recorded ambient noise between the potentially unstable block and the rear massif was detected, for both the H/V spectral ratio and the polar spectrogram. A characteristic resonance frequency of the block is observed around 20 Hz in the direction of the toppling instability mechanism. On the other hand, during the drilling works of the anchor bolts, it was possible to clearly detect when the drilling hammer crossed the rear joint of the block. This allows confirming the assumed geometry of the block and the required anchor length, as well as a qualitative assessment of the persistence of the joint and its mechanical contact.

  Abstract
  The Montserrat Massif (Catalonia, NE of Spain) is a natural and cultural heritage where rockfall risk arises. Therefore, a risk mitigation plan is underway, including rockfall [...]

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• A Review of Laboratory Cone Penetration Test (CPT) in Unsaturated Soil

  R. Li*, A. Leung, A. Yerro, C. Yu, Z. Jiang

  ISC2024.

  
  

  Abstract

  Cone penetration testing (CPT) is a common site investigation method used to determine soil profiles and characterize in-situ soil properties. However, most of the existing interpretations of CPT data are established for dry or saturated soil. In recent years, studies have shown that ignoring the matric suction effect in unsaturated conditions during data interpretation could lead to biased soil characterization and soil property estimates. Still, due to the lack of fundamental understanding of the mechanics during cone penetration in unsaturated soils, accounting for the matric suction effect on the CPT data-soil properties/characterization is not clearly defined, and more laboratory testing in controlled environments is required to fill this gap in knowledge. Existing studies are different in terms of penetrometer diameters (dcpt), chamber dimensions, penetration rate, sample preparation, and suction control techniques. This paper first presents a review of the existing literature on CPTs performed in unsaturated soils in a controlled laboratory environment and discusses the effects of the aforementioned factors on the measured tip resistance. In addition, new results from centrifuge CPTs performed with controlled water levels in a rigid chamber are presented. For the purpose of such experiments, a 12.7 mm diameter miniature cone penetrometer was designed and fabricated to measure tip resistance values. Unsaturated CPT data show that the presence of matric suction in the soil tends to increase the tip resistance measurement during the cone penetration process. More tests are planned in the future to quantify this increase in CPT response with respect to other soil properties.

  Abstract
  Cone penetration testing (CPT) is a common site investigation method used to determine soil profiles and characterize in-situ soil properties. However, most of the existing [...]

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• Interpretation of CPTu in Sensitive Fine-Grained Soils and Prediction of Residual Excess Pore Pressures in Consolidating Soils

  P. Rahardjo*

  ISC2024.

  
  

  Abstract

  Robertson (1986) soil classification on Sensitive Fine Grained Soils using CPTu is of interest since the variation of these soils include those of Consolidating Soils. However, the classification does not include into detail such as the influence of the existence of excess pore pressure prior to penetration testing or what is the contribution of the excess pore pressure to the total penetration resistance. Rahardjo et al (2008) studied this phenomena by extrapolation of the dissipation test data to determine the residual excess pore pressure which play an important role in CPTu testing. Further, Rahardjo et al (2016) continued investigation of the CPTu in Consolidating Soils using Bq, Bq* and Effective Stress Concept (Rahardjo et al. 2017). These findings have been very useful when using CPTu in very soft soils and ultrasoft soils where the undrained shear strength of the soils is very low. This paper is the results of several studies of CPTu testing in marine clays, lacustrine, ultrasoft soils or even peats. The author found that there is significant value of Bq and Bq*, hence are parameters of importance when dealing with soft soils and discussed in more detail. Recent applications are in very soft soils and peats in Sumatera and East Java mud eruption which are are also included.

  Abstract
  Robertson (1986) soil classification on Sensitive Fine Grained Soils using CPTu is of interest since the variation of these soils include those of Consolidating Soils. However, [...]

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• Effective Friction Angle of Intermediate Grain Size Soils from Variable Rate Piezocone Penetration Test

  Y. Liu, Z. Ouyang*

  ISC2024.

  
  

  Abstract

  The effective friction angle (') is one of the most sought soil properties in geotechnical analysis and design that controls the fundamental soil strength behaviour. In this paper, A recently compiled database on intermediate grain size soils that were tested by variable rate piezocone penetration tests (VRCPTU) is used to examine an effective stress limit plasticity solution using piezocone data developed by NTH (Norwegian Institute of Technology) towards prediction of the geomaterials’ effective stress friction angle. It is shown that penetration rate during probe advancement influences the CPTU measured data and the drainage conditions can be indicated by corresponding normalized cone resistance and normalized porewater pressure measurement. Further analysis revealed that an input parameter termed the angle of plastification (β) from the CPTU solution correlates with soil contraction and dilation tendency and can be used to evaluate the 'of investigated soils, together with other normalized CPTU measurements. The tentative suggested formula of β for intermediate soils undergone VRCPTU testing is given based on the investigated database. A comprehensive testing program on the Yellow River Delta (YRD) silts in China and a silty geomaterial from northern Italy in Europe including benchmark laboratory triaxial tests on high quality samples, field and calibration chamber variable rate CPTU are showcased to demonstrate the verification of the NTH solution for evaluating 'of intermediate grain size soils.

  Abstract
  The effective friction angle (') is one of the most sought soil properties in geotechnical analysis and design that controls the fundamental soil strength behaviour. In [...]

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• Effect on the Local Seismic Response Produced by the Construction of Rafted Piles Foundation

  A. Trevisan, M. Lago*, F. Veronese

  ISC2024.

  
  

  Abstract

  The seismic forces must be properly defined as required by European geotechnical design Codes. They are dependent from the morphological and stratigraphic characteristics that determine the local seismic response. The local seismic response can be evaluated using a simplified approach which is based on the classification of the subsoil according to the values of the shear wave propagation speed Vs. In the present case study, to complete the quay of the Rovigo Interporto (facing the River Canal Bianco), where a not negligible load is planned to be applied (50 kPa), has been designed a foundation with a large slab founded with not pre-casted reinforced concrete piles diameter 350 mm, drilled without removing soil, with vibrating casing, for settlement reduction (rafted piles as settlement reducers), on an area of approximately 6000 m2. The subsoil in this area, from geological and geotechnical point of view, is very variable and with layers of soft clay and loose sand or silt, with no presence of a dense and uniform sand layer where to transfer loads to. Moreover, the geotechnical model was complicated because of the presence of an old diaphragm wall with anchors (whose projection in plant covers around half of area) and was designed a large underground basin for hydraulic invariance. For this reason, an extensive campaign of CPTU and DMT tests, together with boreholes, sampling and laboratory tests was carried out in this area, which allowed a detailed characterization of the subsoil. Through direct measurement of seismic micro-tremors, carried out before and after the installation of the piles, has been evaluated the modification of the resonance frequency of the site, and modification of the propagation speed of the shear waves Vs induced by the slab over rafted piles over the entire area.

  Abstract
  The seismic forces must be properly defined as required by European geotechnical design Codes. They are dependent from the morphological and stratigraphic characteristics [...]

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• Application of two analytical CPTU solutions to sensitive clay in Québec

  P. Mayne, J. Greig, E. Cargill

  ISC2024.

  
  

  Abstract

  A recent series of CPTU soundings in sensitive clay at the Louiseville Quebec test site has been published, allowing for the application of two closed-form analytical solutions based on: (1) effective stress limit plasticity and (2) hybrid cavity expansion-critical state methods. These are used for geoparameter interpretations including: effective stress friction angle, undrained shear strength, yield stress ratio, undrained rigidity index, and the coefficient of consolidation. Profiles of these soil parameters are compared with the benchmark values obtained from available series of previous and present laboratory testing programs at this site, including index testing, triaxial compression, and one-dimensional consolidation. Piezocone dissipation tests are used to assess the coefficient of consolidation which are validated by pressuremeter holding tests and lab oedometer tests. An empirical CPTU screening method identifies the Louiseville site as underlain by sensitive clay, versus a regular insensitive clay deposit, whereas soil behavior type charts using Q-F-Bq indicate the soils are either silt (zone 4) or regular clay (zone 3). The alternate screening method is verified by field vane and laboratory fall cone that show the clay is in fact sensitive (average St ≈ 22).

  Abstract
  A recent series of CPTU soundings in sensitive clay at the Louiseville Quebec test site has been published, allowing for the application of two closed-form analytical solutions [...]

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• Back Analysed Interpretation of Yield Pressure from CPT using Bq

  R. Kelly

  ISC2024.

  
  

  Abstract

  A sand and gravel quarry has been backfilled with clays and silts washed from the quarried materials. The quarry is now being repurposed for an industrial development. Prefabricated vertical drains and surcharge have been installed to consolidate the soft sediments. Settlement plates and vibrating wire piezometers were installed to track the performance of the surcharge. CPTs have been performed adjacent to the settlement plate / VWP installations in order to confirm thickness of soft soils and to assess their yield pressure in order to facilitate back analyses. A Medusa dilatometer test was also performed as an independent measurement. Correlation between the CPT and DMT showed that Nkt was much smaller than the normal range and the Nkt factor appeared to be consistent with Bq interpretations. Similarly, the coefficients used to interpret yield pressure lay at the high end of the range and could be justified through correlation with Bq.

  Abstract
  A sand and gravel quarry has been backfilled with clays and silts washed from the quarried materials. The quarry is now being repurposed for an industrial development. Prefabricated [...]

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• Investigation of the Relationship Between CPT Cone Resistance and Relative Density for a Range of Granular Soils

  Y. Tian, B. Lehane

  ISC2024.

  
  

  Abstract

  This paper presents an investigation of the effects of the properties of reconstituted granular soils on the relationship between CPT cone resistance (qc) and friction angle. The results from a large number of calibration chamber tests conducted at a number of stress levels involving soils with varying shapes, compressibility and mineralogy are presented. The paper also provides data recorded in a parallel series of investigations into the mechanical properties of the granular soils employed in the chamber tests. It is shown that the nature of granular deposits has a strong influence on the relationship between qc and relative density, and that there is a near linear relationship between the cone resistance and the critical state friction angle for sands reconstituted at a given density and stress level.

  Abstract
  This paper presents an investigation of the effects of the properties of reconstituted granular soils on the relationship between CPT cone resistance (qc) and friction angle. [...]

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• Estimation of Cone Factor in Undrained Clay Using Spherical and Cylindrical Cavity Expansions

  J. Yu, J. Zhu, M. Huang, Y. Lin, Z. Shi

  ISC2024.

  
  

  Abstract

  The current cone factor of piezocone penetration tests is derived based on the assumption of elastic-perfectly plastic soil, and the soil rigidity index in the formula is empirically determined. This study introduces a novel in-situ testing equipment for determining both undrained shear strength and soil rigidity index of clays. The presented technique combines cone penetration test (CPT) and in-situ expansion. Indoor experiments are conducted to test the equipment. Corresponding theoretical analysis is carried out to interpret the experimental results. A hyperbolic hardening soil model for undrained clay is used throughout the derivation process so that the nonlinear stress-strain relation is taken into account. The ALE (Arbitrary Lagrangian Eulerian) large deformation finite element method is first employed to analyse the influence factors such as rigidity index, cone roughness, and in-situ stress anisotropy during the penetration process. The formula of cone factor is then proposed and correlated with the limit expanding pressure of the spherical cavity. The rationality of the cone factor is verified by comparing with the ALE analysis results and those published studies. Besides, the limit pressure of in-situ expansion tests is determined based on the load-displacement curve of cylindrical cavity expansion, Specific bearing capacity formula is derived and revised based on finite element analyses. Finally, undrained shear strength and soil rigidity index are solved based on the penetration and expansion results. Interpretation of experimental results shows that the proposed method in conjunction with the newly developed CPT can reasonably predict the undrained strength and rigidity index of soft soils.

  Abstract
  The current cone factor of piezocone penetration tests is derived based on the assumption of elastic-perfectly plastic soil, and the soil rigidity index in the formula is [...]

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• Determination of Geotechnical Parameters of a Heterogeneous Tropical Soil Deposit Through Different Penetration Rate CPTu Data

  V. Junqueira, J. Duarte

  ISC2024.

  
  

  Abstract

  Assessing soil properties through geotechnical tests is a crucial activity to understand its behaviour. Field tests serve as a good approach to characterize the geotechnical behaviour of materials according to their in-situ condition. However, the interpretation of these tests often relies on empirical correlations, which can become complex when dealing with soils with notable heterogeneity. This paper objective is to determine the strength parameters and discuss the consolidation effects for a heterogeneous tropical soil deposit using data from field tests with different rates of penetration and laboratory tests. A layer identified as low-strength soil classified as silty-sand to silty-clay exhibited partial drainage during a standard-rate cone penetration. The approach proposed by Randolph and DeJong (2012) was used to determine the penetration rate necessary to mobilize an undrained behaviour of the material, since the cone penetration results shown that the material is mostly contractive and clay-like. CPTu tests were also conducted with penetration rates of 60 mm/s and 100 mm/s, to proper estimate the undrained shear strength (Su). These tests reinforced the presence of a preconsolidated upper layer, enabling the estimation for the overconsolidation ratio (OCR). For the normally consolidated portion of the residual soil, rapid tests that achieved a normalized velocity (V) associated with distinctly undrained penetration were used to derive the undrained shear strength (Su), with a cone factor (Nkt) estimated from standard-rate tests available. The geotechnical parameters estimated were then compared to the laboratory data results showing a convergence with the parameters estimated by the field tests.

  Abstract
  Assessing soil properties through geotechnical tests is a crucial activity to understand its behaviour. Field tests serve as a good approach to characterize the geotechnical [...]

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