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

Cone penetration testing (CPT) is one of the most used site characterisation tools in geotechnical engineering. In offshore areas dominated by carbonate sediments, CPT is extensively used to characterise material types and assess their strength and flow characteristics. However, unlike for non-carbonate sediments where large number of empirical relationships are available correlating the CPT response with the corresponding soil behaviour and associated engineering parameters, there is still a lack of data correlating the CPT response with engineering behaviour of carbonate sediments. This paper presents CPT responses for different types of marine carbonate sediments. First, a brief background on carbonate sediments including key terminologies used and their characteristics in comparison to their non-carbonate counterparts are discussed. This is followed by examples of CPT data from major offshore project sites representing different type of materials ranging from uncemented fine grained (Muds and Silts) and coarse grained (Sand) sediments to variably cemented carbonate materials. The CPT results are then used, in combination with laboratory test data, to evaluate the suitability of standard soil behaviour type charts and indices available in the literature. Typical zone of results for carbonates sediments as a function of normalized cone parameters are also presented for reference purposes. Some challenges on the direct use CPT based methods to engineering analyses for carbonate sediments and the key areas of research from a practical engineering perspective are also briefly discussed.

Abstract

This paper is an extension of our previous research investigating the potential of machine learning models to estimate shear wave velocity (Vs) from piezocone penetration test (CPTu) measurements. The aim of this update is to examine the effect of incorporating geographical information, namely latitude and longitude, as input parameters to the machine learning models. New models are developed by incorporating both CPTu parameters and spatial coordinates as input features and are compared to models developed with only CPTu parameters. Furthermore, SHAP (SHapley Additive exPlanations) analysis is employed to assess the importance of different features and variables in the developed machine learning models. The results show improvement in prediction performance when adding geographical data, indicating the influence of geological variations on Vs. The paper shows the potential of using geospatial information to improve the data-driven approach for estimating soil properties from CPTu tests when large worldwide datasets are available.

Abstract

Characterizing the in-situ state of soils is essential for evaluating their vulnerability and the consequences of failure. The cone penetration test (CPT) enables efficient, repeatable, and continuous soil characterization based on the recorded response to penetration. Particularly for waste storage facilities, analysis of CPT results can help avoid failures that could lead to significant socio-economic and environmental impacts. Human-made soils in waste storage facilities, like coal combustion products and mine tailings, can have a large fraction of silt-sized particles, which makes them prone to experiencing partial drainage during CPT soundings at standard penetration rates. However, the current state of practice still predominantly adopts the assumption of fully drained or undrained conditions, which may lead to inaccurate interpretation of soil properties and state. This study aims to explore a new CPT-based characterization framework for intermediate silty soils using cone tip resistance values to determine the soil state. To do so, CPT soundings were performed in-flight in centrifuge models of a coal combustion product with different initial densities at varying penetration velocities. Soils with a low density and contractive behavior experience a decrease in tip resistance as the penetration velocity is increased due to the generation of excess pore pressures, resulting in high ratios of drained to undrained tip resistance (Qtn,drained/Qtn,undrained). In contrast, the tip resistance increases with penetration velocity, resulting in low Qtn,drained/Qtn,undrained ratios in soils of a high density and dilative behavior. The proposed framework uses Qtn,drained/Qtn,undrained to identify contractive layers and is expected to help assess the vulnerability of soil layers to experience liquefaction failure.

Abstract

A geotechnical assessment of mine tailings state conditions using the static cone penetration test performed at different tailings storage facilities (TSF’s) will be presented in this paper. Both tailings evaluated herein are deposited as a slurry (hydraulic deposition) and have similar grain-size distribution curves. A set of Cone Penetration Tests (CPTu) with pore pressure measurements were performed at each site to evaluate the state of the tailings. To assess the contractive-dilative behavior classical methodologies were adopted such as i) the contractive/dilative boundary suggested by Robertson (2016) ii) the approach suggested by Plewes et al. (1992) and cited by Jefferies and Been (2016) and iii) the yield stress ratio method proposed by Mayne and Sharp (2019). Partial drainage effects will be identified with classical methodologies. The results were compared to evaluate the difference and limitations of each methodology. Comments on the similarity between the two tailings evaluated herein will also be presented to explain the differences in behavior due to aspects such as mineralogy, gradation, stress history and deposition.

Abstract

Major challenges are encountered in characterizing and performing liquefaction assessment of gravelly soils since performing traditional in-situ tests, such as the Cone Penetration Test (CPT), in gravelly soils can be challenging, and since gravelly soils are not well-represented in existing case history databases used to develop semi-empirical methods for liquefaction assessment. This has been the primary reason for the ongoing efforts to develop methods based on other invasive tests, such as shear-wave velocity (Vs), and penetration tests with larger probes and greater energy delivered to the rod, such as the Dynamic Cone Penetration Test (DPT). While CPT-based liquefaction analyses have been comprehensively studied, limited research has been conducted comparatively evaluating the performance of the other two methods. This paper performs liquefaction triggering assessment of gravelly reclamations using data from the welldocumented case history of the port of Wellington (New Zealand) using CPT, DPT, and Vs measurements. Results show that while the Vs measurements overestimate liquefaction resistance, the DPT and CPT agreed relatively well with observations from past earthquakes due to the greater sensitivity of these test methods to soil density and stratigraphy

Abstract

This 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.

Abstract

One of the most significant processes in soil dynamics is liquefaction. It is a loss of strength coupled by a quick increase in pore pressure, causing soil particles to break apart for a brief period. There have been several approaches published for calculating the residual or liquefied shear strength of cohesionless soils. This article gives cone penetration test relationships for assessing vulnerability to loss of strength and liquefied shear strength in a variety of soils. Then, based on the results of our studies, we were able to map the liquefiable zones of the Mnasra region, located in the Gharb basin and extending over an area of 4000 km2, which is characterized by two main facies: (i) a predominantly gravelly and/or conglomeratic facies, separated by silt-clay levels (east of the nappe), (ii) a predominantly sandy, sandstone and calcareous facies, separated by silt-clay levels (coastal zone and southern sector on the Maâmora side). IPL calculations predict a spatial-temporal variation in liquefaction at depths ranging from a low probability of liquefaction to a certainty

Abstract

The state parameter is the main variable employed for predicting the undrained behaviour of artificial soils such as tailings and hydraulic fills. Current practice involves using screening methods and CPTu data (e.g. Robertson (2010)) or cavity expansion based methods (e.g. Shuttle and Jefferies (2016)). However, these methods have drawbacks: they are based on empirical correlations for clean sands and do not consider the effect of partial drainage. This paper presents a site-specific procedure to determine the state parameter of tailings, inspired in the work by Monforte (2022). The procedure consists of: i) calibrating the CASM constitutive model using triaxial tests for different state parameters; ii) determining the plausible range of hydraulic conductivity based on dissipation tests; and iii) conducting numerical simulations of CPTu tests using the Pocket G-PFEM tool for different combinations of state parameters and hydraulic conductivities. By comparing the results of the simulations with the real CPTu data, a site-specific relationship between the state parameter and the CPTu measurements can be established. To validate the procedure, the method is applied to a real tailings deposit and contrasted against routine screening methods. In the particular case studied in this paper, the method predicts more contractive behaviour than the screening methods. While the method is still in an early stage of development, it looks very promising because it allows for using the raw CPTu data to calibrate a constitutive model, without resourcing to any kind of correlations or empirical transformation models.

Abstract

Geotechnical site characterisation of variably cemented material is often challenging due to lack of data. Drilling data is routinely measured as a part of standard geotechnical site investigation and can provide an alternative method to derive continuous ground profiles with depth. This paper examines the use of drilling data for site characterisation purpose. Based on the drilling data obtained from an offshore windfarm project site, where variably cemented materials were found, it is shown that the borehole specific energy calculated using the drilling data reasonably captures the variation in material types with depth. Also, the results show that borehole specific energy can be correlated with the laboratory test data in a similar manner to cone penetration test. Based on the results obtained from different locations covering a range of material types and in-situ state conditions, generalised relationships between different geotechnical parameters and borehole specific energy are presented. An example of how the generalised relationships developed using borehole specific energy can be used to derive design profiles for a selected site is also shown. The data and interpretation approach presented in this paper provide a useful guide for how the drilling data can be used to assess the continuous ground profile for variably cemented sites where only limited or no in-situ test and intermittent sampling data are available.