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

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

The construction of a permanent bridge required a temporary bridge parallel to the permanent bridge alignment. Preloading of the permanent bridge abutment occurred under a separate early earthworks contract. That fill was removed, and the temporary structure was constructed. The fill was then replaced behind the abutment. Movement of the southern abutment of the permanent bridge was identified but with a gap of several weeks in survey monitoring due to a XMAS break period. The abutment had moved towards the river and temporary bridge. Potential causes for movement were investigated by additional investigation adjacent to and far away from the temporary bridge piles. Post movement tests carried out included: Dilatometer Testing (DMT) to assess for shear zones (if any) for slope instability, Cone Penetration Testing (CPTu) to assess strength changes (if any) to proximity of piles and new inclinometer readings. INSAR data was also obtained. A 3-D finite element analysis (FEA) carried out by a consultant matched the measured lateral displacements at the adjacent bridge. Based on that correlation, it was concluded that the removal of the close-ended temporary piles was the main cause of the excessive movement, and this initiated a contractual claim. Correlation is not causation. This case study provides a background on the site data and numerical analysis. The FEA did not include much of the site observational and site data post movement. Given the FEA was given the same credence as the site data, this suggests that data is now considered a point of view.

Abstract

This paper explores the merit of including cyclic episodes in cone penetrometer tests to measure changes in sleeve resistance during cycling. Tests were carried out in a geotechnical centrifuge in a kaolin clay and a dense silica sand. The data from the tests in clay indicate that the cone sleeve mobilises the remoulded undrained shear strength during the initial penetration, but that with continued cycling, the mobilised interface shear strength reduces to around one-third of the remoulded undrained shear strength before increasing. The initial reduction is considered to be due to local consolidation around the cone sleeve (leading to total stress reduction), whereas the subsequent increase is attributed to consolidation- induced strength hardening. Tests in sand also indicate a reduction in sleeve friction during cycling, consistent with the shear band contraction mechanism associated with friction fatigue of piles in sand, but with no consolidation-induced hardening behaviour as these tests were drained. The findings suggest that cyclic cone penetrometer tests may be a convenient means of gathering data for geotechnical design for problems where the cyclic response at the clay/structure interface is of interest. Considerations on the implications for offshore site investigations are provided.

Abstract

Building a ground model through manual processes can be time consuming, as large amounts of data need to be classified to define the extent and spatial distribution of the different soil materials. This paper delves into the application of machine learning (ML) methodologies, in conjunction with in-situ geotechnical testing data, to develop the ground model for a downstream dam founded on both weak and liquefiable soils. The dam covers a linear extent of approximately 800 m and was extensively characterized by means of in-situ tests, including 206 cone penetration tests (CPTu), 37 boreholes and 35 test pits. The performance of two unsupervised ML clustering algorithms are compared: Density-Based Spatial Clustering of Applications with Noise (DBSCAN) and an extended version with a hierarchical component (HDBSCAN). The clustering uses CPTu data, which consists of the normalized cone tip resistance (Qtn) and the normalized sleeve friction (Fr) varying with elevation. Nearby borehole logs are used to evaluate the results of both clustering methods for a single single CPTu sounding using different clustering parameters. Then, a global clustering including several CPTu soundings is done and results are compared with the ground model that was manually made using Leapfrog software. Both methods show very good performance, with HDBSCAN being better and more robust.

Abstract

Cone penetration tests, CPTs, are extensively used in the Netherlands to assess the stability of fourteen thousand kilometres of dykes protecting the country from flooding. On the regional dykes, site testing is planned and executed only from spring to autumn. The data collected in the drier season of the year must be used then in safety factor calculation for dyke stability with reference to the worst expected conditions, including the highest weights and the highest water pressures over the year. Inferring reliable values of the shear strength in a different season implies understanding the unsaturated response of the dyke material and the effect of variable water content on the CPT response. In previous studies referring to CPTs in unsaturated soils, it was observed that both the cone resistance and the sleeve friction depend on suction, however, only the cone resistance was used to determine the shear strength in combination with water content or suction probes installed into the ground. In this contribution, we analyse an extensive set of data, coming from repeated CPTs performed over one year on the Maasdijk near Oijen in the Netherlands. The data are elaborated to investigate whether the entire set of data can be exploited to try to derive the water content and the constant water content shear strength at the same time, if the test is repeated in different seasons.

Abstract

During reclamation projects huge amounts of sands are dredged and placed to create artificial land. To increase the density and therefore to mitigate the potential risk of liquefaction as well as to increase the stiffness and internal friction angle of the sand, it is often necessary to compact the reclaimed sand. The performance targets for compaction are frequently verified by means of achieving a particular relative density that is generally correlated from Cone Penetration Tests (CPT). For many reclamation projects, due to the non-availability of local quartz or silica sands, crushable, carbonate or calcareous sands are used. In these crushable sands, due to the very high stress concertation below the CPT cone, the particles tend to crush. The well-known published correlations between the relative density and cone resistance are established for non-crushable silica sands and are thus not applicable to these crushable sands and can result in over treatment costing time and money. Usually, the crushing effect is quantified in a calibration chamber test and a project specific correction factor is introduced. Alternatively, to avoid this costly and time-consuming procedure the use of measuring the shear wave velocity with seismic CPTs (SCPT) is possible. The Cyclic Stress Ratio (CSR) for liquefaction analysis and other soil parameters required for the design verification can be correlated without being influenced by the crushing of particles due to the non-invasive procedure. This paper gives an overview of the common practice for work verification in crushable sand and shows an approach to determine the required compaction parameters using seismic CPTs.

Abstract

Characterization of the unsaturated zone below an MSW landfill is critical to evaluate the groundwater pollution vulnerability assessment. The permeability of the soil in the unsaturated zone, the depth of the water table, and the quality of pore water in the soil can provide a reliable site-specific estimate of pollution vulnerability. To evaluate these factors, an attempt was made to use the hydraulic profiling tool (HPT) in the unsaturated zone below a non-engineered MSW landfill in Delhi. HPT was equipped with an injection logger capable of qualitatively measuring permeability at the cm scale and an electrical conductivity (EC) dipole that measures the bulk soil conductivity. HPT findings were compared with piezocone penetration tests (CPTu) and the electrical conductivity of extracted pore water from the soil cores. The results indicate that pressure from the injection logger works effectively for medium/fine sand and silt and has greater sensitivity to permeability changes for these soils than CPTu. Pore-water EC was found to have a good correlation with volumetric water content and EC from HPT. A groundwater vulnerability matrix was conceptualized using factors based on the time of leachate travel and maximum pore-water EC observed, both derived from HPT, and risk scores were assigned from 1-5, corresponding to the 9 zones of the matrix. The locations surveyed at the dumpsite received scores of 4 and 5, which depicts high vulnerability. The results indicate that HPT can be used for rapid site-specific groundwater vulnerability assessments.

Abstract

The use of soil data is essential in geotechnical design, but in a preliminary project phase such data are usually limited to that inferred from field tests, like CPT, SPT or DMT. In previous publications by the authors and co-workers, it was shown how such data can be automatically processed into soil profiles and parameter sets for geotechnical finite element analysis. Another publication demonstrated the automated processing and creation of geological models as an intermediate step to more advanced 3D geotechnical modelling in a BIM / Digital Twin environment, which facilitates the link with other disciplines and stakeholders in a project. The major challenge of connecting layers across multiple 1D boreholes to form 3D soil layers is overcome by using a Machine Learning clustering algorithm. As a next step, the previously introduced Automated Parameter Determination (APD) method (connecting correlations using Graph theory) is applied based on averaged CPT parameters from all contributing layer sections. The result is an automated system that creates a complete 2D or 3D finite element model, including constitutive model parameters, for geotechnical analysis purposes. An automated system may be very efficient when exploring different design alternatives in an early stage of a project. However, it is important to emphasize the role and responsibilities of the geotechnical engineer in the design process, which requires the system to be transparent, verifiable, and adaptable. This paper describes the state-of-the-art of this ongoing research project.

Abstract

This paper presents the implementation into the open-source finite element simulation framework OpenSees of the new Unified CPT-based method for driven piles in sands. The formulation incorporates the maximum skin friction and endbearing CPT values based on the new ISO-19901-4 under development, within the non-linear load-transfer curves calibrated against the measured responses from the static pile tests in the unified database. Special attention was paid to maintaining an open-source philosophy during the implementation. The important EURIPIDES research tests in highly dense sands are considered as a worked example to illustrate the application of the implemented method. The numerical benchmark shows good agreement between the model and full-scale measurements.