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

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

The exploration, characterisation, and monitoring of the subsurface is relevant to a wide range of applications, from environmental monitoring and in-situ characterisation to infrastructure construction (e.g., directional drilling and tunnelling) and resource withdrawal. Bio-inspiration offers promising solutions to overcome two of the most important challenges in the development of autonomous subsurface exploration probes: exploration range (related to drag forces) and steerability (i.e., ability to control direction of movement). The work uses a previously proposed bio-inspired intruder shape to study the relationship between tip orientation and the resulting forces (lateral and vertical); and explores the idea that these forces can be used to steer the probe, i.e., control the direction of motion of the probe as it advances. Numerical results with the discrete element method and experimental results with a large-scale test bed show a direct relation between tip orientation and the steering (lift and lateral) forces – supporting the case for steering systems based on intruder tip rotation. In the results, lateral and vertical forces also show a strong relation with tip orientation, however, for the tip shape tested, the vertical forces are limited to the neutral to upwards range (i.e., towards the free surface). Experimental results evidence the significant effect of intruder deformation (bending) and/or path deviation in the penetration forces acting on the intruder.

Abstract

To determine a robust geotechnical model from measurements of drilling parameters is one of the great desires of geotechnical investigations. Drilling parameters have the advantage of presenting very granular data (data-points every centimetre) much like the CPT. They allow for the identification of soil samples during the drilling process and can traverse all terrain types, from soft clays to hard rocks. However, interpreting each parameter, like penetration rate or thrust, in isolation can be challenging, as these parameters can vary greatly within each soil layer due to natural heterogeneity, the drill rig’s configuration and the noise introduced by the discontinuous interaction between soil and drill bit. Various authors propose using compound parameters such as specific energy, penetration resistance and alteration index alongside cautious filtering allows for a better interpretation, giving physical meaning to the measurements. These compound parameters have been developed from simple correlations, aiming to normalise parameters heavily influenced by drilling conditions or even aiming to evaluate the work or the energy spent in excavating the soil. Beyond that, many authors have devised algorithms to automate or standardize the interpretation of drilling logs by identifying homogenous zones or the probability that a given point belongs to a certain layer. This paper presents a comparison of such methodologies for identifying soil layers based on MWD profiles proposed in the literature. Assessment of the geotechnical structure may be made through different analytic and advanced statistical methods. MWD profiles from worksites throughout France will be used to compare and qualify these methods.

Abstract

In this paper, a new innovative method of geotechnical investigation applicable to seafloor is proposed. This method is the improved version of Sampling and Cone Penetration Test (S&CPT) to evaluate geotechnical properties by Cone Penetration Test (CPT) while collecting continuous samples quickly and inexpensively for offshore geotechnical investigations. In the previous study, demonstration tests on soft cohesive soil were conducted, and some problems were found. The purpose of this study is to modify the sampler to improve penetrability, sampling performance, workability and to examine the applicability for cohesionless soils. Using the improved samplers, demonstration tests were conducted at two sand sites (loose and medium-dense) in Japan. The results of each test were used to examine: (1) sampling performance, and (2) workability. As a result, the following conclusions are drawn: 1) In loose sand, sampling of several meters is possible. In medium-dense sand, the same level of sampling may be possible by providing an appropriate shoe to prevent blockage at the sampler tip. 2) The workability of the proposed apparatus is very high compared to the conventional Cone Penetration Test and Standard Penetration Test.