This paper presents an investigation on mechanism of the inclined cone penetration test using the numerical discrete element method (DEM). A series of penetration tests with the penetrometer inclined at different angles (i.e., $$0^{\circ },\,15^{\circ },\,30^{\circ },\,45^{\circ }$$
 and $$60^{\circ }$$
 ) were numerically performed under $$\mu =0.0$$
 and $$\mu =0.5$$
 , where $$\mu $$
 is the frictional coefficient between the penetrometer and the soil. The deformation patterns, displacements of soil particles adjacent to the cone tip, velocity fields, rotations of the principal stresses and the averaged pure rotation rate were analyzed. Special focus was placed on the effect of friction. The DEM results showed that soils around the cone tip experienced complex displacement paths at different positions as the inclined penetration proceeded, and the friction only had significant effects on the soils adjacent to the penetrometer side and tip. Soils exhibited characteristic velocity fields corresponding to three different failure mechanisms and the right side was easier to be disturbed by friction. Friction started to play its role when the tip approached the observation points, while it had little influence on rotation rate. The normalized tip resistance $$(q_{c}=f/\sigma _{v0})$$
 increased with friction as well as inclination angle. The relationship between $$q_{c}$$
 and relative depth $$(y/R)$$
 can be described as $$q_{c}=a\times (y/R)^{-b}$$
 , with parameters $$a$$
 and $$b$$
 dependent on penetration direction. The normalized resistance perpendicular to the penetrometer axis $$q_{p}$$
 increases with the inclination angle, thus the inclination angle should be carefully selected to ensure the penetrometer not to deviate from its original direction or even be broken in real tests.

Investigating mechanism of inclined CPT in granular ground using DEM

Recently, wearable sensors and electronic skin systems have become prevalent, which can be employed to detect the movement status and physiological signals of wearers. Here, a pressure sensor composed of mesh-like micro-convex structure polydimethylsiloxane (PDMS), MXene nanosheet/Ag nanoflower (AgNF) films, and flexible interdigital electrodes was designed by layer-by-layer (LBL) assembly. The unique microstructure of PDMS effectively increases the contact area and improves sensitivity. Moreover, AgNFs were introduced into the MXene as a "bridge," and the synergistic effect of the two further enhanced the performance of the sensor. The pressure sensor has high sensitivity (191.3 kPa-1), good stability (18,000 cycles), fast response/recovery time (80 ms/90 ms), and low detection limit (8 Pa), so it can be used for all-round monitoring of the human body. Sensing arrays were integrated with a wireless transmitter as an intelligent artificial electronic skin for spatial pressure mapping and human-computer interaction sensing. Moreover, we develop a smart glove by a simple method, combining it with a 3D model for wireless accurate detection of hand poses. This provides ideas for hand somatosensory detection technology, leading to health monitoring, intelligent rehabilitation training, and personalized medicine.

Wearable Pressure Sensor Array with Layer-by-Layer Assembled MXene Nanosheets/Ag Nanoflowers for Motion Monitoring and Human-Machine Interfaces.

Integration of anisotropic modified Cam Clay model in finite element analysis: Formulation, validation, and application

In this study, the static lateral behavior of a battered pile group foundation was investigated using three-dimensional finite element (FE) analysis. The FE model was used to simulate the static la...

Study of static lateral behavior of battered pile group foundation at I-10 Twin Span Bridge using three-dimensional finite element modeling

Thin, lightweight, and flexible textile pressure sensors with the ability to detect the full range of faint pressure (<100 Pa), low pressure (≈KPa) and high pressure (≈MPa) are in significant demand to meet the requirements for applications in daily activities and more meaningfully in some harsh environments, such as high temperature and high pressure. However, it is still a significant challenge to fulfill these requirements simultaneously in a single pressure sensor. Herein, a high-performance pressure sensor enabled by polyimide fiber fabric with functionalized carbon-nanotube (PI/FCNT) is obtained via a facile electrophoretic deposition (EPD) approach. High-density FCNT is evenly wrapped and chemically bonded to the fiber surface during the EPD process, forming a conductive hierarchical fiber/FCNT matrix. Benefiting from the large compressible region of PI fiber fabric, abundant yet firm contacting points and high elastic modulus of both PI and CNT, the proposed pressure sensor can be customized and modulated to achieve both an ultra-broad sensing range, long-term stability and high-temperature resistance. Thanks to these merits, the proposed pressure sensor could monitor the human physiological information, detect tiny and extremely high pressure, can be integrated into an intelligent mechanical hand to detect the contact force under high-temperature. 

/pdf/hierarchical-network-enabled-flexible-textile-pressure-26xv49cf.pdf

Hierarchical Network Enabled Flexible Textile Pressure Sensor with Ultrabroad Response Range and High‐Temperature Resistance

Fabrication of a humidity-resistant formaldehyde gas sensor through layering a molecular sieve on 3D ordered macroporous SnO2 decorated with Au nanoparticles

/pdf/numerical-simulation-and-field-verification-of-inclined-36f2b24wdu.pdf

Numerical simulation and field verification of inclined piezocone penetration test in cohesive soils

A large strain finite element analysis is performed to analyze the effect of soil anisotropy on the inclined piezocone penetration test in normally consolidated cohesive soils. The piezocone penetration is numerically simulated using the commercial finite element code ABAQUS. The saturated clay is modeled as a two-phase material and the effective stress principle is used to describe its behavior. A frictional contact interface utilizing Mohr-Coulomb's theory was chosen to represent interactions between the surface of the cone and the soil. The Anisotropic Modified Cam Clay Model (AMCCM) by Dafalias (1987) was chosen and implemented into ABAQUS through user subroutine UMAT. The piezocone penetration is numerically simulated by the three-dimensional finite element method using different inclination angles at different initial stress states. A field testing program of inclined cone penetration is also developed and performed in three different locations with varying soil characteristics in Louisiana, using the Continuous Intrusion Miniature Cone Penetration Test System (CIMCPT). The following conclusions are drawn from this study: 1) As compared to the previously conducted calibration chamber tests, the finite element analysis results based on Anisotropic Modified Cam Clay Model (AMCCM) are overall in good agreement with the actual measurements. This indicates that the soil anisotropy plays an important role during piezocone penetrations. 2) Initial stress state strongly affects the tip resistance, sleeve friction and generated excess pore pressures. Coefficient of lateral earth pressure K indicates the degree of initial stress anisotropy. If K=1, no difference is expected between inclined and vertical penetrations. However, for K‚1, the tip resistance, sleeve friction and generated excess pore pressures tend to increase (K<1) or decrease (K>1) when the orientation of penetration changes gradually from vertical to horizontal. Also, the soil classification derived from inclined penetration data may require special consideration. 3) The effect of anisotropic permeability on the tip resistance, sleeve friction and excess pore pressures during inclined penetrations is negligible for soils with very low hydraulic conductivities. However, it has significant effect on the dissipation of the excess pore pressure at the cone tip. 

Patricia Charlotte Boom

Papers

Hierarchical Network Enabled Flexible Textile Pressure Sensor with Ultrabroad Response Range and High‐Temperature Resistance

Fabrication of a humidity-resistant formaldehyde gas sensor through layering a molecular sieve on 3D ordered macroporous SnO2 decorated with Au nanoparticles

Numerical simulation and field verification of inclined piezocone penetration test in cohesive soils

Numerical simulation and field verification of inclined piezocone penetration test in cohesive soils