Analysis of Vertical Earth Pressure Acting on Box Culverts through Centrifuge Model Test

Due to the lack of surface space, most structures are heading underground. The box culvert is underground infrastructure and serves to protect the buried structure from the underground environments, but it has a different characteristic from other structures in that the inner space is empty. Therefore, in this study, the vertical earth pressure which is the most significant effective stress acting on a box culvert was measured by conducting a geotechnical centrifuge model test. A box culvert was installed following the embankment installation method, and the vertical earth pressure acting on it was measured considering the cover depth, gravitational acceleration, and loading and unloading conditions. The soil pressure measured was greater than the existing theoretical value under high cover depth and the unloading condition, which is considered as the variability of many soils or the residual stress acting under the loading condition. Finally, a goodness-of-fit test was conducted as a part of variability analysis. The measured earth pressure was found to be considerably larger than the existing theoretical value, and the variability was large as well. This means the existing theoretical equation is under-designed, which should be reflected in future designs.

Effects of embedding depth and load eccentricity on lateral response of offshore monopiles in dense sand: A centrifuge study

Two model piles with outer diameter D = 50 mm are loaded laterally at 100×g in a large-beam geotechnical centrifuge. The normal strains on both the tensile and compressive sides are measured using fibre Bragg gratings. An incremental method is introduced to define the pivot point. The testing and analytical program enables the effect of the embedding depth and load eccentricity to be quantified. The key findings are as follows. 1) The piles generate asymmetric tensile and compressive strains during bending, and the tension-compression asymmetry becomes more pronounced at the pile toe and for shorter piles. 2) The piles transition from flexure to rotation as the embedding depth is decreased from 9D to 3D, where the uniqueness of the ground-level rotation and deflection (θg–yg) relationship disappears. 3) The reaction and deflection (P–y) relationship flattens with increasing embedding depth but seems independent of the load eccentricity.

Centrifuge tests on axially loaded tapered piles with different cross-sections under compressive and tensile loading

The compressive behavior of tapered piles, particularly those with circular cross-sections, has been investigated during the last few decades. However, the tensile behavior of such piles has been rarely studied in the literature. In this paper, 12 static axial tests, including six compressive and also six tensile tests, were performed on instrumented piles with uniform and tapered cross-sections by using a geotechnical centrifuge. Three of the piles had correspondingly circular, square and X-shaped uniform cross-sections along their length, while the other three ones were non-uniform (tapered), all of which had the same length and volume. The results are presented in three main forms: the variation of load versus pile head displacement, the distribution of axial force along the pile length, and the distribution of the unit shaft resistance along the pile length. The behavior of tapered piles is compared with that of uniform cross-section piles. The results confirm the superiority of tapered piles over uniform cross-section piles in terms of load-bearing capacity and construction costs under both tensile and compressive loading.

The auto-monitoring of geo-technical centrifuge operating state based on weighted data fusion

There are many parameters which could reflect the operating state of geotechnical centrifuge. However, only one parameter is detected generally ; this is insuficient and unsafe for the running of the geotechnical centrifuge. This paper put forward an auto-running sate monitoring method which based on the multi-parameters’ weighted data fusion. The way by multi-sensor acquirring the running state data of the geotechnical centrifuge, then processing the data with weighted data fusion could produce the comprehensive running state parameter, which feed forward to the control system to keep the equipment running in a safe manner. The method in this paper could be implemented automatically and the result for safety monitroing is sufficient, the effect is much more efficient.

Research on Application of Multi-Channel Selector in Centrifugal Model Test of Anchoring Slope by Frame Beam

An anchoring frame beam is a very common form of support for reinforced slopes, especially in alpine regions. Centrifugal tests have proved to be an intuitive and effective means of investigating the mechanism of action of frame beams. However, the data acquisition system of the geotechnical centrifuge in service has the problem of a small number of acquisition channels. A multi-channel selector based on the existing acquisition system was proposed, designed, processed, and manufactured, and it was debugged, tested, and applied in a no-load centrifugal test, static pressure model test, and centrifugal model test. The results show that the acquisition mode of the multi-channel selector connected with a maximum of 288 sensors has been changed from “one-to-one” to “one-to-many”. Its influence on various sensor signals is negligible. The multi-channel selector can work normally, which communicates and feeds back with the remote controller in the 1–120 g no-load centrifugal test. In the static load model test, 162 sensor signals were well collected through it. And only 51 channels were used to effectively obtain the signals of 187 sensors in a 70 g centrifugal model test of an anchoring slope with a frame beam. The multi-channel selector can be successfully applied in different use environments, saving time and reducing the cost of obtaining a single set of data.

A computational fluid dynamic-based method for analyzing the nonlinear relationship between windage loss and pressure in a geotechnical centrifuge

Temperature control is an important limitation to further increase in geotechnical centrifuge power. Although vacuum pumps can reduce windage loss, they also negatively affect heat transfer performance. Therefore, in this study, we aim to accurately determine the rate at which windage loss decreases with pressure to help assess whether reducing pressure is beneficial to temperature control. A computational fluid dynamic method based on the multi-reference model and k–ω shear-stress transport turbulence model is used to simulate the ZJU400gt geotechnical centrifuge. The windage loss and temperature of ZJU400 at 0–150 gravity acceleration under normal pressure conditions are simulated. Compared with the experimental data, the error is < 20.7%, indicating simulation reliability. Furthermore, the simulation model is used to simulate the windage loss power under low-pressure conditions and predict the relationship between the windage loss power and pressure. Compared with current calculation methods, which yield a linear relationship between windage loss and operating pressure, the simulation results indicate a slightly nonlinear relationship. At 5,000 Pa, the simulated windage loss is 40% larger than the calculated value, severely affecting the temperature control design. Moreover, the velocity exhibits minimal variation with pressure, whereas the effective kinematic viscosity varies substantially. The nonlinear relationship between the windage loss and pressure can be attributed to increased turbulent kinetic energy and the size of the wake region caused by vacuum pumping. A formula for nonlinear windage loss with pressure is proposed, providing a basis for the future design of super-gravity geotechnical centrifuges.

Experimental and numerical investigation of the effect of vertical loading on the lateral behaviour of monopiles in sand

The influence of combined loading on the response of monopiles used to support offshore wind turbines (OWTs) is investigated in this paper. In current practice, resistance of monopiles to vertical and lateral loading is considered separately. As OWT size has increased, the slenderness ratio (pile length, L, normalised by diameter, D) has decreased, and foundations are tending towards intermediate footings with geometries between those of piles and shallow foundations. Whilst load interaction effects are not significant for slender piles, they are critical for shallow footings. Previous research on pile load interaction has resulted in conflicting findings, potentially arising from variations in boundary conditions and pile slenderness. In this study, monotonic lateral load tests were conducted in a geotechnical centrifuge on vertically loaded monopiles in dense sand. Results indicate that for piles with L/D = 5, increasing vertical loading improved pile initial stiffness and lateral capacity. A similar trend was observed for piles with L/D = 3, when vertical loading was below ≈ 45% of the pile’s ultimate vertical capacity. For higher vertical loads considered, results tended towards the behaviour observed for shallow footings. Numerical analyses conducted show that changes in mean effective stress are potentially responsible for the observed behaviour.

Centrifuge Studies of Topographic Effects: Parametric Investigation

ABSTRACT This article presents the results of a comprehensive geotechnical centrifuge experimental program to investigate topographic effects across a series of single-sided slopes. The experimental campaign considered a range of governing factors, including slope inclination and ground-motion amplitude, frequency content, and duration. The testing program was nondestructive, allowing the centrifuge models to be subjected to over 140 different ground motions. Clear evidence of topographic effects, including amplification and deamplification of ground motion, were observed. Topography modified the frequency content and amplitude of the ground motion such that at the slope crest (1) peak ground accelerations ranged from 50% less than to 200% greater than the free-field, and (2) ground-motion mean square frequency shifted by as much as 55%. Higher topographic amplification levels lead to a larger topographic zone of influence, which, on average, spanned a distance equal to the slope height (H) behind and 2H in front of (toward slope) the slope crest. Physical modeling in the centrifuge proved to be a powerful experimental technique for generating empirical data to analyze topographic effects in a systematic and repeatable manner.