DEVELOPMENT OF A HYBRID SOIL PRESSURE SENSOR AND ITS APPLICATION TO SOIL COMPACTION

A new soil pressure sensor based on a combination of the deflecting membrane and fluid filled approaches has been developed. The advantages of this combined approach are that issues of sensor compliance are eliminated without reducing the effectiveness of the sensor to be used for dynamic measurements. Calibration and verification testing performed under controlled laboratory conditions illustrate these benefits. The new system was implemented in a full-scale field trial which involved the construction of a compacted engineered fill 1.8 m in height. As each layer of fill was placed and compacted vertical in-soil pressure and vertical in-soil strain were continuously measured. During the vibratory compaction process both vertical soil pressure and vertical soil strain histories were captured in each layer. The data collected allowed for the determination of fill stiffness for both static and dynamic conditions. The results illustrate the effect of both confining pressure and strain level on fill stiffness. The relationship between compaction pressure and depth is clearly defined.

Four years of soil strain monitoring on Etna Volcano Mount by means of a Three-axial Fiber Bragg Grating Sensor

<p>Rock strains detection is one of the principal ways to monitor geohazards. Classic strainmeters are cumbersome, hard to install and very expensive. Opto-electronics devices based on fiber Bragg grating technology allow to realize strainmeters with high sensitivity, low-cost, small volume and high performance.<br>We present the long term result of continuous soil strain monitoring on the Etna mount by a three-axial fiber Bragg grating sensor. The sensor has been developed in the framework of European Project MED-SUV (MEDiterranean SUpersite Volcanos). The installation site is a 8.5 meters deep borehole at a distance of about 7 km South-West from the summit craters of the Etna mount, at an elevation of about 1740 meters. This kind of sensor has a resolution better than 100 nanostrains on a daily timescale. Despite it is only a prototype, the sensor has worked for four years with a duty-cycle higher than 90% detecting both fast event, as earthquakes, and slow event, as epochal rocks strain behavior.</p>

Design of horizontal shear strain instrument for co-estimation of soil stress-strain

This study aimed to design and fabricate the horizontal shear strain transducer (HST) for measuring the soil strain under the agricultural machinery traffic by using a rotary potentiometer which was an angular strain change detector. The angular movable mechanism was calibrated and evaluated the characteristics of the instrument in the laboratory, and found that the non-linearity and the hysteresis were 4.56 and 4.42%, respectively. Furthermore, the strain measurement device was buried in the field to compare the shear strain at varying tractor velocities (5, 6.5 and 8 km/h). For all vehicle speed at the first passage, the shear strain and soil bulk density obviously increased, whereas the final moisture content decreased; as a result, the lower velocity caused higher shear strain.

Variable moduli of soil strain

The experimental diagrams between stress and strain components for soft soils are non-linear. Nonlinear diagrams qualitatively differ for soils of undisturbed and disturbed structures. It is believed that the manifestations of nonlinear properties of soil are associated with micro-destruction of soil structure under compression and, therefore, with changes in its mechanical characteristics under strain. It follows that the modulus of elasticity, Poisson’s ratio, viscosity and other mechanical parameters are the variables in the process of soil strain. Based on this, from the experimental results given in scientific literature, the changes in the modulus of elasticity and plasticity of soil are determined depending on the values of compression strain. In the process of static and dynamic compression of soil it is almost impossible to determine the boundaries of elastic and plastic strains in soft soil. So, the modulus under soil compression is called the strain modulus. From published results of experiments on dynamic and static compression of soil the most informative ones have been selected. Processing the selected compression diagrams of soft soil, the secant moduli of strain for loess soil and clay have been determined. It is established that the moduli of strain of clay and loess soil under static and dynamic strain vary depending on the rate of strain, the state of the structure and the level of compressive load.

Performance of Embedded Mooring Lines During Keying and Diving of Gravity Installed Anchors

Gravity installed anchors (GIAs) are the most recent generation of anchoring solution to moor floating facilities for deepwater oil and gas developments. After the installation of GIAs, the anchors are connected with the floating facility via the mooring lines, which interact with the anchors at the shackle and influence the keying and diving performance of GIAs. In the present work, a three-dimensional large deformation finite element (LDFE) model is established using the coupled Eulerian–Lagrangian method to investigate the performance of embedded mooring lines during keying and diving of GIAs. To verify the efficiency of the LDFE model, comparisons with the plasticity models are performed. Then, a parametric study is undertaken to quantify the relationship between the drag force Ta and drag angle θah at the shackle and the drag force T0 and drag angle θ0 at the mudline, in terms of the frictional coefficient, drag angle at the mudline and soil strain rate and strain softening. It is demonstrated that the drag angle at the mudline has the most significant effect on the performance of embedded mooring lines and hence the keying and diving of GIAs.