Experimental Investigation Examining Influence of Burial Depth on Stability of Horizontal Boreholes in Sand

Lan, Haitao; Moore, Ian D.

doi:10.1061/(asce)gt.1943-5606.0002222

Cited by 12 publications

(5 citation statements)

References 14 publications

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“…When analyzing the problem of shallow cavities, these assumptions do not necessarily hold true, since the gradient of stresses around the cavity becomes significant and the geostatic stress field can no longer be modelled as a biaxial state. Furthermore, experimental studies on shallow cavities such as [16,31] and limit analysis formulations such as [16], have shown that the failure mechanism of shallow horizontal cavities is dominated by the development of shear planes that follow a catenary/parabolic shape, resembling a passive trapdoor mechanism, see [7,40,42].…”

Section: Cavity Expansion In Geotechnicsmentioning

confidence: 99%

Back-calculation of soil parameters from displacement-controlled cavity expansion under geostatic stress by FEM and machine learning

et al. 2022

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Estimating soil properties from the mechanical reaction to a displacement is a common strategy, used not only in in situ soil characterization (e.g., pressuremeter and dilatometer tests) but also by biological organisms (e.g., roots, earthworms, razor clams), which sense stresses to explore the subsurface. Still, the absence of analytical solutions to predict the stress and deformation fields around cavities subject to geostatic stress, has prevented the development of characterization methods that resemble the strategies adopted by nature. We use the finite element method (FEM) to model the displacement-controlled expansion of cavities under a wide range of stress conditions and soil properties. The radial stress distribution at the cavity wall during expansion is extracted. Then, methods are proposed to prepare, transform and use such stress distributions to back-calculate the far field stresses and the mechanical parameters of the material around the cavity (Mohr-Coulomb friction angle $$\phi $$ ϕ , Young’s modulus E). Results show that: (i) The initial stress distribution around the cavity can be fitted to a sum of cosines to estimate the far field stresses; (ii) By encoding the stress distribution as intensity images, in addition to certain scalar parameters, convolutional neural networks can consistently and accurately back-calculate the friction angle and Young’s modulus of the soil.

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Section: Cavity Expansion In Geotechnicsmentioning

confidence: 99%

Back-calculation of soil parameters from displacement-controlled cavity expansion under geostatic stress by FEM and machine learning

et al. 2022

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“…The failure of such shallow cavities is controlled by tensile stresses (developed at the crown of the cavity) in the case of cohesive materials and by shear stresses (which originate 'blow-out') for cohesion-less media Lan & Moore (2017). Regardless of the nature of the soil, the use of cavity expansion theories (such as the Delft equation) results in an overestimation of the maximum pressure that can be safely imposed to the cavity as shown in (Kennedy et al, 2006;Xia & Moore, 2006;Lan & Moore, 2018) for purely cohesive materials and in (Lan & Moore, 2020) for frictional soils. For instance, the Delft equation overestimates the maximum pressure by by 90%-170%.…”

Section: Introductionmentioning

confidence: 99%

“…Experimental evidence suggests that the shear mechanism that controls the failure of shallow cavities is characterised by the development of shear bands that originate from the waist of the cavity and extend to the free surface. Recently, Lan & Moore (2020) modeled blow-out for HDD and found that mud flow followed (possibly) curved shear planes oriented at a certain angle from the vertical. These findings suggest that the presence of a free surface close to the expanding cavity changes the failure mechanism of the soil, which transitions from a circular/elliptical plastic region around the cavity (as predicted from cavity expansion), to a mechanism dominated by the development of shear planes starting from the cavity and reaching the free surface.…”

Section: Introductionmentioning

confidence: 99%

Deformation and failure mechanisms of granular soil around pressurised shallow cavities

et al. 2023

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The deformation patterns and failure mechanisms of pressurised cavities at shallow depth are relevant to many geotechnical applications, including tunnelling and horizontal directional drilling. In this paper, an experimental study of a reduced-scale pressurised cavity under geostatic stress is presented, in order to measure the effect of cavity length, vertical stress and soil density on soil deformation and failure. X-ray computed tomography is used to acquire images of the system at key stages of the cavity inflation process. A closed-shaped failure region developed around the cavities, beyond which shear planes of elliptic paraboloid shape formed, extending from the bottom of the cavities all the way to the free surface. The plane-strain assumption did not hold beyond the central portion of the longest cavity tested (L = 6D). The volumetric strain and porosity changes inside the shear bands showed significant dilation in dense specimens, but contraction in loose specimens. The average orientation and the thickness of the shear bands were in agreement with those found in the literature for passive arching mechanisms (anchoring). The orientation of the principal strains around the cavity follows catenary shapes, similar to those displayed in active trapdoor mechanisms.

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“…For the recorded image processing of the video from ultra-deep boreholes or multiple boreholes, it needs several weeks to deal with the complex video images and special recorded data, especially for the analysis of horizontal holes or wells, which is a time-consumed work for many researchers. [16][17][18] Therefore, it is very important for us to get an automatic detection approach for the processing analysis of the borehole camera video images.…”

Section: Introductionmentioning

confidence: 99%

Applications of high‐resolution borehole image rapid synthesis method for the refined detection of in‐suit rock mass structural features during deep‐buried geotechnical engineering

Zou

Wang

Song

2021

Num Anal Meth Geomechanics

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The refined detection of in-suit rock mass structural features always plays an important part in geomechanics and geotechnical engineering, but actual image resolution of the obtained borehole image by present borehole camera system cannot meet the requirements of real-time and precise analysis of rock structures. Faced with hundreds of boreholes in the deep-buried geotechnical engineering, a high-resolution borehole image rapid synthesis method is provided for solving the actual application problems during the geological exploration. Results show the rapid synthesis method of high-resolution borehole image by using image mosaic and data fusion techniques can improve the resolution and sharpness of the obtained borehole image with better work efficiency. The lateral resolution and longitudinal resolution of the synthetic borehole images can be up to 0.1 mm for the refined detection of in-suit rock mass structural features in deep-buried boreholes. The applications of this method can improve the refined detection process of in-suit rock mass structural features with automation and intelligent, and promotes the innovation and development of borehole camera technique during the applications in the geological exploration of deep-buried geotechnical engineering.

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Experimental Investigation Examining Influence of Burial Depth on Stability of Horizontal Boreholes in Sand

Cited by 12 publications

References 14 publications

Back-calculation of soil parameters from displacement-controlled cavity expansion under geostatic stress by FEM and machine learning

Back-calculation of soil parameters from displacement-controlled cavity expansion under geostatic stress by FEM and machine learning

Deformation and failure mechanisms of granular soil around pressurised shallow cavities

Applications of high‐resolution borehole image rapid synthesis method for the refined detection of in‐suit rock mass structural features during deep‐buried geotechnical engineering

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