Non-Contact Experiment Investigation of the Interaction between the Soil and Underground Granary Subjected to Water Buoyancy

The buoyancy of underwater can cause the underground granary to overall float, or even overturn, and the interaction between the soil and underground granary is the key to its stability. This paper introduces a non-contact experiment system utilizing the digital image correlation (DIC) technology and particle image velocity (PIV) technology, and its measurement accuracy is analyzed. Then, this system is employed to study the granary displacement and the soil deformation around the granary subjected to the buoyancy of water. Results show that with the increase of the degree of compaction of the soil around the granary, the floating water level increases by 10.77% and the vertical displacement decreases by 17%. When the soils around the granary are loose sands, the soil deformation range shows an obvious inverted triangle. When the soils are medium dense sands, the soil deformation zone concentrates at the junction of the conical granary bottom and granary wall. When the soils are dense sands, the disturbed range of the soil obviously reduces, and the soil deformation concentrates on both sides of the granary wall and is distributed symmetrically. Finally, taking the medium dense sands around the granary as an example, the reasons for the unstable failure of the granary subjected to buoyancy are discussed, assisted by the soil pressure theory of retaining wall. With the granary increasingly inclining, the soil deviating from the inclined direction of the granary loses its support, which drives the soils to reach the active limit state. The soil in the inclined direction of the granary is squeezed, resulting in passive soil pressure on the granary wall. The soil deformation increases continuously to a passive limit equilibrium state, and the soil continuously develops a sliding surface, resulting in the unstable failure of the granary. This research is expected to provide the technical guidance for the design and popularization of underground granaries.

Modeling cover-collapse sinkhole based on the theory of shells

The shape and height of a natural balanced soil arch are two of the critical factors for the development of a sinkhole. The exposure of the natural balanced soil arch can be described as the initiation of the surface-collapse phase of the cover-collapse sinkhole in karst terrain. In this paper, by simplifying the natural balanced soil arch as a thin shell in a limit equilibrium state, a theoretical model is developed using the nonmoment theory of rotary shells with the shape and height of the natural balanced soil arch derived based on the Protodyakonov’s theory. First, the developed model is validated using a case study (a cover-collapse sinkhole occurred in Guizhou, China). It demonstrates that the shell theory used in this study can describe the equilibrium state of a natural balanced soil arch reasonably well. After model validation, a series of numerical simulations are then carried out to investigate the critical factors which govern the collapse of a sinkhole. The results show that buried depth serves as a compulsory condition for the formation of the natural balanced soil arch. Furthermore, it shows that a buried depth less than six times of the radius of a cave could result in the formation of a natural balanced soil arch in the cone surface.

Monitoring Analysis on the Internal Action of Pile-Anchor Support System of Deep Excavation of Wangjing SOHO Plaza in Beijing

Based on the oversize deep excavation project of Wangjing Soho in Beijing, the stress monitoring of top beam, soldier piles and anchor strand were carried out, which shows the development process of the internal force caused by spatial member interaction, reflect the differences from the mechanics principal of the traditional design method such as elastic foundation beam or equivalence beam of limit equilibrium state. Monitoring practice reveals that soldier pile were under the combination state of compression and bending, and are proved safe because of low stress; while the top coupled beam is under the combination state of tension and bending, and the tensile stress might goes to the stress limit, which has much relationship to the anchor arrangement, so the design of top beam should be regarded as one of the key control of construction safety. The tensile force of anchor strand are not easy to be hold with the tapered-type anchorage in site, the actual tested tensile force reaches 150~220KN , only the half of the design value.

A Further Study on Soil Slope Stability Analysis by Finite Element Slip Surface Stress Method

In this paper, it proves that the necessary and sufficient condition for the potential sliding body reaching the ultimate limit equilibrium state is that the summation of shear stresses along the sliding surface equals to that of resistant shear strength. Based on the rigorous theory analyses and derivations, it is clearly shown that the definition of factor of safety (FOS) in the slip surface stress method (SSSM) is irrelevant with the shape of slip surface. Thus, the authors demonstrate that the FOS of noncircular slip surface can also be defined as the ratio of the sum of resistant sliding force along slip surface to that of sliding force. Furthermore, the physical meaning of the FOS in the SSSM, which can be taken as the average evaluation of the strength reduction coefficient that makes the sliding body reach the ultimate limit equilibrium state along the slip surface in nature, is formulated on the basis of strength reserving theory rather than the overloading theory like that in the Limit Equilibrium Method (LEM) and the Shear Strength Reduction Method (SSRM). Finally, the factors of safety (FOS) and the locations of critical failure surfaces obtained by the SSSM, LEM and SSRM are compared for various geotechnical practices. It is found that the SSSM can achieve precise and reasonable stability assessments for the soil slopes on the basis of actual stress field. Consequently, compared with the LEM and SSRM, the SSSM is demonstrated to be effective and efficient alternative approach for routine analysis and design in geotechnical engineering practice with a high level of confidence.

Temporary Supporting Role of Micro Steel Pipe Piles in Landslide Emergency Treatment

Landslide emergency treatment refers to the engineering technology which makes the landslide deformation under control by taking effective mechanical control measure before sliding. Landslides extensively exist in southwestern China, which represent a direct threat not only to the safety of people and facilities in the landslide front areas, but also to that of the major facilities or houses in the slope or the trailing edge areas. While the landslide now has been in the limit equilibrium state, which is very sensitive to external factors; mechanical control measures, such as earth-retaining walls and anti-slide piles, with the disadvantages of mass excavation volume, low construction speed and great interference to the slope, is not conducive to seize the preemptive opportunities of landslide emergency management, to protect the stable and keep the landslide from sliding and temporality protect the major facilities or houses. Hence micro steel pipe pile may after all be accepted as a productive mechanical control measure to, which is simple and easy to carry out and economic and reliable. Taking the example of Wenjialiang landslide emergency repair, this paper studies the important role of micro steel pipe pile in the landslide emergency treatment.

Study of Failure Modes of Suction Anchors

Suction foundations are widely used in deep sea and their ultimate bearing capacity which is closely related with failure modes of suction anchor at limit equilibrium state is a key technology in offshore engineering practice. Based on Coulomb friction theory, an exact finite element model is presented in this paper. On the basis of this FEM model, by use of the finite element analysis software ABAQUS, the effect of mooring point and aspect ratio of a suction anchor on the ultimate bearing capacity and its stability are researched in detail. The results show that the ultimate bearing capacity and stability of the suction anchor are affected vastly by the position of mooring point, and the variation of mooring point on the suction anchor can lead to different failure modes. Simultaneously, the results also shows that tilted rotation of the soil along the direction of the mooring force will occur when the mooring point is near the top of the suction anchor, and the soil near the bottom of the fixed anchor rotates around the center of a circle, so the failure mode is called forward-tilted rotation in this paper; A general translation slip of the soil in front of the anchor along the direction of the mooring force will occur when mooring point is below midpoint of suction anchor, so the failure mode is called the translation slip failure mode in this paper. Anticlockwise tilted rotation of the soil along the direction of mooting force will occur when the mooring point is near the bottom of the anchor, and the soil at the top of the anchor rotates around the center of a circle, so the failure mode is called backward-tilted rotation in this paper.