Sheltering effect of punched steel plate sand fences for controlling blown sand hazards along the Golmud-Korla Railway:Field observation and numerical simulation studies

Sand fences made of punched steel plate(PSP)have recently been applied to control wind-blown sand in desertified and Gobi areas due to their strong wind resistance and convenient in situ construction.However,few studies have assessed the protective effect of PSP sand fences,especially through field observations.This study analyzes the effects of double-row PSP sand fences on wind and sand resistance using field observations and a computational fluid dynamics(CFD)numerical simulation.The results of field observations showed that the average windproof efficiencies of the first-row and second-row sand fences were 79.8%and 70.8%,respectively.Moreover,the average windproof efficiencies of the numerical simulation behind the first-row and second-row sand fences were 89.8%and 81.1%,respectively.The sand-resistance efficiency of the double-row PSP sand fences was 65.4%.Sand deposition occurred close to the first-row sand fence;however,there was relatively little sand on the leeward side of the second-row sand fence.The length of sand accumulation near PSP sand fences obtained by numerical simulation was basically consistent with that through field observations,indicating that field observations combined with numerical simulation can provide insight into the complex wind-blown sand field over PSP sand fences.This study indicates that the protection efficiency of the double-row PSP sand fences is sufficient for effective control of sand hazards associated with extremely strong wind in the Gobi areas.The output of this work is expected to improve the future application of PSP sand fences.

A TWO-DIMENSIONAL NUMERICAL STUDY OF WIND SHELTERING EFFECTS OF SHELTERBELTS

Based on the dynamic and thermodynamic equations in the SBL,the protection characteristics and mech- anism of shelterbelts are numerically studied in this paper.The results are in consistent with those ob- served in fields and wind-tunnels.Research shows that the belts with a permeability of 0.3—0.4 have the maximum sheltering effects.The distance where wind speed reduces at least by 20% is at 18—19 times of tree height(H)behind belts.The protection distance reduces fast with the increase of the permeability and slowly with its decrease.The belts have weaker sheltering effects in upstream,generally beyond 6H in front of belts there are no sheltering effects.In addition,the belts with low permeability at top and high permeability at bottom have much better sheltering effects than the belts with high permeability at top and low permeability at bottom.The belts with 50% overall permeability reduce wind speed at least,by 20% at the distance of 5H on the leeward side and by 10% at 11H.When the air is unstable,the protecting effects will be reduced.For the uniform belts with a permeability of 0.35,the distance where wind speed reduces at least by 20% is 15H under the unstable air and 13H under very unstable air.The belts reduce the turbulent diffusion coefficient at the bottom of belts,but increase it at the top.

WIND SPEED DISTRIBUTION REGULARITY AND WIND REDUCTION EFFECT OF SHELTER NET

Wind speed distribution regularities in a shelter mesh (S. M.) have been deduced from the wind speed distribution in the sheltered area of a single shelter beh (S. B.).The components of a wind vector in a mesh follow the error function distribution model or the logarithmic model of 2-variable power function.The wind vector itself follows the vector composition model of these models.We can calculate the wind speed distribution and wind reduction effect of a mesh under the conditions of any shelter-belt characteristics, any size and shape of a mesh and any wind inclination angle with this model. The results of our field model experiment are in better agreement with the theoretically calculated results.

Influence of reaction piles on test pile response in a static load test

This work presents a new analytical method to analyze the influence of reaction piles on the test pile response in a static load test.In our method,the interactive effect between soil and pile is simulated using independent springs and the shear displacement method is adopted to analyze the influence of reaction piles on test pile response.Moreover,the influence of the sheltering effect between reaction piles and test pile on the test pile response is taken into account.Two cases are analyzed to verify the rationality and efficiency of the present method.This method can be easily extended to a nonlinear response of an influenced test pile embedded in a multilayered soil,and the validity is also demonstrated using centrifuge model tests and a computer program presented in the literature.The present analyses indicate that the proposed method will lead to an underestimation of the test pile settlement in a static load test if the influence of the presence of reaction piles on the test pile response is neglected.