Bearing capacity mechanisms for pipes buried in sand

Abstract

This paper presents results of scaled physical model tests performed to measure the reaction developing on a rigid pipe buried in dry sand, when the pipe is subjected to vertical downwards movement relative to its surrounding soil. The aim of this experimental study is to evaluate the efficacy of methods used to determine the properties of vertical bearing springs, an integral part of beam-on-nonlinear Winkler spring models used for the analysis of buried pipelines subjected to permanent ground displacements. We show that bearing capacity formulas used in practice to estimate the ultimate reaction developing on buried pipes may provide reasonably accurate estimates, provided that they are used together with sand friction angle values that account for the fact that granular materials do not obey an associative flow rule, and with bearing capacity factors compatible with the mode of sand failure observed in the tests. We also provide evidence suggesting that laying pipes in loose sand backfills does not have a beneficial effect on the reaction developing on the pipe, compared to medium dense sand, and we recommend against using loose sand material properties for the estimation of the properties of vertical bearing springs.

Analytical prediction for longitudinal deformation of shield tunnel subjected to ground surface surcharge considering the stiffness reduction

“…However, ALA 30 recommended that it was more reasonable to consider the soil vertical uplift and vertical bearing springs separately when calculating the resistance acting on the pipe in soil layers (Figure 4). Furthermore, it has been observed that the soil resistance acting on the pipe in vertical downward movement is significantly greater than that in upward movement 31 . Therefore, the solution from Liang et al 29 .…”

“…Additionally, it was stipulated that Δ qd was taken as 0.1D for pipe in medium sand, and taken as 0.2D in dense sand. However, Wu et al 31 and Kouretzis and Wu 32 raised that the sand will densify during downwards movement of the pipe, and Δ qd is the function of underlying soil density. Indeed, the diameter of the shield tunnel is considerably lager than that of the pipe.…”

“…Furthermore, it has been observed that the soil resistance acting on the pipe in vertical downward movement is significantly greater than that in upward movement. 31 Therefore, the solution from Liang et al 29 is unsuitable for evaluating k when subjected to the ground surface surcharge, since soil layers provided vertical upward resistance. This paper derives a simplified method based on the research of ALA 30 to calculate an approximate linear result for k (i.e., stiffness of vertical bearing soil springs), which can be written as:…”

Suction effects during uplift of steel pipes buried in compacted soil

“…The results of six uplift experiments performed in dry STK sand [2,3,38,39] are presented to establish a baseline for the experiments with the pipe buried in compacted soil beds. The experiments were performed with the pipe buried in loose (relative density D r = 27%, dry unit weight c dry-= 15.15 kN/m 3 ) to dense (D r = 93%, c dry = 17 kN/m 3 ) sand in shallow depths H/D = 1.5 and H/D = 3 to match the embedment depths of experiments on compacted sandy loam-Kaolin.…”

“…Numerous studies have resulted in methods for estimating the reaction force developing on a pipe as function of the mentioned problem parameters (e.g. [2,3,10,11,28,33,35,38,39]). Most of those are limited to the case of pipes buried in dry or fully saturated soil.…”