Abstract

This paper describes how pipelines are often located in seismic unstable slopes where earthquake-induced movements may cause their collapse. Thus, the analysis of the soil-pipe interaction plays a large role for the seismic hazard prevision. This paper deals with an analytical approach for the study of the interaction phenomena occurring between pipe and surrounding soil when pipelines cross unstable slopes. Some analytical solutions are presented in order to evaluate displacement, lateral deflection and bending moment distribution along the pipe. The Newmark method extended to a 3-D analysis was used to evaluate the permanent earthquake-induced displacement in slope due to ground motion. The aim is the prevention of unacceptable conditions for the pipeline and to avoid the pipe failure. Field and laboratory tests confirm that the soil shows a non-linear behavior even under low loading: so a non-linear behavior for the soil-pipe interaction should be considered to take into account the plastic response. The non-linear model used in the analysis and the results obtained, with particular reference to the influence of the soil modeling are presented in the paper. Document type: Part of book or chapter of book

Abstract

The natural structure of clays has a significant influence on its mechanical behaviour and can be characterized using insitu and laboratory tests. It was reported by Robertson (2016) that soil structure leads to an increased tip resistance (qc) and shear wave velocity (Vs) when performing seismic cone penetration tests. However, only limited studies investigated changes in soil structure by means of in-situ tests. Sensitive, marine clays were investigated within the research project "VIBE – Sustainable Ground Improvement Solution for Oslo" at the Norwegian Geo-Test site Onsøy (Gundersen et al. 2019). Possibilities and limitations of the vibro replacement method were studied for very soft ground conditions based on a full-scale field test. The influence of soil structure on in-situ measurements of piezocone penetration tests (CPTu) and seismic flat dilatometer tests (SDMT) are further studied by intentionally disturbing the soil structure by a vibrator. Results of CPTu and Medusa SDMT, executed before and after treatment, are compared to characterize changes in soil structure. The results indicate that the vibration-induced destructuration led to a significant decrease of CPTu measurements, namely tip resistance (qc), sleeve friction (fs) and measured pore pressure (u2), within medium to high sensitive clays. As the decrease in fs is more significant compared to the decrease in qc, a significant decrease in friction ration (Rf) was observed. In analogy, SDMT resulted in a decrease in shear wave velocity (Vs), horizontal stress index (KD) and dilatometer modulus (ED) after the vibro treatment. It was further shown that the soil behaviour type chart according to Robertson (2016) leads to no sufficient characterization of soil structure in soft, marine clays.