IPLOCA INTERNATIONAL PIPE LINE & OFFSHORE CONTRACTORS ASSOCIATION

Transcription

1 IPLOCA INTERNATIONAL PIPE LINE & OFFSHORE CONTRACTORS ASSOCIATION BRIDGING EMBEDDED PIPELINES: SOME OPTIONS AND RECENT TESTS PRESENTER: Angelina Parlato Onshore Pipeline Engineering Department - Saipem, Italy AUTHORS: Agostino Napolitano, Diego D Alberto, Vincenzo Nisii Onshore Pipeline Engineering Department - Saipem, Italy Pierpaolo Fantini Huesker, Italy Dimiter Alexiew Consultant Geosynthetics & Geotechnics, Germany Geneva, October 17

2 SCOPE OF WORK & ENGINEERING PHILOSOPHY Construction of new infrastructures often requires crossing of pre-existing buried pipeline not specifically designed for new extra loads. These induced extra loads cause additional soil stresses on the pipe backfilling, that could become critical for pipes integrity, if not specifically designed. A wide range of crossing methods has been developed and applied over the years in order to reduce these additional soil stresses around the pipe. Sometimes these solutions are too complicated, expensive or time consuming and could be unsuccessful. Jump over Culvert Concrete slab The bridging methodology here proposed and tested is an EASY TO INSTALL, LOW- COST and MANAGEABLE solution, suitable to reduce significantly additional soil stresses on the buried pipeline. 2

3 SCOPE OF WORK & ENGINEERING PHILOSOPHY The idea is to lay a GEOGRID in the pipe backfilling in order to transfer the ground level extra load in tensile stresses acting on the GEOGRID. Source: HUESKER Geosynthetic material for soil reinforcement applications (e.g. below roads or structures, slope stability etc.); High tensile strength in conjunction with low strain; Uniaxial and biaxial structures of parallel strings; Long-term performance; High resistance to chemicals and microorganisms in soil, UV radiation and mechanical damage; Simple installation (low weight per unit area and flexibility/adaptability); Project-specific choice of raw materials possible. 3

4 FLOW CHART OF THE WORK SCOPE OF WORK & ENGINEERING PHILOSOPHY SENSITIVITY ANALYSIS ANALYTICAL MODEL F.E.M. ANALYSIS FIELD FULL SCALE TEST 4

5 ANALYTICAL MODEL (considers the transfer of external load into internal action of the GEOGRID) SENSITIVITY ANALYSIS (defines influence of different parameters on GEOGRID anchorage length) SENSITIVITY ANALYSIS Bonding coefficient f b tan ' s tan' ' b n b B 1 2S tan' FEM ANALYSIS (validates analytical model & selects pipe-geogrid configuration for full scale test) 5

6 FLOW CHART OF THE WORK SCOPE OF WORK & ENGINEERING PHILOSOPHY SENSITIVITY ANALYSIS ANALYTICAL MODEL F.E.M. ANALYSIS FIELD FULL SCALE TEST 6

7 FIELD FULL SCALE TEST A GEOGRID layout configuration for FIELD FULL SCALE TESTS was defined by sensitivity and FEM analysis. The following tests have been performed: CONTROL CASE pipe backfilling without GEOGRID (as baseline record); GEOGRID CASE pipe backfilling laying the GEOGRID. CONTROL CASE Trench width GEOGRID CASE 7

8 FIELD FULL SCALE TEST FULL SCALE TEST AREA - SOIL CHARACTERIZATION Nos. 3 boreholes (in situ); Soil unit weight determination (in situ); Standard and modified Proctor compaction test (lab); Particle size analysis (lab); Atterberg limits (lab). Depth (m) Soil type (kn/m 3 ) c (kpa) ( ) E (MPa) Disturbed soil Sandy gravel

9 FIELD FULL SCALE TEST EQUIPMENT PIPE DN 12, WT = 10 mm, API 5L X60, L = 6 m, coverage depth = -1.4 m below g.l. GEOGRID (Fortrac R 400/30-30 MPT) raw polymer PVA (polyvinylalcohol) ultimate tensile strength 400 kn/m short term tensile stiffness 8,000 kn/m mesh size 30 mm x 30 mm anchorage system 6 m each pipe side 0.5m depth) Nos. 4 PRESSURE CELLS (range kpa) in the backfilling soil Nos. 4 STRAIN GAUGES (optical cables, range +/ ) fixed on the pipe EXTRA LOAD static 6 concrete blocks (150 kn) dynamic excavator (200 kn) 9

10 FIELD FULL SCALE TEST SOIL STRESSES AROUND THE PIPE FIELD ROW DATA TEST 1 NO EXTRA LOAD TIME HISTORY OF SOIL STRESS PRESSURE CELLS CONTROL CASE GEOGRID CASE TEST 2 EXTRA STATIC LOAD CONTROL CASE GEOGRID CASE CONTROL CASE GEOGRID CASE TEST 3 EXTRA DYNAMIC LOAD CONTROL CASE GEOGRID CASE 10