Offshore Jet Grouting - A Case Study

摘要

Having high budgets and construction difficulties, offshore structures serve sensible and attractive solutions with an expanding application area all over the world. Because of the marine sediment layers, generally offshore structures subject to be constructed on unfavorable soil conditions. A similar problem was encountered in the scope of an offshore plaza structure in Doha Port, Qatar. Since marine sediments exist with a thickness varying between 3 m to 12 m on the Simsima Limestone bedrock, soil improvement was recommended prior to plaza construction. Some locations of the site were filled and as a result dredging of the made ground was required before soil improvement works. Sea bed was dredged at a depth of -6.00 m and a flat platform was formed prior to soil improvement works. For soil improvement, offshore jet grouting technique is designed and implemented in accordance with the soil conditions and structural surface loadings. O80 cm diameter jet grout columns are constructed to a depth of bedrock. System is modeled in Plaxis 3D Foundation and checked in order to fulfill the settlement criteria considering embankment and superstructural loadings. For jet grouting applications a spud barge and a cantilever platform which is carried with a crane are mobilized to the site. Jet grouting is operated on this barge and cantilever platform simultaneously, in order to meet the tight construction schedule. After the soil improvement works, the seabed is dredged and plaza blocks are placed on a granular capping layer which is placed on the jet grout columns. In the scope of the quality control works core samples are taken from the jet grout columns and uniaxial pressure tests are performed to determine the modulus and strength of soilcrete. Since application difficulties and tight schedule of the constructions as in Doha Port, selection of a proper soil improvement method has provided important benefit to the project. It is again proved that, jet grouting is a convenient method because of versatile equipment, high production rate and a reliable output with a sufficient quality control for offshore soil improvement works.