» عنوان : Case histories of ground improvement solutions using jet-grouting
تعداد صفحات : ۶
The aim of this paper is to present the main design and construction criteria considered on some vertical jet-grouting solutions adopted by Tecnasol FGE. On these solutions ground improvement by vertical columns was successfully used as an alternative to traditional solutions, such as concrete cast in-situ pile foundations, earth retaining sheet pile walls and micro-piles for underpinning. On each case history, the following topics are presented: main scenario, geotechnical conditions, initial solution, main design criteria and construction issues.
Jetgrouting methods have initially been developed in Japan, the UK and Italy. For about 20 years it has been applied world-wide. In Portugal the technology has been adopted in the last 5 years, mainly on Lisbon underground extension works. Recently, vertical jet grouting solutions have also become competitive and advisable in several and more usual geotechnical scenarios.
CASE HISTORY 1 – SANTA LUZIA BRIDGE DEEP FOUNDATIONS
Main design and construction criteria Main scenario: Santa Luzia is a 17+27×3+17m twin span concrete bridge on Madeira island, founded on an alluvium zone, filled with boulders. Each one of the 2×2 central piers carries an axial, permanent and live, service load of about 15000kN. Geotechnical conditions: the bridge is founded on an heterogeneous alluvium, filled with weathered basalt boulders. At the surface the alluvium is softer and involved on a sandy matrix, becoming with deep consolidated and involved on a clay matrix. The basalt bed rock is located at a variable deep ranging from 12 to 24m. Initial solution: traditional φ۱۰۰۰mm cast in-situ concrete piles foundation, resting on the basalt bed rock. This solution was changed due to technical difficult on drilling basalt boulders. Main design criteria: a vertical jet grouting solution was designed in order to improve the alluvium behaviour. This solution consisted on the execution of 37 φ۵۰۰mm jet grouted columns forming under each main pier an overall conic shape. Each column carries an axial service load of about 400kN: σcomp = 2,0MPa. This load is transferred to the soil mainly by shaft resistance: τservice=30kPa.