CASE HISTORIES Secugrid and Combigrid

Transcription

1 CASE HISTORIES Secugrid and Combigrid

2 Marbella Hill, Spain project Retaining wall construction facilitates site development in difficult terrain Background Quality building sites near the coast in Marbella, Spain, and the surrounding areas are becoming increasingly scarce, forcing any new holiday resorts to gradually locate in the surrounding steep, mountainous areas. In these potential new development areas, the search is on for geotechnical solutions that allow constructing building sites with a large horizontal area in this diffi - cult terrain. Design Following a meeting with NAUE in which a conceptual design was presented to the investor and the architect, the design firm of BBG, Bauberatung Geo kunststoffe GmbH & Co. KG, Espelkamp, Germany, was commissioned to develop detailed project specifications and drawings for construction of a reinforced retaining wall. Based on calculations addressing the internal, external and compound stability of the reinforced earth structures, five walls were designed. This design would result in a maximum elevation difference of approximately 18 m across the site. A horizontal area of approximately 9,000 m² was created on two plateaus on which the buildings would later be constructed. Construction Construction of the near vertical (85 ) sloping walls began in the summer of The retaining walls were constructed with 60 cm thick compacted soil layers reinforced with Secugrid 80/20 R6 polyester geogrid. Embedment lengths varied from 2.5 to 12 m. Secugrid 200/40 R6 polyester geogrid was placed in areas where extremely high forces were expected, and were located between the 60 cm layer spacing of the 80/20 R6 Secugrid. The highest wall section is composed of 40 individual layers of geogrid all constructed utilising the "wrap-around" method. A galvanised steel grid formwork was used as a permanent formwork while simultaneously providing the construction with an even front face. Fig. 1 Installation of natural rock blocks as facing for the geogrid reinforced soil structure One such situation involved an investor who was seeking a geosynthetic solution to develop a steep, in - clined site (slope inclination between 1:1.5 and 1:2 (H:V)) on which he wanted to build three large villas with swimming pools and tennis courts. In the front wrap-around area, Secutex R 204 non - woven geotextile was incorporated in the design to prevent erosion of the compacted soil and to provide a textured surface permitting the outer shell to be planted with vegetation later on. A part of the wall was clad with natural stone blocks, resulting in a more interesting and aesthetically appealing landscaping treatment. Summary The installation of around 50,000 m² of geogrids and approximately 10,000 m² of geotextiles stabilised around 40,000 m³ of back fill material. By using a creative and innovative geosynthetic design solution utilizing geogrids for soil reinforcement, a hillside unfit for building construction, was converted into over 9,000 m² of buildable construction area. Utilization of these construction methods and geo - synthetic reinforcement products also resulted in a significant increase in the value of the investors' property. Secugrid 80/ 20 R6 45,125 m² Secugrid 200/ 40 R6 6,180 m² Secutex R ,460 m² Reference: "Stabilisation of the New Real Estate in Marbella, Spain, with geogrid reinforced structures," Eurogeo 2004

3 Bus-Station Melle-Wellingholzhausen, Germany Use of Combigrid to reinforce a soft bearing layer Fig. 2 Base course re in forcement for large loads on soils with poor bearing capacity Background The roadway for the old bus station in Wellingholz - hausen, Germany, needed to undergo repair in July The very weak roadway subsoil conditions were undergoing significant settlement in several areas due to the growing traffic loads. There was also ineffective separation between the subsoil and the bearing layer that resulted in an intermixing of the soils and a reduction in the strength of the bearing layer. Some form of subgrade improvement was necessary to correct the situation. Base course Soft bearing layer Fig. 3 Roll imprint on reinforcing strap Sand Pavement Combigrid base course reinforcement Proposed solution The use of a needle-punched nonwoven geotextile could provide the separation and prevent the inter - mixing of the soils. However, it would not prevent the high settlements caused by heavy traffic loads. For this reason the designer and owner decided to use a composite product that would address all the design concerns: separation, filtration and reinforcement. This unique composite product consists of a polypropylene geogrid with an integrated nonwoven polypropylene geotextile. The geogrid has a biaxial tensile strength of 30 kn/m² and a robust needle-punched Secutex nonwoven geotextile integrated between the rigid, vibratory welded cross-laid reinforcing bars. With this technology a strong composite product is manufactured where all the necessary functions separation, filtration and reinforcement are satisfied with one material. This resulted in a cost effective solution for the bus station roadway. The repairs were completed in 2003, with the reconstructed roadway at the bus terminal performing as anticipated. Combigrid 30/30 Q1 1,200 m² Connection between Heidenau and Altenberg, Germany Emergency repair of a washed out railroad embankment Background During the flood disaster in 2002 approximately 80 % of the infrastructure in the valley "Mueglitztal" near Dresden, Germany, was destroyed. Near Weesenstein, a 11 m high railway embankment in the area of an undercut slope was washed away by the flood over a distance of approximately 100 m leaving the rail line unusable. As a result rail traffic on this line was completely cut off. Fig. 4 Combigrid installation After determining the required characteristics for this application, Combigrid 30/30 Q1 was selected for use. Solution To get the rail traffic running again in the shortest possible time, the German National Railways (DB

4 The installation damage reduction factor, RF ID, must be taken into account when calculating the geogrid Long Term Design Strength (LTDS). For this project, this reduction factor (1.1) was determined in a projectspecific field test carried out in accordance with EBGEO by the Saxon Textile Research Institute. Cover material Fig. 5 Railway embankment washed away after a flood Fig. 6 Repair as Secugrid reinforced embankment Projekt-Bau GmbH, NL Sued-Ost) and the engineering company EVP/GIV GmbH, NL Dresden, decided to repair the area by installing a geogrid reinforced soil struc - ture utilising a steel grid formwork as an outer facia. The combination of a geosynthetic reinforcement and covering material would ensure the slope and ground stability. The steel wire mesh on the outer face stabilises the slope surface with a separation/filter layer made of a nonwoven fabric to prevent the surficial soils from eroding. The approximately 5 m high geogrid reinforced portion at the bottom of the slope is constructed with an approximate. 60 face angle. The second phase of construction consisted of a 4 m high unreinforced embankment. Design The structural analysis for the reinforced slope was carried out based on the German recommendations for geosynthetic reinforcements EBGEO, The product specified, Secugrid 120/40 R6, has the Federal Railways Agency's certification. A well graded crushed mix was specified as the cover material. Secugrid provides a highly efficient tensile reinforcement element with minimal deformation of the embankment during both installation and under a traffic loads. Fill material Secugrid soil reinforcement Approval of the recommended solution The Federal Railway Agency approved the reinforced construction subjected to rail traffic load as an emergency repair as a temporary solution. Sometime after repairs were completed and the rail line back in operation, additional fill would be placed surrounding the reinforced slope to ensure the long term stability of the embankment. The final structure could be approved as it was designed and built in accordance with a flood protection plan for the Mueglitz River. Repairs The Secugrid reinforcement element was installed using a spacing of 0.5 m between layers of geogrid in accordance with the design. Within just a few weeks, the whole reinforced earth structure was completed by a pool of 10 local construction companies using simple, fast and cost-efficient construction methods. The consulting firm GEPRO GmbH was responsible for the inspection of the construction documents and the final acceptance of the work. As a result the flow of regular rail traffic was quickly restored. The reinforced slope will remain and serve as the permanent structure. Today, modern construction methods like these can provide quick, cost efficient and safe solutions to disaster repairs. Secugrid 120/40 R6 7,600 m² Steel front facing element with nonwoven geotextile Fig. 7 Cross section of Secugrid reinforced embankment

5 Interstate A7 Fuessen, Germany Floating foundation solves soft subgrade conditions background During the construction of the new Interstate A7 in 2003, close to exit AS Fuessen, approximately 1.6 km of poor subgrade was discovered. Because of right-of-way constraints it was necessary to build a stable foundation for the new Interstate on this very weak subsoil. The subsoil contained major areas of weak peat, chalk and soft sediments in various thicknesses. Due to several feet of weak subsoil con - ditions, the foundation soils needed to be stabilised to minimise potential settlement. exhibits extremely efficient interlocking with the selected fill material, effectively reinforcing the fill material layer and was an economical solution to this soft subgrade dilemma. Fig. 9 View over Secugrid rein forced floating foundation Fig. 8 Cover soil placement over Secugrid geogrid Design The engineer selected a design using a floating foundation, which consisted of crushed materials from mm in size combined with geosynthetic reinforcement. The cross section of the floating foundation was as follows: The bottom reinforcement layer of high tensile strength woven geotextile which was laid over the entire base and sideslope areas and which was protected by a nonwoven geotextile Secutex 301 GRK5. Installation and compaction of a 50 cm thick first layer. Installation of the main uniaxial reinforcing geogrid, Secugrid 180/20 R6, installed under tension. The final base course material, placed over the Secugrid until final grade was achieved. Construction This complicated cross-section required the coordination of all parties to make sure the construction was completed in accordance with the design requirements. The soft subgrade was first covered with the woven geotextile and the protection nonwoven, then fill was placed, and the layer of Secugrid installed under pre-stressing. Then the Secugrid reinforcement was covered with aggregate. A minimum soil cover of approximately 30 cm was required below any construction equipment to avoid any severe damage during installation, as determined in pre-tests. The project was completed in a shorter time than an ti ci pated and is performing as planned. Secugrid 180/20 R6 120,000 m² Secutex 301 GRK 5 120,000 m² Selecting the polyester Secugrid as the main reinforcement for the floating foundation design was based on test results that showed that Secugrid geogrid: has excellent long-term creep behaviour, Visit:

6 Products Secugrid and Combigrid geogrids are the next generation of geogrids produced with state of the art manu - facturing technology, unlike any other geogrid on the marketplace today. The reinforcement element is a highly oriented polypropylene or polyester strap that is extruded and drawn to achieve high modulus and strength at low elongations. This is combined with NAUE patented vibratory welding technology to provide a structurally sound and stable geogrid. Secugrid Q Geogrids These biaxial geogrids have uniform, square-shaped grid openings. With these geogrids the machine and cross direction extruded polypropylene straps exhibit uniform strengths in each direction. The numbers in each of the product names e.g. 30/30 for Secugrid 30/30 Q1 define machine and cross machine direction ultimate strength values [kn/m]. Typical applications of use are base reinforcement. Secugrid R Geogrids These geogrids have rectangular-shaped grid openings. As a rule, machine and cross machine strength are not the same. The numbers in each of the product names e.g. 200/40 for Secugrid 200/40 R6 define machine and cross machine ultimate strength values [kn/m]. Typical applications of use are reinforced walls and slope stabilisation. Combigrid Q Composite The Combigrid series incorporate a needle-punched polypropylene or polyester Secutex nonwoven geotextile separator that is placed firmly between the flat straps on the manufacturing line during the production process. Typical applications of use are soil reinforcement where additionally soil filtration is needed. NAUE GmbH & Co. KG Gewerbestrasse Espelkamp-Fiestel Germany Phone Fax info@naue.com Internet Tel.: Fax: sales@spec-kw.com, Combigrid, Secugrid and Secutex are registered trademarks of NAUE GmbH & Co. KG. The information contained herein is the best to our knowledge, true and accurate. There is no implied or expressed warranty by NAUE GmbH & Co. KG, Espelkamp-Fiestel, Germany All rights reserved. No. 80 Status 07/2009