Basal Reinforcement Constructing embankments over weak ground

Transcription

1 Basal Reinforcement Constructing embankments over weak ground

2 2 Tensar. The value engineered solution In Tensar you ll find a partner with the experience and flexibility to respond to your project requirements. From design to completion, we ll make sure you always benefit from a practical, cost-effective solution to your specific need. Constructing embankments over weak ground Construction of embankments over weak ground is common to many projects. Tensar geogrids can be used to avoid the use of more traditional methods, which involve excavation and subsequent replacement of these soft soils. In other projects, the controlled settlement of a structure may be an option. Again, Tensar products lead the way in providing basal reinforcement solutions to maintain structural integrity during these critical phases. Some projects require negligible settlements or there may not be sufficient time to allow for long-term settlement. In these projects, reference should be made to the complete range of Tensar literature and in particular Foundations Over Piles. This provides information about using load transfer platforms and load distribution rafts to avoid the delay required for consolidation settlement as a result of placing embankment fill over soft, compressible soils. Tensar Biaxial Geogrids Site access is usually the first problem encountered when construction is to take place over weak soils. Tensar biaxial geogrids provide solutions for site access on a daily basis in most parts of the world. THE BENEFITS: Difficult access conditions. Tensar Biaxial Geogrids will allow uninterrupted access over most types of soft and variable soil Enables the construction of a stable and safe working area Reference should be made to the complete range of Tensar literature and in particular Ground Stabilisation Reinforcing unbound layers in roads and trafficked areas. Tensar stabilised construction platform.

3 Tensar Basetex high-strength knitted geotextiles Basetex Soft ground Basetex high-strength geotextiles are used to reinforce the base of embankments to intercept failure surfaces which may extend into a lowstrength foundation soil. Basetex geotextiles can also be used to reduce or avoid staged construction periods. Manufactured using a weft-insertion process, the Basetex range possesses quality-control strength up to 1200kN/m (longitudinal direction) and 500kN/m (transverse direction). The load-bearing yarns are 100% high-tenacity polyester and provide excellent creep performance and high tensile modulus. The Basetex products have an advantage when compared with woven fabrics. The load-bearing yarns are laid across one another and then stitch bonded. This means that the yarns: Remain linear so that they are able to reach their full tensile strength without the initial elongation associated with woven yarns This then enables: Immediate soil to fabric load transfer The high molecular weight of the polyester yarn ensures that the products are highly resistant to environmental damage within the range of normal ph Tensar Basetex Structure. and temperatures encountered in soils. Placement of fill on Basetex. 3

4 4 Reinforcing the base of a marine bund for reclamation (UK). Spanning of voids with Basetex Tensar Basetex can be installed in single or multi-layers to suit embankment design and construction. THE BENEFITS OF BASETEX INCLUDE: Allows rapid construction Basetex Potential voids Spanning of voids. The high short-term strengths and factored long-term strengths of Basetex fabrics allow the product to span subterranean voids in areas prone to subsidence. This ensures long-term void spanning and the control of weak ground, which has the potential to collapse with catastrophic effects. Avoids or accelerates staged construction Avoids excavation and replacement Reduces loss of fill into weak foundations Enables safe spanning of voids Allows pile spacing to be increased, pile caps decreased and raking piles eliminated in piled embankments Basetex strips being cut to design length. Tensar International Support Services Tensar International s experienced engineers are available to provide clients, consultants and contractors with design and construction support. Designs are carried out using sophisticated software developed in-house. Geocell slipline. Basetex. The services offered range from a free of charge application suggestion to a full design and supply service with professional indemnity cover. No liability in negligence or responsibility of any kind is accepted by Tensar International for any project where Tensar products are not used.

5 Proven application of Tensar Geocell over 9 years (UK). The Tensar Geocell - controlling differential settlement Foundation over landfill to control differential settlement. Tensar Geocell has been used successfully in applications since its introduction in A continuous open cellular structure, the Tensar Geocell is typically 1m thick, comprising Tensar uniaxial and biaxial geogrids. It is rapidly assembled and once filled with drainage material, the geocell acts as a stiff platform that initially provides construction access and, ultimately, a stiffened foundation for the embankment itself. The Tensar geocell intersects potential failure planes and its rigidity forces them deeper into firm strata. The critical failure mechanism then becomes that of plastic failure of the soft layer. The rough interface at the base of a Tensar geocell ensures mobilisation of the maximum shear capacity of the foundation soil and significantly increases stability. Differential settlement and lateral spread are also minimised. Weak Soil Tensar geocell Plastic failure condition Firm stratum 5 Stabilisation of motorway embankment over waste deposits and soft silt.

6 6 Geocell installation (Germany). The benefits of Tensar Geocell The rough underside of a geocell. Allows rapid construction Allows safe access for operatives and machinery Controls differential settlement Avoids excavation and replacement of the soft soil Prevents loss of drainage fill into the weak foundation Can be used in conjunction with vertical band drains Avoids potential damage to pipelines caused by sub-soil movements Tensar Geocells are often specified when the thickness of the soft layer is shallow when compared with the embankment width. Design methods have been developed for the Tensar Geocell and are available, together with a detailed installation procedure, on request. Typical Tensar Uniaxial Geogrid Specifications (As used in Tensar Geocell) Tensar Uniaxial Geogrids - typical dimensions (mm) AL AT BWT FWL tb tf 55RE RE SR Tensar Uniaxial Geogrid physical characteristics(1) QC strength Approx peak Tensile creep Weight per Minimum carbon Roll (kn/m)(2) strain rupture strength unit area black content dimensions (%) (kn/m)(3) (kg/m 2 ) (%)(4) (m) 55RE x RE x 1.0 SR x 1.0 (1) All grids are manufactured from high density polyethylene (HDPE). (2) Determined in accordance with BS EN ISO 10319:1996 and as a lower 95% confidence limit in accordance with ISO 2602:1980 (BS 2846:Part 2:1981). (3) These figures are as stated in BBA certificate 99/R109 for RE grids and in BBA certificate 99/R108 for SR grids. Assuming an expected design life of 120 years and an in-soil temperature of 10 C. (4) Carbon black inhibits attack by UV light. Determined in accordance with BS 2782:Part 4:Method 452B:1993. Roll Length (Longitudinal) Roll Width (Transverse)

7 Tensar SS Geogrid Specifications (As used in Tensar Geocell) SS30 and SSLA30 typical dimensions (mm) AL AT WLR WTR tj tlr ttr SS SSLA SS30 and SSLA30 physical characteristics QC Strength (kn/m)(1) Polymer(2) Minimum Weight Roll Roll Ultimate at 2% strain at 5% strain carbon per unit length width black (kg/m 2 ) (m) (m) Transverse Longitudinal Transverse Longitudinal Transverse Longitudinal content(3) SS PP or 4.0 SSLA PP (1) Determined in accordance with BS EN ISO 10319:1996 and as a lower 95% confidence limit in accordance with ISO 2602:1980 (BS 2846:Part 2:1981). (2) Polypropylene. (3) Carbon black inhibits attack by UV light. Determined in accordance with BS 2782:Part 4:Method 452B:1993. Roll Length (Longitudinal) Roll Width (Transverse) tj t TR Ribs tlr Junctions A L W LR A T W TR Tensar Basetex Geotextile Specifications Basetex Knitted Geotextiles physical characteristics Tensile strength Approx Creep-limited Polymer Weight per Roll Roll (kn/m)(1) longitudinal strength for area unit length width strain at Tult(1) 120 years (kg/m 2 ) (m) (m) Longitudinal Transverse (%) (kn/m)(2) 200/ polyester or / polyester or / polyester or / polyester or / polyester or 4.4 (1) Determined as a minimum mean value in accordance with BS EN ISO 10319:1996. (2) Determined as a lower bound using standard extrapolation techniques to creep rupture data obtained following the test procedure in BS EN ISO 13431:1999 extended to 120 year design life using the Stepped Isochronous Method. All tests carried out on samples of Basetex finished product. Bundles of PET Fibres Roll Length (Longitudinal) 7

8 Contact Tensar International or your local distributor to receive further literature covering Tensar products and applications. Also available on request are product specifications, installation guides and specification notes. The complete range of Tensar literature consists of: Tensar Geosynthetics in Civil Engineering A guide to the products and their applications Ground Stabilisation Reinforcing unbound layers in roads and trafficked areas Steep Slopes Constructing embankments with steep slopes Retaining Walls Constructing retaining walls in reinforced soil Foundations over Piles Constructing over weak ground without settlement Basal Reinforcement Constructing embankments over weak ground Railways Reinforcing ballast under railway track Asphalt Pavements Reinforcing asphalt layers in roads and trafficked areas Erosion Controlling erosion on soil and rock slopes Your local distributor is: Tensar International Limited New Wellington Street Blackburn BB2 4PJ United Kingdom Tel: +44 (0) Fax: +44 (0) info@tensar.co.uk Tensar geogrids are manufactured under tightly controlled conditions. The quality assurance procedures covering design and application and the manufacturing process have been certified by the British Standards Institution as a Registered Firm in accordance with BS EN ISO 9001:1994 Q05288 Tensar is a registered trade mark. Copyright Tensar International Limited Printed March 2003 Issue 4, The information provided verbally, or in this document or as a Free Application Suggestion is of an illustrative nature and is supplied without charge. It does not form any contract or intended contract with the user. No liability in negligence will arise from the construction of any project based on such information or material. Final determination of the suitability of any information or material for the use contemplated and the manner of use is the sole responsibility of the user and the user must assume all risk and liability in connection therewith.