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Comparative performance of different geosynthetics on sandy soil overlying clay subgrades of varying strengths

  • Arghadeep BiswasEmail author
Technical Note
  • 52 Downloads

Abstract

A series of laboratory tests are conducted with circular plate (model footing) rested on surfaces of different foundations. Foundations are configured with unreinforced and reinforced sand (Dr = 80%) of varied thicknesses overlying a wide range of clay subgrades, from very soft (cu = 7 kPa) to stiff (cu = 60 kPa). The ‘reinforced layers’ are comprised of an interface geogrid, geocell, and combinations of geocell–geogrid of different thicknesses. The study observed improved performances of foundations (w.r.t. load bearing capacity and reduction in footing settlements) with increasing reinforcement superiority, such as geocell–geogrid > geocell > geogrid > unreinforced soils. However, the reinforcement benefits are reduced with an increase in clay stiffness and thickness of overlying sand layers. The model tests showed a maximum of about 12 times improvements in bearing capacity with the geocell–geogrid combination, whereas the reduction in footing settlement was found in the range of 60–90%, depending on foundation configurations. The findings have provided an excellent insight to indicate the applicability of different reinforcements in varying combinations and configurations with respect to footing settlement, layer thickness, and the subgrade condition (stiffness).

Keywords

Geosynthetics Geogrid Geocell Clay Sand Subgrade strength Foundation 

List of symbols

cu

Undrained shear strength (Pa)

Gs

Specific gravity of soils

φ

Internal angle of frictional (°)

δs

Sand–geogrid interfacial friction angle (°)

Cu

Coefficient of uniformity

Cc

Coefficient of curvature

γd

Dry unit weight (N/m3)

γb

Bulk/placement unit weight (N/m3)

h

Thickness of the geocell mattress (m)

b

Width of reinforcement (m)

u

Placement depth of geocell mattress below the footing (m)

d

Pocket size of geocell mattress (m)

H

Thickness of unreinforced and reinforced sand layer overlying clay subgrades (m)

D

Diameter of model footing (m)

s

Footing settlement (m)

δ

Surface deformation (m)

qc

Bearing pressure of homogeneous clay beds (Pa)

qs

Bearing pressure of unreinforced-layered foundations (Pa)

qsg

Bearing pressure of geogrid-reinforced foundations (Pa)

qsgc

Bearing pressure of geocell-reinforced foundations (Pa)

qsgcg

Bearing pressure of geocell–geogrid-reinforced foundations (Pa)

Ifs

Improvement factor for unreinforced foundations (= qs/qc)

Ifsg

Improvement factor for geogrid-reinforced foundations (= qsg/qc)

Ifsgc

Improvement factor for geocell-reinforced foundations (= qsgc/qc)

Ifsgcg

Improvement factor for geocell–geogrid-reinforced foundations (= qsgcg/qc)

Ifg

Geogrid contribution (= qsg/qs)

Ifgc

Geocell contribution (= qsgc/qs)

Ifbg

Base–geogrid contribution (= qsgcg/qsgc)

kf

Foundation reaction modulus (Pa)

PRSh

Percentage reduction in settlement for reinforced foundations as compared to homogeneous clay beds

PRSs

Percentage reduction in settlement for reinforced foundations as compared to unreinforced layered foundations

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Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  1. 1.Department of Civil EngineeringJalpaiguri Government Engineering CollegeJalpaiguriIndia

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