Modelling of trial embankment on double porosity clay

Transcription

1 Modelling of trial embankment on double porosity clay Jan Najser Department of Engineering Geology, Charles University in Prague, Czech Republic 1

2 Overview 1. Double porosity clay 2. Trial embankment 3. Centrifuge modelling 4. Test results a. Development of excess pore pressures b. Vertical deformations 5. Summary 2

3 Double porosity soil Structure contains two different types of porosity: Intragranular porosity (n i ) Intergranular porosity (n e ) Total porosity (n t ): n = n(1 n ) + n t i e e 3

4 Open cast mines in northern Bohemia, Czech Republic Kurka,

5 Open-cast brown coal mining since about 1960 Clayey overburden dumped in landfills Typical depths: 20-50m Area covered: >100km 2 Old landfills: Large vertical deformations Nonuniform compressibility Difficult prediction of the behaviour photo: M. Vetrovsky 5

6 Trial embankment on the route of the planned motorway Instrumentation: Hydrostatic levelling profiles Depth reference points Pore pressure gauges Surveying reference points on embankment surface Inclinometers Constructed 2001 Measurement m high, crown 20 x 31m Water level at the surface 6

7 DRUM CENTRIFUGE: MODEL FOR TEST AT 150g: 40cm 14.6cm 5cm 5cm 20cm 15cm Wood, 2004 DRUM CENTRIFUGE AT ETH ZÜRICH 7

8 Centrifuge modelling of trial embankment 40cm 20cm vertical time of observation landfill stress under age of lump dimensions after embankment depth the landfill construction embankment in situ conditions 30m 144kPa dust - 50cm years 4 years 8

9 Centrifuge modelling of trial embankment 40cm 20cm landfill depth vertical stress under the embankment lump dimensions age of landfill time of observation after embankment construction in situ conditions 30m 144kPa dust - 50cm years 4 years n = g level = 150 scaling laws 1/n 1/n 1/n 2 1/n mm + model (150g) 16.7cm 144kPa 6 hours 1.5 hours 10%<

10 Dissipation of excess pore pressures after embankment construction Pore pressure (kpa) Prototype depth (m) b; 31days b; 250days b; 688days b; 1281days b; 2266days b; 2922days b; 3781days a; 250days a; 688days a; 1281days a; 2266days a; 2922days a; 3781days a: b: 10

11 Surface deformation of landfill under the surcharge LASER SCANNING IN CENTRIFUGE: cm 190 model thickness (mm) cm mm in situ time (years) after embankment construction:

12 Surface deformation of landfill under the surcharge 0 age of landfill (years) surface deformation - prototype (m) landfill - selfweight consolidation deformation under the embankment 10 12

13 Comparison of surface deformations 0 age of landfill (years) surface deformation - prototype (m) landfill - selfweight consolidation deformation under the embankment 10 0 time after embankment construction (years) surface deformation (m) trial embankment centrifuge model

14 Settlement of depth reference points Settlement (cm) Depth (m) trial embankment centrifuge test 25 14

15 Summary Permeability: controlled by soil structure Fast consolidation through open interlump spaces in the upper part of the fill In the lower part of the fill, the permeability is controlled by the permeability of the clay Deformations: Rapid vertical settlement due to the closing of interlump voids Centrifuge test: bigger vertical deformation in the upper part of the landfill 15