Introduction
Methodology
Proposed Lining System
Geosynthetics
Geosynthetic | Label | Typea | Raw materialb | Mass/area or density | Thicknessc [mm] |
---|---|---|---|---|---|
Geotextiles | GTX-1 | NW | Bidim PET/continuous filament | 270 g/m2 | 2.60 |
GTX-2 | NW | Bidim PET/continuous filament | 550 g/m2 | 4.60 | |
GTX-3 | W | PET/staple fibres | 150 g/m2 | 1.00 | |
Geomembranes | GMB-1 | Smooth | HDPE | > 0.94 g/cm3 | 2.00 |
GMB-2 | Smooth | LLDPE | > 0.94 g/cm3 | 1.50 | |
Synthetic cuspate drain | CD | Cuspate | HDPE | 958 g/m3 | 4.75 |
Geomaterials
Property | Units | Test method | Sand | GS | LCS |
---|---|---|---|---|---|
Cohesion (c') | kPa | ASTM D3080-11 | 0 | 0 | – |
The angle of internal friction (ɸ’) | ° | 35.18 | 35.55 | – | |
Optimum moisture content (OMC) | % | ASTM D698-12 | 3.80 | 7.60 | – |
Maximum dry density (MDD) | Mg/m3 | 1.77 | 2.12 | – | |
Fine gravel (4.75–75 mm) | % | ASTM C136-19 | 0 | 24.78 | 100 |
Medium sand (0.075–4.75 mm) | 99.94 | 75.20 | 0 | ||
Silt (0.002–0.075 mm) | 0.06 | 0.04 | 0 | ||
Clay (< 0.002 mm) | 0 | 0 | 0 | ||
Coefficient of uniformity (Cu) | 2.13 | 4.67 | 1.03 | ||
Coefficient of curvature (Cc) | 1.09 | 0.60 | 1.00 | ||
USCS classification | ASTM D2487-17 | SP | SP with gravel | GP |
Testing Configurations
Single Interfaces
Double Interfaces
Large Direct Shear Equipment
Testing Procedure and Program
Single interfaces | Double interfaces |
---|---|
1. LCS | GTX-1 | 1. LCS | GTX-1 | GS |
2. GTX-1 | GS | 2. GS | GTX-2 | GMB-1 |
3. GS | GTX-2 | 3. GTX-2 | GMB-1 | CD |
4. GTX-2 | GMB-1 | 4. GMB-1 | CD | GMB-2 |
5. GMB-1 | CD | 5. CD | GMB-2 | SAND |
6. CD | GMB-2 | 6. SAND | GTX-3 | SAND |
7. GMB-2 | SAND | |
8. SAND | GTX-3S1a | |
9. GTX-3S2b | SAND |
Data Processing
Results and Discussion
Shear Stress–Horizontal Displacement Relationships
LCS | GTX-1 | GS Interfaces
GS | GTX-2 | GMB-1 Interfaces
GTX-2 | GMB-1 | CD Interfaces
GMB-1 | CD | GMB-2 Interfaces
CD | GMB-2 | SAND Interfaces
SAND | GTX-3 | SAND Interfaces
Critical Interface Assessment for Single Interfaces
At Peak
At Large Displacement
Critical Interface Assessment for Double Interfaces
At Peak
At Large Displacement
Interface configuration | Interface shear strength parameters | |||
---|---|---|---|---|
At peak | At large displacements | |||
δp [°] | cα-p [kPa] | δLD [°] | cα-LD [kPa] | |
Single- | ||||
1. LCS | GTX-1 | 17.1 | 66.3 | 15.4 | 29.7 |
2. GTX-1 | GS | 33.2 | 29.7 | 12.2 | 111.7 |
3. GS | GTX-2 | 38.1 | 13.3 | 35.5 | 21.3 |
4. GTX-2 | GMB-1 | 11.3 | 4.3 | 10.2 | 2.4 |
5. GMB-1 | CD | 18.5 | 0.0 | 18.4 | 0.0 |
6. CD | GMB-2 | 24.0 | 9.3 | 23.8 | 9.5 |
7. GMB-2 | SAND | 29.1 | 0.0 | 22.7 | 0.0 |
8. SAND | GTX-3S1 | 37.7 | 24.7 | 37.0 | 24.7 |
9. SAND | GTX-3S2 | 32.2 | 45.0 | 13.0 | 125.0 |
Double- | ||||
1. LCS | GTX-1 | GS | 42.1 | 30.3 | 41.9 | 24.0 |
2. GS | GTX-2 | GMB-1 | 13.5 | 4.5 | 9.4 | 6.8 |
3. GTX-2 | GMB-1 | CD | 13.4 | 14.8 | 9.3 | 8.3 |
4. GMB-1 | CD | GMB-2 | 20.3 | 10.0 | 20.5 | 5.1 |
5. CD | GMB-2 | SAND | 24.5 | 0.0 | 24.0 | 0.0 |
6. SAND | GTX-3 | SAND | 31.1 | 85.7 | 31.1 | 85.7 |
Comparison of Interface Shear Strength Parameters
Soil–Geosynthetics and Soil–Geosynthetic–Soil Interactions
Soil–Geosynthetic, Geosynthetic–Geosynthetic and Soil–Geosynthetic–Geosynthetic Interactions
Geosynthetic–Geosynthetic and Geosynthetic–Geosynthetic–Geosynthetic Interactions
Design Application
Parameter | Meaning | Value | Units |
---|---|---|---|
B | Width of the new waste mass at the level of the existing waste mass | 35.0 | m |
CSW | Apparent cohesion of solid waste | 3.0 | kN/m2 |
H | Depth of existing waste mass/height of side slope | 30.0 | m |
α | The angle of the front slope, measured from horizontal, 3.5(H):1(V) | 15.9 | ° |
ɸSW | Internal friction angle of solid waste | 30.0 | ° |
γSW | Unit weight of solid waste | 10.2 | kN/m3 |
β | The angle of the back slope, measured from horizontal, 4(H):1(V) | 18.4 | ° |
θ | The angle of landfill cell subgrade, measured from horizontal, 2% | 1.1 | ° |
-
The lowest FoSmin value of 1.1 was obtained at a single-interface GTX-2 | GMB-1. Therefore, it can be deduced that the GTX-2 | GMB-1 interface was the weakest as elaborated previously, and if failure were to occur, this interface would be the first to fail at both locations of the landfill, i.e. at the base and at the side slope. In addition, the highest value of FoSmin observed was 4.3, with the base interface being GS | GTX-2 and the side-slope interface being SAND | GTX-3S1. These two interfaces were noted to be the strongest under the single-interface testing configuration as explained earlier in this study.
-
For a double interface’s FoSmin evaluation, it was observed that an interface with GTX-2 and GMB-1 combination had the lowest FoSmin of 1.2. The highest FoSmin value of 5.5 was obtained at the LCS | GTX-1 | GS interface, indicating that this interface was the strongest in both landfill locations, i.e. at the base and at the side slope. Another double interface that recorded a higher value of FoSmin than those recorded by single-interface configurations was SAND | GTX-3 | SAND interface, with 4.5 at the side slope and 4.4 at the base.
At side slope | 1a | 2a | 3a | 4a | 5a | 6a | 7a | 8a | 9a | ||
---|---|---|---|---|---|---|---|---|---|---|---|
δA [°] | 14.2 | 12.2 | 35.5 | 10.2 | 18.4 | 23.8 | 22.7 | 37.0 | 13.0 | ||
CA [kPa] | 0.0 | 111.7 | 21.3 | 2.4 | 0.0 | 9.5 | 0.0 | 24.7 | 125.0 |
At base | δP [°] | CP [kPa] | FoSmin | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
1p | 17.1 | 66.3 | 1.6 | 1.6 | 2.9 | 1.4 | 1.8 | 2.1 | 2.1 | 3.0 | 1.6 |
2p | 33.2 | 29.7 | 2.5 | 2.5 | 3.8 | 2.3 | 2.7 | 3.0 | 3.0 | 3.9 | 2.5 |
3p | 38.1 | 13.3 | 2.8 | 2.8 | 4.2 | 2.6 | 3.1 | 3.4 | 3.3 | 4.3 | 2.8 |
4p | 11.3 | 4.3 | 1.3 | 1.2 | 2.5 | 1.1 | 1.5 | 1.8 | 1.7 | 2.6 | 1.3 |
5p | 18.5 | 0.0 | 1.6 | 1.6 | 2.9 | 1.4 | 1.8 | 2.2 | 2.1 | 3.0 | 1.6 |
6p | 24.0 | 9.3 | 1.9 | 1.9 | 3.2 | 1.7 | 2.2 | 2.5 | 2.4 | 3.4 | 2.0 |
7p | 29.1 | 0.0 | 2.2 | 2.2 | 3.5 | 2.0 | 2.4 | 2.8 | 2.7 | 3.7 | 2.2 |
8p | 37.7 | 24.7 | 2.8 | 2.8 | 4.2 | 2.6 | 3.0 | 3.4 | 3.3 | 4.3 | 2.8 |
9p | 32.2 | 45.0 | 2.4 | 2.4 | 3.8 | 2.2 | 2.7 | 3.0 | 2.9 | 3.9 | 2.5 |
At side slope | 1a | 2a | 3a | 4a | 5a | 6a | ||
---|---|---|---|---|---|---|---|---|
δA [°] | 44.0 | 10.2 | 10.6 | 20.3 | 24.0 | 31.1 | ||
CA [kPa] | 0.0 | 6.8 | 0.0 | 10.0 | 0.0 | 85.7 |
At base | δP [°] | CP [kPa] | FoSmin | |||||
---|---|---|---|---|---|---|---|---|
1p | 44.7 | 66.3 | 5.5 | 3.2 | 3.2 | 3.8 | 4.0 | 4.5 |
2p | 13.6 | 4.5 | 3.3 | 1.2 | 1.2 | 1.7 | 1.9 | 2.4 |
3p | 13.4 | 14.8 | 3.3 | 1.2 | 1.2 | 1.7 | 1.9 | 2.4 |
4p | 20.3 | 10.0 | 3.7 | 1.5 | 1.5 | 2.1 | 2.3 | 2.8 |
5p | 24.5 | 0.0 | 3.9 | 1.7 | 1.7 | 2.3 | 2.5 | 3.0 |
6p | 31.1 | 85.7 | 4.4 | 2.2 | 2.2 | 2.7 | 3.0 | 3.5 |
Conclusions
-
Higher shear strengths at peak and LD were observed under single-interface configurations. This observation was attributed to specimen clamping in the LSA under a single-interface configuration compared to double-interface configurations.
-
For interfaces that involved geomaterials, i.e. soil and stone in their setups, higher interface friction angles and apparent adhesion parameters were observed at peak but declined at LD. However, interfaces that involved only geosynthetics in their setups, similar interface friction angles and apparent adhesion parameters at peak and LD were observed.
-
Double-interface configuration revealed that failure occurred along the same interface as in the single-interface configuration, provided that the shear plane was the weakest. For instance, tests conducted on a double-interface GS | GTX-2 | GMB-1 produced interface shear strength parameters closely comparable to those of the single-interface GTX-2 | GMB-1. These interfaces were determined to be weakest/critical in this study.
-
In the FoSmin evaluations, it was established that provided the interface recorded lowest values of interface shear strength parameters independent of the testing configuration, low factors of safety were expected. For instance, interface test configurations with a combination of GTX-2 and GMB-1 recorded lowest FoSmin (1.1 to 1.2) irrespective of whether they were evaluated under single- or double-interface configurations.