Preliminary Quality Assurance/Quality Control Program

The Kyrgyz Republic: Disaster Hazard Mitigation Project (DHMP), Component A 2

Relocation of TP3 and TP18 material to TP6

Appendix 7:

Geotechnical Stability Calculations for Evaluation of Proper Relocation Technologies

1 Table of Content

1 Introduction...... 2 2 Input parameters for the stability calculations...... 2 2.1 Soil properties:...... 2 2.2 Excavation Technologies and Loading Scenarios...... 2 2.2.1 A) Standard technology...... 2 2.2.2 B) Alternative Technology...... 2 3 Geotechnical Stability Calculations...... 2 3 Conclusions...... 2

2 1 Introduction

This report compiles the results of geotechnical stability calculations prepared for evaluating the suitability and for dimensioning of excavation technologies (hydraulic excavator), temporary cover placement technology (dozer) and with regard to trafficability of temporary cover surfaces by trucks.

The results of the recent shearvane test program are of critical importance regarding developing the excavation technology. The results show that only a certain part of the tailings volume is char- acterized by undrained shear strength values below 25 kPa. These tailings can also be mixed with the overlying sandy materials in order to allow a conventional transport in standard lorries without encapsulation. In addition such mixed material would also be easier to place and compact in the depository on TP 6. The lower part of the tailings body shows shear strength values above 25 kPa. Based on these results the standard excavation technology has been developed. It consists of a layerwise excavation of an upper 1m thick layer of soil dozed onto the air-exposed tailings together with an underlying tailings layer.

Based on this volume balance this option would start with the local removal of the overlying layer only by dozing within the pond area. The first layer of the tailings will be excavated by a hydraulic excavator standing on a cover layer of ca. 1 m thickness. Tailings and cover material shall be excavated together and mixed by dumping on the truck. Afterwards a dozer places a new cover layer on the free-lying tailings surface. Then the next layer of cover soils and underlying tailings shall be excavated and so on. Air-drying can also be used to the maximum extent possible. Under dry weather conditions the cover layer shall be placed on top of the tailings shortly before excavation. In case of insufficient trafficability of the cover layer the thickness of the cover layer is to be in- creased.

If the consistency of the respective tailings layer do not allow for dozing of soils to create a traffi- cable working platform such tailings will have to be excavated by excavators standing more dis- tant from the excavation place. Such excavators can be hydraulic excavators with long boom or cable excavators. This alternative excavation technology may be needed for relocation of a minor amount of tailings. Such pulpy tailings will then have to be transported using specific lorries with watertight lockable containers. The alternative excavation technology and transport technology is presented with the Working Design.

Due to the excavation of TP 3 material the natural ground profile will be restored. Contaminated subsoil will be removed during ongoing excavation works. It is to be expected that decomposed rock underlying the tailings will be radioactively contaminated by seepage of tailings pore water or processing water. Therefore such weak soil and decomposed rock materials will be removed during ongoing excavation works.

3 2 Input parameters for the stability calculations

2.1 Soil properties:

Soil properties of the interim cover: Soil group according to DIN 18196: SU; GU; GU*; SU* Specific weight, earth-moist: 21.0 kN/m³ Friction angle: 30.0 ° Cohesion: 0 kPa (calculation value: 1 kPa)

Soil properties of the tailings: - water saturated - specific weight, water saturated: 17.5 kN/m³

2.2 Excavation Technologies and Loading Scenarios

2.2.1 A) Standard technology

1. loading case: The temporary interim cover will be placed

Placement of a layer with a thickness of 1.0 m in one layer by a dozer from type Komatsu D37/PX- 21 on air-exposed tailings surface

Technical data of Komatsu D37/PX-21: Weight: 7770 kg; width of the tracks: 600 mm; Length of the tracks between the axes: 2240 mm Footprint of the tracks: 2.688 m2; soil pressure: 28.4 kPa

2. loading case: Excavation of tailings and overlying temporary cover soil by a crawler excavator

A 1.0 m thick interim layer was placed before by the dozer.

Characteristic data of the excavator CAT 319 D L: Weight: 19550 kg Soil pressure (tracks): 45 kPa Width of the tracks: 600 mm Supporting track length: 3650 mm Footprint of the two tracks: 4.38 m2 Width of the outside edge of the tracks: 2800 mm Minimum width of the wooden planks below the excavator for reducing soil pressure (without side overlap) 2.8 m * 3.65 m = 10.22 m2, this means reduction of the soil pressure to a maximum of ca. 19 kPa

Geometric boundary conditions for the location of the excavator: Minimum distance of the excavator from the excavation border: 2.0 m Slope ratio of the edge of the temporary cover v : h = 1 : 1 Slope height: 2.0 m (1 m tailings + 1 m interim cover)

4 Characteristic data of the truck Truck KAMAZ 55111 Transportation truck for bulk material, 3 axes total weight: 22400 kg tyres: 10.00 R20 Axle load, front: 5550 kg Soil pressure, front: ca. 125 KN/m² Axle load, rear: 2 x 8430 kg Soil pressure, rear: ca. 95 KN/m² total length: 6.70 m

2.2.2 B) Alternative Technology

Characteristic data of the equipment: Hydraulic excavator type Liebherr R 934 C Litronic with long arm (11.5 m slope mono arm) maximum range: 21.05 m weight: 34.16 to track width: 750 mm track running length: 3848 mm (axle distance) footprint of 2 tracks: 5.772 m2 (relating to the axes distance) (this means 58.1 kPa calculated soil pressure) Soil pressure (tracks) 55 kPa (statement of producer)

Width of the undercarriage (chassis) HD-SL: 3395 mm (see documentation) Length of the track running gear: 3848 mm (axle distance) Footprint of wooden planks for reducing soil pressure: at least 13.06 m2 Calculated soil pressure: 25.7 kPa

The use of the wooden planks below the excavator will lead to a similar soil pressure as using the standard technology.

5 3 Geotechnical Stability Calculations

FLAC3D 2.1 was used to calculate the stability for different technologies and scenarios.

Only static loading cases were taken into account. The wooden planks below the excavators as stated above shall serve to reduce the soil pressure and shall be used always and all the time.

Development of the model for excavator and truck: - Slope ratio v : h = 1 : 1 - Slope height: 2.0 m (1 m tailings + 1 m interim cover) for the excavators - For calculations with the truck the model was finer discretized because of nearly point load of the tyres

Figure 1: Model for excavator use

Model for using the dozer: - Dozer for a 1.0 m interim cover, tailings underneath - Interim cover at the border v : h = 1 : 1 sloped

Consideration of soil buoyancy: There were calculations done for selected examples under consideration of the buoyancy. It has been assumed that there will be a permanent water table at the level of the slope foot of the tailings. A seepage line within the 1 m tailings slope was not applied, because the water table within the tailings is to be lowered by drainage measures, if needed.

The seepage line can vary in practice during the excavation work (QA/QC programme). By as- sumption of a specific weight and buoyancy the withstanding forces in the stability calculations will be lower and the safety factor will reduce. The calculation results under consideration of the buoyancy are shown in Table 1 in brackets and marked red.

For the static calculations only the undrained strength of the tailings (cohesion) was varied to de- termine the safety factor. The following table shows the calculation results.

6 Table 1: Summary of standard safety calculations Cohe- sion of Standard technology Alternative technology tailings Excavator Dozer Komatsu D37/PX-21 truck Long arm excavator CAT 319 D L 1 m high slope [kPa] KAMAZ Liebherr R 934 C 2 m high Distance to the slope border 55111 2 m high slope slope 0 m 1 m S = 0.95 S = 1.25 10 S = 0.71 S = 1.14 S = 0.92 (Sw=0.92) (Sw=1.23) S = 1.06 15 S = 1.41 S = 1.35 S = 1.72 S = 1.38 (Sw=1.34) (Sw=1.02) 20 S = 1.89 S = 1.39

Results – Excavation without implementation of buoyancy

Use of the dozers:

In this calculation case with the dozer directly at the slope border and cohesion of the tailings of 10 kPa a slope collapse will be stated with S=1.14. The tailings under the interim cover are not af- fected in that case (Figure 2). Experiences with the feasibility of the barely manageable work with those dozers at tailings material with ca. 10 kPa cohesion are confirmed here. To demonstrate that the construction equipment and the existing load are shown as orange rectangle in the figures.

The calculations with the dozer in 1 m distance to the slope edge gives higher safeties. It is therefore required to use the long arm shields and to grant a minimum distance of 1 m from the slope shoulder line to the front of the dozer. The presented figures of soil displacements show the collapse state only qualitatively. The dimension of the displacements is not considered.

Dozer

Figure 2: Displacements in the calculation case with dozer directly at the slope border and cohesion of the tailings = 10 kPa

Use of the excavators: For the calculations of the use of excavators (ordinary and with long arm) on a 2 m high embankment another collapse mechanism is stated. The 1 m thick tailings layer in the lower part of the slope is pressed out affecting a are large area of the embankment. Despite the lower soil pressure of the excavator (standard technology) in comparison to the dozer, lower safety factors are stated at the respective undrained shear strengths of the tailings material. For the calculations it was assumed that also the long arm excavator despite of bigger reach is standing above the tailings material.

7 Excavator

Figure 3: Displacements in the calculation case with a excavator, in 2 m distance from the slope border, cohesion of the tailings = 15 kPa

Use of the trucks: Similarly to the use of excavators the stability calculations for truck use show a large-area press- ing out the tailings material towards the slope. The effects are shown with the displacement figure Figure 4. As the truck tyres will nearly act as point loads, in practice the interim cover must guar- antee a minimum load bearing capacity, that will be reached by compacting.

Figure 4: Displacements in the calculation case with truck on the interim cover, cohesion of the tailings = 15 kPa

Results of the considerations of soil buoyancy

The calculation results show minimum reductions (< 5 %) of the safety factor in comparison to the calculations without buoyancy. For example the following figures 5 and 6 present the grid densities and calculation results for the case “dozer in 1 m distance to the slope border”.

8 Figure 5: Presentation of the density distribution by consideration of the soil buoyancy (densities in kg/m³)

Dozer

Figure 6: Displacements in calculation case with dozer in 1 m distance from the slope border and cohesion of the tailings = 10 kPa, with consideration of soil buoyancy

3 Conclusions

For performing the excavation works a minimum safety factor of 1.3 is to be met. On the basis of the stability calculations and the developed diagrams below the following required minimum values were determined for the undrained shear strength (cohesion) of the tailings:

- ordinary excavator - minimum cohesion cmin= 14 kPa - dozer (in 1m distance from the slope border) - cmin= 11 kPa - truck - cmin= 19 kPa - long arm excavator - cmin= 15 kPa

Please note that the above stated geometric assumptions and load affecting points will apply. The largest undrained strength of 19 kPa of the tailings material will be required by truck use. Because of the relatively small tyre footprint soil pressure caused by trucks is large. The excavators and dozers assumed for these stability calculations can be used if the tailings cohesion would be lar- ger than 15 kPa.

9 Diagram 2: Geotechnical Safety vs. undrained cohesion: Excavator; Standard technology

Normal excavator, 2 m distance to the slope 2 1.9 1.8 1.7 y

t 1.6 e f

a 1.5 S

f 1.4 o

r w ith buoyancy o

t 1.3 c a 1.2 Linear (no buoyancy) F 1.1 1 0.9 0.8 9 10 11 12 13 14 15 16 17 18 19 20 21 Tailings cohesion [kPa]

Diagram 2: Geotechnical Safety vs. undrained cohesion: Dozer; Standard technology

Dozer 1 m distance to the slope 1.8

1.7

y 1.6 t e f a

S 1.5

f o

r 1.4 o t w ith buoyancy c a

F 1.3 Linear (no buoyancy)

1.2

1.1 9 10 11 12 13 14 15 16 Tailings cohesion [kPa]

10 Diagram 3: Geotechnical Safety vs. undrained cohesion: Truck; Standard Technology & Alternative technology

Truck KAMAZ 55111 1.5 1.4 1.3 y t 1.2 e f a

S 1.1

f o

r 1 o t

c w ith buoyancy a 0.9 F Linear (no buoyancy) 0.8 0.7 0.6 9 10 11 12 13 14 15 16 17 18 19 20 21 Tailings cohesion [kPa]

Diagram 4: Geotechnical Safety vs. undrained cohesion: Long-arm Excavator; Alternative technology

Excavator, longarm 10 m distance to the slope 1.5

1.4

y 1.3 t e f a

s 1.2

f o

r 1.1 o t w ith buoyancy c a

F 1 Linear (no buoyancy)

0.9

0.8 9 10 11 12 13 14 15 16 Tailings cohesion [kPa]