June 2022 G-01483.84-017-R-Rev0 Because the 20 5.2 Summary of Geotechnical Characteristics of Soils at Willows Road Farm Logs from test pits and boreholes undertaken on the Willows Road farm site describe fine grained soils up to several metres in depth overlying moderately strong andesite and associated volcanic lithologies. The soils comprise: ▪ Topsoil about 0.3 m thick. ▪ Stiff sandy silt or clay interpreted to comprise weathered volcanic ash. ▪ Highly weathered andesite comprising very stiff or hard silty clay. ▪ Alluvial soils were also encountered beneath the terraces adjacent to Mataura Stream and these included gravels sands and silts, often containing boulders of volcanic rock. In situ testing and laboratory testing suggests that the weathered volcanic ash soils are mainly ‘medium sensitive’. ▪ Weathered volcanic ash soils can display problematic engineering behaviour. This is a result of the mineralogy of the constituent minerals that result in the soil shear strength reducing when the soil is disturbed. ▪ The weathered volcanic ash soils are likely unsuitable as a foundation for structures and will therefore need to be excavated from the WRS site where they have a negative effect on stability of the WRS (refer to Section 6.2) ▪ The excavated material will generally be suitable for use as engineered bulk fill elsewhere ▪ Although some may require significant conditioning, drying out or introduction of lime to be usable, and for these soils it’s likely to make more sense to cut them to waste 6.0 WILLOWS ROCK STACK 6.1 Description of Rock Storage Facilities About 850,000 cubic metre (m³) of rock (mineralized and non-mineralized) will be generated during the development of the WUG Tunnel Network and hauled by truck for temporary storage in the Willows Rock Stack (referred to in this report as ‘WRS’) at the Willows Road farm site. Results of an options analysis study informed the current selected WRS location and configuration. A site location assessment, initially undertaken by Beca in November 2020, identified four potential locations (Appendix F). The two north western WRS options (‘WRS1’ and ‘WRS2’) were selected by OGNZL for the next study level. WSP-Golder undertook a further optimisation study in September 2021, including geotechnical stability analysis and consideration of several alternative configurations and numerous design iterations. Options were presented to OGNZL and other consultants to provide feedback across the multiple technical disciplines involved in the project. A modified design for WRS2 was selected for the project and the design further developed. The WRS is situated in a valley formed by a northeast flowing tributary of Mataura Stream. Figure 8 shows the selected configuration for WRS, portal, access road and main water management elements. Section 8.0 provides further details on the WRS alternatives assessed.
RkJQdWJsaXNoZXIy MjE2NDg3