EGL Ref: 9049 23 June 2022 Page 22 File: WAI-985-000-REP-LC-0050-Rev0.docx This report shall only be read in its entirety. 1. First step is to set up simplified calculations/models to compare theoretical predictions with past recorded groundwater levels and ground settlement. Theoretical prediction models can then be adjusted to better match past predictions and to then aid future estimation of settlements, where the mechanisms involved are similar. 2. Second step is to use the adjusted theoretical models to estimate the settlement effects of dewatering caused by future developments. The theoretical predictions are possible at Waihi because: • There is strong correlation between groundwater levels and observed settlement which allows theoretical models to be essentially calibrated against the observed effects. • Limited dewatering of the shallow groundwater and younger volcanics has occurred and limited future dewatering of these materials is predicted. Modelling of tilt due to changes in general groundwater profiles, depressurisation and geology can be broadly estimated, but cannot reliably predict notable tilts due to localised dewatering at shallow depths. The additional settlement effects due to Waihi North Project have been assessed separately for: • Potential dewatering of the Gladstone vein south of GOP • Potential additional dewatering of the andesite rock due to the proposed MUG decline in andesite beneath Moore Street • Potential dewatering of the ignimbrite between the Wharekirauponga Access Tunnel decline and Boyd Road and Barry Road • Potential dewatering of the andesite veins and rock mass not already dewatered caused by the development of the Wharekirauponga Access Tunnel behind Waihi East • Depressurisation around the Willows Access Tunnel • Dewatering around ventilations shafts • Dewatering due to the development of WUG Calculations for the estimates of settlement have been undertaken using the GeoStudio 2D finite element analysis (FEA) programs, SEEP/W and SIGMA/W. 6.1.1. Gladstone vein dewatering south of GOP Calculation of seepage and settlement has been undertaken for a representative profile south of the Gladstone Open Pit where there could be veins connected with the pit that may extend some limited distance beneath the Ohinemuri River. The assessment was undertaken to estimate the potential additional settlement and tilt around the Heath Road area. The SEEP/W model of the ground and groundwater parameters for GOP were provided by GHD (Ref. 37). This assumes full vein drawdown to match the level of the pit floor (RL1005m). The change in groundwater is assessed against a current condition with the groundwater approximately at the river level with a slight upward flow from the andesite to the river indicated by GLD004 piezometers. The model assumes that the weathered andesite at the
RkJQdWJsaXNoZXIy MjE2NDg3