Report: Black soil stabilisation trials, Narrabri, November 2018

Black soil trials were constructed at River Road at Narrabri on 1 and 2 November 2018. These trials are a joint initiative between Narrabri Shire Council, IPWEA (NSW) and AustStab. They follow previous black soil trials which were constructed at Goondiwindi in October 2016. 1. SCOPE

The purpose of these trials is to develop procedures and methods for stabilising unsealed black soil roads with low traffic volumes, and provide an all-weather surface with reduced maintenance requirements.

AustStab and council’s responsibilities for this trial were shared as follows: AustStab contractors’ responsibilities: • Establishment • Supply and spreading of quicklime as above • Slaking • Stabilising as above (two passes) • Construction testing (spread rate, depth of mixing, field moisture) • Post construction testing (relative compaction, UCS, CBR, two of each per section) • Project management. Council responsibilities: • Traffic control • Water cart • Rollers/compaction • Grader/trimming of final surface profile. 2. LOCATION

The trial was carried out on River Road located approximately 35 kilometres west of Narrabri. The actual site of the works is on River Road, 2 kilometres south of the Kamiloroi Highway. The site is approximately halfway between Narrabri and Wee Waa.

This road is an access road for several properties and is estimated to carry fewer than 50 vehicles per day. The section of this road selected for the trial has been formed from in-situ highly plastic black soil located with no imported local gravel overlay. 3. TRIAL DESCRIPTION

The site sketch below provides details of the trial sections including depth of stabilisation and quicklime percentages. Lot 1 has no lime but has been included as a control section. This lot was simply mixed and compacted with added moisture to assist compaction. TRIAL LAYOUT SKETCH

The trial details were developed in consultation with Narrabri Shire Council after a site investigation and laboratory testing, including lime demand testing, Atterberg Limits, UCS and CBRs.

The investigation testing was carried out with both hydrated lime and a 50/50 blend of slag and lime.

The hydrated lime was found to be the most effective binder. A summary of the results is as below: • The average lime demand for the full soil sample is 3.4 per cent • Average CBR (10-day soak) for 2 per cent hydrated lime is 18 per cent • Average CBR (10-day soak) for 4 per cent hydrated lime is 52 per cent.

The natural material was found to have a CBR of 2.5 per cent with a plasticity index range of 36 to 44. CONSTRUCTION TESTING

As with the initial investigation, CBR results for the unstabilised control section are low at 3 per cent and 4 per cent. Variable CBRs were achieved for both the 3 per cent and 4 per cent binder sections with results in the range of 45 per cent to 140 per cent. These results are generally much higher than those achieved for the initial site investigation laboratory test program, with no discernable difference between the results for the sections with 3 per cent binder compared to 4 per cent binder.

The range of UCS results for both sevenday accelerated and 28-day ambient tests are similar and range from 0.3 megapascals to 1.2 megapascals. 4. FUTURE MONITORING

To assess the performance of these trials over time, regular monitoring will be carried out. This will be predominantly visual monitoring initially at six-month intervals for the first year and then at 12-month intervals.

Any maintenance activities will also be documented to provide long-term performance data on the effectiveness of the lime stabilisation. AUSTSTAB PROVIDES AN OVERVIEW OF THE BLACK SOIL STABILISATION TRIALS THAT TOOK PLACE IN COORDINATION WITH NARRABRI SHIRE COUNCIL AND IPWEA (NSW) ON RIVER ROAD LAST NOVEMBER. LOT 1 0%, 200mm (control) LOT 2 3%, 200mm 9.6kg/m2 LOT 3 4%, 200mm 12.8kg/m2 LOT 4 3%, 300mm 14.4kg/m2 LOT 5 4%, 300mm 19.2kg/m2 LOT 6 3%, 150mm 7.2kg/m2 LOT 7 4%, 150mm 9.6kg/m2 CH 00 CH 100 CH 200 CH 300 CH 400 CH 500 CH 600 CH 700

Note: Lime percentages are for quicklime 6m