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Grouting is typically called for when the roof of a void collapses, or a sink hole or depression forms producing deformation of the ground surface or when pre-construction site testing uncovers such potential defects. The gradual deterioration of the void, usually over a period of years, most often appears as cone shaped depression, or hole at the surface which can result in damage to buildings, utilities, and roads.
Voids can form under a variety of conditions both natural and manmade. Trash and rubbish buried during construction will produce a void as it decomposes. If the trash pit is located under a concrete slab, building footer or foundation structural damage will often result from the subsidence. Sanitary and storm sewer pipes breaking will allow fill materials to carried away producing underground voids.
Damage to structures from void formation may be minimal to severe. These damages may include cracking in foundation walls and floor slabs, cracking of brick veneer, vertical displacement of the structure with severe tilting an inability to properly open and close doors and windows. Under extreme instances, complete structural failures can occur.
Filling of the void is conducted in one of several ways depending upon a variety of factors including location of the water table, the size of the cavity, its proximity to the surface and location in relation to structures.
One common and simple technique used to stabilize the subsurface and prevent subsidence is using cement based Portland cement or chemical grouts and foams to fill the cavity below. This method employs the use of pneumatic or drilling equipment to install pipes that connect the surface to the void below. The pipes act as conduits to the subsurface void allowing grout to be installed. Grout pipes can differ from sizes, depending on grout mixture and placement volume desired. Once the grout pipe or pipes are in place it is a simple matter to fill the cavity. With the use of shut off valves and pressure gauges it is possible to determine when the cavity has been filled. Once the cavity has been filed the pumps and valves are turned off and the grout allowed to cure.
Khumani Cavity Fill
The fill of the cavity with capacity of 83,300 m3.
The project consists of +-52 000 Cubes of dry sand fill and +-30 000 Cubes of a 3-5 mPa grout mix. However, due to the spread of the dry material that is better than anticipated, the possibility has been explored to fill the cavity with more dry sand material. This is something that has not been done in this area before on Khumani mine.
Production strategy:
The fill of the cavity is done by stockpiling wind-blown dry sand next to hoppers/conveyors and then by loading the conveyors with TLB’s the soil will be deposited trough borehole pipes into the cavity and various point within the cavity. These borehole pipe will be key to the effectivity of the sand fill as we have identified that the material deposited in the one bore hole will affect the capacity of the next hole. Therefore, deposition strategy is important to ensure the maximum fill at the most accessible points can be achieved.
Total Contract value Excl Vat: R 41 344 286.58
Raising of Garden Route Dam
The main contract was to construct the new raised dam wall and spillway of the Garden Route Dam.
Esor Constructions was sub-contracted to drill through all strata including concrete to perform water pressure tests and do pressure grouting where needed.
The Garden Route Dam spillway and wall project was completed in January 2020 and increased the dam storage capacity by 25% from 10 million cubic metres to an estimated new capacity of 12,5 million cubic metres.
Our Contract Value : R 2 050 885
Duration : 14 Weeks
The Rehabilitation Of The Sinkhole On National Road R21 Section 2 Northbound
Employer: SOUTH AFRICAN NATIONAL ROADS AGENCY SOC LIMITED
Consultant: Jones & Wagener Jones & Wagener (Pty) Ltd
Contractor: Raubex Esor JV
Contract amount: R 144 245 942.80
Esor Construction Scope of work included the following:
Drilling:
The spec for the site was as follows:
Drill down to +- 25m or 7m into solid rock. The reasoning behind it is during the investigation stage it was found that in the area the maximum size of the boulders is +- 6m. Therefore, if we drill into rock and it exceeds 7m, we are not into a boulder but into solid rock. We expected poor drilling conditions as it is challenging to drill into the weathered dolomite as the material is very fine. We also encountered cavities in places where we did not expect it. The scope of work on the drilling as well as grouting was increased due to very poor soil conditions from +-1400 holes to over 1800 holes.
Grouting:
The spec for this site was as follows:
The grout casings should be inserted to a depth of at least 25m except if the hole was stopped short. Once the bottom of the hole has been reached, we started pumping the approved grout mix. The grout mix is designed to have a strength of at least 5 mpa at 25 days. The anticipated grout take was around 25 000 cubes of grout. The grout takes was much lower than anticipated reaching only 5 000 cubes of grout. This was due to smaller but more frequent cavities.
Base and layer works was done as the drilling damaged the existing road surface which was to be expected. In the area where the primary sinkhole formed, more of the layer works had to be re-instated.
The Project was successfully completed in the Contract Period and within budget.
