|Stabilisation of an existing 7m high reinforced earth slope with soil nails and mini gabion mattress facing at a live superstore site.
|Rotary access platform and Excavator mounted Klemm drilling rig
We were employed to stabilise an existing retained slope supporting one side of an existing superstore car park. The existing slope, up to 7m in height, was formed of reinforced earth with a mesh facing and was showing signs of distress with a loss of alignment in the upper section of the face and cracking/subsidence to the surface of the customer car park above.
Access to the working area was restricted due to the need to minimise disruption to the supermarket during a busy trading period and the boundary fence to the car park had to be temporarily removed and an access ramp installed to enable plant and labour to access the existing slope from the toe. A working zone was maintained with barriers to protect customers and workers at the supermarket at all times and deliveries had to be carefully planned and controlled to minimise any disruption to customers visiting the store.
Unlike a virgin slope, which would generally be stabilised using a top down method, all the works had to be undertaken from the toe of the slope requiring the use of access platforms. It also compromised the finish which could be achieved on the final face because a new face would follow the profile of the existing slope.
Prior to any stabilisation works being commenced a specialist tree surgeon was employed and careful assessment of the working area made to ensure that the minimum amount of trees were removed, to provide access to the working area whilst still maintaining as much shielding as possible for neighbouring properties. The slope was also de-vegetated.
The installation of the soil nails was carried out using a drilling rig located at the bottom of the slope with operatives accessing the upper nail positions from a rotary access platform.
Materials were stored adjacent to the works in the car park at the top of the slope and sections of the boundary fence had to be removed and replaced as the works progressed and safety precautions employed, including the use of harnesses, to protect the workforce at the top of the slope as they passed materials to the operatives working from the access platform.
Once the works were underway and the existing slope had been de-vegetated the overall alignment of the slope was visible and it became obvious that over a large section of the works areas the lower section of the bank sloped back at about 85O with the upper approximately 1m section being almost vertical.
It was considered that if the new facing was just placed against the existing bank it would appear as if the upper section was overhanging and would have a very unsatisfactory appearance.
Therefore in order to improve the overall appearance of the stabilised slope the upper section needed to be realigned by building out the new facing where the angle of the slope changed.
In order to do this additional sections of rear mesh were placed on the upper 2m section of the slope behind the new facing. This additional mesh was anchored to the soil nails and in order to hold it tight to the face was torqued into position. This also enabled the top section of the existing reinforced slope, where the topsoil and facing had become loose to be, to some extent, pulled back into alignment.
The new facing was then formed away from the face, using additional back mesh, plates and nuts. The grid spacing of the rear mesh allowed the void between the existing bank and new facing to be filled as the stone filled up the new facing.
Once the soil nails, structural mesh and gabion facing was formed the baskets were filled with stone from the top using a telehandler and concrete skip.
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