Establishing a Reference

Overview

A stable datum is essential to the performance of the ASP on your project. Even when based outside of the zone of influence, there should be a means of verifying the elevation of the reference sensor.

Reference Pad

A heavy-duty settlement plate provides a simple means to create a mechanical connection between the ASP reference sensor and a surface accessible benchmark. The top of the settlement rod can then be manually surveyed, equipped with a 3D prism for automation with a robotic total station, or fitted with a GNSS node.

A settlement plate typically comprises a 300x300x6mm mild steel plate with a DN40 mild steel socket welded to the centre. Threaded DN40 rods are added to the plate to provide a survey point at the surface. A 75mm PVC pipe is used to protect the riser rods from the earth fill.

Alternatively a concrete pad can be laid with a benchmark or alternative means of deriving a datum fixed to the same pad.

Settlement Plate Reference

• Place your place on the compacted fill within your prepared trench.

• Secure the first rod in the socket and place the protective PVC sleeve over the rod.

• Lay the ASP over the rod and align the ASP reference sensor (200mm from the cable entry) with the riser assembly.

• Where there is excess ASP length, coil the ASP around the plate until the reference sensor can be placed on the plate. Use cable ties to maintain the coil’s shape and diameter.

• Use sandbags to weigh down the ASP reference sensor and any excess hose.

• Backfill and hand compact around the settlement plate riser.

Concrete Slab Reference

1. Prepare Formwork

   • Place formwork in a trench at the reference location

   • Create a concrete pad at least 500 x 500 x 200mm

   • The top of the formwork should be level with the intended alignment of the ASP

2. Ground Support (Soft Ground Only)

   • In very soft ground, drive four star-pickets into the ground

   • Ensure they finish just below the top of the concrete pad

3. IPX Isolation (If Applicable)

   • If the reference pad is being installed around an IPX

   • Use a section of PVC pipe to isolate the access tube from the concrete prior to pouring

4. Pour and Set Concrete

   • Pour concrete and screed level

   • Once the concrete is set, install a settlement point socket in the concrete offset slightly from the centre

5. Install ASP

   • Install the ASP as detailed in the installation methods below

   • Affix the reference end of the ASP to the concrete pad using the ASP fixing bracket

ASP Reference