Sand Drain

EDTP N5-S16 (SITE ENGINEER-ALSON CHIN)

SAND DRAIN/ COLUMN The sand drain / sand column play the same role of the PVD. It provide a shorter and easier drainage path through which the can escape and to accelerate the rate of consolidation and is use in conjunction with surcharging. This method been adopted for Chainage CH5669-CH5770 due to the TNB, High Tension cable crossing the railway. The height limitation is the main concern for the mentioned area. No machines are allowed to excess then 7m height during the construction. The normal PVD machines required at least 15m headroom during installation for the mandrel therefore the management decided to replace the PVD with the conservative waySand drain/ column. The installation of sand drain required an A frame for the bore log machine which similar with the Site Investigation (SI) frame with the total high of less than 4 m.

The original ground treatments (2+5+6+11) had changed to (2+6+14+15) which 5- PVD replaced by the 15- sand drain and additional 14-counterweight berm for the surcharge height stability. This portion treatment involved the 2 stage works, the temporary sheet pile and geowall are required 3 m away from the existing track. Prior to start any construction work, the safety net (goal post was installed) as the safety guideline for the workers to remind them about the headroom constraint of the 132kV high tension cables.

EDTP N5-S16 (SITE ENGINEER-ALSON CHIN)

Goal post section view

Site investigation boring machine use to install sand drain.

EDTP N5-S16 (SITE ENGINEER-ALSON CHIN)

INSTALLATION OF SAND DRAIN 1. Setting out of installation points and clearly marked and labeled for record and identification purpose. 2. Setting up the drilling equipment ( SI frame machine) at the installation point, erecting the mast and preparation to commence drilling. 3. To carry out wash using 165mm diameter casing from the existing ground level to 15m below ground (required depth as design) 4. Flush out the all cuttings in the borehole using clean water supplied by the single piston pump. 5. Lower circular geotextile bag of diameter 150mm and 15m long to he bottom of the cased borehole 6. Carry out sand filling from the bottom of the borehole using 100mm diameter tremie pipe (PVC). 7. At the same time, lift up the outer casing slowly and continue sand filling as 300mm above the ground level. 8. Sand filling as the horizontal drainage system prior preloading with the surcharge.

Layout plan for sand drain

EDTP N5-S16 (SITE ENGINEER-ALSON CHIN)

SI boring machine

Pegs / marks

150mm pipe casing

Drilling the borehole to required depth (measured by tape) Inserted the 150mm sand drain bag to the borehole. Sand fills as the adding weight to bring the sand drain bag to the bottom of hole. Tighten the sand bag to prevent to sand bag to fall / slip down.

EDTP N5-S16 (SITE ENGINEER-ALSON CHIN)

Sand filling

100mm tremie pipe

Sand filling into the borehole through the PVC pipe until the sand drain bag fully filled.

Goal Post Boring machine

Sand drain bag

Measuring the sand drain bag’s length as per design