Mini-piles are small-diameter (5-20 cm),
high-capacity (up to 60 tons) piles. They are used to anchor and support retaining walls.
While they may be driven in place, mini-piles are often installed by drilling a steel
cased hole, placing reinforcing bars in the casing, and then bonding the soil, casing and
reinforcement together by grouting. The mini-piles used in erecting the retaining wall are
divided into two types: one is vertical mini-pile and the other raking mini-piles with 1
in 4 raking angle with vertical.
- A mini-pile contains 4 nos. T50 hot rolled high strength steel bars of Grade 460
- 61 mini-piles needed for constructing retaining wall RW 5
- Grout mix is a mixture of water and Ordinary Portland Cement with W/C ratio of 0.42 by
weight, the minimum strength being 40MPa at 28 days
- Pile length for most of the mini-piles is about 12m with varied length of rock socket
from 4.5m to 8.5m
Method Statement for Constructing Mini-piles:
- Set out the exact location of the mini-pile.
- Lower the permanent circular steel casing to the required depth using hydraulic crawler
drill with oscillator according to ODEX drilling method. Casing remains in-situ to rock
head level.
- When bedrock is encountered, a rock socket will be formed by using 190mm flat bit with
hydraulic down-the-hole hammer mounted on a drilling rig. A drilled hole of min. 190mm
diameter is formed.
- Clean the bored hole by flushing with compressed air and water.
- Install a reinforcement bar group fabricated by bundling four high yield steel bars with
tie wires and separated from each other by a bar spreader. Use couplers to connect the
reinforcement bars to the desired length. Two 21mm diameter grout tubes are tied to the
whole length of the bar group for grouting.
- Grout the min-pile by tremmie method; cement grout is pumped down to the bottom of the
hole displacing water upwards.
