Subgrade Preparation

1.0 Introduction

Sub grade preparation shall be carried out using selected materials where the exposed surface is not suitable for the sub grade.

2.0 Abbreviation

QAE    – Quality Assurance Engineer

SE    – Site Engineer

TO    – Technical Officer

QAS    – Quality Assurance System

ME    – Materials Engineer (Contractor)

TS    – Technical Specification

3.0 Resourse Allocation

Man Power Equipments & Tools Material
Site Engineer Back-hoe loader Selected sub grade material which
Technical Officer Water pump meets the engineering properties,
Single Supervisor Dump trucks approved by the Engineer
Double Flagmen (minimum) Level Instrument
Unskilled labors Camber board/ Straight edges
Operators Mortar pans
Pick axes
Wheel barrows

3.0 Quality Control Procedures

1. Sampling and testing

Suitable materials would be employed in the preparation of sub grade as those materials have been classified to use as sub grade materials by the all preliminary tests done on it. Sampling of these materials would be made in a manner to identify easily their status of test and all the necessary details would be entered to the sample register. In case of placing these materials, the specified layer thickness and degree of compaction for each layer would be achieved. Field density test would be carried out in case of checking the degree of compaction according to the method stipulated in the relevant BS codes. See Inspection Test Plan.

2. Inspection Check list

To ensure that the all activities being performed with the expected quality, an inspection check list would be filled by the person in charge for this work in case of pre-construction, during construction. The inspection check list shall include the specific requirements, safety and environmental measures.

3. Dimension Control

Preparation of sub grade would be carried out according to the designed cross sections. The required depth and length of the excavation would be properly maintained during construction and those requirements would be checked with the inspection check list.

4.0 Methodology

• If the exposed layer of soil unsuitable for sub grade, these layers would be excavated up to the required depth by using a back-hoe loader and the required levels of the excavation would be controlled by the surveyor.

• Selected suitable material would be placed and compacted in successive layers by using rammers or vibrating rollers to a minimum depth of 150 mm.

• If the exposed layer of soil suitable for the sub grade, the layer would be thoroughly compacted by using vibrator rollers or rammers until reach the required compaction.

• The top 150mm sub grade layer in cut areas would be compacted to not less than 95% of the maximum dry density of the material at moisture content within 2% of the optimum moisture content as determined by AASHTO T-180. Water would be sprayed while compacting for achieving a better compaction.

• The surface of the finished sub grade would be neat and workmanlike and would have the form, super elevation, levels, grades and cross section

as shown on the drawings.See methodology flow Chart

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