Engineering for Calcareous Sediments Volume 1

D. Andrews, R. Jewell

• Publisher: CRC Press
• Year: 2021
• ISBN:
  9781000446821
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

Volume 1 of the Proceedings of the International Society of Soil Mechanics and Foundation Engineering, Institution of Engineers Australia with the main topic of Engineering for Calcareous Sediments held in 1988.

1 Genesis, fabric and structure of calcareous deposits

Coralline calcareous pavement and foundation aggregate

F. Bullen

Queensland Institute of Technology, Australia

D. Williams

University of Queensland, Australia

ABSTRACT: Shallow depth calcareous deposits in the Pacific region frequently occur as either on-shore uplifted, or live active submerged coral reefs. Many of the Pacific islands, including Australia’s barrier reef islands, must rely heavily on these calcareous (or more specifically coralline) materials for aggregate for pavement construction and foundation fill. Deposits vary greatly with respect to engineering properties due to variation in coral type, degree of recrystallization, amount of self cementation and level of contamination by plastic fines. Routine classification testing carried out on Papua New Guinean and Australian coralline materials has indicated that these materials, when used as pavement aggregates, demonstrate a propensity to gain strength and stiffness with time and generally behave as ‘superior’ construction materials. Overall satisfactory performance was found to be dependent on level of plastic fines and vesicularity of the material. The use of coralline calcareous materials as foundation fill is made complicated due to the variability in the source material both horizontally and vertically. The paper suggests some guidelines for selection and use of the material.

1 INTRODUCTION

The high cost of producing quality crushed rock in Papua New Guinea and the neighbouring Pacific Islands, combined frequently with a lack of suitable deposits, has resulted in a revived interest in coral derived construction materials. These coralline deposits, widely used throughout the Pacific, are known locally as “coronus” a pidgin English term from the neo-Melanesian “karanas” (Hosking 1967). Coral reefs are made up of accumulated calcareous secretions by coral polyps and nullipore algae. The calcium carbonate secreted by the coral polyps is in the form of aragonite while that secreted by nullipore algae is in the form of calcite and some dolomite. Voids within a coral reef are filled with shells, shell particles and coralline detritus from the reef itself.

This creates a type of porous rock on the recently grown surface and fringe of the reef. Calcite precipitates to form a more dense material lower in the reef (Beaven 1963), which is normally termed reef rock.

Individual coral colonies are bound together by the limey skeletons of the coralline algae which enables the reef to act as a single unit to withstand heavy surf action. This phenomena has led to the development of theories that coralline pavement materials possess a self cementing property due to the resolution and redeposition of calcium carbonate (Beaven 1963, Frost 1970).

There are three main types of coral reef. The fringing reef is a narrow reef attached to the land. The barrier reef is a reef separated from the shore by a lagoon. The atoll is a circular reef enclosing a lagoon. Reef building corals normally exist at depths less than 30 m, in water temperatures with an annual minimum of 18°C and a mean of the coldest month not below 21°C. This means that they are confined to shallow waters in the region 30°N – 30°S of the equator. This geographical band takes in many nations including Malaysia, Thailand, Indonesia, Philippines, Samoa, areas of the United States, Australia, South America and Africa. The reef most familar to Australians is of course the Great Barrier Reef. This reef, which is actually a system of coral reefs, extends southward from above Cape York for more than 1900 kilometres with a variable width of up to 350 kilometres (Endean 1982) and terminates at approximately 24°S.

The use of coral as a building material is not confined to recent history. In Florida, Latin America, the Carribean and the Pacific, coral has been used in the as excavated condition for many years (Bullen and Welsford 1985, Phelan 1952). During the World War II years the full potential of coralline materials was realised (Dod 1966). The Allies considered coral to be a superior pavement and foundation material as it was available in abundance, easily mined, spread quickly, compacted well and set up with good limey qualities of adhesion (Luce 1945, Lindau 1944). Its use was almost always spectacularly successful and aided greatly in operations against the Japanese Empire (Flanders 1947). It was thus confusing when rigid analysis of the coral used revealed it to be a rather poor material. At one stage it was considered such a poor substitute for crushed rock that Army and Navy Construction Agencies considered the possibility of shipping acceptable grades of crushed rock for the construction of advanced bases in the Pacific (Flanders 1947).

2 AVAILABILITY

In a growing living reef much of the material is inaccessible for excavation and thus only available for use after extensive costly dredging operations. In the course of history local uplift of the sea bed has caused many reefs to now be found on land in the form of coral rock, coral gravel or coral sand depending on original reef condition and weathering action applied to the original reef subsequent to reef uplift. Much of the coralline material used throughout the Pacific occurs as inland deposits. In Papua New Guinea Pliocene limestone of predominantly coralline nature is found outcropping at heights from about 30 metres up to 1000 metres above sea level on the ridges and slopes of coastal hills and ranges on both the mainland and the islands. Quaternary coralline limestones ranging in age from Pleistocene to the present are common on the islands and coastal area of the mainland. Both the Tertiary and Quaternary inland deposits are termed coronus by the local inhabitants. These coronus deposits are readily available in most coastal areas which allows for minimal transport costs when construction is carried out in the coastal areas. Overburden is stripp...

Table of contents

• Cover
• Halfitle Page
• Title Page
• Copyright Page
• Table of Contents
• Foreword
• Preface
• 1 Genesis, fabric and structure of calcareous deposits
• 2 Sampling and laboratory testing
• 3 In situ testing such as CPT andpressuremeter tests
• 4 Model and large scale testing
• 5 Foundation design and construction in calcareous deposits