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ORIGINAL PAPER

Effect of Insitu Moisture Content in Shrink-Swell Index A. M. A. N. Karunarathne

. E. F. Gad . P. Rajeev

Received: 16 April 2018 / Accepted: 28 June 2020 Ó Springer Nature Switzerland AG 2020

Abstract Expansive soils (also called reactive soils) undergo heave and settlements due to moisture changes and could result in differential movements in light weight structures. Hence, an estimation of potential ground movement is essential for designing footings for such structures. Shrink-swell index (Iss) is commonly used as a measure of soil reactivity and it is used in Australian standard of residential footing design to calculate ground movement. The shrinkswell test estimates the strain change per unit suction of an undisturbed soil sample; assuming the strain is independent of the insitu moisture content. In this study, 14 undisturbed soil samples were collected from an expansive soil site at different times over a two-year period. The sample locations were very close to each other. The samples had different insitu moisture contents varied from 22 to 37%. Test results indicate that increase in insitu moisture within that range resulted about 50% increase in Iss. Similar increment was observed in a set of samples obtained from another expansive soil site. The impact of insitu moisture content on Iss could lead to incorrect site A. M. A. N. Karunarathne (&)  E. F. Gad  P. Rajeev Swinburne University of Technology, Hawthorn, VIC, Australia e-mail: [email protected] E. F. Gad e-mail: [email protected] P. Rajeev e-mail: [email protected]

classification. Consequently, the results of this study indicate that if the site is tested during different times of the year, it will result in different footing recommendations. Keywords Moisture

Expansive  Soil  Shrink-swell 

1 Introduction In general, the expansive soils cause a greater damage to the light weight structures (i.e., residential buildings) and significant financial loss to property owners. As Fig. 1 shows, approximately 20% of the surface soils in Australia are found to be moderate to highly expansive (Richards et al. 1983). These expansive soils are more frequently found in all the populated areas. Expansive soils around Australian states contain Montmorillonite clays that are capable of absorbing water and increase in volume. This change in volume can exert enough force on a building or other structure to cause damage. In order to minimize the damages induced by ground movement, designing of residential slabs in Australia is entirely based on the reactivity of the site (AS2870 2011). The sites are classified from slight to extreme reactive based on characteristic ground movement (ys) as shown in Table 1. The standard—

123

Geotech Geol Eng Hs X

ðIpt  DU  hÞ

ð1Þ

Ipt ¼ a  reactivity index

ð2Þ

ys ¼

0

Fig. 1 Distribution of expansive soils (Richards et al. 1983)

AS2870 2011 subsequently provides appropriate footing details for each site class. Moreover, for extremely reactive si