###### Abstract
Accordingly, the crack self-healing properties of the asphalt core in dams were investigated in several references [4; 11; 12]. Cracks and/or dilations in the asphalt core in dams may occur because of large differential settlements during construction and operation. Measured results showed that the differential settlements between the upstream side and the downstream face of the core were about 36 cm and 13 cm, respectively, for the 85 m high Feistritzbach Dam and for the 155 m high Finstertal Dam (core height of 96 m) [13]. The two dams, Finstertal Dam, completed in 1980, and Feistritzbach Dam, completed in 1990, have performed well for over 40 and 30 years, respectively. However, if an asphalt core dam with a dam height of over 200 m is situated on a deep compressive overburden, the differential settlements between the upstream and downstream faces of the core will be much large, and in the case, cracks and/or dilations may occur in the asphalt core. An asphalt core model test showed that the air porosity in the upstream and downstream face layers of the 15 cm wide asphalt core wall model was increased up to 4.0% (dilation) after simulating the cycles of reservoir impounding and drawdown [14]. Under unrestraint conditions, a water pressure of 0.2 MPa in a central hole (20 mm in diameter and 160 mm in depth) in an asphalt specimen (100 mm in diameter and 200 mm in height) could cause a radial tensile strain up to about 1.0% and fracture the specimen at about 15 \({}^{\circ}\)C [15]. Model tests showed that a pore water pressure of 0.13 MPa inside the asphalt specimen of 3.5% air porosity would cause the vertical tensile strains up to 4.2% over time and would fracture the specimen under vertical unrestraint conditions at about 15 \({}^{\circ}\)C [16]. Weak bond between layers and an air porosity larger than 3.0% in the asphalt core may occur during construction from poor construction quality. An asphalt core is placed and compacted in layers at a temperature of about 150 \({}^{\circ}\)C. If the previous layer is cooled down, the top surface has to be heated to ensure a good bond with the upper layer. The top surface should not be overheated, to avoid bitumen ageing. The bond between two layers, especially in the upstream and downstream faces of the core, could be weaker than the native layers. The asphalt layers after placing and compaction keep a temperature range of 60-100 \({}^{\circ}\)C for a few days. There have not been any very reliable tools for timely quality checks on sites to date. Practically, the daily field quality control has strongly relied on experienced engineers' observations and judgements on site. Under such an artificial control condition, it is unavoidable that some weak bonds between layers and an air porosity larger than 3.0% may exist in the asphalt core. Occasionally, a few drilled asphalt core samples show that the air porosity is about 3.0%. An asphalt core is a slender impervious wall with a width of 0.5-1.2 m located in the central centre of embankment dams. The core wall in dams has to keep flexibility and watertightness in operation. Cracks and/or dilations in the asphalt core may be caused by either severe earthquake shaking, large differential settlements during construction and operation, or poor construction quality. Furthermore, they are difficult to discover, and hydraulic fracturing may result from them. Therefore, the following studies were undertaken: (1) preparing asphalt specimens with cracks of either different depths or different air porosities and then developing a model test apparatus; (2) investigating the possibility of hydraulic fracturing for the asphalt specimens with either cracks or a large air porosity; (3) investigating the behaviour of asphalt specimens with cracks under the unrestraint conditions by conducting numerical back analyses; and (4) discussing and comparing the hydraulic fracturing between the asphalt core and the earth core in dams.