Heterogeneous small-cell networks (HetSNets) are considered as a standard part of the future mobile networks where multiple low-power, low-cost base stations (e.g., femtocells) complement the existing macrocell infrastructure. In this paper, we propose a heterogeneous network where multiple tiers of small-cells are deployed which in turn expand the network coverage and increase the frequency reuse distance without compromising the frequency reuse factor. The resultant network is referred to as K-tier HetSNets, where small-cells are padded between the macrocells such that each of the macrocells in the network employs aggressive frequency reuse scheme, i.e., same set of frequencies is used in each macrocell. It has been shown that the co-channel interference due to neighboring macrocells has been reduced significantly without increasing the frequency reuse factor. The large scale deployment of the small-cells may increase the downlink power consumption of the considered HetSNet. Therefore, we show that the population of small-cells in each of the K-tiers is probabilistically dependent on the traffic load due to active mobile users, such that the small-cells in the network turn on their sleep mode under low and medium traffic load during the day. Several simulation results are included to illustrate the impact of the aggressive frequency reuse scheme and traffic load dependent population of small-cells on the system interference and downlink power consumption of the small-cell base stations.