## 2 Literature Review
### Network Resilience  
In recent years, research on network resilience has focused on defining, evaluating, and improving it. Some studies have provided a detailed overview of the concepts of vulnerability, reliability, and resilience in transportation networks. They defined resilience as the interaction between managing organizations, infrastructure, and users [25; 26; 27]. In the pursuit of alleviating the detrimental impacts associated with the implementation of intelligent transportation systems on urban transit, [PERSON] et al. [28] applied a percolation theory model to statistically analyze delays resulting from damage to roads and nodes. They introduced the concept of resilience within this context. Scholars have classified many aspects of the assessment methods for network resilience. They proposed five indicators--queue, length, time, speed, and delay time--to evaluate traffic network elasticity and resilience under attacks [29; 30; 31]. In the domain of evaluating the resilience of transportation networks, a predominant approach involves employing metrics like delay duration and attack time as indicators to assess network resilience [32]. Additionally, a model was established to comprehensively assess the resilience of transportation networks by considering the cost of attack, system stress, and exhaustion level [33]. Regarding resilience improvement, current research has mostly focused on the network structure. For example, studies have proposed different recovery strategies based on different statuses--increasing network lines as strategies to improve traffic network resilience and considering network connectivity, road traffic time, accessibility, and effectiveness as resilience indicators [34; 35; 36]. In addition, two methods were proposed to improve the resilience of the network. The first is to improve the capacity and reliability of key lines, and the second is to change the topology of the network by considering driving time, shortest path, and other factors [30]. Apart from structural resilience, resilience to performance is also essential for the network. The ability to maintain and recover after attacks needs to be considered when assessing performance resilience [37]. Moreover, a parallel can be drawn between the recovery phase in post-disaster logistics networks and the emphasis on network resilience in this study. [PERSON] et al. [38] addressed gaps in modeling the recovery phases of humanitarian logistics post-disasters by introducing a hybrid approach named HNSGA-II. This approach highlights the trade-off between fairness and cost in decision-making processes. However, compared to research on network structural resilience, there are fewer studies on performance resilience.  
To address the identified research gaps, this paper focuses on maximizing the resilience of underground logistics network planning. The contributions of this paper are articulated as follows:  
* Resilience assessment perspective: This study introduces a distinctive approach to resilience assessment. In contrast to conventional methods centered on structural resilience through efficiency assessments, our emphasis lies on appraising the network service level.
* Resilience improvement strategies: Departing from conventional methods that enhance resilience through the allocation of resources for disaster supplies and preparedness, we propose improving the resilience of ground logistics networks by constructing underground networks.
* Network planning perspective: In the planning phase, we not only account for cost and capacity constraints but also assess the impact of constructing an underground logistics network on the resilience of the ground network.