## 1 Introduction  
China has a vast area of frozen soil area of which permafrost accounts for about 21.5% of the total land area, and seasonal frozen soil accounts for 53.5%. It is one of the most widespread distributed countries in the world [1, 2]. Bohai Sea is located between 37\({}^{\circ}\)-41\({}^{\circ}\) N and consists of Liaodong Bay, Bohai Bay, Laizhou Bay, and the central shallow sea basin. Surrounded by land on three sides, it is a semi-enclosed sea area with little heat exchange with external seawater. Under the influence of factors, such as the Siberian High and Pacific Subtropical High in winter, the freezing phenomenon is significant [3, 4, 5, 6]. At the same time, during the period of rapid industrial development, the ecological environmental problems in some parts of the Bohai Sea have become more prominent. The proportion of stations with water quality worse than class four in the coastal waters of Liaoning and Shandong Bohai increased from 3.6% in 2016 to 16.1% in 2018 [7]. Nowadays, the cargo throughput of major ports around the Bohai Sea (Yantai Port, Tianjin Port, Yingkou Port, Dalian Port) is increasing, water transport projects are developing rapidly [8], and the construction of the Yantai undersea tunnel has been put on the agenda [9]. In the harsh environment of the Bohai Sea, these coastal and marine projects are inevitably affected (asshown in Figure 1a). There are often many cracks and pores in the deep rock mass [10]. Under the action of a long-term hydrochemical environment and a freeze-thaw cycle, the water-ice phase transformation occurs in these macro and micro defects, resulting in frost heave force, which drives the expansion of original defects and the initiation of new cracks. Eventually, joints and fractures join or break, threatening coastal and underwater engineering structures [11; 12; 13; 14]. With the increasing construction of geotechnical engineering in Bohai Bay, grouting reinforcement technology should be considered to maintain the stability of deep fractured, weak surrounding rock in these areas [15]. Grouting reinforcement technology is one of the most effective methods to solve rock fracture damage under a freeze-thaw and hydrochemical environment (as shown in Figure 1b). However, under the action of an acid water environment in a coastal seasonal frozen area, the grout-reinforced specimens will still be affected by an acid environment and a freeze-thaw cycle, and the internal structure and mechanical properties will change, which brings great hidden dangers to the stability and safety of rock mass engineering. Therefore, in order to prevent and solve the disaster problems of the grouting reinforcement projects in an acidic freeze-thaw environment and reduce unnecessary engineering waste, it is particularly important to study the mechanical properties of the grout-reinforced specimens damaged in coastal seasonal frozen areas in an acidic environment. With the continuous development of engineering technology, research results in grouting materials, grouting technology, and diffusion mechanisms that are increasing [16; 17; 18; 19; 20]. Grouting material is the primary factor that determines the construction effect of the grouting reinforcement project. It is generally composed of base material, an external reference agent, and a solvent. After more than two centuries of development, grouting materials have evolved from'single grouting material' to'modified grouting material' and then to 'composite grouting material' to meet the requirements of different engineering needs, technical levels, and composite material development [21]. In the excavation stage of underground engineering construction, an important reason for engineering instability is the shear failure of the rock mass joint area [22; 23; 24; 25]. In order to solve this problem, the grouting reinforcement of fractured rock mass arises at the historic moment. It can improve the mechanical structure of the fracture surface and then improve  
Figure 1: Bohai Bay key project and grouting reinforcement technology.