_Applied_  
_sciences_  
_Article_  
Experimental Study on the Shear Properties of Soil around Piles with Permeation Grouting  
[PERSON] 1,2, [PERSON] 1,2, [PERSON] 1,3,*, [PERSON] 1,2, [PERSON] 1,2 and [PERSON] 1,2  
while the quantity of injected cement slurry and the mechanical qualities of the soil around piles also affects the piles' bearing capabilities and load transmission mechanisms [9]. Based on a full-scale field test, [PERSON] et al. [10] pointed out that combining pile-side and pile-tip grouting may significantly enhance the mechanical properties of the soil around piles. For piles with a length of more than 15 m and high requirements for increasing bearing capacity, combined grouting at the pile tip and pile side should be adopted. In combined post-grouting, pile-side grouting first can effectively increase the pressure during pile-tip grouting, which is helpful to form an enlarged solid at the pile tip [11]. Many engineering practices have identified post-grouting as an exceptionally successful approach for improving the engineering performance of bored piles [12; 13; 14; 15]. This can increase the loading capacity of the pile tip, improve the frictional resistance of the pile side, and reduce uneven settlement. While post-grouting technology is widely used, researchers have also studied the shear resistance of post-grouting piles through a variety of methods. For example, [PERSON] et al. [16] researched the shear performance of the interface between post-grouting cohesive soil and concrete piles with different roughnesses. The interface of the cement soil-pile is different from that of the soil-pile, and the cement soil produces a cohesive force at the interface after grouting. For the former, some researchers have studied the shear properties of the soil-concrete interface, cement grout, loess of cement-treated, cemented soil-concrete interface, and clay-cement soil interface [17; 18; 19; 20; 21]. Furthermore, the influence of the unloading effect on the shear strength of the post-grouting sand-concrete interface was also considered [22; 23]. [PERSON] et al. [24] investigated the influence of roughness on the shear performance of the soil-concrete interface and found that there was a good correlation between the tangential deformation at failure and roughness. The location of shear failure surfaces for soil and concrete can be classified into three types based on the differential between normal pressure and the roughness of the contact surface. It contains the concrete surface, the interface between the soil and concrete, and the internal shear failure of the soil. The so-called internal shear failure of soil refers to the failure caused by the insufficient resistance of the soil around the pile to deformation in the actual project. As indicated in Figure 1, the soil around post-grouting piles is classified into two types [25]. The first type is the soil around the compaction grouting piles, which is close to the grouting port and closely connected with the pile interface. The second type is the soil around permeation grouting piles far away from the grouting port. However, the two types are assumed to be a continuous whole in current engineering practice, which ignores the soil around permeation grouting piles beyond the pile-soil interface. As the slurry wall protection technology is adopted for bored piles, the mud cake existing on the pile-soil interface also influences the loading performance of the piles [26]. For the thin layer of weak mud cakes formed between the pile and the bore wall during pile formation, post-grouting can greatly enhance the thin layer's shear resistance, hence  
Figure 1: Schematic diagram of post-grouting at pile tip and pile side. improving the pile's bearing capacity [27]. [PERSON] et al. [28] conducted a triaxial undrained shear test on mud cakes surrounding a pile and found that the water content, void ratio, and compressibility of the mud cakes after grouting were all significantly reduced, and the shear strength was dramatically enhanced.