# Analysis of Load-Settlement Curve Based on Load Transfer at Pile-Soil Interface
###### Abstract
[18; 19] performed series of in situ pullout experiments on soil-nailing systems using both pressurized grouting and common gravitational grouting to compare the pullout loads of both cases and to verify the effectiveness of the pressurized grouting on the soil-nailing system. The pullout load of soil nailing using pressurized grouting was approximately 36% higher than that of soil nailing using gravitational grouting. This was attributed to the additional compaction of soil by cavity expansion and the increase in the residual stress and the dilatancy angle by pressurized grouting. Based on the Brillouin Optical Time Domain Reflectometry (Gossen Metrawatt GmbH, Nurnberg, Germany) (BOTDR) fiber optic strain profile, the profiles of axial load, skin friction, and displacement can be obtained. Meanwhile, numerous researchers had studied the influence of stress history on the friction coefficient and cohesiveness at the pile-soil interface using loading-unloading systems. [PERSON] et al. [20] investigated the sinking process of hydrostatic piles in sandy soils utilizing indoor half-pile model tests, revealing the movement patterns of the soil at different locations around the piles. It was well known that the method of installation of pile foundations had a great influence on the behavioral characteristics of the piles. Most of the current research on the installation form of pile foundations focused on driven piles and hydrostatic piles, but there was some research on the pile-soil interface characteristics of bored piles under hydrostatic pressure [21; 22; 23]. [PERSON] et al. [24] analyzed the mechanical behaviors and law of the grouting mode transition of the unloading grout sand-concrete interface with different grout conditions. [PERSON] et al. [25] investigated the influence of the soil and grout material properties as well as, the cover depth on the surface settlements and the loading and deformation of the tunnel lining in shield-driven tunnels. [PERSON] et al. [26] investigated the strength of soil-nails that depend on the behavior of the soil-cement grout interface at saturated and unsaturated conditions. As well, the dilation values of the soil-cement interface for different grouting pressures were less than that of completely decomposed granite (CDG) soil under different suctions. The interface shear strength increased with the grouting pressure at saturated conditions, in which a downward trend was obvious--as the suction value was increased from saturated conditions. [PERSON] et al. [27] investigated the effect of grouting volume on the shearing characteristics of the interface between cohesive soil and concrete piles with different roughness, and combined grouting equipment and a direct shear apparatus to carry out a total of 48 groups of direct shear tests on cohesive soil-concrete interfaces that incorporate the grouting process. The test results showed that the shear behavior of the grouted cohesive soil-concrete interface was improved mainly because of the increase in the grouting volume, and the roughness increased the interfacial apparent cohesion. Recent advances in strain measurement using optical fibers provide new opportunities for monitoring the performance of piles. If the pile-soil interaction (e.g., load transfer functions t-z or p-y) is of interest, then BOTDR optical fiber sensing may be sufficient when a continuous distribution of axial forces and/or bending moments needs to be established [28]. [PERSON] et al. [29] discussed the advantages of distributed strain measurement by BOTDR compared to conventional discrete measurements (e.g., strain sensors) through the theoretical analysis of the pile-soil interaction problems. [PERSON] et al. [30] discussed the BOTDR-distributed monitoring technology and explored its application in a number of pile load test cases (both top-loaded using an external reference frame and bidirectionally loaded using an Osterberg cell) in London.