# Optimization and Experimental Study of Penetration Depth of Pocket Penetrometer
## 1 Introduction  
Traditional shear strength testing methods, such as the triaxial test [1, 2, 3], direct shear test [4, 5, 6], and plate shear test [7, 8, 9] provide very accurate measurements, but they are usually time-consuming to operate and require specialized equipment and technical support. By contrast, the pocket penetrometer is an ideal tool for the rapid testing of soil parameters in the field due to its portability, simplicity of operation, and cost-effectiveness. The instrument provides a quick estimate of shear strength by manually pressing the probe into the soil and directly measuring the resistance of the soil. The testing process is simple and efficient, requiring no complicated preparation, and it is suitable for quick multi-point measurements at construction sites.  
Research on the pocket penetrometer test has yielded preliminary results. [PERSON] [10] assessed the shear strength of different soil layers and related the undrained shear strength of the soil to the tip resistance. In a study by [PERSON] [11], ninety-nine remolded samples were prepared for a given water content and energy level, yielding values of undrained shear strength that could be accurately assessed for remolded cohesive soils using only the pocket penetrometer test. [PERSON] [12] conducted experimental studies using soil samples with four different water contents (14%, 25%, 31%, and 36%; n = 180 measurements) and showed that the pocket penetrometer test could accurately predict the unconfined compressive strength of the soil. [PERSON] [13] conducted pocket penetrometer tests in five sampling pits at different locationsin Brazil; the data showed that the soil structure has a significant effect on soil strength, and to improve the reliability of penetrometer in predicting pre-consolidation pressures, it is better to classify the soils into different categories rather than analyzing them jointly. [PERSON] (2014) noted that the coefficient of variation for the pocket penetrometer test may be greater than 0.25 using unsuitable sampling methods. [PERSON] (2015) estimated the undrained shear strength of soil using three different tests: the Unconfined Compression Test (UCT), pocket penetrometer test (PPT), and Miniature Vane Shear Test (MVST). The data showed that the results of MVST and PPT were compatible, but it was observed that there was a significant difference between the results of these two tests and the UCT. At the same time, the pocket penetrometer has shown good potential for application in a number of emerging fields, including wind erosion control, stratigraphic analysis, and the strength assessment of biopolymer-treated soils (2016; 2017; 2018; 2019; 2020; 2021; 2022; 2023; 2024; 2025; 2026; 2027; 2028; 2029; 2020; 2021; 2022; 2023; 2024; 2025; 2026; 2027  
rate. The detection function area (2) consists of a pressure sensor 1, a pull 2, and a cord displacement sensor 1, which are responsible for detecting the penetration resistance and penetration depth and ensure the accuracy of the detection data while guaranteeing that the detection range is large enough, and they also have the reading and transmission rate once every 100 milliseconds. The monitoring function area (3) is a computer program, which can directly draw and store data in real time according to the data in the detection area to ensure that the detection results are obtained the first time while ensuring the timeliness of data storage. Therefore, although the self-developed penetrometer has little improvement in performance compared with the existing penetrometer, it is able to derive the penetration resistance versus depth curve, which provides the testing conditions for the study in this paper. As shown in Figure 2, In terms of probe design, the penetrometer is equipped with a cylindrical probe with a diameter of 6.2 mm and a height of 6 mm, along with an extension rod with a diameter of 4 mm and a length of 10 cm. The extended probe design provides the necessary experimental conditions to study the variation of penetration resistance at depths up to 10 cm.