The basic principles of geotechnical exploration technology are high practicality and strong pertinence. When conducting geotechnical investigation under complex geological conditions, in order to obtain effective measurement and evaluation indicators and relevant parameters of rock and soil layers, the main investigation technologies include engineering geological mapping, geological drilling, in-situ testing, and laboratory testing.

　　(1) Geological mapping technology

　　The main purposes of geological mapping in geotechnical work are to carefully investigate and analyze the terrain of the project area, and to conduct in-depth research on the geomorphological features, strata, geological structures, and adverse geological conditions of the area, so as to better understand the geomorphological units, properties of rock and soil, distribution of rock and soil, causes of formation, and ages in areas with complex geological conditions, thereby completing the identification of the weathering degree of rock and soil layers.

　　(2) Rock stratum drilling technology

　　For rock stratum drilling, 100A-D drilling rigs, KY-250 drilling rigs, etc. can be used. Drilling methods can include mud wall protection, full core recovery, and rotary drilling. The core recovery rates for sandy soil layers and cohesive soil layers should be greater than 75% and 90%, respectively, and the macroscopic characteristics of each soil layer should be carefully observed and described. In order to better study the distribution characteristics of the stratum structure, samples should be taken from the bottom layers at different depths, then carefully analyzed, and the changes in each soil layer in the horizontal and vertical directions should be recorded in detail, ultimately determining the relevant indicators for geotechnical investigation.

　　(3) In-situ testing technology

　　The static cone penetration test is adopted, using an original hydraulic static cone penetration probe, and the collected information is transmitted to a computer for analysis and organization. When the standard penetration test is conducted using the standard drop hammer free-fall method, attention should be paid to cleaning the hole before the test and maintaining the hammering rate at about 20 blows/min. The dynamic penetration method can also be used, which can effectively determine the physical and mechanical indicators of weathered bedrock.

　　(4) Laboratory testing technology

　　That is, simulating geotechnical engineering problems that may occur in the site environment and conducting targeted analysis tests indoors. This can scientifically determine indicators of physical and mechanical properties related to rock and soil, providing more effective standards for engineering evaluation and classification. Tests of physical indicators generally include determination of soil physical properties, water quality analysis, particle size analysis, compression tests, etc.

2. Foundation treatment technologies for geotechnical engineering under complex geological conditions

　　In many regions of China, the soil particle composition of sedimentary strata belongs to the fine sand and silty fine sand category, with diameters between 1.6 and 2.2 mm. In some areas, the surface sand has low water content, and the silty fine sand is mostly loose, making it unsuitable as natural foundation, so necessary treatment must be carried out. The main methods are as follows:

　　(1) Cushion method: also known as the water-settling method, mainly applied to loose silty fine sand layers in loess areas. First, excavate the foundation pit to the designed treatment depth, set sample piles on both sides of the foundation pit, and lay a sand layer, controlling the thickness of the sand layer at 0.25 m; then inject water into the foundation pit to a level even with the sand layer; afterward insert steel forks into the sand and shake evenly. If the sand has settled and compacted, withdraw the steel forks and reinsert them at intervals of 0.1 m to shake evenly, then repeat.

　　(2) Dynamic compaction method: an effective method for reinforcing soft soil foundations. Because of its advantages such as simple construction, fast speed, and low cost, it is widely used in foundation treatment. Through the huge shock waves and energy generated when the tamper falls, the foundation soil layer can be quickly compacted, effectively reducing the vibration liquefaction phenomenon of sandy soil, the collapsibility of soil, and the compressibility of the foundation, achieving the dual goals of high bearing capacity and stability of the foundation.

　　(3) Vibroflotation method: mainly divided into two types, one requiring added filling materials (gravel, sand, etc.) and the other not requiring them, using in-situ vibro-compaction. In loess areas, the vibroflotation gravel pile method is often used, while for medium and relatively coarse gravel foundations, the vibro-compaction method is used more often. The vibroflotation method, which reinforces soil by means of water flushing and vibration, is commonly used to densify loose sand foundations. Through the strong vibration brought by the vibrator, the loose saturated sand layer undergoes a certain degree of liquefaction, and then the vibration causes the sand particles to rearrange and the void ratio to decrease. At the same time, backfill material is added, ultimately achieving compression and densification of the sand layer.

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