Corrosion is an inevitable problem of metallic grounding grids. To propose an effective method avoiding the above corrosion, a new type of non-metallic grounding material was made in this paper. It is called flexible graphite composite grounding material, namely flexible graphite composite grounding material for short. It is made by high-purity flake graphite with a stranded wire hierarchical structure. And a series of experiments have been carried out to verify its feasibility as electrical grounding material, including material resistivity and its contact resistance measurement, temperature tolerance test, mechanical performance test, and scaled electrical grounding test of several typical electrical grounding grids. These experimental results all indicate that characteristics of the new flexible graphite composite grounding material can well meet practical electrical engineering requirements.

In order to further reveal the pile-soil interaction mechanism during precast pile driving in saturated soft soil in coastal areas, the compaction effect and excess pore pressure response of a single pile and adjacent pile penetration under hammer driven pile construction are analyzed by using the cavity expansion and model test method. The results show that pile driving in saturated soil layer will cause large soil compaction and accumulation of excess pore water pressure. Under the model test conditions, the variation range of soil pressure and excess pore pressure is about 0.7–3.0 times and 0.5–1.5 times of soil mass weight stress. As the driving of adjacent pile, soil pressure at the constructed pile-soil interface increases gradually and fluctuates at the same time, and multi peak phenomenon appears under the influence of different soil layers. At the initial stage of driving, the pile driving force is mainly borne by the pile side friction, and the pile tip resistance will actions as the increase of penetration depth, and the relationship between them is basically linear. These results have certain guiding and reference value for the construction of precast pile driving in saturated soft soil in coastal areas.

The flexible graphite composite grounding electrode is a non-metallic grounding electrode with good electrical conductivity, corrosion resistance and non-ferromagnetic properties. In order to analyze the impulse characteristics of the graphite composite grounding electrode, this paper builds a frequency domain electrical network model and an equivalent radius iterative algorithm, considering skin effect, inductance effect, capacitance effect and spark discharge effect. The impulse characteristics of typical metal grounding electrodes and graphite composite grounding electrodes are analyzed by simulation. The research results show that: Compared with the traditional metal grounding electrode, the graphite composite grounding electrode has a smaller skin and inductance effect under the action of the impulse current, and a better current flowing capability; as the soil resistivity increases, the inductance effect and the skin effect are weakened, while the spark discharge effect is gradually enhanced and dominates. The spark discharge effect can effectively decrease the grounding resistance. The obtained critical value of the normalized parameter of 412 kA Ω, can be taken as the threshold to discriminate the conditions with dominate inductance effect from the conditions with dominant spark discharge effect.

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