In view of the dynamic response of geogrid-reinforced gravel under high-speed train load, this paper explores the dynamic characteristics of geogrid-reinforced gravel under semi-sine wave cyclic loading. A number of large scale cyclic triaxial tests were performed on saturated gravelly soil reinforced with geogrid to study the influence of the number of reinforcement layers and loading frequencies on the dynamic responses of reinforced gravelly sand subgrade for high speed rail track. The variation of cumulative axial and volumetric strains, excess pore pressure and resilient modulus with number of loading cycles, loading frequency, and reinforcement arrangement are analyzed. The test results reveal that the cumulative axial strain decreases as the number of reinforcement layers increases, but increases with loading frequency. The resilience modulus increases with the number of reinforcement layers, but decreases as the loading frequency increases. The addition of geogrid can reduce the excess pore water pressure of the sample, but it can slightly enhance the rubber mold embedding effect of the sand sample. As the loading frequency increases, the rubber mold embedding effect gradually weakens.

Carbonaceous rock is a special soft rock containing TOC organic carbon 6%∼40%. In order to reveal the influence of engineering characteristics of carbonaceous rock on the engineering construction, firstly the stratigraphic distribution of carbonaceous Rocks in Guangxi is investigated, and the genetic mechanism and tectonic environment of carbonaceous rocks are discussed. Secondly, the influence of pore microstructure on the disintegration characteristics of carbonaceous rocks is analyzed. The role of geochemical characteristics of carbonaceous rocks (mineral composition, TOC total organic matter content, and type) on engineering properties is revealed. Finally, combined with the distribution, structure, microstructure, and microscopic characteristics of the previous studies, the disintegration mechanism of carbonaceous rocks in water swelling and heat dehydration is discussed. The results are as follows. (1) Carbonaceous rocks in Guangxi are mainly distributed in Devonian, Carboniferous, and Cambrian systems. It is mainly formed in anoxic and reductive deep water basins, slopes, and relatively confined coastal lagoons and swamps. The carbonaceous rocks in the Devonian Luofu formation are most typical. (2) The pores of carbonaceous rocks are divided into mineral pores, organic matter pores, and microfracture, which are mainly mineral pores. The more developed pores in mineral pores are intragranular dissolved pores. Secondly, mineral intergranular pores and a small amount of intergranular dissolution pores and less inner pores. Organic matter porosity increases with the increase of shale organic carbon content and maturity, but the shale porosity and adsorption capacity decrease when shale maturity reaches more than 2.4%. (3) Clay minerals in carbonaceous shale mainly consist of illite and illite/montmorillonite layer, which have water swelling and heat dehydration. The total average value of TOC (total organic matter content) is more than 1%, which belongs to carbonaceous rocks of medium high grade hydrocarbon source rocks. Organic matter is mainly dominated by type I and II1-II2 type with large hydrocarbon generating potential, which is prone to oxidation-reduction reaction and cause rock disintegration.

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To solve the environmental protection issue of carbonaceous rock slope, the failure mechanism of carbonaceous rock slope and the protection mechanism of vegetation concrete are analyzed based on the engineering characteristics of carbonaceous rock and vegetation concrete. Therefore, the field test of vegetation concrete was carried out to obtain the optimal dosage of vegetation concrete greening additive. The application of environmental protection technology of vegetation concrete on carbonaceous rock slope is applied in slope engineering of Hebai highway, and the change law of soil fertility was analyzed to verify the effect of ecological protection. The results show that the protection mechanism of vegetation concrete slope protection technology is mainly categorized into two groups, namely, the surface sealing effect of vegetation concrete substrate in the early stage and the plant ecological protection effect in the later stage. The experiment results show that the optimum dosage of green additive for vegetation concrete is ranging from 30 kg/m3 to 40 kg/m3. According to the field application, within one year after the construction of vegetation concrete, the contents of available phosphorus, potassium, and organic matter increased by 70.2%, 24.9%, and 76.8%, respectively. Moreover, the content of alkali hydrolyzed nitrogen decreased by 44.8% and bulk density by 17.4%; the content of total phosphorus changed little. After 60 days of construction, the vegetation coverage rate of the slope can reach more than 95% and there is no obvious soil erosion phenomenon after three times of heavy rainfall.

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