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To better understand the shallow sea geological information and avoid the risk caused by potential geo-disasters, the efficient offshore geological exploration methods are required. Better detection resolution can be obtained by using a spark source. As the foundation, the observation system plays an important role for geological detection. The influence of the variation of the parameters of the observation system on the detection accuracy is analysed theoretically. Then, the numerical simulations based on the finite difference method was applied, and imaging characteristics of observation system with different parameter were studied. For submarine acoustic exploration, the spark source with frequency over 200 Hz can obtain the clear reflections for geological interpretation; besides, the receiver array with the interval of 5 m–10 m helps to obtain better wave signals when the buried depth of a geological body is less than 300 m, and the width is more than 10 m. Based on numerical simulations, the observation system was optimized and designed. The results of numerical examples show that the accurate position information of the structure can be obtained by using the observation system proposed in this paper. Different imaging performances are obtained by adjusting the parameters of the observation system. On this basis, combined with directivity analysis, the optimal observation system parameters are proposed. Finally, the proposed observation system is used to image the fault model. The research results of this paper can provide reference for the observation system design in similar projects.

This study establishes a more reasonable and effective rutting prediction model called the quadratic modified Burgers rheological model by considering dynamic loads. Use ABAQUS to simulate the rutting depths through the existing Burgers model and the quadratic modified model and compare with the measured values of the multitemperature and load rutting tests and triaxial repeated load tests. The real tests were conducted on four asphalt mixtures, including SK-90 asphalt mixture, styrene-butadiene-styrene (SBS) modified asphalt mixture, direct coal liquefaction residue (DCLR) modified asphalt mixture, and compound DCLR modified asphalt mixture. The results showed that the range of error ratio and residual sum of squares between simulated and measured rutting depth based on the two different models are 5–35%/5.0–8.74% and 3–15%/0.9–3.1%, respectively, which show that the quadratic modified Burgers rheological model has a more accurate prediction.

Negative vacuum pressure hardly reaches deep soils due to the drain board bending and serious blockage with the existing vacuum preloading methods (VPMs), thus resulting in poor reinforcement relative to practical engineering applications. To address this issue, this paper proposes a vacuum preloading method with pumping and discharging (a new dredger filling foundation processing technique based on vacuum preloading). This new VPM is developed through technological improvement and plastic drain board innovations in traditional VPMs. The new VPM uses a plastic vertical drainage board with double drainage channels, and the core board is in a “tic-tac-toe” shape with a hollow centre and square pipeline channels. It can execute air and water drainage. Vacuum transfer holes were set at two grooves, every 2-3 m from the central pipeline of the core board. Grooves at two sides of the core board and filter membrane were rolled together to improve drainage. In addition, the vacuum pipe, tube connector, and core board centre of the vertical plastic drainage board were connected directly and securely. A stereoscopic vacuum transmission system composed of a horizontal and vertical drainage system was built. In this vacuum transmission system, the transfer route was shortened, and the loss of vacuum along the route was decreased. The negative vacuum pressure was transferred to different soil depths through the central pipeline of the core board to accelerate the dissipation of pore pressure in soil mass and prevent vacuum pressure loss caused by drainage board bending, thus improving the reinforcement effect. Dredger filling silt foundation reinforcement by VPM and VPM with pumping and drainage were compared in laboratory simulations and field tests with different drainage boards. Test results show that the loss of vacuum pressure along the drainage path was relatively smaller in the new physical vapor deposition (PVD), and the pressure transfer efficiency was increased. Deep soil mass was reinforced effectively by using the new PVD. After reinforcement, the physical and mechanical properties of soil layers were improved. Moreover, soil strengths were remarkably improved, with sharp reductions in natural moisture content and porosity. Then, the transfer law of vacuum on different drainage boards and the reinforcement mechanism of VPM with pumping and drainage were analysed. Research conclusions show the superiority of VPM with pumping and drainage in terms of effectiveness and soft foundation reinforcement. This study provides a theoretical basis for the application and development of the new VPM.

This study investigates the permeability characteristics of unsaturated compacted loess by focusing on the anisotropy parallel and perpendicular to the compaction. Three tests are conducted on compacted loess: permeability test, soil-water characteristic curve test, and scanning electron microscope (SEM) test. Samples are maintained and tested at different dry densities under optimal moisture conditions. Test results showed that the horizontal saturated permeability coefficient of compacted loess was larger than in the vertical direction, showing obvious anisotropy. Based on the saturated permeability coefficient, the permeability coefficient of unsaturated compacted loess can be predicted according to the soil-water characteristic curve fitted using the van Genuchten model combined with the Childs and Collis-Geroge model. The relational formula was established between the unsaturated permeability anisotropy ratio and the matrix suction through introducing a pore connectivity-tortuosity parameter, which represents the relationship between unsaturated permeability anisotropy ratio and matrix suction. The difference of pore characteristics between horizontal and vertical directions of compacted loess is the main reason for the permeability anisotropy.

This paper investigates the permeability characteristics of compacted loess by focusing on the anisotropy parallel and perpendicular to the compaction. Three tests are conducted on compacted loess: triaxial permeability test under confining pressure consolidation, triaxial permeability test under K0 consolidation, and SEM test. Samples are maintained and tested at different dry densities under saturated conditions. The test results show that the saturated permeability coefficient of compacted loess is exponentially related to the initial dry density under both confining pressure consolidation and K0 consolidation. The fitting equation can estimate the saturated permeability coefficient of compacted loess at different depths. The horizontal saturated permeability coefficient of compacted loess is larger than that in the vertical direction, showing obvious anisotropy. The saturated permeability anisotropy ratio is linearly related to the initial dry density. Comparing and analysing the saturated permeability coefficient, the saturated permeability coefficient of compacted loess under the K0 consolidation condition is smaller than that under the confining pressure consolidation condition. Under the condition of K0 consolidation, the connectivity of vertical and horizontal pores of compacted loess is weakened, the tortuosity is strengthened, and the void ratio is decreased. K0 consolidation makes the flake-, plate-, and needle-like particles in compacted loess rotate continuously parallel to the compaction surface, which enhances the orientation of particles and leads to the saturated permeability anisotropy increase. The research results provide the basis for water field analysis in loess filling engineering.