Internal erosion at soil-structure interfaces is a dangerous failure pattern in earth-fill water-retaining structures. However, existing studies concentrate on the investigations of internal erosion by assuming homogeneous materials, while ignoring the vulnerable soil-structure-interface internal erosion in realistic cases. Therefore, orthogonal and single-factor tests are carried out with a newly designed apparatus to investigate the critical hydraulic gradient of internal erosion on soil-structure interfaces. The main conclusions can be draw as follows: (1) the impact order of the three factors is: degree of compaction > roughness > clay content; (2) the critical hydraulic gradient increases as the degree of compaction and clay content increases. This effect is found to be more obvious in the higher range of the degree of soil compaction and clay content. However, there exists an optimum interface roughness making the antiseepage strength at the interface reach a maximum;(3) the evolution of the interface internal erosion develops from inside to outside along the interface, and the soil particles at the interface flow as a whole; and (4) the critical hydraulic gradient of interface internal erosion is related to the shear strength at the interface and the severity and porosity of the soil.

No abstract

Fracture grouting has been a mitigation measure widely used against seepage in the Yellow River Embankment. However, there is currently a lack of systematic investigations studying the anti-seepage effect of the fracture grouting employed in this longest river embankment in China. Therefore, in this work, laboratory and in situ experiments are carried out to investigate the reinforcement effect of fracture grouting in the Jinan section of the Yellow River Embankment. In particular, laboratory tests concentrate on studying the optimum strength improvement for cement-silicate grout by varying the content of backfilled fly ash and bentonite as admixtures. Mechanical strength and Scanning Electron Microscope photographs are investigated for assessing the strength and compactness improvement. Subsequently, based on the obtained optimum admixtures content, in situ grouting tests are carried out in the Jinan section of the Yellow River Embankment to evaluate the reinforcement and lapping effect of fracture grouting veins, where geophysical prospecting and pit prospecting methods are employed. Laboratory results show that, compared with pure cement-silicate grouts, the gelation time of the improved slurry is longer and gelation time increases as fly ash content increases. The optimum mixing proportion of the compound cement-silicate grout is 70% cement, 25% fly ash, and 5% bentonite, and the best volume ratio is 2 for the investigated cases. Geophysical prospecting including the ground penetrating radar and high-density resistivity method can reflect the lapping effect of fracture grouting veins on site. It shows that the grouting material mainly flows along the axial direction of the embankment. The treatment used to generate directional fracture is proved to be effective. The injection hole interval distance is suggested to be 1.2 m, where the lapping effect of the grouting veins is relatively significant. For the investigated cases, the average thickness of the grouting veins is approximately 6.0 cm and the corresponding permeability coefficient is averagely 1.6 × 10 −6 cm/s, which meets the anti-seepage criterion in practice.

Lishi loess is an important component of loess slope. To explore the structure and strength change characteristics of Lishi loess caused by shock (vibration) action, and to reveal the mechanism of loess slope catastrophe, the dynamic triaxial test was performed by using equivalent sine wave under strain controlling. The results show that:① There is an obvious stress relaxation phenomenon during the same cyclic loading test, the degree decreases with the increasing of dynamic strain and confining pressure. And the influence of dynamic strain variation on stress relaxation degree is less under high confining pressure than under low confining pressure;② Under a confining pressure of 40kPa, within 1% strain ranges, the needed dynamic stress to reach the specified strain is just 0.01kN, and the peak stress decreases with the augmentation of dynamic strain, when peak stress increases to 0.204kN, the sample is destructed; Under a confining pressure of 90kPa, soil radial particles are closely spaced, within 2% strain ranges also only a dynamic stress of 0.01kN is needed to reach the specified strain, and with the increase of dynamic strain, the samples are destructed when dynamic strain increases to 0.267kN. The dynamic failure stress of Lishi loess increases gradually with the increase of confining pressure, and the linear regression equation is бd=0.0011б3+0.1590, the correlation coefficient is 0.9944. ③According to Mohr-Coulomb failure criterion, the strength parameters of Lishi loess in somewhere of the north of shaanxi are C=30.33kPa，φ=14°. Under the dynamic shearing action, the dynamic effective strength parameters are obviously less than static effective strength parameters, this indicates that the soil consolidation effect reduced and the particles displaced and occluded each other.

Ensuring the stability of the shaft structure is one of the key technologies for the application of raise boring method. In the process of reaming through rock formations with water disintegration characteristics, the impact of water gushing and drenching may induce partial collapse. To solve this problem, an intelligent temporary while-boring support technology is proposed in this paper. Firstly, the main characteristics of the technology are introduced. Utilizing the space inside the raise boring pipes, the material conveying pipes and nozzle can reach the lower part of the reamer to realize spraying support. Secondly, a composite cementitious supporting material with good mechanical properties is developed to ensure the sealing and waterproofing of the surrounding rock. Thirdly, a test study was carried out on key process parameters. The results show that the best engineering economic benefits under the condition that the rotation speed is 2r/min and the distance between the nozzle and the surrounding rock is 1m. Fourthly, an image classification algorithm based on Resnet-34 convolutional neural network is proposed, which realizes the intelligent judgment of the effect of surrounding rock support. Finally, an industrial test was carried out in Lijiahao Coal Mine. The test results show that the intelligent temporary while-boring support technology proposed in this paper has a good performance, effectively achieving the sealing and water resistance of the surrounding rock, and the shaft structure has not been damaged.