In view of the high cost and poor accuracy in monitoring the internal layered settlement of foundation soil mass, this study has introduced an ultrasonic ranging technique into the layered settlement monitoring of civil engineering foundations. It has also developed a special ultrasonic monitor capable of generating different frequencies (e.g., 200kHz, 400kHz). It has also selected two oscilloscopes that can match the frequencies, the pipe fitting materials, reflecting materials, and propagation mediums that are related to the burying of the ultrasonic monitoring system into a soil mass. After that, it has calibrated the propagation velocity of ultrasonic waves under different water temperatures, tested the ranging technique, and obtained an effective range of at least 45 m. Then, it has carried out actual measurement comparison and error analysis, which show that the accuracy of the ultrasonic monitoring system is in the order of millimeters. Finally, an indoor ultrasonic-monitored settlement simulation test has been carried out. The ultrasonic-monitored burying system has been buried into the soil mass, and the ultrasonic monitoring system has been used to measure the layered settlement of the soil mass after rolling compaction and compression. The comparison with the actual measurements shows that the measurements by the ultrasonic monitoring system are highly accurate. The ultrasonic monitoring system can therefore be used to monitor the settlement of foundation soil mass.

MTS-810 material testing machine and acoustic emission signal analyzer were adopted to explore the mechanical behavior of concrete beams broken by the static load and the nonlinear cumulative damage law of concrete beams broken by fatigue bending from single-stage loading. Then, by introducing the Ramesh Talreja’s Damage Criterion, the damage rule of single-stage loading was extended to the damage accumulation rule under multi-stage loading, and the results were verified by the results of two-stage and three-stage fatigue loading tests. Two main conclusions are achieved: first, affected by four-point bending load, the fatigue life of the concrete specimen is in line with the law of the two-parameter Weibull distribution, namely the higher the stress level is, the shorter the fatigue life is. Second, an obvious nonlinear relationship was discovered in the damage of concrete. The model deduced in this paper and the Palmgren-Miner linear damage accumulation model were adopted to compare the test results of flexural fatigue under single, two and three stage loads. The calculation results of this model were more reliable.

The numerical simulations were employed to establish an edge-corner repair model with magnesium phosphate cement (MPC) concrete as the repair material and ordinary Portland cement concrete as the old pavement. After the simulation of repair construction by using MPC concrete with different coarse aggregates, the effect of sudden temperature drop during the stable stage of hydration reaction on the stress distribution at each bonding interface was analyzed. The numerical calculations indicate that the sudden temperature drop led to temperature-induced stress on the bonding interfaces. The stress distribution at each bonding interface was obtained and the maximum principal stress at each bonding interface was at the intersection angle of three bonding interfaces. The relationship between the temperature and stress at each bonding interface was found when different coarse aggregates were used to prepare the repairing material. Also, the effect of different coarse aggregates on the bonding interface of the repairing material was obtained when basalt was the coarse aggregate of old concrete. The stability of bonding surface from best to worst was as follows: basalt > limestone > granite > conglomerate > sandstone > quartzite.

The measured diffusion coefficient and soil-water characteristic curve (SWCC) of remolded loess were used to modify the Mualem model for increasing its accuracy. The obtained results show that the goodness of fit between the Mualem model and the variable parameter-modified Mualem method comparing with the test results was not high. The saturation of 0.65 was introduced as the boundary to divide the curve of the measured diffusion coefficient into two segments. When the segmentation method combined with the variable parameter method was used to modify the Mualem model, the fitting correlation coefficient was increased to 0.921–0.998. The modified parameters Ko and L corresponding to remolded loess were calculated for different dry densities. Based on the exponential function between Ko and dry density and the linear relation between L and dry density, the segmentally modified Mualem model was established for remolded loess by considering variation in dry density. The results of the study can be used for directly determining the unsaturated infiltration coefficient and for indirectly determining the SWCC through diffusion coefficient.