Hydraulic compactor is an efficient reinforcement machine for loess subgrade. However, it is difficult to control the layered compaction quality of the subgrade. This research presents a real-time layered compactness monitoring method for hydraulic compactor reinforcement of subgrade in loess areas. The hydraulic force coefficient is first introduced, and the dynamic response model of the hydraulic rammer and soil is established. The relationship between the acceleration of the hydraulic rammer and the compactness of subgrade is then obtained based on the collision theory in elastic half space. A full-scale test using a hydraulic compactor to reinforce loess subgrade was also carried out. Results show that the hydraulic compactor obtains the effective influence depth for the reinforcement of loess subgrade. Within the effective reinforcement depth, the relationship between the peak acceleration of the rammer and the layered compactness of subgrade can be well fitted by a quadratic function model. The layered compactness of the subgrade and the working state of the hydraulic compactor can then be remotely monitored at a mobile terminal in real time. Furthermore, the monitoring technology was applied to Huangling-Yan’an Expressway in China, significantly improving the accuracy and efficiency of real-time monitoring of the layered compactness of subgrade in the loess area.

This paper presented trilinear load transfer models for both pile shaft-–soil system and pile tip-soil system to analyze the load–settlement relationship of bored pile in loess area. Based on the differential equation of load transfer, the load transfer functions in different stages were deduced. Furthermore, combined with the trilinear model of pile tip-soil system, the load-settlement functions were obtained and the calculation method was completed. A static load test for a single pile was then carried out to obtain the required pile-soil system parameters, and the calculated results were presented and compared to those of the static load test, proving the feasibility of the proposed method. Moreover, the influence of each pile-soil system parameters on the load–settlement relationship of single pile was studied, and the results provide guidance for the pile foundation engineering in loess area.

The dam embankment (DE) is a highway structure used in the Loess Plateau to integrate the functions of a highway embankment and a dam. This paper studies the upper limit water level mechanism of the reservoir in the upstream of the DE to determine the criterion for setting upper culverts on the DE. A reservoir model is first established, and then the replenishment and loss of the reservoir water is simulated. The principle of water balance is employed to obtain water level formulas for the reservoir. Finally, an engineering example is used to verify the upper limit water level mechanism. The results show that the water level of the reservoir fluctuates near an ideal balance water level and an upper limit water level exists. Moreover, the upper limit water level has no relation to the water storage time, and is only related to the reservoir shape with big upper and small bottom, the small amount of water entering the reservoir each year, and the large water loss caused by evaporation and leakage. The upper culvert setting criterion is obtained through the upper limit water level mechanism, and it will provide important reference significance for the necessity of the DE culvert setting.

Precast prestressed reinforced concrete (PRC) pipe piles are increasingly adopted where static pressing is impractical; however, design-oriented evidence for their vertical bearing behavior in stiff silty clays remains limited. This study combines site static cone penetration tests with full-scale static load tests on hammer-driven PRC pipe piles with open-ended and closed-ended tips to clarify the governing load transfer mechanism and to improve capacity prediction for engineering design. The results show that pile tip configuration was a key factor influencing the bearing behavior of PRC pipe piles. Open-ended piles experience stronger driving-induced disturbance in the tested stiff clay layers, leading to lower mobilized shaft resistance than closed-ended piles. The responses of both pile types can be well described by a bilinear strain hardening load transfer relationship. Building on these observations, a three-stage load transfer function based on Rusch elastoplastic theory was developed and calibrated using test data, achieving improved ultimate bearing capacity prediction compared with conventional design parameter selection. For designs in stiff silty clay, median values of shaft resistance are recommended for open-ended piles; however, the upper-bound values of shaft and base resistances can be adopted for closed-ended piles. These recommendations should be applied cautiously beyond the tested pile configurations, soil properties, and installation method.