In the InSAR solution, the uneven distribution of permanent scatterer candidates (PSCs) or slowly decoherent filtering phase (SDFP) pixel density in a region of variable radar reflection feature can cause local low accuracy in single interferometry. PSCs with higher-order coherence in Permanent Scatter InSAR (PS-InSAR) are generally distributed in those point targets of urban built-up areas, and SDFP pixels in Small Baseline Subset InSAR (SBAS-InSAR) are generally distributed in those distributed targets of countryside vegetation areas. According to the respective reliability of PS-InSAR and SBAS-InSAR for different radar reflection features, a new land subsidence monitoring method is proposed, which combines PS-SBAS InSAR by data fusion of different interferometry in different radar reflection regions. Density-based spatial clustering of applications with noise (DBSCAN) clustering analysis is carried out on the density of PSCs with higher-order coherence in PS-InSAR processing to zone the region of variable radar reflection features for acquiring the boundary of data fusion. The vector monitoring data of PS-InSAR is retained in the dense region of PSCs with higher-order coherence, and the vector monitoring data of SBAS-InSAR is used in the sparse region of PSCs with higher-order coherence. The vertical displacements from PS-InSAR and SBAS-InSAR are integrated to obtain the optimal land subsidence. The verification case of 38 SAR images acquired by the Sentinel-1A in Suzhou city indicates that the proposed method can automatically choose a matched interferometry technique according to the variability of radar reflection features in the region and improve the accuracy of using a single interferometry method. The integrated method of the combined field is more representative of overall subsidence characteristics than the PS-InSAR-only or SBAS-InSAR-only results, and it is better suited for the assessment of the impact of land subsidence over the study area. The research results of this paper can provide a useful comprehensive reference for city planning and help decrease land subsidence in Suzhou.

Due to low splitting tensile strength, cement soil is more likely to experience dry shrinkage and cracking in practical engineering. In this study, the mixing procedure of the cement soil reinforced with basalt fibers was investigated; the influences of cement content, curing time, basalt fiber content and length on the splitting tensile strength of the cement soil reinforced with basalt fibers were studied; and the correlation of the splitting tensile strength vs. the compressive strength of the cement soil reinforced with basalt fibers was discussed. The contribution of basalt fibers on performance improvement of the cement soil was also addressed based on the microstructural analysis and the toughening mechanism exposition. Results indicate that the best mixing method for the cement soil reinforced with basalt fibers is to mix the muddy silty clay with basalt fibers first, then with cement slurry. The increase of cement content and curing time can improve the splitting tensile strength of the cement soil effectively. The splitting tensile strength of the cement soil increases first and then decreases with the content and length of basalt fibers. The optimal content and length of basalt fibers for the cement soil are 0.4% and 12 mm, respectively. The relationship between the splitting tensile strength and the compressive strength of the cement soil reinforced with basalt fibers can be described as a linear relationship with the correlation coefficient of 0.245 and the determination coefficient of 0.990. The contribution of basalt fibers on the toughening mechanisms of cement soil shows that the fiber-matrix interaction would be the dominant effect to control the tensile strength of the soil-cement-fiber composites. The results of this study can provide a reference for the design and application of cement soil reinforced with basalt fibers in actual engineering.

Enhancing strength performance while reducing cement consumption for soil stabilization is the key to improving the economic benefits of engineering construction projects like retaining structures of underground engineering, subgrade bases, and foundation reinforcement. This study employed metakaolin as the additive to realize these two aims. A series of compression and microstructural observation tests on cement- and metakaolin-stabilized fine sandy soils (CMSFSS) were conducted with different cement–metakaolin ratios, water–binder ratios, dosages of the binder (the mixture of cement and metakaolin), and curing ages. The influences of these factors on the mechanical performance of the CMSFSS were studied. The empirical relationships between compressive strength and these influence factors were discussed. Then, the strengthening mechanism of the CMSFSS at different curing ages was investigated. The results showed that the optimal cement–metakaolin ratio for fine sandy soil stabilization was 5:1, which did not change with the total consumption of cement and metakaolin. The compressive strength of the CMSFSS decreased linearly with the water–binder ratio but increased linearly with the curing age. Four empirical prediction formulas about these strength-influencing factors were summarized. The evolution of microstructural characteristics discovered by scanning electron microscope and mercury intrusion tests showed that the hydrated gels in CMSFSS were being formed during the early curing age and resulted in decreasing pore sizes with an initial rapid rate and then a slower rate over the curing age. The gradual disappearance of calcium hydroxide (by-products of cement hydration) over the curing age proved the promoting effect of metakaolin on the strength improvement of cement-stabilized fine sandy soils. This study can provide a reference for applying cement and metakaolin in soil stabilization practices.