Hongtao Jiang

Engineering geological characteristics of expansive soils in China

Expansive soils are widely distributed in China. Six types and subtypes of expansive soils are classified based on their origins and geological times in this paper. The soil samples from six representative areas in China were tested and analyzed, including their clay content, clay mineral composition, chemical constitutes, physico-chemical indices, swelling and shrinkage. In light of the test results, the engineering geological characteristics of each type of expansive soil are assessed.

Effect of polyurethane on the stability of sand–clay mixtures

Three types of polyurethane were synthesized from mixtures of toluene diisocyanate, polyethylene glycol and polypropylene glycol for use in soil stabilization to improve the erosion resistance. The three polyurethanes were tested at different aqueous concentrations and sand:clay mixtures at weight ratios of 1:1, 1:3 and 1:5. The results of the rainfall simulation, unconfined compression and direct shear tests showed that the polyurethanes improve both strength and erosion resistance significantly. The observed improvement in soil erosion resistance is attributable to the physico-chemical interaction of the long-chain macro-molecules of polyurethane with the clay fraction of the soil.RésuméTrois types de polyuréthane ont été synthétisés à partir de mélanges de diisocyanate de toluène, de polyéthylène glycol et de polypropylène glycol pour utilisation dans la stabilisation de sols en vue d’améliorer leur résistance à l’érosion. Les trois polyuréthanes ont été testés pour différents mélanges de sable et d’argile dans les proportions 1/1, 1/3 et 1/5, avec différentes teneurs en eau. Les résultats de simulations de pluie, d’essais de compression simple et de cisaillement direct ont montré que le polyuréthane augmente à la fois la résistance mécanique et la résistance à l’érosion de façon significative. L’amélioration observée de la résistance à l’érosion est attribuable à l’interaction physico-chimique des macromolécules à longue chaîne de polyuréthane avec la fraction argileuse des sols.

Quantifying Fiber-Optic Cable–Soil Interfacial Behavior Toward Distributed Monitoring of Land Subsidence

Land subsidence is often associated with strata compaction, which can be measured by InSAR, GPS or extensometers. Despite considerable efforts, recording detailed subsurface deformation using these methods has proven to be difficult in some cases. The distributed fiber-optic sensing (DFOS) technique may overcome this dilemma by distributed strain measurement at kilometer scales and beyond. However, one crucial issue remains to be solved is the mechanical coupling between borehole backfill and embedded fiber-optic (FO) strain-sensing cable, which affects the quality of strain measurements. Here we perform laboratory pullout tests using a self-devised apparatus to investigate the interaction mechanism between FO cable and soil under confining pressures (CPs) up to 1.6 MPa. Our results indicate a critical CP that ensures a good cable–soil coupling, which has a direct application to the analysis of groundwater extraction-induced land subsidence in Shengze (Suzhou, China). A simple estimation of the CP exerted on the borehole-embedded cable suggests a strong coupling of the cable to the backfill for the main compaction zone. Taken together, these findings provide a basis for monitoring land subsidence and the associated strata compaction using the DFOS technique.

Evaluation of Land Subsidence Based on Distributed Monitoring and SEM Analysis

A better understanding on the relationship between macro compression behavior and microstructure of soil is essential in order to evaluate the trend of land subsidence. In this paper, distributed fiber optic sensing (DFOS) technology was applied in a borehole located in Guangming Village, Wuxi, China, to obtain the deformation of soil layers after the prohibition of deep groundwater withdrawal in this area. DFOS provided detailed information on the movement of soil layer within any depth range. The microstructure of undisturbed soil samples from the borehole was analyzed using SEM images. With the application of Particle/Pore and Crack Analysis System (PCAS), the micro porosity of samples were characterized by two statistical parameters called area probability distribution index and fractal dimension. Area probability distribution index described the distributions of micro-porosities and fractal dimension described the shape of pores in nature regardless of complexity. Good correlations between the deformation of soil layers and the two parameters about the microstructure characteristics were illustrated.