No abstract

Thixotropy is a hot topic in the field of rheology of dispersed systems. Studying the quantitative index and evaluation method for thixotropy of clay is of great significance to evaluate the safety of foundation under long-term load. To explore the index system and classification methods for the thixotropy of clay, unconfined compressive strength tests were carried out on three groups of undisturbed soil and remolded soil that were cured at different times after remodeling of the Zhanjiang Formation in China to obtain the unconfined compressive strength values of the samples and establish the relationship between unconfined compressive strength and curing time of the remodeled soil. The concept of thixotropic sensitivity is introduced to reflect the relationship between thixotropy and structure. According to the relationship between thixotropy sensitivity and curing time and its logarithmic value, two indexes of structural recovery coefficient K and structural recovery index Ke were established to evaluate the thixotropy of structural clay in the Zhanjiang Formation. Following the structural classification method of soil, the boundary values of structural recovery coefficients KI and KII are calculated to classify the thixotropy of soil. When the value of K is less than that of KI, the thixotropy of soil is weak. When the value of K is greater than that of K but less than that of KII, the thixotropy of soil is moderate. When the value of K is greater than that of KII, the thixotropy of soil is strong. The method is used to discuss the thixotropy of soil in the literature, and the rationality of the method is verified. Results show that this method can be used to preliminary classify the thixotropy of soil.

Thixotropy is a hot topic in the field of rheology of dispersed systems. Many researchers have proposed different models and hypotheses to explain the thixotropy of clay. In this paper, the strength recovery model of Zhanjiang Formation clay in the process of thixotropy is studied. Firstly, through unconfined compressive strength test, the influence of soil sensitivity, moisture content, and density on the strength growth of remolded soil was studied. The results show great influence of sensitivity, moisture content, and density on the thixotropic strength of the Zhanjiang Formation clay: the higher the sensitivity and the density, the stronger the thixotropy of soil; the higher the moisture content, the weaker the thixotropy of soil. Based on the test results, a strength recovery model of Zhanjiang Formation clay in the process of thixotropy was established. The model was verified by the validation test data and the data obtained from the existing literature. The results suggest that the model prediction is in good agreement with the verification test data and data from existing literature, which proves the confidence of the model in predicting the degree of strength recovery in the process of thixotropy of Zhanjiang Formation clay. The model provides basis for stability calculation of surrounding soil after construction disturbance of underground structures in this stratum.

In this paper, we prepared reduced graphene oxide (rGO) films by first drop-casting graphene oxide (GO)/ethanol dispersion on top of silicon nanowires array, followed by thermal reduction in 95% Ar-5% H 2 (volume ratio) atmosphere. A series of rGO thin films were prepared by thermal reduction at different annealing temperatures ranging from 100 ℃ to 1200 ℃, and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, four-probe square resistance tester and scanning electron microscopy (SEM). The experimental results indicate that reduction of oxygen-containing groups, dehydrogenation of C-H groups and reconstruction of C＝C skeleton occurred significantly on the GO plane. Compared with the insulating GO film, the resistance of rGO thin films decreases greatly, and the sheet resistance of rGO films shows a decreasing trend with increase of reduction temperature. Then, flexible polydimethylsiloxane (PDMS) encapsulated graphene-based devices (P-rGO-P) were fabricated by spin-coating PDMS on the surface of obtained rGO films with evaporated Au interdigital electrodes. The flexible devices maintained the integrity of the rGO films while providing self-supporting characteristics. The rGO film in the device had a clear layered structure, and a certain movable space between the upper and lower PDMS layers. This sandwich structure ensures that when the P-rGO-P flexible detector is bent and squeezed, the rGO film has sufficient buffer space, and would not be subjected to excessive stress arising from adhesion to PDMS. In short, the sandwich structure endows the originally fragile device with excellent flexibility. The P-rGO-P detector was successfully applied to detecting infrared laser irradiation, human body infrared radiation, bending motions and pressure changes. The experimental results showed that the flexible encapsulated P-rGO-P infrared detectors derived from the rGO thin films reduced at varied temperatures all had response to near-infrared (1064 nm) laser irradiation, and the maximum response reached up to 2.78 mA/W. In addition, the P-rGO-P flexible detector also demonstrated fast and sensitive response to human body infrared radiation and bending changes, and could maintain its integrity and responsiveness after repeated bending.

The setting of the late poured band is an effective measure to control the differential settlement and the stress concentration of the foundation. However, the lag of the pouring time of the late poured band will also bring adverse effects to the construction process. Taking a large commercial complex as an example, Midas GTS NX finite element software is used for the overall foundation modeling, and the collaborative calculation of settlement is carried out by adjusting the composite foundation scheme. The calculation results of conventional codes are compared and analyzed, and the scheme is verified and optimized. Then, the variation value of differential settlement on both sides of the late poured band with loading is studied by simulating the graded loading of each area in the whole process of construction. By comparing the variation value of differential settlement and the calculation value of differential deformation that the stiffness of the late poured band can resist and the limit value of codes, the time node of late poured band pouring in advance can be obtained, and finally the influence of early pouring of the late poured band on the collaborative settlement of the foundation is verified and calculated. The results show that: the settlement calculation of finite element analysis is generally smaller than that of standard calculation; The settlement at the edge of the raft is small, and the settlement at the center of the raft and the places with large load is large; Considering the interaction of the whole raft and subgrade under the raft, this method can verify and optimize the design scheme of composite foundation and save the pouring time of the late poured band. The experience and achievements so made can be used as a reference for similar projects.