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Microbial-induced calcite precipitation (MICP) has been a promising method to improve geotechnical engineering properties through the precipitation of calcium carbonate (CaCO3) on the contact and surface of soil particles in recent years. In the present experiment, water absorption and unconfined compressive strength (UCS) tests were carried out to investigate the effects of three different fiber types (glass fiber, polyester fiber, and hemp fiber) on the physical and mechanical properties of MICP-treated calcareous sand. The fibers used were at 0%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, and 0.40% relative to the weight of the sand. The results showed that the failure strain and ductility of the samples could be improved by adding fibers. Compared to biocemented sand (BS), the water absorption of these three fiber-reinforced biocemented sands were, respectively, decreased by 11.60%, 21.18%, and 7.29%. UCS was, respectively, increased by 24.20%, 60.76%, and 6.40%. Polyester fiber produced the best effect, followed by glass fiber and hemp fiber. The optimum contents of glass fiber and polyester fiber were 0.20% and 0.25%, respectively. The optimum content of hemp fiber was within the range of 0.20–0.25%. Light-emitting diode (LED) microscope and scanning electron microscope (SEM) images lead to the conclusion that only a little calcite precipitation had occurred around the hemp fiber, leading to a poor bonding effect compared to the glass and polyester fibers. It was therefore suggested that polyester fiber should be used to improve the properties of biocemented sand.

The safety and reliable operation of power grid is directly related to the ability of power transformer to withstand short-circuit, therefore, it is a problem to be solved to improve the ability of large power transformer windings to withstand short-circuit. Taking a three-phase five-limb power transformer as an example, the transient electromagnetic field, short-circuit electrodynamics force of windings and mechanical strength of coils are analyzed in depth. Firstly, the three-dimensional finite element model of the prototype is established, and the magnetic flux density distribution of the three-dimensional transient electromagnetic field of transformer under short-circuit operation and the axial and radial static force magnitude of the winding are calculated by using the field-circuit coupling method, and the distribution law can be obtained. At the same time, the mechanical strength of power transformer winding in its height direction is discussed, and the modal vibration mathematical model of transformer low-voltage winding in Z-axis direction is established. The displacement change and resonance frequency of the winding wire cake in the axial direction caused by short-circuit are calculated, and the short-circuit electrodynamics force of the winding is also checked. The research in this paper provides a theoretical basis for strengthening the design of short-circuit withstanding capacity of windings, and has a certain theoretical and engineering application value.