Experimental study on freezing point of deep clay under high external load conditions

Abstract

A rational evaluation of freezing point of deep clay under high pressure is required for artificial freezing construction of deep mining works. The freezing point of deep clay under high external load was measured via a self-designed apparatus with soil temperature monitored by high-precision temperature transducer and external load applied by servo-hydraulic system. The feasibility of the apparatus was verified by comparing the test result to that of the common cooling curve method under no external load. Cooling curves for deep clay sampled from a coal mine at 510–515 m were acquired at six load levels (0.0, 2.0, 4.0, 6.0, 8.0 and 10.0 MPa) and four water contents (25.0%, 30.0%, 34.0% and 38.0%). Results show that the greater the water content, the more pronounced the equilibrium freezing stage. In the absence of external load, equilibrium freezing was observed, whereas temperature jump becomes more noticeable with increasing load. Freezing point and initial nucleation temperature both rise with greater water content, while depress approximately linearly with higher load. A simple model for evaluating the freezing point of deep clay was developed based on the Mizoguchi model, incorporating both matric and pressure potential. The results will provide theoretical evidence for determining the thickness and location of frozen wall during artificial freezing construction in deep strata.