A composite sealing layer structure of “bentonite-thin steel plate” has been constructed in the lined rock caverns (LRC) for compressed air energy storage (CAES). In this sealing layer

bentonite absorbs water and expands

thereby squeezing the thin steel plate. The thin steel plate generates an elastic reaction force under pressure

which in turn restrains the expansion of bentonite. Therefore

the swelling behavior of bentonite falls under the category of expansion under constant stiffness constraint. To simulate this behavior

a swelling apparatus with comprehensive functions

convenient operation and low cost was developed. The instrument mainly consists of the instrument base

sample chamber

piston

constant stiffness constraint reaction frame

water injection controller

data acquisition box

and so on. With granular bentonite as the research object

verification tests were conducted. The findings indicate that the instrument is capable of accurately replicating the swelling behavior of bentonite under the constant stiffness constraint. Compared with the results obtained by the staged loading equilibrium method

the swelling pressure of the former is generally higher than that of the latter at the same swelling ratio. Moreover

the results of the former are more consistent with the real situation. By changing the constraint combination of the reaction frame

the instrument can also be used to simulate swelling behaviors under constant volume constraint and zero-loading constraint. Meanwhile

in conjunction with the specially designed high- pressure loading system (with a maximum loading capacity of 20 MPa)

the loading and unloading tests of bentonite after expansion can be carried out to investigate the deformation behavior of bentonite during the charging and discharging processes of the CAES. The preliminary demonstration of the rationality of the “bentonite-thin steel plate” composite sealing layer structure fully underscores the reliability and scalability of the instrument

highlighting its functional advantage of “one machine serving multiple purposes”