Abstract: Sand and pebble stratum is a typical mechanically unstable stratum, which is composed of a pebble skeleton and a filled sand layer, with poor plasticity, no cohesion, and larger porosity. In order to ensure the smoothly discharge of the muck and to prevent water inrush and mud spraying problems that may occur in some sections during the construction of the earth pressure balance shield in the waterrich sand and pebble stratum. Taking Luoyang Rail Transit Line 1 Qingniangong Station to Jiamaying Station as the engineering background, the viscosity test is used to test whether the slurry meets engineering pumping requirements. Then tests of permeation and slump are carried out to test the effect of bentonite and carboxymethyl cellulose(CMC) mixed mud on waterrich sand and pebble formations. The suggested mixing ratio was proposed according to the results of the improvement of the mud. The test results show that the combination of sodium bentonite and CMC can effectively improve the workability of the sandy pebble stratum residue，and it can also prevent water and sand inrush problems that may occur during the construction of the earth pressure balance shield.

Key words: earth pressure balance shield, water-rich sand and pebble formation, muck improvement, sodium bentonite-carboxymethyl cellulose mixed mud