Experimental study on optimization of pipe jacking mud mixture ratio based on MICP technology

Abstract

In the course of pipe jacking construction, the carrying-soil effect frequently arises, influenced by factors such as excavation unloading, ongoing disturbance from successive pipe sections, and the progressive accumulation of soil adhesion. The pipe jacking slurry serves as a critical agent for friction reduction and strata support, essential for the secure advancement of the construction process. This study introduces the Microbial-Induced Calcium Carbonate Precipitation (MICP) technology into the realm of pipe jacking slurry, aiming to enhance its friction-reduction capabilities and the stability of the soil enveloping the pipe. An optimal MICP-slurry formulation was determined using the uniform design approach. Subsequent model tests were carried out to assess the friction-reducing efficacy of the MICP-slurry, while the mechanism by which the MICP-slurry reinforces strata stability was investigated through soil mechanics and scanning electron microscopy (SEM) analyses. The findings indicate that the optimal MICP-slurry composition is as follows: bentonite: sodium carboxymethyl cellulose: soda ash: polyacrylamide: xanthan gum = 12%: 0.31%: 0.36%: 0.25%: 0.54%. The MICP-slurry achieves a 42.2% reduction in the friction coefficient between the test block and the sand. In comparison with the untreated sample, the cohesion of the MICP-treated sample is enhanced by 38.12%, and the internal friction angle increases by 14.01%. SEM examination reveals that the calcium carbonate crystals precipitated by the MICP-slurry within the soil populate the pores, increase the inter-particle bite force, and bolster the soil's mechanical characteristics.

Keywords: Carrying-soil effect; Friction reduction effect; MICP; Mechanical properties; Microstructure; Mud.

Fig. 1

(a) Schematic diagram of montmorillonite crystal. (b) Schematic diagram of bentonite hydration and expansion.

Fig. 2

Microbial growth curve and urease activity curve.

Fig. 3

(a) Funnel viscosity test. (b) Fluid loss test. (c) Water separation rate test. (d) Measurement of mud cake thickness.

Fig. 4

Test device for determining coefficient of friction.

Fig. 5

(a) Cumulative particle size curve. (b) Reaction vessel.

Fig. 6

Correspondence Curve between Shear Displacement and Shear Stress of (a) Sample S-1.Correspondence Curve between Shear Displacement and Shear Stress of (b) Sample S-2.

Fig. 7

Sample Strength Curve.

Fig. 8

(a,b) Scan diagram of sample S-1. (c,d) Scan diagram of sample S-2.

Fig. 9

Schematic diagram of microbial induced reaction process.