A Newly Developed Jet Grouting Technology: The Twin-Jet Method

1. Introduction

Technologies for improving soft soil by chemical reactions, like deep mixing and jet grouting, are frequently utilized to do so in order to assure safety while deep excavations and tunnel building are being done. With the use of small-diameter nozzles, high-speed fluids are pumped into the subsurface to erode the soil. The eroded soil is then mixed with grout to create a quasi-cylindrical soil-cement column.

The jet grouting technology can be categorized as a single fluid system (only grout), a double fluid system (grout + air), or a triple fluid system (water + grout + air) depending on the various fluids injected into the subsoil.

However, because of the high jetting pressure of the water (or grout), the following issues could arise as a result of soil erosion:

(a)Because so much water was injected, the cement and soil mixture was in a fluid state. It takes several hours or days for the mixture to gel and become strong enough for admixture.

(b)It is simple to produce quicksand when jet grouting is used in sandy soil below the groundwater table, which could lead to the separation of sand and cement particles before the grout hardens.

(c)The fluid admixture may leak out of the horizontal hole when jet grouting is done horizontally, making horizontal construction more challenging.

Accelerating the grout-soil mixture's hardening process is necessary to address these issues. Therefore, a Twin-Jet Method for instant solidification of soft ground employing two different types of binders has been created based on the triple fluid technology of jet grouting.

2. Basic principles

The hardening process of an admixture of grout and soil must be sped up by adding a binder in order to obtain a fast gel of soft ground following jet grouting. The grout-soil mixture can gel in 5 to 10 seconds when water-glass is chosen as the binder.

This conventional triple fluid system serves as the foundation for the Twin-Jet Method. By jetting out highly pressurized grout that has been cloaked in compressed air to erode the soil, the Twin-Jet Method creates an admixture of grout and dirt. The water-glass solution that is encasing the high-pressure grout is then shot into the additive for a brief gel, and after hardening, a jet grout column can be created.

The new display design is the Twin-Jet Method's key technical component. The monitor has two injection nozzles on the opposite side and a one-way valve at the tip. The inner pipe is attached to the one-way valve, which uses fluid pressure to automatically control the liquid flow. The inner pipe and the second pipe are connected to the first nozzle's dual outputs, which allow for the simultaneous injection of the highly pressurized grout and water-glass solution. In order to get both pressured grout and air simultaneously, the second nozzle likewise has dual exits attached to the inner pipe and the outer pipe.

While the inner outlet progressively shrinks into the outer outlet, Nozzle1 gradually shrinks to several millimeters. To prevent the backflow of the highly pressurized grout from the outlet to the water-glass solution, the outer outlet assumes the shape of a funnel within the recession distance of the inner outlet. Near the nozzle outlet, Nozzle 2 also gradually narrows to a few millimeters. Compressed air jetted from the outer outlet surrounds the grout that shoots out of the inner outlet, which can make the grout more erosive and expand the column's diameter.