The Production of Soil Cement Column

October 28, 2024

Soil-Cement Column (SCC) are becoming increasingly popular in the construction industry for soil improvement projects. SCC is a method similar to traditional piling (Prestressed Concrete Pile), but it differs in that SCC involves creating the piles directly on-site by mixing cement with the existing soil. This is considered a new technology that uses specialized machinery to mix soil, cement, and water, enhancing the strength of the soil in areas that need improvement.

In this article, the admin will take everyone through a detailed understanding of how to create Soil-Cement Columns using Jet Grouting and Deep Cement Mixing (DCM) methods. We will also learn about the use of DCM techniques through examples of projects where this technology was applied to construct Soil-Cement Columns in real past projects.

How to create Soil-Cement Column?

In the construction industry, Soil-Cement Columns (SCC) can be constructed using various methods. Understandably, the Jet Grouting method finds widespread use across various sites in Thailand. However, the Deep Cement Mixing (DCM) method is another technology that can also be employed. Both methods have technical differences and factors that affect their implementation. This article will explain the details and compare the advantages and disadvantages of each method in the following sections.

Jet Grouting Method

For the first method used to create Soil-Cement Columns, we will discuss Jet Grouting, which is a commonly seen method in Thailand. It is particularly effective in confined spaces because it utilizes smaller machinery.

The principle of Jet Grouting involves injecting liquid cement at high pressure through a drill string that is inserted into soft soil layers. Subsequently, high pressure (100-600 bar) is applied to disrupt the existing soft soil and mix it with the cement, forming a strong Soil-Cement Column.

Nevertheless, there may still be some mistakes made while building Soil-Cement Columns (SCC) with this technique in some places, particularly in regions with a lot of soil heterogeneity. To determine the link between soil strength and injection pressure, sophisticated geotechnical engineering knowledge is required.

The diameter of the resulting SCC may be less than intended if the pressure is applied incorrectly, such as applying low pressure on extremely hard soil. On the other hand, the diameter might be greater than planned if soft soil is subjected to high pressure.

Additionally, other important factors affect the quality of Soil-Cement Columns (SCC), such as the rotation rate of the drill head, the rate of lifting the drill string, the water-to-cement ratio (W/C), and the amount of cement used. If these factors cannot be adequately controlled, the results of the constructed SCC may not meet standards.

For instance, the size of the column may not be uniform throughout its depth, or when samples of the SCC are tested, the unconfined compressive strength (UCS) and rock quality designation (RQD), as well as core recovery (CR), may fall below the specified limits.

Deep Cement Mixing (DCM) Method

Another method used to create Soil-Cement Columns (SCC) is the Deep Cement Mixing (DCM) technique, which constructs SCC using low-pressure mechanical mixing.

The Deep Cement Mixing (DCM) method, also known as deep mixing of cement, operates by using mixing blades to penetrate and disrupt the existing soil. Liquid cement is then injected and mixed with the soil at low pressure while raising and lowering the drill string to form the Soil-Cement Column (SCC).

A notable advantage of using the DCM method is its ability to effectively control the diameter of the SCC. The size of the mixing blades determines the cross-sectional area of the column, and the flow rate of cement can be regulated to prevent excessive cement loss. However, like the Jet Grouting method, DCM also requires advanced geotechnical engineering knowledge to achieve the highest quality columns.

Example of Soil Cement Column Project

Recently, Geoharbour Construction has had experience implementing technology in the construction of Soil-Cement Columns, specifically in the soil improvement project for the Matarbari Power Plant Project, a large coal-fired power plant funded by JICA, located in the southern region of Bangladesh.

In this instance, Geoharbour participated in the project by choosing the Deep Cement Mixing (DCM) method to construct Soil-Cement Columns, aimed at increasing the stability of the embankment.

The project site is located near the sea and features soft soil conditions, with soil layers found to be 10-20 meters deep, consisting of clay, silt, and mixed sandy soil. Additionally, some areas underwent dredging and reclamation, leading to highly variable soil conditions, with SPT-N values ranging from below 4 in soft clay to over 30 in sandy layers.

If soil quality is not improved in the future, there could be risks of settlement and embankment failure. Therefore, the project implemented soil improvement using PVD surcharge in the central area, alongside constructing Soil-Cement Columns (SCC) around the site to enhance stability.

Geoharbour chose the DCM machine model DH-658, equipped with a 250 HP motor. This large machinery allows for the rapid and efficient construction of Soil-Cement Columns with a diameter of 1.2 meters. So far, 2.2 million cubic meters of SCC have been completed out of a total of 3.75 million cubic meters, accounting for 59% of the contract with the main contractor, Penta-Ocean Construction Co., Ltd.

Conclusion

Both Jet Grouting and Deep Cement Mixing (DCM) are effective methods for constructing Soil-Cement Columns (SCC) to improve soil quality. The two methods differ in their working techniques and environmental impacts. If we focus on maintaining equal cross-sectional sizes of SCC, the DCM method typically uses less energy (electricity or fuel) and generates less waste compared to Jet Grouting.

However, the choice of method for constructing SCC depends on various factors that need careful consideration, such as site conditions, soil characteristics, budget, and project timeline. For example, if the work area is limited, Jet Grouting may be more suitable due to its smaller machinery, which can easily access narrow spaces. Conversely, for large open areas, DCM is a better choice because it allows for better cost control and reduced environmental impact.

How was this article for you? We hope that after reading, everyone has gained a better understanding and knowledge about the methods of constructing Soil-Cement Columns. For those interested in more insights and information, you can follow Geoharbour on various platforms, including our website, Facebook, Instagram, TikTok, and YouTube.