The concept of using dry quick lime for deep soil mixing was presented first in Sweden around 1967. The idea of injecting quick lime into soil to form a vertical column was innovated by Mr. Kjeld Paus, who worked several years as a road engineer and he used quick lime for surface soil stabilization. At the Swedish Geotechnical Institute (SGI), research was carried out in many years in order to find a chemical stabilization method to stabilizing soft marine clays of the Scadinavian type. Around 1976, Prof. Bengt Broms started further research at the Royal Institute of Technology (KTH) to complete the method, so called the lime column method (LC method).
In 1979, in the aid program of SIDA, SAREC of Sweden, IBST of Vietnam (Institute of Construction Science and Technology) was fortunate to be selected to cooperate with SGI. Two soft soil stabilization technologies invented by Sweden were selected to be transferred to Vietnam: the lime column and vertical band drain method.
In 1980, two construction equipment for the lime column and vertical band drain methods were imported into Vietnam. Along with that, two leading Swedish professors, Bengt Broms, an expert in the lime column method, and Sven Hansbo, the father of vertical band drain method, travelled to Hanoi to Vietnam in 1979 and 1980, respectively to introduce these technologies into Vietnam.
In the beginning, everyone believed that the LC method would be most suitable to Vietnam, because lime is a common local material. After quite a short time, it turned out that it is not. Dry quick lime is very difficult to be preserved in a humid condition as in Vietnam. This problem appeared to make Vietnam a pioneer in using cement instead of lime. IBST informed SGI of its decision to use cement as an alternative to lime, and the studies on samples with cement mixed with soil were conducted. The determination of the strength and deformation properties for different combinations of soil and cement mix were intensively performed in laboratory.
In the international conference on “Dry Mix Methods for Deep Soil Stabilization”, Stockholm (1999), in his “Keynote lecture: Equipment for deep soil mixing with the dry jet mix method”, Dr. Håkan Bredenberg, the chairman of the conference organizing committee, emphasized that: “Experience from Vietnam demonstrated that mixing lime with cement could improve the effectiveness”, see page 324 of the conference proceedings. Although this is not entirely true as in the studies at IBST, only cement was used as a binder, without lime. Using a 50/50 mix of quick lime and standard cement became rapidly the standard binder and Lime Cement Columns (LCC method) was named for the method. This method is still very common in Scandinavia. Today, quick lime only is almost never used in Scandinavia. Many time more cement than lime is used, for example in a 25/75% lime/cement is common for many organic soils.
IBST study results are still saved at the SGI Library. In 1982, during his 4-month visiting study at SGI, engineer Nguyen Manh Dau wrote a report “Some results from laboratory investigation on soil-lime mixture”, in which cement was studied as a binder, see Figure 4 on the left. Six reports that Mr. Dau and his colleagues wrote in the SGI-IBST cooperation program, from 1982 to 1999, can be found at the SGI Library, see Figure 4, on the right. Dr. Bredenberg was also a participant in the SGI-IBST cooperation program, and has traveled to Vietnam many times (Figure 3). He reorganized the contribution of the Vietnamese colleagues, and emphasized this in his keynote lecture.
Reference
Bredenberg, H. (1999) Keynote lecture: Equipment for deep soil mixing with the dry jet mix method. Proc. Int. Conf. Dry Mix Methods for Deep Soil Stabilization, Stockholm, pp. 323-331.
Nguyen Manh Dau (1982) Some results from laboratory investigations on soil-lime mixture. SGI Varia 108, 35p.