The dry deep mixing (DDM) method has been used extensively – and exclusively – in the Nordic countries since its development in the 1970s. Despite being a versatile method, it is mainly limited to sensitive clays with low shear strengths and the method has limitations due to considerable verticality deviations. However, increasing ground improvement needs for stiffer clays, improved homogeneity, and better verticality at greater depths has led to the introduction of the wet deep mixing method (WDM) in both Sweden and Norway. This paper summarizes some experiences from three projects where WDM recently have been employed both onshore and offshore to increase stability and reduce settlements. Two Swedish projects, one large scale commercial and one trial test, were performed in clays with low shear strengths and high water contents for stability purposes offshore for land reclamation. The Norwegian project involved improvement of a low water content clay for settlement reduction of a building foundation. Results from strength verification using wet grab and core sampling are presented and are compared to experiences from DDM and preceding laboratory tests. The paper furthermore discusses some practical issues around execution and strength verification in the three projects. Overall, it is concluded that WDM in many cases is suitable also for Scandinavian clays and can therefore replace or supplement DDM. However, the lack of experience still calls for certain conservatism. Trial columns are recommended until there is more field experience from WDM in Scandinavian clays.

In recent years, the expansion of the Electronic Commerce (EC) market and real estate investment market, as well as the introduction of automation and robotics, has led to a rapid increase in the construction of large logistics centers. This paper reports on the construction problems, countermeasures, and management details of the cement deep mixing method adopted for the foundation work of a large logistics center built on a hilly area with a large uneven bearing layer.

As part of the Hobsons Bay Main Sewer - Yarra River Duplication project, there was a requirement for the existing sewer system on the eastern bank of the river to be redirected to a new siphon tunnel by a new Upstream Connection Structure (UCS) connected to a new Siphon Inlet Structure (SIS) by a short, mined tunnel. Deep mixing ground treatment was adopted to: mitigate the risk of hydrostatic ground fracture in the base of the UCS and SIS shafts and control ground water inflows during shaft excavation; act as an earth retention system between the toe of the secant-piled walls and the operating Hobsons Bay Main Sewer in the UCS; create suitably stable ground to enable mined excavation between the UCS and SIS shafts. The proposed ground treatment principally consisted of overlapping deep soil mixing columns forming a homogenous treated block installed from ground surface. Achieving this critical ground treatment required overcoming technical challenges, as detailed in this paper, which include but are not limited to (i) adapting the grouting parameters to accommodate for the significant geological & geotechnical variability, (ii) managing surface heave and spoil return in very soft soil conditions, (iii) working around existing 3.0m diameter sewer pipes running above and though the proposed ground treatment block, (iv) maintaining alignment for both vertical and inclined columns through pre-survey methods and drilling deviation measurements, (v) ensuring design grouted column diameters with sufficient overlap were constructed, and (vi) remediation of treated ground zone defects based on as-built 3D monitoring. To achieve this, the authors relied on a range of state-of-the-art trial-associated geotechnical testing, monitoring and mapping techniques. In addition, a comprehensive regime of in-situ testing was carried out from the ground surface confirming performance of the ground treatment to demonstrate that the project water tightness and mechanical requirements were consistently met. It includes full-length cored boreholes and the Cyljet electric cylinder method.

A vertical soil deep mixing wall, known as the TRD (Trench cutting Remixing Deep wall) method was developed in Japan in the early 1990s as a technology for constructing soil cement diaphragm continuous underground walls. In this method, a cutter post built into the ground is moved laterally to excavate the ground with a cutter bit attached to a cutter chain, while mixing and stirring the solidified liquid and in-situ soil in a vertical direction to create a wall-like solidified body in the ground. One of the characteristics of this method is the continuity of the wall and high water sealing performance due to its unique excavation mechanism, and it is applied not only to earth retaining walls but also to impervious walls such as impervious revetments and underground counterfort revetments, as well as to containment of contaminated soil. In recent years, a new type of TRD has been developed that enables the construction of walls as wide as 900-1200 mm, in contrast to the 450-850 mm wall thickness of the conventional type. This paper describes a case study of the application of the wide type of TRD method to an earth retaining wall of a ditched road, in addition to the outline and development history of the TRD method.

The refurbishment, the increase of the capacity of urban buildings and transport infrastructure is an important stake of the sustainable development. The related challenges are on one hand, to renew and densify urban area without using new land resources and on the other hand, to maintain and strengthen the existing transport networks without interruption of service. However, foundation techniques that are essential to maintain and strengthen these structures are often expensive and/or incompatible with the available space: This usually leads to the destruction and replacement of the existing structure – to the detriment of the sustainable development goals.For this reason, a low invasive technology was developed several years ago, based on deep cement mixing columns built with small diameter drilling machines. This configuration allows to build up to 800mm diameter columns, from vertical to sub-horizontal position, inside existing buildings, under low headroom or confined space conditions, and/or underpinning existing structures (railway ballast, road subgrade, slabs or shallow foundations). Through various case histories and examples, this paper shows the range of application of this deep mixing technique and its advantages compared to jet grouting columns of modest diameter.

Ground improvement (deep mixing treatment work) was conducted during Tokai Kanjo Expressway construction work. The target ground has been subjected to repeated open pit mining and burial in the past, and the buried soil is a residue (slime) mainly consisting of a dehydrated cake of soft cohesive soil generated during stone crushing. Based on the results of the laboratory mixing test, we conducted test construction to confirm the compatibility with the actual ground and the effect on construction when the water-hardening material ratio was set to 2.0. The usual construction method (single stirring) of only slurry injection with W/C = 2.0, mixing with preliminary water drilling, and stirring and mixing again with slurry injection of W/C = 1.0, resulting in a total of W/C = 2.0. As a result of implementing the construction method (double stirring), we were able to satisfy the required quality in double stirring. We will also report on construction management and quality control during this construction.1,2,3,4)

The CDM-EXCEED method is one of the machine-stirred deep mixing treatment methods (CDM methods) that improve soft ground by discharging cement slurry into the soft ground and rotating the stirring mixing blade. In this study, we focused on low displacement, which was regarded as a secondary effect of the internal pressure-relief blade, and measured the displacement in the ground using a new insertion-type inclinometer. It is clear that this method has less impact on the surrounding ground than the conventional machine agitation deep mixing method.

In applications of deep mixing to retaining wall, water cutoff wall and bottom sealing barrier etc., the unification of columns is highly required. Although the unification is ensured by overlapping of deep mixing columns generally, jet grouting may be used partially for the cases such as water sealing or unification to other structures. However its slow construction speed and expensive cost become problems frequently. As a method to ensure unification quality while minimizing cost increase, a combined mixing method have been developed, which uses not only blade mixing but also jet grouting for cutting and mixing soil existing in outer area of the blade. In this method, high-pressured binder slurry is injected from the end of a 1.2 m-diameter mixing blade with 20 cm of cutting distance. Due to the small 20 cm cutting distance, a 1.6 m-diameter stabilized column can be constructed with about 1/10 of jet energy required for typical jet grouting machines. This method was applied to a construction of an earth retaining wall that also served as a water cutoff wall. In this project, the water cutoff wall was constructed firstly by regular deep mixing method overlapping in the direction of wall extension. Then, the earth retaining wall was constructed by using the combined mixing method to be unified with the existing water cutoff wall. This combined mixing method created a highly continuous solidified soil at a low cost and in a short time.

Infrastructure development like the Trans-Sumatra Toll Road, Jakarta-Bandung high-speed railway, Patimban Port, and Capital relocation are proceeding at a rapid pace. In large-scale infrastructures development and the need to complete the construction, it is necessary to overcome the soft ground and Ground Improvement work must be needed. Indonesia is a volcanic country, and unlike the deltaic land widespread in Southeast Asia, it has a wide variety of geology, including alluvial soil distributed in river deltas, soft soil deposited in valley bottoms formed by mountain building and erosion, and organic soil resulting from the jungle, all of which are layered in complex formations. In Indonesia, many of the soil improvement works for such complex ground use the Prefabricated Vertical Drains (PVD) method and Pile Slab method due to economic and technical matters. However, in the case of multi-layered ground, a construction method that can handle various geology is required, and a construction method specialized for the geology such as PVD construction is not suitable, and there are many cases where the results are different from what was expected. In addition, structural measures such as pile slab construction require a huge amount of maintenance in the future. Therefore, we planned the technology transfer of the Deep Mixing method, which has been widely used in Japan, a volcanic country where has many predominance of interlayered grounds. In specific, we attempted transfer the technology of Deep Mixing method as below: 1) To make it easier to introduce Deep Mixing construction method, cement produced locally will be used. 2) Introducing Deep Mixing dedicated machine to be able to start the work instantly, instead of the general-purpose construction machine which needs the attachment attached to do the work. 3) Introduce a construction system used in Japan (i.e. methods for determining the amount of cement to be mixed in/construction management methods/improved quality control methods, etc.). 4) Conducting demonstration construction and site tour at the local site. 5) For the demonstration construction, our team will prepare in accordance with the construction system together with local engineers to get them learn with practical training. We will focus on the results of demonstration construction (test construction) proceeded in Pekanbaru-Dumai section of the Trans Sumatera Toll Road Project in Indonesia.1)