Ground Improvement

ArthaGeo’s wide spectrum of ground improvement techniques. Customized solutions for a variety of ground conditions from very soft clays to very loose sand and to varying degree of improvement

The geotechnical services and ground improvement can be simplified as below:

RIGID INCLUSION

Rigid Inclusion (RI) is a ground improvement method using high modulus columns constructed through compressible soils to reduce settlement and increase bearing capacity. Ground improvement efficiency depends on the stiffness relationship between the soil and the columns.

Rigid inclusion, also known as Controlled Modulus Columns (CMC) / Controlled Stiffness Columns (CSC) or locally translated as Kolom Grout Modular (KGM) in Indonesia, is installed using a special full displaced auger where the soil is not removed as the auger penetrates but displaced laterally and indirectly densify the surrounding soft soil. Due to the nature of its installation, it is also called Full Displacement Columns (FDC) among others. The material forming the Rigid Inclusion columns were generally made of grout or cement mortar. When a high strength of columns is required, a concrete material can be used to form RI columns with an aggregate size of 1-2 cm. ArthaGeo has also experienced in doing Rigid Inclusion using cement with fly-ash and gravel, which recently became well known as a CFG Pile (Cement Fly-ash Gravel).

The concept of Rigid Inclusion is quite different from pile foundations concept. In RI, the loads sustained by the soft soil is reduced (usually between 60% and 90%) in order to reduce the global and differential settlements. Nevertheless, the loads are not directly transmitted to depth. Here, the soft soil plays a role, and supports part of the load whereas in the pile foundation concept the soft soil is just bypassed (or used for skin friction consideration).

When we work with rigid inclusions, a Load Transfer Platform (LTP) is often used with a thickness generally ranging between 50 and 100 cm. In general, the load transfer platform consist of well compacted granular material (often sand, crushed stones or gravels).

DYNAMIC COMPACTION

Dynamic compaction (DC) is a mechanical ground improvement process used to provide rapid densification by means of short-term external forces caused by impacts. It is predominantly used to densify granular natural or fill soils with percentage of fines (i.e., particles less than 63 μm) not exceeding 20 to 25%. Soil strength is increased while compressibility and settlements are decreased as a result of the densification. In addition, dynamic compaction also increases the cyclic stress resistance of cohesionless soil and hence can be used as an effective method for anti-liquefaction treatment.

VIBRO COMPACTION

Vibro compaction is mechanical densification technique using vibration energy generated by vibroflot machine, combined with flush water and air. The vibration energy will shear and re-arrange soil particle into denser configuration. This method is applicable to densify the granular soil with percentage of fine content less than 30%. The treatment increase compressibility of soil and improve cyclic stress resistance of soil, hence can be used as anti-liquefaction solution.

DYNAMIC REPLACEMENT

Dynamic replacement (DR) is an extension of the dynamic compaction technique. In contrast with dynamic compaction, dynamic replacement is developed to treat soft cohesive soil and even peaty soil.

This technique starts out by producing a crater with light pounding. The craters are then backfilled with granular materials (e.g., aggregate, stone, gravel or rock pieces up to 300 mm size) that will lock together under subsequent heavy pounding. This pounding process is repeated until a noticeable decrease in crater formation occurs. This essentially results in a large diameter granular column being formed. The large diameter granular column, which is usually called as DR column can have diameter of 2.5 to 3.0 m and length of 5 to 7 m.

STONE COLUMNS

• Wet Method

Wet vibro stone columns using the support of water to penetrate the soil during penetration to the design depth. The stone is filled into the the soil from the top ground by gravity.

Stone columns are suitable for the improvement of both weak natural soils and made ground with typical improved bearing capacities ranging from: 50kN/m2 to 150kN/m2. Stone columns can be installed in groups under isolated loads or directly under linear loads such as strip footings. Columns can also be arranged in a grid pattern to provide support to uniformly loaded structures such as ground floor slabs and embankments.

• Dry Method

Similar concept to the wet stone column method, Dry stone column is not using water instead using compressed air as in the dry method. They are particularly useful if washout of soil to the surface is to be prevented or where handling of process water for the Wet Top Feed method is problematic.

The conventional dry method is suited for firmer soils with a relatively low ground water table (FHWAA, 1983). However, the main controlling factor is the availability of a nearby source of water for wet method. Otherwise, it would be the dry method or as it required by local regulations.

PVD & VACUUM PRELOADING

• Prefabricated Vertical Drain (PVD) with Preloading

When the anticipated time for consolidation exceeds the allowable construction schedule, vertical drains are installed to accelerate the rate of consolidation. Vertical drains provide an artificial drainage path for the water flow. It consists of a central core, whose function is to act as a free draining channel enclosed by a geotextile filter sleeve which prevents the fine soil particles from entering the central core but allows free entry of pore water into the core.  Two types of vertical drains commonly used; the band shaped and the cylindrical shaped vertical drains.

The effectiveness of vertical drains depends on the permeability of the filter and the discharge capacity of the drain. The discharge capacity will be significantly reduced when the filter is pressed into the grooves of the central core due to lateral pressure from the surrounding soils and/or as a result of ground settlement, the drain buckles. Hence, in very soft soils where large settlement is expected, a more rigid cylindrical drain is preferred.

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