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Sustainable foundation engineering Banzhaf

SUSTAINABLE FOUNDATION ENGINEERING – MIXED-IN-PLACE TECHNIQUES FOR DURABLE CUT-OFF WALLS

Peter, Banzhaf

BAUER Spezialtiefbau GmbH, Schrobenhausen, Germany, +49 8252 974266, +49 8252 971496, [email protected]

Abstract Sustainability in construction means, among other aspects, the limited use of

construction material, the reduced number of construction equipment, the minimized number of transports and overall decreased use of energy, therefore reduced cost without compromising on quality.

Due to the long history of Mixed-in-Place (MIP) in foundation engineering, these techniques with remarkable developments in the way of execution and the equipment used have turned into an internationally accepted method to install durable permanent MIP-cut-off walls even in levees and embankment dams.

Historical MIP-auger techniques have been advanced to mix and homogenize soils ranging from gravels and sands to silt with some parts of clay – important is the slurry mix used and the mixing technique as such. The MIP-auger technique is lately supplemented by the MIP-cutter technique. Key advantages are cutting and mixing into soft rock, penetrating and mixing limited rock layers and reaching depths not attainable with the auger technique. 1. INTRODUCTION

1.1 History and Utilization

Mixed-in-Place (MIP) techniques to form vertical elements in appropriate soils are in-situ deep mixing construction methodologies known since more than 50 years. They will be distinguished between dry and wet methods and for the wet method between different ways of mixing to achieve the designed improved soil property. Porbaha et al (2005) categorized deep mixing application into six main applications, namely:

− Hydraulic barrier systems − Retaining wall systems − Foundation support systems

− Excavation support systems − Liquefaction/Seismic mitigation systems − Environmental remediation systems

1.2 Techniques provided

For forming vertical elements in the ground to install seepage barriers or structural elements primarily the wet mixing methods are being used. Methods applied are:

− Single auger mixing method − Triple auger mixing method − Multiple auger mixing method − Cutter soil mixing method

− Trench cutting Re-mixing deep method (TRD)

− FMI (Misch-Injektionsverfahren) trenching machine method

In particular, the triple auger mixing method – the MIP-TAT – has successfully been used by Bauer since beginning of the 90ties of the last century. This technique proved to be

DFI INDIA 2014: Deep Foundation Technologies for Infrastructure Development in India 1


ideal to reach depths to 25 m and to homogenize different types of soils including small cobbles with the binder slurry. The binder is introduced at the tip of the middle auger proving to be ideal for uniform distribution of the slurry into the entire mixing area. The technique of reversible augers together with the back-step sequencing of panel installation demonstrated to produce continuous, uniform seepage barriers and construction pit walls. The tested permeability of MIP walls successfully reached ≤ 1008 m/s after 56 days. Strengths achieved after 56 days range between 1.5 and 3 N/mm² as shown in Figure 1.

Age of the samples in days [d]

Com

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[N/m

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Figure 1. Compressive strength reached of MIP-TAT samples after 56 days of curing (BST).

The Cutter soil mixing method – MIP-CSM – supplements the MIP-TAT by reaching depths of more than 45 m with the Monokelly configuration. Very specialist machines reach rope-suspended up to 60 m. Furthermore, the cutter technique is able to penetrate limited rock layers and is designed for embedment of the MIP-panels into rock. In this paper the main focus is on the economical MIP triple auger mixing method – the MIP-TAT achieving high performance rates in granular-silty-clayey soils.

Photo 1. BAUER BG40 rig with MIP-triple auger technique (MIP-TAT) set-up (BST). 1.3 Materials used

Soil stabilization involves the use of stabilizing agents (binder materials) in weak soils to improve its geotechnical properties such as compressibility, strength, permeability and durability. Different cementitious materials are being used to prepare the slurry being mixed with the soils resulting in a type of earth-concrete. Binding or stabilizing agents like cement, pozzolan, slag or lime are used in different proportions depending on design requirements and the soils being mixed. Additives support the mix-design to adapt to site

DFI INDIA 2014: Deep Foundation Technologies for Infrastructure Development in India 2

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Photo 7. A levee at the river Iller in Germany overtopped during the 2005 floods – still the installed MIP-TAT wall stayed in place and prevented the complete discharge of the river

(BST).

REFERENCES 1 EuroSoilStab. (2002). Development of Design and Construction Methods to Stabilize Soft

Organic Soils: Design Guide for soft soil stabilization. CT97-0351, European Commission, Industrial and Materials Technologies Program (Rite-EuRam III). Brussels.

2 Porbaha, A., Weatherby, D., Macnab, A., Lambrechts, J., Burke, G., Yang, D. and Puppala, A. J. (2005). Report: American Practice of Deep Mixing Technology. Proceeding of the International Conference on Deep Mixing-Best Practice and Recent Advances, Stockholm.

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