Arun Mihsra Upsidc Ground Improvement Techniques

Ground Improvement
Ground improvement techniques utilising Vibro methods, Deep Soil Mixing and Grouting
technologies are finding increasing application in Malaysia to solve a broad spectrum of geotechnical problems.
This paper will describe recent applications in Malaysia for four separate projects – Jet Grouting to form stable cutter-head interventions for a tunnel project; Deep Soil Mixing to support deep vertical basement excavation with limestone interface for a commercial complex; Vibro Concrete Columns to found reinforced concrete tanks in former domestic landfill for a sewage treatment plant; Vibro Stone Columns to support high reinforced soil walls for a highway project. The importance of quality control measures are emphasized and available proving methods are also discussed. The case histories presented demonstrate that the techniques can provide effective solutions to challenging engineering problems.

Introduction
Malaysia has seen extensive growth for the past one decade with many infrastructure projects in the construction industry. Current technology affords many ground improvement techniques to suit a variety of soil conditions, structure types and performance criteria. These ground improvement techniques can offer alternative foundation systems to the conventional pile foundation systems. For more details on various available ground improvement techniques, the reader is referred to “Ground Improvement 2nd
Edition” book edited by Moseley & Kirsch (2004).

This paper illustrates four recent case histories in Malaysia, where innovative ground improvement techniques
were employed to suit varying needs of application type and performance criteria.
The construction methodology and quality control procedures during execution of works were in accordance with relevant Code of Practices (e.g. BS EN 12716:2001, BS EN 14679:2005, BS EN 14731:2005, etc.). These techniques offered reasonably environmental friendly solutions, especially in urban areas.

This paper will describe following four different case histories from four separate projects; where ground
improvement techniques were utilised to solve challenging problems in difficult ground conditions:
a) Jet Grouting to form stable tunnel boring machine cutter-head interventions for a tunnel project.
b) Deep Soil Mixing to support vertical basement excavation over limestone for a commercial complex.
c) Vibro Concrete Columns to support reinforced concrete process tanks in a former domestic landfill for a
sewage treatment plant.
d) Vibro Stone Columns to support high reinforced soil walls for a highway project.
3 Application of Jet Grouting
3.1 Background
A tunnel project in Kuala Lumpur involved the construction of a 13m diameter bored tunnel over approximately 10km stretch. The tunnel will function mainly as a storm water storage and diversion channel but also incorporates a 3km motorway in a triple deck arrangement. The geology encountered along the tunnel path was ex-mining soils and limestone formation. For more details of the project, the reader is referred to Raju & Yee (2006).
The cutter-head of the Tunnel Boring Machine (TBM) required maintenance at regular intervals (about 150m to 200m). At such TBM stops (referred as “cutter-head intervention”), the slurry pressure will be switched off and the stability of the rock/soil face in front of the TBM relies on air pressure and inherent strength of the in-situ rock/soil.
Due to the existence of loose sandy material, there was a risk of ground disturbance and subsequent ground
subsidence, if left untreated. Most of the cutter-head interventions were located within limestone bedrock and rock grouting was carried out at some locations depending on quality of the bedrock. At locations, where cutter-head interventions are located partially in soil stratum and partially in bedrock, combination of compaction grouting and rock grouting was utilised. At other locations, where cutter-head interventions are located completely in soil stratum a capping shield made of “Jet Grout block” was designed to ensure face stability whilst maintenance of cutter-head was carried out. Figure 2 represents the schematic of different types of grouting schemes implemented depending on the geological conditions. The subsequent sections explain the details of grouting scheme using large diameter Jet Grout columns to form a stable block in the soil stratum.
3.2 Soil conditions
In general, the subsoil conditions consist of highly variable mixed soils, comprising mainly of loose silty sand and sandy silt underlain by highly variable karstic limestone formation (see Figure 3). Standard penetration test (SPT) blow counts typically vary from 0 blows/0.3m (especially along “slump zones” above rock-head) to 20 blows/0.3m. Historically, mining activities took place at some of the sections which explain the varying nature of the soil. Groundwater was generally at about 3m to 4m below ground.
3.3 Solution
The capping shield made of Jet Grout columns was designed to form a stable block at the cutter-head
intervention locations as shown in Figure 4. The shield was formed using 2 rows of 2m diameter Jet Grout
columns in front of the cutter-head of TBM. The front row (Line-B) was designed to be full depth section, whereas back row (Line-A) designed to be hollow section to ease the cutting process and also for economy reasons. The Jet Grout block was installed from 9m to 28m below existing ground level.
The construction challenges of the Jet Grout block were as follows:
a) Formation of consistent 2m diameter Jet Grout columns in the highly variable soil.
b) Proper interlocking of each Jet Grout column down to
28m depth which requires the verticality of drilling to be
within 0.5% to 1%.
c) Required minimum unconfined compressive strength (UCS) of 1MPa for each Jet Grout column.
d) Existing underground utilities which required careful attention to avoid damages.
e) High power transmission towers which limited the working head-room and associated safety issues.
A trial was performed prior to the commencement of working columns to confirm the erodability of in-situ soils and 3673 adequacy of operating parameters. The jetted column was exposed and core samples were taken to verify the as-
built diameter and achieved strength. The diameter formed was proven to be more than 2m and UCS was more than 1MPa. The site pictures showing exposed trial columns and execution of working columns using HT 400 pump and D-system.

 

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