A numerical study on backfilling of the tail void with two-component grout based on laboratory tests

Tipo di pubblicazione: Tesi di dottorato
Tipologia MIUR: Tesi di dottorato > Tesi di dottorato - Polito
Titolo: A numerical study on backfilling of the tail void with two-component grout based on laboratory tests
Autori: Shah, Ravi
Autori di ateneo:
Tutor: Prof. Daniele Peila
Dottorato di ricerca: XXIX Ciclo > INGEGNERIA AMBIENTALE
Istituzione: Politecnico di Torino
Numero di pagine: 176
Abstract: In mechanized tunneling the annular gap between the segmental lining and the surrounding soil caused by tunnel driving must be backfilled instantaneously with an adequate mortar. The annular gap is caused due to the conical shape, overcut and design of the shield. The soft ground tunneling has a prime focus on the settlement control and optimization of the parameters involved. The backfilling is a key component to reduce the surface settlements and deformations after the passage of the TBM. The main functions of backfilling are to 1. lock the segmental lining in position avoiding movements due to self-weight of the lining and other forces present; 2. To bear the loads transmitted by TBM backup weight; 3. Provide a uniform contact between the lining and surrounding soil and 4. Waterproofing the tunnel. Recent developments in the field of backfilling have led to the development of a state-of-the-art two-component grouting system. A two-component grout consists of two components, Component A (Bentonite, water, cement and a retarder), component B (Sodium silicate based accelerator and water). When these two components are mixed just behind the annular gap, the grout starts to attain plasticity in a very quick time and thus, is able to transfer the load to the segmental lining in a very short time after its injection to the annular gap. For a good backfilling grout it is important to satisfy certain engineering aspects (Fluidity, binding and gelling time, mechanical strength). The aim of this research is to understand the behavior of a two component grout in its fresh and hardened state and implement those obtained parameters in a numerical code. A series of laboratory tests are to perform on the two-component grout to determine its physical and mechanical behaviour. Bleeding, Marsh cone and gelling time tests are conducted on the fresh grout sample to test its chemical binding, viscosity and time taken to achieve plastic strain. A series of uniaxial compressive strength (UCS) tests are conducted on the grout sample to obtain its elastic modulus in its early days of setting (up to 28 days). In order to obtain and examine the state and strength of the grout in long term, a string of UCS tests are carried out on two-component grout samples cured at natural humidity of the soil in long terms (up to 1080 days). In addition to this, permeability and dewatering properties of a two-component are determined in its early state. Furthermore, the stiffness of the hardened grout sample in confined condition is determined by conducting oedometer tests. The oedeometer tests are conducted at various time intervals to obtain a complete time-dependent stiffness of the grout. The research deals with the development of a robust numerical model taking into account all the relevant factors involved in mechanized tunnelling but focusing mainly on the backfilling procedure using FDM software FLAC 3D. The backfilling in the tail grout is modeled as normally applied pressure in a liquid state and later a time-dependent hardening behavior of the grout is initiated. The time-dependent behavior parameters are obtained from the laboratory tests conducted. A new constitutive model (CM) named as Plastic-Hardening (PH) is implemented to model the behavior of the surrounding soil. This CM gives the user a freedom to implement different stiffness for loading and unloading. Since the Mohr-Coulomb (MC) model specifies only one elastic modulus for both loading and unloading, it is unsuitable for cyclic and staged excavation procedures such as mechanized tunnelling itself. The PH CM is validated with the FEM software PLAXIS 3D before implementing it in FLAC 3D. Moreover, Hydro-mechanical coupled analysis is also conducted in the near-field domain of the grouting zones to update the permeability and stiffness of the grout due to consolidation.
Data: 2017
Status: Pubblicato
Lingua della pubblicazione: Inglese
Parole chiave: flac, plaxis., mechanized tunneling, backfilling, numerical simulation, two-component grout
Dipartimenti (originale): DIATI - Dipartimento di Ingegneria dell'Ambiente, del Territorio e delle Infrastrutture
URL correlate:
    Area disciplinare: Area 09 - Ingegneria industriale e dell'informazione > INGEGNERIA E SICUREZZA DEGLI SCAVI
    Area 08 - Ingegneria civile e Architettura > GEOTECNICA
    Data di deposito: 13 Set 2017 17:23
    Data ultima modifica (IRIS): 13 Set 2017 17:41:39
    Data inserimento (PORTO): 15 Set 2017 02:10
    Permalink: http://porto.polito.it/id/eprint/2680098


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