Tunnels In Sand Research Articles

Experimental study on face instability of shield tunnel in sand

Face stability is critical for ground settlement and construction safety control in shield tunneling. In this paper, a series of 3D large-scale model tests with a tunnel of 1m diameter were conducted in dry sand for various cover-to-diameter ratios C/D=0.5, 1, and 2 (i.e., relative depth; C is the cover depth and D is the diameter of tunnel). Each test provided a measurement of the support pressure and the ground settlement with the advance of face displacement. The evolution of soil arching during face failure was investigated by monitoring the redistribution of earth pressure in front of the face in the test case of C/D=2. In the displacement-controlled face failure tests in the medium density sands, the support pressure dropped steeply to the minimum value, then increased to a steady state with the continuing increase in the face displacement. Relationships between the support pressure and face displacement for various cover depths were also verified by the numerical analysis using the finite difference program, FLAC3D (Itasca, 2005). The limit support pressure increases with the increase of the relative depth C/D and then tends to be constant. A significant rotation of principal stress axes in the upward arches in the soil during face failure was found in the tests. A two-stage failure pattern is proposed based on the observation of earth pressure. The theoretical and empirical formulas for estimating limit support pressure were verified by the tests results.

Centrifuge Modeling of Seismic Loading on Tunnels in Sand

Abstract The purpose of the work is to provide an experimental benchmark on the seismic behavior of tunnels, with the final aim of calibrating numerical and analytical design methods. A series of plane-strain centrifuge tests with dynamic loading on a model tunnel was, therefore, carried out at the Schofield Centre of the Cambridge University Engineering Department (CUED). Four samples of dry uniform fine sand were prepared at two different densities, in which an aluminum-alloy tube was installed at two different depths. The tube was instrumented with strain gauges to measure hoop forces and bending moments at significant locations. To monitor the amplification of ground motion from the base to the surface, vertical arrays of accelerometers were placed in the soil model and along the box. The instrumentation also included linear variable differential transformers (LVDTs) that measured the soil surface settlement during all test phases. The test procedure and the results are described in this paper, showing the evolution of both accelerations and internal forces along the tunnel lining during the model earthquakes.

Tunnels in sands: the effect of size, depth and volume loss on greenfield displacements

This paper examines the effect that tunnel size, depth and volume loss have on greenfield soil displacements above tunnels in sandy ground. The results of a series of plane-strain centrifuge tests performed on tunnels in a dry silica sand are examined. The cover-to-diameter ratio, C/D, of the tunnels ranged from 1·3 to 4·4. Features of greenfield settlement trough shape, both surface and subsurface, are illustrated by examining soil displacement data obtained using an image-based deformation measurement technique. The effects of tunnel size, depth and volume loss are demonstrated, and the suitability of typical fitting curves is discussed. The complex volumetric behaviour of drained soil is illustrated by comparing tunnel volume loss with the volume loss experienced by the soil. A set of equations is developed that provide a method of evaluating the change of settlement trough shape with tunnel size, depth and volume loss.

Checking Analysis of Lining Structural Strength in Aeolian Sand Tunnel

The crushing and loosening arised from the characteristics such as single particle, bad gradation, lacking of self-stability, low cohesion, loose structure and shear strength happen frequently in the aeolian sand formation. These characteristics lead to tremendous difficulty for tunnel's design and construction. Loading such as formation pressure must be undertaken by secondary lining. In this paper, relying on Shen-Mu Tunnel of Yu-Shen expressway, the strength of lining section has been checked according to internal force combination through imitating the interaction of rock and lining by applying elastic resistance. The bearing force of secondary lining in aeolian sand tunnel has been discussed through calculation by ANSYS, which plays an important directive role on the construction process and keeps the project going on well.

Research on Grouting Experiment in Aeolian Sand Tunnel

Portland cement, superfine cement and modified sodium silicate have been taken as grouting materials in the aeolian sand tunnel which is characterized by single particle, bad gradation and loose structure. In this paper, penetration grouting and rotary jet grouting have been adopted in site grouting experiment, whose effects are tested by excavation sampling test and field excavation detection. The grouting feature of aeolian sand formation has been revealed. In the meantime, the applicability of different kinds of grouting materials in aeolian sand tunnel have been clarified which provides useful significance and reference value on the selection of grouting parameter and construction in aeolian sand tunnel.

The Foraging Tunnel System of the Namibian Desert Termite,Baucaliotermes hainesi

The harvester termite, Baucaliotermes hainesi (Fuller) (Termitidae: Nasutitermitinae), is an endemic in southern Namibia, where it collects and eats dry grass. At the eastern, landward edge of the Namib Desert, the nests of these termites are sometimes visible above ground surface, and extend at least 60 cm below ground. The termites gain access to foraging areas through underground foraging tunnels that emanate from the nest. The looseness of the desert sand, combined with the hardness of the cemented sand tunnels allowed the use of a gasolinepowered blower and soft brushes to expose tunnels lying 5 to 15 cm below the surface. The tunnels form a complex system that radiates at least 10 to 15 m from the nest with crossconnections between major tunnels. At 50 to 75 cm intervals, the tunnels are connected to the surface by vertical risers that can be opened to gain foraging access to the surrounding area. Foraging termites rarely need to travel more than a meter on the ground surface. The tunnels swoop up and down forming high points at riser locations, and they have a complex architecture. In the center runs a smooth, raised walkway along which termites travel, and along the sides lie pockets that act as depots where foragers deposit grass pieces harvested from the surface. Presumably, these pieces are transported to the nest by a second group of termites. There are also several structures that seem to act as vertical highways to greater depths, possibly even to moist soil. A census of a single nest revealed about 45,000 termites, of which 71% were workers, 9% soldiers and 6% neotenic supplementary reproductives. The nest consisted of a hard outer “carapace” of cemented sand, with a central living space of smooth, sweeping arches and surfaces. A second species of termite, Promirotermes sp. nested in the outer carapace.

Observed Behaviour of a Tunnel in Sand Subjected to Shear Deformation in a Centrifuge

The paper describes observed behaviour of a model tunnel embedded in dry sand subjected to cyclic ground shear deformation in a centrifuge, as well as the behaviour of the model ground during shear deformation. Detailed data on earth pressures acting on the tunnel lining and the sectional forces of the lining are presented during ground shear deformation. The data suggest that the earth pressure at tunnel crown before ground shear deformation is smaller than the full overburden pressure probably due to the formation of arch action and the arch action may deteriorate with the cyclic ground shear deformation, resulting in an increase in the earth pressure at crown and changing the distribution of the sectional forces, which are largely influenced by conditions between tunnel lining and invert.

Experimental investigation of the face stability of shallow tunnels in sand

Various models have been proposed for the prediction of the necessary support pressure at the face of a shallow tunnel. To assess their quality, the collapse of a tunnel face was modelled with small-scale model tests at single gravity. The development of the failure mechanism and the support force at the face in dry sand were investigated. The observed displacement patterns show a negligible influence of overburden on the extent and evolution of the failure zone. The latter is significantly influenced, though, by the initial density of the sand: in dense sand a chimney-wedge-type collapse mechanism developed, which propagated towards the soil surface. Initially, loose sand did not show any discrete collapse mechanism. The necessary support force was neither influenced by the overburden nor the initial density. A comparison with quantitative predictions by several theoretical models showed that the measured necessary support pressure is overestimated by most of the models. Those by Vermeer/Ruse and Léca/Dormieux showed the best agreement to the measurements.

Sexual differences in behaviour during the breeding season in the soldier crab (Mictyris brevidactylus)

The soldier crab Mictyris brevidactylus breeds in winter. Large females spawned over a few days in early winter after most had decalcified their vulvar opercula. Some females spawned in their first winter, less than 1 year after settlement. The crabs probably copulate during a few days before spawning while the vulvar opercula are decalcified. During the daytime low tide in the breeding season, large males emerged and fed on the sediment surface. Females, on the other hand, made a sand roof above themselves using sand pellets from which they had sorted out food particles, and they fed while hiding under it. After the males had ceased their surface activities, they entered the sand tunnel made by the female. The roof was connected with a hollow shaft, which had been made when the crab had ascended to the surface. Before the habitat was submerged, the shaft was plugged from within with sand to form an air chamber, which suggests that the male and female descend together in the air chamber and copulate there. It is possible that the crab uses the sand roof as a visible signal to attract mates.

Back analysis of the measurements performed during the excavation of a shallow tunnel in sand

The results of back analyses based on the displacements measured during the construction of a railroad tunnel in an alluvial sand deposit are presented. After illustrating the characteristics of the construction technique, the main aspects of the in situ measurement programme and of the finite element approach used for back analysis are summarized. Then, the results of a series of calculations are discussed that concern both the determination of the ‘secant’ elastic moduli of the soil deposit and the attempt to identify the ‘mechanism’ governing the development of the surface settlements. On the basis of these results some comments are presented on possible improvements of the adopted excavation/construction procedure. Copyright © 1999 John Wiley & Sons, Ltd.

The effect of tunnelling technology on ground control

The effects of tunnelling technology on ground control are studied for the Hydroshield Boring Machine. The studies are based on field measurements obtained at a tunnel in sand constructed for the Light Rail Transit system in Edmonton, Canada. Particular attention is given to the relationships between the slurry pressure and face displacements, between the grout pressure and the tail displacements, and between the liner convergence and the final displacements. The results are generalized using the concept of a Ground Reaction Curve. Different curves are obtained for different stratigraphic conditions and for different grout pressures. The results are fundamental for understanding the relative importance of various sources of ground displacements (face, tail, liner), as well as for a quantitative insight into the mechanics of ground-support interaction for a slurry shield. The results also have direct practical significance for design decisions (slurry pressure, grout pressure, stiffness of liner) associated with this tunnelling technique. Les effets de la technologie de creusement de tunnel sur le contrôle desmouvements de sous-sol sont étudiés dans le cadre de la machine à forer type ‘Hydroshield’. Les études sont basées sur des mesures faites lors de la construction d'un tunnel dans du sable pour le Light Rail Transit System à Edmonton au Canada. Une attention particuliére est prêtée aux relations qui existent entre la pression de la bentonite et les déplacements à l'avant du tunnel, entre la pression du béton et les déplacements à l'arrière du tunnel, entre la convergence du revêtement et les déplacements finaux. Les résultats sont généralisés à l'aide d'une courbe de réaction du sous-sol. Différentes courbes sont obtenues pour différentes conditions stratigraphiques et différentes pressions du béton. Les résultats sont d'une nature fondamentale d'une part pour la compréhension de l'importance relative des différentes sources de déplacement (avant, arrière et revêtement), et d'autre part pour obtenir une idée quantitative de l'interaction entre le support et le sous-sol. Les résultatsont une signification pratique directe pour le choixdes paramètres de construction (pression de la bentonite, pression du béton, rigidité du revêtement) associées avec la technique de creusement du tunnel.

Shape, Structure, and Optics of the Eyes of Two Lysiosquilloid Stomatopods

ABSTRACT Lysiosquilla and Coronis belonging to the same family and living in the same habitat, both in sand tunnels, have several differences in the structure and optics of the eye. Coronis has spherical, Lysiosquilla elongated eyes. A large part of the cornea in Coronis is occupied by the middle band, whereas this in Lysiosquilla covers only a small part of the cornea. Lysiosquilla has a larger number and more strongly skewed ommatidia adjacent to the middle band. Though the ommatidial dimensions are different for the two species, acceptance and aperture angles are rather similar. Both species have in common the hexagonal facets in the six rows of ommatidia in the middle band which characterize the superfamily. Both have stronger differences in structure and optics of ommatidia between the dorsal and ventral half of the eye than other stomatopods. Differences in eye structure probably are correlated with behavioral differences, while similarities might be explained by evolutionary developments.

Settlements observed above a tunnel in sand : Eadie, H S Tunn Tunnlg, V9, N5, 1977, P93–94

Settlements observed above a tunnel in sand : Eadie, H S Tunn Tunnlg, V9, N5, 1977, P93–94

Subsidence above Shallow Tunnels in Soft Ground

The paper investigates the influence of the depth of burial and crown settlement on the surface subsidence above shallow tunnels driven in soft ground. Model tests were conducted on tunnels in sand and in clay, and these are compared with one another and with observations of settlements above some real tunnels. There is good agreement between the model behavior and the field records. The error, or normal probability curve, may be used as an approximation for the trough of surface subsidence, and the standard deviation is an appropriate measure of the width. Empirical relationships exist between the depth of burial, the trough width and the crown and surface settlements for tunnels in sands and in clays.

Centrifugal model tests on shallow tunnels in sand : Atkinson, J H; Potts, D M; Schofield, A N Tunn Tunnlng, V9, N1, 1977, P59–64

Centrifugal model tests on shallow tunnels in sand : Atkinson, J H; Potts, D M; Schofield, A N Tunn Tunnlng, V9, N1, 1977, P59–64

Research studies into the behaviour of tunnels and tunnel linings in soft ground : ATKINSON, JH CAMBRIDGE UNIV., GB ORR, TLL CAMBRIDGE UNIV., GB POTTS, DM CAMBRIDGE UNIV., GB 5F DEPT. ENVIR. TRANSP. ROAD RES. LAB. SUPPL. REP., 176UC, 1975, 34P

The report covers work carried out in the Cambridge University engineering department under a Transport and Road Research Laboratory sponsored research contract to study the behaviour of tunnels and tunnel linings in soft ground. The work consists of model studies coupled with theoretical analyses of the deformations around, collapse of, and lining loads in, shallow tunnels in sands and clays. In the model tests soil displacements were measured by lead shot radiographic techniques and lining stresses and moments were found from strain gauges bonded to the inner and outer surfaces of thin aluminium linings. The theoretical analyses of stresses and deformations were based on finite element and associated fields methods using models for the soils obtained from a critical state approach to soil behaviour. The report discusses the scope and objectives of the research and presents and discusses in some detail the results of model tests on a lined and an unlined tunnel in overconsolidated clay. It also considers methods of estimating the stability of lined and unlined tunnels. (A) /TRRL/

Model tests on shallow tunnels in sand and clay : 7F, 9R. Tunnels and tunnelling, July, 1974, P28–32

Model tests on shallow tunnels in sand and clay : 7F, 9R. Tunnels and tunnelling, July, 1974, P28–32

Shield method for the construction of tunnels with monolithically pressed concrete lining in sands and clayey sands

For obtaining a high quality, molithically pressed lining for tunnels in sands and clayey sands at nautral moisture content, the following basic conditions should be fulfilled: