Backfilling Process Research Articles

Numerical study of performance of soil-steel bridge during soil backfilling

This paper presents results of a numerical analysis performed on a corrugated steel plate (CSP) bridge during a backfilling process. The analysed bridge structure was a box culvert having a span of 12315 mm as well as a clear height of 3550 mm. Obtained calculation results were compared with the experimental ones. The paper is presented with the application of the Fast Lagrangian Analysis of Continua (FLAC) program based on the finite differences method (FDM) to determine behaviour of the soil-steel bridge structure during backfilling. The assumptions of a computational 2D model of soil-steel structure with a non-linear interface layer are described. Parametric analysis of the interface element is also given in order to receive the most realistic calculation results. The method based on this computational model may be used with large success to design calculations of this specific type of structure instead of the conventional and fairly inaccurate analytical methods. The conclusions drawn from such analysis can be helpful mostly for the assessment of the behaviour of steel-soil bridge structures under loads of backfilling. In consideration of an even more frequent application of this type of structure, conclusions from the conducted analysis can be generalized to a whole class of similar structural bridge solutions.

The geoarchaeology of Mycenaean chamber tombs

This study presents a revised methodology for the excavation and analysis of the stratigraphy in Mycenaean chamber tombs and other multi-use burials. For our excavation of chamber tombs at Ayia Sotira and Barnavos, Nemea, we followed a geoarchaeological approach to provide details about the process of backfilling and re-opening of the tombs and to identify the location, number, and slope of these re-openings.In the studied fill of tomb entrance corridors (dromoi) at Ayia Sotira we observed a suite of sedimentary structures based on field and micromorphological observations. These are attributed to grain flow and debris fall processes associated with the formation of small piles during the shoveling of debris into the tomb. During ancient re-opening of the tombs extensive planar erosional surfaces were produced, occasionally associated with a basal stone line feature and an abrupt change in the degree of compaction. Constructed plastered floors were identified in the dromoi and the chambers during both the initial opening and the subsequent re-openings of the tombs.The proposed geoarchaeological analysis will enable the reconstruction of complex histories of mortuary practices and their social meanings. Moreover, this analysis shows that some anthropogenic processes of sediment accumulation can be analyzed and interpreted with paradigms of natural processes. Therefore, it provides a framework for understanding other types of earthworks that involve digging and filling.

Backfilling technology and strata behaviors in fully mechanized coal mining working face

Based on the principle of fully mechanized backfilling and coal mining technology and combined with the Xingtai Coal Mine conditions, we mainly optimized the coal mining equipment and adjusted the coal mining method in the Xingtai Coal Mine 7606 working face for implementation this technology. Firstly, we define the practical backfilling process as the “(from backfilling scraper conveyor’s) head to tail backfilling, step by step swinging up of the tamping arm, gradual compacting, moving formed backfilling scraper conveyor when the second tamping arm cannot pass and connecting the immediate roof by back material push front material movement”. Meanwhile, the stress changes of backfill body in coal mined out area was monitored by stress sensors, and the roof caving law was analyzed by monitoring the dynamic subsidence of −210 west roadway of this face. The site tests results show that using this new backfilling and coal mining integrated technology, the production capacity in the 7606 working face can reach to 283,000ton a year, and 282,000ton of solid materials (waste and fly ash) is backfilled, which meets the needs of high production and efficiency. The goaf was compactly backfilled with solid material and the strata behavior was quite desirable, with an actual maximum vertical stress of the backfill body of 5.5MPa. Backfill body control the movement of overburden within a certain range, and there is no collapses of major areas in the overlying strata upon backfilled gob. The maximum subsidence and speed were 231mm and 15.75mm/d respectively, which proved the practical significance of this integrated technology.

Effect of Construction Sequences on the Behaviour of a Backfilled Retaining Wall

Backfilled L-shaped retaining walls are considered as complex types of geotechnical structures, which are particularized by the fact that they are not only supported by the soil, as is the case with foundations, but also loaded by the soil. Actual design methodology does not take into account the construction sequences which simulate the process by which the soil and the retaining wall are brought together. However, in reality, at least during the backfilling process, the retaining wall undergoes many displacements that are not so far considered in the design. In the present investigation, the influence of the construction sequences on the behaviour of an L-shaped stiff retaining wall is investigated with a numerical model. For validating the proposed numerical model, reference was made to the results of a centrifuge experiment conducted on a reduced prototype. The numerical analysis shows that for the type of wall and soil investigated, considerable displacements of the wall (rotation and translation) occur during the backfilling process. The rotational movement of the wall is not occurring around the toe as it is usually assumed in design practices, but it follows a total displacement path of the toe. It is recommended that a better estimation of the rotation (s) of the wall is necessary to reach the state in which active earth pressure can be fully mobilized. numerical investigation, where the behaviour of an L- shaped retaining wall is simulated. The Plaxis programme (2) was used for the numerical modelling. The effect of the construction sequence on the behaviour of the retaining wall is simulated by the mean of the multiphasic 'staged construction' procedure incorporated in the Plaxis.

Vikingetidens gravskik i Danmark – Spor af begravelsesritualer i jordfæstegrave

Vikingetidens gravskik i Danmark – Spor af begravelsesritualer i jordfæstegrave

Development and validation of a CFD model predicting the backfill process of a nuclear waste gallery

Nuclear waste material may be stored in underground tunnels for long term storage. The example treated in this article is based on the current Belgian disposal concept for High-Level Waste (HLW), in which the nuclear waste material is packed in concrete shielded packages, called Supercontainers, which are inserted into these tunnels. After placement of the packages in the underground tunnels, the remaining voids between the packages and the tunnel lining is filled-up with a cement-based material called grout in order to encase the stored containers into the underground spacing. This encasement of the stored containers inside the tunnels is known as the backfill process. A good backfill process is necessary to stabilize the waste gallery against ground settlements. A numerical model to simulate the backfill process can help to improve and optimize the process by ensuring a homogeneous filling with no air voids and also optimization of the injection positions to achieve a homogeneous filling. The objective of the present work is to develop such a numerical code that can predict the backfill process well and validate the model against the available experiments and analytical solutions. In the present work the rheology of Grout is modelled as a Bingham fluid which is implemented in OpenFOAM – a finite volume-based open source computational fluid dynamics (CFD) tool box. Volume of fluid method (VOF) is used to track the interface between grout and air. The CFD model is validated and tested in three steps. First, the numerical implementation of the Bingham model is verified against an analytical solution for a channel flow. Second, the capability of the model for the prediction of the flow of grout is tested by means of a comparison of the simulations with experimental results from two standard flowability tests for concrete: the V-funnel flow time and slump flow tests. As a third step, the CFD model is compared with experiments in a transparent Plexiglas experimental test setup performed at Delft University of Technology, to test the model under more practical and realistic conditions. This experimental setup is a 1:12.5 scaled version of the setup of the full-scale mock-up test for backfilling of a waste gallery with emplaced canisters used in the European 6th framework project ESDRED ( Bock et al., 2008). Furthermore, the plexiglas setup is used to study the influence of different backfill parameters. The CFD results for a channel flow shows good comparison against the analytical solution, demonstrating the correct implementation of the Bingham model in OpenFOAM. Also, the CFD results for the flowability tests show very good comparison with the experimental results, thereby ensuring a good prediction of the flow of grout. The simulations of the backfill process show good qualitative comparison with the plexiglas experiment. However, occurrence of segregation and also varying rheological properties of the grout in the plexiglas experiment results in significant differences between the simulation and the experiment.

Consolidation in accreting sediments: Gibson's solution applied to backfilling of mine stopes

There is increasing use of hydraulically placed tailings backfill in mined-out voids (‘stopes') in underground mining, with the backfill being retained in the stopes by barricades built across the stope access tunnels. The forces acting on these barricades depend on the degree of consolidation that occurs during the backfilling process. A solution to the problem of consolidation in a layer increasing in thickness owing to ongoing sedimentation was proposed by Gibson in 1958. This solution appears to be directly relevant to the stope backfilling process, although there are limitations in applying it. Using material properties from two mine sites, the applicability of the Gibson solution to stope filling is examined. In particular, since one of the basic assumptions of the Gibson solution (that cv remains constant during filling) is generally violated, the effect of having a varying cv is explored using numerical modelling. Finally, the limitations of applying the Gibson solution to the stope backfilling problem are discussed. These relate particularly to the three-dimensional nature of stope geometry and drainage (compared with the assumption of one-dimensional conditions in the Gibson solution) and the fact that cement is generally added to backfill, such that the analysis herein is only valid up to the start of cement hydration.

Seismicity patterns and variation of the frequency-magnitude distribution of microcracks in salt

SUMMARY We analyse the statistical behaviour of about 1.6 E+6 high-frequency, acoustic emission events recorded in a rock mass in a salt mine over a 3-yr time period. The rock mass is directly located above a cavity that is backfilled during a 6 months time interval within the investigated time period. The rock mass consists mainly of rock salt with large anhydrite blocks in it. Location, event rate and strength of the events are studied in 3 months time intervals before, during, and after the backfilling process. We observe strong temporal and spatial changes of event rate and b-values that correlate with the structural features and the loading of the rock mass: two regions with a b-value maximum above the cavity start developing with the beginning of backfilling. They reach extremely high b-values of up to b= 3.18 and are located at the transition zones between the different materials. The b-value ratio in anhydrite and rock salt anti-correlates during times of equilibrium and fast loading. We conclude that b-value mapping during transient loading is useful to investigate structural heterogeneities in the rock volume, whereas b-values during equilibrium phases better indicate the level of ambient stress and visco-plastic stress relaxation in the salt rock.

Autocyclic behaviour of fan deltas: an analogue experimental study

AbstractFan deltas are excellent recorders of fan‐building processes because of their high sedimentation rate, particularly in tectonically active settings. Although previous research focuses mainly on allogenic controls, there is clear evidence for autogenically produced storage and release of sediment by flume and numerical modelling that demands further definition of characteristics and significance of autogenically forced facies and stratigraphy. Analogue experiments were performed on fan deltas with constant extrinsic variables (discharge, sediment supply, sea‐level and basin relief) to demonstrate that fan‐delta evolution consists of prominent cyclic alternations of channellized flow and sheet flow. The channellized flow is initiated by slope‐induced scouring and subsequent headward erosion to form a channel that connected with the valley, while the removed sediment is deposited in a rapidly prograding delta lobe. The resulting decrease in channel gradient causes a reduction in flow strength, mouth‐bar formation, flow bifurcation and progressive backfilling of the channel. In the final stage of channel filling, sheet flow coexists for a while with channellized flow (semi‐confined flow), although in cycle 1 this phase of semi‐confined flow was absent. Subsequent autocyclic incisions are very similar in morphology and gradient. However, they erode deeper into the delta plain and, as a result, take more time to backfill. The duration of the semi‐confined flow increases with each subsequent cycle. During the period of sheet flow, the delta plain aggrades up to the ‘critical’ gradient required for the initiation of autocyclic incision. This critical gradient is dependent on the sediment transport capacity, defined by the input conditions. These autogenic cycles of erosion and aggradation confirm earlier findings that storage and release of sediment and associated slope variation play an important role in fan‐delta evolution. The erosional surfaces produced by the autocyclic incisions are well‐preserved by the backfilling process in the deposits of the fan deltas. These erosional surfaces can easily be misinterpreted as climate, sea‐level or tectonically produced bounding surfaces.

Field Behavior of an Integral Abutment Bridge Supported on Drilled Shafts

The abutments of integral bridges are traditionally supported on a single row of steel-H-piles that are flexible and that are able to accommodate lateral deflections well. In Hawaii, steel-H-piles have to be imported, corrosion tends to be severe in the middle of the Pacific Ocean, and the low buckling capacity of steel-H-piles in scour-susceptible soils has led to a preference for the use of drilled shaft foundations. A drilled shaft-supported integral abutment bridge was monitored from foundation installation to in-service behavior. Strain gauge data indicate that drilled shaft foundations worked well for this integral bridge. After 45 months, the drilled shafts appear to remain uncracked. However, inclinometer readings provide a conflicting viewpoint. Full passive earth pressures never developed behind the abutments as a result of temperature loading because thermal movements were small and the long term movements were dominated by concrete creep and shrinkage of the superstructure that pulled the abutments towards the stream. In the stream, hydrodynamic loading during the wet season had a greater effect on the abutment movements than seasonal temperature cycling. After becoming integral, the upright members of the longitudinal bridge frame were not vertical because the excavation and backfilling process caused deep seated movements of the underlying clay resulting in the drilled shafts bellying out towards the stream. This indicates the importance and need for staged construction analysis in design of integral bridges in highly plastic clays. Also, the drilled shaft axial loads from strain gauges are larger than expected.

PNA-PEG Modified Silicon Platforms as Functional Bio-Interfaces for Applications in DNA Microarrays and Biosensors

The synthesis and characterization of two types of silicon-based biofunctional interfaces are reported; each interface bonds a dense layer of poly(ethylene glycol) (PEG(n)) and peptide nucleic acid (PNA) probes. Phosphonate self-assembled monolayers were derivatized with PNA using a maleimido-terminated PEG(45). Similarly, siloxane monolayers were functionalized with PNA using a maleimido-terminated PEG(45) spacer and were subsequently modified with a shorter methoxy-terminated PEG(12) ("back-filling"). The long PEG(45) spacer was used to distance the PNA probe from the surface and to minimize undesirable nonspecific adsorption of DNA analyte. The short PEG(12) "back-filler" was used to provide additional passivation of the surface against nonspecific DNA adsorption. X-ray photoelectron spectroscopic (XPS) analysis near the C 1s and N 1s ionization edges was done to characterize chemical groups formed in the near-surface region, which confirmed binding of PEG and PNA to the phosphonate and silane films. XPS also indicated that additional PEG chains were tethered to the surface during the back-filling process. Fluorescence hybridization experiments were carried out with complementary and noncDNA strands; both phosphonate and siloxane biofunctional surfaces were effective for hybridization of cDNA strands and significantly reduced nonspecific adsorption of the analyte. Spatial patterns were prepared by polydimethylsiloxane (PDMS) micromolding on the PNA-functionalized surfaces; selective hybridization of fluorescently labeled DNA was shown at the PNA functionalized regions, and physisorption at the probe-less PEG-functionalized regions was dramatically reduced. These results show that PNA-PEG derivatized phosphonate monolayers hold promise for the smooth integration of device surface chemistry with semiconductor technology for the fabrication of DNA biosensors. In addition, our results confirm that PNA-PEG derivatized self-assembled carboxyalkylsiloxane films are promising substrates for DNA microarray applications.

A simple numerical model for inlet sedimentation at intermittently open–closed coastal lagoons

This contribution aims to model the dominant processes that control sedimentation within the ocean inlet to intermittently open–closed coastal lagoons; focussing on the role of infilling, backfilling and morphodynamic feedback. The key elements that have been included in the present model are: (1) the delivery of sediment to the mouth of the estuary by littoral processes; (2) sediment transport processes within the inlet due to non-linear tidal flow; and (3) the down-slope diffusion of sediment. The model discussed here includes a simple one-dimensional (1-D), non-linear flow parameterisation that predicts the spatial variability in the magnitude and non-linearity of the tidal flow. The predicted third and fourth velocity moments are used to drive a morphodynamic module. Down-slope diffusion of sediment is dealt with in a separate diffusion term in the bed-evolution equation. Feedback between the evolving morphology and the flow field are integral to the model. Numerical simulations are used to investigate different modes of evolution for this type of inlet system. Inlet closure due to infilling is critically controlled by the balance between sediment addition at the mouth due to littoral processes and the removal of sediment by non-linear tidal flow. Rapid widening or deepening of the inlet at its landward margin leads to the deposition of a flood shoal. Under conditions of high sedimentation (and low diffusion) the flood shoal can become sufficiently well developed to present a physical barrier to sediment entering the lagoon. Under these circumstances backfilling can become significant. The infilling and backfilling processes are ameliorated by efficient down-slope diffusion which is controlled in the present model by a diffusion parameter, D. High diffusion coefficients slow inlet closure and allow sediment to propagate further into the lagoon.

Anatomy and Evolution of a Slope Channel-Complex Set (Neoproterozoic Isaac Formation, Windermere Supergroup, Southern Canadian Cordillera): Implications for Reservoir Characterization

Abstract A detailed architectural analysis was conducted in Isaac Unit 5 of the Isaac Formation in the Castle Creek area (east-central B.C., Canada). Isaac Unit 5 developed within a turbidite-dominated slope system on the Neoproterozoic passive margin of western North America where sediment gravity flows and mass movements were common. Isaac Unit 5 crops out over a 3.5-km-long section oriented oblique to mean paleoflow direction and represents a long-lived pathway for transport and deposition that accumulated ~ 100 m of mostly sand in a deep-marine slope setting. It consists of three stacked, high net-to-gross channel-complex fills (8–30 m thick) that correspond to shorter-term flow conduits, which, in turn, are capped by mudstone-rich units. Fine-grained conglomerate and sandstone beds deposited from high-concentration sediment flows constitute most of channel-complex fills. In addition, muddy debrite and slump deposits occur, but although laterally extensive, are volumetrically minor. Laterally persistent, thin-bedded strata (4–20 m thick) composed mostly of Bouma Tc–e turbidites occur at the top of each channel complex and indicate episodes of local complex abandonment (interchannel complex deposition). Different kinds of channel-fill elements were identified within Isaac Unit 5, each characterized by a unique combination of facies assemblage, internal geometry, and bounding surfaces. Most commonly, channel fills consist of amalgamated, thick-bedded, normally graded sandstone (Bouma Ta and Tab divisions) associated with backfilling processes. Poorly stratified mudstone-clast breccia, associated with Ta beds and dune cross-stratified sandstones occur in channel fills that exhibit aggradational and laterally migrating stacking patterns. Inner-bend levee deposits are associated with this type of channel fill. Channel fills with inclined sandstone- and mudstone-rich strata, on the other hand, relate to non-aggradational, high-sinuosity channel conditions that developed during gradual abandonment of the pathways for coarse-sediment transport. In contrast, sudden deactivation of these pathways, most probably related to abrupt updip channel avulsion, led to accumulation of structureless sandstone passively filling the deactivated thalweg. In terms of hydrocarbon reservoir analogues, each of the five different channel-fill elements have unique reservoir attributes (connectivity and continuity), amalgamated and poorly stratified elements having the best (excellent to good) reservoir attributes. Due to high amalgamation at channel-fill scale, channel complexes would represent individual fluid-flow units where only laterally discontinuous permeability barriers (< 500 m long) are present. On the other hand, extensive thin-bedded elements and muddy debrites constitute kilometer-scale barrier-type facies that would effectively compartmentalize channel complexes within the channel-complex set. Strata of Isaac Unit 5 document the detailed stratigraphic complexity, evolution, and reservoir characterization that can be expected in turbidite-dominated slope channel systems developed on passive margins. Further, it is a potential analogue for similar systems developed in continent-margin basins that until now were known mostly from subsurface core and seismic data.

Peaking Deflections of Flexible Pipe during Initial Backfilling Process

Most thermoplastic pipes exhibit peaking behavior during the initial backfilling process. It is shown with the actual field data that the peaking deflections can be beneficial for minimizing the long-term deflections of the pipe. An approach similar to the one proposed by Spangler is used to derive a formula for estimating the peaking deflections of thermoplastic pipe due to forces generated during the initial backfilling. The formula is tested in light of a number of field installation cases. The results show that the proposed formula predicts peaking deflections of both polyvinyl chloride and high density polyethylene pipes accurately under a variety of backfilled conditions.

English

In 1996, a multidisciplinary group of researchers at the University of Kentucky initiated a study on the Starfire surface mine in eastern Kentucky to evaluate the effects of soil compaction and two organic amendments on the survivability and growth of high value tree species. Three types of prepared rooting medium were examined: compacted spoil, lightly compacted spoil, and uncompacted spoil. The compacted spoil was prepared using normally accepted spoil handling techniques that resulted in a smooth graded surface. The lightly compacted spoil was loose-dumped and struck-off with one or two passes of a bulldozer. The uncompacted spoil was loose-dumped and not further disturbed. In addition, organic amendments (mulches) were evaluated within the three reclamation techniques. The organic amendments used were processed hardwood bark mulch and a combination of straw and horse manure mulch. The following six species of trees were planted: white oak (Quercus alba), white ash (Fraxinus americana), eastern white pine (Pinus strobus), northern red oak (Quercus rubra), black walnut (Juglans nigra), and yellow poplar (Liriodendron tulipifera). Five of the six species, the exception being white ash, showed increased survivability as compaction was minimized. Additionally, the loose-graded techniques led to enhanced growth in height for the seedlings. The addition of organic amendments also showed additional benefit but results varied by species and by treatment. Results definitively show that strike-off and loose-dump techniques improve seedling height and survival. The data also suggest that even a small amount of traffic (i.e., one or two passes per the strike-off method) may result in enough compaction to significantly reduce survival and growth in some species, such as yellow poplar and white pine. In the backfilling and grading process, spoil material should be placed and compacted according to standard engineering practices so that the required stability and approximate original contour is achieved. However, the top 1.2 to 1.8 meters (4 to 6 feet) of material should not be graded or only lightly graded so that it is as uncompacted as possible.

Surface traces and bioturbate textures from bubbler crabs: an indicator of subtropical to tropical tidal flat environments

The surface traces and bioturbate textures genereated by the bubbler crabsScopimera sp.,Dotilla blanfordi, Ilyoplax pusilla, etc., occurring in the tropical supra- to shallow-subtidal environments of the east coast of India have been studied. During foraging these organisms make various patterns on the substrate by their feeding pellets. These patterns are primarily dependant on grain-size characteristics, moisture conditions, and emergence level of the substrate. The crabs also produce typical ichnofabrics caused by back-filling of the burrows which do not exceed 10 cm in length. The internal fabric of the burrow-fills shows both concave-upward and concave-downward laminae resulting from upward or downward movement of the organism within the sediment. In sections perpendicular to burrow orientation the process of back-filling generates concentric laminae. Such a fabric occurs not only in coastal intertidal sediments, but also in sediments of estuarine point bars located 50 kilometres inland where these tiny crabs also occur. Such subsurface bioturbation features may represent a better tool for the identification of tidal environment than surface traces since the latter have a low preservation potential because of the erosional effects of wave and current action. The bioturbate texture, however, occurs over a wide range of the intertidal zone and, hence, in fossil record this bioturbate texture can be useful to identify tidal environments. These crabs can withstand a definite range of salinity and, therefore, this texture can also provide information about salinity conditions of palaeo-tidal environments.

Oxidation of Structured Silicon Thin Films for Inverse Silicon Square Spiral Photonic Crystal Fabrication

ABSTRACTPhotonic Band Gap (PBG) crystals are artificially engineered structures of periodically alternating dielectric materials that enable manipulation of light in unique ways. As proposed by O. Toader and S. John, large bandwidth PBG crystals based on the diamond lattice can be constructed by fabricating a two-dimensional periodic array of silicon square spirals. Furthermore, an improved photonic crystal can be constructed by fabricating the inverse of this structure, such that void square spirals are situated in a silicon backfill. This structure yields a theoretical maximum PBG of 24%, while the direct silicon square spiral structure yields a theoretical maximum of 16%. [1]The direct silicon square spiral structure has previously been successfully fabricated using the glancing angle deposition (GLAD) process [2]. The GLAD fabrication process uses advanced substrate motion and oblique incidence deposition to engineer precise nanostructures such as helices, chevrons, or polygonal spirals. These nanostructures are grown with lateral and longitudinal periodicity using a pre-patterned substrate consisting of a tetragonal array of relief structures.Upon successful fabrication of the direct silicon square spiral structure, it was proposed that fabrication of the inverse structure could be completed using a backfill process with a silica template [2]. A periodic array of silica square spirals would be fabricated using the GLAD technique. The template would then be filled with amorphous silicon using low-pressure chemical vapour deposition (LPCVD). To reveal the inverse silicon structure, the silica template would be removed by means of chemical etching with an isotropic chemical etchant. Creation of a suitable template for the inversion of silicon square spirals is an important step in the realization of the inverse silicon square spiral PBG crystal. However, we have seen empirically that silica square spiral films grown directly via the GLAD technique are structurally inferior to silicon films. We present an intermediate step for the fabrication of a suitable template, whereby a silicon structure is fabricated with appropriate geometries and subsequently oxidized. The procedure has been optimized to ensure a thorough oxidization of the silicon posts, while minimally distorting the structure of the square spiral template.

Evaluation of trench backfills at highway cross-drains

A highway cross-drain is an important element in a highway drainage system. This structure, however, has been related to the ride quality deterioration caused by pavement surface dips above this structure. In-situ probing techniques, such as the cone penetration test (CPT), miniature cone penetration test (Mini-cone) and dynamic cone penetrometer (DCP), were used to diagnose the causes of the dip problem. The field evaluations indicated that when a pavement surface dip occurred, the trench backfill underneath was softer than the adjacent subgrade soil. Because of its simplicity and potential as a quality control tool during the backfill process, the DCP test was given special attention. The field case histories and full-scale laboratory tests confirmed that DCP results can provide a reasonable estimation of the stiffness (modulus) of different trench backfills and subgrade soils. A possible way to prevent a pavement dip from occurring at a cross drain is to make a backfill stiffer than adjacent subgrade soils. The compaction results from the full-scale laboratory tests indicated that sand is not always successfully used for highway cross-drains due to its poor gradation and difficulty in compaction. Other materials, such as crushed limestone and recycled asphalt pavement (RAP), are good alternates because of their good workability and high stiffness when compacted.

Minería neolítica de sílex de Casa Montero (Vicálvaro, Madrid)

The research during the construction of the M-50 highway has allowed the documentation and conservation of the first Neolithic flint mine in the Iberian Peninsula. This work presents the preliminary results of the first phase of archaeological excavations. Thus far, the site plan documented shows a group of more than 2.500 extraction pits. Presented here are a description of the pits, their types and distribution, as well as the abundant archaeological materials found inside them. The characteristcs of the features and their backfilling processes indicate the existence of precise working strategies that may ompel a revision of our understanding of the Neolithic in the Madrid region. Moreover, three other phases have also been recorded in the site: Pleistocene, Middle Bronze Age and Contemporary.

Design of photonic band gap structures through a dual-beam multiple exposure technique

We present a dual-beam multiple exposure technique that can generate complex 2-D and 3-D band gap template structures in a photosensitive material. The system parameters related to the planar interference pattern produced by two laser beams and reorientation effect of the sample relative to these planes is presented. Structures such as the 2-D, square and hexagonal arrays of dielectric “rods” and “holes” and the 3-D, cubic, Yablonovite and other profiles are given. We perform band gap calculations on these structures when the dielectric contrast has been increased using a backfill process and discuss techniques for increasing the band gap by sculpting the dielectric profile.