CONTENTS

1.0 INTRODUCTION...................................................................................................2

2.0 STRUCTURAL COMPONENT.................................................................................3

2.1 Thrust bed..................................................................................................3

2.2 Precast R.C.C. Box......................................................................................4

2.3 Front Cutting Shield & Rear Jacking Shield.................................................5

3.0 PUSHING OPERATION OF THE BOX.....................................................................6

3.1 Hydraulic Equipment..................................................................................7

3.2 Intermediate Jacking Station......................................................................8

4.0 DESIGN EXAMPLE.............................................................................................10

4.1 Introduction..............................................................................................10

4.2 Box pushing methodology........................................................................10

4.3 Analysis and Design methodology............................................................10

4.4 Material properties...................................................................................11

4.5 Primary load cases...................................................................................11

4.6 Detailed design calculations.....................................................................11

5.0 CONCLUSION....................................................................................................11

APPENDIX A

APPENDIX B

1.0 INTRODUCTION

This Present day Intensity of Traffic, both Rail & Road due to the fast

development of Industries and other Infrastructures, is very heavy and so it cannot

the disturbed, for construction of under bridges or Canal Crossings, drainage etc

by conventional construction methods. So to construct such structures, Box

Pushing Technique is developed where in R.C.C. Boxes in segments are cast

outside and pushed through the heavy embankments of Rail or Road by Jacking.

The required thrust is generated through thrust bed, as well as line and level of

precast boxes are also controlled

2.0 STRUCTURAL COMPONENT

2.1 Thrust bed

The thrust bed, thrust Beam and keys are designed in R.C.C. to resist the

required Thrust extorted by Jacking force and transfer it to soil at bottom and

sides. In cohesive soils even shallow piles are required to transfer the load.

Provision for jacking supports is made by providing suitable pockets in the thrust

bed to accommodate pin supports. During the construction of precast box

segments on the thrust bed, the thrust bed are filled with sand or any other filling

material, and the same is covered with screed layer of cement mortar of 50mm

thickness.

2.1 Casting bed showing jacking pin pockets in position

2.2 Construction of casting bed

2.2 Precast R.C.C. Box

The Precast Box is cast in segments of convenient lengths of Total pushing

length. The Box section is designed as per IRS / IRC codes of practice for loading.

Concrete grade normally kept as M-35. Front face of the precast box segment

which pierce into the embankment is provided with inclined edge as shown in the

following figure.

2.3 Front face of concrete precast segment

2.3 Front Cutting Shield & Rear Jacking Shield

The First Segment of the precast box is provided with a specially designed

structure named as cutting shield which forms the front working face with a cutting

edge fabricated from 16 to 20 mm thick M.S. Plates and housed on RCC Box

section with suitable anchor bolts. Necessary strengthening is provided by

stiffeners and face plates of Box in front on completion of jacking the outer shell of

the shield is cut and removed

The Rear Jacking shield is provided by anchoring steel plate on the face of

Bottom slab of RCC Box suitably designed to distribute the jacking load uniformly

on concrete area.

3.0 PUSHING OPERATION OF THE BOX

The purpose of pushing of Box is to form a horizontal opening below

ground or through embankments, can say a tunnel, by providing precast box units

underground or an embankment, without disturbing the overhead amenities, like

traffic & structures.

To reduce the frictional resistance, a thin film of Grease and thick gauge plastic

sheet is provided between the top of the thrust bed & Bottom of the Box. This is

done before casting of the Bottom slab of the box. A Glossy Epoxy layer is also

provided to reduce friction on the top and prevent the disturbance of the mass

over box to least during progress of pushing

Where mass of embankment is less or the soil is of poor quality, drag sheet

system is also considered for least resistance of friction and disturbance of mass

above box. This avoids disturbance of track structure due to the pushing operation

where minimum depth of earth cushion is provided over the top of box. Typical

drag sheet arrangement is shown in the following figure.

Figure 3.4 Drag sheet arrangement over box

Figure 3.5 Drag sheet arrangement over box with truss

Auxiliary beds are also provided for casting of the other segments with thin

film of grease and plastic and segments are then brought in alignment of pushing

as and when required as pushing progresses.

With the progress of jacking, the front unit with shield penetrates into the

embankment and there after excavation within the shield is done either manually

or mechanically and the excavated stuff is transported outside the working area.

After the first segment advances to the end of the thrust bed, the second

segment is brought in alignment of the front Box & intermediate jacking space is

lift between the two. The progress of pushing is kept continuous and the system of

side shifting of remaining box segments from Auxiliary bed and bring in pushing

alignment is adopted till total length is pushed.

3.1 Hydraulic Equipment

The entire Box Pushing system is matter of proper selection of Hydraulic

equipments, as tremendous driving force is required for pushing of medium to

large size of Boxes. So for this, Number of Jack units are provided in series for

distribution of pushing load evenly on the face of the concrete, and all Jacks are

operated simultaneously with a common power pack, which supplies uniform flow

of pressure through network of Hydraulic pipes of required pressure capacity,

commencing from front unit to rear unit. Jacking force is applied in sequence. This

way pushing cycles are repeated till total pushing is completed.

Figure 3.6 Jacking of end segment of box from thrust bed

3.2 Intermediate Jacking Station

As total length of Box is casted in Segments, each segment is pushed turn

by turn with necessary jacking force and so for this necessary intermediate jacking

stations are provided, with jacking pockets in bed & walls.

Figure 3.7 Jacking of intermediate segment

4.0 DESIGN EXAMPLE

4.1 Introduction

Design of RUB which is proposed for a rail connectivity taking off from

railway station is covered in this document. The RUB is a RCC box of size 1 x 7.5

x 5.888m which has to be constructed below the railway track. It is proposed to

use Box pushing methodology for making the underpass without interrupting the

rail traffic above it. Barrel length of the box is 22.0m.

4.2 Box pushing methodology

Box pushing Methodology is a well suited construction method for making

underpass below the rail tracks without disturbing the rail traffic. Number of RCC

box segments to be pushed is depending upon the barrel length of the RUB. In

this project, two box segments of 11.0m each is used. The entire operation takes

place by pushing the box against thrust bed, and removing the soil at the front end

of the first box segment. Thrust bed consists mainly of thrust wall, pin pockets and

keys for additional resistance. Thrust bed is designed for box pushing force which

depends on the frictional resistance of the soil.

4.3 Analysis and Design methodology

Analysis of the box has been done by moment distribution method

by considering all the loads on it and with suitable load combinations. IRC-6 : 2010

has been followed for arriving the effect of road traffic on the base slab. In addition

to these loads pushing force on the box and frictional resisting force due to soil

also considered for the design. Design bending moments and design shear forces

have been taken from the moment distribution method. The design of structural

elements has been carried out using IRS codes - Limit state method as per codes:

IRS Substructure Code, Concrete Bridge Code and Bridge rules.

4.4 Material properties

Table 4.1 Material Properties

Material Grade

Grade of Concrete for box M35

Grade of Steel reinforcement Fe 500

Grade of Steel reinforcement for Shear Fe 415

4.5 Primary load cases

i. Self weight, and earth fill over the box

ii. Super imposed dead load

iii. Rail Live load and traction forces (Bridge rules, IRS)

iv. Box pushing forces and resisting forces from the soil

v. Earth Pressure

vi. Surcharge Pressure(Due to DL & LL)

vii. Road traffic loads

4.6 Detailed design calculations

Detailed load calculation, analysis, Calculation of pushing force, Design of

RUB and thrust bed are provided in Appendix A

5.0 CONCLUSION

The entire system is purely technical, dependent on Hydraulic system, &

safest method of crossing underground / Embankment, without disturbing

overhead traffic / structures for R.U.B., Canal siphon and other drainage

crossings.

Appendix A

Design Calculations

Appendix B

Drawings