ICS 93.080.20

ROMANIAN STANDARD

STAS 10796/3-88 Classification index G 71

Replacing: STAS 10796/3-79

Previous editions: 1979

Road works � CONSTRUCTIONS FOR WATER COLLECTION.

DRAINAGE AND TRENCHES - Design and laying-out specifications

Lucrări de drumuri � Constructii pentru colectarea apelor - Drenuri de asanare - Prescripţii de proiectare şi amplasare

Travaux routiers � Constructions pour la collecte des eaux � Drains d `assainissement � Prescriptions de conception et mise en place

Validation date: 1988-03-01

1 GENERAL TERMS

1.1 Scope

This standard refers to design and laying-out specifications for drainage trenches for road infrastructure and its contiguous area. Drainage trenches are road constructions necessary for the entrapment, collection, and evacuation of water seepages, as well as for the decreasing of ground-water sheet level when this can affect the behavior of the road body. No drainage trenches will be carried out if the ground-water sheet level is located at a depth more than 20 cm below the roadbed and if the land has a permeability coefficient higher than 10-3 cm/s according to STAS 1243-83. 1.2 According to STAS 10796/1-77, drainage trenches can be:

- longitudinal; - interception transversal; - cup-shaped; - slope banks; - drilled.

1.3 Drainage works are carried out according to the stipulations of this standard, to the gauge projects and to the execution documentations elaborated by specialty institutes.

1.4 Terminology, according to STAS 4032/1-82 and STAS 10796/1-77.

1.5 Normative references

- STAS 10796/2-79 Road works. Contiguous constructions for water collection and evacuation. Gutters, ditches, and side ditches. Design and execution specifications.

- STAS 2916-87 Road and railway works. The protection of slope banks and water effluent drains. General design specifications.

- STAS 1243-83 Foundation soil. Soil classification and identification. - STAS 6054-77 Foundation soil. Minimum frost depths. Zonation of Romania�s territory.

2 DESIGN SPECIFICATIONS

2.1 The drainage trenches design will be carried out taking into account:

- the location of the road platform in regard to the natural landscape line (acclivity, declivity, or mixed profile);

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STAS 10796/3-88 2 - the lithologic profile accompanied by the description of the soil layers (nature of the soil, physical and

mechanic characteristics and hydro-geological conditions in the area); - evacuation possibilities for the waters collected in the drainage system; - soil stability.

2.2 The depth of the drainage trenches will be established according to:

- frost depth, determined according to STAS 6054-77; - the maximum level of the ground-water sheet.

For the roads located in the mountainous area, the depth is set based on the chemical and mineralogical nature of the rocks and on the ground-water status, determined by geological and hydro-geological studies. 2.3 The depth of the drainage trenches carried out by manual digging is established based on the depth, according to table 1.

Table 1

In the case of longitudinal trenches carried out mechanically, the width is established based on the width of the digging equipment, but at least 25 cm. 2.4 The trench body, figure 1, comprises:

- raft for water collection and evacuation (1); - drain filling (2); - cased catch (3);

1 � foundation raft; 2 � drain filling; 3 � cased catch Fig.1

2.4.1 The trench raft can be:

- rigid - elastic

The rigid raft is carried out on soils that are stable, practically incompressible, of low or medium compressibility, according to STAS 1243-83. The elastic soil is carried out on soils of high or very high compressibility, and on soils that are affected by instability phenomena. 2.4.1.1 The rigid raft is made of class Bc 5 plain concrete, with a gutter on the upper side. The longitudinal slope of the raft trenches can be of 0.2 to 10 %.

The collection and leading of waters to rigid raft trenches is made through: - gutters covered by half-round catches 25 cm-long, pre-cast on building site, of class Bc 7.5 concrete, with a 30

cm exterior diameter (as shown in figure 2 a), and installed with a 2 cm interspace; - gutters covered in dry masonry, executed manually on the raft, as shown in figure 2 b;

Trench depth, in m (H)

Trench width, in m (L)

STAS 10796/3-88 3

- perforated PVC drain pipes, with bottom, according to technical regulations in force, with an interior diameter of 80 to 150 mm, as shown in figure 2 c;

- perforated PVC drainpipes, grooved, according to technical regulations in force, with an interior diameter of 65 to 150 mm, as shown in figure 2 d. grooved pipes are used for trenches with a maximum depth of 2.0 m.

Fig. 2

The access of water to the PVC pipes is supplied through slots of 1.0 by 5 mm or 1.5 by 5 mm, in a number that would lead to an active surface (for the water entering the pipe) of 24 to 50 cm2 per linear meter of pipe. 2.4.1.2 The elastic raft is made by means of:

- compacting the soil at the bottom of the trench digging, in the case of perfect trenches, figure 3 a; - a 20 cm-thick layer of ballast, in the case of imperfect trenches, figure 3 b.

Fig. 3

The longitudinal slope of elastic raft trenches will not exceed the maximal slope accepted for unprotected gullies and gutters, according to STAS 10796/2-79. NOTE � When the trench slope exceed the maximal slope accepted, steps of class Bc 5 plain concrete are required.

The slope for drilled trenches is established according to the length of the trench, with a 1 to 2 cm / m slope reduction. The collection and leading of waters to elastic raft trenches is made through:

- plain concrete sewage pipes according to STAS 816-80, having a diameter of 200 to 300 mm; - perforated PVC drainpipes, with bottom, having the characteristics of point 2.4.1.1.; - perforated PVC drainpipes, grooved, having the characteristics of point 2.4.1.1..

The pipes are set directly on the ground, at the bottom of the trench, as shown in figure 3 a, in the case of perfect trenches, or on a layer of ballast, as shown in figure 3 b, in the case of imperfect trenches. 2.4.2 The drain filling (figure 4) is made of 7 to 40 mm gravel, STAS 662-82, and of 0. to 71 mm ballast, STAS 662-82.

1 � Foundation raft; 2 � half-round catch; 3 � gravel; 4 � ballast; 5 � road gutter.

Fig. 4

STAS 10796/3-88 4

2.4.3 The cased catch is made of: - revetment masonred in rubble or rolling stones with cement mortar, as shown in figure 5 a, b, under the shape of a side ditch or a gutter, STAS 10796/2-79; - revetment made of plain concrete tiles cast on-site or of prefabricated tiles, STAS 10796/2-79; - clay clog covered by vegetal seeded soil, figure 5 c.

Longitudinal trtransversal tren 2.5 The evtrenches. The leaSTAS 6675/2-8200 to 300 mm

2.6 For trenout at a maximtrenches.

2.7 At the collected water

2.8 At the unatural ventilat

3.1 The lay- longitud

as in fig

a � Longi

Gutter S h C

Longitudinal drainage axis

ide Ditc

Fig. 5 enches, cup-shaped trenches, and slope banks trencches are made without cased catch.

acuation of the waters collected in the drainage

ding of waters to the evacuation trenches is m6, with a 90 to 110 mm diameter, or plain concre

diameter, STAS 816-80.

ch functioning control and maintenance, inspectionum distance of 70 m one from another, for direction

downstream end, drainage trenches are fitted with s, for functioning control and maintenance.

pstream trench end, ventilating shafts are requiredion.

3 LAYING-OUT SPEC

-out for drainage trenches is established for each treninal trenches are laid out along the road, under the gure 6;

tudinal trench; b � inspection chamber; c - interc

Roa

d ax

is Inspection

chamber axis

Roa

d ax

is

Roa

d ax

is

lay clog

hes are made with cased catch, while interception

trenches system is provided through evacuation

ade through smooth PVC pipes, according to te sewage tubes, with or without bottom, with a

chambers are required. These chambers are laid changes and at the intersection of two or several

trench heads, for providing the evacuation of the

with a view to reduce the soil humidity through

IFICATIONS

ch type specified under point 1.2., as follows: utter, the ditch, or under part of the road shoulder,

eption transversal trench; d � trench head

STAS 10796/3-88 5Fig. 6

- interception transversal trenches are laid out on road sections with declivities higher than 4%, under the road

bed foundation, at a 50 to 100 m distance one from another, and a slope-way tilt under un angle of about 60% to the road axis, at a depth H=1.0 to 1.5 m, as in figure 7, in the purpose of intercepting and evacuating the waters running through the road foundation;

a � Interception transversal tren

Fig. 7

- cup-shaped trenches are laid out on the acclivity slope banevacuating spring waters. Water evacuation is performed thro

a � Cup-shaped trench; b � ventilating

Fig. 8

Roa

d ax

is

Roa

d ax

is

Roa

d ax

is

Road axis

ch; b � trench head

ks, as in figure 8, in the purpose of capturing and ugh a trench head;

shaft; c � trench head

STAS 10796/3-88 6

- slope banks trenches are made up of transversal trenches bound with angle-shaped trenches according to figure 9. Transversal trenches are laid out at a 6 m distance, while angle-shaped trenches are laid out on one or several levels, according to the slope bank height.

s

h

trenches

Fig. 9

a � Transversal trench; b

� ventilating

haft; c � trench ead; d�angle-shaped

STAS 10796/3-88 7 - drilled trenches are laid out on one or several levels, suiting the morphology and hydrology of the land in that

area. At the same level, trenches can be set radially, in groups of 2 to 3 trenches, as shown in figure 10.

4 C

4.1 Drainage trenches can be carrie 4.1.1 In the case of manual digging, downstream, suitably supported, perma

4.1.2 In the case of building the trenthe trench body be coordinated lest the 4.1.3 In the case of drilled trenches,areas to be drained. The fitting of the ddrilling operation. 4.2 On lands that are stable and hsupport until depths of:

- 1.00 m, on plastically strong so- 1.50 m, on hard soils.

When the depth of the diggingor with slope banks, on natural humisupports. Diggings are signaled. 4.2.1 Keeping diggings open is forbrequired quota. 4.3 The soil resulted from the diggthe digging, and materials, at more than

Roa

d ax

is

Road axis

a � Drilled trenches; b � trench head Fig. 10

ARRYING-OUT SPECIFICATIONS

d out through manual or mechanical digging or drilling.

the trenches are carried out on portions of 4 to 6 meters of length, upstream to nently discharging the collected waters.

ch by mechanical digging, it is necessary that the digging and the building of digging be kept open.

drilling is carried out from a platform arranged so as to suit the levels of the rillings with PVC or perforated polyethylene pipes is carried out right after the

ave natural humidity, diggings can be performed with vertical walls, with no

ils and compact-state sands;

s exceeds these values, diggings are performed with vertically supported walls dity lands. Moreover, diggings on instable lands are also carried out under

idden. The trench body is carried out as soon as the digging has reached the

ing is temporarily deposited at a distance higher than 0.50 m from the edge of 2.00 m.

STAS 10796/3-88 8 4.4 The granular material from the trench body will be compacted as it is being laid, in order to prevent cased catch subsidence.

4.4.1 The catch made of clay soil clog is compacted in layers of 15 to 20 cm of thickness, at a compaction degree of 90 to 95%. 4.5 To ensure appropriate functioning for the drilled trenches, before they begin to operate, a low-pressure water washing will be performed. The water will be introduced in the drilling in several turns, through a hose.

_____________________ Project coordinator: MTTc � Vehicle, Naval and Airspace Ships Research Institute Eng. Gheorghe Niţoiu Final elaboration: Romanian Institute for Standardization Eng. Paula Stănescu

Contributors: − Constructions Institute � Bucharest − General headquarters for Railways Bucharest − Research Institute for Pedology and Agricultural Chemistry − Research Institute for Tehcnologic Design in Transports − Research and Design Institute for Urbanism, Housing and City

Administration