Introduction of each part of retaining wall
In the cross-section of retaining wall, the part directly contacted with
the supported soil is called the back of the wall; the empty part
opposite the back of the wall is called the wall; the part directly
contacted with the foundation is called the base; the top of the wall
opposite to the base is called the top of the wall; the front end of the
base is called the toe of the wall; and the back end of the base is
called the heel of the wall.
1. Wall Structure
1) back of the wall
The back of the inclined wall is suitable for the shoulder wall or
embankment wall with flat ground at the cutting wall and the toe of the
wall. The slope of the back of the inclined wall should not be slowed
down to 1:0.3, usually from 1:0.15 to 1:0.25.
The oblique wall back is suitable for embankment wall and shoulder wall.
It is commonly used from 1:0.15 to 1:0.25. Low walls not exceeding 4m
can be used with vertical wall back. The convex broken-line wall back is
mostly used for cutting wall, but also for shoulder wall. The wall
height ratio of upper and lower walls is generally 2:3. Weight-balancing
wall is suitable for shoulder wall and embankment wall in steep
mountainous terrain. It can also be used for cutting wall. The slope of
the top wall is 1:0.25-1:0.45, the lower wall is about 1:0.25, and the
wall height ratio of the upper wall to the lower wall is generally 2:3.
2) The wall surface is generally flat, and the gradient should be
coordinated with the gradient of the back of the wall. Wall slope
directly affects the height of retaining wall. Therefore, when the cross
slope of the ground is steep, the slope of the wall is generally
1:0.05-1:0.20, and the low wall can be steep and straight. When the
ground is gentle, it is more economical to use 1:0.20-1:0.35.
3) The width of the top wall is the smallest. The masonry retaining wall
is not less than 50 cm and the dry masonry is not less than 60 cm.
Masonry shoulder wall top should generally be made of coarse stone or
concrete, the thickness of which is 40 cm. If no cap is made, for
shoulder wall and cutting wall, the top of the wall should be built with
large stones, jointed with mortar, or flattened with No. 5 mortar, the
thickness of which is 2 cm. The top of the dry retaining wall is within
50 cm in height. No. 25 mortar is used to increase the stability of the
wall. The height of the dry retaining wall should not be greater than 6 m
4) In order to ensure traffic safety, guardrails should be set on the
top of shoulder walls in steep terrain or over-high and over-long areas.
In order to keep the minimum width of soil shoulder, the distance
between the inner edge of guardrail and the edge of road surface should
be no less than 0.75m for the second and third grade roads and no less
than 0.5m for the fourth grade roads. Guardrails are divided into two
types: wall type and column type. The material, height and width of
guardrails are determined according to actual needs.
1) Basic type
Most retaining walls are built directly on natural foundations. When the
foundation bearing gravity is insufficient and the topography at the
toe of the wall is relatively flat, and the wall body is over a certain
height, in order to reduce the compressive stress of the foundation and
increase the stability against overturning, the enlarged foundation is
often used. When the compressive stress of the foundation exceeds the
bearing capacity of the foundation, the widening value should be larger.
In order to avoid the step of the widened part being too high, the
reinforced concrete floor can be used.
2) Foundation embedding depth for soil foundation should meet the
following requirements: 1) when there is no erosion, it should be at
least 1m below natural ground; 2) when there is erosion, it should be at
least 1m below the scour line; 3) when affected by frost heave, it
should be at least 0.25m below the freezing line; when the frost depth
exceeds 1m, it should be 1.25m, but the foundation should be compacted
with a certain thickness of sand or gravel cushion, cushion. The bottom
of the layer should also be at least 0.25m below the freezing line.
3. Drainage facilities
Retaining wall drainage measures usually consist of surface drainage and wall drainage.
1) Ground drainage, mainly to prevent surface water from infiltrating
into the soil or foundation behind the wall, has the following methods:
(1) Setting up surface drainage ditches to intercept and divert surface
water; (2) compacting the top surface of backfill soil and loosening
soil on the surface to prevent rainwater and ground water seepage, and
laying paving layer if necessary; (3) The side ditch in front of the toe
of cutting retaining wall should be paved and strengthened to prevent
side ditch water from seeping into the foundation.
2) Wall Drainage
A drainage pipe (Fig. a) should be installed above the ground in front
of the wall. When the wall is high, a drainage hole (Fig. b) can be
installed on the top of the wall. The size of the drainage hole can be
determined by the square hole of 5 cm *10 cm, 10 cm *10 cm, 15 cm *20
cm, or the round hole of 5-10 cm in diameter. The hole spacing is
generally 2-3 m; for the immersed retaining wall, the hole spacing is
generally 1.0-1.5 M. In arid areas, the hole spacing can be increased
appropriately. The outlet of the lower drainage hole should be 0.3 m
higher than that of the ground or the front wall.
In order to prevent water from infiltrating into the foundation, the
bottom of the lower drainage hole should be paved with clay water-proof
layer of 30 cm thick, and the inlet part of the drainage hole should be
paved with coarse-grained material filter layer to avoid the blockage of
the channel. When the permeability of the backfill is poor or frost
heave may occur, the sand and pebble with thickness not less than 0.3 m
should be laid in the range from the lowest drainage hole to 0.5 m below
the top of the wall.
4. Settlement and expansion joints
Flat stone should be used on both sides of dry retaining wall joints to form vertical joints.