FOUNDATIONS
| section | section | ||
| Interpretation of terms | 1 | ||
| Adjacent buildings, support of | 12 | Investigation of building site. | 2 |
| Ants’ nests. | 10 | Made-up ground | 9 |
| Bearing capacity, maximum safe | 5 | Narrow foundations | 6 |
| Bearing pressure, maximum. | 5 | Non-cohesive soils | 6 |
| Cavities | 11 | Piling | 21 |
| Collapsing subsoils | 8 | Stable foundation, provision of | 4 |
| Concrete foundations | 18 | Steel foundations | 19 |
| Different levels | 16 | Support of adjacent buildings | 12 |
| Drainage of building site | 3 | Termite proofing | 23 |
| Empirically constructed foundations | 22 | Termites | 10 |
| Excavations: depth | 14 | Trenches close to buildings | 13 |
| Foundations material | 17 | Underpinning adjacent structures | 12 |
| narrow | 6 | Undesirable excavations | 11 |
| piers. | 20 | Watercourses | 3 |
| Heaving subsoil | 7 |
ARRANGEMENT OF SECTIONS.
Preliminary
- Interpretation of terms
Part 1
BUILDING SITES AND EXCAVATIONS.
2. Investigation of building site.
3. Drainage of building site
4.Provision of stable foundation
5.Maximum allowable bearing pressure on and maximum safe bearing capacity of subsoil.
6. Narrow foundations on non-cohesive soils.
7.Heavy subsoils
8.Collapsing subsoils.
9.Made-up ground.
10.Ants nests and termites.
11.Undesirble excavations and cavities.
12.Underpinning and support of adjacent buildings and structures
13.Trenches close to buildings.
14.Excavations :depth below ground-level
15.Foundations to be horizontal or horizontally stepped
Part II
CONSTRUCTION OF FOUNDATION
16.Different levels.
17.Foundation material
18.Concrete foundations
19.Steel foundations
20.Foundation piers
21.Piling
22.Empirically constructed foundations
23.pre-constructional termite -proofing
Schedule: Required method of recording soil profiles.
Preliminary
1. INTERPRETATIONOF TERMS.
In this Chapter-
“bearing area of foundation” means the contact area between the underside of the foundation and the subsoil;
“foundation” means that part of the building or structure which is in direct contact with, and transmits loads to, the subsoil;
“maximum allowable bearing pressure” means the maximum allowable net loading intensity on the subsoil in any given case, the following being taken into account: the maximum safe bearing capacity, and the ability of the structure to accommodate itself to this settlement;
“maximum safe bearing capacity” means the maximum net loading intensity which the subsoil will safely carry without risk of shear failure, irrespective of any consolidation settlement which may result;
“net loading intensity” means the additional intensity of loading on the subsoil or any horizontal plane due to the mass of the new building or structure, including earthworks if any; that is to say, it is the difference the total intensity of pressure before building operations are commenced and the total intensity of pressure after the structure is complete and fully loaded;
“sleeper wall” means a foundation wall erected between other foundation walls to provide an intermediate support to the lowest floor, and having no corresponding wall directly above it;
“subsoil” means the ground which receives the load from the foundation.
2. INVESTIGATION OF BUILDING SITE-PLANS.
When required by the local authority to do so and subject to the provisions of subsection(1) of section 22 of this Chapter and section 23 of Chapter 2, every building site shall be investigated from the point of view of soil conditions which will affect the foundations by a person who, to the satisfaction of the local authority, is qualified by training and experience to do so, and, if required by the local authority a copy of the report of the site investigation shall be submitted to such authority. Except where the local authority permits otherwise, such investigation shall include one or more soil profiles recorded in accordance with the Schedule.
3. DRAINAGE OF BUILDING SITE.
(1) If a building is, or to be, so situated that water of any kind will drain towards it, adequate drainage shall be provided to divert such water away from the building in such a manner that no erosion of the soil supporting the building and no dampness arising from such water which might adversely affect the stability of the building will occur.
(2) No building shall be erected in or adjacent to any natural watercourse unless the floor level of such building is raised above the maximum known flood level of the watercourse, and precautions are taken, to satisfaction of the local authority, to ensure no obstruction occurs to the flow of slood waters in the watercourse.
4.PROVISION OF STABLE FOUNDATION.
Every building, wall or structure shall be supported on a stable foundation designed and constructed to transmit safely to the subsoil the total load to be carried by the foundation without undue differential settlement of the building or structure:
Provided that-
i) the local authority may permit the omission of such foundations where the building is supported directly on rock; and
ii) any decision taken by the local authority regarding the classification of a subsoil or to require or to dispense with the making of a site investigation or on the recording of one or more soil profiles on the building site shall not
involve the local authority in any responsibility for the safety of the proposed building or structure.
5. MAXIMUM ALLOWABLE BEARING PRESSURE ON, AND MAXIMUM SAFE BEARING CAPACITY OF, SUBSOIL.
(1) Empirical values.- The net loading intensity applied to the subsoil shall not exceed the maximum allowable bearing pressure of the subsoil, and such maximum allowable bearing pressure shall in no case exceed the maximum safe bearing capacity of the subsoil.
(2) In the absence of tests or other supporting evidence, and subject to the provisions of section 6, the maximum safe bearing capacity of the subsoil shall be deemed to be set out in the Table
(3) Where there is any doubt as to the classification of a subsoil, the decision of the local authority shall be accepted in the absence of professional expert advice.
(4) In arriving at the value of the maximum allowable bearing pressure in any particular case, account shall be taken of the amount and kind of settlement which may be permitted in the building or structure.
(5) Assessed values of maximum allowable bearing bearing pressure on subsoil.- The value of the maximum safe bearing capacity of the subsoil and the maximum allowable bearing pressure on the subsoil may be assessed by a person who, to the satisfaction of the local authority, is qualified by training and experience to do so.
(6) Such person shall embody such assessments in a report which he shall lodge with the local authority, which may accept and adopt assessment.
(7) If the local authority is not satisfied with the report, it may call for a second assessment of the value of the maximum bearing allowable bearing pressure thereon by a second and similarly qualified independent investigator
(8) The second investigator shall submit his assessment in a report to the local authority, which shall be entitled, if the assessed values in the two reports differ, to decide which shall be adopted.
(9) The maximum allowable bearing pressure on the subsoil shall not exceed the assessed value thereof which has been adopted in terms of subsection(6) or (8).
TABLE
MAXIMUM BEARING CAPACITY FOR SUBSOILS UNDER HORIZONTAL FOUNDATIONS AT 600 MILLIMETERS DEPTH BELOW THE ADJOINING FINISHED GROUND-LEVEL SUBJECT TO VERTICAL STATIC LOADING
| 1 | 2 | 3 | 4 |
| Class | Type and description of soils and rocks | Maximum bearing Capacity in Kilopascals. | |
| i. Rock | 1 2 3 | Fresh Rock Massively bedded, intact, igneous, metamorphic or sedimentary requiring blasting for excavation. fresh rock, fractured or jointed which can be excavated with difficulty by pneumatic picks but which usually requires light blasting. Decomposed rock to be assessed as soil as below. | |
| ii. Non-Cohesive soils | 4 5 6 7 | Compact well graded sands, gravels and gravel sand mixtures Permanently above all water tables. Compact well graded sands, gravels and gravel sand mixtures Permanently above all water tables at any stage of life of the structure. Compact but poorly graded sands, gravels and gravel sand mixtures Permanently above all water tables. lose sands and gravels. | |
| iii. Cohesive Soils | 8 9 10 11 12 | Very stiff clays, sandy soils, silty clays, sandy silts and silty sands. stiff clays, sandy soils, silty clays, sandy silts and silty sands. Firm clays, sandy soils, silty clays, sandy silts and silty sands. Soft clays, sandy soils, silty clays, Sandy silts and silty sands. Very soft clays, sandy soils, silty clays, sandy silts and silty sands | |
| iv. Artficially ocurring soils | 13 | Made up ground, compacted fills, waste dump and the likes. | |
6. NARROW FOUNDATIONS ON NON-COHESIVE SOILS.
Notwithstanding the provisions of subsections (1),(2),(3) and (4) of section 5, the maximum allowable bearing pressure for non-cohesive soils where the least lateral dimension of the foundation is less than 1 meter shall be ascertained by the formula-
maximum allowable bearing pressure = P x b kilopascals
where-
P= the maximum allowable bearing pressure for that type of soil prescribed in subsections (1), (2), (3) and (4) of section 5 , in kilopascals; and
b = the least lateral dimension of the foundation, in meters.
7. HEAVING SUBSOIS.
Where a heaving subsoil is suspected at the building site ( as where shattered or micro-shattered desiccated cohesive subsoil is present) or where previous experience in the area concerned indicated the presence of such a condition, the local authority-
a) may require a report to be submitted with the building plans, specifying and justifying the measures proposed to be taken to make provision for the differential movements in the building which are likely to arise; and
b) shall have the power to enforce these proposed measured in full or in part.
8. COLLAPSING SUBSOILS.
Where a collapsing subsoil is suspected at the building (as where loose fine sands or soft damp silty sands, of altered Aeolian origin or from the decomposition of certain granites, are present in the subsoil), the local authority-
a) may require a report to be submitted with the building plans, specifying and justifying the measures proposed to be taken to make provision for the possible differential settlements which may occur in the building; and
b) shall have the power to enforce these proposed measures in full or in part.
9. MADE-UP GROUND.
(1)No foundations shall bear on fill or other made-up ground except where the local authority has-
a) been provided with a thorough report on the state of the ground; and
b) approved precautions proposed to ensure the stability of the proposed building.
(2) Any precautions approved in terms of subsection(1) may be enforced by the local authority.
10. ANTS’ NEST AND TERMITES.
(1) Where the nests of ants and termites are encountered, or the roots of trees have to be removed, during excavations for the foundations, the resulting holes shall be refilled and consolidated to the satisfaction of the local authority.
(2) Where the local authority considers that there is a danger to timber from insect pests, or that the area in which a site is located is infested with termites, it may require that-
a) the soil under the building and foundations be poisoned against termites; and
b) the floors and frame-members of timber-frame buildings be impregnated with a preservative in accordance with the appropriate recommendations of SABS 05, Preservative treatment of timber (metric).
11. UNDESIRABLE EXCAVATIONS AND CAVITIES.
Where an excavation, ditch, pond watercourse, made-up ground, or similar condition adjoins or is on or adjacent to the subsoil on which any building is to be erected, and, in the opinion of the local authority, is likely to impair the stability of the building-
a) the foundation of such building shall be constructed at such depth that the effect of such condition is entirely obviated; or
b) the excavation or cavity shall be adequately backfilled and consolidated with approved material, or
c) such other works shall be undertaken as are adequate for the purpose of securing the stability of the building to be erected.
12. UNDERPINNING AND SUPPORT OF ADJACENT BUILDINGS AND STRUCTURES.
Where an excavation is liable to cause consequential damage to adjoining buildings, structures, or property, regard shall be had to the provisions of Part II of Chapter 2.
13. TRENCHES CLOSE TO THE BUILDINGS.
No excavation or trench for building purposes shall be made closer to a building than a distance equal to one and one-half times depth of the excavation or trench, or, 1,25 meters, whichever is greater, unless the local authority is satisfied that the stability of such building will not be impaired thereby.
14. EXCAVATIONS: DEPTH BELOW GROUND-LEVEL.
(1) Excavations for foundations shall be taken down to firm natural ground, except as otherwise provided in section 9.
(2) Unless a foundation is placed on solid rock, the bottom of the foundation shall be not less that 450 millimeters below the adjoining finished ground-level unless otherwise authorized by the local authority.
(3) If a foundation is placed on solid rock, the bearing area shall be cleaned and, if necessary, stepped or dowelled adequately to prevent lateral movement.
15. FOUNDATIONS TO BE HORIZONTAL OR HORIZONTALLY STEPPED.
(1) Except otherwise provided in section 14 or as shown in the plans approved by the local authority, the surfaces of contact between a foundation and any wall, pier or column, and all bottom surfaces of foundations, shall be horizontal or in the form of steps with horizontal and vertical surfaces.
(2) Where such steps are made in the longitudinal section of the foundation, the portions of the foundation on adjacent levels shall overlap for a distance at least equal to the vertical thickness of the foundation or the difference between adjacent levels, whichever is greater.
16. DIFFERENT LEVELS.
(1) Where the bottom surfaces of foundations in a building submitted for approval shall, where required by the local authority, include sectional elevations showing such variations in level.
(2) Wherever such changes in level occur, adequate provisions shall be made for the proper support of the higher foundation.
Part 2 : CONSTRUCTION OF FOUNDTIONS.
17. FOUNDATION MATERIAL.
All foundations below finished ground-level shall be constructed of plain or reinforced concrete, except that-
a) masonry foundations constructed of stone, brick or block shall be permitted, provided that they comply with the provisions of Chapter 5 and, further, with the provisions of section 22; and
b) structural steel shall be permitted in according with the provisions of section 19.
18. CONCRETE FOUNDATIONS.
(1) Plain concrete foundations.- Concrete in plain concrete foundations shall be proportioned and mixed in accordance with the provisions of Chapter 3.
(2) When flexural calculations are made, a plain concrete foundation shall be designed on the assumption that critical sections are at the face of the wall, pier or column which it supports, and, in a stepped foundation, also at the face of each step.
(3) A foundation referred to in subsection (2) shall be so proportioned that maximum tensile stress at any critical section will not exceed 0,03 times the design 28-day compressive strength of the concrete, shall be determined in accordance with the provisions of Chapter 3.
(4) When flexural calculations are not made, the ratio of the vertical thickness of any plain concrete foundation to its maximum projection beyond any face of the wall, pier or column which it supports, and the ratio of the depth to the projection of any step the cross-section of the foundation, shall be not less than 1,5, if the bearing pressure on the subsoil is not greater than 300 kilopascals.
(5) If the bearing pressure is greater than 300 kilopascals, the ratio specified in subsection(4) shall be increased by a minimum value of 0,1 for each increase of 50 kilopascals or remaining part thereof over 300 kilopascals in the bearing pressure under the foundation.
(6) For plain concrete foundations supporting columns and sleep-piers, the punching shear stress calculated on the area obtained by multiplying the perimeter of the column or sleep-pier by the thickness of such foundation shall not exceed 0,06 times the design 28-day comprehensive strength of the concrete determined as described in subsection (3).
(7) Plain concrete foundations are permitted to be constructed in accordance with the empirical rules set in section 22.
(8) Reinforced- concrete foundations. – Reinforced-concrete foundations shall be designed and constructed in accordance with the provisions of Chapter 3.
19. STEEL FOUNDATIONS
(1) Structural steel sections used in foundations shall have a concrete cover with thickness of at least 75 millimeters, and all spaces between adjacent sections shall be filled with concrete, Grade 20.
(2) Except where a foundation comprising structural steel members surrounded by concrete has been specifically designed to act as a reinforced member as a whole, the concrete casing shall not be taken into account in determining the stresses in the structural steel members, which shall be designed in accordance with the provisions of Chapter 3.
(3) Structural steel beams used used in a grillage foundation shall rest on at least 200 millimeters of concrete of the grade specified in subsection (1).
20. FOUNDATION PIERS.
(1) Foundation piers shall be constructed of concrete or of reinforced masonry or reinforced brickwork:
Provided that, wherever the eccentricity of the centre-line of its load with respect to the centre-line of a foundation pier exceeds one-sixteenth of the height of the pier or one-tenth of the least lateral dimension, the pier shall be reinforced, and shall be designed and constructed in accordance with the requirements of these by-laws for reinforced concrete or reinforced brickwork
(2) The height of a plain concrete foundation pier shall not exceed twelve times its least lateral dimension.
(3) When the height of such pier does not exceed six times its least lateral dimension, the compressive stress therein shall not exceed 0,2 times the design 28-day compressive strength of the concrete.
(4) When the height of the pier exceeds six times but does not exceed twelve times its least lateral dimension, the compressive stress in such pier shall not exceed-
(1.3 – (L÷20D)) * p
Pascals
where
L = the height of the pier, in meters
D = its least lateral dimension, in meters, and
p = the permissible stress for (L÷D) = 6, in pascals.
(5) Subject to the provisions of subsections (6) and (7), reinforced concrete foundation piers shall be designed in accordance with the requirements for reinforced concrete columns, and such requirements shall be determined in accordance with the provisions of Chapter 3.
(6) If the soil provides lateral support, such piers may be designed without reduction of permissible stress on account of slenderness, where the ration of the effective height, determined as specified for concrete, to the least lateral dimension of the pier, does not exceed 18
(7) Where such ration exceeds 18, the permissible stress in the pier for such conditions of support from the soil shall be-
(1,5 – L’ divided by 36D ) *p’ pascals
where-
L’= the effective height of the pier, in meters
D= its least lateral dimension, in meters, and
p’= the permissible stress for L’/D=18 , in pascals
(8) Whenever the base of any foundation pier is made larger than its shaft, the base of the pier shall have a vertical thickness of not less than 150 millimeters as its edge. In such cases, the effective height of the pier shall be deduced from height measures from the top of the enlarged base to the underside of the member supported by the pier.
21. PILING.
(1) Details of piled foundations shall be submitted for the approval of the local authority as [part of the working-drawings provided for in section 14 of chapter 2, and shall include-
a) drawings and complete specifications for the piles and the loads which they have been designed to carry; and
b) if required by the local authority, the designed calculations and the methods proposed for driving or constructing piles.
(2) If deemed necessary by the local authority, tests shall be made, at the owner’s expense, to determine whether the piles will safely carry the loads specified.
(3) Complete field record, giving full details of the construction and the placing or driving of the piles, shall be kept for each pile in all piled foundations by the person constructing such foundations.
(4) Such records shall be available for the inspection by the local authority at all reasonable times.
22. EMPIRICALLY CONSTRUCTED FOUNDATIONS.
(1) In any case where the local authority is satisfied, from a knowledge of the subsoil conditions in the locality within which a proposed building is to be situated, or from experience of the behavior of buildings in such locality, that it would not endanger a proposed building to do so, it may permit the erection of such building without a site investigation in terms of section 3.
(2) Unless the local authority specifically calls for a site in terms of section 2, buildings may be erected without such an investigation in cases where-
a) the proposed building is a dwelling-house not exceeding a height of two storeys; or
b) the proposed building is a single-storey building, the supporting walls of which do not exceed 4 meters in height.
(3) Buildings falling within the description contained in subsection (2) may be built on foundations constructed in accordances with the empirical rules contained in subsections (4) to (7).
(4) Concrete foundations shall so be constructed that-
a) the foundation under sleep-piers not less than 450 millimetres either in length or in breadth, and the width of foundations under sleeper-walls shall be not less than 300 millimetres;
b) the vertical thickness of other foundations shall be-
i) not less than 200 millimetres for walls of 200-millimetre thickness and over;
ii) not less than 150 millimetres for walls of less than 200-millimetre thickness;
c) the width of foundations under walls, other than sleep-walls, shall be not less than the thickness of the wall plus twice the vertical thickness of the foundation.
(5) For the purposes of subsection (4)-
a) the thickness of the wall shall be measures just above the ground-floor level, except where the foundation wall is higher than 1,5 metres, in which case the thickness of the wall shall be measures just above the foundation; and
b) the thickness of a cavity-wall shall be regarded as the sum of the thickness of leaves of such a wall.
(6) Masonry Foundations constructed with stone, brick or solid concrete blocks shall be permitted:
Provided that the local authority may require that any such foundations be built on an approved bed of concrete.
(7) Masonry foundations shall comply with the following requirements-
a) such foundations or columns or sleeper-piers hall be permitted only on rock or on coarse sand or compact gravel;
b) the vertical thickness shall be not less than 225 millimetres and not less than twice the maximum projection from the face of the wall, column or pier being supported, whichever is the greater, exclusive of any bed of concrete which may have been provided;
c) the lateral dimensions of foundations under sleep-piers and walls shall be as given for concrete foundations in paragraph (a) of subsection (4);
d) the width of other foundations shall be-
i) for single-storey buildings, not less than the thickness of the wall plus 150 millimetres; and
ii) for double-storey dwellings, not less than twice the thickness of the wall;
e) when such a foundation is stepped is cross-section, the height of any step shall not exceed 225 millimetres and the projection of any step shall not exceed half the height of the step;
f) the mortar used shall be not weaker than class A or class B, as specified in Chapter 5.
23. PRE-CONSTRUCTIONAL TERMITE-PROOFING.
All pre-constructional termite-proofing shall comply with C.A.S. No. C.A. &.
SCHEDULE (section 2)
REQUIRED METHOD OF RECORDING SOIL PROFILES
I. Soil profiles recorded on the building site as required by section
2 shall be recorded as specified in this Schedule.
INFORMATION ON SOIL PROFILES
2. Every soil profile shall be recorded from data obtained from a freshly excavated trial hole carried to a depth sufficient to ensure that the whole depth of subsoil which will be affected by the building has been adequately examined. Each stratum in any profile shall be described in terms of color, consistency, soil structure and soil type. The level of the permanent water-table and of any perched water-table which may be present, and the date on which the examination is made, shall be recorded on each profile.
CLASSIFICATION AND DESCRIPTION OF SUBSOILS TO RE GIVEN IN SOIL PROFILES
3. The following standard terminology and descriptions shall be used in all soil profile records—
(a) Soil colour.–Soil colour shall be described by comparison with standard colours given in the Mansell* Soil colour charts or, alter-natively, in the Burlane Colour chart. Two colours should be recorded for each stratum–
(i) the colour of a slurry of the consistency of thick cream rubbed with water on the palm of the hand; and
(ii) the colour of the natural soil, asobserved in the freshly cut profile;
(b) Consistency.—
The soils shall be described as falling into either the cohesive or the non-cohesive (granular) 4roup, and shall be further described within each group according to consistency (a measure of the hardnes of the soil in its natural state) into one of the grades set out in the Table, in which the moulding referred to means the moulding cf a fresh sample taken from a trial hole are the freshly exposed surface referred to is the surface within a trial hole:
Soil structure.–Soil structure, which is a description of the jointing condition in the natural soil, shall be recorded as one of the followinetypical structural forms—”intact” indicates an absence of fissures ce joints;
“fissured” indicates the presence of random closed joints. These are frequently stained with iron and manganese oxides. When cut with a pick, the soil tends to b along these joints:
“slickensided” indicates the presence more or less continuous joints, which striated and highly polished;
“shattered” indicates fissures in which joi have opened up and arc filled with The soil fragments are usually stiff or s stiff, and break out in a cubical or gran fashion when the soil is cut with a Generally the fragments break down difficulty when wetted and worked in hands;
“micro-shattered” means shattered ex Seely, with the shattered fragments of size of coarse sand grains. When mi shattering is well developed, and the is cut with a pick, it appears granular, these grains break down into a clay or or some combination of clay and silt, rubbed with water on the palm of hand. Micro-shattering is a sign potential heaving conditions;
“laminated” or
“foliated” indicates that soils show the laminated or &Ilia structure of the parent rock from w they are derived;
(d) Soil type. —Soil type, which is a descriptive mainly according to the grain-size of soil, shall be recorded as rock, or as one the types set out below. Most natural sd arc a combination of one or more of types described, and in any description such a soil the adjective is used to denote lesser type; for example, a silty clay is day with some silt, whereas a silt-clay approximately equal portions of both type The basic classification of soils into gravel sands, silts, and clays relates to the drairut characteristics of the soils. All clays ■ most silts are slow-draining soils, giving ri to time-effects in soil behavior which of great importance, particularly as regatt the resistance of the soil in shear. Consequently (depending upon the type
engineering structure under consideration), differences in the behaviour of silty clay, silt-clay or clayey silt are likely to involve only differences in time-effects; “fresh rock” means a natural geological material which has not been weathered, and normally requires blasting for break-ing in excavation; alternatively, where the rock is intact, a solid core can be recovered by diamond drilling with a single-tube core barrel, using water as a drilling-fluid; “decomposed rock” means natural geo-logical material which can be excavated without blasting; a solid tort cannot be recovered by drilling with a single-tube core barrel using water as a drilling-fluid; coring requires sophisticated drilling prac-tices. Such decomposed rock should be , classified and described as a soil; “boulders” means fragments of rock larger than 150 millimetres in cross-sectional dimension. State whether these are rounded, subongular or angular. Record the rock types and range of sizes. State whether there is a matrix in the voids between the boulders. Describe this matrix as a soil, and state whether or not it fills the voids between the boulders. (Where the volume of matrix material is significantly greater than that of the “minimum voids”, the engineering be-haviour of the soil will be determined by this matrix, and not by the boulders.);
“gravel” means fragments of rock measuring between 150 millimeters and three millimeters across. The description shall follow that for boulders as above; particular care shall be given to the description of the matrix;
“sand” means discrete particles which are clearly visible to the naked eye. Sand is clearly distinguished by these gritty particles, which do not break down when rubbed with water on the palm of the hand;
“silt” means soil having particles which are smaller than 60 micrometers but larger than two micrometers. In general, silts arc very fine, discrete particles which may be felt when rubbed with water on the palm of the hand. When a small quantity of the wetted soil is placed on the tongue, the particles can be clearly distinguished against the teeth. When molded with water into a ball, it exhibits dilatancy;
“clay” means soil having particles smaller than two micrometers. In general, the particles are flaky, and, when rubbed on the palm with water, this soil has a soapy or greasy feel. There is no feel of grittiness when a small quantity of the soil is placed between tongue and teeth.
SUBSURFACE WATER CONDITIONS
(I) “The water-table” is that level or those levels in the soil where the water in pores of the soil is at atmospheric pressure.
(2) “The permanent water-table” is the water-table which persists throughout the seasons of the year with only minor fluctuations of level.
(3) “A perched water-table” is a water-table which is only temporarily present in the soil: it will disappear and sometimes reappear, depending upon seasons or drainage conditions of the site.
| 1 | 2 |
| COHESIVE SOILS | NON-COHESIVE SOILS |
| (4. Silts and clays and com-binations of silts and clays with sand and gravel, generally slow-draining) | (i.e. gravels and clean sands, Facially free-drain-ing) |
| “Very soft” means easily molded in the lingers: a freshly exposed surface shows distinct hcel.marks when stood upon. | “Very loose” means very easily excavated with a spade: having a dry density Ins than about 1 450 kilograms per cubic meter. |
| “Soft” means can be molded in the fingers with strong Pressure; a freshly exposed surface shows faint heel-marks when stood upon. | “Loose” means lasing small resistance to shoveling or to penetration by hand bar; having a dry density of about 1 450 to 1600 kilogram per cubic meter. |
| “Firm” means very difficult to mold in the lingua, and difficult to cut with a hand spade. | “Medium dense” means having considerable resistance to shoveling or to penetration by hand bar, having a dry density of about 1600 to 1 730 kilograms pa cubic meter. |
| “Stiff” means cannot be molded in the fingers, and cannot be cut with a hand spade, and requiring hand picking for excavation. | “Dense” means having say high resistance to penetration by hand but and requiring a hand, pick for excavation; having a dry density of about I 790 to 1 900 kilograms per cubic meter |
| “Very stiff” means very difficult to excavate using a hand pick and requiring a pneumatic spade for economic excavation. | “Very dense” means having very high resistance to excavation by hand picking and requiring a pneumatic spade or pick for economic excavation: having a dry density of 1900 kilograms per cubic meter or more. |