Soil studies are carried out to learn about the properties of the soil and the types of foundations that are appropriate for them. Various forms of soil studies, their reports, and appropriate foundations for various types of soils are described in this article. Test borings, delivered by a soil engineer, are used to investigate subsoil conditions (geotechnical). The number and position of borings are determined by the building type and site circumstances. Borings are typically placed 100-150 feet apart for uniform soil conditions, and 50 feet apart for more comprehensive work where soil footings are closely spaced and soil conditions are not level. Larger open warehouse spaces with fewer columns (long span) demanded less boring designs.
Table of Contents
Soil Investigations Surface
Borings must reach hard Strata (pass through unsuitable foundation soil) before continuing for at least another 20 feet into acceptable soil. The locations of the borings samples are marked on the engineer’s plan. These aren’t directly pulled from the intended columns. Borings show depth, soil classification (according to the unified soil system), moisture content, and, in some cases, ground water level. (Particle size, moisture content, and density are examples of physical attributes.) The recommendations in the subsurface soil study report should be based on testing of materials collected from on-site borings and should include: Recommendations for foundation construction based on soil bearing capacity Design suggestions for paving Compression of the soil Strength on the sides (active, passive, and coefficient of friction) Permeability Depth of frost.
Engineers working in the field of soil mechanics developed a simple classification system that tells them what attributes a particular soil has. The unified soil classification system is based on identifying soils based on their textural and plasticity properties, as well as classifying them according to their behaviour. Soils are commonly found in nature as mixes of particles of various sizes, with each of these components contributing to the soil mixture. The percentage of gravel, sand, and particles in the soil is used to classify it.Grain pattern. Characteristics of soil plasticity and compressibility The soil is assigned a descriptive name and a letter symbol indicating its main qualities in the unified soil classification system (uscs). The placement of a solid into its appropriate group is achieved via.
Classifications of Soil
Coarse Gained – soils made up of gravel and/or sands and containing a wide range of particles. When well drained and well restricted, these are ideal for foundations. They’re soils having a high carrying capacity. The G series, in particular (GW, GP, GM, GC). The percentage amount of gravel and sand is used to identify it. Fine-grained soils include Silts and Clays (L,H). Smaller silt and clay particles are present. These are good for foundations, however they will need to be compacted. The CL is the most appropriate of this series (L). The cohesive characteristics and permeability of these soils are used to identify them. Highly Organic Soils – These are soils that are typically exceedingly compressible and unsuitable for construction. They have grass and leaf particles in them.
The unified soil classification system associates particular grain size and textural features with soil names. This is especially true of coarse-grained soils. The names for silts and clay are based on the soil’s flexibility. The following are examples of relevant information from digging samples that can assist a geotechnical engineer in determining foundations: For coarse grain soil, particle size, mineralogical content, grain shape, and binder character are all factors to consider.Strength, moisture, and plasticity for fine-grained soils. A visual inspection can be performed to identify the behaviour of the soil when employed as a component in the construction of a proposed building in the early phases. The classification categories of the unified soil classification system can be used to classify soil.
problems of soil
Gravels that are properly drained and free draining can help to alleviate soil uplift stresses (GW, GP). Fine-grained soils including silts and clays can experience uplift forces, causing foundation shifting and the production of boils. Due to the possibility of frost,Regardless of the frost susceptibility of the various soil types, two requirements must be present at the same time for frost action to be considered: a source of water during the freezing period and enough time for the freezing temperature to reach the ground.Silts and clays (ML, CL, OL) are more vulnerable to freezing in general (as they contain moisture). Granular soils with good drainage are less likely to freeze and cause foundation difficulties.
The permeability of soils is directly reflected in their drainage characteristics. Moisture can cause pore water pressure to build up in base, sub-base, and sub-grade materials, resulting in a loss of strength. The drainage qualities of gravelly and sandy soils with little or no particles (GW, GP, SW, SP) are excellent. The drainage qualities of fine-grained and highly organic soils are poor. Compression of the Soil Sheeps foot and rubber-tired rollers are two typical types of soil compacting machinery. The sheepsfoot roller is said to have an advantage in that it leaves a rough surface that allows for better layer bonding. Granular soils with well-graded materials (GW, SW) perform better in terms of compaction than poorly graded soils (GP, SP).
Fine grained soils
It is generally beneficial to evaluate the compaction characteristics of the soil using a field test section for most building projects of any size.The strength, cohesiveness, and consolidation characteristics of soils determine their suitability for foundations. The adaptability of a soil as an acceptable foundation material is greatly determined by the type of structure, load, and use.A soil may be perfectly acceptable for one form of construction but require specific preparation for another.Gravel and gravelly soils (GW, GP, GM, GC) in general have a high bearing capacity and low consolidation under load.Sands that are well graded (SW) usually have a high bearing capacity.Sands with poor grades and silty sands (SP, SM) have varying capacities.
Simple spread footings may be sufficient for most fine-grained soils (including silt and clays), although this is mostly dependent on the amount of the load. The foundations’ position in relation to the soil (need to be aware of foundation walls and hydrostatic pressure as moisture is present in the soil). Alternative methods are required if the soil is poor and the construction loads are relatively heavy. When fine cohesive silt and clay soil are available, piling foundations may be necessary. (OH, CH) Over excavating to remove non-bearing soils, compacting and filling back in, or importing other engineered soil may be desirable and economically possible at times.
Role of Foundations
Based on borings, the geotechnical engineer will offer appropriate foundation systems or alternative solutions, as well as beating capacity, minimum depths, and unique design or construction methods. The ultimate bearing capacity of soil is divided by a safety factor to get the safe bearing capacity (usually 2-4). The maximum unit pressure a soil can withstand without allowing considerable levels of settlement is known as ultimate bearing capacity. The safe bearing capacity of bedrock is the highest. 3,000–12,000 PSF is the safe bearing capacity of well-graded gravel and sand that has been contained and drained. Silts and clays have a reduced safe bearing capacity, ranging between 1,000 and 4,000 PSF. The Function of Foundations.
It’s appropriate for most structures with mild loads and/or strong shallow soils. Single spot square pads where bearing walls have an elongation form are found at columns. Almost always, these are strengthened. The weight is delivered directly to the supporting soils via these footing. The area of spread footing is calculated by multiplying the applied force by the safe bearing capacity of the soil (f=P/A). In general, low-rise buildings are a good fit (1-4 Stories). Requires stable soil conditions capable of supporting the structure on the spread footings’ area. When necessary, grade beams can be used to connect footings at columns to give additional support.
Moisture Content Test. This is a very important test for building construction.
Foundations are generally broken into two categories mainly, shallow foundations and deep foundations.
Adequate depth The foundation must have an adequate depth to prevent frost damage.