Is the whole foundation uniform or uneven? The uniformity evaluation of natural foundation under a foundation can only be regarded as a whole and can only have one conclusion.
In the statistics of the frequency of common violations of mandatory provisions, article 14.3.3 of code for investigation of geotechnical engineering gb50021-2001 (2009 Edition) accounts for 18.05%, second only to article 4.9.1 (52.68%).
The investigation results in the project initiation stage shall meet the requirements of project initiation, and the investigation results in the feasibility study shall meet the requirements of site selection scheme; In the preliminary survey stage of the project, the engineering geology, hydrogeology and geotechnical characteristics of the foundation of the proposed building site shall be preliminarily found out, the stability of the site shall be conclusively evaluated, and the preliminary basis shall be provided for selecting the most appropriate design and construction scheme of foundation and foundation engineering.
Some projects directly enter the preliminary survey (corresponding to the preliminary design) stage or the detailed survey (corresponding to the construction drawing design) stage without carrying out the survey work in the early stage, resulting in the lack of relevant work contents such as the suitability of the engineering construction of the construction site, the possible adverse geological effects of the proposed site and the seismic risk assessment.
Evaluation of soil corrosivity The evaluation of soil corrosivity is groundless and incomplete.
Various geotechnical property indexes, recommended values of geotechnical strength parameters, deformation parameters and foundation bearing capacity; 6.
1、 Article 14.3.3 of code for investigation of geotechnical engineering gb50021-2001 (2009 Edition): 14.3.3 the geotechnical investigation report shall be prepared according to the specific conditions such as task requirements, investigation stage, engineering characteristics and geological conditions, and shall include the following contents: 1.
Overview of the proposed project; 3.
From the statistical table of the frequency of common violations of mandatory provisions and the pie chart of the frequency of common violations of mandatory provisions, it can be seen that there are mainly 8 clauses (items), of which the top 5 items with the highest frequency are involved in turn, including the requirements for pile foundation survey, the requirements to be included in the survey report, the depth and number of exploration holes involved in foundation soil liquefaction evaluation The minimum number of soil samples and in-situ tests shall be taken, and the shear wave velocity method shall be used to determine the type of construction site, hereinafter referred to as high-frequency strong strip.
In another case, when tunnels, pipe galleries and trenches are set and underground pipelines are placed in them, only the corrosivity of water and soil to the “shell” is analyzed and evaluated.
For pipeline engineering in municipal engineering, when the pipeline material is steel and cast iron metal pipeline, only water and soil samples are taken for corrosion analysis and evaluation, but resistivity test and corrosion analysis and evaluation are not carried out.
The uniformity of natural foundation is a qualitative evaluation, the basic content of geotechnical investigation report and indispensable.
In some survey reports, a single building is divided into several areas for natural foundation evaluation, which is very irregular.
This paper will prompt the relevant precautions in article 14.3.3 of code for investigation of geotechnical engineering gb50021-2001 (2009 Edition), hoping to provide some practical help for geotechnical investigators to enhance their understanding and application of high-frequency provisions, reduce or even avoid violating these high-frequency provisions.
Site topography, landform, stratum, geological structure, geotechnical properties and uniformity; 5.
Article 4.9.1 was analyzed in the previous issue.
Natural foundation analysis and evaluation refers to the evaluation of the foundation under the condition of natural foundation of the project.
Just imagine that if the mathematical differential method is used to differentiate the foundation of a single building under the same foundation small enough, even if it is an obviously uneven foundation, each micro unit can “become” uniform.
The problem comes.
The survey report shall be comprehensive and meet the requirements of the preparation depth of survey documents.
Evaluation of site stability and suitability.
Evaluation of foundation uniformity The uniformity of natural foundation was not evaluated.
Groundwater burial, type, water level and its change; 7.
Although some survey reports also involve the content of natural foundation uniformity evaluation, they are not willing to clarify the evaluation conclusion.
The preliminary survey results shall meet the requirements of the preliminary design; In the detailed survey stage of the project, on the premise of confirming the site stability evaluation, it is necessary to find out the composition of the bedrock soil layer of the building ground, the strength and compressibility of the geotechnical medium, and whether it meets the requirements of the superstructure of the building on the foundation bearing capacity and the allowable deformation value of the foundation, and put forward relevant conclusions and suggestions, The detailed survey results shall meet the requirements of construction drawing design; For projects with complex site conditions or special requirements (such as deep foundation pit excavation, foundation treatment, etc.), it is necessary to provide geotechnical engineering technical parameters for relevant design through construction survey, so as to carry out construction monitoring or test the expected effect of design and control construction quality.
Reasonable suggestions on foundation bearing layer shall be put forward according to the design conditions such as foundation form and load size of the proposed building (structure).
3、 Common outstanding problems 1.
The conclusion that the soil of the proposed site is not corrosive to building materials is obviously lack of necessary and sufficient basis without taking soil samples and “sufficient experience or sufficient data” referred to in code for investigation of geotechnical engineering gb5002-2001 (2009 Edition).
The conclusive evaluation of construction site, geotechnical parameters and recommended value of foundation bearing capacity provided shall be reliable and based.
Corrosivity of soil and water to building materials; 8.
Description of adverse geological processes that may affect the stability of the project and evaluation of the degree of harm to the project; 9.
Survey methods and survey work layout; 4.
It mainly includes evaluating the feasibility of using natural foundation, providing stratum bearing capacity under natural foundation state, and evaluating foundation uniformity.
That is, in any case, we should be realistic, reasonable and in line with the basic theories and concepts..
Unless otherwise agreed in the entrustment contract, the work shall be undertaken by the engineering survey unit directly entering the preliminary survey stage or detailed survey stage.
According to the statistical data of construction drawing review in recent two years, the preliminary sorting is carried out according to the frequency of violation of mandatory provisions of more than 3 (inclusive), the statistical table of the frequency of common violation of mandatory provisions is prepared, and the pie chart of the frequency of common violation of mandatory provisions is drawn.
Investigation purpose, task requirements and technical standards; 2.
Original text of article 14.3.3: In view of the different scale of rock engineering and the great differences in purpose requirements, engineering characteristics and natural conditions, it is obviously impractical to formulate a unified report content and chapter name applicable to each project.
Some carried out resistivity test, but did not carry out corrosion analysis and evaluation according to the test results.
2.
The work content of the geotechnical investigation report proposed by the investigation unit shall meet the requirements of the investigation task and comply with the provisions of the current relevant standards.
2、 Problem analysis Although geotechnical engineering has its own characteristics, it is difficult to formulate a unified survey report applicable to each project, and only its basic contents can be specified, the survey work contents and requirements for geotechnical survey report are different in different survey stages, such as: In the project initiation and feasibility study stage, the geotechnical investigation (report) shall focus on the suitability of the construction site, the possible adverse geological effects and seismic risk evaluation of the proposed site.
Therefore, this article only specifies the basic contents of geotechnical investigation report.
Even if the pipelines placed in them are steel and cast iron metal pipelines, resistivity test and corrosivity analysis and evaluation are not required, because the pipe body is not in direct contact with water and soil.