FOUNDATION EXCAVATION, UNDERPINNING, AND FIELD LOAD TESTS.

INTRODUCTION
There are many types of services performed by the geotechnical engineer during the actual construction of the project. Examples of these types of services are as follows:

1. Excavation of the foundation. During the construction of the project, the geotechnical engineer will often be asked or required to review the foundation excavation. This type of service involves measuring the dimension of geotechnical elements (such as the depth and width of footings) to make sure that they conform to the requirements of the construction plans. This service is often performed at the same time as the field observation of the foundation bearing conditions, such as confirming the presence of dense soil or intact rock.

In many cases, field observations to confirm bearing conditions and check foundation dimensions will be required by the local building department. In addition, a letter indicating the outcome of the observations must be prepared by the engineer to satisfy the local building department. Building departments often refer to these types of reports as foundation inspection reports. The local building department often considers these reports to be so important that they may not issue a certificate of occupancy until the reports have been submitted and accepted.


Slope failure during the grading of a site. The backpack located in the middle of the photograph provides a scale for the size of the ground crack
FIGURE 16.1 Slope failure during the grading of a site. The backpack located in the middle
of the photograph provides a scale for the size of the ground cracks.


Foundation excavations will be discussed later.

2. Field load or performance tests. There are numerous types of field load or performance tests.

For example, load tests are common for pile foundations and are used to determine their load carrying capacity. Field load tests will be discussed later.

Besides load tests, there can be all types of performance tests during construction that will need to be observed by the geotechnical engineer. An example is the field-testing of tieback anchors as discussed later and Table 11.3.

TABLE 11.3 Test Procedures and Acceptance Criteria for Each Tieback


3. Underpinning. There are many different situations where a structure may need to be under-
pinned. Common reasons for underpinning include supporting a structure that is sinking or tilt-
ing due to ground subsidence or instability of the structure. Foundation underpinning will be
discussed later.

4. Observational method. There are numerous types of subsurface conditions that can lead to delays
and additional expenses during construction. If it is anticipated that there will be earth failure, ground subsidence, or groundwater seepage, then it is important that the geotechnical engineer plan for such site conditions. Earth movement and failure can affect all types of construction projects. For example, Fig. 16.1 shows a slope failure during the grading of a project. The process of grading can undermine the toe of a slope or surcharge the head of a slope, leading to a failure such as shown in Fig. 16.1. The observational method is one approach that can be used to anticipate such conditions and modify the design if needed during construction. The observational method will be discussed later.

0 comentarios:

Post a Comment