Abstract:
A sounding device for measuring the thickness of sediments at the base of dry or wet drilled shaft excavations for the assessment of drilled shaft bottom cleaning operations. The sounding device provides a simple and reliable means to quantitatively evaluate drilled shaft bottom cleanliness.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    Not Applicable 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0003]    This invention relates to the assessment of drilled shaft bottom cleaning operations. The invention provides a simple, reliable and quantitative means of measuring the thickness of sediments when accessing drilled shaft base cleanliness. 
         [0004]    Drilled shafts are high capacity deep foundation bored piles that are constructed by excavating a hole in the ground and placing fluid concrete within the excavation. Drilled shafts have several advantages over other types of deep foundations, and one of its advantages is the ability to resist high axial loads. The axial load resistance of a drilled shaft is derived for the side resistance of the concreted shafts in the surrounding soils or rock, and from end bearing resistance of the poured concrete on soil or rock. Therefore, the cleanliness of drilled shaft bases is important to achieve the desired end bearing resistance, to limit shaft settlement and to ensure that the poured concrete is not contaminated with sediments. 
         [0005]    To achieve the desired end bearing resistance of a drilled shaft, the base of the drilled shaft must be cleaned by personnel lowered into the excavation; by mechanical means such as using a muck-bucket; or by vacuum methods. Drilled shaft base cleanliness criteria are typically specified in construction documents to limit the average thickness of sediments at the excavated shaft base to a maximum of ½ inch to 2 inches. The current state of practice to check the drilled shaft bottom cleanliness is to either: lower personnel to the bottom of the excavation to conduct downhole visual inspection; perform visual inspection using video/camera devices by personnel on the ground surface near the shaft top; or by sounding with a weighted tape lowered by personnel on the ground surface near the shaft top. These methods currently have limitations to the efficiency and effectiveness of assessing shaft bottom cleanliness, such as: 
         [0006]    Downhole inspection by personnel lowered to the excavated drilled shaft bottom is typically avoided due to safety concerns and cannot practically be performed in wet drilled shafts. 
         [0007]    Visual inspection using video/camera devices is relatively time consuming, uses expensive equipment and requires specialized trained personnel. 
         [0008]    Sounding with a weighted tape is quick and easy to perform but determination of sediment thickness is subjective because it&#39;s based on a “feel” of how the weight reacts when it strikes the bottom, and is thus subject to interpretation. This can potentially lead to drilled shaft settlement and disputes. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    This invention consists of a sounding device and was developed to provide: 
         [0010]    A safe, simple, reliable and quantitative method of measuring the thickness of sediments or spoils at the base of a drilled shaft hole. 
         [0011]    A more reliable method of assessing drilled shaft bottom cleanliness than sounding with a weighted tape. 
         [0012]    A more cost effective method of assessing drilled shaft bottom cleanliness than using visual inspection devices. 
         [0013]    The sounding device is designed to measure the thickness of sediments at the bottom of dry and wet drilled shaft excavations. The term sediment used in this specification refers to soil or rock material from the shaft excavation operation that are deposited, disturbed, or accumulated at the base of drilled shafts from the excavation process. The embodiments of the invention are described in the following paragraphs: 
         [0014]    An invention for measuring the thickness of sediments at the base of drilled shaft excavations, consisting of: a probe shaft with a probe point at one end and a weighted piston at the other end; a bearing plate and measuring ring centered around the axis of the probe shaft and free to move along the length of the probe shaft; and a measuring tape attachment connected to the weighted piston for lowering and retrieving the invention within the drilled shaft hole. The probe shaft includes a graduated measuring scale. 
         [0015]    The embodiments of the invention will improve the state of the current practice. It will measure the sediment thickness at the base of drilled shafts using sounding methods by providing a simple, reliable and quantitative means of measuring the sediment thickness. The invention measures the sediment thickness by using the mass of a weighted piston to push a probe shaft into the sediments, and uses a bearing plate and measuring ring centered around the axis of the probe shaft to measure the distance the probe point penetrates the sediments. 
         [0016]    Another embodiment of the invention is to provide a lightweight and portable system for measuring the thickness of the sediment at the base of drilled shafts. The invention is designed to be less than  5  pounds in weight and can be transported, setup, and used by a single operator. 
         [0017]    Yet another embodiment of the invention is to provide a reliable system for measuring the thickness of sediments at the base of drilled shafts—where the measurements obtained by the invention are not subject to interpretation and can be duplicated by different operators using the same device. 
         [0018]    Other embodiments of the invention also include: the invention is designed to be simple enough to be operated by construction and engineering personnel. It is designed to check shaft bottom cleanliness without the operator entering into the drilled shaft. It is also designed to be more cost effective than visual inspection devices by having a lower cost; less complex to operate, and takes little time to perform the test to determine the sediment thickness at the base of the drilled shafts. 
         [0019]    The advantages of the invention include, without limitation: lightweight; low cost; provides quantitative measurements; portable; easy to transport; easy to operate; and measurements can be performed quickly and duplicated. 
         [0020]    The invention is not limited by the claims, embodiments and the system descriptions described herein, but is claimed for all embodiments and methods within the scope and spirit of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The appended drawings provide an illustration of the invention and provide a clear understanding of its key features as summarized above. It should be noted that the drawings only provide an illustration of the concept of the invention. They should not be considered as the limit of the size, shape or function of the elements used in the invention, as these can be changed based on the type, composition, and thickness of the sediment to be tested. The drawings are not necessarily drawn to scale and are referenced accordingly: 
           [0022]      FIG. 1  is an illustration of the invention showing a simplified elevation view. 
           [0023]      FIG. 2  is an illustration of the invention showing a simplified elevation view of the invention showing the probe point penetrating sediments, the bearing plate on top of the sediments and the measuring ring pushed up by the bearing plate to record the thickness of the sediment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    The invention consists of a sounding device that is designed to measure the thickness of sediments at the base of drilled shaft excavations. The system and features of the sounding device are described in the following paragraphs and the references are on the appended drawings: 
         [0025]      FIG. 1  shows the concept of the sounding device. The sounding device includes the following elements: 
         [0026]    The probe point  10  is conical (pointed) in shape. 
         [0027]    The probe shaft  12  will have a measurement scale annotated on it. The measurement scale will be in either inches or millimeters. The graduated length of the probe shaft  12  will be a minimum of 2 inches. Probe shafts  12  with longer lengths will be used if the thickness of the sediment  22  is expected to exceed 2 inches. 
         [0028]    The bearing plate  14  size (diameter) will vary from 1 to 3 inches in diameter and will be mounted on a sleeve to allow free movement along the probe shaft  12  and to prevent tilt of the bearing plate  14 . Selection of the bearing plate  14  size will depend on the type of sediment  22  to be tested. Small diameter bearing plate  14  will be used for course sediments  22 . Larger diameter bearing plates  14  will be used when fine grained sediments  22  are anticipated. 
         [0029]    The measuring ring  16  will be split and fitted close around the probe shaft  12 . The measuring ring  16  will be fitted close on the probe shaft  12  so that a force of 0.5 to 1.5 pounds will be required to move it along the probe shaft  12 . When measuring ring  16  is pushed up by the bearing plate  14 , it will stay in the new position and not move back down by gravity forces after the bearing plate  14  returns to its “zero” position under gravity forces. 
         [0030]    The weighted piston  18  will provide the mass necessary to push the probe point  10  through the sediments  22  at the drilled shaft base. The mass of the weighted piston  18  will vary from 2 to 4 pounds. 
         [0031]    The measuring tape attachment  20  will allow a measuring tape to be easily attached to the sounding device. 
         [0032]      FIG. 2  shows a simplified elevation view of the sounding device with the probe point  10  penetrating sediments  22 , the bearing plate  14  on top of the sediments  22  and the measuring ring  16  pushed up by the bearing plate  14  to record the thickness of the sediment  22 . Before lowering the sounding device into the drilled shaft, the measuring ring  16  will first be set to the “zero” location at the top of the bearing plate  14  with the bearing plate  14  at the lowest point on the probe shaft  12 . The sounding device will be lowered using a measuring tape to the base of the drilled shaft at a slow rate of descent until it touches the sediments  22  at the bottom of the drilled shaft. After it touches the sediments  22 , the sounding device will be raised 2-feet above the sediments  22  and held in place for 5 seconds, or as long as needed, to allow it to stop swinging. The sounding device is then allowed to freefall to penetrate the sediments  22  at the drilled shaft base. When the sounding device strikes the sediment, probe point  10  first, the bearing plate  14  will be suspended on top of the sediments  22  while the probe point  10  will be pushed through the sediments  22  by the weighted piston  18  and will stop on top of the drilled shaft bearing material  24  (firm soil or rock). As the probe point  10  moves down through the sediment  22 , the bearing plate  14  will restrain the measuring ring  16  from going down with probe point  10  and probe shaft  12 , and will push the measuring ring  16  up along the probe shaft  12 —relative to its original location—to a distance equal to the depth of penetration of the probe point  10  through the sediments  22 . When the device is raised, the bearing plate  14  will return to its zero position near the probe point  10 . However, the measuring ring  16  will remain in place so that when retrieved at the ground surface, the sediment  22  thickness can be determined based on the measuring ring  16  location—distance traveled on probe shaft  12 .