Method for compaction detection and control when compacting a soil with a deep vibrator

Abstract

A method for detecting and controlling compaction when compacting a soil by a depth vibrator which has a rotationally drivable imbalance ( 3 ) and at least one sensor ( 6, 12, 13, 14, 19 ), comprising the steps of: inserting the depth vibrator ( 2 ) into the soil ( 17 ) up to a desired final depth (Tm); compaction of the soil ( 17 ) during which the forward angle (φ) of the imbalance ( 3 ) as well as the oscillation amplitude (A) of the depth vibrator ( 2 ) are determined; detection of a soil stiffness profile from soil stiffness values (k) determined over time (t); determination of a first soil stiffness value (k1) and a second soil stiffness value (k2) from the soil stiffness profile (k), for which it applies that a rate of increase (k′2) of the second soil stiffness value (k2) exceeds a rate of increase (k′1) of the first soil stiffness value (k1) by a defined factor; calculation of a transition soil stiffness value (k12) which is between the first soil stiffness value (k1) and the second soil stiffness value (k2); and storing the transition soil stiffness value (k12) detected in the respective compaction step to the associated depth (T).

We claim: 
     
       1. A method for compaction of soil by means of a depth vibrator comprising an imbalance rotationally driveable in a vibrator housing and at least one sensor, the method further comprising the steps of:
 inserting the depth vibrator into the soil to a desired final depth (Tm); 
 compacting the soil by the depth vibrator in a series of compaction steps, wherein during the compaction to a respectively measured depth (T) a forward running angle (φ) of the imbalance and a vibration amplitude (A) of the depth vibrator are determined; 
 during a compaction step, detecting a soil stiffness profile comprising soil stiffness values (k) determined over time (t) on the basis of said forward running angle (φ) and vibration amplitude (A); 
 determining a first soil stiffness value (k1) and a second soil stiffness value (k2) from the soil stiffness profile for which a rate of increase (k′2) of the second soil stiffness value (k2) exceeds a rate of increase (k′1) of the first soil stiffness value (k1) by a defined factor; 
 calculation of a transition soil stiffness value (k12) that is between said first soil stiffness value (k1) and said second soil stiffness value (k2); 
 storing the transition soil stiffness value (k12) recorded in the respective compaction step to the corresponding depth (T). 
 
     
     
       2. The method of  claim 1  further comprising a step of terminating a compaction step when the rate of increase (k′2) of the second soil stiffness value (k2) is greater than 1.5 times the rate of increase (k′1) of the first soil stiffness value (k1). 
     
     
       3. The method of  claim 2 , wherein said step of terminating a compaction step comprises terminating said compaction step when the rate of increase (k′2) of the second soil stiffness value (k2) is greater than twice the rate of increase (k′1) of the first soil stiffness value (k1). 
     
     
       4. The method of  claim 1 , wherein after completion of compaction at a compaction depth (T) the depth vibrator is pulled to the next stepwise depth to be compacted. 
     
     
       5. The method of  claim 1 , wherein said at least one sensor comprises at least one acceleration sensor configured to measure acceleration of the depth vibrator during compaction. 
     
     
       6. The method of  claim 5 , wherein said at least one sensor comprises at least one position sensor configured to detect a signal representing the position of the imbalance mounted on the depth vibrator. 
     
     
       7. The method of  claim 5 , wherein said at least one acceleration sensor comprises a plurality of acceleration sensors mounted in different planes on the depth vibrator. 
     
     
       8. The method of  claim 1 , wherein said step of determining the first soil stiffness value (k1) and second soil stiffness value (k2) comprises a calculation based on modal resonating soil mass (ΔM). 
     
     
       9. The method of  claim 8 , wherein said step of determining the first soil stiffness value (k1) and second soil stiffness value (k2) comprises calculating based on the imbalance (m·e), oscillation amplitude (A) and mass (M) of the depth vibrator. 
     
     
       10. The method of  claim 9 , wherein said calculation comprises a formula: 
       
         
           
             
               
                 Δ 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 M 
               
               = 
               
                 
                   
                     m 
                     · 
                     e 
                   
                   A 
                 
                 - 
                 M 
               
             
           
         
       
     
     
       11. The method of  claim 1 , wherein said step of determining the first soil stiffness value (k1) and second soil stiffness value (k2) comprises a calculation based on measured amplitude (A) and a reference amplitude (A∞) of the vibrator at free oscillation. 
     
     
       12. The method of  claim 11 , wherein said step of determining the first soil stiffness value (k1) and second soil stiffness value (k2) comprises a calculation according to the formula: 
       
         
           
             
               V 
               = 
               
                 
                   A 
                   
                     A 
                     ∞ 
                   
                 
                 = 
                 
                   
                     A 
                     · 
                     
                       ( 
                       
                         M 
                         + 
                         
                           Δ 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           M 
                         
                       
                       ) 
                     
                   
                   
                     m 
                     · 
                     e 
                   
                 
               
             
           
         
       
       where
 V is the amplification factor, 
 A is the vibration amplitude of the depth vibrator during compaction, 
 A∞ is the vibration amplitude of the depth vibrator while free oscillation or with an excitation frequency towards infinity, 
 M is the mass of the depth vibrator, 
 ΔM is the modal resonating soil mass, 
 m is the imbalance mass, and 
 e the eccentricity of the rotating imbalance m relative to the rotary axis. 
 
     
     
       13. The method of  claim 1 , wherein a forward angle (φ) of the imbalance relative to the vibrator motion is set to a value greater than 90° and less than 180°. 
     
     
       14. The method of  claim 13 , wherein the forward angle (φ) of the imbalance relative to the vibrator motion is set to a value greater than 100° and less than 170°. 
     
     
       15. The method of  claim 1 , wherein said step of determining the first soil stiffness value (k1) and second soil stiffness value (k2) comprises a calculation according to the formula: 
       
         
           
             
               k 
               = 
               
                 m 
                 · 
                 e 
                 · 
                 
                   ω 
                   2 
                 
                 · 
                 
                   ( 
                   
                     
                       1 
                       
                         A 
                         ∞ 
                       
                     
                     - 
                     
                       
                         1 
                         A 
                       
                       · 
                       
                         
                           sign 
                           ⁡ 
                           
                             ( 
                             
                               φ 
                               - 
                               
                                 90 
                                 ⁢ 
                                 ° 
                               
                             
                             ) 
                           
                         
                         
                           
                             1 
                             + 
                             
                               
                                 tan 
                                 2 
                               
                               ⁢ 
                               φ 
                             
                           
                         
                       
                     
                   
                   ) 
                 
               
             
           
         
       
       where
 A is the vibration amplitude of the depth vibrator during compaction, 
 A∞ is the vibration amplitude of the depth vibrator while free oscillation or with an excitation frequency towards infinity, 
 m is the imbalance mass, 
 e is the eccentricity of the rotating imbalance m relative to the axis of rotation, 
 ω is the angular frequency of the rotating imbalance, and 
 φ is the phase advance of the rotating imbalance m relative to motion of the mass M of the depth vibrator. 
 
     
     
       16. A method for improving the ground by a depth vibrator, comprising the steps of:
 establishing a first compaction body by insertion of the depth vibrator into the ground to a desired final depth (Tm); 
 after reaching the final depth (Tm) with the depth vibrator, stepwise vibration and removal of said vibrator out of the ground in vibration intervals of a defined amount (ΔT), thereby compacting the subsoil step by step in depth sections, 
 performing the method of  claim 1  during vibration of the vibrator at each compaction depth section. 
 
     
     
       17. The method of  claim 16 , wherein a soil stiffness profile derived from transition soil stiffness values (k12) detected over the depth (T) is used for controlling construction of at least one compaction body. 
     
     
       18. The method of  claim 17 , wherein said soil stiffness profile is used for grid optimization of a grid of a plurality of compaction bodies to be constructed. 
     
     
       19. The method of  claim 16 , wherein said step of performing the method of  claim 1  during vibration of the vibrator at each compaction depth section comprises terminating compaction at said compaction depth section based on a transition soil stiffness value (k12) associated with the respective compaction depth section. 
     
     
       20. A method for controlling compaction of soil with an eccentric-weight depth vibrator comprising the steps of:
 inserting the depth vibrator into the soil to a desired depth; 
 compacting the soil at said depth by the depth vibrator; 
 during said compaction step, detecting a soil stiffness profile comprising a plurality of soil stiffness values measured over time; 
 determining a soil stiffness value in said profile beyond which further vibration markedly increases subsequent soil stiffness values measured over time, said determined soil stiffness value representing a point at which said soil is as compacted as possible. 
 
     
     
       21. The method of  claim 20 , wherein said step of determining a soil stiffness value in said profile beyond further comprises measuring rate of increase of successive soil stiffness values and determining a time at which said rate of increase markedly rises.